Electrode for organic thin-film solar cells and method for manufacturing the same

Abstract

An object of the present invention is to provide a self-standing electrode for perovskite solar cells that has low electrical resistance, and a method for producing the same at low cost. [Solution] The present invention relates to a copper film electrode for perovskite solar cells, in which, based on the XRD spectrum peaks of the copper film electrode, the copper crystallite sizes are 700 Å to 937 Å for the (111) plane, 609 Å to 651 Å for the (200) plane, 397 Å to 537 Å for the (220) plane, and 348 Å to 364 Å for the (311) plane, and when converted to an orientation index of 1 for the (200) plane, the orientation index for the (111) plane is 0.347 to 0.465, the orientation index for the (220) plane is 0.032 to 0.142, and the orientation index for the (311) plane is 0.036 to 0.102, and a method for manufacturing the electrode.

Description

[Technical Field]

[0001] The present invention relates to an electrode for organic thin-film solar cells, specifically an electrode for perovskite solar cells, and a method for producing the same. [Background technology]

[0002] BACKGROUND ART As one type of solar cell, a perovskite solar cell in which the main component of the photoelectric conversion layer is a perovskite compound is known.

[0003] Known perovskite solar cells include, for example, a substrate, a first electrode layer, a first carrier layer (e.g., a hole transport layer or an electron transport layer), a photoelectric conversion layer containing a perovskite compound, a second carrier layer (e.g., an electron transport layer or a hole transport layer), and a second electrode layer.

[0004] As a method for manufacturing an electrode layer, for example, Patent Document 1 discloses a method for manufacturing a metal electrode for a solar cell, which includes the steps of: etching a polymer thin film with a laser according to a desired electrode shape to manufacture a mask; and fixing the mask on a substrate and plating a metal film on the mask by a physical vapor deposition method to grow a metal electrode or an electrode seed layer of a desired shape on the substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2023-521863 Summary of the Invention [Problem to be solved by the invention]

[0006] The battery is provided with an electrode as a current outlet. For example, International Publication No. 2014 / 017449 discloses a surface-treated copper foil as an electrode for a lithium-ion secondary battery, characterized in that on at least one side of the copper foil, a surface treatment film is formed in which the total content (atomic %) of carbon and nitrogen in the depth direction of the copper foil, as measured by XPS (X-ray photoelectron spectroscopy), is greatest at the outermost surface of the copper foil, and at a depth where the total content (atomic %) of carbon and nitrogen is half that at the outermost surface, the decrease rate of the total content (atomic %) of carbon and nitrogen in the depth direction of the copper foil is 50% / nm or more, and the surface resistance defined in JIS-K7194:1994 is 2.5 mΩ to 40 mΩ.

[0007] Such surface-treated copper foil is produced using an apparatus equipped with a cathode drum with a mirror-finished surface and a metallic copper anode. The cathode drum is immersed in an electrolyte, and the metallic copper anode is placed underneath to receive the electrolyte. When a potential is applied between the electrodes, the copper metal on the anode becomes cations, dissolves into the electrolyte, and deposits on the cathode drum to form copper foil. The cathode drum is rotated until the copper foil reaches the required thickness. Once the copper foil reaches the required thickness, it is continuously peeled from the cathode drum and wound up. However, increasing the copper foil thickness requires a reduction in the rotation speed of the cathode drum, and further requires surface treatment of the copper foil, which reduces productivity and increases production costs.

[0008] On the other hand, in the method for manufacturing a metal electrode in Patent Document 1, a metal film serving as an electrode is plated onto a substrate by physical vapor deposition. Therefore, the resulting metal film is formed in a state where it is adhered to the substrate, i.e., it is not self-supporting, and the equipment required for manufacturing is expensive and has low flexibility.

[0009] Therefore, an object of the present invention is to provide a self-standing electrode for perovskite solar cells that has low electrical resistance, and a method for producing the same at low cost. [Means for solving the problem]

[0010] The present inventors have discovered that in the manufacture of electrodes for perovskite solar cells, a free-standing copper film (hereinafter also referred to as a "copper film electrode" or "free-standing copper film") with low electrical resistance can be obtained as an electrode by solid-phase electrodeposition (SED) using a high-concentration electrolyte and a copper substrate, and by passing a current at a high current density for a short period of time and then at a low current density for a long period of time, thereby completing the present invention.

