JP2020205348A - Electrolyte for photoelectric conversion element, photoelectric conversion element arranged by use thereof, and electrode structure for photoelectric conversion element - Google Patents

Abstract

To provide: an electrolyte for a photoelectric conversion element, which enables the enhancement in the photoelectric conversion property of a photoelectric conversion element; a photoelectric conversion element arranged by use of such an electrolyte; and an electrode structure for a photoelectric conversion element.SOLUTION: An electrolyte 40 for a photoelectric conversion element contains a solid imidazole compound which is solid at 25°C so that a concentration of the solid imidazole compound is larger than a solubility of the imidazole compound at 25°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolyte for a photoelectric conversion element, a photoelectric conversion element using the electrolyte, and an electrode structure for a photoelectric conversion element.

The photoelectric conversion element generally includes an electrode substrate, a counter electrode facing the electrode substrate, an oxide semiconductor layer provided on the electrode substrate, and an electrolyte arranged between the electrode substrate and the counter electrode.

It is important to improve the photoelectric conversion characteristics in the photoelectric conversion element, and for that purpose, various proposals focusing on, for example, an electrolyte have been made.

For example, in Patent Document 1 below, the photoelectric conversion characteristics of a photoelectric conversion element are described by an electrolyte containing iodine, an iodine compound, and a benzimidazole derivative having a saturated hydrocarbon group having 3 to 11 carbon atoms directly bonded to a benzimidazole ring. It has been proposed to increase the value and greatly improve the durability.

Japanese Unexamined Patent Publication No. 2009-23105

However, the photoelectric conversion element provided with the electrolyte described in Patent Document 1 still has room for improvement in the photoelectric conversion characteristics.

The present invention has been made in view of the above circumstances, and provides an electrolyte for a photoelectric conversion element capable of improving the photoelectric conversion characteristics of the photoelectric conversion element, a photoelectric conversion element using the electrolyte, and an electrode structure for the photoelectric conversion element. The purpose is to do.

The present inventors have conducted intensive studies to solve the above problems. As a result, the present inventors have found that the above problems can be solved by the following inventions.

That is, the present invention is an electrolyte for a photoelectric conversion element, which contains a solid imidazole compound at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C.

The electrolyte for a photoelectric conversion element of the present invention contains a solid imidazole compound at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C. Therefore, when the electrolyte for a photoelectric conversion element of the present invention is used as an electrolyte for a photoelectric conversion element having an oxide semiconductor layer, for example, at 25 ° C., a part of the imidazole compound is not dissolved in the electrolyte and mainly , Precipitates as a solid on the surface of an oxide semiconductor layer having a large surface area. For this reason, the oxide semiconductor layer is covered with the solid imidazole compound, which makes it difficult for dark current to flow and raises the open circuit voltage of the photoelectric conversion element. As a result, the electrolyte of the present invention can improve the photoelectric conversion characteristics of the photoelectric conversion element.

In the above-mentioned electrolyte for a photoelectric conversion element, it is preferable that R defined by the following formula (1) satisfies the following formula (2).
R = m2 / (m-m2) ... (1)
(In the above formula (1), m2 is the mass of the imidazole compound precipitated in the electrolyte at 25 ° C. after heating the electrolyte to dissolve the imidazole compound in the electrolyte and leaving it for 12 hours. g) is represented, and m represents the mass (g) of the electrolyte before the imidazole compound is precipitated in the electrolyte.)

0 <R <0.05 ... (2)

In this case, the photoelectric conversion characteristics of the photoelectric conversion element can be further improved as compared with the case where R is 0 or R is 0.05 or more.

In the electrolyte for a photoelectric conversion element, it is preferable that the imidazole compound contains a benzimidazole compound.

In this case, when the electrolyte is used as the electrolyte of the photoelectric conversion element, the photoelectric conversion characteristics of the photoelectric conversion element can be improved particularly effectively.

