Solar cell

Abstract

A solar cell 10 according to the present disclosure comprises a first electrode 2, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. The photoelectric conversion layer 4 contains a perovskite compound. The hole transport layer 5 includes a supporting salt material and a supporting salt dispersion material. In the solar cell 10, a value obtained by dividing a substance amount of the supporting salt dispersion material by a substance amount of the supporting salt material is greater than 0 and equal to or less than 0.4.

Description

solar cells

[0001] The present disclosure relates to solar cells.

[0002] In recent years, research and development of perovskite solar cells has been progressing, using perovskite crystals represented by the composition formula ABX3 (A is a monovalent cation, B is a divalent cation, and X is a halogen anion) and structures similar thereto (hereinafter referred to as "perovskite compounds") as photoelectric conversion materials. Various efforts have been made to improve the photoelectric conversion efficiency and durability of perovskite solar cells. Generally, perovskite solar cells have a photoelectric conversion layer containing a perovskite compound and a hole transport layer disposed between a first electrode and a second electrode.

[0003] For example, Non-Patent Documents 1 to 5 report on matters that are thought to be related to the photoelectric conversion efficiency and durability of perovskite solar cells.

[0004] Non-Patent Document 1 discloses that a perovskite compound reacts with metallic lithium and decomposes.

[0005] Non-Patent Document 2 reports that in dye-sensitized solar cells and perovskite solar cells, an imidazole-based material, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (hereinafter, sometimes abbreviated as "HMI-TFSI"), is added to the hole transport layer as a p-type dopant.

[0006] Non-Patent Document 3 indicates that the photodegradation of perovskite solar cells is increased by 4-tert-butylpyridine (hereinafter sometimes abbreviated as "tBP"), a supporting salt dispersion material, added to 2,2',7,7'-Tetrakis[N,N-di-p-methoxyphenylamino]-9,9'-spirobifluorene (hereinafter sometimes abbreviated as "Spiro-MeOTAD"), which mainly constitutes the hole transport layer.

[0007] Non-Patent Document 4 reports the results of analyzing, using hard X-ray photoelectron spectroscopy, the changes in the chemical bonding state at the electron transport layer / perovskite layer interface and the perovskite layer / hole transport layer interface before and after light irradiation in a perovskite solar cell containing a halide perovskite compound. The perovskite layer in Non-Patent Document 4 is the photoelectric conversion layer described above. For example, when the halide perovskite contains Pb as a divalent cation, 2+ and the halogen anion is I - When the perovskite solar cell is kept in an open state under light irradiation, zero-valent iodine (I 0 Alternatively, I accumulates near the perovskite layer / hole transport layer interface, while Pb 0 is accumulated at the electron transport layer / perovskite layer interface. Non-Patent Document 4 proposes a model in which iodine accumulates near the perovskite layer / hole transport layer interface, and iodine vacancies accumulate near the electron transport layer / perovskite layer interface.

[0008] Non-Patent Document 5 reports that treating the perovskite layer / hole transport layer interface with the imidazolium-based material 1-hexyl-3-methylimidazolium iodide forms a one-dimensional perovskite compound (HMI) PbI3 that passivates defects on the perovskite layer surface, improving photoelectric conversion efficiency.

[0009] James A. Dawson et al., ACS Energy Letters, 2017, vol. 2, pp. 1818-1824. A. Abate et al., Journal of the American Chemical Society, 2013, vol. 135, no. 36, pp. 13538-13548. Joao P. Bastos et al., Advanced Energy Materials, 2018, vol. 8, p. 1800554. T. Sekimoto et al., 5 others, ACS Applied Energy Materials, 2019, vol. 2, pp. 5039-5049. E. Christopoulos et al., ACS Applied Electronic Materials, 2023, vol. 5, no. 4, pp. 2093-2105.

[0010] An object of the present disclosure is to provide a perovskite solar cell that maintains initial efficiency and has excellent heat resistance.

[0011] The solar cell of the present disclosure comprises a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode, wherein the photoelectric conversion layer contains a perovskite compound, and the hole transport layer contains a supporting salt material and a supporting salt dispersion material, and in the solar cell, a value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not more than 0.4.

[0012] The present disclosure provides a perovskite solar cell that maintains initial efficiency and has excellent heat resistance.

[0013] Fig. 1 is a schematic cross-sectional view showing a first example of a solar cell according to an embodiment. Fig. 2 is a schematic cross-sectional view showing a second example of a solar cell according to an embodiment. Fig. 3 is a schematic cross-sectional view showing a third example of a solar cell according to an embodiment. Fig. 4 is a schematic cross-sectional view showing a fourth example of a solar cell according to an embodiment.

[0014] <Findings that Form the Basis of the Present Disclosure> The hole transport layer provided in a solar cell generally contains a hole transport material and a supporting salt material. For example, lithium bis(trifluoromethanesulfonyl)imide (hereinafter sometimes abbreviated as "Li-TFSI") is often used as the supporting salt material. Li-TFSI functions as a p-type dopant. However, the size of the cation Li ion in Li-TFSI is small, and it easily thermally diffuses through grain boundaries into the perovskite layer, which is the photoelectric conversion layer. If Li-TFSI diffuses into the photoelectric conversion layer, the built-in electric field within the photoelectric conversion layer weakens, resulting in a decrease in photoelectric conversion efficiency. Furthermore, the Li ions that thermally diffuse into the photoelectric conversion layer are converted into metallic lithium with a valence of zero by photogenerated high-energy electrons. Here, as reported in Non-Patent Document 1, perovskite compounds react with metallic lithium and decompose. That is, when the supporting salt material contained in the hole transport layer is thermally diffused into the photoelectric conversion layer, the photoelectric conversion layer is deteriorated, resulting in a decrease in photoelectric conversion efficiency.

[0015] A supporting salt dispersion material is usually added to the hole transport layer for the purpose of uniformly dispersing the supporting salt material in the hole transport layer. When the supporting salt dispersion material coordinates with the cations of the supporting salt material, the anions of the supporting salt material coordinate with the hole transport material, facilitating the doping of holes into the material. This can improve the initial efficiency. Generally, when Li-TFSI is used as the supporting salt material, tBP is widely used as the supporting salt dispersion material. However, degradation of the perovskite compound due to residual supporting salt dispersion material has become a problem.

[0016] Non-Patent Document 3 reports that the addition of tBP to Spiro-MeOTAD, which primarily constitutes the hole transport layer, increases the photodegradation of perovskite solar cells. This is thought to be because tBP dissolves perovskite compounds, increasing defects in the photoelectric conversion layer. As a result, as shown in Non-Patent Document 4, iodine ions are more likely to diffuse within the photoelectric conversion layer, leading to the accumulation of zero-valent iodine near the photoelectric conversion layer / hole transport layer interface, resulting in reduced light durability. Furthermore, the inventors' investigations have found that the increase in defects in the photoelectric conversion layer due to tBP also facilitates the thermal diffusion of Li ions within the hole transport layer into the photoelectric conversion layer. Because tBP easily forms complexes with Li ions, it is likely to remain in the device together with the Li ions. In other words, the inventors' investigations have found that the remaining supporting salt dispersion material (tBP in the above example) is a factor that significantly reduces heat resistance.