[0011] That is, the gist of the present invention is as follows. (1) A copper film electrode for a perovskite solar cell, wherein, based on the XRD spectrum peaks of the copper film electrode, the copper crystallite sizes are 700 Å to 937 Å for the (111) plane, 609 Å to 651 Å for the (200) plane, 397 Å to 537 Å for the (220) plane, and 348 Å to 364 Å for the (311) plane; and, when the orientation index of the (200) plane is defined as 1, the orientation index of the (111) plane is 0.347 to 0.465, the orientation index of the (220) plane is 0.032 to 0.142, and the orientation index of the (311) plane is 0.036 to 0.102. (2) The electrode according to (1), wherein the particle size on one surface of the copper film electrode is smaller than the particle size on the other surface. (3) The electrode according to (2), wherein the average particle diameter on one surface of the copper film electrode is 0.10 μm to 1.0 μm and the average particle diameter on the other surface is 1.5 μm to 5.0 μm, as measured by a scanning ion microscope photograph. (4) A method for producing a copper film electrode for a perovskite solar cell, comprising: 2+ ] A copper solution with a concentration of 1.25 mol / L or more is used, a copper plate is used as a substrate for forming a copper film electrode, and the current density is 10 mA / cm 2 ~100mA / cm 2 a first electrodeposition step in which electrodeposition is carried out for 100 to 500 seconds under the condition of 2 ~70mA / cm 2 The method includes a second electrodeposition step of electrodepositing the solution in the above-mentioned state for 500 to 1000 seconds. [Effects of the Invention]

[0012] The present invention makes it possible to provide a self-standing electrode for a perovskite solar cell that has low electrical resistance, and a method for producing the same at low cost. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram schematically illustrating an example of a film forming apparatus capable of carrying out a manufacturing method according to the present invention. [Figure 2] 1 shows cross-sectional SIM photographs of the SED copper freestanding film of Example 3 (A) and the electrolytic copper foil of Comparative Example 1 (B). [Figure 3] 1 is a graph showing the orientation index (A) of Examples 1 to 3 and Comparative Examples 1 to 3, and the crystallite size (B) of Examples 1 to 3 and Comparative Examples 1 and 3. [Figure 4] 1 is a graph showing the surface resistivity (A) and volume resistivity (B) of Example 3 and Comparative Example 1. [Figure 5] 1 is a diagram schematically illustrating the mechanism for producing a free-standing copper film by solid-phase electrodeposition in the present invention. FIG. [Figure 6] 1A is a schematic cross-sectional view showing an example of the structure of a solar cell of the present invention, and FIG. 1B is a schematic diagram showing a perovskite crystal structure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will now be described in detail. In this specification, the features of the present invention will be described with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity, and the actual dimensions and shapes are not accurately depicted. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Note that the electrode for organic thin-film solar cells and the manufacturing method thereof of the present invention are not limited to the following embodiments, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art, without departing from the gist of the present invention.

[0015] The present invention relates to a copper film electrode for a perovskite solar cell.

[0016] In the copper film electrode of the present invention, based on the XRD spectrum peaks of the copper film electrode, the copper crystallite sizes are 700 Å to 937 Å for the (111) plane, 609 Å to 651 Å for the (200) plane, 397 Å to 537 Å for the (220) plane, and 348 Å to 364 Å for the (311) plane.

[0017] Here, a crystallite refers to the smallest unit of a crystal grain that can be regarded as a single crystal. The size of the crystallite for each lattice plane based on the XRD spectrum peak of the copper film electrode can be determined from the half-width of the peak for each lattice plane.

[0018] Furthermore, based on the XRD spectrum peaks of the copper film electrode, when the orientation index of the (200) plane is assumed to be 1, the orientation index of the (111) plane is 0.347 to 0.465, the orientation index of the (220) plane is 0.032 to 0.142, and the orientation index of the (311) plane is 0.036 to 0.102.

[0019] The orientation index of each lattice plane based on the XRD spectrum peak of the copper film electrode can be calculated using the Willson formula, which uses the relative diffraction intensity of the ASTM copper standard sample. The Wilson formula is as follows: Orientation index=IF(hkl) / IFR(hkl) IF(hkl)=I(hkl) / (I(111)+I(200)+I(220)+I(311)) IFR(hkl)=IR(hkl) / (IR(111)+IR(200)+IR(220)+IR(311)) In the formula, IF(hkl) is the relative intensity of the diffraction intensity of the (hkl) surface of the copper film electrode, IFR(hkl) is the relative intensity of the diffraction intensity of the (hkl) surface of the standard sample, I(hkl) is the diffraction intensity of the (hkl) surface of the copper film electrode, and IR(hkl) is the diffraction intensity of the (hkl) surface of the standard sample.

[0020] Therefore, when the orientation index of the (200) plane is defined as 1, the orientation index is expressed by the following formula: Orientation index when the orientation index of the (200) plane is set to 1 = {IF(hkl) / IFR(hkl)} / IF(200)

[0021] The diffraction intensity of the ASTM standard sample of copper is IR(111)=30 IR(200)=25 IR(220)=16 IR(311)=30 It can be said that:

[0022] Here, the conditions for obtaining the XRD spectrum peak of the copper film electrode are as follows. Analysis is performed using an X-ray diffractometer (e.g., SmartLab, manufactured by Rigaku Corporation) in accordance with JIS K0131:1996, under conditions of an X-ray source: CuKα radiation, 1.54050 Å, 40.0 kV, 40.0 mA, and 2θ in the range of 20° to 100°. Note that X-rays may be incident from either the cathode side or the anode side of the copper film electrode. In one embodiment, X-rays are incident from the cathode side of the copper film electrode.

