Method for manufacturing perovskite solar cell, and perovskite solar cell

Abstract

Provided is a method for manufacturing a perovskite-type solar cell having high conversion efficiency and high durability. One embodiment of the present invention relates to a method for manufacturing a perovskite solar cell, comprising: a coating step for coating a carrier transport layer with a precursor solution containing a precursor substance that generates a perovskite crystal, an additive represented by formula (I), and a solvent; and a heating step in which the precursor layer obtained in the coating step is subjected to a heat treatment to form a photoelectric conversion layer including a perovskite film. Another aspect of the present invention relates to a perovskite-type solar cell.

Description

Technical Field

[0001] This invention relates to a method for manufacturing perovskite solar cells and perovskite solar cells. Background Technology

[0002] In recent years, the development of perovskite solar cells has been advancing as a technology for achieving carbon neutrality. Perovskite solar cells have a perovskite film containing perovskite crystals as the photoelectric conversion layer.

[0003] For example, Patent Document 1 discloses a method for manufacturing a micronized perovskite film, which involves coating and drying a solution formed by dissolving a precursor material for generating perovskite crystals and an ionic liquid in a solvent, followed by annealing. The same document also discloses a method for manufacturing a functional element such as a perovskite solar cell, characterized by using a micronized perovskite film manufactured by the above method.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6501303 Summary of the Invention

[0007] For example, Patent Document 1 describes a method that micronizes perovskite crystals to the nanoscale, thereby improving optical properties. However, Patent Document 1 does not investigate durability under high temperature and high humidity conditions. Thus, in conventional perovskite solar cells, there is a challenge in balancing conversion efficiency and durability.

[0008] Therefore, the object of the present invention is to provide a method for manufacturing perovskite solar cells with high conversion efficiency and high durability.

[0009] The inventors have conducted various studies on methods for solving the aforementioned problems. They have discovered that by using a precursor solution containing specific additives to form a perovskite film used as a photoelectric conversion layer in a perovskite solar cell, the conversion efficiency and durability of the photoelectric conversion layer can be improved. Based on the above insights, the inventors have completed this invention.

[0010] That is, the present invention includes the following methods and implementation methods.

[0011] (Embodiment 1) A method for manufacturing a perovskite solar cell, comprising:

[0012] In the coating process, a precursor solution comprising a precursor material for generating perovskite-type crystals, an additive as shown in formula (I), and a solvent is coated onto the carrier transport layer; and

[0013] The heating process involves heating the precursor layer obtained in the coating process to form a photoelectric conversion layer containing a perovskite film.

[0014]

[0015] [In the formula, n is an integer greater than or equal to 6.]

[0016] (Implementation Method 2) According to the method described in Implementation Method 1, where n is an integer from 6 to 11.

[0017] (Implementation Method 3) The method according to Implementation Method 1 or 2, wherein n is 7.

[0018] (Embodiment 4) The method according to any one of Embodiments 1-3, wherein the precursor is a halogenated organic amine or a halogenated amidine. A mixture of metal halides.

[0019] (Embodiment 5) According to the method of Embodiment 4, the precursor is methylammonium iodide or formamidine iodide. A mixture of cesium iodide and lead iodide.

[0020] (Embodiment 6) A perovskite solar cell, comprising at least: a photoelectric conversion layer containing a perovskite film containing perovskite crystals and two carrier transport layers disposed on both sides of the photoelectric conversion layer, wherein the orientation index of at least (100) plane, (002) plane and (220) plane in the perovskite film contained in the photoelectric conversion layer, calculated using the Wilson method, is 1 or more.

[0021] According to the present invention, a method for manufacturing perovskite solar cells with high conversion efficiency and high durability can be provided. Attached Figure Description

[0022] Figure 1 This is a cross-sectional view showing one embodiment of a perovskite solar cell manufactured by a method according to one aspect of the present invention.

[0023] Figure 2 This is a graph showing the relationship between the number of carbon atoms in the side-chain alkyl groups of the additive used in the fabrication of the perovskite film in the examples and the melting point. In the graph, the horizontal axis represents the number of carbon atoms in the side-chain alkyl groups, and the vertical axis represents the melting point (K). In the additive shown in formula (I), the side-chain alkyl groups are composed of H3C-(CH2). n - indicates that the side-chain alkyl group has n+1 carbon atoms.

[0024] Figure 3This is a graph showing the relationship between the number of carbon atoms of the side-chain alkyl groups in the additives used in the fabrication of the perovskite film in the examples and the average particle size of the perovskite particles contained in the fabricated perovskite film. In the graph, the horizontal axis represents the number of carbon atoms of the side-chain alkyl groups, and the vertical axis represents the average particle size of the perovskite particles (μm).