[0017] Therefore, in order to increase the initial efficiency of perovskite solar cells, a supporting salt material and a supporting salt dispersion material are necessary as additives to the hole transport layer. However, in order to suppress thermal degradation of perovskite solar cells and improve their heat resistance, it is necessary to reduce the amount of supporting salt dispersion material remaining in the element.

[0018] Based on the above findings, the inventors further conducted research and arrived at the solar cell of the present disclosure. Specifically, the inventors have arrived at a solar cell that has excellent heat resistance while maintaining initial efficiency by selecting an appropriate combination of a supporting salt material and a supporting salt dispersion material such that the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not more than 0.4, in a solar cell that includes a first electrode, a photoelectric conversion layer containing a perovskite compound, a hole transport layer, and a second electrode.

[0019] <Embodiments of the Present Disclosure> A solar cell according to an embodiment of the present disclosure includes a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode. The photoelectric conversion layer contains a perovskite compound. The hole transport layer contains a supporting salt material and a supporting salt dispersion material. In the solar cell according to this embodiment, the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and equal to or less than 0.4.

[0020] By including a supporting salt material and a supporting salt dispersion material in the hole transport layer, the solar cell according to this embodiment can maintain the initial efficiency of conventional solar cells, i.e., can achieve an initial efficiency comparable to or even better than conventional solar cells. Furthermore, in the solar cell according to this embodiment, the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not greater than 0.4. With this configuration, the solar cell according to this embodiment has extremely little supporting salt dispersion material remaining in the solar cell, thereby suppressing a decrease in heat resistance due to the supporting salt dispersion material. As a result, the solar cell according to this embodiment can achieve excellent heat resistance.

[0021] Here, the amount of substance of the supporting salt material is defined by the amount of substance of the anions of the supporting salt material. The amount of substance of the anions of the supporting salt material contained in the solar cell can be quantified, for example, using a liquid chromatograph mass spectrometer (LC-MS). The amount of substance of the supporting salt dispersion material contained in the solar cell can be quantified, for example, using a gas chromatograph mass spectrometer (GC-MS). By creating a calibration curve in advance using standard samples with known concentrations, the concentration can be quantified from the area value of the sample.

[0022] The solar cell according to this embodiment may include, for example, a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode in this order. The solar cell according to this embodiment may further include an electron transport layer between the first electrode and the photoelectric conversion layer.

[0023] In the solar cell according to the present embodiment, the difference in Hansen solubility parameter distance between the cation of the supporting salt material and the supporting salt dispersion material is 10 MPa. 0.5 Hereinafter, the Hansen solubility parameter distance will be referred to as "R a" is written as ". R a is the formula R a = (4 (δ D,2 -δ D,1 ) 2 + (δ P,2 -δ P,1 ) 2 + (δ H,2 -δ H,1 ) 2 ) 0.5 where δ D is the energy due to intermolecular dispersion forces, δ P is the energy due to intermolecular dipole interactions, δ H is the energy due to intermolecular hydrogen bonds, and the subscripts 1 and 2 indicate the difference in materials.

[0024] Generally, R a The difference is 10 MPa 0.5 The compatibility of the materials is high if the R estimated for the cations of the supporting salt material and the supporting salt dispersion material is less than or equal to a The difference is 10 MPa 0.5 When the solubility parameter of each material is less than 1 / 2 of the solubility parameter of the supporting salt dispersion material, it prevents the formation of complexes between the cations and anions of the supporting salt material, promoting p-type doping. This improves the photoelectric conversion efficiency of the solar cell. In addition to being determined directly through experiments, the solubility parameter of each material can also be estimated using calculation software such as "SoluVISION" (manufactured by Material Doors Co., Ltd.), which quantitatively evaluates the affinity of materials.

[0025] The supporting salt material may be an imidazolium-based material. In this specification, an imidazolium-based material that functions as a supporting salt material refers to an imidazolium salt in which the cation of the supporting salt material has an imidazole ring.

[0026] When the cation of the supporting salt material is composed of a cation having an imidazole ring constituting an imidazolium salt, the large size of the imidazolium salt molecule makes it difficult for the supporting salt material to form a coordination complex with the supporting salt dispersion material. Therefore, when the hole transport layer is fabricated, the supporting salt dispersion material that does not form a coordination complex is likely to volatilize, resulting in the supporting salt material being less likely to remain in the solar cell. Furthermore, compared to the size of a typical lithium ion (59 pm for a +1 valent, tetracoordinated lithium ion), the size of the imidazolium salt molecule is more than 10 times larger, making it far larger. Therefore, when the supporting salt material is an imidazolium-based material, the supporting salt material is less likely to pass through the defects introduced by the supporting salt dispersion material, making it less likely to thermally diffuse from the hole transport layer into the photoelectric conversion layer and remaining in the hole transport layer. Therefore, in addition to the supporting salt dispersion material being less likely to remain in the solar cell, degradation of the perovskite compound due to the cations of the supporting salt material is less likely to occur, improving heat resistance. Furthermore, as shown in Non-Patent Document 5, some imidazolium-based materials are known to passivate surface defects in the perovskite layer. Therefore, the cations of the imidazolium-based material in contact with the photoelectric conversion layer can also be expected to have the effect of improving photoelectric conversion efficiency. In order to further obtain the effect of improving photoelectric conversion efficiency by the imidazolium-based material, it is preferable to perform interface treatment on the surface of the photoelectric conversion layer using an imidazolium-based material and then form a hole transport layer using an imidazolium-based material as a supporting electrolyte material, in order to improve heat resistance and further improve photoelectric conversion efficiency.

[0027] The imidazolium-based material used as the supporting electrolyte material may contain a cation having a structure in which a methyl group is bonded to a nitrogen atom constituting an imidazole ring.

[0028] Imidazolium-based materials containing cations with a structure in which a methyl group is bonded to a nitrogen atom constituting an imidazole ring have large molecular sizes. Therefore, imidazolium-based materials with such a structure are less likely to thermally diffuse from the hole transport layer into the photoelectric conversion layer and remain within the hole transport layer. Therefore, degradation of the perovskite compound due to the cations of the supporting salt material is less likely to occur, improving the heat resistance of solar cells.

[0029] The imidazolium-based material used as the supporting salt material has an alkyl chain (CH2) attached to the nitrogen atom that constitutes the imidazole ring. n Here, the alkyl chain (CH2) may contain a cation having a structure in which n In the above formula, n satisfies, for example, 3≦n≦9.

[0030] Alkyl chain (CH2) on the nitrogen atom that constitutes the imidazole ring n In the imidazolium-based material containing a cation having a structure in which a The difference between the two tends to become smaller. Therefore, the supporting salt dispersion material prevents complex formation between the cations and anions of the supporting salt material, promoting p-type doping. This improves the photoelectric conversion efficiency of the solar cell. However, if the alkyl chain of the imidazolium-based material becomes too long (i.e., if n is too large), the heat resistance of the imidazolium-based material decreases. This is because as n increases, the conductivity of the imidazolium-based material decreases, and the electrical resistance of the hole transport layer increases, making the material more susceptible to deterioration near the photoelectric conversion layer / hole transport layer interface. Specifically, as the electrical resistance of the hole transport layer increases, it becomes more difficult for carriers to be extracted from the photoelectric conversion layer to the hole transport layer. Carriers are more likely to be captured by interfacial defects, which are deterioration near the photoelectric conversion layer / hole transport layer interface, and to recombine and disappear. Therefore, to achieve high efficiency and high heat resistance, it is necessary to use an alkyl chain (CH2) bonded to the nitrogen atom constituting the imidazole ring. n There is an optimum range for n. To achieve high efficiency and high heat resistance, n is preferably in the range of 3≦n≦9. The structure of the terminal of the alkyl chain bonded to the nitrogen atom constituting the imidazole ring is not particularly limited, and the alkyl chain terminal may contain a CH group, CH═CH group, OH group, SO group, or the like.

