Method for manufacturing perovskite solar cells and perovskite solar cells

Abstract

The present invention provides a means for manufacturing a perovskite solar cell having high conversion efficiency and high durability. [Solution] One aspect of the present invention relates to a method for manufacturing a perovskite solar cell, comprising a coating step of coating a carrier transport layer with a precursor solution containing a precursor material for generating perovskite crystals, an additive represented by formula (I), and a solvent, and a heating step of heating the precursor layer obtained in the coating step to form a photoelectric conversion layer containing a perovskite film. Another aspect of the present invention relates to a perovskite solar cell. TIFF2026075720000004.tif27160

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a perovskite solar cell and to a perovskite solar cell. [Background technology]

[0002] In recent years, perovskite solar cells have been developed as a technology to achieve carbon neutrality. Perovskite solar cells have a perovskite film containing perovskite crystals as the photoelectric conversion layer.

[0003] For example, Patent Document 1 describes a method for producing a microparticle perovskite film, which is obtained by coating and drying a solution obtained by dissolving a precursor material for generating perovskite crystals and an ionic liquid in a solvent, and then performing an annealing treatment. The same document also describes a method for producing a functional device such as a perovskite solar cell, characterized by using a microparticle perovskite film produced by the above method. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 6501303 [Overview of the project] [Problems that the invention aims to solve]

[0005] For example, Patent Document 1 describes how perovskite crystals can be micronized to the nanoscale by the method described in the document, thereby improving optical properties and other characteristics. However, Patent Document 1 does not consider durability under high temperature and high humidity environments. Thus, conventional perovskite solar cells have had challenges in terms of achieving both conversion efficiency and durability.

[0006] Therefore, the present invention aims to provide a means for manufacturing a perovskite solar cell having high conversion efficiency and high durability. [Means for solving the problem]

[0007] The inventors investigated various means to solve the above-mentioned problems. The inventors found that the conversion efficiency and durability of the photoelectric conversion layer can be improved by forming a perovskite film used as a photoelectric conversion layer in a perovskite solar cell using a precursor solution containing a specific additive. Based on the above findings, the inventors completed the present invention.

[0008] In other words, the present invention encompasses the following aspects and embodiments. (Embodiment 1) A method for manufacturing a perovskite solar cell, A precursor material that produces perovskite-type crystals, and formula (I): [ka] [In the formula, n is an integer greater than or equal to 6. A coating step involves coating a carrier transport layer with a precursor solution containing an additive represented by and a solvent. Heating step, the precursor layer obtained in the coating step is heat-treated to form a photoelectric conversion layer containing a perovskite film. The method, including the method described above. (Embodiment 2) The method according to Embodiment 1, wherein n is an integer between 6 and 11. (Embodiment 3) The method according to Embodiment 1 or 2, wherein n is 7. (Embodiment 4) The method according to any one of Embodiments 1 to 3, wherein the precursor substance is a mixture of a halogenated organic amine, an amidinium halide, and a metal halide. (Embodiment 5) The method according to Embodiment 4, wherein the precursor substance is a mixture of methylammonium iodide, formamidinium iodide, cesium iodide, and lead iodide. (Embodiment 6) A perovskite solar cell having at least a photoelectric conversion layer including a perovskite film containing a perovskite-type crystal and two carrier transport layers disposed on both sides of the photoelectric conversion layer, In the perovskite film contained in the photoelectric conversion layer, among the orientation indices in X-ray diffraction (XRD) calculated using the Wilson method, the orientation indices for at least the (100) plane, (002) plane, and (220) plane are 1 or more. The perovskite solar cell.

Advantages of the Invention

[0009] According to the present invention, it becomes possible to provide a means for manufacturing a perovskite solar cell having high conversion efficiency and high durability.