Further, the present invention includes a photoelectric conversion cell, wherein the photoelectric conversion cell includes an electrode substrate, an opposing substrate facing the electrode substrate, an oxide semiconductor layer provided on the electrode substrate, the electrode substrate, and the opposing substrate. The electrolyte is a photoelectric conversion element including the above-mentioned electrolyte for a photoelectric conversion element.

In the photoelectric conversion element of the present invention, the electrolyte comprises the above-mentioned electrolyte for a photoelectric conversion element, and the electrolyte contains a solid imidazole compound at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C. Therefore, when the photoelectric conversion element of the present invention is used, for example, at 25 ° C., a part of the imidazole compound is not dissolved in the electrolyte and is mainly precipitated as a solid on the surface of the oxide semiconductor layer having a large surface area. .. For this reason, the oxide semiconductor layer is adhered with the solid imidazole compound, which makes it difficult for dark current to flow and raises the open circuit voltage of the photoelectric conversion element. As a result, the photoelectric conversion element of the present invention can improve the photoelectric conversion characteristics.

In the photoelectric conversion element, a part of the imidazole compound may or may not be precipitated on the surface of the oxide semiconductor layer, but it is preferable that a part of the imidazole compound is precipitated, for example, during power generation.

Further, the present invention is an electrode for a photoelectric conversion element, which comprises an electrode substrate and an oxide semiconductor layer provided on the electrode substrate, and a solid imidazole compound adhered to the surface of the oxide semiconductor layer at 25 ° C. It is a structure.

According to the electrode structure for a photoelectric conversion element, the following effects can be obtained. That is, first, an electrolyte component is arranged between the electrode structure and the facing substrate to manufacture a photoelectric conversion element. At this time, as the electrolyte component, an electrolyte component containing a solid imidazole compound at 25 ° C. is used, and the solid imidazole compound at 25 ° C. in the electrolyte component and the imidazole compound adhering to the surface of the oxide semiconductor layer are the electrolytes. The concentration should be higher than the solubility of the imidazole compound in the component at 25 ° C. Then, in the photoelectric conversion element, the solid imidazole compound remains attached to the surface of the oxide semiconductor layer at 25 ° C. Therefore, for example, at 25 ° C., the imidazole compound adhering to the surface of the oxide semiconductor layer is not completely dissolved in the electrolyte component and remains adhering to the surface of the oxide semiconductor layer. Therefore, it becomes difficult for dark current to flow, and the open circuit voltage of the photoelectric conversion element rises. As a result, the electrode structure of the present invention can improve the photoelectric conversion characteristics of the photoelectric conversion element.

In the present invention, the unit of solubility is "M", that is, "mol / L".

According to the present invention, there is provided an electrolyte for a photoelectric conversion element capable of improving the photoelectric conversion characteristics of the photoelectric conversion element, a photoelectric conversion element using the electrolyte, and an electrode structure for the photoelectric conversion element.

It is sectional drawing which shows one Embodiment of the photoelectric conversion element of this invention. It is a cut surface end view which shows one Embodiment of the electrode structure for a photoelectric conversion element of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view showing an embodiment of the photoelectric conversion element of the present invention.

As shown in FIG. 1, the photoelectric conversion element 100 includes a photoelectric conversion cell 60. The photoelectric conversion cell 60 includes an electrode substrate 10, an opposing substrate 20 facing the electrode substrate 10, an oxide semiconductor layer 30 provided on the electrode substrate 10, a dye adsorbed on the oxide semiconductor layer 30, and the electrode substrate 10. And an electrolyte 40 provided between the facing substrates 20. The electrolyte 40 is surrounded by a sealing portion 50 that connects the electrode substrate 10 and the facing substrate 20. The electrolyte 40 contains the imidazole compound, which is solid at 25 ° C., at a concentration higher than the solubility of the imidazole compound at 25 ° C.

