Photoelectric conversion element and its manufacturing method

Abstract

This photoelectric conversion element (100) is obtained by integrating a multilayer body which sequentially comprises a light-transmitting substrate (1), a transparent conductive film (2), a first conductive layer (5), a power generation layer (6) and a second conductive layer (7) in this order. The second conductive layer (7) is formed of a porous free-standing sheet that contains at least single-walled carbon nanotubes, while internally containing an ionic compound.

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion element and a method for manufacturing the same. [Background technology]

[0002] Solar cells have attracted attention as photoelectric conversion elements that convert light energy into electricity. There are various types of solar cells, such as perovskite solar cells that use perovskite compounds as the power generation layer. In recent years, much research has been done to improve the photoelectric conversion efficiency of photoelectric conversion elements and solar cells.

[0003] For example, Patent Document 1 proposes a solar cell having a transparent electrode layer, a perovskite layer, and a carbon electrode layer adjacent to the perovskite layer, in which the carbon electrode layer contains a carbon material modified with a functional group having a hydrogen atom.

[0004] Furthermore, Patent Document 2 proposes a photoelectric conversion element including a first electrode, a second electrode including a substrate including a plurality of structures including carbon and a first material portion provided between the plurality of structures and including a carrier transport material, a photoelectric conversion layer provided between the first electrode and the second electrode and including a material having a perovskite structure, and a first layer provided between the photoelectric conversion layer and the second electrode and including a carrier transport material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-88316 [Patent Document 2] Patent No. 6339037 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional photoelectric conversion elements have room for improvement in terms of exhibiting excellent photoelectric conversion efficiency and ease of manufacture.

[0007] Therefore, an object of the present invention is to provide a photoelectric conversion element that exhibits excellent photoelectric conversion efficiency and is easy to manufacture, and a method for manufacturing the same. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have found that by providing a porous free-standing sheet containing at least single-walled carbon nanotubes on a power generation layer of a photoelectric conversion element, the porous free-standing sheet can function as a hole transport layer and a current collecting electrode, thereby completing the present invention.

[0009] The photoelectric conversion element of the present invention is a photoelectric conversion element comprising a laminate including a translucent substrate, a transparent conductive film, a first conductive layer, a power generation layer, and a second conductive layer, which are integrated in this order, wherein the second conductive layer is made of a porous free-standing sheet containing at least single-walled carbon nanotubes and contains an ionic compound therein. With this configuration, it is possible to provide a photoelectric conversion element that exhibits excellent photoelectric conversion efficiency and is easy to manufacture.

[0010] In the present invention, the term "porous free-standing sheet" refers to a sheet having a plurality of pores formed therein, which maintains its shape even without a support. The porous free-standing sheet used in the present invention maintains its shape without tearing even when the porous free-standing sheet is immersed in a predetermined solution, pulled out, and then attached to an object to be attached. Furthermore, the porous free-standing sheet used in the present invention does not tear or deform even when, for example, chlorobenzene, which is a poor solvent for perovskite compounds, is dropped onto the sheet or when it is handled using a jig for attaching the sheet. The porous free-standing sheet used in the present invention has a thickness of 1 μm to 200 μm, an area of ​​1 mm, and a thickness of 1 μm to 200 μm.2 ~100cm 2 It is preferable that the sheet maintains its shape without a support at this size.

[0011] In the photoelectric conversion element of the present invention, the ionic compound is preferably present at least at the interface between the power generation layer and the second conductive layer, which can further improve the performance of the photoelectric conversion element.

[0012] In the photoelectric conversion element of the present invention, the ionic compound preferably contains a metal cation. With this configuration, the performance of the photoelectric conversion element can be further improved.

[0013] In the photoelectric conversion element of the present invention, the porous free-standing sheet preferably has a thickness of 20 μm or more, which allows the second conductive layer to fully function as a collecting electrode.

[0014] In the photoelectric conversion element of the present invention, the power generation layer preferably contains a perovskite compound. This configuration reduces the manufacturing cost of the photoelectric conversion element and improves the ease of manufacturing the photoelectric conversion element.

[0015] In the photoelectric conversion element of the present invention, the average diameter (Av) and the standard deviation (σ) of the single-walled carbon nanotubes preferably satisfy the relation: 0.20<(3σ / Av)<0.60. This configuration can further increase the photoelectric conversion efficiency.

[0016] The "average diameter (Av) of single-walled carbon nanotubes" and the "standard deviation of the diameters of single-walled carbon nanotubes (σ: standard deviation)" can be determined by measuring the diameters (outer diameters) of 100 randomly selected single-walled carbon nanotubes using a transmission electron microscope. The average diameter (Av) and standard deviation (σ) of single-walled carbon nanotubes may be adjusted by changing the manufacturing method or manufacturing conditions of the single-walled carbon nanotubes, or by combining multiple types of single-walled carbon nanotubes obtained by different manufacturing methods.

[0017] In the photoelectric conversion element of the present invention, the single-walled carbon nanotubes preferably exhibit an upwardly convex t-plot obtained from an adsorption isotherm. This configuration makes it possible to produce a more stable porous free-standing sheet, thereby enabling the stable production of a photoelectric conversion element.

[0018] Furthermore, the present invention provides a method for producing a photoelectric conversion element, which is any of the methods for producing a photoelectric conversion element described above, and which includes the steps of: laminating the porous free-standing sheet on the power generation layer while a solvent is retained on at least one bonding surface of the power generation layer and the porous free-standing sheet; and applying a solution containing an ionic compound to the porous free-standing sheet laminated on the power generation layer, followed by drying. This configuration makes it possible to easily produce a photoelectric conversion element that exhibits excellent photoelectric conversion efficiency. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a photoelectric conversion element that exhibits excellent photoelectric conversion efficiency and is easy to manufacture, and a method for manufacturing the same. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional view schematically showing the configuration of a photoelectric conversion element according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The photoelectric conversion element of the present invention is not particularly limited and can be used, for example, as a perovskite solar cell. One embodiment of the photoelectric conversion element of the present invention will be described in detail below with reference to FIG.

