Perovskite film, thin film solar cell, method for producing perovskite film, and method for producing thin film solar cell

Abstract

When viewed in a plan view from the lamination direction, this perovskite film has a plurality of grains, and the most frequent grain size of the grains is 1 μm or more.

Description

Perovskite film, thin-film solar cell, method for manufacturing perovskite film, and method for manufacturing thin-film solar cell

[0001] This disclosure relates to a perovskite film, a thin-film solar cell, a method for manufacturing a perovskite film, and a method for manufacturing a thin-film solar cell. This application claims priority to Japanese Patent Application No. 2024-008315, filed on January 23, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, thin-film solar cells using thin films with a perovskite structure have been developed. The perovskite structure has the general formula ABX ３ It is a cubic crystal structure represented by the following formula. Different atoms or molecules are arranged at the vertices of the cube (A site), the center of each face of the cube (B site), and the center of the cube (X site). For example, CH ３ NH ３ ＋ , C.H. ５ N ２ ＋ Organic materials such as the above are used.

[0003] Perovskite films are vulnerable to water. Therefore, they must be manufactured in an inert gas atmosphere or a dry atmosphere with a relative humidity of 20% or less, which increases manufacturing costs. Furthermore, perovskite films have low durability in a humid atmosphere, and their performance deteriorates significantly within about a month.

[0004] Patent Document 1 discloses that an ionic liquid is added to a precursor solution of a perovskite film and the perovskite film is formed by spin coating. The perovskite film in Patent Document 1 has a film structure in which nano-sized particles are aggregated.

[0005] Patent No. 6501303

[0006] Perovskite films are expected to be applied to various elements such as photoelectric conversion elements, piezoelectric conversion elements, and thermoelectric conversion elements, and further performance improvements and reductions in production costs are required. There is also a need for a method for producing perovskite films in normal air, rather than in the restricted environment of an inert gas. For example, as described in Patent Document 1, adding an ionic liquid to a precursor solution makes it possible to produce perovskite films in air. However, the production method disclosed in Patent Document 1 is not suitable for mass production, and further improvements in the durability of the produced perovskite films are also required.

[0007] The present disclosure has been made in view of the above problems, and aims to provide a highly durable perovskite film, a thin-film solar cell, and methods for manufacturing the same.

[0008] To solve the above problems, the present disclosure provides the following means.

[0009] The perovskite film according to the first aspect has a plurality of grains when viewed in a plan view from the stacking direction, and the most frequent grain size of the plurality of grains is 1 μm or more.

[0010] The perovskite film and thin-film solar cell according to this embodiment have high durability. The method for manufacturing a perovskite film and the method for manufacturing a thin-film solar cell according to this embodiment make it possible to manufacture a perovskite film or a thin-film solar cell at low cost.

[0011] FIG. 1 is a scanning electron microscope (SEM) image of a perovskite film according to the present embodiment; FIG. 2 is a conceptual diagram of a characteristic portion of the perovskite film according to the present embodiment; FIG. 3 shows water contact angles of a perovskite film according to the present embodiment and a perovskite film having no hydrophobic functional groups; FIG. 4 is a flow diagram of a method for manufacturing a perovskite film according to the present embodiment; FIG. 5 is a diagram for explaining a mixed solution preparation step in the method for manufacturing a perovskite film according to the present embodiment; FIG. 6 is a diagram for explaining an underlayer preparation step in the method for manufacturing a perovskite film according to the present embodiment; FIG. 7 is a diagram for explaining a coating step in the method for manufacturing a perovskite film according to the present embodiment; FIG. 8 is a diagram for explaining a homogenization step in the method for manufacturing a perovskite film according to the present embodiment; FIG. 9 is a comparative image of a perovskite film that has undergone a homogenization step and a perovskite film that has not undergone a homogenization step; FIG. 10 is a diagram for explaining an annealing step in the method for manufacturing a perovskite film according to the present embodiment; 1 is a scanning electron microscope (SEM) image of a perovskite film according to a second comparative example. 2 is a scanning electron microscope (SEM) image of a perovskite film according to a third comparative example. 3 is a schematic diagram of a solar cell according to the present embodiment. 4 is a schematic diagram for explaining the characteristics of a solar cell according to the present embodiment. 5 shows X-ray diffraction images of the first example and the second comparative example. 6 shows the characteristics of thin-film solar cells using the perovskite films of the first example and the second comparative example. 7 shows the results of measuring the durability of thin-film solar cells using the perovskite films of the first example, the first comparative example, the second comparative example, and the third comparative example. 8 shows the output characteristics (PCE) of the thin-film solar cells of the first example, the third to sixth examples, and the second comparative example.

[0012] The present embodiment will be described in detail below. The following description is an example of the present invention, and the present invention is not limited thereto, and can be implemented with appropriate modifications within the scope of the present invention.