Brief Description of the Drawings

[0010] [Figure 1] It is a cross-sectional view showing an embodiment of a perovskite solar cell manufactured by the method of one aspect of the present invention. [Figure 2] It is a graph showing the relationship between the number of carbon atoms of the side-chain alkyl group and the melting point in the additive used for producing the perovskite film in the examples. In the figure, the horizontal axis represents the number of carbon atoms of the side-chain alkyl group, and the vertical axis represents the melting point (K). In the additive represented by formula (I), the side-chain alkyl group is represented by H3C-(CH2)n-. Therefore, the number of carbon atoms of the side-chain alkyl group is n + 1. [Figure 3] It is a graph showing the relationship between the number of carbon atoms of the side-chain alkyl group in the additive used for producing the perovskite film in the examples and the average particle diameter of the perovskite particles contained in the produced perovskite film. In the figure, the horizontal axis represents the number of carbon atoms of the side-chain alkyl group, and the vertical axis represents the average particle diameter (μm) of the perovskite particles. [Figure 4]These are scanning electron microscope (SEM) images of the perovskite films prepared in the examples. In the figures, A is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), B is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms in the side-chain alkyl group (i.e., n = 15), C is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms in the side-chain alkyl group (i.e., n = 3), D is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms in the side-chain alkyl group (i.e., n = 5), and E is an SEM image of a control perovskite film prepared using a precursor solution without additives. [Figure 5] These are SEM images of perovskite films treated with high-temperature testing. In the figure, A is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), B is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms in the side-chain alkyl group (i.e., n = 15), C is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms in the side-chain alkyl group (i.e., n = 3), and D is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms in the side-chain alkyl group (i.e., n = 5). [Figure 6] This graph shows the orientation index of each plane index in X-ray diffraction (XRD) calculated using the Wilson method. In the figure, the horizontal axis represents the plane index, and the vertical axis represents the orientation index of each plane index. [Figure 7]This graph shows the relationship between the number of carbon atoms in the side-chain alkyl group of the additive used to prepare the perovskite film in the examples, and the XRD area ratio (PbI2 / PVK) of the (001) plane peak of lead iodide (PbI2) and the (110) plane peak of the α-phase of the perovskite compound (PVK) contained in the prepared perovskite film. In the figure, the horizontal axis represents the number of carbon atoms in the side-chain alkyl group, and the vertical axis represents the XRD area ratio (PbI2 / PVK). [Figure 8] This graph shows the relationship between the temperature of the heat treatment test for perovskite films prepared in the examples without additives (control) or with an additive having 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), and the XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α-phase of PVK contained in the perovskite film after treatment. In the figure, the horizontal axis is the temperature of the heat treatment test (°C), and the vertical axis is the XRD area ratio (PbI2 / PVK). [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below.

[0012] One aspect of the present invention relates to a method for manufacturing a perovskite solar cell.

[0013] In each embodiment of the present invention, a perovskite solar cell means a dye-sensitized solar cell having at least a photoelectric conversion layer containing a perovskite film and two carrier transport layers disposed on both sides of the photoelectric conversion layer. In a perovskite solar cell, one of the two carrier transport layers is a hole transport layer and the other is an electron transport layer.

[0014] Figure 1 shows a cross-sectional view representing one embodiment of a perovskite solar cell manufactured by the method of this embodiment. As shown in Figure 1, the perovskite solar cell 100 includes at least a substrate 11, a first electrode 12a disposed on the upper surface of the substrate 11, a first carrier transport layer 13a disposed on the upper surface of the first electrode 12a, a photoelectric conversion layer 14 disposed on the upper surface of the first carrier transport layer 13a, a second carrier transport layer 13b disposed on the upper surface of the photoelectric conversion layer 14, and a second electrode 12b disposed on the upper surface of the second carrier transport layer 13b. For example, if the perovskite solar cell 100 has a standard structure, the substrate 11 is a transparent substrate made of glass or resin, the first electrode 12a is a transparent electrode, the first carrier transport layer 13a is an electron transport layer, the second carrier transport layer 13b is a hole transport layer, and the second electrode 12b is a back electrode. Alternatively, if the perovskite solar cell 100 has an inverted structure, the substrate 11 is a transparent substrate made of glass or resin, the first electrode 12a is a transparent electrode, the first carrier transport layer 13a is a hole transport layer, the second carrier transport layer 13b is an electron transport layer, and the second electrode 12b is a back electrode.

[0015] The perovskite film contained in the photoelectric conversion layer typically contains perovskite crystals. Perovskite crystals typically consist of perovskite compounds having the compositional formula ABX3 (wherein A is a monovalent cation, B is a divalent cation, and X is a monovalent anion) and possessing a cubic unit cell.

[0016] Examples of monovalent cation A constituting perovskite crystals include monovalent organic ammonium ions, monovalent amidinium-based ions, and monovalent metal ions. Monovalent organic ammonium ions include CH3NH3 + (Methylammonium ion, hereafter also referred to as "MA"), C2H5NH3 + , C3H7NH3 + Or C4H9NH3 + It is preferable that the monovalent amidinium-based ion is HC(NH2)2 +It is preferably (formamidinium ion, hereinafter also referred to as "FA"). The monovalent metal ion is preferably rubidium ion (Rb + ) or cesium ion (Cs + ). The monovalent cation A may be only one of the cations exemplified above, or a combination of two or more of the cations exemplified above. The monovalent cation A is preferably only MA, FA or Cs + , a combination of MA, FA and Cs + , or a combination of MA, FA and / or Cs + with other cations, and more preferably a combination of MA, FA and Cs + .

[0017] Examples of the divalent cation B constituting the perovskite-type crystal include divalent metal ions. The divalent metal ion is preferably lead ion (Pb 2+ ) or tin ion (Sn 2+ ). The divalent cation B may be only one of the cations exemplified above, or a combination of two or more of the cations exemplified above. The divalent cation B is preferably Pb 2+ .

[0018] Examples of the monovalent anion X constituting the perovskite-type crystal include halogen ions. The halogen ion is preferably fluoride ion (F - ), chloride ion (Cl - ), bromide ion (Br - ) or iodide ion (I - ). The halogen ion may be only one of the anions exemplified above, or a combination of two or more of the anions exemplified above. The monovalent anion X is preferably I - , Cl - or Br - , and more preferably I - .