In the photoelectric conversion element 100, the electrolyte 40 contains the imidazole compound which is solid at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C. Therefore, when the photoelectric conversion element 100 is used, for example, at 25 ° C., a part of the imidazole compound is not dissolved in the electrolyte 40 and is mainly precipitated as a solid on the surface of the oxide semiconductor layer 30 having a large surface area. .. For this reason, the oxide semiconductor layer 30 is adhered with the solid imidazole compound, which makes it difficult for dark current to flow and raises the open circuit voltage of the photoelectric conversion element 100. As a result, the photoelectric conversion element 100 can improve the photoelectric conversion characteristics. When the electrolyte 40 is placed at a temperature higher than 25 ° C., the solubility of the imidazole compound in the electrolyte 40 increases due to the temperature rise, so that a part of the imidazole compound is solid on the surface of the oxide semiconductor layer 30. In some cases, it does not precipitate, that is, the entire imidazole compound remains dissolved in the electrolyte 40. However, even in this case, the concentration of the imidazole compound in the electrolyte 40 is higher than that in the case where the electrolyte 40 contains the imidazole compound solid at 25 ° C. so as to have a concentration equal to or lower than the solubility of the imidazole compound at 25 ° C. Therefore, it is possible to further improve the photoelectric conversion characteristics of the photoelectric conversion element 100.

Next, the electrode substrate 10, the counter substrate 20, the oxide semiconductor layer 30, the electrolyte 40, the sealing portion 50, and the dye will be described in detail.

<Electrode substrate>
As shown in FIG. 1, the electrode substrate 10 includes a transparent substrate 11 and a transparent conductive layer 12 provided on the transparent substrate 11.

The material constituting the transparent substrate 11 may be a transparent material, and examples of such a transparent material include borosilicate glass, soda lime glass, white plate glass, glass such as quartz glass, polyethylene terephthalate (PET), and the like. Insulating materials such as polyethylene naphthalate (PEN), polycarbonate (PC), and polyether sulfone (PES) can be mentioned. The thickness of the transparent substrate 11 is appropriately determined according to the size of the photoelectric conversion element 100, and is not particularly limited, but may be, for example, in the range of 50 μm to 40 mm.

Examples of the material constituting the transparent conductive layer 12 include conductive metal oxides such as tin-added indium oxide (ITO), tin oxide (SnO ₂ ), and fluorine-added tin oxide (FTO). The transparent conductive layer 12 may be a single layer or may be composed of a laminate of a plurality of layers composed of different conductive metal oxides. When the transparent conductive layer 12 is composed of a single layer, the transparent conductive layer 12 is preferably composed of FTO because it has high heat resistance and chemical resistance. The thickness of the transparent conductive layer 12 may be, for example, in the range of 0.01 to 2 μm.

<Opposite board>
As shown in FIG. 1, the opposing substrate 20 includes a conductive substrate 21 and a conductive catalyst layer 22 provided on the electrode substrate 10 side of the conductive substrate 21 and contributing to the reduction of the electrolyte 40.

The conductive substrate 21 is formed by forming a film made of a corrosion-resistant metal material such as titanium, nickel, platinum, molybdenum, tungsten, aluminum, or stainless steel, or a film made of a conductive oxide such as ITO or FTO on the transparent substrate 11 described above. Consists of. Further, the conductive substrate 21 may be composed of a laminate in which the substrate and the electrode are separated and a transparent conductive layer made of a conductive oxide such as ITO or FTO is formed as an electrode on the above-mentioned insulating transparent substrate 11. Good. The thickness of the conductive substrate 21 is appropriately determined according to the size of the photoelectric conversion element 100, and is not particularly limited, but may be, for example, 5 μm to 4 mm.

Examples of the catalyst layer 22 include a metal catalyst component and a non-metal catalyst component. Examples of the catalyst component of the metal include platinum, gold, silver, palladium and rhodium. Examples of the non-metal catalyst component include carbon atom-containing materials containing carbon atoms such as carbon and conductive polymers, titanium oxides, and titanium composite oxides. Above all, it is preferable that the non-metal catalyst component is a carbon atom-containing material. In this case, higher power generation performance can be obtained as compared with the case where the non-metal catalyst component is not a carbon atom-containing material. When the conductive substrate 21 contains a non-metal catalyst component, the second electrode substrate 20 does not necessarily have to have the catalyst layer 22. In this case, the conductive substrate 21 also serves as the catalyst layer 22.