[0023] In the copper film electrode of the present invention, when the crystallite size is as described above and the orientation index in each lattice plane is as described above, the electrical resistance of the copper film electrode is reduced, and therefore the conductivity is improved.

[0024] The copper film electrode of the present invention has a columnar structure extending in the longitudinal direction in a cross section perpendicular to the film surface of the electrode, where the direction connecting the surfaces is the longitudinal direction. In the columnar structure of the copper film electrode of the present invention, the ratio of the average major axis to the average minor axis (major axis / minor axis) is not limited, but is typically 1.5 to 100, and in one embodiment, 5 to 10. Furthermore, in the copper film electrode of the present invention, the particle diameter on one surface of the electrode is smaller than the particle diameter on the other surface. In the copper film electrode of the present invention, the average particle diameter (diameter equivalent to a circle having a projected area of ​​100 or more particles) measured by a scanning ion microscope (SIM) photograph is typically 0.050 μm to 1.5 μm, and in one embodiment, 0.10 μm to 1.0 μm, while the particle diameter on the other surface, for example, the anode side, is typically 1.0 μm to 10 μm, and in one embodiment, 1.5 μm to 5.0 μm.

[0025] In the copper film electrode of the present invention, which has a gradient in particle size within the film, the surface with smaller particle sizes has lower electrical resistance and improved conductivity. For example, by arranging the copper film electrode of the present invention so that the surface with smaller particle sizes is in contact with a photoelectric conversion layer or a carrier transport layer composed of a perovskite layer, a perovskite solar cell with low electrical resistance, improved conductivity, and excellent power generation performance can be realized.

[0026] The present invention also relates to a method for producing a copper film electrode for a perovskite solar cell.

[0027] The manufacturing method of the present invention uses solid-phase electrodeposition (SED). Here, solid-phase electrodeposition is a method in which a solid electrolyte membrane containing a metal solution is placed between an anode and a substrate serving as a cathode, the solid electrolyte membrane is brought into contact with the substrate, and a voltage is applied between the anode and the substrate, optionally applying a pressure of 0.1 MPa to 2 MPa, to deposit metal from metal ions in the metal solution contained inside the solid electrolyte membrane onto the surface of the substrate, thereby forming a metal coating made of the metal on the surface of the substrate. In the present invention, a copper coating is formed by solid-phase electrodeposition.

[0028] In the present invention, the anode may be, for example, oxygen-free copper. The anode may be a soluble anode or an insoluble anode.

[0029] In the present invention, a copper plate, which is a substrate made of copper metal, is used as the base material (cathode).

[0030] In the present invention, the solid electrolyte membrane is not particularly limited as long as it can be impregnated with copper ions by contacting it with a copper solution and can precipitate copper derived from the copper ions on the surface of the substrate when a voltage is applied. Examples of materials for the solid electrolyte membrane include fluorine-based resins such as Nafion (registered trademark) manufactured by DuPont, hydrocarbon-based resins, polyamic acid resins, and resins with ion exchange functions such as Selemion (CMV, CMD, CMF series) manufactured by Asahi Glass Co., Ltd.

[0031] In the present invention, the thickness of the solid electrolyte membrane is usually 50 μm to 400 μm, and in one embodiment, 100 μm to 200 μm.

[0032] In the present invention, examples of copper compounds that are added to and dissolved in a solvent to prepare a copper solution include halogen compounds such as chlorides and bromides, inorganic salts such as sulfates and nitrates, and organic acid salts such as acetates and citrates. Specific examples of copper compounds include copper chloride, copper sulfate, and copper acetate. These compounds can be used alone or in combination of two or more. The concentration of copper ions in the copper solution in the present invention [Cu 2+ is typically 1.25 mol / L to 2.00 mol / L, in one embodiment 1.30 mol / L to 1.70 mol / L, and in one embodiment 1.40 mol / L to 1.60 mol / L.

[0033] In the present invention, the pH of the copper solution is preferably 2.0 to 5.0, more preferably 2.5 to 4.5. By setting the pH in this range, the copper deposition current efficiency can be improved, making it easier to form a copper film at a high speed. The copper film formation rate can be adjusted by conditions other than pH, such as copper ions in the copper solution, current value, anode material, anode area, and temperature.

[0034] In the present invention, the copper solution may contain any other components in addition to copper ions. The copper solution may contain, for example, a solvent and a pH buffer. Examples of the solvent include water and ethanol. Examples of the pH buffer include acetic acid-copper acetate or succinic acid-copper succinate.