[0013] Figure 1 is a scanning electron microscope (SEM) image of a perovskite film 10 according to this embodiment. When viewed in plan from the stacking direction, the perovskite film 10 according to this embodiment has a plurality of grains. The most frequent grain size of the grains is 1 µm or more, preferably 2 µm or more, more preferably 10 µm or more, even more preferably 30 µm or more, and particularly preferably 50 µm or more. The most frequent grain size of the perovskite film shown in Figure 1 is 70 µm.

[0014] The most frequent grain size can be determined by the following procedure. First, a scanning electron microscope (SEM) is used to capture images at three locations at 800x magnification. Then, ten grains are randomly extracted from each of the captured images. The major axis diameter of each extracted grain is measured. The measured major axis lengths of the grains are plotted as a histogram, and the most frequent value is defined as the most frequent grain size. The histogram used to determine the most frequent grain size is graphed with the major axis diameter of the grain on the horizontal axis and the frequency on the vertical axis, and the horizontal axis is divided into intervals of 1 / 10 of the average grain size to set the most frequent value.

[0015] 2 is a diagram schematically showing characteristic portions of the perovskite film 10 according to this embodiment. The perovskite film 10 may contain hydrophobic functional groups H. The hydrophobic functional groups H are present, for example, at the grain boundaries of at least a plurality of grains G. The hydrophobic functional groups H may also be attached to the entire surface of the perovskite film 10.

[0016] The presence of the hydrophobic functional group H can be confirmed by water contact angle measurement. In water contact angle measurement, a drop of water is dropped on the film surface, and the contact angle between the drop of water and the film is measured. When the hydrophobic functional group H is present on the surface of the perovskite film 10, the water contact angle will be 70° or greater. It is more preferable that the water contact angle of the perovskite film 10 be 75° or greater.

[0017] Figure 3 shows the water contact angles of the perovskite film according to this embodiment and a perovskite film without hydrophobic functional groups. The left diagram in Figure 3 shows the results of measuring the water contact angle of the perovskite film according to this embodiment, in which an ionic liquid was used when the perovskite film was prepared. The right diagram in Figure 3 shows the results of measuring the water contact angle of the perovskite film according to a comparative example, in which an ionic liquid was not used when the perovskite film was prepared. As shown in Figure 3, the water contact angle of the perovskite film 10 according to this embodiment, which has hydrophobic functional groups H, exceeds 70°, whereas the water contact angle of the perovskite film 10 according to the comparative example, which does not have hydrophobic functional groups H, is approximately 50°.

[0018] The hydrophobic functional group H may be a hydrophobic group derived from a surfactant or a hydrophobic group derived from an ionic liquid. For example, the ionic liquid bonds with the perovskite via an N-H bond. When the ionic liquid bonds with the perovskite film, the hydrophobic groups of the ionic liquid are exposed on the surface of the perovskite film 10.

[0019] Furthermore, the perovskite film 10 according to this embodiment has few holes that can be confirmed when viewed in plan from the stacking direction. Holes are confirmed as black dots in a scanning electron microscope (SEM) image. The average density of holes in the perovskite film 10 according to this embodiment is, for example, 0.2 holes / μm ２ or less, and ２ Preferably, the number is 0.5 or less per μm. ２ More preferably, it is:

[0020] The average hole density can be determined by the following procedure. First, a scanning electron microscope (SEM) is used to take images of three locations at a magnification of 10,000 times. Then, the number of holes in each image is confirmed, and the hole density in each image is determined by dividing the number of holes by the area of ​​the image. The average hole density can be obtained by averaging the hole densities determined in each image.

[0021] Next, a method for manufacturing the perovskite film 10 according to this embodiment will be described. Fig. 4 is a flow diagram of the method for manufacturing the perovskite film according to this embodiment. The method for manufacturing the perovskite film according to this embodiment includes a mixed solution preparation step S1, a base layer preparation step S2, a coating step S3, a homogenization step S4, and an annealing step S5.

[0022] 5 is a diagram illustrating the mixed solution preparation step S1 in the method for producing a perovskite film according to this embodiment. In the mixed solution preparation step S1, an ionic liquid 2 is added to a perovskite precursor solution 1.

[0023] The perovskite precursor solution 1 contains a precursor material for forming a perovskite crystal. The perovskite precursor solution 1 contains, for example, a halogenated alkylamine and a metal halide as precursor materials. The halogenated alkylamine is, for example, CH ３ NH ３ I, CH ３ NH ３ Br, CH ４ N ２ HI. The metal halide is, for example, PbI ２ , PbBr ２ is.

[0024] The solvent constituting the perovskite precursor solution 1 is, for example, an amide-based solvent, butyrolactone, or dimethyl sulfoxide (DMSO). Examples of the amide-based solvent include dimethylformamide (DMF), diethylformamide (DEF), diethylacetamide (DMAC), N-methylpyrrolidone (MPD), tetramethylurea (TMU), and hexamethylphosphoric triamide (HMPA).