[0022] (Photoelectric conversion element) FIG. 1 is a cross-sectional view schematically illustrating the configuration of a photoelectric conversion element according to one embodiment of the present invention. The photoelectric conversion element 100 is formed by integrating a laminate having, in this order, a light-transmitting substrate 1, a transparent conductive film 2, a first conductive layer 5 consisting of an underlayer 3 and a porous semiconductor layer 4, a power generation layer 6, and a second conductive layer 7. The second conductive layer 7 is made of a porous free-standing sheet containing at least single-walled carbon nanotubes (hereinafter, carbon nanotubes will be referred to as "CNTs") and contains an ionic compound therein. Each of the components constituting the photoelectric conversion element 100 will be described below in order.

[0023] <Transparent substrate 1> The light-transmitting substrate 1 constitutes the base of the photoelectric conversion element 100. The light-transmitting substrate 1 is not particularly limited, and examples thereof include a substrate made of glass or synthetic resin, and a film made of synthetic resin.

[0024] Examples of the glass that constitutes the light-transmitting substrate 1 include inorganic glass such as soda glass.

[0025] Examples of synthetic resins that can be used to form the light-transmitting substrate 1 include polyacrylic resin, polycarbonate resin, polyester resin, polyimide resin, polystyrene resin, polyvinyl chloride resin, polyamide resin, and polycycloolefin resin. Among these, from the viewpoint of obtaining a thin, lightweight, and flexible photoelectric conversion element 100, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are preferred synthetic resins.

[0026] The thickness of the light-transmitting substrate 1 is not particularly limited as long as it can maintain its shape as a substrate. The thickness of the light-transmitting substrate 1 can be, for example, 0.1 mm or more and 10 mm or less.

[0027] <Transparent conductive film 2> The transparent conductive film 2 is a film made of a metal oxide formed on the surface of the light-transmitting substrate 1. By providing the transparent conductive film 2, the surface of the light-transmitting substrate 1 can be made conductive.

[0028] Examples of metal oxides constituting the transparent conductive film 2 include fluorine-doped tin oxide (FTO), tin oxide (SnO), indium oxide (In2O3), tin-doped indium oxide (ITO), zinc oxide (ZnO), indium oxide / zinc oxide (IZO), and gallium oxide / zinc oxide (GZO). Although the photoelectric conversion element 100 shown in FIG. 1 has one transparent conductive film 2 on the translucent substrate 1, the translucent substrate 1 may have two or more transparent conductive films 2. When the photoelectric conversion element 100 has two or more transparent conductive films 2, the transparent conductive films may be made of the same metal oxide or different metal oxides.

[0029] The thickness of the transparent conductive film 2 is not particularly limited as long as it can impart the desired conductivity to the light-transmitting substrate 1, and can be, for example, 1 nm or more and 1 μm or less. The transparent conductive film 2 may be formed on the entire surface of the light-transmitting substrate 1, or may be formed on only a part of the surface of the light-transmitting substrate 1, as shown in FIG.

[0030] <First conductive layer 5> The first conductive layer 5 is a layer that functions as a charge transport layer and is made of an n-type semiconductor. In this embodiment, the first conductive layer 5 is made of two layers, the base layer 3 and the porous semiconductor layer 4, but is not limited to this, and the first conductive layer 5 may be a single layer made of an n-type semiconductor.

[0031] <Base layer 3> The underlayer 3 is an optional layer. By providing the underlayer 3, the light-transmitting substrate 1 and the transparent conductive film 2 are prevented from coming into direct contact with the porous semiconductor layer 4. This prevents loss of electromotive force, thereby improving the photoelectric conversion efficiency of the photoelectric conversion element 100.

[0032] The underlayer 3 may be a porous film or a non-porous dense film, as long as it is made of, for example, an n-type semiconductor. However, from the viewpoint of sufficiently preventing contact between the light-transmitting substrate 1 and the transparent conductive film 2 and the porous semiconductor layer 4, the underlayer 3 is preferably a non-porous dense film. The thickness of the underlayer 3 is not particularly limited and may be, for example, 1 nm or more and 500 nm or less. Furthermore, the underlayer 3 may optionally contain an insulating material other than an n-type semiconductor in a proportion that does not impair the properties of the underlayer 3 as an n-type semiconductor.

[0033] <Porous semiconductor layer 4> The porous semiconductor layer 4 is a porous layer. When the first conductive layer 5 includes the porous semiconductor layer 4, the photoelectric conversion efficiency of the photoelectric conversion element 100 can be further improved.

[0034] The thickness of the porous semiconductor layer 4 is not particularly limited, but is usually 5 nm or more, preferably 10 nm or more, and usually 500 nm or less, preferably 100 nm or less. The porous semiconductor layer 4 may be formed from one layer, as shown in Figure 1, or may be formed from multiple layers.

[0035] <Power Generation Layer 6> The power generation layer 6 is a layer made of a material that generates electromotive force by absorbing light, and is preferably a layer containing a perovskite compound, and more preferably a layer made of a perovskite compound (perovskite layer).

[0036] The perovskite compound constituting the power generation layer 6 is not particularly limited, and known perovskite compounds can be used. Specifically, examples of perovskite compounds include CH3NH3PbI3, CH3NH3PbBr3, (CH3(CH2)nCHCH3N H3)2PbI4[n=5-8], (C6H5C2H4NH3)2PbBr4, etc. can be used.

[0037] The thickness of the power generating layer 6 is not particularly limited, but is preferably 100 nm or more, more preferably 200 nm or more, and is preferably 1 μm or less, more preferably 800 nm or less. By making the thickness of the power generating layer 6 100 nm or more, the electromotive force of the power generating layer 6 can be increased.

[0038] <Second conductive layer 7> The second conductive layer 7 is a layer made of a porous free-standing sheet and containing an ionic compound therein. The porous free-standing sheet must contain at least single-walled CNTs, and is preferably a sheet made of single-walled CNTs, more preferably a sheet made of buckypaper. The use of a porous free-standing sheet containing at least single-walled CNTs can impart to the second conductive layer 7 the functions of an excellent hole transport layer and a current collecting electrode. The ionic compound contained in the second conductive layer 7 is preferably present at least at the interface between the power generating layer 6 and the second conductive layer 7. The ionic compound may be contained not only in the second conductive layer 7 but also in the power generating layer 6 (for example, near the interface between the power generating layer 6 and the second conductive layer 7).

