Method for manufacturing perovskite solar cell

Abstract

To provide a method for manufacturing a perovskite solar cel, capable of suppressing occurrence of pinholes.SOLUTION: The present invention relates to a method for manufacturing a solar cell including a photoelectric conversion layer containing a perovskite compound. The method includes the steps of: applying a precursor solution containing the perovskite compound as a solute over an application surface; and applying a poor solvent having a lower solubility for the perovskite compound than that of a solvent of the precursor solution over the application surface with the precursor solution applied, a gas concentration of a volatile organic compound in a vicinity of the application surface being less than 15,000 ppm at a timing when an application of the poor solvent is started.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates 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 manufacturing a perovskite solar cell, for example, Patent Document 1 describes a method in which a perovskite thin film material film is applied, and then a gaseous or mist-like poor solvent is sprayed onto the perovskite thin film material film to dry and crystallize the perovskite thin film material film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-148126 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional methods for manufacturing perovskite solar cells have sometimes resulted in the generation of pinholes in the photoelectric conversion layer. Therefore, an object of the present invention is to provide a method for manufacturing a perovskite solar cell that can suppress the generation of pinholes. [Means for solving the problem]

[0006] The present inventors have discovered that in the production of perovskite solar cells, the occurrence of pinholes in the photoelectric conversion layer can be suppressed by controlling the gas concentration at the timing of applying a poor solvent, and have completed the present invention.

[0007] That is, the gist of the present invention is as follows. (1) A method for producing a solar cell having a photoelectric conversion layer containing a perovskite compound, comprising: applying a precursor solution containing the perovskite compound as a solute to a coating surface; a step of applying a poor solvent, which has a lower solubility for the perovskite compound than the solvent of the precursor solution, to the surface on which the precursor solution has been applied, wherein the gas concentration of volatile organic compounds in the vicinity of the applied surface is less than 15,000 ppm at the timing when application of the poor solvent is started; A method for manufacturing a solar cell, comprising: (2) The method for producing a solar cell according to (1) above, wherein the gas concentration of volatile organic compounds in the vicinity of the coating surface is 1000 ppm or more at the timing when coating of the poor solvent is started. (3) The method for producing a solar cell according to (1) or (2), wherein the gas concentration of volatile organic compounds in the vicinity of the coating surface is 4000 ppm or less at the timing when the application of the poor solvent is started. (4) The method for producing a solar cell according to any one of (1) to (3), wherein the gas concentration of volatile organic compounds in the vicinity of the applied surface during the period from when the precursor solution is applied to when the poor solvent is applied is less than 15,000 ppm. (5) The method for producing a solar cell according to any one of (1) to (4), wherein the gas concentration of volatile organic compounds in the vicinity of the applied surface during the period from when the precursor solution is applied to when the poor solvent is applied is 7000 ppm or less. [Effects of the Invention]

[0008] The present invention makes it possible to provide a method for manufacturing a perovskite solar cell that can suppress the occurrence of pinholes in the photoelectric conversion layer. [Brief explanation of the drawings]

[0009] [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. [Figure 6] FIG. 10 is a schematic cross-sectional view for explaining step S3. [Figure 7] 10 is a graph showing a change in gas concentration over time when the gas concentration of a volatile organic compound is changed by exhaust. [Figure 8] FIG. 8 is a partially enlarged view of the graph in FIG. 7. [Figure 9] 10 is a graph showing a change in gas concentration over time when the gas concentration of a volatile organic compound is changed by blowing air. [Figure 10] FIG. 10 is a partially enlarged view of the graph in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will now be described in detail.

[0011] The present invention relates to a method for producing a solar cell having a photoelectric conversion layer containing a perovskite compound. The method for producing a solar cell of the present invention includes a step of applying a precursor solution containing a perovskite compound as a solute to a coating surface (step S1), and a step of applying a poor solvent to the coating surface to which the precursor solution has been applied (step S2). In the present invention, the occurrence of pinholes in the photoelectric conversion layer is suppressed by controlling the gas concentration of the volatile organic compound near the coating surface within a specific range at the timing when coating of the poor solvent is started in step S2.

[0012] <Solar cell configuration> First, the structure of the 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.

[0013] 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.

[0014] (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.

[0015] 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.

[0016] As will be described in detail later, the manufacturing method of the present invention suppresses the occurrence of pinholes in the photoelectric conversion layer 4. Since the solar cell of the present invention suppresses the occurrence of pinholes in the photoelectric conversion layer, it has excellent power generation performance and is also prevented from short circuits.

[0017] 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.

[0018] 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.