[0035] In the present invention, first, in the first electrodeposition step, a voltage is applied between the anode and the cathode to obtain a current density of 10 mA / cm. 2 ~100mA / cm 2 , in one embodiment 50 mA / cm 2 ~100mA / cm 2 , e.g., 90mA / cm 2 In this state, electrodeposition is carried out for 100 to 500 seconds, and in one embodiment, for 190 to 380 seconds.

[0036] Subsequently, in the second electrodeposition step, the voltage applied between the anode and the cathode was changed so that the current density was 5 mA / cm 2 ~90mA / cm 2 , in one embodiment 5 mA / cm 2 ~70mA / cm 2 , 10 mA / cm in one embodiment 2 ~70mA / cm 2 , e.g., 70mA / cm 2 In one embodiment, the electrodeposition is carried out for 200 to 1000 seconds, and in one embodiment, for 500 to 1000 seconds. In one embodiment, the current density in the first electrodeposition step is higher than the current density in the second electrodeposition step. In one embodiment, the electrodeposition time in the first electrodeposition step is shorter than the electrodeposition time in the second electrodeposition step.

[0037] In the present invention, in the first electrodeposition step, copper nuclei are formed in the ion channels of the solid electrolyte membrane by short-term electrodeposition at a high current density. Then, in the second electrodeposition step, copper particles grow in the ion channels of the solid electrolyte membrane by long-term electrodeposition at a low current density, forming an inter-copper particle network. As a result, the copper substrate, copper film, and copper inter-particle network are connected, and hydrogen is generated by water decomposition. The hydrogen generated by water decomposition accumulates at the interface between the solid electrolyte membrane and the copper film and at the interface between the copper substrate and the copper film. Furthermore, because the copper solution is highly concentrated, copper sulfate is repeatedly deposited and dissolved on the copper film, making it prone to peeling from the copper substrate and the solid electrolyte membrane. The copper film thus formed is a free-standing copper film that is not adhered to either the solid electrolyte membrane or the copper substrate.

[0038] An example of a film-forming apparatus capable of carrying out the manufacturing method according to the present invention using such a solid-phase electrodeposition method is shown in FIGS. 1A and 1B.

[0039] 1A is a schematic cross-sectional view of a film formation apparatus 1A. The film formation apparatus 1A includes an anode 11, a substrate B as a cathode, a solid electrolyte membrane 13 disposed between the anode 11 and the substrate B, and a power supply unit 16 that applies a voltage between the anode 11 and the substrate B.

[0040] The film formation apparatus 1A further includes a housing 20. The housing 20 is formed with a first storage chamber 21 that stores the copper solution L such that the copper solution L is disposed between the anode 11 and the solid electrolyte membrane 13. The copper solution L stored in the first storage chamber 21 is in contact with the solid electrolyte membrane 13 and the anode 11.

[0041] The first storage chamber 21 has a first opening 22 formed therein, the first opening 22 being larger than the surface Ba of the substrate B. The first opening 22 is covered with a solid electrolyte membrane 13, and the copper solution L is sealed in the first storage chamber 21 in a flowable state.

[0042] The film forming apparatus 1A further includes a mounting table 40 on which the substrate B is placed.

[0043] The film forming apparatus 1A further includes a pressing part 30A on the upper part of the housing 20.

[0044] FIG. 1B illustrates a process of forming a copper film F on a surface Ba of a substrate B using the film forming apparatus 1A of FIG. 1A.

[0045] As shown in FIG. 1B, with the substrate B placed on the mounting table 40, the mounting table 40 and the housing 20 are moved relative to each other to sandwich the substrate B between the solid electrolyte membrane 13 and the mounting table 40, and a copper solution L is placed on the surface Ba of the substrate B via the solid electrolyte membrane 13.

[0046] Next, a voltage is applied between the anode 11 and the substrate B by the power supply unit 16, and the copper ions contained in the solid electrolyte membrane 13 are reduced by the surface Ba of the substrate B, causing copper to deposit on the surface Ba, thereby forming a copper coating F.

[0047] In the first and second electrodeposition steps, a specific voltage is applied between the anode and the substrate while the solid electrolyte membrane is in contact with the substrate, and copper ions contained in the solid electrolyte membrane are reduced in the solid electrolyte membrane and on the substrate surface. As a result, copper is deposited in the solid electrolyte membrane and on the substrate surface, and hydrogen generated by water electrolysis is present between the copper particles in the solid electrolyte membrane, the copper film on the substrate surface, and the copper substrate, forming a self-supporting, i.e., peelable, copper film.

[0048] The method of the present invention does not require a rolling step or a surface treatment step, which allows for low costs. Furthermore, the obtained copper coating has a columnar structure extending longitudinally in the direction of current flow (the direction perpendicular to the surface of the copper coating), which allows for low electrical resistance.

