Method for manufacturing organic thin film solar cell

Abstract

To provide a method of manufacturing a perovskite solar cell in which lead iodide in a photoelectric conversion layer is reduced.SOLUTION: The present invention relates to a method for manufacturing a solar cell including a photoelectric conversion layer containing a perovskite compound as a main component, the method including a coating step of coating a coating surface with a precursor solution containing the perovskite compound as a solute, and an annealing step of heating the coating surface coated with the precursor solution at a temperature in a range of 80 °C or higher and 120 °C or lower for a time of 15 minutes or longer and shorter than 40 minutes.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an organic thin-film solar cell, and more particularly to a method for manufacturing a perovskite solar cell. [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] As a method for producing a perovskite layer in a perovskite solar cell, for example, Patent Document 1 discloses a method for producing a perovskite layer represented by the formula (I): AM n1 X m1 (I) (In formula (I), A is a methylammonium cation (CH3NH3 + ), formamidinium cation (NH2CHNH2 + ) or cesium cation (Cs + ) and M is Pb2 + , Ge2 + , or Sn2 + and X is F - , Cl - , Br - , or I - where n1 is 0.8 to 1.2, and m1 is 2.8 to 3.2. and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)pyrimidinone, sulfolane, tetramethylene sulfoxide, or N,N-dimethylacetamide onto a substrate to obtain a coating layer; a poor solvent adding step of adding a poor solvent to the coating layer after the coating step; and a heating step of heating the substrate after the poor solvent adding step, wherein the time from the end of the coating step to the poor solvent adding step is 10 seconds or more and 5 minutes or less.

[0004] Non-Patent Document 1 describes a method for manufacturing a perovskite solar cell.

[0005] Non-Patent Document 2 describes the treatment of the perovskite layer with a methylamine iodide (MAI) solution in the perovskite layer formation step in the perovskite solar cell manufacturing method of Non-Patent Document 1. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-148126 [Non-patent literature]

[0007] [Non-Patent Document 1] Michael Saliba et al., "Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility, and high efficiency," Energy and Environmental Science, June 2016, Vol. 9, No. 6, pp. 1989-1997, and its Supporting Information [Non-patent document 2] Atsushi Kogo et al., "Improving the efficiency of perovskite solar cells by methylamine iodide treatment," Proceedings of the 65th Spring Meeting of the Japan Society of Applied Physics, 2018, 18a-G202-6 Summary of the Invention [Problem to be solved by the invention]

[0008] In perovskite solar cells, the technology to fabricate a uniform, highly crystalline perovskite layer is extremely important because it reduces recombination and resistance within the layer, leading to high energy conversion efficiency.

[0009] In the manufacturing method of perovskite solar cells described in Non-Patent Document 2 and the like, lead iodide (PbI2), which is cited as a factor in reducing photoelectric conversion efficiency, is reacted with MAI to form MAPbI3 by immersing the substrate in an MAI solution. However, although this method has a certain reduction effect, not all of the lead iodide reacts with MAI, and therefore there is a problem in that lead iodide cannot be sufficiently removed from the perovskite layer, i.e., the photoelectric conversion layer.

[0010] Therefore, an object of the present invention is to provide a method for manufacturing a perovskite solar cell in which the amount of lead iodide in the photoelectric conversion layer is reduced. [Means for solving the problem]

[0011] The present inventors have discovered that in the manufacture of perovskite solar cells, the generation of lead iodide in the photoelectric conversion layer during the annealing step can be suppressed by controlling the temperature and time, which are heating conditions, in the annealing step, and have completed the present invention.

[0012] That is, the gist of the present invention is as follows. (1) A method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound as a main component, the method comprising: a coating step of coating a surface with a precursor solution containing the perovskite compound as a solute; and an annealing step of heating the surface coated with the precursor solution at a temperature in the range of 80°C to 120°C for 15 minutes to less than 40 minutes. (2) The perovskite compound is represented by the following formula (1): AMX3...Formula (1) (In the formula, A is a mixed cation of cesium ion, methylammonium ion, and formamidinium ion, M is a divalent lead ion, and X is a halogen ion.) The method for producing a solar cell according to (1), (3) The method for producing a solar cell according to (1) or (2), wherein the heating temperature in the annealing step is in the range of 90°C or higher and 110°C or lower. (4) The method for producing a solar cell according to any one of (1) to (3), wherein the heating time in the annealing step is 20 minutes or more and 30 minutes or less. (5) The method for producing a solar cell according to any one of (1) to (4), wherein in the coating step, the precursor solution is coated so that the thickness of the photoelectric conversion layer becomes 100 nm to 1000 nm. (6) The method for manufacturing a solar cell according to any one of (1) to (5), wherein in the coating step, the content of lead halide in the precursor solution is in the range of 50% by weight or more and 90% by weight or less, based on the total weight of the solute. (7) The method for manufacturing a solar cell according to any one of (1) to (6), further comprising the step of applying a poor solvent, in which the solubility of the perovskite compound is lower than that of the solvent of the precursor solution, to the surface onto which the precursor solution has been applied. [Effects of the Invention]