<Oxide semiconductor layer>
The oxide semiconductor layer 30 is composed of oxide semiconductor particles. Oxide semiconductor particles include, for example, titanium oxide (TiO ₂ ), zinc oxide (ZnO), tungsten oxide (WO ₃ ), niobium oxide (Nb ₂ O ₅ ), strontium titanate (SrTIO ₃ ), tin oxide (SnO ₂ ). , Indium oxide (In ₂ O ₃ ), Zirconium oxide (ZrO ₂ ), Tallium oxide (Ta ₂ O ₅ ), Lanthanum oxide (La ₂ O ₃ ), Yttrium oxide (Y ₂ O ₃ ), Formium oxide (Ho ₂ O) ₃ ), bismuth oxide (Bi ₂ O ₃ ), cerium oxide (CeO ₂ ), aluminum oxide (Al ₂ O ₃ ), or two or more of these. The thickness of the oxide semiconductor layer 30 is not particularly limited, but may be, for example, 0.1 to 100 μm.

<Electrolyte>
The electrolyte 40 may contain the imidazole compound which is solid at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C.

The imidazole compound is not particularly limited as long as it is solid at 25 ° C. The fact that the imidazole compound is solid at 25 ° C. means that the melting point of the imidazole compound is higher than 25 ° C. Therefore, the imidazole compound becomes a solid not only at 25 ° C but also below 25 ° C. Also, the solubility of the imidazole compound decreases as the temperature decreases. Therefore, a part of the imidazole compound can be precipitated as a solid at 25 ° C. or lower. Examples of such an imidazole compound include a benzimidazole compound, a purine compound and an imidazole [1,2-a] pyridine compound. These can be used alone or in combination of two or more. The imidazole compound preferably contains a benzimidazole compound. In this case, the photoelectric conversion characteristics of the photoelectric conversion element 100 can be improved particularly effectively. Examples of the benzimidazole compound include 1H-benzimidazole, 1-methyl-1H-benzimidazole and 2-methyl-1H-benzimidazole.

In the electrolyte 40, it is preferable that R defined by the following formula (1) satisfies the following formula (2).
R = m2 / (m-m2) ... (1)
(In the above formula (1), m2 is the mass (g) of the imidazole compound precipitated in the electrolyte 40 at 25 ° C. after heating the electrolyte 40 to dissolve the imidazole compound in the electrolyte 40 and leaving it for 12 hours. Represents m, and represents the mass (g) of the electrolyte 40 before the imidazole compound is precipitated in the electrolyte 40.)

0 <R <0.05 ... (2)

In this case, as compared with the case where R is 0.05 or more, the electron transfer reaction is less likely to be inhibited at the interface between the oxide semiconductor layer 30 and the electrolyte 40, and the decrease in short-circuit current is further suppressed. Therefore, the photoelectric conversion characteristics of the photoelectric conversion element 100 can be further improved.

R is more preferably 0.015 or more. In this case, the photoelectric conversion characteristics of the photoelectric conversion element 100 can be further improved as compared with the case where R is less than 0.015.

R is even more preferably 0.035 or less. In this case, the photoelectric conversion characteristics of the photoelectric conversion element 100 can be further improved as compared with the case where R is larger than 0.035.

The electrolyte 40 usually contains a redox pair and an organic solvent in addition to the imidazole compound described above.

As the organic solvent, acetonitrile, methoxyacetonitrile, methoxypropionitrile, propionitrile, ethylene carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, valeronitrile, pivalonitrile and the like can be used.

Further, as the electrolyte 40, an ionic liquid may be used instead of the organic solvent. As the ionic liquid, for example, a known iodine salt such as a pyridinium salt, an imidazolium salt, or a triazolium salt, which is a room temperature molten salt that is in a molten state near room temperature is used. Examples of such a room temperature molten salt include 1-hexyl-3-methylimidazolium iodide, 1-ethyl-3-propylimidazolium iodide, 1-ethyl-3-methylimidazolium iodide, 1,2. -Dimethyl-3-propyl imidazolium iodide, 1-butyl-3-methyl imidazolium iodide, or 1-methyl-3-propyl imidazolium iodide is preferably used.