[0031] The imidazolium-based material used as the supporting salt material may contain, as a cationic species, at least one selected from the group consisting of 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-methyl-3-n-octylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, 1-(2-hydroxyethyl)-3-methylimidazolium cation, and 1-methyl-3-(4-sulfobutyl)imidazolium cation. Hereinafter, 1-butyl-3-methylimidazolium may be abbreviated as "BMI," 1-hexyl-3-methylimidazolium as "HMI," 1-decyl-3-methylimidazolium as "DMI," and 1-butyl-2,3-dimethylimidazolium as "BDMI."

[0032] The supporting salt material containing the above cations improves the initial efficiency of the solar cell, and also minimizes the amount of the supporting salt dispersion material remaining in the solar cell, thereby achieving superior heat resistance.

[0033] The imidazolium-based material used as the supporting salt material may contain, as an anion species, at least one selected from the group consisting of a bis(trifluoromethane)sulfonimide anion, a tetrafluoroborate ion, and a hexafluorophosphate ion.

[0034] A supporting salt material containing the above anion can improve the initial efficiency of a solar cell and also minimize the amount of supporting salt dispersion material remaining in the solar cell, thereby achieving superior heat resistance. In order to further improve the initial efficiency and heat resistance, a supporting salt material containing a bis(trifluoromethane)sulfonimide anion is preferred.

[0035] The supporting salt dispersing material may include at least one selected from the group consisting of tBP, pyridine, and n-methylpyrrolidone.

[0036] The supporting salt dispersion material containing the above substance can improve the initial efficiency of the solar cell and can also minimize the amount of supporting salt dispersion material remaining in the solar cell, thereby achieving superior heat resistance. In order to further improve the initial efficiency and heat resistance, the supporting salt dispersion material preferably contains tBP.

[0037] The hole transport layer contains, as a hole transport material, 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter, sometimes abbreviated as "PTAA"), Spiro-MeOTAD, Poly(3-hexylthiophene-2,5-diyl) (hereinafter, sometimes abbreviated as "P3HT"), 4,4',4"-tris[9,9-dimethyl-2-fluorenyl(4-methoxyphenyl )amino]triphenylamine (hereinafter may be abbreviated as "MeO-TFATA"), polyaniline, Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (hereinafter may be abbreviated as "PCPDTBT"), and poly(3,4-ethylenedioxythiophene) (hereinafter may be abbreviated as "PEDOT").

[0038] A hole transport layer containing the above substance as a hole transport material can improve the initial efficiency of a solar cell and can also achieve better heat resistance by minimizing the amount of supporting salt dispersion material remaining in the solar cell. In order to further improve the initial efficiency and heat resistance, it is preferable that PTAA is contained as the hole transport material.

[0039] The solar cell of this embodiment will be described in detail below with reference to the drawings.

[0040] FIG. 1 is a schematic cross-sectional view showing a first example of a solar cell according to the present embodiment.

[0041] 1 includes, in this order, a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. The solar cell 10 does not necessarily have to include the substrate 1. The solar cell 10 does not necessarily have to include the electron transport layer 3.

[0042] When light is irradiated onto the solar cell 10, the photoelectric conversion layer 4 absorbs the light and generates excited electrons and holes. These excited electrons pass through the electron transport layer 3 and move to the first electrode 2. Meanwhile, the holes generated in the photoelectric conversion layer 4 pass through the hole transport layer 5 and move to the second electrode 6. This allows the solar cell 10 to extract current from the first electrode 2, which functions as a negative electrode, and the second electrode 6, which functions as a positive electrode.

[0043] The solar cell 10 can be produced, for example, by the following method.

[0044] First, a first electrode 2 is formed on the surface of the substrate 1 by chemical vapor deposition, sputtering, solution coating, atomic layer deposition, or the like. Next, an electron transport layer 3 is formed on the first electrode 2 by chemical vapor deposition, sputtering, solution coating, atomic layer deposition, or the like. Next, a photoelectric conversion layer 4 is formed on the electron transport layer 3. For example, a perovskite compound may be cut to a predetermined thickness to form the photoelectric conversion layer 4, which is then placed on the electron transport layer 3. Next, a hole transport layer 5 is formed on the photoelectric conversion layer 4 by chemical vapor deposition, sputtering, solution coating, atomic layer deposition, or the like. Next, a second electrode 6 is formed on the hole transport layer 5 by chemical vapor deposition, sputtering, solution coating, atomic layer deposition, or the like. In this manner, a solar cell 10 can be obtained.

[0045] In the solar cell of this embodiment, an electron transport layer may be formed on the first electrode 2 by a solution coating method using a nanoparticle dispersion. In this case, the electron transport layer has a porous structure. Figure 2 is a schematic cross-sectional view showing a second example of a solar cell according to this embodiment. As shown in Figure 2, the solar cell 20 of the second example includes an electron transport layer 21 having a porous structure.

[0046] 3 is a schematic cross-sectional view showing a third example of a solar cell according to an embodiment. As in the solar cell 30 of the third example shown in FIG. 3, an electron transport layer 31 may be formed on the first electrode 2 by chemical vapor deposition, sputtering, solution coating, atomic layer deposition, or the like, and an electron transport layer 32 may be formed on the electron transport layer 31 by solution coating of a nanoparticle dispersion, or the like. In this case, the electron transport layer 32 has a porous structure.

[0047] 4 is a schematic cross-sectional view showing a fourth example of a solar cell according to an embodiment. Like the solar cell 40 of the fourth example, the solar cell according to this embodiment does not need to have an electron transport layer (i.e., electron transport layer 3, or electron transport layers 31 and 32).

[0048] Each component of the solar cell will be specifically described below.

[0049] (Substrate 1) The substrate 1 is an ancillary component. The substrate 1 serves to support each layer of the solar cell. The substrate 1 can be formed from a transparent material. For example, a glass substrate or a plastic substrate can be used as the substrate 1. The plastic substrate can be, for example, a plastic film. Examples of materials that can be used for such plastic films include polyimide, polyethylene terephthalate, polyethylene naphthalate, and cycloolefin polymer. When using a plastic substrate, it is preferable to form a barrier layer with weather resistance. Furthermore, when the second electrode 6 is translucent, the material of the substrate 1 may be a non-translucent material. For example, the material of the substrate 1 can be metal, ceramic, or a resin material with low translucency. If the first electrode 2 has sufficient strength, the first electrode 2 can support each layer, and therefore the substrate 1 is not necessary.