[0049] The copper film electrode for perovskite solar cells of the present invention can be used as an electrode for ordinary perovskite solar cells. By using the copper film electrode for perovskite solar cells of the present invention, it is possible to realize a perovskite solar cell with excellent power generation performance due to the low electrical resistance of the electrode.

[0050] An example of the configuration of a perovskite solar cell in which the copper film electrode for a perovskite solar cell of the present invention can be used is shown below.

[0051] <Configuration of perovskite solar cells> The structure of a perovskite solar cell (hereinafter also simply referred to as a solar cell) will be described in detail. Fig. 6A is a schematic cross-sectional view showing an example of the structure of a solar cell.

[0052] As shown in FIG. 6A, in one embodiment, a solar cell C has a substrate 1, a first electrode layer 2a, a first carrier transport layer 3a, a photoelectric conversion layer 4, a second carrier transport layer 3b, and a second electrode layer 2b.

[0053] (Photoelectric conversion layer 4) The photoelectric conversion layer 4 is a layer located between the first carrier transport layer 3a and the second carrier transport layer 3b. The photoelectric conversion layer 4 generates charge carriers by receiving light. The charge carriers generated in the photoelectric conversion layer 4 move to either the first carrier transport layer 3a or the second carrier transport layer 3b.

[0054] More specifically, positive charge carriers, i.e., holes, generated in the photoelectric conversion layer 4 are transported to the first electrode layer 2a or the second electrode layer 2b via the layer that corresponds to the hole transport layer, either the first carrier transport layer 3a or the second carrier transport layer 3b. Furthermore, the negative charge carriers, i.e., electrons, generated in the photoelectric conversion layer 4 are transported to the first electrode layer 2a or the second electrode layer 2b via the layer that corresponds to the electron transport layer, either the first carrier transport layer 3a or the second carrier transport layer 3b.

[0055] The photoelectric conversion layer 4 contains a perovskite compound, preferably as a main component. The content of the perovskite compound in the photoelectric conversion layer 4 is usually 60% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, particularly preferably 95% by weight or more, and most preferably 100% by weight. The ideal film thickness of the photoelectric conversion layer is 100 nm to 1000 nm, in one embodiment 400 nm to 600 nm, and in another embodiment 500 nm to 600 nm.

[0056] A perovskite compound is a compound having a perovskite-type crystal structure. FIG. 6B is a schematic diagram showing a perovskite-type crystal structure. As shown in FIG. 6B, the perovskite-type crystal structure has a cubic unit cell, with A located at each vertex of the cubic crystal, B located at the body center, and X located at each face center of the cubic crystal centered on A. The fact that a compound has a perovskite-type crystal structure can be confirmed, for example, by X-ray diffraction measurement.

[0057] The perovskite compound can be represented, for example, by the following formula (1). ABX3(1) (wherein A is a monovalent cation, B is a divalent cation, and X is a monovalent anion.)

[0058] In one embodiment, in formula (1), A is at least one selected from a monovalent organic ammonium ion, a monovalent amidinium ion, and a monovalent metal ion. Examples of monovalent organic ammonium ions include CH3NH3 + (Methylammonium ion: MA), C2H5NH3 + , C3H7NH3 + and C4H9NH3 + Examples include: Examples of monovalent amidinium ions include HC(NH2)2 + (formamidinium ion: FA). Examples of monovalent metal ions include rubidium ions (Rb + ) and cesium ions (Cs + ) are listed. In formula (1), A may be a combination of a monovalent organic ammonium ion, a monovalent amidinium ion, and a monovalent metal ion. In formula (1), A is preferably MA, FA, or Cs +In formula (1), A is preferably Cs + , MA, and FA. When A is a mixed cation, the mixing ratio of each cation is not limited.

[0059] In one embodiment, in formula (1), B is a divalent metal ion, for example, a lead ion (Pb 2+ ), tin ions (Sn 2+ ) and their combinations. From the viewpoint of durability, B is Pb 2+ It is preferable that:

[0060] In one embodiment, in formula (1), X is a halogen ion, for example, a fluoride ion (F - ), chloride ions (Cl - ), bromide ion (Br - ) and iodide ion (I - ) and at least one selected from Cl - , Br - and I - At least one selected from the following is preferred, and I - is more preferred.

[0061] (First carrier transport layer 3a and second carrier transport layer 3b) Returning to the description of FIG. 6A. The first carrier transport layer 3a receives charge carriers generated in the photoelectric conversion layer 4 and transports the charge carriers to the first electrode layer 2a. When the first carrier transport layer 3a is a hole transport layer (HTL), the first carrier transport layer 3a transports holes to the first electrode layer 2a. When the first carrier transport layer 3a is an electron transport layer (ETL), the first carrier transport layer 3a transports electrons to the first electrode layer 2a. The hole transport layer and the electron transport layer will be described in detail later.