Further, as the electrolyte 40, a mixture of the ionic liquid and the organic solvent may be used instead of the organic solvent.

Examples of the redox pair include redox pairs containing halogen atoms such as iodide ion / polyiodide ion (for example, I ⁻ / I ₃ ⁻ ) and bromide ion / poly bromide ion, as well as zinc complex, iron complex, and cobalt complex. Redox pairs such as. The iodide ion / polyiodide ion can be formed by iodine (I ₂ ) and a salt (ionic liquid or solid salt) containing iodide (I ⁻ ) as an anion. When using an ionic liquid having iodide as an anion, only iodine needs to be added, and when an organic solvent or an ionic liquid other than iodide is used as an anion, it is used as an anion such as LiI or tetrabutylammonium iodide. A salt containing iodide (I ⁻ ) may be added.

Further, an additive can be added to the electrolyte 40. Examples of the additive include 4-t-butylpyridine, guanidium thiocyanate and the like.

Further, as the electrolyte 40, a nanocomposite gel electrolyte which is a pseudo-solid electrolyte obtained by kneading nanoparticles such as SiO ₂ , TiO ₂ and carbon nanotubes into the electrolyte to form a gel may be used, or polyvinylidene fluoride. , An electrolyte gelled with an organic gelling agent such as a polyethylene oxide derivative or an amino acid derivative may be used.

<Sealing part>
The material constituting the sealing portion 50 is not particularly limited, but the material constituting the sealing portion 50 includes, for example, a modified polyolefin resin, a thermoplastic resin such as a vinyl alcohol polymer, and an ultraviolet curable resin. Resins such as. Examples of the modified polyolefin resin include ionomer, maleic anhydride-modified polyolefin, ethylene-vinyl acetate anhydride copolymer, ethylene-methacrylic acid copolymer and ethylene-vinyl alcohol copolymer. These resins can be used alone or in combination of two or more. Among them, maleic anhydride-modified polyolefin is preferable as the material constituting the sealing portion 50. In this case, higher adhesive strength can be obtained with respect to the electrode substrate 10 and the opposing substrate 20.

<Dye>
Examples of the dye include a ruthenium complex having a ligand containing a bipyridine structure, a terpyridine structure, and the like, a photosensitizing dye such as an organic dye such as porphyrin, eosin, rodanine, and merocyanine, and an organic dye such as a lead halide perovskite crystal. Examples include inorganic composite dyes. As the lead-halogenated perovskite, for example, CH ₃ NH ₃ PbX ₃ (X = Cl, Br, I) is used. Here, when a photosensitizing dye is used as the dye, the photoelectric conversion element 100 becomes a dye-sensitized electric conversion element, and the photoelectric conversion cell 60 becomes a dye-sensitized electric conversion cell.

Among the above dyes, a photosensitizing dye composed of a ruthenium complex having a ligand containing a bipyridine structure or a terpyridine structure is preferable. In this case, the photoelectric conversion characteristics of the photoelectric conversion element 100 can be further improved.

Next, an example of the method for manufacturing the photoelectric conversion element 100 described above will be described.

First, an electrode substrate 10 having a transparent conductive layer 12 formed on one transparent substrate 11 is prepared.

As a method for forming the transparent conductive layer 12, a sputtering method, a vapor deposition method, a spray thermal decomposition method, a CVD method and the like are used.

Next, the oxide semiconductor layer 30 is formed on the transparent conductive layer 12. The oxide semiconductor layer 30 is formed by printing a paste for forming a porous oxide semiconductor layer containing oxide semiconductor particles and then firing the paste.

The paste for forming an oxide semiconductor layer contains, in addition to the oxide semiconductor particles described above, a resin such as polyethylene glycol and a solvent such as telepineol.

As a printing method of the oxide semiconductor layer forming paste, for example, a screen printing method, a doctor blade method, a bar coating method, or the like can be used.