[0025] 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 (i.e., n=7) containing a side-chain alkyl group; B is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms (i.e., n=15) containing a side-chain alkyl group; C is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms (i.e., n=3) containing a side-chain alkyl group; D is an SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms (i.e., n=5) containing a side-chain alkyl group; and E is an SEM image of a control perovskite film prepared using a precursor solution without additives.

[0026] Figure 5 These are SEM images of perovskite films after high-temperature testing. In the figure, A is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms (i.e., n=7) containing side-chain alkyl groups; B is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms (i.e., n=15) containing side-chain alkyl groups; C is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms (i.e., n=3) containing side-chain alkyl groups; and D is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms (i.e., n=5) containing side-chain alkyl groups.

[0027] Figure 6 This is a graph representing the orientation indices of each plane in X-ray diffraction (XRD) calculated using the Wilson method. In the graph, the horizontal axis represents the plane indices, and the vertical axis represents the orientation indices of each plane.

[0028] Figure 7 This is a graph showing the relationship between the number of carbon atoms of the side-chain alkyl groups in the additives used in the fabrication of the perovskite film in the examples, and the XRD area ratio (PbI2 / PVK) of the (001) peak of lead iodide (PbI2) contained in the fabricated perovskite film and the (110) peak of the α phase of the perovskite compound (PVK). In the graph, the horizontal axis represents the number of carbon atoms of the side-chain alkyl groups, and the vertical axis represents the XRD area ratio (PbI2 / PVK).

[0029] Figure 8This is a graph showing the relationship between the temperature of the heat treatment test and the XRD area ratio (PbI2 / PVK) of the perovskite films prepared with additives without additives (control) or with additives containing 8 carbon atoms of side-chain alkyl groups (i.e., n=7) in the treated perovskite films. In the graph, the horizontal axis is the temperature of the heat treatment test (°C), and the vertical axis is the XRD area ratio (PbI2 / PVK).

[0030] Symbol Explanation

[0031] 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 Detailed Implementation

[0032] The preferred embodiments of the present invention will now be described in detail.

[0033] One aspect of the present invention relates to a method for manufacturing a perovskite solar cell.

[0034] In various embodiments of the present invention, a perovskite solar cell refers to a pigment-sensitized solar cell having at least a photoelectric conversion layer comprising a perovskite film and two carrier transport layers disposed on both sides of the photoelectric conversion layer. In the perovskite solar cell, one of the two carrier transport layers is a hole transport layer, and the other is an electron transport layer.

[0035] Figure 1 This is a cross-sectional view showing one embodiment of a perovskite solar cell manufactured by the method described herein. Figure 1 As shown, 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, when the perovskite solar cell 100 has a forward 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, when the perovskite solar cell 100 is in a reverse 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.

[0036] The perovskite film contained in the photoelectric conversion layer typically contains perovskite crystals. Perovskite crystals are usually composed of perovskite compounds with the composition ABX3 (where A is a monovalent cation, B is a divalent cation, and X is a monovalent anion), and have cubic crystal cells.

[0037] Examples of monovalent cations A that constitute perovskite-type crystals include monovalent organic ammonium ions and monovalent amidine ions. The compounds include monovalent and monovalent metal ions. Monovalent organic ammonium ions are preferably CH3NH3. + (Methylammonium ion, hereinafter also referred to as "MA") C2H5NH3 + C3H7NH3 + or C4H9NH3 + Monovalent amine The preferred ion is HC(NH2)2. + (Formamid) Ions (hereinafter also referred to as "FA"). The preferred monovalent metal ion is rubidium ion (Rb). + ) or cesium ions (Cs + The monovalent cation A can be only one cation as exemplified above, or it can be a combination of two or more cations as exemplified above. Preferably, the monovalent cation A is only MA, FA, or Cs. + , MA, FA and Cs + Combinations of MA, FA and / or Cs + Combinations with other cations, more preferably MA, FA and Cs + The combination of .

[0038] Examples of divalent cations, such as lead (Pb), that constitute perovskite-type crystals include divalent metal ions. Lead ions (Pb) are particularly preferred as divalent metal ions. 2+ ) or tin ions (Sn 2+ The divalent cation B can be only one cation as illustrated above, or it can be a combination of two or more cations as illustrated above. The divalent cation B is preferably Pb. 2+ .

[0039] Examples of monovalent anions X constituting perovskite crystals include halide ions. Halogen ions are preferably fluoride ions (F...). - ), chloride ions (Cl) - ), bromide ions (Br) - ) or iodide ions (I - The halide ion can be just one anion as exemplified above, or a combination of two or more anions as exemplified above. The monovalent anion X is preferably I. - Cl -or Br - I is preferred. - .