[0062] The second carrier transport layer 3b receives charge carriers generated in the photoelectric conversion layer 4 and transports the charge carriers to the second electrode layer 2b. When the second carrier transport layer 3b is a hole transport layer, the second carrier transport layer 3b transports holes to the second electrode layer 2b. When the second carrier transport layer 3b is an electron transport layer, the second carrier transport layer 3b transports electrons to the second electrode layer 2b.

[0063] In the first embodiment, the first carrier transport layer 3a is an electron transport layer, and the second carrier transport layer 3b is a hole transport layer. That is, in the first embodiment, the solar cell C of the present invention has, in the stated order, a substrate, a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode.

[0064] In the second embodiment, the first carrier transport layer 3a is a hole transport layer, and the second carrier transport layer 3b is an electron transport layer. That is, in the second embodiment, the solar cell C of the present invention has a substrate, an anode, a hole transport layer, a photoelectric conversion layer, an electron transport layer, and a cathode, in the stated order.

[0065] The hole transport layer has a function of transporting holes generated by photoelectric conversion in the photoelectric conversion layer to the first electrode layer or the second electrode layer. As a material for the hole transport layer, known organic or inorganic materials usable for hole transport layers can be used.

[0066] Organic materials that can be used as the material for the hole transport layer are not particularly limited, and examples thereof include 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), polyethylenedioxythiophene:polystyrenesulfonic acid (PEDOT:PSS), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), and 3PATAT-C3 (Non-patent document: Journal of the American Chemistry Society, 2023, Vol. 145, p. 7528).

[0067] The inorganic material that can be used as the material for the hole transport layer is not particularly limited, and examples thereof include nickel oxide and copper oxide.

[0068] In the first embodiment of the solar cell of the present invention described above, the materials of the hole transport layer are preferably Spiro-OMeTAD, PTAA, and nickel oxide. In the second embodiment of the solar cell of the present invention, the material of the hole transport layer is preferably PEDOT:PSS, PTAA, and nickel oxide.

[0069] The electron transport layer has a function of transporting electrons generated by photoelectric conversion in the photoelectric conversion layer to the first electrode layer or the second electrode layer. As a material for the electron transport layer, known organic or inorganic materials usable for electron transport layers can be used.

[0070] The organic material that can be used as the material for the electron transport layer is not particularly limited, and examples thereof include fullerene compounds, phenanthroline derivatives (e.g., bathocuproine), polyethyleneimines, etc. Examples of fullerene compounds include fullerenes (e.g., C60 fullerene, C70 fullerene), derivatives in which a substituent is added to fullerene (e.g., [6,6]-phenyl-C 61 -methyl butyrate (also known as PCBM or

[60] PCBM), [6,6]-phenyl-C 71 -methyl butyrate (also known as PCBM or

[70] PCBM).

[0071] Inorganic materials that can be used as the material for the electron transport layer include titanium oxide, tin oxide, and zinc oxide.

[0072] In the first embodiment of the solar cell of the present invention, the material of the electron transport layer is preferably fullerene, PCBM, bathocuproine, polyethyleneimines, titanium oxide, and tin oxide. In the second embodiment of the solar cell of the present invention, the material of the electron transport layer is preferably fullerene, PCBM, bathocuproine, or polyethyleneimines.

[0073] (First electrode layer 2a and second electrode layer 2b) The first electrode layer 2a is an electrode in contact with the first carrier transport layer 3a, and the second electrode layer 2b is an electrode in contact with the second carrier transport layer 3b. The copper film electrode of the present invention can be used as the material for the first electrode layer 2 a and the second electrode layer 2 b. The copper film electrode of the present invention can be used for either or both of the first electrode layer 2 a and the second electrode layer 2 b. When the copper film electrode of the present invention is not used, materials known as electrodes for solar cells can be used, such as metal materials such as aluminum (Al), silver (Ag), and gold (Au), transparent conductive films such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum-doped zinc oxide (AZO), and fluorine-doped tin oxide (FTO), and carbon nanotubes. As the material for the first electrode layer 2a and the second electrode layer 2b, in addition to the copper film electrode of the present invention, ITO, IZO and FTO are preferred.

[0074] (Substrate 1) The substrate 1 is a plate-like or film-like member, and supports the first electrode layer 2a, the first carrier transport layer 3a, the photoelectric conversion layer 4, the second carrier transport layer 3b, and the second electrode layer 2b. The material of the substrate 1 is not particularly limited, and examples thereof include inorganic materials such as glass, organic materials such as polyethylene, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide, liquid crystal polymer, and cycloolefin polymer, and metal materials such as stainless steel and silicon.

[0075] The substrate 1 may be transparent or opaque. When light is incident from the surface of the substrate, a transparent substrate is used. As a transparent substrate, a substrate made of glass, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide, or cycloolefin polymer can be used. When light is incident from the opposite side of the substrate, the substrate can be opaque.