The firing temperature varies depending on the material of the oxide semiconductor particles, but is usually 350 to 600 ° C., and the firing time also varies depending on the material of the oxide semiconductor particles, but is usually 1 to 5 hours.

Next, the sealing portion forming body is prepared. The sealing portion forming body can be obtained, for example, by preparing a sealing resin film and forming one square-shaped opening in the sealing resin film.

Then, the sealing portion forming body is adhered onto the electrode substrate 10. At this time, the sealing portion forming body is arranged so as to surround the oxide semiconductor layer 30. Further, the sealing portion forming body can be adhered to the electrode substrate 10 by, for example, heating and melting the sealing portion forming body.

Next, the dye is adsorbed on the surface of the oxide semiconductor layer 30 of the electrode substrate 10. For this purpose, for example, the electrode substrate 10 is immersed in a solution containing a dye, the dye is adsorbed on the oxide semiconductor layer 30, and then the excess dye is washed away with the solvent component of the solution and dried. Just do it.

Next, the electrolyte 40 is prepared. The electrolyte 40 can be obtained by mixing a solid imidazole compound at 25 ° C. with an organic solvent or the like so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C.

Next, the electrolyte 40 is placed on the oxide semiconductor layer 30. The electrolyte 40 can be arranged, for example, by a screen printing method.

In this way, a laminate is obtained.

Next, the opposed substrate 20 is prepared, arranged so as to close the opening of the sealing portion forming body, and then bonded to the sealing portion forming body. At this time, the sealing portion forming body may be adhered to the facing substrate 20 in advance, and the sealing portion forming body may be bonded to the sealing portion forming body on the electrode substrate 10 side. The bonding of the opposing substrate 20 to the sealing portion forming body may be performed under atmospheric pressure or reduced pressure, but it is preferably performed under reduced pressure.

As described above, the photoelectric conversion element 100 can be obtained. At this time, the sealing portion forming body becomes the sealing portion 50.

Next, another example of the method for manufacturing the photoelectric conversion element 100 described above will be described with reference to FIG. FIG. 2 is a cut surface end view showing an embodiment of the electrode structure for a photoelectric conversion element of the present invention.

First, as shown in FIG. 2, the electrode structure 70 is prepared. The electrode structure 70 includes an electrode substrate 10, an oxide semiconductor layer 30 provided on the electrode substrate 10, and a sealing portion forming body 50A provided on the electrode substrate 10 and surrounding the oxide semiconductor layer 30. , Solid imidazole compound A is adhered on the surface of the oxide semiconductor layer 30 at 25 ° C.

The electrode structure 70 can be obtained, for example, by immersing the oxide semiconductor layer 30 in a solution in which a solid imidazole compound is dissolved in an organic solvent at 25 ° C., and then removing the organic solvent. At this time, the solid imidazole compound A at 25 ° C. precipitates and adheres to the surface of the oxide semiconductor layer 30.

Next, the electrolyte component is arranged on the oxide semiconductor layer 30 of the electrode structure 70. At this time, as the electrolyte component, an electrolyte component containing an imidazole compound that is solid at 25 ° C. and is dissolved in the electrolyte component is used. In this electrolyte component, the total concentration of the imidazole compound dissolved in the electrolyte component at 25 ° C. and the imidazole compound A solid at 25 ° C. adhering to the oxide semiconductor layer 30 is 25 with respect to the electrolyte component. The concentration should be higher than the solubility of the solid imidazole compound at ° C.

On the other hand, the facing substrate 20 is prepared, and the facing substrate 20 is arranged so as to close the opening of the sealing portion forming body 50A, and then bonded to the sealing portion forming body 50A. The bonding of the opposing substrate 20 to the sealing portion forming body may be performed under atmospheric pressure or reduced pressure, but it is preferably performed under reduced pressure.

The photoelectric conversion element 100 can be obtained even as described above. At this time, the sealing portion forming body 50A becomes the sealing portion 50. Further, the electrolyte 40 is composed of the electrolyte component and the imidazole compound A adhering to the surface of the oxide semiconductor layer 30.