[0040] In the perovskite solar cell manufactured by this method, the perovskite film contained in the photoelectric conversion layer contains perovskite crystals with the characteristics described above, which can be confirmed, for example, by analyzing the perovskite film contained in the photoelectric conversion layer using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) or X-ray diffraction (XRD).

[0041] This method includes at least a coating process and a heating process. The coating and heating processes are used to form a photoelectric conversion layer. This method may, as needed, include a material preparation process and an electrode and carrier transport layer formation process. The electrode and carrier transport layer formation process can be implemented using electrode and carrier transport layer formation techniques commonly practiced in this technical field. The coating and heating processes, as well as the material preparation process used to perform these processes, are described in detail below.

[0042] [1: Material preparation process]

[0043] This process includes preparing a precursor solution for the perovskite film used in the coating and heating processes to form the photoelectric conversion layer. The precursor solution prepared in this process typically contains at least a precursor material for forming perovskite-type crystals, additives, and a solvent.

[0044] The components of the precursor solution can be prepared by purchasing commercially available products or by synthesizing them yourself.

[0045] The components of the precursor solution are described in further detail below.

[0046] [2: Coating process]

[0047] This process involves coating a precursor solution containing a precursor material, additives, and a solvent for forming perovskite-type crystals onto the carrier transport layer. This process enables the formation of a precursor layer containing the precursor material, additives, and solvent on the surface of the carrier transport layer.

[0048] The precursor material for forming perovskite crystals can be appropriately selected based on the composition of perovskite crystals described above. For example, the monovalent cation A constituting the perovskite crystal can be a monovalent organic ammonium ion and a monovalent amidine. When the ion is a divalent cation B (a divalent metal ion) and the anion X is a halide ion, the precursor is a halogenated organic amine or a halide. A mixture of metal halides is acceptable. For example, in perovskite-type crystals, the monovalent cations A are MA, FA, and Cs. + The combination of divalent cation B is Pb2+ The monovalent anion X is I - In this case, the preferred precursor is methylammonium iodide (MAI) or formamidinium iodide. A mixture of FAI, cesium iodide (CsI), and lead iodide (PbI2).

[0049] In this method, the additive is a compound represented by formula (I).

[0050]

[0051] The compound represented by formula (I) has the properties of an ionic liquid. The perovskite film obtained by performing this process using a precursor solution containing the compound shown in formula (I) as an additive has a larger grain size of perovskite-type crystals and higher durability under high temperature conditions compared to existing perovskite films obtained using a precursor solution without additives.

[0052] In formula (I), n is an integer of 6 or more. n is preferably an integer from 6 to 11, and more preferably 7. When n is an integer less than 6 and / or greater than 11, not only is there a possibility that the melting point of the compound shown in formula (I) exceeds the desired upper limit, but the particle size of the perovskite particles contained in the perovskite film prepared using a precursor solution containing this compound as an additive may decrease and / or become non-uniform. Therefore, by performing this process using a precursor solution containing a compound of formula (I) having the above-described exemplary characteristics as an additive, it is possible to manufacture perovskite solar cells with high conversion efficiency and high durability.

[0053] The melting point of the compound shown in Formula (I) is typically above 150°C, particularly above 170°C. The melting point of the compound shown in Formula (I) is preferably below 250°C or in the range of 150 to 250°C, more preferably below 200°C or in the range of 150 to 200°C. When the melting point of the compound shown in Formula (I) exceeds the 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 non-uniform. Therefore, by performing this process using a precursor solution containing the compound shown in Formula (I) having a melting point within the above-described exemplary range as an additive, it is possible to manufacture perovskite solar cells with high conversion efficiency and high durability.

[0054] 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 ​​high-resistivity grain boundaries. Therefore, perovskite solar cells with 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 upon contact with water vapor. This hydrolysis reaction is generally promoted under high-temperature conditions (e.g., 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. Therefore, by performing 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.

[0055] Examples of solvents include aprotic polar solvents such as amide solvents, lactone solvents, lactam solvents, and sulfoxide solvents. Preferably, the solvent is N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone, or N-methylpyrrolidone, or mixtures thereof, more preferably a mixture of DMF and DMSO. By using a precursor solution containing the solvents exemplified above, the precursor solution can be uniformly coated.

[0056] In this process, there is no particular limitation on the method of coating the precursor solution onto the carrier transport layer, and various methods commonly used in this technical field can be applied. Examples of coating methods include blade coating, die coating, inkjet coating, spray coating, and spin coating. Any of the methods exemplified above can be applied to this process.