[0039] <<Porous self-standing sheet>> The single-walled CNTs contained in the porous free-standing sheet preferably have the following properties.

[0040] -(3σ / Av)- The single-walled CNTs contained in the porous free-standing sheet preferably have a ratio (3σ / Av) of the standard deviation (σ) of diameters multiplied by 3 (3σ) to the average diameter (Av) of the single-walled CNTs greater than 0.20, more preferably greater than 0.25, even more preferably greater than 0.50, and preferably less than 0.60. If 3σ / Av is greater than 0.20 and less than 0.60, even if the amount of single-walled CNTs contained in the porous free-standing sheet is small, the second conductive layer 7 can be provided with sufficient functions as a hole transport layer and a current collecting electrode.

[0041] -Average diameter of single-walled CNTs (Av)- The average diameter (Av) of the single-walled CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, and preferably 15 nm or less, and more preferably 10 nm or less. If the average diameter (Av) of the single-walled CNTs is 0.5 nm or more, aggregation of the single-walled CNTs can be suppressed, and the dispersibility of the single-walled CNTs in the second conductive layer 7 can be increased. Furthermore, if the average diameter (Av) of the single-walled CNTs is 15 nm or less, the second conductive layer 7 can fully function as a current collecting electrode.

[0042] -t-plot- The single-walled CNTs preferably have a convex t-plot obtained from the adsorption isotherm. Such single-walled CNTs are more preferably those that have not been subjected to an aperture treatment. The use of single-walled CNTs that have a convex t-plot obtained from the adsorption isotherm allows for the second conductive layer 7 to have excellent strength.

[0043] The inflection point of the t-plot for single-walled CNTs is preferably in the range satisfying 0.2≦t(nm)≦1.5, more preferably in the range of 0.45≦t(nm)≦1.5, and even more preferably in the range of 0.55≦t(nm)≦1.0.

[0044] Measurement of the adsorption isotherm of single-walled CNT, creation of t-plots, and analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0045] Single-walled CNTs having the properties described above can be efficiently produced by, for example, a method in which raw material compounds and a carrier gas are supplied to a substrate having a catalyst layer for CNT production on its surface, and CNTs are synthesized by chemical vapor deposition (CVD) using a method in which the catalytic activity of the catalyst layer is dramatically improved by adding a trace amount of oxidizing agent (catalytic activator) to the system (super-growth method; see WO 2006 / 011655), and the catalyst layer is formed on the substrate surface using a wet process.

[0046] Among these, from the viewpoint of easily obtaining a porous free-standing sheet with a large thickness, it is preferable to use single-walled CNTs obtained by the super-growth method.

[0047] Furthermore, the porous free-standing sheet preferably contains, within the porous free-standing sheet, the material (e.g., perovskite compound) that constitutes the power generation layer 6. More specifically, the porous free-standing sheet preferably contains, within the multiple pores of the porous free-standing sheet, the material (e.g., perovskite compound) that constitutes the power generation layer 6.

[0048] The proportion of single-walled CNTs contained in the porous free-standing sheet is not particularly limited, but is preferably 50% by mass or more, and more preferably 75% by mass or more.

[0049] Furthermore, materials other than single-walled CNTs that may be optionally contained in the porous free-standing sheet include, for example, organic and inorganic materials as p-type semiconductors, and fibrous carbon nanostructures other than single-walled CNTs.

[0050] Examples of organic materials that can be contained in the porous free-standing sheet include 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-MeOTAD), poly(3-hexylthiophene) (P3HT), and polytriallylamine (PTAA).

[0051] Examples of inorganic materials that can be contained in the porous free-standing sheet include CuI, CuSCN, CuO, and Cu2O.

[0052] The thickness of the porous free-standing sheet is preferably 20 μm or more, more preferably 30 μm or more, and is preferably 200 μm or less, and more preferably 80 μm or less. If the thickness of the porous free-standing sheet is 20 μm or more and 200 μm or less, the second conductive layer 7 can exhibit a better function as a collecting electrode.

[0053] <<Method of manufacturing porous freestanding sheets>> The method for producing a porous free-standing sheet is not particularly limited, and for example, a method including a step of removing the solvent from a fibrous carbon nanostructure dispersion containing fibrous carbon nanostructures containing at least single-walled CNTs, a dispersant, and a solvent to form a porous free-standing sheet (film formation step) can be adopted. Furthermore, the method for producing a porous free-standing sheet may optionally include a step of dispersing a crude dispersion containing fibrous carbon nanostructures containing at least single-walled CNTs, a dispersant, and a solvent to prepare the fibrous carbon nanostructure dispersion (dispersion preparation step) before the film formation step.

[0054] -Dispersion liquid preparation process- In the dispersion preparation step, a crude dispersion containing at least single-walled CNT-containing fibrous carbon nanostructures, a dispersant, and a solvent is preferably subjected to a dispersion treatment that produces, but is not particularly limited to, a cavitation effect or a disintegration effect, as described below, to disperse the single-walled CNT-containing fibrous carbon nanostructures and prepare a fibrous carbon nanostructure dispersion. By performing a dispersion treatment that produces a cavitation effect or a disintegration effect in this manner, a fibrous carbon nanostructure dispersion in which the single-walled CNT-containing fibrous carbon nanostructures are well dispersed can be obtained. Furthermore, by producing a porous free-standing sheet using fibrous carbon nanostructures in which the single-walled CNTs are well dispersed, the single-walled CNTs can be uniformly dispersed, resulting in a porous free-standing sheet with excellent properties such as electrical conductivity, thermal conductivity, and mechanical properties. The fibrous carbon nanostructure dispersion used to produce the porous free-standing sheet may also be prepared by dispersing the single-walled CNT-containing fibrous carbon nanostructures in a solvent using a known dispersion treatment other than the above.

[0055] The fibrous carbon nanostructures used in preparing the fibrous carbon nanostructure dispersion may be any that contain at least single-walled CNTs, and may be, for example, a mixture of single-walled CNTs and fibrous carbon nanostructures other than single-walled CNTs (e.g., multi-walled CNTs).