[0050] (First Electrode 2) The first electrode 2 is conductive. When the solar cell does not include an electron transport layer 3, the first electrode 2 is composed of a material that does not form ohmic contact with the photoelectric conversion layer 4. Furthermore, the first electrode 2 has the property of blocking holes from the photoelectric conversion layer 4. The blocking property for holes from the photoelectric conversion layer 4 means that only electrons generated in the photoelectric conversion layer 4 pass through, while holes are blocked. A material having such a property is a material whose Fermi energy is higher than the energy of the top of the valence band of the photoelectric conversion layer 4. The above material may also have a Fermi energy higher than the Fermi energy of the photoelectric conversion layer 4. A specific example of such a material is aluminum. When the solar cell includes an electron transport layer 3 between the first electrode 2 and the photoelectric conversion layer 4, the first electrode 2 does not necessarily have the property of blocking holes migrating from the photoelectric conversion layer 4. The first electrode 2 may be composed of a material that can form ohmic contact with the photoelectric conversion layer 4.

[0051] The first electrode 2 is translucent. For example, it transmits light from the visible region to the near-infrared region. The first electrode 2 can be formed using, for example, a transparent and conductive metal oxide and / or metal nitride. Examples of such materials include titanium oxide doped with at least one element selected from the group consisting of lithium, magnesium, niobium, and fluorine, gallium oxide doped with at least one element selected from the group consisting of tin and silicon, gallium nitride doped with at least one element selected from the group consisting of silicon and oxygen, tin oxide doped with at least one element selected from the group consisting of antimony and fluorine, zinc oxide doped with at least one element selected from the group consisting of boron, aluminum, gallium, and indium, indium-tin composite oxide, and composites thereof.

[0052] The first electrode 2 can also be formed using a non-transparent material and provided with a light-transmitting pattern. Examples of light-transmitting patterns include linear, wavy, lattice, and punched metal patterns in which numerous fine through-holes are regularly or irregularly arranged. When the first electrode 2 has such a pattern, light can transmit through areas where no electrode material is present. Examples of non-transparent electrode materials include platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, and alloys containing any of these. Alternatively, a conductive carbon material can also be used.

[0053] The light transmittance of the first electrode 2 may be, for example, 50% or more, or may be 80% or more. The wavelength of light to be transmitted depends on the absorption wavelength of the photoelectric conversion layer 4. The thickness of the first electrode 2 is, for example, in the range of 1 nm to 1000 nm.

[0054] (Electron Transport Layer 3) The electron transport layer 3 includes a semiconductor. The electron transport layer 3 may be a semiconductor having a band gap of 3.0 eV or more and 3.8 eV or less. By forming the electron transport layer 3 from a semiconductor having a band gap of 3.0 eV or more, visible light and infrared light can be transmitted to the photoelectric conversion layer 4. An example of the semiconductor is an inorganic n-type semiconductor.

[0055] Examples of inorganic n-type semiconductors that can be used include oxides of metal elements, nitrides of metal elements, and perovskite oxides. More specific examples include TiO (rutile type: 3.0 eV, anatase type: 3.2 eV), SnO (3.6 eV), NbO (3.4 eV), GaN (3.4 eV), SrTiO (3.2 eV), and CaTiO (3.4 eV). The values ​​in parentheses indicate typical band gap values.

[0056] The electron transport layer 3 may include multiple layers made of different materials or structures (e.g., electron transport layers 31 and 32). For example, by making the electron transport layer 3 porous or by arranging a porous structure on the photoelectric conversion layer 4 side of the electron transport layer 3, the photoelectric conversion layer 4 can be easily formed. The material of the photoelectric conversion layer 4 penetrates the voids of the porous structure, and the porous structure serves as a scaffold for the photoelectric conversion layer 4. Therefore, the material of the photoelectric conversion layer 4 is less likely to be repelled or aggregate on the surface of the electron transport layer 3 having a porous structure. Therefore, the photoelectric conversion layer 4 can be easily formed as a uniform film. Examples of materials that form the porous structure include porous bodies composed of interconnected insulating or semiconducting particles. Examples of porous body particles having electron transport properties include titanium oxide, tin oxide, and niobium oxide particles. On the other hand, when particles of, for example, aluminum oxide or silicon oxide are used as particles of a porous body with poor electron transport properties, they only function as a scaffold for forming the photoelectric conversion layer 4, and do not provide the effect of the electron transport layer 3. The electron transport layer 3 having a porous structure is formed, for example, by coating a nanomolecular dispersion of the porous body.

[0057] The surface roughness of the electron transport layer 3 having a porous structure may have a surface roughness coefficient, given by effective area / projected area, of 10 or more, or even 100 or more. The projected area is the area of ​​the shadow cast behind an object when illuminated with light from directly in front of it. The effective area is the actual surface area of ​​the object. The effective area can be calculated from the volume determined from the projected area and thickness of the object, and the specific surface area and bulk density of the material constituting the object. The specific surface area is measured, for example, by a nitrogen adsorption method.

[0058] The voids in the electron transport layer 3 having a porous structure are connected from one main surface to the other main surface of the electron transport layer 3. This allows the material of the photoelectric conversion layer 4 to fill the voids in the electron transport layer 3.

[0059] The porous structure of the electron transport layer 3 is expected to cause light scattering and increase the optical path length of light passing through the photoelectric conversion layer 4. It is predicted that the increase in the optical path length will increase the amount of electrons and holes generated in the photoelectric conversion layer 4.

[0060] (Photoelectric Conversion Layer 4) The photoelectric conversion layer 4 contains a perovskite compound represented by the composition formula ABX3. A is a monovalent cation. Examples of the monovalent cation include monovalent cations such as alkali metal cations and organic cations. More specifically, methylammonium cation (MA + or CH3NH3 + ), formamidinium cation (FA + or HC(NH2)2 + ), ethylammonium cation (CH3CH2NH3 + ), guanidinium cation (CH6N3 + ), potassium cation (K + ), cesium cation (Cs + ), and rubidium cation (Rb + ) and the like. B is a divalent lead cation (Pb 2+ ) and tin cations (Sn 2+ ) X is a monovalent anion such as a halogen anion. Each of the A, B, and X sites may be occupied by multiple types of ions.

[0061] The thickness of the photoelectric conversion layer 4 is, for example, 50 nm to 10 μm. The photoelectric conversion layer 4 can be formed by a solution coating method, a printing method, a vapor deposition method, a sputtering method, or the like. The photoelectric conversion layer 4 may also be formed by cutting out a perovskite compound.

[0062] The photoelectric conversion layer 4 may primarily contain a perovskite compound represented by the composition formula ABX3. Here, "the photoelectric conversion layer 4 primarily contains a perovskite compound represented by the composition formula ABX3" means that the photoelectric conversion layer 4 contains 60 mass% or more of the perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 4 may also contain 95 mass% or more of the perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 4 may be made of a perovskite compound represented by the composition formula ABX3. The photoelectric conversion layer 4 may contain a perovskite compound represented by the composition formula ABX3, and may contain defects or impurities.

[0063] The photoelectric conversion layer 4 may further contain a compound other than the perovskite compound represented by the composition formula ABX. Examples of the other compound include a compound having a Ruddlesden-Popper type layered perovskite structure.

[0064] (Hole Transport Layer 5) The hole transport layer 5 contains a hole transport material. The hole transport material is a material that transports holes. The hole transport layer 5 is made of a hole transport material such as an organic material or an inorganic material.