[0057] This process may further include coating a poor solvent onto the precursor layer as needed. In this embodiment, a poor solvent refers to a solvent with lower solubility in the perovskite crystal compared to the solvent contained in the precursor solution. The poor solvent is preferably an aliphatic hydrocarbon, aromatic hydrocarbon, alcohol, ether, or fatty acid; more preferably, dichloromethane, chloroform, toluene, benzene, chlorobenzene, tetrahydronaphthalene, propanol, butanol, diethyl ether, tetrahydrofuran, or acetic acid, or mixtures thereof; and even more preferably, chlorobenzene. In this embodiment, the method of coating the poor solvent onto the precursor layer can be the same as the method of coating the precursor solution exemplified above onto the carrier transport layer. By using the poor solvent exemplified above, this process can promote the growth of the perovskite crystal and improve the conversion efficiency of the resulting perovskite solar cell.

[0058] [3: Heating process]

[0059] This process includes heat-treating the precursor layer obtained in the coating process. Through this process, the precursor layer can be annealed to form a photoelectric conversion layer containing a perovskite film.

[0060] In this process, the heat treatment temperature is preferably in the range of 70°C to 200°C. The heat treatment time is preferably in the range of 1 to 60 minutes. By performing this process under the conditions illustrated above, the precursor layer can be annealed to promote the growth of perovskite crystals.

[0061] This step may further include drying the precursor layer as needed. In this embodiment, the drying process can be performed as the same process as the annealing process, or it can be performed as another process. Examples of drying methods include heat drying, vacuum drying, and spraying with drying gas. When heat drying is applied, it is preferable to perform the same process as the annealing process in this step.

[0062] The perovskite film contained in the photoelectric conversion layer of a perovskite solar cell manufactured or manufactureable by the method described above preferably has a dense structure without pinholes, and more preferably has no pinholes, has a flat surface, and is densely filled with perovskite particles of large size without gaps. In the photoelectric conversion layer of a perovskite solar cell, lattice defects of impurities existing at the interface (grain boundaries) between the crystal surface and crystal particles act as trapping centers (traps) for electrons and holes, blocking charge movement and potentially causing energy loss. Here, when the perovskite particles contained in the photoelectric conversion layer have a large particle size, the specific surface area of ​​the perovskite particles is reduced, and the area of ​​the grain boundaries can also be reduced, thus reducing the amount of lattice defects. Furthermore, if the particle size of the perovskite particles is equal to or greater than the thickness of the perovskite film, grain boundaries are generated only in the thickness direction of the perovskite film, but not in the planar direction. Therefore, when the perovskite particle size is equal to or greater than the perovskite film thickness, the likelihood of lattice defects at grain boundaries acting as trapping centers for electrons and holes, thus blocking charge movement and causing energy loss, can be reduced. Furthermore, when the perovskite particles contained in the photoelectric conversion layer have a large particle size, the area of ​​the grain boundaries is reduced, and the perovskite film can become a polycrystalline film, thereby suppressing charge recombination.

[0063] The thickness of the perovskite film in the photoelectric conversion layer of a perovskite solar cell manufactured or manufactureable by the method described above is typically 2.0 μm or less, for example, 1.8 μm or less, 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 0.5 to 1.8 μm, even more preferably 0.5 to 1.0 μm, and still more preferably in the range of 0.5 to 1.0 μm. As mentioned above, the surface structure and thickness of the perovskite film in the photoelectric conversion layer of a perovskite solar cell are closely related to the light energy conversion efficiency of that perovskite solar cell. Therefore, a perovskite solar cell containing a perovskite film with a thickness within the range illustrated above can have a high light energy conversion efficiency.

[0064] The perovskite particles present in the perovskite film contained in the photoelectric conversion layer of the perovskite solar cell manufactured or manufactureable by the method described above typically have a particle size of 2.0 μm or less, 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 1.3 to 2.0 μm, even more preferably 1.4 to 1.8 μm, and still 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 the perovskite solar cell is closely related to the light energy conversion efficiency of the perovskite solar cell. Therefore, by having perovskite particles with a particle size within the range illustrated above in the perovskite film, the perovskite solar cell containing the perovskite film in the photoelectric conversion layer can have a high light energy conversion efficiency.

[0065] The surface state of the perovskite film contained in the photoelectric conversion layer of a perovskite solar cell manufactured or fabricated by the method 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 spectrophotometer (SEM-EDX) or a scanning electron microscope (SEM) in the following order: Observe the surface state of the perovskite film using SEM-EDX or SEM. Use image processing software to measure the particle size of multiple perovskite particles in the SEM images of each perovskite film, and calculate their average value and standard deviation.

[0066] The perovskite solar cells manufactured or manufactured by the method described above have high conversion efficiency. For example, this can be evaluated 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.