[0056] Here, the content ratio of single-walled CNTs and fibrous carbon nanostructures other than single-walled CNTs in the fibrous carbon nanostructure dispersion can be, for example, 50 / 50 to 75 / 25 in mass ratio (single-walled CNTs / fibrous carbon nanostructures other than single-walled CNTs).

[0057] =Dispersant= The dispersant used in preparing the fibrous carbon nanostructure dispersion is not particularly limited as long as it can disperse at least the fibrous carbon nanostructures containing single-walled CNTs and can be dissolved in the solvent used in preparing the fibrous carbon nanostructure dispersion. Examples of such dispersants that can be used include surfactants, synthetic polymers, and natural polymers.

[0058] Examples of surfactants include sodium dodecyl sulfonate, sodium deoxycholate, sodium cholate, and sodium dodecylbenzenesulfonate.

[0059] Examples of synthetic polymers include polyether diols, polyester diols, polycarbonate diols, polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, acetal group-modified polyvinyl alcohol, butyral group-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, ethylene-vinyl alcohol-vinyl acetate copolymer resin, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, acrylic resins, epoxy resins, modified epoxy resins, phenoxy resins, modified phenoxy resins, phenoxy ether resins, phenoxy ester resins, fluorine-based resins, melamine resins, alkyd resins, phenolic resins, polyacrylamide, polyacrylic acid, polystyrene sulfonic acid, polyethylene glycol, and polyvinylpyrrolidone.

[0060] Further, examples of natural polymers include polysaccharides such as starch, pullulan, dextran, dextrin, guar gum, xanthan gum, amylose, amylopectin, alginic acid, gum arabic, carrageenan, chondroitin sulfate, hyaluronic acid, curdlan, chitin, chitosan, and cellulose, as well as salts or derivatives thereof, where derivatives refer to conventionally known compounds such as esters and ethers.

[0061] These dispersants can be used alone or in combination of two or more. Among them, surfactants are preferred as dispersants because they have excellent dispersibility for fibrous carbon nanostructures including single-walled CNTs, and sodium deoxycholate is more preferred.

[0062] =Solvent= The solvent for the fibrous carbon nanostructure dispersion is not particularly limited, and examples thereof include water, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and amyl alcohol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, esters such as ethyl acetate and butyl acetate, ethers such as diethyl ether, dioxane, and tetrahydrofuran, amide-based polar organic solvents such as N,N-dimethylformamide and N-methylpyrrolidone, and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, and paradichlorobenzene. These solvents may be used alone or in combination of two or more.

[0063] In the dispersion liquid preparation step, it is preferable to carry out a dispersion treatment that can obtain, for example, the cavitation effect or the disintegration effect described below.

[0064] ~Dispersion processing that produces a cavitation effect~ Dispersion treatment that utilizes the cavitation effect is a dispersion method that utilizes shock waves generated by the bursting of vacuum bubbles generated in water when high energy is applied to the liquid. This dispersion method can be used to effectively disperse single-walled CNTs.

[0065] Specific examples of dispersion treatments that can achieve the cavitation effect include dispersion treatment using ultrasonic waves, dispersion treatment using a jet mill, and dispersion treatment using high-shear stirring. These dispersion treatments may be performed alone or in combination. More specifically, for example, ultrasonic homogenizers, jet mills, and high-shear stirring devices are preferably used. These devices may be conventionally known.

[0066] When using an ultrasonic homogenizer to disperse single-walled CNTs, the crude dispersion liquid is irradiated with ultrasonic waves using the ultrasonic homogenizer. The irradiation time can be appropriately set depending on the amount of single-walled CNTs, and is, for example, preferably 3 minutes or more, more preferably 30 minutes or more, and preferably 5 hours or less, more preferably 2 hours or less. Furthermore, for example, the output is preferably 20 W or more and 500 W or less, more preferably 100 W or more and 500 W or less, and the temperature is preferably 15 °C or more and 50 °C or less.

[0067] Furthermore, when a jet mill is used, the number of times of treatment may be appropriately set depending on the amount of single-walled CNTs, etc., and is, for example, preferably 2 times or more, more preferably 5 times or more, and preferably 100 times or less, more preferably 50 times or less. Furthermore, for example, the pressure is preferably 20 MPa or more and 250 MPa or less, and the temperature is preferably 15°C or more and 50°C or less.

[0068] Furthermore, when high shear mixing is used, the coarse dispersion can be stirred and sheared using a high shear mixing device. The faster the rotation speed, the better. For example, the operating time (the time the machine is rotating) is preferably 3 minutes to 4 hours, the peripheral speed is preferably 5 m / s to 50 m / s, and the temperature is preferably 15°C to 50°C.

[0069] It is more preferable that the dispersion treatment that produces the above-mentioned cavitation effect is carried out at a temperature of 50° C. or less, because this suppresses changes in concentration due to evaporation of the solvent.

[0070] ~Dispersion processing that produces a crushing effect~ Dispersion treatments that produce a crushing effect are not only able to uniformly disperse single-walled CNTs in a solvent, but are also more advantageous than dispersion treatments that produce the cavitation effect described above in that they can suppress damage to single-walled CNTs caused by shock waves when bubbles disappear.

[0071] In the dispersion process that produces this disintegration effect, shear force is applied to the coarse dispersion to disintegrate and disperse the aggregates of fibrous carbon nanostructures containing single-walled CNTs, and then back pressure is applied to the coarse dispersion, and the coarse dispersion is cooled as necessary, thereby suppressing the generation of bubbles and uniformly dispersing the single-walled CNTs in the solvent.

[0072] When a back pressure is applied to the crude dispersion, the back pressure applied to the crude dispersion may be reduced to atmospheric pressure in one go, but it is preferable to reduce the pressure in multiple stages.

[0073] -Film forming process- In the film-forming step, the solvent is removed from the above-mentioned fibrous carbon nanostructure dispersion to form a porous free-standing sheet. Specifically, in the film-forming step, the solvent is removed from the fibrous carbon nanostructure dispersion to form a porous free-standing sheet, for example, by using either of the following methods (A) and (B). (A) A method in which a dispersion liquid of fibrous carbon nanostructures is applied to a film-forming substrate, and then the applied dispersion liquid of fibrous carbon nanostructures is dried. (B) A method in which a fibrous carbon nanostructure dispersion is filtered using a porous film-forming substrate, and the resulting filtrate is dried.