[0019] In a perovskite solar cell manufactured by the method of this embodiment, it can be confirmed, for example, by analyzing the perovskite film contained in the photoelectric conversion layer with a perovskite-type crystal having the characteristics described above, using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) or X-ray diffraction (XRD).

[0020] The method of this embodiment includes at least a coating step and a heating step. The coating step and the heating step are steps for forming a photoelectric conversion layer. The method of this embodiment may optionally include a material preparation step and an electrode and carrier transport layer formation step. The electrode and carrier transport layer formation step can be carried out by applying electrode and carrier transport layer formation techniques commonly practiced in the art. The coating step and the heating step, as well as the material preparation step for carrying out these steps, will be described in detail below.

[0021] [1: Material preparation process] This process includes preparing a precursor solution for a perovskite film used in a coating and heating process for forming a photoelectric conversion layer. The precursor solution prepared in this process typically comprises at least a precursor material that produces perovskite crystals, an additive, and a solvent.

[0022] The components of the precursor solution may be prepared by purchasing commercially available products, or by synthesizing them oneself.

[0023] The components of the precursor solution will be described in more detail below.

[0024] [2: Coating process] This process involves coating a carrier transport layer with a precursor solution containing a precursor material for generating perovskite-type crystals, an additive, and a solvent. This process allows the precursor layer containing the precursor material, the additive, and the solvent to be formed on the surface of the carrier transport layer.

[0025] The precursor material for generating perovskite crystals can be appropriately selected based on the composition of the perovskite crystal described above. For example, if the monovalent cation A constituting the perovskite crystal is a monovalent organic ammonium ion and a monovalent amidinium-based ion, the divalent cation B is a divalent metal ion, and the monovalent anion X is a halogen ion, the precursor material can be a mixture of halogenated organic amines, amidinium halides, and metal halides. For example, if the monovalent cation A constituting the perovskite crystal is MA, FA, and Cs + This is a combination where the divalent cation B is Pb 2+ And the monovalent anion X is I - In this case, the precursor substance is preferably a mixture of methylammonium iodide (MAI), formamidinium iodide (FAI), cesium iodide (CsI), and lead iodide (PbI2).

[0026] In the method of this embodiment, the additive is of formula (I): [ka] The compound is represented by formula (I). The compound represented by formula (I) has the properties of an ionic liquid. The perovskite film obtained by carrying out this process using a precursor solution containing the compound represented by formula (I) as an additive has a larger grain size of perovskite crystals contained in the perovskite film and higher durability under high-temperature conditions compared to conventional perovskite films obtained using a precursor solution without additives.

[0027] In formula (I), n is an integer greater than or equal to 6. Preferably, n is an integer greater than or equal to 6 and less than or equal to 11, and more preferably 7. If n is an integer less than 6 and / or greater than 11, not only may the melting point of the compound represented by formula (I) exceed the desired upper limit, but the particle size of the perovskite particles contained in the perovskite film prepared using a precursor solution containing the compound as an additive may decrease and / or become heterogeneous. Therefore, by carrying out this process using a precursor solution containing the compound represented by formula (I) having the characteristics exemplified above as an additive, a perovskite solar cell with high conversion efficiency and high durability can be manufactured.

[0028] The melting point of the compound represented by formula (I) is usually 150°C or higher, and particularly 170°C or higher. Preferably, the melting point of the compound represented by formula (I) is 250°C or lower or in the range of 150 to 250°C, and more preferably 200°C or lower or in the range of 150 to 200°C. If the melting point of the compound represented by formula (I) exceeds the above upper limit, the particle size of the perovskite particles contained in the perovskite film prepared using a precursor solution containing the compound as an additive may decrease and / or become heterogeneous. Therefore, by carrying out this process using a precursor solution containing the compound represented by formula (I) having a melting point within the range exemplified above, a perovskite solar cell with high conversion efficiency and high durability can be manufactured.

[0029] In perovskite solar cells, the larger the grain size of the perovskite crystals contained in the perovskite film used as the photoelectric conversion layer, the smaller the area of ​​grain boundaries with high electrical resistance. Therefore, perovskite solar cells having a perovskite film containing large-grained perovskite crystals as the photoelectric conversion layer have high light energy conversion efficiency. Furthermore, the perovskite crystals contained in the perovskite film can be hydrolyzed when in contact with water vapor. This hydrolysis reaction is generally accelerated under high-temperature conditions (for example, temperatures above 100°C). Therefore, the higher the durability of the perovskite film used as the photoelectric conversion layer under high-temperature conditions, the higher the durability of the perovskite solar cell. Accordingly, by carrying out this process using a precursor solution containing the additives exemplified above, it is possible to manufacture perovskite solar cells with high conversion efficiency and high durability.

[0030] Examples of solvents include aprotic polar solvents such as amide solvents, lactone solvents, lactam solvents, and sulfoxide solvents. The solvent is preferably N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone, or N-methylpyrrolidone, or a mixture thereof, and more preferably a mixture of DMF and DMSO. By carrying out this step using a precursor solution containing the solvents exemplified above, the precursor solution can be uniformly coated.