[0019] The perovskite compound can be represented by, for example, the following formula (1). ABX3(1) (wherein A is a monovalent cation, B is a divalent cation, and X is a monovalent anion.)

[0020] 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 + , and combinations of two or three of these.

[0021] 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:

[0022] 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 - is preferred.

[0023] (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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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).

[0033] Inorganic materials that can be used as the material for the electron transport layer include titanium oxide, tin oxide, and zinc oxide.

[0034] 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.

[0035] (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.

[0036] (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.

[0037] 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.

[0038] <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.

[0039] The film-forming process for the photoelectric conversion layer 4 will be described in detail below. FIG.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 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. AXE (2) BX2(3)

[0044] 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.

[0045] 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 selected appropriately 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.

[0046] 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.

[0047] 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.

[0048] Returning to the explanation of Fig. 3, in the film-forming process of the photoelectric conversion layer 4, after step S1, a poor solvent is applied to the surface on which the precursor solution has been applied (step S2). 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.

[0049] As shown in FIG. 5, by performing step S2 according to this embodiment, a liquid film 4b in which the precursor solution and the poor solvent are mixed 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.

[0050] 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 %.

[0051] 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.

[0052] Step S2 according to this embodiment is performed while controlling the concentration of the volatile organic compound gas in the vicinity of the coating surface to within a specific range. More specifically, in step S2 according to this embodiment, the concentration of the volatile organic compound gas is controlled so that the concentration of the volatile organic compound gas near the application surface is less than 15,000 ppm at the timing when application of the poor solvent starts. The vicinity of the coating surface may be defined as a region where the gas concentration of the volatile organic compound measured in the region correlates with the evaporation rate of the solvent contained in the liquid film 4a or 4b located on the coating surface. In one embodiment, the vicinity of the coating surface refers to, for example, a region within 25 mm in the vertical direction from the coating surface.

[0053] In step S2, the evaporation rate of the solvent in the liquid film 4b is controlled within an appropriate range by controlling the gas concentration of the volatile organic compound at the timing of applying the poor solvent, and as a result, 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 uniformly generating a sufficient number of crystal nuclei in step S2, pinholes are suppressed, and a photoelectric conversion layer 4 containing a uniform perovskite compound can be formed.

[0054] That is, in the method for manufacturing a solar cell according to this embodiment, the formation of pinholes in the photoelectric conversion layer 4 can be suppressed by configuring step S2 as described above. Furthermore, 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.

[0055] In step S2 according to this embodiment, the gas concentration of volatile organic compounds near the coating surface at the timing when coating of the poor solvent starts is less than 15,000 ppm, preferably 10,000 ppm or less, more preferably 7,000 ppm or less, and particularly preferably 4,000 ppm or less. When the gas concentration of the volatile organic compound in the vicinity of the coating surface is reduced, the occurrence of pinholes in the photoelectric conversion layer is further suppressed.

[0056] On the other hand, if the gas concentration of the volatile organic compound in the vicinity of the coating surface at the timing when coating of the poor solvent starts is made excessively low, the surface roughness of the photoelectric conversion layer increases. Therefore, in step S2, the gas concentration of volatile organic compounds near the coating surface at the timing when coating of the poor solvent begins is preferably 100 ppm or more, more preferably 1000 ppm or more, and particularly preferably 2000 ppm or more.

[0057] When the gas concentration of the volatile organic compound near the coating surface is 1000 ppm or more, the surface roughness of the photoelectric conversion layer becomes sufficiently small. If the surface roughness of the photoelectric conversion layer is sufficiently small, the film thickness of the layer adjacent to the photoelectric conversion layer can be made sufficiently small, thereby suppressing an increase in the resistance of the solar cell.

[0058] From the above, in step S2, the gas concentration of volatile organic compounds near the coating surface at the timing when coating of the poor solvent begins is preferably 1000 ppm or more and less than 15000 ppm, more preferably 1000 ppm or more and 10000 ppm or less, and particularly preferably 1000 ppm or more and 4000 ppm or less. When the gas concentration of the volatile organic compound near the coating surface is within this range, the generation of pinholes in the photoelectric conversion layer is suppressed, and the surface roughness of the photoelectric conversion layer is sufficiently small.

[0059] In the present invention, ppm used for gas concentration represents volume ppm.

[0060] In one embodiment, the timing at which application of the poor solvent starts may refer to the timing immediately before application of the poor solvent starts. For example, the timing at which application of the poor solvent starts may mean the timing within one second before application of the poor solvent starts. In another embodiment, when the precursor solution is applied by dropping it as droplets, the timing at which the application of the poor solvent starts may refer to the timing at which the dropping of the poor solvent starts.

