Ionic compound, hole transport material containing ionic compound, perovskite solar cell containing hole transport material, method for producing ionic compound, method for producing hole transport material, and method for producing perovskite solar cell

Abstract

The present invention is an ionic compound composed of a molecular cation and a molecular anion. The molecular cation contains at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium, the organic ammonium has an organic portion having 1-20 carbon atoms inclusive, and the molecular anion contains a fluorine-containing bissulfonylimide.

Description

Ionic compound, hole transport material containing ionic compound, perovskite solar cell containing hole transport material, method for producing ionic compound, method for producing hole transport material, and method for producing perovskite solar cell

[0001] The present disclosure relates to an ionic compound, a hole transport material containing an ionic compound, a perovskite solar cell containing the hole transport material, and methods for producing the same.

[0002] Ionic compounds are compounds containing anions and cations. These ionic compounds have properties such as non-volatility, non-flammability, and electrical conductivity, and are used in a variety of applications, such as additives and reagents for electronic materials and solvents for organic synthesis. For example, in electronic materials, ionic compounds are added as additives (dopants) to organic electronic materials to change their electrical conductivity.

[0003] Perovskite solar cells are a representative example of devices using organic electronic materials. Perovskite solar cells are known as solar cells whose light absorption layer is made of a material called a perovskite material, which contains organic cations such as formamidium, inorganic cations such as lead cations, and halogen anions (Patent Documents 1 and 2). This perovskite layer is known to be hydrophilic and form hydrates (Non-Patent Document 1). This solar cell can be fabricated using a wet coating method and can achieve performance comparable to or even higher than that of crystalline silicon solar cells, making it attractive as a next-generation solar cell. In particular, its open-circuit voltage is higher than that of conventional crystalline silicon solar cells, making it suitable for applications requiring high electromotive force, such as as a power source for water electrolysis. In many perovskite solar cells, an organic electronic material is bonded to the perovskite layer as a hole transport material. This hole transport material provides anisotropy in charge transport, enabling high-performance perovskite solar cells. A dopant is added to the hole transport material to improve hole mobility.

[0004] Adding such a dopant to a hole-transporting material facilitates the movement of holes, resulting in high photoelectric conversion efficiency. A representative ionic compound dopant is Li-TFSI, which is composed of a lithium (Li) cation and a bis(trifluoromethanesulfonyl)imide (TFSI) anion (Patent Documents 1 and 2).

[0005] Furthermore, Non-Patent Document 2 discloses the use of TBA-TFSI, which is composed of tetrabutylammonium (TBA) cations, as a dopant.

[0006] Non-Patent Document 3 discloses the addition of 4-tert-butylpyridine to the dopant of a hole transport material. 4-tert-butylpyridine has a relatively low boiling point and is known to adversely affect the heat resistance of solar cells.

[0007] On the other hand, ionic compounds are used not only as additives for electrical materials, but also as base materials for electrical materials, electrolytes, solvents and precursors for material synthesis, gas adsorbents, etc. In particular, those with a melting point of 100°C or less are known as ionic liquids, and have high chemical stability such as nonvolatility and nonflammability, are easy to handle at low temperatures, and also have properties such as electrical conductivity. Therefore, they are suitable as base materials for the above-mentioned electrical materials, and there is also potential for further expansion of their applications.

[0008] As anions of ionic compounds, molecular anions containing fluorinated bis(sulfonylimides), such as the aforementioned TFSI anion, are known to have high electronegativity and are promising anions for ionic liquids. Also, cations based on quaternary ammonium, imidazole, and pyridine are known.

[0009] International Publication No. 2021 / 131428 Japanese Patent Application Laid-Open No. 2019-96891

[0010] PV Kamat et al., J. Am. Chem. Soc. 2015, 137, 1530-1538Jinbao Zhang et al., ACS Energy Lett. 2018, 3, 1677-1682Shen Wang et al., Nano Lett. 2016, 16, 5594-5600

[0011] As described above, ionic compounds are widely used in electronic materials, reagents, solvents for organic synthesis, and the like, but improvements in various properties are required. In particular, the cations constituting the ionic compounds are required to have better reactivity. Specifically, superior nucleophilic reactivity and / or electrophilic reactivity, and more specifically, strong cationicity and a wide electron orbital are required for various applications.