[0065] Representative examples of organic substances used as hole transport materials include PTAA, Spiro-MeOTAD, P3HT, MeO-TFATA, polyaniline, PCPDTBT, and PEDOT. As described above, the hole transport layer 5 may contain at least one selected from the group consisting of PTAA, Spiro-MeOTAD, P3HT, MeO-TFATA, polyaniline, PCPDTBT, and PEDOT as the hole transport material. Examples of main solvents used for these organic substances include toluene, xylene, mesitylene, dichlorotoluene, chlorobenzene, dichlorobenzene, methoxypyridine, acetonitrile, chloroform, dichloromethane, and propylene glycol monomethyl ether acetate.

[0066] The inorganic semiconductor used as the hole transport material is a p-type semiconductor. Examples of inorganic semiconductors include CuO, CuGaO, CuSCN, CuI, and NiO. x , MoO x , VO, or carbon materials such as graphene oxide. These inorganic semiconductors may be mixed with organic materials. For example, nanoparticles of an inorganic semiconductor may be mixed with an organic material such as PTAA.

[0067] The hole transport layer 5 may include multiple layers made of different materials. For example, multiple layers may be stacked so that the ionization potentials (or HOMO levels) of the hole transport layer 5 become progressively shallower relative to the ionization potential of the photoelectric conversion layer 4, thereby improving the hole transport properties.

[0068] The thickness of the hole transport layer 5 may be 1 nm or more and 1000 nm or less, or 10 nm or more and 50 nm or less. Within this range, sufficient hole transport properties can be exhibited and low resistance can be maintained, allowing for highly efficient photovoltaic power generation.

[0069] The hole transport layer 5 can be formed by a coating method, a printing method, a vapor deposition method, or the like. Examples of coating methods include a doctor blade method, a bar coating method, a spray method, a dip coating method, and a spin coating method. Examples of printing methods include a screen printing method. If necessary, the hole transport layer 5 may be formed by mixing a plurality of materials, and then the mixture may be pressurized or baked. When the material of the hole transport layer 5 is an organic low-molecular-weight substance, the hole transport layer 5 can also be formed by a vacuum vapor deposition method.

[0070] The hole transport layer 5 contains a supporting salt material (i.e., a supporting electrolyte) and a supporting salt dispersion material. The supporting salt material has the effect of improving the conductivity when added to the hole transport material. The supporting salt dispersion material, when added to the hole transport material together with the supporting salt material, can disperse the supporting salt material uniformly within the hole transport layer, thereby enhancing the conductivity-improving effect of the supporting salt material. In other words, the supporting salt material and the supporting salt dispersion material have the effect of stabilizing holes in the hole transport layer 5, contributing to an improvement in photoelectric conversion efficiency, particularly an improvement in initial efficiency.

[0071] Examples of the supporting salt material include alkali metal materials and imidazolium materials. An example of the alkali metal material is Li-TFSI. The imidazolium materials that can be used as the supporting salt material are as described above.

[0072] As described above, examples of the supporting salt dispersing material include heterocyclic compound solvents such as tBP, pyridine, and n-methylpyrrolidone.

[0073] In order to achieve high efficiency and high heat resistance of the solar cell, the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material needs to be greater than 0 and equal to or less than 0.4. This configuration is, for example, when the difference in the Hansen solubility parameter distance between the cation of the supporting salt material and the supporting salt dispersion material is 10 MPa. 0.5 This can be achieved by using a combination of the supporting salt material and the supporting salt dispersion material as described below, or by using a method that includes reducing the content ratio of the supporting salt dispersion material when manufacturing a solar cell.

[0074] For example, tBP of the supporting salt dispersion material and BDMI of the cation of the supporting salt material + , BMI + , HMI + , DMI + with R a The differences are 1.5, 2.3, 1.5, and 0.7 MPa, respectively. 0.5 and 10 MPa 0.5 where R a was calculated using the software "SoluVISION".

[0075] For example, the method for manufacturing the solar cell according to this embodiment may include preparing a precursor of the hole transport layer 5 and reducing the content of the supporting salt dispersion material in the precursor to obtain the hole transport layer 5. Here, examples of the method for reducing the content of the supporting salt dispersion material in the precursor of the hole transport layer 5 include a decompression method, a drying method, and a heating method.

[0076] The above-described manufacturing method may further include drying the obtained hole transport layer. In this case, the drying temperature of the hole transport layer may be lower than the boiling point of the supporting salt dispersion material. According to this method, the supporting salt dispersion material is not completely removed from the hole transport layer 5, and a minimum amount of the supporting salt dispersion material remains so as not to reduce the initial efficiency and heat resistance of the solar cell. This makes it possible to more reliably achieve uniform dispersion of the supporting salt dispersion material in the hole transport layer 5, thereby enabling the manufacture of solar cells with improved initial efficiency and heat resistance.

[0077] (Second electrode 6) When the solar cell includes the hole transport layer 5, the second electrode 6 does not need to have blocking properties against electrons from the photoelectric conversion layer 4. In other words, the material of the second electrode 6 may be a material that is in ohmic contact with the photoelectric conversion layer 4. Therefore, the second electrode 6 can be formed to have light-transmitting properties.

[0078] Of the first electrode 2 and the second electrode 6, it is sufficient that the electrode on the light incident side has light-transmitting properties. Therefore, one of the first electrode 2 and the second electrode 6 does not have to have light-transmitting properties. In other words, one of the first electrode 2 and the second electrode 6 does not have to use a light-transmitting material or have a pattern including openings that transmit light.

[0079] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0080] (Technology 1) A solar cell comprising a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode, wherein the photoelectric conversion layer contains a perovskite compound, and the hole transport layer contains a supporting salt material and a supporting salt dispersion material, and wherein a value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not greater than 0.4.

[0081] By including a supporting salt material and a supporting salt dispersion material in the hole transport layer, the solar cell of Technology 1 can maintain the initial efficiency compared to conventional solar cells, i.e., can have an initial efficiency comparable to or improved than conventional solar cells. Furthermore, in the solar cell of Technology 1, the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not greater than 0.4. With this configuration, the solar cell of Technology 1 has extremely little supporting salt dispersion material remaining in the solar cell, and can suppress a decrease in heat resistance caused by the supporting salt dispersion material. As a result, the solar cell according to Technology 1 can achieve excellent heat resistance. In this way, the solar cell of Technology 1 can provide a perovskite solar cell that maintains initial efficiency and has excellent heat resistance.

[0082] (Technology 2) The difference in Hansen solubility parameter distance between the cation of the supporting salt material and the supporting salt dispersion material is 10 MPa 0.5 The solar cell according to Technology 1, which is as follows:

[0083] The above configuration can improve the initial efficiency and heat resistance of the solar cell of Technology 2. Furthermore, the above configuration can more easily realize a solar cell of Technology 2 in which the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and equal to or less than 0.4.

[0084] (Technology 3) The solar cell according to Technology 1 or 2, wherein the supporting electrolyte material is an imidazolium-based material.

[0085] With the above configuration, the solar cell of Technique 3 can improve the initial efficiency and heat resistance.

[0086] (Technology 4) The solar cell according to Technology 3, wherein the imidazolium-based material contains a cation having a structure in which a methyl group is bonded to a nitrogen atom constituting an imidazole ring.