[0031] In this process, the means for coating the precursor solution onto the carrier transport layer are not particularly limited, and various means commonly used in the art can be applied. Examples of coating methods include blade coating, die coating, inkjet, spray, and spin coating. Any of the methods exemplified above can be applied to this process.

[0032] This step may optionally further include coating the precursor layer with a poor solvent. In this embodiment, the poor solvent means a solvent in which the solubility of the perovskite crystal is lower compared to the solvent contained in the precursor solution. The poor solvent is preferably an aliphatic hydrocarbon, an aromatic hydrocarbon, an alcohol, an ether, or a fatty acid, more preferably dichloromethane, chloroform, toluene, benzene, chlorobenzene, tetralin, propanol, butanol, diethyl ether, tetrahydrofuran, or acetic acid, or a mixture thereof, and even more preferably chlorobenzene. In this embodiment, the means for coating the precursor layer with the poor solvent may be the same as the means for coating the carrier transport layer as exemplified above. By carrying out this step using the poor solvent exemplified above, the growth of the perovskite crystal can be promoted, and the conversion efficiency of the resulting perovskite solar cell can be improved.

[0033] [3:Heating process] This step includes heat treatment of the precursor layer obtained in the coating step. This step allows the precursor layer to be annealed to form a photoelectric conversion layer containing a perovskite film.

[0034] In this process, the heat treatment temperature is preferably in the range of 70 to 200°C. The heat treatment time is preferably in the range of 1 to 60 minutes. By carrying out this process under the conditions exemplified above, the precursor layer can be annealed to promote the growth of perovskite-type crystals.

[0035] This step may optionally further include drying the precursor layer. In this embodiment, the drying process may be carried out as the same process as the annealing process or as a separate process. Examples of drying methods include heat drying, vacuum drying, and spray drying of a drying gas. When heat drying is applied, it is preferable to carry it out as the same process as the annealing process in this step.

[0036] The perovskite film contained in the photoelectric conversion layer of a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above preferably has a dense structure without pinholes, and more preferably has a flat surface without pinholes, and is densely packed without gaps with perovskite particles having a large particle size inside. In the photoelectric conversion layer of a perovskite solar cell, lattice defects of impurities present at the interface (grain boundary) between the crystal surface and the crystal particles act as electron and hole trapping centers (traps), blocking charge transfer and causing energy loss. Here, if the perovskite particles contained in the photoelectric conversion layer have a large particle size, the specific surface area of ​​the perovskite particles decreases, and the area of ​​the grain boundary may also decrease, so as a result the amount of lattice defects may also decrease. Furthermore, if the particle size of the perovskite particles is equal to or greater than the thickness of the perovskite film, grain boundaries may occur only in the direction of the thickness of the perovskite film, but not in the plane direction of the perovskite film. Therefore, if the particle size of the perovskite particles is equal to or greater than the thickness of the perovskite film, lattice defects at the grain boundaries can act as electron and hole trapping centers, blocking charge transfer and potentially reducing energy loss. Furthermore, if the perovskite particles contained in the photoelectric conversion layer have a large particle size, the area of ​​the grain boundaries decreases, and the perovskite film can become a polycrystalline film, thus suppressing charge recombination.

[0037] The thickness of the perovskite film included in the photoelectric conversion layer of a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above is usually 2.0 μm or less, for example, 1.8 μm or less, and particularly 1.0 μm or less. The thickness of the perovskite film is preferably in the range of 0.5 to 2.0 μm, more preferably in the range of 0.5 to 1.8 μm, and even more preferably in the range of 0.5 to 1.0 μm. As described above, the surface structure and thickness of the perovskite film included in the photoelectric conversion layer of a perovskite solar cell are closely related to the light energy conversion efficiency of the perovskite solar cell. Therefore, a perovskite solar cell that includes a perovskite film having a thickness in the range exemplified above in its photoelectric conversion layer can have a high light energy conversion efficiency.

[0038] The particle size of the perovskite particles present in the perovskite film contained in the photoelectric conversion layer of a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above is usually 2.0 μm or less, and particularly 1.8 μm or less. The particle size of the perovskite particles is preferably in the range of 1.2 to 2.0 μm, more preferably in the range of 1.3 to 2.0 μm, and even more preferably in the range of 1.4 to 1.8 μm. As described above, the particle size of the perovskite particles present in the perovskite film contained in the photoelectric conversion layer of a perovskite solar cell is closely related to the light energy conversion efficiency of the perovskite solar cell. Therefore, the presence of perovskite particles having particle sizes in the range exemplified above in the perovskite film allows a perovskite solar cell containing the perovskite film in the photoelectric conversion layer to have a high light energy conversion efficiency.

[0039] The surface state of the perovskite film contained in the photoelectric conversion layer of a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above, and the particle size of the perovskite particles present in the perovskite film, can be observed and measured, for example, using a scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDX) or a scanning electron microscope (SEM) by following the procedure below. Observe the surface state of the perovskite film using SEM-EDX or SEM. Measure the particle size of multiple perovskite particles in the SEM image of each perovskite film using image processing software, and calculate the average value and standard deviation.