[0067] The perovskite solar cells manufactured or manufactured using the method described above exhibit high durability, which 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, following these steps: The perovskite film is exposed to high-temperature test conditions (e.g., 120°C) for a specified time. Then, the surface state of the perovskite film (e.g., the presence of pores resulting from the thermal decomposition of perovskite particles by the high-temperature test) is observed using SEM-EDX or SEM. Alternatively, the crystal structure of the perovskite particles contained in the exposed perovskite film 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 is calculated, and this XRD area ratio is confirmed to be the desired value as described below.

[0068] The perovskite solar cell manufactured by the method described above can be confirmed, for example, by analyzing it with equipment such as XRD, nuclear magnetic resonance spectroscopy (NMR) or mass spectrometry (MS) to identify the compound shown in formula (I) in the perovskite film contained in the photoelectric conversion layer of the perovskite solar cell.

[0069] Another aspect of the present invention relates to perovskite solar cells manufactured or manufactureable by the method described above. Perovskite solar cells of this type typically have at least: a photoelectric conversion layer comprising a perovskite film containing perovskite crystals, and two carrier transport layers disposed on both sides of the photoelectric conversion layer.

[0070] In this type of perovskite solar cell, the perovskite film contained in the photoelectric conversion layer typically has an orientation index of at least 1 or higher for the (100) plane, (002) plane, and (220) plane, based on the orientation index calculated using the Wilson method using XRD. Figure 6 It is known that in crystals, the orientation index calculated using Wilson's method in XRD is an indicator of high crystallinity (Hiroshi Takada et al., Journal of the Japan Society for Metals, Vol. 55, No. 12 (1991) 1368-1374). For example, if all the orientation indices of a crystal are 1, it is presumed that the crystal is unoriented. When there is a direction in which the orientation index of a crystal is greater than 1, it is presumed that the crystal is oriented in that direction. Furthermore, when there are multiple directions in which the orientation index of a crystal is greater than 1, it is presumed that the direction in which the crystal has the maximum value is oriented.

[0071] In this type of perovskite solar cell, the XRD area ratio (PbI2 / PVK) of the (001) peak of lead iodide (PbI2) and the (110) peak of the α phase of the perovskite compound (PVK) in the XRD of the perovskite film included in the photoelectric conversion layer is typically below 0.1, especially 0. Figure 7). In particular, in the perovskite solar cell of this method, the XRD area ratio (PbI2 / PVK) of the perovskite film contained in the photoactive layer is usually 0.3 or less, particularly 0, even after heat treatment (for example, exposure at 100 °C or less, particularly about 100 hours at 90 °C or less). Figure 8 ). As described 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 generated by the decomposition of the perovskite compound. Therefore, it can not only be an index for the deterioration of the perovskite film or perovskite compound used in the perovskite solar cell, but also be an index for the performance of the perovskite solar cell. Therefore, the perovskite solar cell of this method, in which the XRD area ratio (PbI2 / PVK) of the perovskite film contained in the photoactive layer has a value within the range exemplified above, can not only exhibit a high conversion efficiency of the light energy of the perovskite film, but also exhibit high durability under high-temperature conditions.

[0072] As described above, by the method of this method, a perovskite solar cell having high conversion efficiency and high durability can be manufactured. The perovskite solar cell manufactured or manufacturable by the method of this method has a high conversion efficiency of the light energy of the perovskite film used as the photoactive layer and high durability of the perovskite film under high-temperature conditions. Therefore, the perovskite solar cell manufactured or manufacturable by the method of this method is suitable for uses such as vehicle-mounted uses such as automobiles, or installation uses such as the roofs or walls of buildings, which are used in outdoor environments continuously exposed to high-temperature environments (for example, temperatures above 100 °C). The perovskite solar cell manufactured or manufacturable by the method of this method can exhibit high conversion efficiency and high durability for a long time even when applied to the uses exemplified above.

[0073] Examples

[0074] <I: Fabrication of perovskite film>

[0075] [I-1: Preparation of precursor solution]

[0076] Methylammonium iodide (MAI) and formamidinium iodide, which are precursor substances for generating perovskite crystals, were prepared separately. A mixture of formamidinium iodide (FAI), cesium iodide (CsI), and lead iodide (PbI2) (all manufactured by Tokyo Chemical Industry Co., Ltd.), a compound represented by formula (I) (where n is an integer from 0 to 18) as an additive (manufactured by Kanto Chemical Co., Inc.), 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) as a solvent (4:1), and chlorobenzene as a poor solvent (manufactured by Sigma-Aldrich). The precursor substance and the additive (0.75 mol%) were dissolved in the solvent under the conditions of 70 °C and 5 minutes. The 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 without the additive was prepared.