[0087] With the above configuration, the solar cell of Technique 4 can improve heat resistance.

[0088] (Technology 5) The imidazolium-based material has an alkyl chain (CH2) attached to a nitrogen atom constituting an imidazole ring.n The alkyl chain (CH2) n 5. The solar cell according to claim 3, wherein n satisfies 3≦n≦9.

[0089] With the above configuration, the solar cell of Technique 5 can improve the initial efficiency and heat resistance.

[0090] (Technology 6) The solar cell according to any one of Techniques 3 to 5, wherein the imidazolium-based material contains, as a cationic species, at least one selected from the group consisting of 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-methyl-3-n-octylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, and 1-methyl-3-(4-sulfobutyl)imidazolium cation.

[0091] With the above-described configuration, the solar cell of Technique 6 can improve the initial efficiency and heat resistance.

[0092] (Technology 7) The solar cell according to any one of Technologies 3 to 6, wherein the imidazolium-based material contains, as an anion species, at least one selected from the group consisting of a bis(trifluoromethane)sulfonimide anion, a tetrafluoroborate ion, and a hexafluorophosphate ion.

[0093] With the above-described configuration, the solar cell of Technique 7 can improve the initial efficiency and heat resistance.

[0094] (Technology 8) The solar cell according to any one of Technologies 1 to 7, wherein the supporting salt dispersion material contains at least one selected from the group consisting of 4-tert-butylpyridine, pyridine, and n-methylpyrrolidone.

[0095] With the above-described configuration, the solar cell of Technique 8 can improve the initial efficiency and heat resistance.

[0096] (Technology 9) The hole transport layer contains, as a hole transport material, 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], 2,2',7,7'-tetrakis[N,N-di-p-methoxyphenylamino]-9,9'-spirobifluorene, Poly(3-hexylthiophene-2,5-diyl), 4,4',4" -tris[9,9-dimethyl-2-fluorenyl(4-methoxy-phenyl)amino]triphenylamine, polyaniline, Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)], and poly(3,4-ethylenedioxythiophene), The solar cell according to any one of techniques 1 to 8, comprising at least one selected from the group consisting of:

[0097] With the above-described configuration, the solar cell of Technique 9 can improve the initial efficiency and heat resistance.

[0098] (Technology 10) The method for manufacturing a solar cell according to any one of Technologies 1 to 9, comprising: preparing a precursor of the hole transport layer; and reducing a content of the supporting salt dispersion material in the precursor to obtain the hole transport layer.

[0099] According to the manufacturing method of Technique 10, the solar cell according to any one of Techniques 1 to 9 can be easily manufactured.

[0100] (Technology 11) The method for producing a solar cell according to Technology 10, further comprising drying the obtained hole transport layer, wherein the drying temperature of the hole transport layer is lower than the boiling point of the supporting salt dispersion material.

[0101] The present disclosure will be described in more detail below with reference to examples and comparative examples, although the present invention is not limited to the following examples.

[0102] In the examples and comparative examples, solar cells were fabricated using perovskite compounds, and the initial efficiency and heat resistance of the solar cells were evaluated. Here, the heat resistance test was performed by placing the solar cells in a drying oven (in a dark place) set at 85°C.

[0103] The solar cells of Examples 1 to 13 and Comparative Examples 1 to 8 were configured as follows. The solar cells of Examples 1 to 13 and Comparative Examples 1 to 8 had the same structure as the solar cell 10 shown in Figure 1. Substrate 10: glass substrate (thickness: 1.3 mm) First electrode 2: fluorine-doped tin oxide film (thickness: 400 nm) Electron transport layer 3: tin oxide (SnO2) (thickness: 30 nm) Photoelectric conversion layer 4: layer containing a perovskite compound (thickness: 500 nm) Hole transport layer 5: layer mainly containing PTAA (thickness: 50 nm) Second electrode 6: indium-tin composite oxide (thickness: 100 nm)

[0104] <Fabrication of Solar Cell> (Example 1) First, a substrate 1 was prepared, the substrate 1 having, on its surface, a transparent conductive layer (i.e., a fluorine-doped tin oxide film layer) that functions as a first electrode 2. In this example, a glass substrate having a thickness of 1.3 mm was used as the substrate 1.

[0105] As the first electrode 2, a layer of fluorine-added tin oxide film was formed on the substrate 1 by thermal CVD.

[0106] Next, a solution obtained by mixing a SnO2 colloidal dispersion (15%, manufactured by Alfa Aesar) and ultrapure water (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at a volume ratio of SnO2 colloidal dispersion:ultrapure water = 2:7 was applied onto the first electrode 2 by spin coating, thereby forming a porous tin oxide layer as the electron transport layer 3.

[0107] Next, a raw material solution of a photoelectric conversion material was applied by spin coating to form a photoelectric conversion layer 4 containing a perovskite compound. The raw material solution was a solution containing 0.75 mol / L lead(II) iodide (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.45 mol / L lead(II) bromide (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.9 mol / L formamidinium iodide (manufactured by GreatCell Solar), 0.3 mol / L methylammonium iodide (manufactured by GreatCell Solar), and 0.4 mol / L methylammonium chloride (manufactured by GreatCell Solar). The solvent for the solution was a mixed solvent of dimethyl sulfoxide (manufactured by Acros) and N,N-dimethylformamide (manufactured by Acros). The mixing ratio of dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in this mixed solvent (DMSO:DMF) was 1:4 by volume.

[0108] Next, a raw material solution of a hole transport material was applied onto the photoelectric conversion layer 4 by spin coating to form a hole transport layer 5 containing PTAA. Specifically, a layer mainly containing PTAA (with tBP (manufactured by Tokyo Chemical Industry Co., Ltd.) and DMI-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd.) as additives) was formed. PTAA was included as the hole transport material, tBP as the supporting salt dispersion material, and DMI-TFSI as the supporting salt material. The solvent for the raw material solution of the layer mainly containing PTAA was toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The raw material solution contained 10 g / L of PTAA, 6.5 mg / L of tBP, and 5.1 mg / L of DMI-TFSI.

[0109] Next, an indium-tin composite oxide film was formed by sputtering on the hole transport layer 5 to form the second electrode 6. In this way, the solar cell of Example 1 was obtained.

[0110] Example 2 In Example 2, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 4.6 mg / L of tBP, and 3.2 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 2 was obtained in the same manner as in Example 1.

[0111] Example 3 In Example 3, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 4.1 mg / L of tBP, and 4.4 mg / L of BDMI-TFSI. PTAA was included as a hole transport material, tBP as a supporting salt dispersion material, and BDMI-TFSI as a supporting salt material. The solvent for the raw material solution for the layer mainly containing PTAA was a solution obtained by mixing mesitylene (manufactured by Nacalai Tesque) and ortho-dichlorobenzene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in a volume ratio of mesitylene:ortho-dichlorobenzene = 7:3. Otherwise, the solar cell of Example 3 was obtained in the same manner as in Example 1.

[0112] Example 4 In Example 4, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 4.1 mg / L of tBP, and 4.2 mg / L of BMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and BMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 4 was obtained in the same manner as in Example 3.

[0113] Example 5 In Example 5, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 4.1 mg / L of tBP, and 4.5 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 5 was obtained in the same manner as in Example 3.