[0040] The high conversion efficiency of a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above can be evaluated, for example, by observing and measuring the surface state of the perovskite film contained in the photoelectric conversion layer of the perovskite solar cell and the particle size of the perovskite particles present in the perovskite film, using the method described above.

[0041] The high durability of perovskite solar cells manufactured or that can be manufactured by the method of this embodiment described above can be evaluated, for example, by performing a high-temperature test using the perovskite film contained in the photoelectric conversion layer of the perovskite solar cell in the following procedure: The perovskite film is exposed to high-temperature test conditions (e.g., 120°C) for a predetermined time. Then, the surface state of the perovskite film (e.g., the presence of vacancies created by the thermal decomposition of perovskite particles due to the high-temperature test treatment) is observed using SEM-EDX or SEM. Alternatively, the crystal structure of the perovskite particles contained in the perovskite film after exposure is observed using XRD. The XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α phase of PVK in XRD is calculated and confirmed to be the desired value described below.

[0042] That a perovskite solar cell was manufactured by the method of this embodiment described above can be confirmed, for example, by identifying the compound represented by formula (I) in the perovskite film contained in the photoelectric conversion layer of the perovskite solar cell through instrumental analysis such as XRD, nuclear magnetic resonance spectroscopy (NMR), or mass spectroscopy (MS).

[0043] Another aspect of the present invention relates to a perovskite solar cell manufactured or that can be manufactured by the method of this embodiment described above. The perovskite solar cell of this embodiment typically comprises at least a photoelectric conversion layer comprising a perovskite film containing a perovskite crystal, and two carrier transport layers disposed on both sides of the photoelectric conversion layer.

[0044] In the perovskite solar cell of this embodiment, the perovskite film included in the photoelectric conversion layer typically has orientation indices of 1 or more in at least the (100), (002), and (220) planes in the XRD calculated using the Wilson method (Figure 6). In crystals, the orientation index in the XRD calculated using the Wilson method is known to be an indicator of high crystallinity (Hiroshi Takada et al., Journal of the Japan Institute of Metals, Vol. 55, No. 12 (1991) 1368-1374). For example, if all the orientation indices of a crystal are 1, the crystal is presumed to be unoriented. If there is a direction in which the orientation index of the crystal is greater than 1, the crystal is presumed to be oriented in that direction. Furthermore, if there are multiple directions in which the orientation index of the crystal is greater than 1, the crystal is presumed to be oriented in the direction with the largest value among them.

[0045] In the perovskite solar cell of this embodiment, the perovskite film included in the photoelectric conversion layer has an XRD area ratio (PbI2 / PVK) of the (001) plane peak of lead iodide (PbI2) and the (110) plane peak of the α phase of the perovskite compound (PVK) in XRD, which is usually 0.1 or less, and in particular 0 (Figure 7). In particular, in the perovskite solar cell of this embodiment, the perovskite film included in the photoelectric conversion layer has an XRD area ratio (PbI2 / PVK) which is usually 0.3 or less, and in particular 0, even after heat treatment (for example, exposure at 100°C or below, particularly at 90°C or below for about 100 hours) (Figure 8). As explained in the examples, the XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α phase of PVK contained in the perovskite film has a certain correlation with the amount of PbI2 produced by the decomposition of the perovskite compound. Therefore, it can serve not only as an indicator of degradation of the perovskite film or perovskite compound used in perovskite solar cells, but also as an indicator of performance of the perovskite solar cell. Accordingly, the perovskite solar cell of this embodiment, in which the XRD area ratio (PbI2 / PVK) of the perovskite film contained in the photoelectric conversion layer is within the range exemplified above, can not only exhibit high light energy conversion efficiency in the perovskite film, but also high durability under high-temperature conditions.

[0046] As described in detail above, a perovskite solar cell having high conversion efficiency and high durability can be manufactured by the method of this embodiment. The perovskite solar cell manufactured or that can be manufactured by the method of this embodiment has high conversion efficiency of light energy in the perovskite film used as the photoelectric conversion layer and high durability of the perovskite film under high temperature conditions. Therefore, the perovskite solar cell manufactured or that can be manufactured by the method of this embodiment is suitable for applications used in an outdoor environment continuously exposed to a high temperature environment (for example, a temperature of 100° C. or higher), such as in-vehicle applications such as automobiles, or for installation on the roof or wall surface of a building. The perovskite solar cell manufactured or that can be manufactured by the method of this embodiment can exhibit high conversion efficiency and high durability over a long period even when applied to the applications exemplified above.