In the photoelectric conversion element 100, the solid imidazole compound A remains attached to the surface of the oxide semiconductor layer 30 at 25 ° C. Therefore, for example, at 25 ° C., the imidazole compound A adhering to the surface of the oxide semiconductor layer 30 is not completely dissolved in the electrolyte component and remains adhering to the surface of the oxide semiconductor layer 30. Therefore, it becomes difficult for dark current to flow, and the open circuit voltage of the photoelectric conversion element 100 rises. As a result, the photoelectric conversion element 100 can improve the photoelectric conversion characteristics. When the electrolyte component is placed at a temperature higher than 25 ° C., the solubility of the imidazole compound in the electrolyte 40 increases due to the temperature rise, so that the solid imidazole adhering to the surface of the oxide semiconductor layer 30 increases. All of compound A may be dissolved in the electrolyte component. However, even in this case, the concentration of the imidazole compound in the electrolyte 40 is higher than that in the case where the electrolyte 40 contains the imidazole compound solid at 25 ° C. so as to have a concentration equal to or lower than the solubility of the imidazole compound at 25 ° C. Therefore, it is possible to further improve the photoelectric conversion characteristics of the photoelectric conversion element 100.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the photoelectric conversion element is composed of one photoelectric conversion cell 60, but the photoelectric conversion element may include a plurality of photoelectric conversion cells 60.

Further, in FIG. 2, the electrode structure 70 includes the sealing portion forming body 50A, but the electrode structure 70 does not necessarily have to include the sealing portion forming body 50A.

Hereinafter, the content of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

(Examples 1 to 4 and Comparative Examples 1 to 2)
<Preparation of electrolyte for photoelectric conversion element>
Iodine is 0.01M, 1,2-dimethyl-3-propylimidazolium iodide is 0.6M, and solid 1H-benzimidazole at 25 ° C is concentrated c (M) as shown in Table 1. A mixture was prepared by mixing with methoxypropionitrile, and iodine, 1,2-dimethyl-3-propylimidazolium iodide and 1H-benzimidazole were dissolved while gently heating the mixture to prepare an electrolyte. .. The solubility of 1H-benzimidazole in the electrolyte thus prepared was 0.44M.

Then, the electrolyte was allowed to stand at room temperature for 12 hours. Then, a solid-liquid separation operation was performed on this electrolyte by filtration. At this time, at 25 ° C., the mass m2 (g) of the solid 1H-benzimidazole precipitated in the electrolyte was measured, and the measured value of m2 and the mass m of the electrolyte before the imidazole compound was precipitated in the electrolyte. From (g), R was calculated based on the following formula (1). The results are shown in Table 1.

R = m2 / (m-m2) ... (1)

<Manufacturing of photoelectric conversion element>
First, FTO glass was prepared as an electrode substrate. Then, a titanium oxide nanoparticle paste containing titanium oxide was applied onto the electrode substrate by screen printing to prepare a 47 mm × 102 mm film, which was dried at 150 ° C. for 15 minutes. In this way, an unfired substrate was obtained. Then, this unfired substrate was placed in an oven and the titanium oxide nanoparticle paste was fired at 500 ° C. for 1 hour to form a porous titanium oxide layer having a thickness of 9 μm on the FTO film to obtain a working electrode.

Next, a thermoplastic resin sheet made of maleic anhydride-modified polyethylene and having an opening was placed on the working electrode. At this time, the porous titanium oxide layer was arranged in the opening of the thermoplastic resin sheet. Then, the thermoplastic resin sheet was heated at 200 ° C. for 1 minute to be melted and adhered to the working electrode.

Next, the photosensitizing dye Z907 was dissolved in a solvent consisting of a 1: 1 mixture of acetonitrile and tert-butyl alcohol to prepare a dye solution. Then, the working electrode was immersed in this dye solution for 16 hours to support the photosensitizing dye on the porous titanium oxide layer.

Next, the electrolyte prepared as described above was applied to the working electrode by a screen printing method so as to cover the porous titanium oxide layer. In this way, a laminate was obtained.