[0013] The present invention makes it possible to provide a method for producing a perovskite solar cell with reduced lead iodide in the photoelectric conversion layer. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view showing an example of the structure of a solar cell of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing a perovskite crystal structure. [Figure 3] 10 is a flowchart showing the film formation process of the photoelectric conversion layer 4. [Figure 4] FIG. 10 is a schematic cross-sectional view for explaining step S1. [Figure 5] FIG. 10 is a schematic cross-sectional view for explaining step S2 (optional step). [Figure 6] FIG. 10 is a schematic cross-sectional view for explaining step S3. [Figure 7] 10 is a graph showing X-ray diffraction spectra of perovskite films when the conditions of the annealing step (step S3) are changed in an example. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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 manufacturing method of the organic thin-film solar cell of the present invention is not limited to the following embodiments, and can be implemented 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.

[0016] The present invention relates to a method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound as a main component.

[0017] The method for manufacturing a solar cell of the present invention includes a coating step (step S1) of coating a surface with a precursor solution containing a perovskite compound as a solute, and an annealing step (step S3) of heating the surface coated with the precursor solution at a temperature in the range of 80°C to 120°C for 15 minutes to less than 40 minutes. In the present invention, by controlling the temperature and time in the annealing step in step S3 within specific ranges, the production of lead iodide in particular in step S3 can be suppressed, and the content of lead iodide in the photoelectric conversion layer can be reduced.

[0018] <Solar cell configuration> First, the structure of a perovskite solar cell (hereinafter also referred to as the solar cell of the present invention) produced by the production method of the present invention will be described in detail. Fig. 1 is a schematic cross-sectional view showing an example of the structure of the solar cell of the present invention.

[0019] As shown in FIG. 1, in one embodiment, a solar cell C of the present invention 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.

[0020] (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.

[0021] 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.

[0022] The manufacturing method of the present invention suppresses the formation of lead iodide in the photoelectric conversion layer 4. The solar cell of the present invention has excellent power generation performance because the formation of lead iodide in the photoelectric conversion layer is suppressed.

[0023] 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 thickness of the photoelectric conversion layer is usually 100 nm to 1000 nm, and in one embodiment, 400 nm to 600 nm.

[0024] A perovskite compound is a compound having a perovskite-type crystal structure. FIG. 2 is a schematic diagram showing a perovskite-type crystal structure. As shown in FIG. 2, 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.

[0025] 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.)

[0026] 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 mentioned. 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.

[0027] 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:

[0028] 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.

[0029] (First carrier transport layer 3a and second carrier transport layer 3b) Returning to the explanation of Figure 1. 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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).

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] Inorganic materials that can be used as the material for the electron transport layer include titanium oxide, tin oxide, and zinc oxide.

[0040] 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.

[0041] (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. Materials that can be used for the first electrode layer and the second electrode layer include 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, which are known materials for use as electrodes in solar cells. The materials of the first electrode layer and the second electrode layer are preferably ITO, IZO and FTO.

[0042] (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.

[0043] 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.

[0044] <Solar cell manufacturing method> Next, the method for producing a solar cell, that is, the production method of the present invention, will be described in more detail. In the manufacturing method according to this embodiment, a solar cell is 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 in the stated order on a substrate 1. The manufacturing method according to this embodiment is characterized by the deposition process of the photoelectric conversion layer 4, and the deposition processes for the other parts can be performed using methods similar to those used for conventional photoelectric conversion elements.

[0045] The film-forming process for the photoelectric conversion layer 4 will be described in detail below. FIG.