Example

[0047] <I: Fabrication of Perovskite Film> [I-1: Preparation of Precursor Solution] As a precursor substance for generating perovskite crystals, a mixture of methylammonium iodide (MAI), formamidinium iodide (FAI), cesium iodide (CsI), and lead iodide (PbI2) (all manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared. As an additive, a compound represented by formula (I) (where n is an integer of 0 or more and 18 or less) (manufactured by Kanto Chemical Co., Inc.) was prepared. As a solvent, a mixture of N,N-dimethylformamide (DMF) (manufactured by Fujifilm Wako Pure Chemical Corporation) and dimethyl sulfoxide (DMSO) (manufactured by Fujifilm Wako Pure Chemical Corporation) (4:1) was prepared. As a poor solvent, chlorobenzene (manufactured by Sigma-Aldrich) was prepared. The precursor substance and the additive (0.75 mol%) were dissolved in the solvent under the conditions of 70° C. and 5 minutes. This solution was further stirred under the conditions of 40° C. and 30 minutes to prepare a precursor solution. As a comparative example, a precursor solution not containing an additive was prepared.

[0048] [I-2: Film Formation of Perovskite Film] By the spin coating method, the precursor solution prepared in I-1 was dropped onto a glass substrate (manufactured by Nippon Sheet Glass Co., Ltd.) washed with isopropanol, and then the glass substrate was rotated at a high speed of 6000 rpm to uniformly coat the precursor solution on the glass substrate. Next, after dropping a poor solvent onto the applied precursor solution, the glass substrate was rotated at a high speed of 6000 rpm to form a precursor layer on the surface of the glass substrate (coating step). Then, the glass substrate was heated on a hot plate at 100 °C for 30 minutes to dry and anneal the precursor layer (heating step). By such treatment, the solvent and poor solvent contained in the precursor layer were removed, and perovskite crystals were grown to form a perovskite film ((FA 0.8 MA 0.15 Cs 0.05 )PbI3).

[0049] [II: Performance Evaluation of Perovskite Film] [II-1: Observation of Perovskite Crystals and Measurement of Particle Size] The surface state of the prepared perovskite film was observed using a scanning electron microscope - energy dispersive X-ray spectrometer (SEM-EDX, Nano Shield, manufactured by Hitachi High-Tech Corporation). Using image processing software (WinROOF2023, manufactured by Mitani Corporation), the particle sizes of a plurality of perovskite particles were measured in the SEM photographs (10,000 times) of each perovskite film, and the average value and standard deviation were calculated.

[0050] The crystal structure of the perovskite particles contained in the prepared perovskite film was observed using an X-ray diffractometer (XRD). Using the Wilson method, the orientation index of each plane index in XRD was calculated (Hiroshi Takada et al., Journal of the Japan Institute of Metals, Vol. 55, No. 12 (1991) 1368-1374). In addition, the XRD area ratio (PbI2 / PVK) of the (001) plane peak of lead iodide (PbI2) and the (110) plane peak of the α-phase of the perovskite compound (PVK) in XRD was calculated.

[0051] [II-2: Melting Point Measurement Test of Additive] To prepare a precursor solution containing an ionic liquid additive, the additive must melt under the dissolution conditions (70°C and 5 minutes) described in procedure I-1. Therefore, the melting point of the additive was measured using a differential scanning calorimeter (Q1000, TA Instruments).

[0052] [II-3: Heat Treatment Test] The fabricated perovskite films were exposed to high-temperature conditions (120°C) for 100 hours. The surface state of the exposed perovskite films was then observed using SEM-EDX. Additionally, the fabricated perovskite films were exposed to high-temperature conditions (25, 80, or 90°C) from room temperature to 100 hours under an argon atmosphere. The crystal structure of the perovskite particles contained in the exposed perovskite films was then observed using XRD. The XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α-phase of PVK was calculated.

[0053] [II-4: Evaluation Results] Figure 2 shows the relationship between the number of carbon atoms in the side-chain alkyl group and the melting point of the additive used in the fabrication of the perovskite film. In the figure, the horizontal axis represents the number of carbon atoms in the side-chain alkyl group, and the vertical axis represents the melting point (K). In the additive represented by formula (I), the side-chain alkyl group is H3C-(CH2) n It is represented by -. Therefore, the number of carbon atoms in the side-chain alkyl group is n+1.

[0054] As shown in Figure 2, the additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) exhibited a minimum melting point. In the range of 2 to 8 carbon atoms in the side-chain alkyl group (i.e., n = 1 to 7), the melting point decreased with increasing carbon number. This is presumed to be due to the cation asymmetry and flexibility of the side-chain alkyl group in the additive represented by formula (I). On the other hand, in the range of 8 to 16 carbon atoms in the side-chain alkyl group (i.e., n = 7 to 15), the melting point increased with increasing carbon number. This is presumed to be due to the interaction (stereostructural stabilization) of the side-chain alkyl groups between multiple additive molecules represented by formula (I), which forms a crystalline structure in which the side-chain alkyl groups are arranged in parallel.

[0055] Figure 3 shows the relationship between the number of carbon atoms in the side-chain alkyl group of the additive used to prepare the perovskite film and the average particle size of the perovskite particles contained in the prepared perovskite film. In the figure, the horizontal axis represents the number of carbon atoms in the side-chain alkyl group, and the vertical axis represents the average particle size (μm) of the perovskite particles.