[0077] [I-2: Film Formation of Perovskite Film]

[0078] After dropping the precursor solution prepared in I-1 onto a glass substrate (manufactured by Nippon Sheet Glass Co., Ltd.) washed with isopropyl alcohol by spin coating, the glass substrate was rotated at a high speed of 6000 rpm to uniformly coat the precursor solution on the glass substrate. Then, after dropping the poor solvent into the coated 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 process). Then, the glass substrate was heated on a hot plate under the conditions of 100 °C and 30 minutes to dry and anneal the precursor layer (heating process). Through this treatment, the solvent and the poor solvent contained in the precursor layer were removed, and perovskite-type crystals grew to form a perovskite film ((FA 0.8 MA 0.15 Cs 0.05 )PbI3).

[0079] <II: Performance Evaluation of Perovskite Film>

[0080] [II-1: Observation of Perovskite-Type Crystals and Measurement of Particle Size]

[0081] Using a scanning electron microscope - energy dispersive X-ray spectroscopy analyzer (SEM-EDX, NanoShield, manufactured by Hitachi High-Tech Corporation), the surface state of the fabricated perovskite film was observed. Using image processing software (WinROOF 2023, manufactured by Mitani Corporation), the particle sizes of multiple perovskite particles were measured in the SEM photos (10,000 times magnification) of each perovskite film, and the average value and standard deviation were calculated.

[0082] The crystal structure of the perovskite particles contained in the fabricated perovskite film was observed using an X-ray diffraction (XRD) apparatus. The orientation indices of each plane in the XRD were calculated using the Wilson method (Hiroshi Takada et al., Journal of the Japan Society for Metals, Vol. 55, No. 12 (1991) 1368-1374). Furthermore, 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) was calculated.

[0083] [II-2: Melting Point Determination Test for Additives]

[0084] To prepare a precursor solution containing an additive as an ionic liquid, the additive must be dissolved under the dissolution conditions (70°C and 5 minutes) of step I-1. Therefore, the melting point of the additive was determined using a differential scanning calorimeter (Q1000, TA Instruments).

[0085] [II-3: Heat Treatment Test]

[0086] The fabricated perovskite film was exposed to high temperature (120°C) for 100 hours. The surface morphology of the exposed perovskite film was then observed using SEM-EDX. Additionally, the fabricated perovskite film was exposed to argon atmosphere at temperatures ranging from room temperature to high temperatures (25°C, 80°C, or 90°C) for 100 hours. Afterwards, the crystal structure of the perovskite particles contained in the exposed perovskite film was observed using XRD. The XRD area ratio (PbI2 / PVK) of the (001) peak of PbI2 and the (110) peak of the α phase of PVK was calculated.

[0087] [II-4: Evaluation Results]

[0088] The relationship between the number of carbon atoms of the side-chain alkyl groups in the additives used to make perovskite films and their melting point is shown in the figure. Figure 2 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 shown in formula (I), the side-chain alkyl group is composed of H3C-(CH2). n - indicates that the side-chain alkyl group has n+1 carbon atoms.

[0089] like Figure 2As shown, additives with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) exhibit extremely low melting points. When the number of carbon atoms in the side-chain alkyl group is in the range of 2 to 8 (i.e., n = 1 to 7), the melting point decreases with increasing carbon number of the side-chain alkyl group. This is presumably due to the asymmetry of the cation and the flexibility of the side-chain alkyl group in the additive represented by formula (I). On the other hand, when the number of carbon atoms in the side-chain alkyl group is in the range of 8 to 16 (i.e., n = 7 to 15), the melting point increases with increasing carbon number of the side-chain alkyl group. This is presumably because the interaction of the side-chain alkyl groups between the additive molecules represented by multiple formulas (I) (stabilization of the stereostructure) forms a crystal structure with parallel alignment of the side-chain alkyl groups.

[0090] The relationship between the number of carbon atoms of the side-chain alkyl groups in the additives used to make perovskite films and the average particle size of the perovskite particles contained in the produced perovskite films is shown in the figure. Figure 3 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 (μ) of the perovskite particles.

[0091] like Figure 3 As shown, the perovskite film made using an additive with 8 carbon atoms in its side-chain alkyl group (i.e., n = 7) exhibits a maximum average particle size of 1.65 ± 0.604 μm. In contrast, the perovskite film made using an additive with more carbon atoms in its side-chain alkyl group, such as 16 (i.e., n = 15), exhibits an average particle size of 0.817 ± 0.256 μm. Furthermore, the perovskite film made using an additive with 6 carbon atoms in its side-chain alkyl group (i.e., n = 5) as described in Patent Document 1 exhibits an average particle size of 1.29 ± 0.681 μm.