[0025] Ionic liquid 2 is a salt obtained by combining a cation and anion and remains liquid even at temperatures below 100°C. Because ionic liquids are liquids composed only of ions, they exhibit strong electrostatic interactions and are characterized by being nonvolatile and nonflammable. Examples of ionic liquid 2 include imidazolium salts, pyridinium salts, ammonium salts, pyrrolidinium salts, phosphonium salts, and sulfonium salts. Examples of imidazolium cations that form imidazolium salts include 1-hexyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, and 1-dodecyl-3-methylimidazolium. Examples of salts include halides, tetrafluoroborates, hexafluorophosphates, acetates, hydrogen sulfates, alkyl sulfates, tosylates, and methanesulfonates. The ionic liquid is, for example, 1-hexyl-3-methylimidazolium chloride (HMImCl) or 1-hexyl-3-methylimidazolium iodide (HMImI).

[0026] A mixed solution is obtained by adding ionic liquid 2 to perovskite precursor solution 1. The mass ratio of ionic liquid 2 in the mixed solution is preferably 0.17 wt% or more and 0.83 wt% or less, more preferably 0.33 wt% or more and 0.66 wt% or less, and even more preferably 0.42 wt% or more and 0.58 wt% or less. When the mass ratio of ionic liquid 2 in the mixed solution is within the above range, the crystals are prevented from becoming finer when the perovskite structure crystallizes, and a perovskite film with a large grain size can be obtained. For example, if the concentration of ionic liquid 2 in the mixed solution is high, the ionic liquid may cause the crystal nuclei to form micelles. In contrast, if the concentration of ionic liquid 2 in the mixed solution is sufficiently low, the risk of the crystal growth of the fine particles being inhibited by micellization is reduced.

[0027] The mixed solution may be prepared in any number of stages. For example, a solution containing an ionic liquid may be prepared as a first solution, and a solution containing no ionic liquid may be prepared as a second solution, and the two solutions may be mixed to prepare the mixed solution. The first solution may be, for example, CH ３ NH ３ I and PbI ２The first solution is prepared by adding 1-hexyl-3-methylimidazolium chloride (HMImCl) as an ionic liquid to the first solution. The solvent of the first solution is, for example, dimethylformamide. The second solution is prepared by adding, for example, CH ４ N ２ HI, PbI ２、 PbBr ２ The mass ratio of the ionic liquid in the first solution is, for example, preferably 1 wt % or more and 5 wt % or less, more preferably 2 wt % or more and 4 wt % or less, and even more preferably 2.5 wt % or more and 3.5 wt % or less.

[0028] Alternatively, instead of the ionic liquid, any additive having a hydrophobic functional group may be used, such as phenethylammonium chloride (PEACl), potassium thiocyanate (KSCN), guanabenzene acetate, L-α-phosphatidylcholine, or tetradecyldimethyl(3-sulfopropyl)ammonium hydroxide inner salt (TAH).

[0029] 6 is a schematic diagram illustrating the underlayer preparation step S2 of the method for manufacturing a perovskite film according to this embodiment. In the underlayer preparation step S2, a substrate 3 having an underlayer on which a perovskite film will be formed is prepared. The underlayer preparation step S2 is not an essential step and may not be performed. For example, a commercially available substrate may be used as is.

[0030] The substrate 3 having a base layer is, for example, glass on which a transparent conductive film is formed, such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide, fluorine-doped tin oxide (FTO), titanium oxide, or the like.

[0031] First, it is preferable to ultrasonically clean the substrate 3 having the underlayer, using, for example, ultrapure water, acetone, or ethanol.

[0032] Next, the substrate 3 with the underlayer is subjected to plasma treatment. In the plasma treatment, oxygen plasma is irradiated onto the surface of the underlayer of the substrate 3. By surface treating the underlayer, impurities adhering to the surface of the underlayer are removed and the activity of the surface of the underlayer is increased. By plasma treating the surface of the underlayer, the wettability of the mixed solution to the underlayer is improved. The plasma treatment is performed, for example, at room temperature for 20 minutes under conditions of 115 V, 18 W, and a vacuum of 0.1 MPa.

[0033] 7 is a schematic diagram illustrating an example of the coating step S3 in the method for manufacturing a perovskite film according to this embodiment. In the coating step S3, the mixed solution 4 is applied onto the underlayer by a predetermined coating method to form a coating film 8.

[0034] Here, the predetermined coating methods are bar coating, blade coating, slot die coating, spray coating, gravure coating, reverse coating, and comma coating. When the coating film 8 is formed by these predetermined coating methods, the modal grain size of the grains G in the perovskite film 10 increases. The reason for this is not clear, but it is thought that the gradual removal of the solvent promotes the grain growth of the grains G, increasing the size of the grains G. When a spin coating method is used, which forcibly removes the solvent by rotation, the size of the grains G decreases.