[0074] [Film-forming base material] Here, the film-forming substrate is not particularly limited, and any known substrate can be used.

[0075] Specifically, in the above-mentioned method (A), examples of the film-forming substrate onto which the fibrous carbon nanostructure dispersion is applied include resin substrates, glass substrates, etc. Here, examples of the resin substrate include substrates made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytetrafluoroethylene (PTFE), polyimide, polyphenylene sulfide, aramid, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polycarbonate, polymethyl methacrylate, alicyclic acrylic resin, cycloolefin resin, triacetyl cellulose, etc. Furthermore, examples of the glass substrate include substrates made of ordinary soda glass.

[0076] In the above method (B), examples of the film-forming substrate for filtering the fibrous carbon nanostructure dispersion include filter paper and porous sheets made of cellulose, nitrocellulose, alumina, and the like.

[0077] [Coating] In the above method (A), the fibrous carbon nanostructure dispersion can be applied to the film-forming substrate by a known coating method, such as dipping, roll coating, gravure coating, knife coating, air knife coating, roll knife coating, die coating, screen printing, spray coating, or gravure offset.

[0078] [Filtration] In the above method (B), the fibrous carbon nanostructure dispersion can be filtered using a film-forming substrate by any known filtration method, such as natural filtration, reduced pressure filtration, pressure filtration, centrifugal filtration, etc.

[0079] [Drying] The fibrous carbon nanostructure dispersion applied to the film-forming substrate in the above method (A) or the filtered product obtained in the above method (B) can be dried by a known drying method. Examples of the drying method include hot air drying, vacuum drying, hot roll drying, and infrared irradiation. The drying temperature is not particularly limited, but is usually room temperature to 200°C, and the drying time is not particularly limited, but is usually 0.1 to 150 minutes.

[0080] <Post-treatment of porous freestanding sheets> Here, the porous free-standing sheet formed as described above typically contains the components contained in the fibrous carbon nanostructure dispersion, such as single-walled CNTs, fibrous carbon nanostructures other than single-walled CNTs, and dispersants, in the same proportions as in the fibrous carbon nanostructure dispersion. Therefore, in the method for producing a porous free-standing sheet, the porous free-standing sheet formed in the film formation step may optionally be washed to remove the dispersant from the porous free-standing sheet. Removing the dispersant from the porous free-standing sheet can further improve the properties of the porous free-standing sheet, such as its conductivity.

[0081] The porous free-standing sheet can be washed by contacting it with a solvent capable of dissolving the dispersant and dissolving the dispersant in the porous free-standing sheet into the solvent. The solvent capable of dissolving the dispersant in the porous free-standing sheet is not particularly limited, and the solvents described above that can be used as solvents for the fibrous carbon nanostructure dispersion can be used, preferably the same solvents as the fibrous carbon nanostructure dispersion. The contact between the porous free-standing sheet and the solvent can be achieved by immersing the porous free-standing sheet in the solvent or by applying the solvent to the porous free-standing sheet. After washing, the porous free-standing sheet can be dried using a known method.

[0082] Furthermore, when producing a porous free-standing sheet, the porous free-standing sheet formed in the film formation step may be optionally pressed to further increase the density, etc., to adjust the voids as needed. From the viewpoint of suppressing deterioration of properties due to damage or destruction of the single-walled CNTs, the pressing pressure during pressing is preferably less than 3 MPa, and it is more preferable not to perform pressing.

[0083] <<Ionic compounds>> The ionic compound contained inside the second conductive layer 7 is not particularly limited, and known ionic compounds can be used. Specifically, metal cations, organic cations, etc. can be used as cations constituting the ionic compound. These may be used alone or in combination of two or more. Among these, it is preferable to contain a metal cation.

[0084] The cations constituting the ionic compound are not particularly limited, and examples thereof include metal cations such as lithium ions, sodium ions, and potassium ions, and organic cations such as guanidinium ions. These may be used alone or in combination of two or more. The anions constituting the ionic compound are not particularly limited, and examples thereof include imide ions such as bis(trifluoromethanesulfonyl)imide ions and bis(fluorosulfonyl)imide ions, and halogen ions such as fluoride ions and chloride ions. These may be used alone or in combination of two or more.

[0085] The ionic compound is not particularly limited, and examples thereof include lithium salts such as lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide, and sodium salts such as sodium bis(trifluoromethanesulfonyl)imide and sodium bis(fluorosulfonyl)imide. These may be used alone or in combination of two or more.

[0086] According to the photoelectric conversion element 100 described above, the second conductive layer 7 alone can function as both a hole transport layer and a collecting electrode. Furthermore, since the second conductive layer 7 is made of a porous freestanding sheet containing at least single-walled CNTs, its shape is stable. Therefore, with this configuration, it is easy to increase the area of ​​the photoelectric conversion element. Furthermore, since the second conductive layer 7 contains an ionic compound, excellent photoelectric conversion efficiency can be achieved.

[0087] The photoelectric conversion element of the present invention may further include other layers, etc., as long as the photoelectric conversion element is an integrated laminate in which the order of the above-mentioned components is maintained, the second conductive layer is made of a porous free-standing sheet containing at least single-walled CNTs, and the photoelectric conversion element contains an ionic compound therein, as long as the effects of the present invention are not impaired.

[0088] (Method of manufacturing a photoelectric conversion element) Next, the method for manufacturing a photoelectric conversion element of the present invention will be described again with reference to FIG. 1. The method for manufacturing a photoelectric conversion element 100 of the present invention must include the steps of laminating a porous free-standing sheet on a power generation layer 6 while at least one bonding surface of the power generation layer 6 and the porous free-standing sheet retains a solvent (hereinafter referred to as solvent X), and applying a solution containing an ionic compound to the porous free-standing sheet laminated on the power generation layer 6, and drying it. Note that the "bonding surface" mentioned above refers to the surface on which the power generation layer 6 and the porous free-standing sheet face each other. The method for manufacturing a photoelectric conversion element 100 will be described in detail below.