[0114] Example 6 In Example 6, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 4.1 mg / L of tBP, and 5.1 mg / L of DMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and DMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 6 was obtained in the same manner as in Example 3.

[0115] Example 7 In Example 7, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 3.0 mg of tBP, and 6.8 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 7 was obtained in the same manner as in Example 3.

[0116] Example 8 In Example 8, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 6.2 mg of tBP, and 6.8 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 8 was obtained in the same manner as in Example 3.

[0117] Example 9 In Example 9, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 12.3 mg of tBP, and 6.8 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 9 was obtained in the same manner as in Example 3.

[0118] Example 10 In Example 10, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 5.5 mg of tBP, and 3.9 mg / L of HMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and HMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 10 was obtained in the same manner as in Example 1.

[0119] Example 11 In Example 11, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 5.5 g / L of tBP, and 4.4 g / L of DMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and DMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 11 was obtained in the same manner as in Example 1.

[0120] Example 12 In Example 12, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 5.5 g / L of tBP, and 3.6 g / L of BMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and BMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 12 was obtained in the same manner as in Example 1.

[0121] Example 13 In Example 13, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 5.5 g / L of tBP, and 3.7 g / L of BDMI-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and BDMI-TFSI was contained as a supporting salt material. Except for this, the solar cell of Example 13 was obtained in the same manner as in Example 1.

[0122] Comparative Example 1 In Comparative Example 1, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA. Otherwise, the solar cell of Comparative Example 1 was obtained in the same manner as in Example 1.

[0123] Comparative Example 2 In Comparative Example 2, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 9.2 mg of tBP, and 4.1 mg of Li-TFSI. Otherwise, the solar cell of Comparative Example 2 was obtained in the same manner as in Example 1.

[0124] (Comparative Example 3) In Comparative Example 3, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA. That is, in Comparative Example 3, the raw material solution for forming the hole transport layer did not contain a supporting salt material or a supporting salt dispersion material. The solvent for the raw material solution for the layer mainly containing PTAA was a solution obtained by mixing mesitylene and orthodichlorobenzene at a volume ratio of mesitylene:orthodichlorobenzene = 7:3. Otherwise, the solar cell of Comparative Example 3 was obtained in the same manner as in Example 3.

[0125] Comparative Example 4 In Comparative Example 4, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA and 6.8 mg / L of HMI-TFSI. That is, in Comparative Example 4, the raw material solution for forming the hole transport layer did not contain a supporting salt dispersion material. Except for this, the solar cell of Comparative Example 4 was obtained in the same manner as in Example 3.

[0126] Comparative Example 5 In Comparative Example 5, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 7.5 mg of tBP, and 4.0 mg / L of Li-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and Li-TFSI was contained as a supporting salt material. Except for this, the solar cell of Comparative Example 5 was obtained in the same manner as in Example 1.

[0127] Comparative Example 6 In Comparative Example 6, the raw material solution for the layer mainly containing PTAA contained 10 g / L of PTAA, 12.4 mg of tBP, and 3.9 mg / L of Li-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and Li-TFSI was contained as a supporting salt material. Except for this, the solar cell of Comparative Example 6 was obtained in the same manner as in Example 1. That is, the amount of Li-TFSI contained in the raw material solution for the layer mainly containing PTAA used in Comparative Example 2 was the same as the amount of Li-TFSI contained in the raw material solution for the layer mainly containing PTAA used in Comparative Examples 5 and 6, but the amount of tBP contained in the raw material solution for the layer mainly containing PTAA used in Comparative Example 2 was between the amounts of tBP contained in the raw material solutions for the layer mainly containing PTAA used in Comparative Examples 5 and 6.

[0128] (Comparative Example 7) In Comparative Example 7, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 8.0 g / L of tBP, and 4.3 g / L of Li-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and Li-TFSI was contained as a supporting salt material. The solvent for the raw material solution for the layer mainly containing PTAA was mesitylene. Except for this, the solar cell of Comparative Example 7 was obtained in the same manner as in Example 1.

[0129] (Comparative Example 8) In Comparative Example 8, the raw material solution for the layer mainly containing PTAA contained 14 g / L of PTAA, 13.2 g / L of tBP, and 4.3 g / L of Li-TFSI. PTAA was contained as a hole transport material, tBP was contained as a supporting salt dispersion material, and Li-TFSI was contained as a supporting salt material. The solvent for the raw material solution for the layer mainly containing PTAA was mesitylene. Except for this, the solar cell of Comparative Example 8 was obtained in the same manner as in Example 1.

[0130] <Measurement of Photoelectric Conversion Efficiency (Initial Efficiency)> The photoelectric conversion efficiency of the obtained solar cells of Examples 1 to 9 and Comparative Examples 1 to 4 was measured.

[0131] The current-voltage characteristics of the solar cell under light irradiation were measured using an electrochemical analyzer (ALS660B, manufactured by BAS) and a fluorescent lamp. Before the measurement, the light intensity was calibrated to 1 Sun using a standard cell. The voltage sweep rate was 1 mV / s. No prior adjustments such as irradiation with a light intensity of 1 Sun or application of a forward bias for a long period of time were performed before the start of the measurement. To fix the effective area and reduce the influence of scattered light, an opening of 0.1 cm was used. 2 The solar cell was masked with a black mask and irradiated with light from the mask / substrate side. The output power was measured at room temperature in dry air (<2% RH).

[0132] Table 1 shows the initial efficiencies and efficiencies after a heat resistance test (288 hours) for Examples 1 and 2 and Comparative Examples 1 and 2. The normalized efficiency is a value normalized by the efficiency after the heat resistance test for Comparative Example 1. The retention rate was calculated by (efficiency after heat resistance test / initial efficiency) x 100. In Examples 1 and 2 shown in Table 1, the "value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material" for the raw material solution for forming the hole transport layer, i.e., the "charged tBP / X-TFSI molar ratio" was 4.7 for all cases. In Tables 1 to 4 below, "X" in "X-TFSI" represents the cation of the supporting salt material.

[0133] From the relationship between the "charged tBP / X-TFSI molar ratio" and the "measured tBP / X-TFSI molar ratio" values ​​in Examples 10 to 13 described later, it can be determined that the measured tBP / X-TFSI molar ratios were 0.4 or less in the solar cells of Examples 1 to 6. Furthermore, from the relationship between the "charged tBP / X-TFSI molar ratio" and the "measured tBP / X-TFSI molar ratio" values ​​in Comparative Examples 5 to 8 described later, it can be determined that the measured tBP / X-TFSI molar ratio in the solar cell of Comparative Example 2 was approximately the same as in Comparative Examples 5 to 8, that is, a value within the range of 0.44 to 0.71, and exceeded 0.4.

[0134]

[0135] As shown in Table 1, by using the imidazolium-based materials of Examples 1 and 2 as the supporting salt material, the initial efficiency and the efficiency after the heat resistance test were greatly improved compared to when no supporting salt material was added in Comparative Example 1. Furthermore, when the imidazolium-based materials of Examples 1 and 2 were used as the supporting salt material, the efficiency and retention rate after the heat resistance test were greatly improved compared to when Li-TFSI, a common supporting salt material in Comparative Example 2, was used.