[0035] FIG. 7 shows a specific example in which the predetermined coating method is bar coating. First, the mixed solution 4 is dropped onto a dummy substrate 5. The type of dummy substrate 5 is not particularly important. Next, a bar 6 is brought into contact with the mixed solution 4 dropped onto the dummy substrate 5, and the mixed solution 4 is adhered to the surface of the bar 6. Next, the bar 6 is placed on the substrate 3 with an underlayer to be coated. A support 7 may be placed on the side of the substrate 3 with an underlayer to prevent the bar 6 from tilting during bar coating. Next, the bar 6 is translated relative to the substrate 3 with an underlayer. For example, tilting the apparatus causes the bar 6 to roll. Here, the bar 6 is moved by tilting the apparatus, but the bar 6 may also be simply translated. The mixed solution 4 adhering to the bar 6 adheres to the surface of the underlayer, forming a coating film 8.

[0036] 8 is a schematic diagram illustrating the homogenization step S4 in the method for producing a perovskite film according to this embodiment. The homogenization step S4 is not an essential step, but is preferably performed. In the homogenization step S4, the coating film 8 is held for a certain period of time before annealing. Holding for a certain period of time means that heating or the like is not performed while maintaining the relative positional relationship of the coating film 8 with respect to the substrate 3 with the underlayer, and the coating film 8 may move together with the substrate 3 with the underlayer. The homogenization step is preferably performed for 5 minutes or more, and more preferably for 5 to 10 minutes.

[0037] Figure 9 is a comparative image of perovskite films in an example where the homogenization step S4 was performed and an example where it was not performed. In Figure 9, the top two samples are perovskite films that were not subjected to the homogenization step S4, and the bottom two samples are perovskite films that were subjected to the homogenization step S4. The top two samples that were not subjected to the homogenization step S4 are lighter in color and more uneven than the bottom two samples that were subjected to the homogenization step S4. In other words, the top two samples that were not subjected to the homogenization step S4 are of lower quality than the bottom two samples that were subjected to the homogenization step S4.

[0038] 8 , in the homogenization step S4, before the substrate 3 with the coating film 8 is held for a certain period of time, a liquid pool 8a formed in the coating film 8 may be removed. By removing the liquid pool 8a, unevenness in the coating film 8 can be further suppressed.

[0039] 10 is a schematic diagram illustrating the annealing step S5 of the method for manufacturing a perovskite film according to this embodiment. In the annealing step, the coating film 8 is annealed. For example, the substrate 3 with the coating film 8 is heated with a heater 9 to anneal the coating film 8. The annealing temperature is, for example, 100° C. or higher, and the annealing time is, for example, 1 hour or longer. When the coating film 8 is annealed, the solvent is removed from the coating film 8 and the perovskite is crystallized, resulting in a perovskite film 10.

[0040] The perovskite film 10 is formed of a compound represented by the general formula ABX ３It has a cubic crystal structure represented by the following formula: Different atoms or molecules are arranged at the vertices of the cube (A sites), the center of each face of the cube (X sites), and the center of the cube (B site). For example, CH ３ NH ３ , C.H. ５ N ２ Materials such as Pb, Sn, and Ge are used for the B site. Materials such as I, Cl, and Br are used for the X site. The perovskite film 10 is made of, for example, CsFAMA (general formula: Cs ０．０５ (FA ０．８３ MA ０．１７ ) ０．９５ Pb(I ０．８３ Br ０．１７ ) ３ ) perovskite film.

[0041] The mixed solution preparation step S1, underlayer preparation step S2, coating step S3, homogenization step S4, and annealing step S5 can be performed even in an air atmosphere with a humidity of 40% or higher. The perovskite film 10 is vulnerable to moisture. Therefore, the perovskite film 10 is generally prepared in an inert gas atmosphere such as nitrogen or argon. In contrast, in the method for preparing a perovskite film according to this embodiment, the hydrophobicity of the perovskite film is improved by adding ionic liquid 2 to the mixed solution. Furthermore, in the perovskite film prepared by the bar coating method, rapid evaporation of the solvent is suppressed, thereby improving the quality of the prepared perovskite film 10. As a result, the perovskite film 10 can be appropriately prepared even under film-forming conditions such as an air atmosphere with a humidity of 40% or higher.

[0042] The method for manufacturing a perovskite film according to this embodiment is carried out using a coating method such as bar coating, which is easily applicable to a roll-to-roll method. Spin coating can only form perovskite films using a single-wafer method. Compared to the single-wafer spin coating method, the roll-to-roll method makes it easier to fabricate large-area films and has lower process costs.

[0043] The perovskite film 10 according to this embodiment has high durability, which is thought to be because moisture is less likely to penetrate into the perovskite film 10.

[0044] In the perovskite film 10 according to this embodiment, the grains G are large in size and there are few grain boundaries between the grains G.

[0045] 11 is a scanning electron microscope image of the perovskite film according to the first comparative example. The first comparative example differs from the method for manufacturing a perovskite film according to this embodiment in that the coating film 8 is formed by spin coating. The perovskite film according to the first comparative example has a most frequent grain size of 1 μm or less. The perovskite film according to the first comparative example has smaller grain sizes and more grain boundaries than the perovskite film 10 according to this embodiment.