[0089] <Preparation of Light-Transmitting Substrate 1> In the method for manufacturing the photoelectric conversion element 100 of the present invention, first, a light-transmitting substrate 1 is prepared. As the type of light-transmitting substrate 1, those listed in the "Photoelectric conversion element" section can be used.

[0090] <Formation of transparent conductive film 2> Next, a transparent conductive film 2 is formed on the light-transmitting substrate 1. The method for forming the transparent conductive film 2 is not particularly limited, and known methods such as sputtering and vapor deposition can be used. Note that the formation of the transparent conductive film 2 may be omitted by using a commercially available light-transmitting substrate on the surface of which a transparent conductive film is formed.

[0091] <Formation of First Conductive Layer 5> Furthermore, a first conductive layer 5 is formed on the transparent conductive film 2. The first conductive layer 5 is obtained by forming an underlayer 3 on the transparent conductive film 2, and then forming a porous semiconductor layer 4 thereon.

[0092] [Formation of Underlayer 3] The method for forming the underlayer 3 is not particularly limited, and for example, it can be formed by spraying a solution containing a material that forms an n-type semiconductor onto the transparent conductive film 2.

[0093] Here, examples of methods for spraying the fine particles include spray pyrolysis, aerosol deposition, electrostatic spray, and cold spray.

[0094] [Formation of Porous Semiconductor Layer 4] The method for forming the porous semiconductor layer 4 is not particularly limited, and it can be formed, for example, by applying a solution containing a precursor of an n-type semiconductor onto the underlayer 3 by a spin coating method or the like, and drying it.

[0095] Here, examples of precursors for n-type semiconductors include titanium tetrachloride (TiCl4), peroxide, and the like. Examples include titanium alkoxides such as titanium alkoxide (PTA), titanium ethoxide, and titanium isopropoxide (TTIP); and metal alkoxides such as zinc alkoxide, alkoxysilane, zirconium alkoxide, and titanium diisopropoxide bis(acetylacetonate).

[0096] The solvent used for the solution containing the precursor of the n-type semiconductor is not particularly limited, and for example, an alcohol solution such as ethanol can be used.

[0097] Furthermore, the temperature and time for drying the solution applied onto the underlayer 3 are not particularly limited, and may be adjusted appropriately depending on the type of n-type precursor and the type of solvent used.

[0098] <Formation of power generation layer 6> Then, the power generation layer 6 is formed on the first conductive layer 5. The method for forming the power generation layer 6 includes, but is not limited to, vacuum deposition and coating methods. For example, the power generation layer 6 can be formed by applying a precursor-containing solution containing a precursor of a perovskite compound onto the first conductive layer 5 and baking it. Here, examples of the precursor of the perovskite compound include lead iodide (PbI2), iodide (PbI3), and the like. Examples of suitable solvents include methylammonium chloride (CH3NH3I). The solvent contained in the precursor-containing solution is not particularly limited, and examples thereof include N,N-dimethylformamide and dimethyl sulfoxide. After applying these solutions, it is also possible to promote the precipitation of the perovskite compound by using a poor solvent. In this specification, a poor solvent refers to a solvent that does not substantially change the perovskite compound during the preparation process. If no visible changes in the appearance of the perovskite compound, such as cloudiness of the film, are observed during the preparation process, it can be said that the perovskite compound does not substantially change.

[0099] Here, the concentration of the precursor of the perovskite compound in the precursor-containing solution may be appropriately selected depending on the solubility of the materials that make up the perovskite compound, and may be, for example, about 0.5M to 1.5M.

[0100] The method for applying the precursor-containing solution onto the first conductive layer 5 is not particularly limited, and known application methods such as spin coating, spraying, and bar coating can be used.

[0101] <Formation of second conductive layer 7> After forming the power generating layer 6, the second conductive layer 7 is formed on the power generating layer 6. Specifically, the porous free-standing sheet is laminated on the power generating layer 6 in a state in which the solvent X is retained on at least one bonding surface of the power generating layer 6 and the porous free-standing sheet. This allows the porous free-standing sheet to be efficiently attached to the power generating layer 6.

[0102] The solvent X is not particularly limited, and examples thereof include poor solvents such as chlorobenzene, toluene, anisole, etc. If such poor solvents are used, for example, when the power generation layer 6 is a perovskite layer made of a perovskite compound, the porous free-standing sheet can be successfully attached to the power generation layer 6.

[0103] Furthermore, by using a porous self-supporting sheet impregnated with the solvent X, the solvent X can be well retained on at least one of the bonding surfaces of the power-generating layer 6 and the porous self-supporting sheet.

[0104] Here, a porous free-standing sheet impregnated with solvent X can be obtained, for example, by immersing a porous free-standing sheet in solvent X and then removing it. In this case, the immersion time is not particularly limited and may be set appropriately depending on the type of solvent used, etc.

[0105] <Heat pressing> In the method for manufacturing the photoelectric conversion element 100 of the present invention, after laminating the porous free-standing sheet on the power generation layer 6, the porous free-standing sheet is preferably hot-pressed before applying a solution containing an ionic compound to the porous free-standing sheet. This allows for the production of a photoelectric conversion element 100 with excellent integrity. The heating temperature is not particularly limited, but can typically be selected from room temperature to 200°C based on the boiling point of the solvent X and a temperature that has minimal effect on the perovskite layer. The pressing time is also not particularly limited, but typically is 1 second to 10 minutes. The pressure applied during hot-pressing is not particularly limited as long as it does not affect the substrate or the formed film, and can be, for example, 0.01 to 0.5 MPa. To facilitate removal of the solvent component from the porous free-standing sheet, hot-pressing is preferably performed in a manner that ensures a solvent evaporation path. Specifically, to ensure a solvent evaporation path, hot-pressing is preferably performed via a porous member such as a thick wipe, porous rubber, porous metal, or porous ceramic.