[0076] <Solar cell manufacturing method> The solar cell can be manufactured by depositing a first electrode layer, a first carrier transport layer, a photoelectric conversion layer, a second carrier transport layer, and a second electrode layer on a substrate 1 in the order described above. The solar cell can be manufactured by a method similar to a conventional manufacturing method, except that the copper film electrode of the present invention is used as the first electrode layer and / or the second electrode layer. [Example]

[0077] The present invention will be explained in more detail below using examples, but the technical scope of the present invention is not limited to these examples.

[0078] <Copper film electrode formation> The free-standing copper films of Examples 1 to 3 were formed by a hydraulic method using the film-forming apparatus 1A shown in FIGS. 1A and 1B described above, using the solid-phase electrodeposition (SED) conditions shown below, as well as the current and time shown in Table 1.

[0079] Electrolyte: 1.5mol / L CuSO4 aqueous solution Film forming area: 3cm x 3cm Substrate: Hull cell substrate (49cm x 49cm x 0.3cm) Electrolyte membrane: Nafion™ 117 (thickness 183 μm, immersed in 1.5 mol / L CuSO4 aqueous solution for 24 hours) Substrate temperature: 25℃

[0080] [Table 1]

[0081] <Evaluation of copper film electrodes> The obtained copper film electrodes were subjected to the following evaluations. ·Cross-sectional structure Observation was performed using a FIB-SIM (FB-2100, manufactured by Hitachi, Ltd.). Crystal structure Analysis was performed by X-ray diffraction (SmartLab, manufactured by Rigaku Corporation, X-ray source: CuKα radiation, 1.54050 Å, 40.0 kV, 40.0 mA, 2θ = 20° to 100°) using X-rays incident from the cathode side according to JIS K0131:1996. The orientation index was calculated using the Willson formula. ·Surface resistivity Measurement was performed using a resistivity meter (Loresta-GXII MCP-T710, manufactured by Nitto Seiko Analytech Co., Ltd.) based on JIS K7194. Volume resistivity Measurement was carried out using a contact resistivity measuring device (manufactured by Kyowa) based on JIS K6911.

[0082] The comparative materials used were Comparative Example 1 (electrolytic copper foil NC-WS, thickness 8 μm, manufactured by Furukawa Electric Co., Ltd.), Comparative Example 2 (electrolytic copper foil (STD), thickness 25 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), and Comparative Example 3 (rolled copper (thick copper foil for heat dissipation substrate), thickness 300 μm, manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

[0083] <Evaluation results of copper film electrodes> ·Cross-sectional structure FIG. 2 shows cross-sectional SIM photographs of the SED copper freestanding film (A) of Example 3 and the electrolytic copper foil (B) of Comparative Example 1. In the case of an SED copper freestanding film such as that of Example 3, the film formation surface is pressed by physical pressure in accordance with the manufacturing principle of solid-phase electrodeposition. Therefore, in Example 3, a denser film can be formed than when no pressure is applied. On the other hand, in the case of an electrolytic copper film such as that of Comparative Example 1, the surface conditions of the front and back of the electrolytic copper foil are completely different in accordance with the manufacturing principle of electroforming. Therefore, in Comparative Example 1, the surface that was in contact with the cathode drum becomes flat during the manufacturing process, but fine irregularities of the order of several μm are formed on the opposite side where plating is to be applied.

[0084] 2, it was found that in the SED copper freestanding film of Example 3, the particle diameter on the cathode side was φ0.10 μm to 1.0 μm and the particle diameter on the anode side was φ1.5 μm to 5.0 μm, and the particles had a columnar structure with the longitudinal direction in the current-carrying direction. On the other hand, it was found from Fig. 2 that in the electrodeposited copper foil of Comparative Example 1, crystal grains with particle diameters of φ2.5 μm to 7.5 μm grew randomly.

[0085] Crystal structure Copper foils formed by electroforming processes such as those in Comparative Examples 1 and 2 have a different crystalline structure from pure copper because they are wound while being electrodeposited, resulting in relatively hard and brittle mechanical properties. For this reason, copper foil manufacturers perform heat treatment to improve flex resistance. On the other hand, SED copper freestanding films such as those in Examples 1 to 3 are electrodeposited under pressure, and are therefore thought to have a unique crystalline structure. Therefore, the crystal structure of the SED copper freestanding films was analyzed by X-ray diffraction using X-rays incident from the cathode side of the SED copper freestanding film. Table 2 and FIG. 3A show the calculated results (Willson's formula) of the orientation index for the SED copper freestanding films of Examples 1 to 3, the electrolytic copper foils of Comparative Examples 1 and 2, and the rolled copper of Comparative Example 3. Table 3 and FIG. 3B show the calculated results (Scherrer's formula) of the crystallite size for the SED copper freestanding films of Examples 1 to 3, the electrolytic copper foil of Comparative Example 1, and the rolled copper of Comparative Example 3.