[0046] Moisture (H ２ O) penetrates through the grain boundaries of the grains G that make up the perovskite film 10. In the perovskite film 10 according to this embodiment, the grains G are large in size, and therefore there are few grain boundaries between the grains G, and therefore there are few paths for moisture to penetrate.

[0047] Furthermore, the use of an ionic liquid when producing the perovskite film 10 according to this embodiment is one of the factors that enhance the durability of the perovskite film 10. Figure 12 is a schematic diagram for explaining one of the reasons why the perovskite film 10 according to this embodiment has high durability.

[0048] As shown in Figure 12, when hydrophobic functional groups H are contained in the grain boundaries of at least a plurality of grains G, the hydrophobic functional groups H repel moisture and prevent water from penetrating into the grain boundaries of the grains G. A portion of the ionic liquid forms an N-H bond with the perovskite and functions as the hydrophobic functional group H. The hydrophobic functional group H of the ionic liquid 2 is exposed at least at the grain boundaries of the grains G. The hydrophobic functional group H has low affinity for water and therefore prevents water from penetrating into the grain boundaries of the grains G.

[0049] Fig. 13 is a scanning electron microscope image of a perovskite film according to Comparative Example 2. Fig. 14 is a scanning electron microscope image of a perovskite film according to Comparative Example 3. Comparative Example 2 differs from the perovskite film according to this embodiment in that no ionic liquid was used. Comparative Example 3 differs from the perovskite film according to Comparative Example 1 in that no ionic liquid was used.

[0050] 13 and 14, when an ionic liquid is not used, pinholes are formed in the perovskite film. The pinholes become a path for moisture to penetrate, reducing the durability of the perovskite film. In other words, the use of an ionic liquid in the method for producing the perovskite film 10 according to this embodiment is also a factor in improving the durability of the perovskite film 10.

[0051] As shown in FIGS. 13 and 14, even when no ionic liquid was used, differences in grain size due to differences in coating methods were confirmed.

[0052] The perovskite film according to this embodiment can be applied to various elements such as photoelectric conversion elements, piezoelectric conversion elements, thermoelectric conversion elements, etc. Below, an example of the application of the perovskite film will be described, in which the perovskite film is used in a thin-film solar cell.

[0053] Fig. 15 is a side view of a thin-film solar cell 100 according to this embodiment. The thin-film solar cell 100 includes a substrate 101, an electron transport layer 102, a power generation layer 103, a hole transport layer 104, an electrode layer 105, an electrode layer 106, and an electrode layer 107. The electrode layer 105 is a positive electrode layer, and the electrode layers 106 and 107 are negative electrode layers. In Fig. 15, the electron transport layer 102, the power generation layer 103, and the hole transport layer 104 are stacked in this order on the substrate 101. The positional relationship between the electron transport layer 102 and the hole transport layer 104 may be reversed.

[0054] The substrate 101 is not particularly limited as long as it can support the structure composed of the above layers. The substrate 101 is preferably a transparent conductive substrate with excellent light transmittance, and more preferably has a visible light transmittance of 90% or more. The substrate 101 is also preferably flexible. Examples of materials constituting the substrate 101 include glass and plastic film. Examples of resins that can be used to form the plastic film include polyethylene terephthalate and polyethylene naphthalate.

[0055] The electrode layer 106 is, for example, a transparent electrode. The electrode layer 106 is on the substrate 101. A known electrode layer can be used as the electrode layer 106. The electrode layer 106 is, for example, a conductive transparent oxide film, graphene, carbon nanotubes, or a conductive polymer film. The conductive transparent oxide can be, for example, fluorine-doped tin oxide (FTO), indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide, tin oxide, titanium oxide, or the like.

[0056] The electron transport layer 102 is a layer that collects electrons generated in the power generation layer 103 and efficiently transports them toward the electrode layer 106. Examples of materials that can be used to form the electron transport layer 102 include inorganic materials such as zinc oxide, titanium oxide, tin oxide, niobium oxide, and aluminum oxide, as well as inorganic materials such as PCBM and fullerene C ６０ Examples of n-type semiconductors include organic materials such as:

[0057] The power generation layer 103 is a layer (photoelectric conversion layer) that receives light and generates electricity. The power generation layer 103 is made of a material having a perovskite structure. The perovskite film 10 described above can be used for the power generation layer 103.

[0058] The hole transport layer 104 is a layer that collects holes generated in the power generation layer 103 and efficiently transports them toward the electrode layer 105. Examples of materials that constitute the hole transport layer 104 include inorganic materials such as nickel oxide, copper iodide, copper oxide, and copper sulfide, and p-type semiconductors such as organic materials such as Spiro-OMeTAD, PTAA, and PEDOT:PSS (a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS)).

[0059] The electrode layers 105 and 107 are each made of a conductive material such as a metal, such as gold, silver, or aluminum, or an organic conductive ink, such as PEDOT:PSS.

[0060] The thin-film solar cell 100 according to this embodiment is obtained by sequentially stacking the layers that make up the thin-film solar cell 100 .