[0046] In the film-forming step of the photoelectric conversion layer 4, first, a precursor solution is applied to the application surface (step S1). Fig. 4 is a schematic cross-sectional view for explaining step S1. More specifically, FIG. 4 is a schematic cross-sectional view showing a cross section of a photoelectric conversion element C1 before step S1 is performed and a photoelectric conversion element C2 in the process of being manufactured after step S1 is performed.

[0047] 4, the photoelectric conversion element C1 before step S1 is performed includes a substrate 1, a first electrode layer 2a, and a first carrier transport layer 3a. As described above, the photoelectric conversion element C1 before step S1 is performed can be manufactured by forming the first electrode layer 2a and the first carrier transport layer 3a on the substrate 1 using a known method.

[0048] In step S1 according to this embodiment, the precursor solution is applied to the surface of the first carrier transport layer 3a. That is, in this embodiment, the surface of the first carrier transport layer 3a corresponds to the application surface. The precursor solution applied to the surface of the first carrier transport layer 3a forms a liquid film 4a, as shown in the schematic cross-sectional view of the photoelectric conversion element C2.

[0049] The precursor solution refers to a solution containing a perovskite compound as a solute, and can be prepared by dissolving the perovskite compound, a solvent adduct of the perovskite compound, or raw materials for multiple perovskite compounds in a suitable solvent. For example, when the perovskite compound is represented by the above-mentioned formula (1), the precursor solution can be prepared by dissolving one or more compounds represented by the following formula (2) and one or more compounds represented by the following formula (3) in an appropriate solvent. For example, the content of BX2, which is a compound represented by the following formula (3) in the precursor solution, such as a lead halide such as PbI2, is typically 50% by weight or more and 90% by weight or less, and in one embodiment, 60% by weight or more and 80% by weight or less, for example, 70% by weight or more and 80% by weight or less, based on the total weight of the solute. AXE (2) BX2(3)

[0050] The solvent for the precursor solution is preferably a polar solvent from the viewpoint of solubility of the perovskite compound, and is preferably an aprotic solvent from the viewpoint of stability of the perovskite compound in the solution. Examples of solvents that can be used as the solvent for the precursor solution include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone, and mixed solvents containing one or more of these. When the solvent for the precursor solution is a mixed solvent, the mixing ratio of each solvent is not limited.

[0051] In step S1 according to this embodiment, the surface of the first carrier transport layer 3a corresponds to the coating surface, but the coating surface in step S1 is not limited to the surface of the first carrier transport layer 3a. For example, when the manufactured solar cell C does not have a first carrier transport layer, the precursor solution is applied to the first electrode layer 2a, and the surface of the first electrode layer 2a corresponds to the application surface. Furthermore, if the manufactured solar cell C has other layers between the photoelectric conversion layer 4 and the first carrier transport layer 3a, the precursor solution is applied to the other layers, and the surfaces of the other layers correspond to the application surface. That is, the surface to be coated in step S1 is appropriately selected depending on the configuration of the manufactured solar cell C. More specifically, the surface to be coated in step S1 is the surface of the manufactured solar cell C that will come into contact with the photoelectric conversion layer 4 on the substrate side.

[0052] The precursor solution can be applied by a known method. The precursor solution may be applied by any method as long as it can apply the precursor solution to the surface to be coated in a substantially uniform layer, and examples of such methods include spin coating, inkjet coating, spray coating, blade coating, and die coating.

[0053] From the viewpoint of the stability of the perovskite compound, step S1 is preferably carried out in a dry air atmosphere, more preferably in an inert gas atmosphere. Any inert gas may be used as long as it does not react with the perovskite compound, such as nitrogen or argon.

[0054] Returning to the explanation of Fig. 3, in the film-forming process of the photoelectric conversion layer 4, after step S1, a poor solvent may be applied to the surface on which the precursor solution has been applied (step S2). Note that step S2 is an optional step. Fig. 5 is a schematic cross-sectional view illustrating step S2. More specifically, Fig. 5 is a schematic cross-sectional view illustrating a cross section of a photoelectric conversion element C2 before step S2 is performed and a photoelectric conversion element C3 in the process of being manufactured after step S2 is performed.

[0055] As shown in FIG. 5, by performing step S2 according to this embodiment, a liquid film 4b of a mixture of the precursor solution and the poor solvent is formed on the surface of the first carrier transport layer 3a. By carrying out step S2 according to this embodiment, the generation of crystal nuclei of the perovskite compound in the mixed liquid film 4b is promoted.