[0086] [Table 2]

[0087] [Table 3]

[0088] From Table 2 and Figure 3A, it was found that the crystal structure of the SED copper freestanding film is different from that of electrolytic copper foil and rolled copper because the (200) plane orientation index of the SED copper freestanding film is preferentially large.

[0089] 3B, it was found that the crystallite size of the electrolytic copper foil of Comparative Example 1 was larger than 1500 Å, and the crystallite size of the SED copper freestanding films of Examples 1 to 3 was smaller than 700 Å. Note that, because the crystallite size of the electrolytic copper foil of Comparative Example 1 was larger than 1500 Å, the exact size could not be calculated using the Scherrer formula.

[0090] Surface and volume resistivity As shown in Figures 2 and 3, the crystal structure and cross-sectional structure of the SED copper freestanding films of Examples 1 to 3 are different from those of the electrolytic copper foils of Comparative Examples 1 and 2. Therefore, it was considered that the electrical resistance of the SED copper freestanding films of Examples is different from that of the electrolytic copper foils of Comparative Examples 1 and 2. Therefore, the surface resistivity and volume resistivity of the SED copper freestanding film of Example 3 were measured and compared with those of Comparative Example 1. Figure 4A shows the surface resistivity of the SED copper freestanding film of Example 3 and the electrolytic copper foil of Comparative Example 1, and Figure 4B shows the volume resistivity of the SED copper freestanding film of Example 3 and the electrolytic copper foil of Comparative Example 1.

[0091] 4, it was found that the electrical resistance of the SED copper freestanding film of Example 3 was lower than that of the electrolytic copper foil of Comparative Example 1. The SED copper freestanding film of the example that was not subjected to surface treatment has an asymmetric structure (columnar structure) in which the crystal orientation is oriented in the (200) plane, and further has few voids, which is thought to be why it has low electrical resistance.

[0092] Figure 5 shows the mechanism for producing a free-standing copper film by the solid-phase electrodeposition method of the present invention. In the present invention, the conditions for the solid-phase electrodeposition method are a high-concentration solution (1.5 mol / L CuSO4) and two stages of current and time (high current density x short time + low current density x long time). First, in the first stage (high current density x short time), copper can be nucleated in the ion channels of the solid electrolyte membrane (Cu 2+ +2e -→Cu), which limits copper transport in the copper diffusion pathway. Therefore, copper nuclei are uniformly distributed in the solid electrolyte film. After copper nuclei are formed, the second stage (low current density x long time) causes copper particle growth and the formation of a network between copper particles in the ion channels of the solid electrolyte film. When the copper substrate, the copper film on the copper substrate, and the copper particle network in the solid electrolyte film are connected, hydrogen is generated by water decomposition (2H + +2e - →H2↑). The hydrogen generated by water decomposition remains at the interface between the solid electrolyte membrane and the copper film, and at the interface between the copper substrate and the copper film. In addition, in a highly concentrated solution, copper sulfate repeatedly deposits and dissolves on the copper film. As a result, the copper film peels off from the copper substrate and the solid electrolyte membrane, allowing it to become a free-standing film. [Explanation of symbols]

[0093] 11 anode, 13 solid electrolyte membrane, 16 power supply unit, 20 housing, 21 first storage chamber, 22 first opening, 30A pressing unit, 40 mounting table, L copper solution, B substrate (cathode), Ba surface of substrate, F copper film

Claims

1. A copper film electrode for a perovskite solar cell, Based on the XRD spectrum peaks of the copper film electrode, The copper crystallite sizes are 700 Å to 937 Å for the (111) plane, 609 Å to 651 Å for the (200) plane, 397 Å to 537 Å for the (220) plane, and 348 Å to 364 Å for the (311) plane; When the orientation index of the (200) plane is assumed to be 1, the orientation index of the (111) plane is 0.347 to 0.465, the orientation index of the (220) plane is 0.032 to 0.142, and the orientation index of the (311) plane is 0.036 to 0.

102. electrode.

2. 2. The electrode of claim 1, wherein the grain size on one surface of the copper film electrode is smaller than the grain size on the other surface.

3. 3. The electrode according to claim 2, wherein the average particle size on one surface of the copper film electrode is 0.10 μm to 1.0 μm and the average particle size on the other surface is 1.5 μm to 5.0 μm, as measured by a scanning ion microscope photograph.

4. A method for producing a copper film electrode for a perovskite solar cell, comprising: As an electrolyte, [Cu ２＋ ] A copper solution having a concentration of 1.25 mol / L or more is used, and a copper plate is used as a substrate on which a copper film electrode is formed, Current density is 10 mA / cm ２ ~100mA / cm ２ A first electrodeposition step in which electrodeposition is performed for 100 seconds to 500 seconds in a state in which Current density is 5 mA / cm ２ ~90mA / cm ２ A second electrodeposition step in which electrodeposition is carried out for 200 to 1000 seconds in the state A method comprising:

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