[0061] For example, first, a substrate 101 is prepared on which an electrode layer 106 is formed. For example, the electrode layer 106 is made of FTO, and the substrate 101 is made of glass. The substrate 101 with the electrode layer 106 may be purchased commercially.

[0062] Next, the substrate 101 with the electrode layer 106 is subjected to ultrasonic cleaning and plasma treatment, and then the electron transport layer 102 is formed on one surface of the electrode layer 106. The electron transport layer 102 is made of, for example, dense TiO ２ layer and TiO ２ The electron transport layer 102 corresponds to the underlayer in the perovskite film manufacturing method described above.

[0063] Next, the surface of the electron transport layer 102 is subjected to plasma treatment. This plasma treatment corresponds to the plasma treatment applied to the underlayer in the method for manufacturing a perovskite film described above.

[0064] The power generation layer 103 is formed on the plasma-treated surface of the electron transport layer 102 by a predetermined coating method. The predetermined coating method is the coating method used in the above-mentioned method for manufacturing a perovskite film. The predetermined coating method is, for example, a bar coating method. The power generation layer 103 is a perovskite film, and is formed according to the above-mentioned method for manufacturing a perovskite film.

[0065] The hole transport layer 104 is formed on one surface of the power generation layer 103. For example, the hole transport layer 104 is formed by spin coating Spiro-OMeTAD.

[0066] Next, portions of the electron transport layer 102, the power generation layer 103, and the hole transport layer 104 are cut out, and the electrode layers 105 and 107 are formed thereon. The electrode layers 105 and 107 are made of, for example, gold and can be formed by vapor deposition. By this procedure, the thin-film solar cell according to this embodiment can be manufactured.

[0067] The thin-film solar cell according to this embodiment has excellent output characteristics and durability. The reason why the thin-film solar cell according to this embodiment has excellent durability is because the perovskite film constituting the power generation layer 103 has high durability, as described above.

[0068] The reason why the thin-film solar cell according to this embodiment has excellent output characteristics is believed to be because the grains of the power generation layer 103 are large.

[0069] FIG. 16 is a schematic diagram illustrating the characteristics of a thin-film solar cell according to this embodiment. FIG. 16(a) shows the configuration of a thin-film solar cell of a first comparative example, which is a thin-film solar cell in which the power generation layer 103 is fabricated by spin coating. FIG. 16(b) shows the configuration of a thin-film solar cell according to this embodiment, which is a thin-film solar cell in which the power generation layer 103 is fabricated by bar coating. The crystal grain size of the power generation layer 103 of this embodiment (FIG. 16(b)) is larger than the crystal grain size of the power generation layer 103 fabricated by spin coating (FIG. 16(a)).

[0070] Electrons E and holes H generated in the power generation layer 103 by irradiation with sunlight L or the like flow toward the electrode layer 106 and the electrode layer 105, respectively, but some of them are trapped at the crystal grain boundaries 103C present in the flow path. The trapped electrons E and holes H recombine, reducing the number of electrons E reaching the electrode layer 106 and the number of holes H reaching the electrode layer 105, resulting in a corresponding loss of output current. In the power generation layer 103 of this embodiment shown in FIG. 16(b), the grain size of the crystal grains is large, and the distribution density (volume density) of the crystal grain boundaries 103C is low. Therefore, in the power generation layer 103 of this embodiment, fewer carriers are trapped at the crystal grain boundaries 103C and recombine. The more carriers that reach the electrodes without recombining, the greater the output current and the improved power conversion efficiency (PCE) of the thin-film solar cell.

[0071] Although the preferred embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure as set forth in the claims.

[0072] First Example In the first example, a thin-film solar cell was fabricated having the following configurations as shown in FIG. 15: Substrate 101: Glass, Electrode layer 106: FTO, Electron transport layer 102: TiO ２ Power generation layer 103: Cs ０．０５ (FA ０．８３ MA ０．１７ )０．９５ Pb(I ０．８３ Br ０．１７ ) ３ Hole transport layer 104: Spiro-OMeTAD Electrode layers 105 and 107: Gold

[0073] The power generation layer 103 of the first embodiment was fabricated by mixing a first solution containing 3 wt % ionic liquid and a second solution containing no ionic liquid, applying the mixed solution by a bar coating method, and annealing the mixture.

[0074] The ionic liquid was 1-hexyl-3-methylimidazolium chloride (HMImCl). The perovskite precursor contained in the first solution was CH ３ NH ３ I and PbI ２ The solvent was dimethylformamide (DMF). The perovskite precursor contained in the second solution was CH ４ N ２ HI, PbI ２、 PbBr ２ The first solution was 200 μl, and the second solution was 373 μl. The first solution was mixed with the second solution to obtain CsI. ０．０５ (FA ０．８３ MA ０．１７ ) ０．９５ Pb(I ０．８３ Br ０．１７ ) ３ The mass ratio of the ionic liquid in the mixed solution was 0.5 wt %.