[0061] In step S2, the gas concentration of the volatile organic compound in the vicinity of the coating surface can be adjusted, for example, by exhausting or blowing air. In the case of adjustment by exhaust, for example, the gas concentration can be adjusted by removing the gas from the vicinity of the workpiece using an exhaust mechanism such as an exhaust pipe. In addition, in the case of adjustment by blowing air, the gas concentration can be adjusted by blowing air toward the workpiece using a blowing mechanism such as a circulator.

[0062] 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.

[0063] In step S2, the poor solvent can be applied in the same manner as in the application of the precursor solution in step S1.

[0064] Returning to the explanation of Fig. 3, in the film formation process of the photoelectric conversion layer 4, after step S2, an annealing treatment 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.

[0065] 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 treatment carried out in step S3 is usually a treatment of heating the liquid film 4b at a temperature of 70°C or higher and 200°C or lower.

[0066] The production method according to the present invention may include a drying step between step S2 and step S3. In the drying step, the solvent in the liquid film is removed using a known drying method such as heating, blowing a dry gas, or vacuuming. When a drying step is not included between step S2 and step S3, step S3 may be understood as a process in which the annealing treatment and the drying treatment are performed in one step.

[0067] As described above, in the manufacturing method according to this embodiment, the gas concentration of volatile organic compounds near the coating surface is set to less than 15,000 ppm, more preferably 4,000 ppm or less, at the timing when coating of the poor solvent begins. With this configuration, the manufacturing method according to this embodiment can suppress the occurrence of pinholes in the photoelectric conversion layer.

[0068] In addition, in the manufacturing method according to the present embodiment, the gas concentration of the volatile organic compound in the vicinity of the coating surface may be 1000 ppm or more at the timing when coating of the poor solvent starts. With this configuration, the manufacturing method according to the present embodiment can reduce the surface roughness of the photoelectric conversion layer.

[0069] Furthermore, the gas concentration of volatile organic compounds in the vicinity of the application surface during the period from application of the precursor solution to application of the poor solvent may be set to less than 15,000 ppm, more preferably 7,000 ppm or less. With this configuration, the manufacturing method according to this embodiment can further suppress the occurrence of pinholes in the photoelectric conversion layer. [Example]

[0070] 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.

[0071] A laminate 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.

[0072] The precursor solution was applied to the electron transport layer of the substrate under an argon gas atmosphere at room temperature (25°C) while varying the gas concentration of the volatile organic compound during application. A poor solvent was added dropwise to the applied precursor solution, followed by annealing, to form a perovskite film containing the perovskite compound on the substrate. The gas concentration of volatile organic compounds during application was adjusted by exhaust and airflow. The gas concentration of volatile organic compounds was measured using a PID gas concentration meter installed with the tip of the VOC (volatile organic compound) sensor positioned approximately 25 mm vertically from the application surface.

[0073] Change in gas concentration by exhaust (Examples 1 to 6 and Comparative Examples 1 and 2) An exhaust pipe was installed in the spin coater, and the opening of the valve installed in the exhaust pipe was set to three levels: large, medium, and small, to exhaust the gas inside the spin coater. Experiments were conducted twice for each exhaust condition.

[0074] The perovskite film was formed by the following procedure. 1.Start exhaust 2. Place the substrate on the spin coater stage 3. Dropping the precursor solution onto the substrate 4. Start spin coater rotation 5. While rotating, add chlorobenzene (poor solvent) with a pipette. 6. Spin coater rotation ends 7. Remove the substrate and place it on a hot plate for annealing (120°C).

[0075] Changing gas concentration by blowing air (Examples 7 and 8) The circulator was placed about 15 cm horizontally from the workpiece, and the airflow was directed toward the workpiece. The circulator's airflow volume was set to two levels: high and low.

[0076] The perovskite film was formed by the following procedure. 1. Start blowing air 2. Place the substrate on the spin coater stage 3. Dropping the precursor solution onto the substrate 4. Start spin coater rotation 5. While rotating, add chlorobenzene (poor solvent) with a pipette. 6. Spin coater rotation ends 7. Remove the substrate and place it on a hot plate for annealing (120°C).

[0077] The perovskite film formed on the substrate was analyzed as follows.

[0078] Pinhole measurement Images of the perovskite film were taken using a transmitted light digital microscope. The images were observed while shining light from the opposite side of the lens, and the pinholes that were visualized were analyzed to measure the area (total area) and number of pinholes.