[0056] As shown in Figure 3, perovskite particles contained in a perovskite film prepared using an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) showed an average particle size of 1.65 ± 0.604 μm, which is the maximum value. In contrast, perovskite particles contained in a perovskite film prepared using an additive with a higher number of carbon atoms in the side-chain alkyl group, for example, 16 carbon atoms (i.e., n = 15), showed an average particle size of 0.817 ± 0.256 μm. Furthermore, perovskite particles contained in a perovskite film prepared using the additive with 6 carbon atoms in the side-chain alkyl group (i.e., n = 5) described in Patent Document 1 showed an average particle size of 1.29 ± 0.681 μm.

[0057] SEM images of the fabricated perovskite films are shown in Figure 4. In the figure, A is an SEM image of a perovskite film fabricated using a precursor solution containing an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), B is an SEM image of a perovskite film fabricated using a precursor solution containing an additive with 16 carbon atoms in the side-chain alkyl group (i.e., n = 15), C is an SEM image of a perovskite film fabricated using a precursor solution containing an additive with 4 carbon atoms in the side-chain alkyl group (i.e., n = 3), D is an SEM image of a perovskite film fabricated using a precursor solution containing an additive with 6 carbon atoms in the side-chain alkyl group (i.e., n = 5), and E is an SEM image of a control perovskite film fabricated using a precursor solution without additives.

[0058] As shown in Figure 4, perovskite particles contained in perovskite films prepared using a precursor solution containing an additive with 7 or more carbon atoms in the side-chain alkyl group (i.e., n is 6 or more) had homogeneous particle sizes (Panels A and B). In contrast, perovskite particles contained in perovskite films prepared using a precursor solution containing an additive with less than 7 carbon atoms in the side-chain alkyl group (i.e., n is less than 6) had a larger average particle size than the perovskite particles contained in the control perovskite film (Panel E), but their average particle size was somewhat smaller and heterogeneous (Panels C and D).

[0059] Figure 5 shows SEM images of perovskite films treated with high-temperature testing. In the figure, A is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), B is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms in the side-chain alkyl group (i.e., n = 15), C is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms in the side-chain alkyl group (i.e., n = 3), and D is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms in the side-chain alkyl group (i.e., n = 5).

[0060] As shown in Figure 5, perovskite films prepared using a precursor solution containing an additive with side-chain alkyl groups having 7 or more carbon atoms (i.e., n being 6 or more) did not show significant changes even after high-temperature testing (Panels A and B). In contrast, perovskite films prepared using a precursor solution containing an additive with side-chain alkyl groups having less than 7 carbon atoms (i.e., n being less than 6) underwent thermal decomposition of the perovskite particles and the formation of voids after high-temperature testing (Panels C and D). This is presumed to be due to the heterogeneous particle size of the perovskite particles contained in the perovskite film in its initial stage of preparation, resulting in heterogeneous heat conduction between particles.

[0061] Figure 6 shows the orientation index of each face index in the XRD calculated using Wilson's method. In the figure, the horizontal axis represents the face index, and the vertical axis represents the orientation index of each face index.

[0062] As shown in Figure 6, in perovskite films prepared using an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), the orientation index in the XRD calculated using the Wilson method was 1 or greater in at least the (100), (002), and (220) planes.

[0063] Figure 7 shows the relationship between the number of carbon atoms in the side-chain alkyl group of the additive used to prepare the perovskite film and the XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α-phase of PVK contained in the prepared perovskite film. In the figure, the horizontal axis represents the number of carbon atoms in the side-chain alkyl group, and the vertical axis represents the XRD area ratio (PbI2 / PVK).

[0064] As shown in Figure 7, perovskite films prepared using additives with side-chain alkyl groups having 3 or more carbon atoms (i.e., n being 2 or more) had an XRD area ratio (PbI2 / PVK) of 0.

[0065] Figure 8 shows the relationship between the temperature of a heat treatment test of perovskite films prepared with no additives (control) or with an additive having 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) and the XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 and the (110) plane peak of the α-phase of PVK contained in the treated perovskite film. In the figure, the horizontal axis represents the temperature of the heat treatment test (°C), and the vertical axis represents the XRD area ratio (PbI2 / PVK).

[0066] As shown in Figure 8, in the control perovskite film prepared without additives, the XRD area ratio (PbI2 / PVK) was 0.4 after treatment at 25°C, and the XRD area ratio (PbI2 / PVK) increased with increasing treatment temperature. In contrast, in the perovskite film prepared using an additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), the XRD area ratio (PbI2 / PVK) was 0 at all treatment temperatures of 25, 80, and 90°C.