[0106] <Addition of a solution containing an ionic compound> A porous free-standing sheet is laminated on the power-generating layer 6, and optionally subjected to the above-mentioned hot pressing. Then, a solution containing an ionic compound (hereinafter referred to as solution Y) is applied to the porous free-standing sheet and allowed to penetrate. The solvent for dissolving the ionic compound is not particularly limited, but examples include poor solvents such as chlorobenzene, toluene, and anisole. As the ionic compound, those listed in the "Ionic Compound" section can be used. The concentration of the ionic compound in the solution varies depending on the amount of liquid applied and the application method, so it can be appropriately selected depending on the method. It is not particularly limited, but is preferably 0.001 M or more, more preferably 0.01 M or more, and preferably 0.3 M or less, and more preferably 0.1 M or less.

[0107] The specific method for applying solution Y to the porous self-supporting sheet is not particularly limited, and examples of coating methods that can be used include dipping, roll coating, gravure coating, knife coating, air knife coating, roll knife coating, die coating, screen printing, spray coating, and gravure offset.

[0108] <Drying> After applying solution Y to the porous free-standing sheet, the porous free-standing sheet is dried. Known drying methods can be used to dry the porous free-standing sheet. Examples of drying methods include hot air drying, vacuum drying, heat roll drying, infrared irradiation, and heat pressing. The drying temperature and drying time can be appropriately selected depending on the solvent used in solution Y and the amount of liquid applied. The drying temperature is not particularly limited, but is preferably room temperature or higher, more preferably 80°C or higher, and preferably 200°C or lower, and more preferably 120°C or lower. The drying time is not particularly limited, but is preferably 1 second or longer, more preferably 10 seconds or longer, and preferably 10 minutes or shorter, and more preferably 1 minute or shorter.

[0109] Among the above, the hot pressing method is preferably used. When the hot pressing method is used, the heating temperature and heating time can be appropriately selected depending on the solvent used for solution Y and the amount of liquid applied. Furthermore, when hot pressing, in order to promote the removal of the solvent component contained in the porous free-standing sheet, it is preferable to press in a manner that ensures a solvent evaporation path. Specifically, in order to ensure a solvent evaporation path, it is preferable to hot press through a member having pores, such as a thick wipe, porous rubber, porous metal, or porous ceramic.

[0110] According to the above-described manufacturing method, it is possible to easily manufacture a photoelectric conversion element 100 that exhibits excellent photoelectric conversion efficiency. Note that the manufacturing method of the photoelectric conversion element of the present invention is not limited to the above-described method, and may include steps other than the above-described steps as long as the effects of the present invention are not impaired. [Example]

[0111] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, the cell performance of the fabricated perovskite solar cells was measured using the following method.

[0112] <Battery performance> A solar simulator (WXS-90S-L2, AM1.5GMM, manufactured by Wacom Electronics Co., Ltd.) was used as the light source. The light source was 1 sun [AM1.5G, 100 mW / cm 2 (JIS C The fabricated perovskite solar cell was connected to a source meter (6244 type DC voltage / current source, manufactured by ADC) and the following current-voltage characteristics were measured.

[0113] Under 1 sun of light irradiation, the output current was measured while changing the bias voltage in 0.01 V increments from -0.2 V to 1.0 V. The output current was measured by integrating the value from 0.5 seconds to 0.6 seconds after changing the voltage at each voltage step.

[0114] From the measurement results of the current-voltage characteristics above, the short-circuit current density (mA / cm 2 ), open circuit voltage (V), form factor, and photoelectric conversion efficiency (%) were calculated.

[0115] <Fabrication of perovskite solar cells> A perovskite solar cell was manufactured as a photoelectric conversion element by the following procedure.

[0116] Example 1 [Preparation of a light-transmitting substrate having a transparent conductive film formed thereon] A conductive glass substrate (Sigma-Aldrich) with a fluorine-doped tin (FTO) film formed as a transparent conductive film on the surface of the glass substrate was used, and part of the FTO film was removed by etching. This resulted in a light-transmitting substrate on which a transparent conductive film was formed (hereinafter referred to as a "light-transmitting substrate with a transparent conductive film").

[0117] [Formation of First Conductive Layer] A solution of titanium diisopropoxide bis(acetylacetonate) in isopropanol (Sigma-Aldrich) was sprayed onto the surface of the FTO film on the transparent substrate with the transparent conductive film. The titanium dioxide paste (Sigma-Aldrich) was sprayed onto the FTO film by spray pyrolysis. This resulted in the formation of a base layer (30 nm thick) made of titanium dioxide on the FTO film. A solution diluted with ethanol was prepared, and the resulting solution was applied to the surface of the underlayer by spin coating. The solution was then heat-treated at 450°C for 30 minutes to form a porous semiconductor layer (120 nm thick) made of titanium dioxide (TiO2), thereby obtaining a first conductive layer.

[0118] [Formation of power generation layer] A N,N-dimethylformamide (DMF) solution containing 1.0 M lead iodide (PbI) and 1.0 M methylammonium iodide (CHNHI) was prepared as solution (1) containing a precursor of the perovskite compound. The resulting solution (1) was applied to the surface of the first conductive layer by spin coating while adding chlorobenzene dropwise. The resulting solution was then baked at 100°C for 10 minutes to form a perovskite layer (450 nm thick) as a power generation layer. This resulted in a pre-press laminate comprising a transparent substrate with a transparent conductive film, a base layer, a first conductive layer, and a power generation layer (perovskite layer) in that order.

[0119] [Preparation of porous free-standing sheet] A porous free-standing sheet containing single-walled CNTs was fabricated according to the following procedure.

[0120] A 500 mL aqueous solution of 2 mass% sodium deoxycholate (DOC) as a solvent containing a dispersant was added with single-walled CNTs (manufactured by Zeon Corporation, product name "ZEONANO SG101", average diameter: 3.5 nm, G / D ratio: 2.1, untreated) as a fibrous carbon nanostructure containing single-walled CNTs. 1.0 g of DOC (the t-plot shows an upward convexity in the opening treatment) was added to obtain a crude dispersion containing DOC as a dispersant. This crude dispersion was filled into a high-pressure homogenizer (manufactured by Beryu Co., Ltd., product name "BERYU SYSTEM PRO") equipped with a multistage pressure control device (multistage pressure reducer) that applies back pressure during dispersion, and the crude dispersion was dispersed at a pressure of 100 MPa. Specifically, shear force was applied to the crude dispersion while applying back pressure to disperse fibrous carbon nanostructures containing single-walled CNTs, obtaining a fibrous carbon nanostructure dispersion containing single-walled CNTs. The dispersion was carried out for 10 minutes while the dispersion flowing out of the high-pressure homogenizer was returned to the high-pressure homogenizer.