[0092] SEM images of the fabricated perovskite film are shown below. Figure 4 In the figure, A is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms (i.e., n=7) containing side-chain alkyl groups; B is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms (i.e., n=15) containing side-chain alkyl groups; C is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms (i.e., n=3) containing side-chain alkyl groups; D is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms (i.e., n=5) containing side-chain alkyl groups; and E is a SEM image of a control perovskite film prepared using a precursor solution without additives.

[0093] like Figure 4As shown, perovskite films prepared using precursor solutions containing additives with 7 or more carbon atoms (i.e., n is 6 or more) containing side-chain alkyl groups exhibit perovskite particles with uniform particle size (panels A and B). In contrast, perovskite films prepared using precursor solutions containing additives with fewer than 7 carbon atoms (i.e., n is less than 6) containing side-chain alkyl groups exhibit perovskite particles with a larger average particle size than those in the control perovskite film (panel E), but their average particle size is slightly smaller and non-uniform (panels C and D).

[0094] SEM images of the perovskite film treated with high-temperature experiments are shown below. Figure 5 In the figure, A is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 8 carbon atoms (i.e., n=7) containing a side-chain alkyl group; B is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 16 carbon atoms (i.e., n=15) containing a side-chain alkyl group; C is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 4 carbon atoms (i.e., n=3) containing a side-chain alkyl group; and D is a SEM image of a perovskite film prepared using a precursor solution containing an additive with 6 carbon atoms (i.e., n=5) containing a side-chain alkyl group.

[0095] like Figure 5 As shown, in perovskite films prepared using precursor solutions containing additives with 7 or more carbon atoms (i.e., n is 6 or more) containing side-chain alkyl groups, no significant changes occurred even after high-temperature testing (panels A and B). In contrast, in perovskite films prepared using precursor solutions containing additives with fewer than 7 carbon atoms (i.e., n is less than 6) containing side-chain alkyl groups, the perovskite particles thermally decomposed after high-temperature testing, resulting in pores (panels C and D). It is speculated that this is because the perovskite particles in the initial stage of fabrication have an uneven particle size, thus leading to uneven thermal conduction between particles.

[0096] The orientation indices of each facet in the XRD calculated using the Wilson method are shown below. Figure 6 In the figure, the horizontal axis represents the surface index, and the vertical axis represents the orientation index of each surface index.

[0097] like Figure 6 As shown, in the perovskite film made using an additive with 8 carbon atoms in the side chain alkyl group (i.e., n is 7), the orientation indices of at least the (100) facet, (002) facet, and (220) facet are 1 or higher in the XRD calculated using the Wilson method.

[0098] Figure 7The figure shows the relationship between the number of carbon atoms in the side-chain alkyl groups in the additives used in the fabrication of the perovskite film and the XRD area ratio (PbI2 / PVK) of the (001) peak of PbI2 and the (110) peak of the α phase of PVK contained in the fabricated perovskite film. In the figure, the horizontal axis represents the number of carbon atoms in the side-chain alkyl groups, and the vertical axis represents the XRD area ratio (PbI2 / PVK).

[0099] like Figure 7 As shown, in perovskite films made using additives with 3 or more carbon atoms in the side-chain alkyl group (i.e., n is 2 or more), the XRD area ratio (PbI2 / PVK) is 0.

[0100] The relationship between the heat treatment temperature of perovskite films prepared using additive-free (control) or additives with 8 carbon atoms (i.e., n=7) of side-chain alkyl groups and the XRD area ratio (PbI2 / PVK) of the (001) peak of PbI2 and the (110) peak of the α phase of PVK in the treated perovskite film is shown in the figure. Figure 8 In the figure, the horizontal axis represents the temperature (°C) of the heat treatment test, and the vertical axis represents the XRD area ratio (PbI2 / PVK).

[0101] like Figure 8 As shown, in the control perovskite film prepared without additives, the XRD area ratio (PbI2 / PVK) of the perovskite film treated at 25°C was 0.4, and the XRD area ratio (PbI2 / PVK) increased with increasing treatment temperature. In contrast, in the perovskite film prepared using additives with 8 carbon atoms in the side-chain alkyl group (i.e., n=7), the XRD area ratio (PbI2 / PVK) was 0 regardless of any treatment temperature of 25, 80, or 90°C.

[0102] It is known that perovskite solar cells with perovskite compounds containing an α-phase perovskite film as the photoelectric conversion layer have high conversion efficiency. In such perovskite solar cells, the perovskite compounds contained in the perovskite film decompose upon heating, humidification, and / or light irradiation, generating PbI2. 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 is correlated with the amount of PbI2 generated by the decomposition of the perovskite compounds. Thus, it can not only serve as an indicator of the degradation of the perovskite film or perovskite compounds used in perovskite solar cells, but also as a performance indicator of the perovskite solar cells. For example, if the XRD area ratio (PbI2 / PVK) of 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 judged to have a small degree of degradation. Furthermore, perovskite solar cells with this perovskite film as the photoelectric conversion layer can be considered to have good performance.