On the other hand, a titanium foil having a size of 52 mm × 107 mm × 40 μm was prepared, and platinum was sputtered on the titanium foil to obtain an opposed substrate.

Then, after the facing substrate is arranged so as to close the opening of the sealing portion forming body of the laminated body, the sealing portion is formed by heating and melting under reduced pressure (1000 Pa) while pressurizing the sealing portion forming body. I stuck it to my body.

In this way, a photoelectric conversion element was obtained. At this time, the sealing portion forming body became a sealing portion.

<Evaluation of photoelectric conversion characteristics>
The photoelectric conversion elements of Examples 1 to 4 and Comparative Examples 1 and 2 obtained as described above were irradiated with light having an illuminance of 200 lux at room temperature (25 ° C.) using a white LED light source. V measurement was performed to obtain an output P. Then, the output P obtained for the photoelectric conversion element of Comparative Example 2 was set to P0, and P / P0 was calculated. The results are shown in Table 1.

From the results shown in Table 1, P / P0 was larger than 1 in the photoelectric conversion elements of Examples 1 to 4. On the other hand, in the photoelectric conversion element of Comparative Example 1, P / P0 was smaller than 1.

From the above, it was confirmed that the electrolyte for a photoelectric conversion element of the present invention can improve the photoelectric conversion characteristics of the photoelectric conversion element.

In the photoelectric conversion element after the IV measurement, the opposing substrate was peeled off from the laminated body, the internal electrolyte was extracted, and the absorption spectrum thereof was measured to determine the absorbance. When the concentration of 1H-benzimidazole dissolved in the electrolyte was calculated from the obtained absorbance, in all of Examples 1 to 4 and Comparative Examples 1 and 2, the concentration of 1H-benzimidazole dissolved in the electrolyte was calculated. The concentration was 0.44M, which was the same. Nevertheless, the photoelectric conversion characteristics of Examples 1 to 4 based on Comparative Example 2 were improved. Therefore, it was found that the imidazole compound precipitated from the electrolyte contributed to the improvement of the photoelectric conversion characteristics.

10 ... Electrode substrate 20 ... Opposing substrate 30 ... Oxide semiconductor layer 40 ... Electrolyte 60 ... Photoelectric conversion cell 70 ... Electrode structure 100 ... Photoelectric conversion element A ... Solid imidazole compound at 25 ° C

Claims (6)

An electrolyte for a photoelectric conversion element containing an imidazole compound solid at 25 ° C. so as to have a concentration higher than the solubility of the imidazole compound at 25 ° C. The electrolyte for a photoelectric conversion element according to claim 1, wherein R defined by the following formula (1) satisfies the following formula (2).
R = m2 / (m-m2) ... (1)
(In the above formula (1), m2 is the mass of the imidazole compound precipitated in the electrolyte at 25 ° C. after heating the electrolyte to dissolve the imidazole compound in the electrolyte and leaving it for 12 hours. g) is represented, and m represents the mass (g) of the electrolyte before the imidazole compound is precipitated in the electrolyte.)

0 <R <0.05 ... (2)
The electrolyte for a photoelectric conversion element according to claim 1 or 2, wherein the imidazole compound contains a benzimidazole compound. Equipped with a photoelectric conversion cell
The photoelectric conversion cell
With the electrode substrate
Opposing substrate facing the electrode substrate and
The oxide semiconductor layer provided on the electrode substrate and
It is provided with an electrolyte provided between the electrode substrate and the facing substrate.
A photoelectric conversion element in which the electrolyte is the electrolyte for a photoelectric conversion element according to any one of claims 1 to 3. The photoelectric conversion element according to claim 4, wherein a part of the imidazole compound is precipitated on the surface of the oxide semiconductor layer in the electrolyte. With the electrode substrate
It is provided with an oxide semiconductor layer provided on the electrode substrate.
An electrode structure for a photoelectric conversion element in which a solid imidazole compound is adhered on the surface of the oxide semiconductor layer at 25 ° C.

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