[0079] Surface roughness Sa The surface of the perovskite film was observed using a white light interference microscope, and the surface roughness Sa was calculated.

[0080] Table 1 shows the analysis results of perovskite films when the gas concentration of volatile organic compounds was changed by evacuation. Figure 7 shows a graph illustrating the change in gas concentration over time when the gas concentration of volatile organic compounds was changed by evacuation. Figure 8 shows an enlarged view of a portion of the graph in Figure 7.

[0081] [Table 1]

[0082] 7, in the case where no exhaust was used (Comparative Examples 1 and 2), the upper measurement limit of the gas concentration meter (15,000 ppm) was reached before the poor solvent was added. Thus, in Comparative Examples 1 and 2, the gas concentration before the poor solvent was added exceeded 15,000 ppm.

[0083] 7 and 8, the gas concentration of the volatile organic compound increased significantly after the addition of the poor solvent in Examples 1 to 6. This shows that the gas concentration of the volatile organic compound before the addition of the poor solvent corresponds to the concentration of the gas obtained by volatilizing the solvent of the precursor solution, and that the gas concentration of the volatile organic compound after the addition of the poor solvent corresponds to the total concentration of the gas obtained by volatilizing the solvent of the precursor solution and the poor solvent gas obtained by volatilizing the poor solvent.

[0084] As shown in Table 1, many pinholes were generated in the perovskite films in Comparative Examples 1 and 2. This is presumably because the high gas concentration in the environment caused the solvent in the liquid film to evaporate slowly and unevenly, resulting in uneven crystal nucleation within the surface, resulting in a state where perovskite crystals were not formed in some areas.

[0085] 7 and 8, when the exhaust was small and medium (Examples 1 and 2 and Examples 3 and 4, respectively), the generated solvent gas was exhausted, and the gas concentration in the environment was reduced compared to when no exhaust was performed. As shown in Table 1, in Examples 1 to 4, the solvent in the liquid film was appropriately evaporated, thereby suppressing the formation of pinholes.

[0086] As shown in Figures 7 and 8, when the exhaust was high (Examples 5 and 6), the gas concentration in the environment was significantly reduced. As shown in Table 1, in Examples 5 and 6, pinhole formation was significantly suppressed, and no pinholes were observed under a microscope, but the surface roughness Sa value increased. This is presumably because the low gas concentration in the environment caused the solvent in the liquid film to evaporate more quickly, resulting in uneven crystal nucleation and crystal growth within the surface, and partial crystal swelling, which increased the surface unevenness.

[0087] These results demonstrate that the quality of perovskite crystals can be improved by maintaining an appropriate gas concentration of the volatile organic compound at the timing of applying the poor solvent during perovskite film formation.

[0088] Table 2 shows the analysis results of the perovskite film when the gas concentration of the volatile organic compound was changed by blowing air. Figure 9 shows a graph showing the change in gas concentration over time when the gas concentration of the volatile organic compound was changed by blowing air. Figure 10 shows an enlarged view of a portion of the graph in Figure 9.

[0089] [Table 2]

[0090] As shown in Figures 9 and 10 and Table 2, by maintaining an appropriate gas concentration of the volatile organic compound at the timing of applying the poor solvent, the formation of pinholes was suppressed, and the surface roughness Sa was also sufficiently small. [Explanation of symbols]

[0091] 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, comprising: applying a precursor solution containing the perovskite compound as a solute to a coating surface; a step of applying a poor solvent, which has a lower solubility for the perovskite compound than the solvent of the precursor solution, to the surface on which the precursor solution has been applied, wherein the gas concentration of volatile organic compounds in the vicinity of the applied surface is less than 15,000 ppm at the timing when application of the poor solvent is started; A method for manufacturing a solar cell, comprising:

2. 2. The method for manufacturing a solar cell according to claim 1, wherein the gas concentration of the volatile organic compound in the vicinity of the coated surface is 1000 ppm or more at the timing when the application of the poor solvent is started.

3. 3. The method for manufacturing a solar cell according to claim 1, wherein the gas concentration of volatile organic compounds in the vicinity of the coated surface is 4000 ppm or less at the timing when the application of the poor solvent is started.

4. 2. The method for manufacturing a solar cell according to claim 1, wherein a gas concentration of volatile organic compounds in the vicinity of the applied surface during the period from when the precursor solution is applied to when the poor solvent is applied is less than 15,000 ppm.

5. 5. The method for manufacturing a solar cell according to claim 4, wherein a gas concentration of volatile organic compounds in the vicinity of the applied surface during the period from when the precursor solution is applied to when the poor solvent is applied is 7000 ppm or less.

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