[0121] 50 g of the prepared fibrous carbon nanostructure dispersion containing single-walled CNTs was added to a 200 mL beaker, and 50 g of distilled water was added to dilute it two-fold. This was then filtered under 0.09 MPa using a vacuum filtration system equipped with a membrane filter. After filtration, the carbon film formed on the membrane filter was washed by passing isopropyl alcohol and water through the vacuum filtration system, and then air was passed through for 15 minutes. The prepared carbon film / membrane filter was then immersed in ethanol, and the carbon film was peeled off from the membrane filter to obtain carbon film (A).

[0122] The obtained carbon membrane (A) was equivalent in size to the membrane filter, had excellent film-forming properties, and maintained its film state even after being peeled off from the filter, exhibiting excellent self-supporting properties. The film density of the obtained carbon membrane (A) was measured, and the density was found to be 0.85 g / cm. 3 From these results, it was found that the carbon membrane (A) was a porous self-supporting sheet (A).

[0123] [Formation of second conductive layer] The porous free-standing sheet (A) was immersed in chlorobenzene for 10 seconds, and then pulled out of the chlorobenzene to obtain a porous free-standing sheet (1) impregnated with chlorobenzene. The porous free-standing sheet (1) was laminated onto a pre-press laminate heated on a hot plate at 100°C, and the resulting laminate was pressed (heat-pressed) from the porous free-standing sheet (1) side at a pressure of 0.05 MPa. Then, 100 ml of chlorobenzene containing 0.03 M lithium bis(trifluoromethanesulfonyl)imide (Sigma-Aldrich) was poured onto the laminate. The perovskite solar cell was obtained by drying under pressure and heat while pressing it with a wipe. The cell performance of the obtained perovskite solar cell was measured, and the results are shown in Table 1.

[0124] Example 2 Lithium bis(trifluoromethanesulfonyl)imide (Sigma-Aldrich) at a concentration of 0.03 M was dissolved in the laminate obtained by laminating the porous free-standing sheets in Example 1. A perovskite solar cell was fabricated in the same manner as in Example 1, except that a wipe soaked in chlorobenzene was pressed against the surface and then heated and dried at 100°C.

[0125] Example 3 Lithium bis(trifluoromethanesulfonyl)imide (Sigma-Aldrich) with a concentration of 0.03 M was dissolved on the laminate obtained by laminating the porous free-standing sheets in Example 1. A perovskite solar cell was fabricated in accordance with Example 1, except that the coated substrate was sprayed with chlorobenzene and dried by heating at 100°C.

[0126] (Comparative Example 1) A perovskite solar cell was produced in accordance with Example 1, except that the steps up to laminating the porous free-standing sheet in Example 1 were carried out, and the subsequent steps were not carried out.

[0127] (Comparative Example 2) A perovskite solar cell was fabricated in accordance with Example 1, except that 10 μL of chlorobenzene was dropped onto the laminate in Example 1.

[0128] (Comparative Example 3) After forming a pre-press laminate in which the perovskite layer was formed in Example 1, a chlorobenzene solution containing lithium bis(trifluoromethanesulfonyl)imide at a concentration of 0.03 M was spin-coated onto the pre-press laminate, and then dried at 100° C. Thereafter, a porous free-standing sheet was placed in accordance with the method of Example 1, but the porous free-standing sheet did not adhere to the pre-press laminate, and a laminate could not be obtained.

[0129] [Table 1]

[0130] The results shown in Table 1 demonstrate that the methods of Examples 1 to 3 make it possible to manufacture perovskite solar cells with excellent photoelectric conversion efficiency. [Industrial Applicability]

[0131] According to the present invention, it is possible to provide a photoelectric conversion element that exhibits excellent photoelectric conversion efficiency and is easy to manufacture, and a method for manufacturing the same. [Explanation of symbols]

[0132] 1 Transparent substrate 2. Transparent conductive film 3 Base layer 4. Porous semiconductor layer 5 First conductive layer 6 Power generation layer 7 Second conductive layer (porous self-supporting sheet) 100 Photoelectric conversion element

Claims

1. A photoelectric conversion element including a laminated body including a light-transmitting substrate, a transparent conductive film, a first conductive layer, a power generation layer, and a second conductive layer, which are integrated together in this order, the second conductive layer is made of a porous free-standing sheet containing at least single-walled carbon nanotubes, contains an ionic compound therein, and is in a dry state; the ionic compound comprises a metal cation; The photoelectric conversion element, wherein the power generation layer contains a perovskite compound.

2. The photoelectric conversion element according to claim 1 , wherein the ionic compound is present at least at the interface between the power generation layer and the second conductive layer.

3. 3. The photoelectric conversion element according to claim 1, wherein the porous free-standing sheet has a thickness of 20 [mu]m or more. Conversion element.

4. The photoelectric conversion element according to any one of claims 1 to 3, wherein the single-walled carbon nanotubes have an average diameter (Av) and a standard deviation (σ) of the diameters that satisfy the relationship: 0.20 < (3σ / Av) < 0.

60.

5. 5. The photoelectric conversion element according to claim 1, wherein a t-plot obtained from an adsorption isotherm of said single-walled carbon nanotubes exhibits an upwardly convex shape.

6. A method for manufacturing a photoelectric conversion element, comprising: the photoelectric conversion element is formed by integrating a laminate including a light-transmitting substrate, a transparent conductive film, a first conductive layer, a power generation layer, and a second conductive layer in this order; the second conductive layer is made of a porous free-standing sheet containing at least single-walled carbon nanotubes and contains an ionic compound therein; A method for manufacturing a photoelectric conversion element, comprising: a step of laminating the porous free-standing sheet on the power generation layer while a solvent is retained on at least one bonding surface of the power generation layer and the porous free-standing sheet; and a step of applying a solution containing an ionic compound to the porous free-standing sheet laminated on the power generation layer, and drying the porous free-standing sheet.

Images