[0067] Perovskite solar cells, which have a perovskite film containing the α phase of a perovskite compound as a photoelectric conversion layer, are known to have high conversion efficiency. In such perovskite solar cells, when the perovskite compound contained in the perovskite film is decomposed by heating, humidification and / or light irradiation, PbI2 is generated. Therefore, the XRD area ratio (PbI2 / PVK) of the (001) plane peak of PbI2 contained in the perovskite film and the (110) plane peak of the α phase of PVK has a certain correlation with the amount of PbI2 generated by the decomposition of the perovskite compound. Thus, it can serve not only as an indicator of degradation of the perovskite film or perovskite compound used in perovskite solar cells, but also as an indicator of the performance of the perovskite solar cell. For example, if the XRD area ratio (PbI2 / PVK) in the perovskite film or perovskite compound is small, it is presumed that the amount of PbI2 generated is small. In this case, the perovskite film or perovskite compound can be determined to have a small degree of degradation. Furthermore, a perovskite solar cell having this perovskite film as a photoelectric conversion layer can be determined to have good performance.

[0068] The size of the perovskite crystal grains can affect the power generation efficiency of perovskite solar cells. This is because lattice defects present at the interfaces (grain boundaries) between the surfaces of multiple perovskite crystals trap electrons and / or holes, causing recombination and reducing power generation efficiency. Therefore, increasing the grain size of perovskite crystal grains reduces the specific surface area of ​​the crystal grains and the area of ​​the grain boundaries, thereby improving the power generation efficiency of perovskite solar cells. Furthermore, when the grain size of perovskite crystal grains exceeds 1 μm, grain boundaries occur only in the thickness direction of the perovskite film and not in the plane direction, thus reducing the effect of grain boundary defects on obstructing charge transfer. Thus, increasing the grain size of perovskite crystal grains is effective in improving the power generation efficiency of perovskite solar cells. Furthermore, in order to improve the durability of perovskite solar cells, it is effective to improve the stability of the perovskite crystal particles so that their particle size and / or crystal structure do not substantially change under high-temperature test conditions.

[0069] Generally, crystallization consists of the processes of nucleation, grain growth, coalescence, and crystallization. Of these, the processes of nucleation and coalescence (Ostwald maturation) are important for controlling the grain size of the crystal. Ostwald maturation is a coalescence mechanism in which, because the surrounding vapor pressure differs due to the different radii of minute particles, larger nuclei incorporate smaller nuclei and grow, continuing to grow until there are no more small nuclei left. In the preparation of perovskite crystals by the poor solvent method, Ostwald maturation easily occurs during annealing because the evaporation rate of the poor solvent is slow. In Ostwald maturation, since there are many minute particles (nuclei) in the initial state, it is important to control the nucleation of perovskite crystals by adding an ionic liquid additive.

[0070] In the additive represented by formula (I), the polar portion (methylimidazolium ring and chloride ion) and the nonpolar portion (side-chain alkyl group) generally form domain structures. These domain structures then form the intermolecular network of the additive represented by formula (I). As shown in Figure 2, the additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) exhibited a minimum melting point. Furthermore, as shown in Figure 3, the perovskite particles contained in a perovskite film prepared using the additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) exhibited a maximum average particle size of 1.65 ± 0.604 μm. From these results, it is inferred that in the preparation of perovskite crystals using the additive with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7), the additive and the precursor material are in close proximity at the atomic level, allowing for the formation of many uniform nuclei, and thus promoting Ostwald aging. In such a reaction system, the domain structure of the additive is stabilized electrically and stereostructurally by forming an intermolecular network, and as a result, it is presumed that a large number of highly symmetrical, large-grained perovskite crystals can be obtained. Furthermore, it is presumed that perovskite solar cells having a perovskite film containing these large-grained perovskite crystals as a photoelectric conversion layer will have high durability.

[0071] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. In addition, it is possible to add, delete, and / or replace some of the configurations in each embodiment with other configurations. [Explanation of symbols]

[0072] 100... Perovskite solar cell, 11... Substrate, 12a... First electrode, 12b... Second electrode, 13a... First carrier transport layer, 13b... Second carrier transport layer, 14... Photoelectric conversion layer

Claims

1. A method for manufacturing perovskite solar cells, A precursor material that produces perovskite crystals, and formula (I): 【Chemistry 1】 [In the formula, n is an integer greater than or equal to 6. A coating step involves coating a carrier transport layer with a precursor solution containing an additive represented by and a solvent. Heating step, the precursor layer obtained in the coating step is heat-treated to form a photoelectric conversion layer containing a perovskite film. The method, including the method described above.

2. The method according to claim 1, wherein n is an integer between 6 and 11.

3. The method according to claim 1, wherein n is 7.

4. The method according to claim 1, wherein the precursor substance is a mixture of a halogenated organic amine, an amidinium halide, and a metal halide.

5. The method according to claim 4, wherein the precursor substance is a mixture of methylammonium iodide, formamidinium iodide, cesium iodide, and lead iodide.

6. A perovskite solar cell having at least a photoelectric conversion layer including a perovskite film containing a perovskite crystal, and two carrier transport layers disposed on both sides of the photoelectric conversion layer, The perovskite film contained in the photoelectric conversion layer has an orientation index of 1 or higher in at least the (100), (002), and (220) planes, as determined by X-ray diffraction (XRD) calculated using the Wilson method. The aforementioned perovskite solar cell.

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