[0103] The grain size of perovskite crystals affects the power generation efficiency of perovskite solar cells. This is because lattice defects at the interfaces (grain boundaries) of multiple perovskite crystals act as traps for electrons and / or holes, leading to recombination and reduced power generation efficiency. Therefore, increasing the grain size of perovskite crystal particles reduces the specific surface area of ​​the crystal particles, thereby reducing the area of ​​grain boundaries and ultimately improving the power generation efficiency of perovskite solar cells. Furthermore, if the grain size of perovskite crystal particles exceeds 1 μm, grain boundaries are generated only in the thickness direction of the perovskite film and not in the planar direction. Therefore, the presence of grain boundary defects reduces the impact of blocking charge movement. Thus, increasing the grain size of perovskite crystal particles is effective in improving the power generation efficiency of perovskite solar cells. Additionally, to improve the durability of perovskite solar cells, it is effective to improve the stability of the crystal particles in a way that the grain size and / or crystal structure of the perovskite crystal particles remain substantially unchanged under high-temperature testing conditions.

[0104] Typically, crystallization consists of several processes: nucleation, grain growth, aggregation, and crystallization. Among these, nucleation and aggregation (Ostwald ripening) are crucial for controlling crystal grain size. Ostwald ripening refers to the aggregation mechanism where, due to the varying vapor pressures around tiny particles depending on their radius, larger nuclei absorb smaller nuclei for growth, continuing until the smaller nuclei disappear. In the preparation of perovskite crystals using poor solvent methods, the slow evaporation rate of the poor solvent makes Ostwald ripening more likely during annealing. In the initial state of Ostwald ripening, a large number of tiny particles (nuclei) exist; therefore, controlling nucleation in perovskite crystals by adding an additive as an ionic liquid is important.

[0105] In the additives shown in formula (I), typically, the polar portion (methylimidazole) The ring and chloride ion) and the nonpolar moiety (side chain alkyl) each form a domain structure. Furthermore, this domain structure forms the intermolecular network of the additive shown in formula (I). Figure 2 As shown, additives with 8 carbon atoms in the side-chain alkyl group (i.e., n = 7) exhibit extremely low melting points. Additionally, as... Figure 3 As shown, the perovskite film prepared using an additive with 8 carbon atoms in its side-chain alkyl group (i.e., n = 7) exhibits a maximum average particle size of 1.65 ± 0.604 μm. These results suggest that in the preparation of perovskite crystals using an additive with 8 carbon atoms in its side-chain alkyl group (i.e., n = 7), the additive is atomically close to the precursor material, enabling the formation of numerous uniform nuclei and promoting Ostwald ripening. It is speculated that in such a reaction system, the domain structure of the additive is electrically / sterically stabilized by forming an intermolecular network, resulting in a greater number of large-particle-size perovskite crystals with high symmetry. Furthermore, it is speculated that perovskite solar cells using perovskite films containing such large-particle-size perovskite crystals as photoelectric conversion layers exhibit high durability.

[0106] It should be noted that the present invention is not limited to the embodiments described above, but includes various modifications. For example, the embodiments described above are provided for the purpose of readily understanding and illustrating the present invention, and are not limited to having all the structures described. In addition, for a part of the configuration of each embodiment, other configurations can be added, deleted, and / or replaced.

Claims

1. A method for manufacturing a perovskite solar cell, comprising: In the coating process, a precursor solution containing a precursor material for generating perovskite-type crystals, an additive shown in formula (I), and a solvent is coated onto the carrier transport layer. as well as The heating process involves heating the precursor layer obtained in the coating process to form a photoelectric conversion layer containing a perovskite film. In the formula, n is an integer greater than or equal to 6.

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

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

4. The method according to claim 1, wherein, The precursors are halogenated organic amines and halogenated amidines. A mixture of metal halides.

5. The method according to claim 4, wherein, The precursors are methylammonium iodide and formamidinium iodide. A mixture of cesium iodide and lead iodide.

6. A perovskite solar cell, comprising at least: a photoelectric conversion layer including a perovskite film containing perovskite crystals, and two carrier transport layers disposed on both sides of the photoelectric conversion layer. In the perovskite film contained in the photoelectric conversion layer, the orientation indices of at least the (100) plane, (002) plane, and (220) plane are greater than 1 in the X-ray diffraction (XRD) calculated using the Wilson method.

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