[0056] Here, the poor solvent is a solvent in which the solubility of the perovskite compound is at least lower than that of the solvent of the precursor solution, and more preferably a solvent in which the perovskite compound cannot substantially dissolve. A poor solvent is, for example, a solvent in which the solubility of the perovskite compound at 25° C. (weight ratio of solute to 100 g of solvent) is usually less than 1 wt %, preferably less than 0.5 wt %.

[0057] The solvent that can be used as the poor solvent is not particularly limited, and examples thereof include organic solvents such as substituted aliphatic hydrocarbons such as dichloromethane and chloroform; aromatic compounds such as toluene, benzene, chlorobenzene, and tetralin; ethers such as diethyl ether and tetrahydrofuran (THF); alcohols having 3 or more carbon atoms; hydrocarbons having 4 to 10 carbon atoms; and acetic acid. In the present invention, the aromatic compound also includes a compound partially containing an aromatic ring. As the poor solvent, these solvents may be used alone or in combination of two or more. In one embodiment, the poor solvent is chlorobenzene.

[0058] In step S2, by applying the poor solvent, a sufficient number of crystal nuclei of the perovskite compound are uniformly generated in the liquid film 4b. The generated crystal nuclei of the perovskite compound undergo crystal growth through the steps described below to become the photoelectric conversion layer 4. Therefore, by performing step S2, a sufficient number of crystal nuclei are uniformly generated, thereby forming a photoelectric conversion layer 4 that uniformly contains the perovskite compound.

[0059] That is, in the method for manufacturing a solar cell according to this embodiment, a sufficient number of crystal nuclei of the perovskite compound can be uniformly generated in the photoelectric conversion layer 4 by performing step S2. Therefore, in the method for manufacturing a solar cell according to this embodiment, by configuring step S2 as described above, it is possible to form a photoelectric conversion layer 4 that uniformly contains a perovskite compound.

[0060] From the viewpoint of the stability of the perovskite compound, step S2 is preferably carried out in a dry air atmosphere, more preferably in an inert gas atmosphere. Any inert gas may be used as long as it does not react with the perovskite compound, such as nitrogen or argon.

[0061] In step S2, the poor solvent can be applied by dropping or in the same manner as the application of the precursor solution in step S1.

[0062] Returning to the explanation of Fig. 3, in the film formation process of the photoelectric conversion layer 4, after step S2, an annealing step is performed, thereby completing the film formation of the photoelectric conversion layer 4 (step S3). Fig. 6 is a schematic cross-sectional view illustrating step S3. More specifically, Fig. 6 is a schematic cross-sectional view illustrating a cross section of a photoelectric conversion element C3 before step S3 is performed and a photoelectric conversion element C4 in the process of being manufactured after step S3 is performed.

[0063] As shown in FIG. 6, by performing step S3 according to this embodiment, a photoelectric conversion layer 4 is formed on the surface of the first carrier transport layer 3a. The annealing step performed in step S3 is a treatment of heating the liquid film 4b at a temperature in the range of 80°C or higher and 120°C or lower, preferably 90°C or higher and 110°C or lower, more preferably 95°C or higher and 105°C or lower, for example, 100°C, for a time of 15 minutes or higher but less than 40 minutes, preferably 18 minutes or higher and 35 minutes or lower, more preferably 20 minutes or higher and 30 minutes or lower, and even more preferably 20 minutes or higher and 25 minutes or lower, for example, 20 minutes.

[0064] From the viewpoint of the stability of the perovskite compound, step S3 is preferably carried out under vacuum or in a dry air atmosphere, and more preferably in an inert gas atmosphere. Any gas that does not react with the perovskite compound may be used as the inert gas, such as nitrogen or argon.

[0065] In step S3, by controlling the temperature and time in the annealing step within specific ranges, the production of lead iodide in step S3 is suppressed, and the content of lead iodide in the photoelectric conversion layer can be reduced.

[0066] Therefore, in the manufacturing method according to this embodiment, it is not necessary to carry out the treatment step of immersing the photoelectric conversion layer in an MAI solution as described in Non-Patent Document 2 after step S3.

[0067] As described above, in the manufacturing method according to this embodiment, the heating temperature in the annealing step is set to a temperature in the range of 80° C. to 120° C., and the heating time is set to a time in the range of 15 minutes to less than 40 minutes. With this configuration, the manufacturing method according to this embodiment can reduce the content of lead iodide in the photoelectric conversion layer. [Example]

[0068] 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.