[0075] Before applying the mixed solution by the bar coating method, the surface of the electron transport layer 102 was subjected to oxygen plasma treatment. The plasma treatment was performed at room temperature for 20 minutes under conditions of 115 V, 18 W, and a vacuum of 0.1 MPa. After applying the mixed solution by the bar coating method, the solution was left to stand for 5 minutes as a homogenization step. The applied film was annealed at 100°C for 1 hour. The power generation layer 103 was fabricated in an atmosphere with a humidity of 40% or higher.

[0076] Second Example The second example differs from the first example in that the plasma treatment on the surface of the electron transport layer 102 and the standing step during the production of the power generation layer were not performed. The other conditions were the same as those of the first example.

[0077] The above-mentioned Fig. 9 shows the comparison results between Example 1 and Example 2. As shown in Fig. 9, the power generation layer according to Example 1 (the two bottom samples in Fig. 9) was less uneven and more uniform than the power generation layer according to Example 2 (the two top samples in Fig. 9).

[0078] (First Comparative Example) The first comparative example differs from the first example in that the power generation layer 103 was fabricated by a two-step spin coating method. The other conditions were the same as those in the first example, and a thin-film solar cell was fabricated.

[0079] In the first step, a solution containing an ionic liquid added to a perovskite precursor solution was spin-coated. The mass ratio of the ionic liquid was, for example, 1 wt %. Next, in the second step, a solution containing CsFAMA perovskite was spin-coated. The coated layer was then annealed at 100°C for 1 hour.

[0080] Second Comparative Example The second comparative example differs from the first example in that no ionic liquid was used when fabricating the power generation layer 103. The other conditions were the same as those in the first example, and a thin-film solar cell was fabricated.

[0081] (Third Comparative Example) The third comparative example differs from the first comparative example in that no ionic liquid was used when fabricating the power generation layer 103. The other conditions were the same as those of the first comparative example, and a thin-film solar cell was fabricated.

[0082] SEM images of the surfaces of the power generation layers of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were observed. The power generation layer of Example 1 corresponds to FIG. 1 . The power generation layer of Comparative Example 1 corresponds to FIG. 11 . The power generation layer of Comparative Example 2 corresponds to FIG. 13 . The power generation layer of Comparative Example 3 corresponds to FIG. 14 .

[0083] In the second and third comparative examples, which did not use an ionic liquid, pinholes were formed in the power generation layer 103. Furthermore, the grain size of the power generation layer 103 of the first example and second comparative example, which was produced by the bar coating method, was larger than the grain size of the power generation layer 103 of the first and third comparative examples, which was produced by the spin coating method.

[0084] FIG. 17 shows the results of X-ray diffraction (XRD) measurements of the power generation layers of the first example and the second comparative example. In FIG. 17, "w / IL" indicates that an ionic liquid was used, and corresponds to the results of the first example. In FIG. 17, "w / o IL" indicates that an ionic liquid was not used, and corresponds to the results of the second comparative example. As shown in FIG. 17, the second comparative example, which did not use an ionic liquid, had a PbI peak near 2θ = 13°. ２ A peak due to PbI was confirmed. ２ is a decomposition product of perovskite. In other words, it is clear that the film quality of the power generation layer according to the first example is superior to the film quality of the power generation layer according to the second comparative example.

[0085] FIG. 18 shows the characteristics of the thin-film solar cells of the first example and the second comparative example. In FIG. 18, "w / IL" indicates that an ionic liquid was used, and corresponds to the results of the first example. In FIG. 18, "w / o IL" indicates that an ionic liquid was not used, and corresponds to the results of the second comparative example. As shown in FIG. 18, the output characteristics (PCE) of the thin-film solar cell of the first example were superior to those of the second comparative example.

[0086] FIG. 19 shows the results of measuring the durability of thin-film solar cells using the perovskite films of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. In FIG. 19, "Bar coat w / IL" indicates that the power-generating layer was formed by the bar coating method using an ionic liquid, and corresponds to the results of Example 1. "Bar coat w / o IL" indicates that the power-generating layer was formed by the bar coating method without using an ionic liquid, and corresponds to the results of Comparative Example 2. "Spin coat w / IL" indicates that the power-generating layer was formed by the spin coating method using an ionic liquid, and corresponds to the results of Comparative Example 1. "Spin coat w / o IL" indicates that the power-generating layer was formed by the spin coating method without using an ionic liquid, and corresponds to the results of Comparative Example 3. The horizontal axis of FIG. 19 indicates the operating time of the thin-film solar cell, and the vertical axis of FIG. 19 indicates the change in PCE when the PCE of the initial thin-film solar cell is normalized to 1. In this durability test, the PCE was determined by leaving the unsealed element in a dark atmosphere with a relative humidity (RH) of 40% to 70%, and measuring the IV under sunlight irradiation approximately every week.