[0136] Table 2 shows the initial efficiency and the efficiency after the heat resistance test (112 hours) for Examples 3 to 6 and Comparative Example 3. The normalized efficiency is a value normalized by the efficiency after the heat resistance test for Comparative Example 3. As in Table 1, the retention rate was calculated by (efficiency after heat resistance test / initial efficiency)×100. In Examples 3 to 6 shown in Table 2, the "value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material" for the raw material solution for forming the hole transport layer, i.e., the "charged tBP / X-TFSI molar ratio" was 3.0 in all cases.

[0137] From the relationship between the "charged tBP / X-TFSI molar ratio" and the "measured tBP / X-TFSI molar ratio" in Examples 10 to 13 shown below, it can be determined that the measured tBP / X-TFSI molar ratio in the solar cells of Examples 3 to 6 was 0.4 or less.

[0138]

[0139] As shown in Table 2, by using the imidazolium-based materials of Examples 3 to 6 as the supporting electrolyte material, the initial efficiency and the efficiency after the heat resistance test were greatly improved compared to the case where no supporting electrolyte material was added in Comparative Example 3. In particular, the case where HMI-TFSI of Example 5 was used resulted in the highest initial efficiency and the highest efficiency after the heat resistance test.

[0140] The initial efficiencies of Examples 7 to 9 and Comparative Example 4 are shown in Table 3. Here, the charged tBP / X-TFSI molar ratio was changed in the range of 0 to 6. The normalized efficiency is a value normalized by the initial efficiency of Comparative Example 4.

[0141]

[0142] Non-Patent Document 2 discloses an example in which HMI-TFSI is used as a supporting salt material for the hole transport material Spiro-MeOTAD, but no supporting salt dispersion material such as tBP is added to the HMI-TFSI. As shown in Comparative Example 4 of Table 3, the initial efficiency was lowest when no tBP was added (when the tBP / HMI-TFSI molar ratio of the charge was 0), indicating that the HMI-TFSI supporting salt material must be properly dispersed in the hole transport layer by the tBP of the supporting salt dispersion material. In other words, if a supporting salt dispersion material is not added, the initial efficiency of a solar cell equipped with a hole transport layer containing both a supporting salt material and a supporting salt dispersion material decreases, making it difficult to realize a solar cell that maintains initial efficiency and has excellent heat resistance. However, as shown in Examples 7 to 9, there is an optimal value for the amount of tBP added, and the initial efficiency reaches its maximum when the tBP / HMI-TFSI molar ratio of the charge is around 3 (Example 8).

[0143] Table 4 shows the charged amounts and measured amounts of tBP / X-TFSI (X = Li, HMI, DMI, BMI, BDMI) molar ratios for Examples 10 to 13 and Comparative Examples 5 to 8. Here, the amount of substance of X-TFSI was determined by quantifying the TFSI ion content in the solar cell using LC-MS, and the amount of substance of tBP was determined by GC-MS.

[0144]

[0145] In the cases of Comparative Examples 5 to 8, the charged tBP / Li-TFSI molar ratio was 4.0 to 6.6, while the measured tBP / Li-TFSI molar ratio was 0.44 to 0.70, indicating that a large amount of tBP remained in the solar cell. On the other hand, in the case of Example 10, the charged tBP / HMI-TFSI molar ratio was 4.7, while the measured tBP / HMI-TFSI molar ratio was 0.07, indicating that almost no tBP remained in the solar cell. Therefore, compared to the case where Li-TFSI and tBP were added, when HMI-TFSI and tBP were added, the amount of remaining tBP, which is a degradation factor, was extremely small, and therefore it can be said that the heat resistance was high. In the cases of Examples 11, 12, and 13, the measured tBP / DMI-TFSI molar ratio, the measured tBP / BMI-TFSI molar ratio, and the measured tBP / BDMI-TFSI molar ratio were 0.04, 0.06, and 0.13, respectively, and similarly to the case of adding HMI-TFSI, there was little tBP remaining in the solar cell, and the heat resistance was high.

[0146] From the above results, it has been confirmed that a solar cell having a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode, wherein the photoelectric conversion layer contains a perovskite compound and the hole transport layer contains a supporting salt material and a supporting salt dispersion material, can achieve excellent heat resistance by selecting an appropriate combination of the supporting salt material and the supporting salt dispersion material so that the amount of substance of the supporting salt dispersion material divided by the amount of substance of the supporting salt material in the solar cell is greater than 0 and not greater than 0.4, while maintaining initial efficiency and suppressing a decrease in heat resistance due to remaining supporting salt dispersion material.

[0147] The present disclosure can be applied to solar cells that require high efficiency and high heat resistance, and has extremely high industrial applicability.

Claims

1. A solar cell comprising a first electrode, a photoelectric conversion layer, a hole transport layer, and a second electrode, wherein the photoelectric conversion layer contains a perovskite compound, and the hole transport layer contains a supporting salt material and a supporting salt dispersion material, and wherein the value obtained by dividing the amount of substance of the supporting salt dispersion material by the amount of substance of the supporting salt material is greater than 0 and not greater than 0.

4.

2. The difference in Hansen solubility parameter distance between the cation of the supporting salt material and the supporting salt dispersion material is 10 MPa. 0.5 The solar cell according to claim 1 , wherein:

3. The solar cell according to claim 1, wherein the supporting electrolyte material is an imidazolium-based material.

4. The solar cell according to claim 3, wherein the imidazolium-based material contains a cation having a structure in which a methyl group is bonded to a nitrogen atom constituting an imidazole ring.

5. The imidazolium-based material has an alkyl chain (CH2) attached to the nitrogen atom that constitutes the imidazole ring. n The alkyl chain (CH2) n The solar cell according to claim 3 , wherein n satisfies 3≦n≦9.

6. The solar cell according to claim 3, wherein the imidazolium-based material contains, as a cationic species, at least one selected from the group consisting of 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-methyl-3-n-octylimidazolium cation, 1-decyl-3-methylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, and 1-methyl-3-(4-sulfobutyl)imidazolium cation.

7. The solar cell according to claim 3, wherein the imidazolium-based material contains, as an anion species, at least one selected from the group consisting of a bis(trifluoromethane)sulfonimide anion, a tetrafluoroborate ion, and a hexafluorophosphate ion.

8. The solar cell according to claim 1, wherein the supporting salt dispersing material includes at least one selected from the group consisting of 4-tert-butylpyridine, pyridine, and n-methylpyrrolidone.

9. The hole transport layer contains, as a hole transport material, 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], 2,2',7,7'-tetrakis[N,N-di-p-methoxyphenylamino]-9,9'-spirobifluorene, Poly(3-hexylthiophene-2,5-diyl), 4,4',4" 2. The solar cell according to claim 1, comprising at least one selected from the group consisting of: tris[9,9-dimethyl-2-fluorenyl(4-methoxy-phenyl)amino]triphenylamine, polyaniline, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)], and poly(3,4-ethylenedioxythiophene).

10. A method for manufacturing a solar cell according to any one of claims 1 to 9, comprising: preparing a precursor of the hole transport layer; and reducing the content of the supporting salt dispersion material in the precursor to obtain the hole transport layer.

11. The method for producing a solar cell according to claim 10, wherein the production method further comprises drying the obtained hole transport layer, and the drying temperature of the hole transport layer is lower than the boiling point of the supporting salt dispersion material.

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