[0069] A laminate (30 mm × 30 mm) consisting of a glass plate, a fluorine-doped tin oxide (FTO) film (transparent conductive film), and a titanium oxide (TiO2) layer (electron transport layer) was used as the substrate. A precursor solution was prepared by dissolving the ternary system CsFAMAPbI3 in a solvent consisting of DMF and DMSO, with PbI2 at 74.6 wt% of the total solute weight.

[0070] 150 μl of the prepared precursor solution was applied onto the electron transport layer of the substrate by spin coating (800 rpm for 10 seconds → 5000 rpm for 20 seconds) under an argon gas atmosphere at room temperature (25° C.). Five seconds before the end of the spin coating rotation, 200 μl of a poor solvent (chlorobenzene) was added dropwise to the applied precursor solution.

[0071] Then, the conditions listed below Condition 1: 100℃ / 20min, Condition 2: 100℃ / 40min, Condition 3: 100°C / 60 min, or Condition 4: 100℃ / 80min An annealing step was carried out at 400°C to form a perovskite film containing the perovskite compound on the substrate.

[0072] The perovskite film formed on the substrate was subjected to X-ray diffraction analysis using an X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation).

[0073] The results are shown in FIG. 7 and Table 1.

[0074] [Table 1]

[0075] Regarding the presence or absence of PbI2 in the perovskite film in Table 1 (PbI2 presence or absence), if the peak value of PbI2 is lower than the peak value of FTO (i.e., the ratio of the peak values ​​of FTO / PbI2 is less than 1), it was determined that PbI2 was absent.

[0076] From Figure 7 and Table 1, When the heating temperature is 100°C, PbI2 depends on the heating time, and the shorter the heating time, the more PbI2 tends to decrease. Under condition 3 (the same conditions as in Non-Patent Document 2), a peak exists at 2θ = 12.7°, which is the peak position of PbI2, and therefore, it is confirmed that PbI2 exists in the perovskite film. When the heating temperature is 100°C and the heating time is 20 minutes under condition 1, there is no peak at 2θ=12.7°, which is the peak position of PbI2, and PbI2 is not present. I found out.

[0077] In other words, it is suggested that the annealing process, performed at high temperature for a long time, causes the perovskite crystals to decompose and return to PbI2. Therefore, the PbI2 present in the photoelectric conversion layer, i.e., the perovskite layer, is derived from the annealing process, not from the raw materials. Therefore, by performing the annealing process at an appropriate temperature for an appropriate time, it is thought that the decomposition of perovskite to PbI2 can be suppressed and the PbI2 content in the perovskite layer can be reduced. [Explanation of symbols]

[0078] 1: Circuit board 2a: First electrode layer 2b: Second electrode layer 3a: First carrier transport layer 3b: Second carrier transport layer 4: Photoelectric conversion layer 4a: Liquid film of precursor solution 4b: Liquid film of precursor solution and poor solvent C: Solar battery C1, C2, C3, C4: Photoelectric conversion elements

Claims

1. A method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound as a main component, comprising: a coating step of coating a surface with a precursor solution containing the perovskite compound as a solute; an annealing step of heating the surface coated with the precursor solution at a temperature in the range of 80° C. to 120° C. for 15 minutes to less than 40 minutes; A method for manufacturing a solar cell, comprising:

2. The perovskite compound is represented by the following formula (1): AMX ３ ・・・Form (1) (In the formula, A is a mixed cation of cesium ion, methylammonium ion, and formamidinium ion, M is a divalent lead ion, and X is a halogen ion.) 2. The method for producing a solar cell according to claim 1, wherein the organic compound is represented by the formula:

3. The method for manufacturing a solar cell according to claim 1 , wherein the heating time in the annealing step is 20 minutes or more and 30 minutes or less.

4. 2. The method for producing a solar cell according to claim 1, wherein in the coating step, the precursor solution is coated so that the photoelectric conversion layer has a film thickness of 100 nm to 1000 nm.

5. 5. The method for manufacturing a solar cell according to claim 1, further comprising the step of applying a poor solvent, in which the solubility of the perovskite compound is lower than that of the solvent of the precursor solution, to the surface to which the precursor solution has been applied.

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