[0087] As shown in Figure 19, the thin-film solar cells according to Example 1 and Comparative Example 2, which were fabricated using the bar coating method, had better durability than the thin-film solar cells according to Comparative Example 1 and Comparative Example 3, which were fabricated using the spin coating method. This is thought to be because the use of the bar coating method increased the grain size of the power generation layer, reducing the gaps between the grains through which water could penetrate. Furthermore, Example 1, which contained an ionic liquid, had better solar cell durability than Comparative Example 2, which did not contain an ionic liquid. This is thought to be because the inclusion of an ionic liquid made it less likely for pinholes to form in the power generation layer, and the hydrophobic groups of the ionic liquid prevented water from penetrating.

[0088] (Examples 3 to 6) Examples 3 to 6 differ from Example 1 in that the concentration of the ionic liquid was changed when forming the power generation layer. Other conditions were the same as in Example 1, and thin-film solar cells were fabricated using the same procedures. In each of Examples 3 to 6, the mass ratio of the ionic liquid in the first solution and the mass ratio of the ionic liquid in the mixed solution are as follows. For comparison, the mass ratios of the ionic liquid in Comparative Example 2 and Example 1 are also shown below.

[0089] Second Comparative Example Mass ratio of ionic liquid in first solution: 0 wt% Mass ratio of ionic liquid in mixed solution: 0 wt%

[0090] Third Example Mass ratio of ionic liquid in first solution: 1 wt% Mass ratio of ionic liquid in mixed solution: 0.17 wt%

[0091] First Example: Mass ratio of ionic liquid in first solution: 3 wt% Mass ratio of ionic liquid in mixed solution: 0.5 wt%

[0092] Fourth Example Mass ratio of ionic liquid in first solution: 5 wt% Mass ratio of ionic liquid in mixed solution: 0.83 wt%

[0093] Fifth Example Mass ratio of ionic liquid in first solution: 7 wt% Mass ratio of ionic liquid in mixed solution: 1.17 wt%

[0094] Sixth Example Mass ratio of ionic liquid in first solution: 10 wt% Mass ratio of ionic liquid in mixed solution: 1.66 wt%

[0095] 20 shows the power output characteristics (PCE) of the thin-film solar cells of the first example, the third to sixth examples, and the second comparative example. The specific values ​​of PCE in each example and comparative example are as follows: Second comparative example: 12.59% Third example: 12.67% First example: 15.28% Fourth example: 13.18% Fifth example: 11.27% Sixth example: 10.64%

[0096] As shown in Figure 19, it was confirmed that the output characteristics of the thin-film solar cell were most improved when the mass ratio of the ionic liquid in the first solution was 3 wt% (the mass ratio of the ionic liquid in the mixed solution was 0.5 wt%).

[0097] REFERENCE SIGNS LIST 1 Perovskite precursor solution 2 Ionic liquid 3 Substrate 4 Mixed solution 5 Dummy substrate 6 Bar 7 Support 8 Coating film 9 Heater 10 Perovskite film 100 Thin-film solar cell 101 Substrate 102 Electron transport layer 103 Power generation layer 103C Grain boundary 104 Hole transport layer 105, 106, 107 Electrode layer G Grain H Hydrophobic functional group S1 Mixed solution preparation step S2 Underlayer preparation step S3 Coating step S4 Homogenization step S5 Annealing step

Claims

1. A perovskite film having a plurality of grains when viewed in plan view from the stacking direction, wherein a most frequent grain size of the plurality of grains is 1 μm or more.

2. The perovskite film according to claim 1, having a hydrophobic functional group, wherein the hydrophobic functional group is at least at grain boundaries of the plurality of grains.

3. The perovskite film according to claim 2, wherein the hydrophobic functional group is a hydrophobic group derived from an ionic liquid.

4. Having holes confirmed when viewed in plan view from the stacking direction, and the average density of the holes being 0.2 holes / μm ２ The perovskite film according to claim 1, which is as follows.

5. A thin-film solar cell including the perovskite film according to claim 1 as a light-emitting layer.

6. A method for manufacturing a perovskite film, comprising: a step of preparing a mixed solution by adding an ionic liquid to a perovskite precursor solution; a step of applying the mixed solution to a base layer by bar coating, blade coating, slot die coating, spray coating, gravure coating, reverse coating, comma coating to form a coating film; and a step of annealing the coating film.

7. The method for manufacturing a perovskite film according to claim 6, wherein the coating film is annealed after 5 minutes or more have elapsed since the coating film was formed.

8. The method for manufacturing a perovskite film according to claim 6, wherein the surface of the base layer is plasma-treated before the coating film is formed.

9. The method for manufacturing a perovskite film according to claim 6, wherein a film-forming atmosphere is air having a humidity of 40% or more.

10. The method for manufacturing a perovskite film according to claim 6, wherein a mass ratio of the ionic liquid in the mixed solution is 0.17 wt% or more and 0.83 wt% or less.

11. A method for manufacturing a thin-film solar cell, comprising forming a light-emitting layer having a perovskite structure using the method for manufacturing a perovskite film according to any one of claims 6.

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