[0012] For example, in perovskite solar cells, further performance improvements using ionic compounds are required, and in particular, further improvements in the open-circuit voltage, which is a characteristic of perovskite solar cells, are desired. Furthermore, solar cells are desired to have high durability and long life. However, the present inventors have discovered that quaternary ammonium and pyridine, which have been used as conventional additives, have weak cationic properties. Specifically, imidazole and pyridine are cations with sp2 electron orbitals, which are inferior in electron orbital breadth to sp3 cations, and are thought to have limited their effectiveness. Furthermore, catalysts, photocatalysts, gas adsorbents, and solvents are required to have strong cationic properties and large electron orbital breadth in order to more effectively exhibit catalytic activity, photocatalytic activity, gas adsorption ability, or substance solubility.

[0013] The present disclosure provides an ionic compound containing a highly reactive cation and a method for producing the ionic compound, a hole transport material containing such an ionic compound, a method for producing the hole transport material, a perovskite solar cell containing the hole transport material, and a method for producing the perovskite solar cell.

[0014] The present inventors have discovered that an ionic compound comprising a cation containing an organic ammonium having an organic moiety having from 1 to 20 carbon atoms and a molecular anion containing a fluorinated bis(sulfonylimide) has excellent reactivity, and have completed the present disclosure.

[0015] The present invention relates to an ionic compound comprising a molecular cation and a molecular anion, wherein the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium, the organic ammonium having an organic moiety having from 1 to 20 carbon atoms, and the molecular anion comprises a fluorinated bissulfonylimide. The present invention also relates to a hole transport material comprising the ionic compound. The present invention also relates to a perovskite solar cell comprising a perovskite layer and a hole transport layer on the perovskite layer, wherein the hole transport layer comprises the hole transport material.

[0016] The method for producing the ionic compound includes a step of ion-exchanging an organic ammonium halide having an organic moiety containing 1 to 20 carbon atoms with an alkali metal salt of a fluorinated bis-sulfonylimide, and a step of extracting the ionic compound obtained by the ion exchange. The method for producing the ionic compound also includes a step of neutralizing an organic amine having an organic moiety containing 1 to 20 carbon atoms with an acid of the fluorinated bis-sulfonylimide. The method for producing a hole transport material also includes a step of mixing the ionic compound with a raw material compound for the hole transport material.

[0017] A method for manufacturing a perovskite solar cell by stacking an electron transport layer, a perovskite layer, and a hole transport layer between a conductive substrate and an electrode, the method comprising the step of forming the hole transport layer, and the step of forming the hole transport layer comprising the step of forming a film on the perovskite layer using the hole transport material.

[0018] According to the present disclosure, it is possible to provide an ionic compound containing a highly reactive cation and a method for producing the ionic compound, a hole transport material containing such an ionic compound, a method for producing the hole transport material, a perovskite solar cell containing the hole transport material, and a method for producing the perovskite solar cell.

[0019] 1 is a schematic diagram showing an example of the basic structure of a perovskite solar cell. 1H-NMR spectrum of n-octylammonium TFSI. (Example 1) 19F-NMR spectrum of n-octylammonium TFSI. (Example 1) 1H-NMR spectrum of n-octylammonium TFSI. (Example 2) 1H-NMR spectrum of n-dodecylammonium TFSI. (Example 3) 1H-NMR spectrum of n-butylammonium TFSI. (Example 4) 1H-NMR spectrum of ethylammonium TFSI. (Example 5) 1H-NMR spectrum of 2-phenylethylammonium TFSI. (Example 6) 1H-NMR spectrum of n-methyl-n-octylammonium TFSI. (Example 7) 1H-NMR spectrum of n-octylammonium FSI. (Example 8) 1H-NMR spectrum of methylammonium TFSI. (Example 9) 1H-NMR spectrum of n-octylammonium PFSI. (Example 18) 1H-NMR spectrum of n-octylammonium NFSI. (Example 19) 1H-NMR spectrum of n,n-dimethyl-n-octylammonium TFSI. (Example 20)

[0020] The present disclosure will be described in detail below, but is not limited to the following description. An ionic compound according to an embodiment of the present disclosure is composed of a molecular cation and a molecular anion, wherein the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium, wherein the organic ammonium has an organic moiety having from 1 to 20 carbon atoms, and the molecular anion comprises a fluorinated bis(sulfonylimide). Note that, in this specification, when a numerical range is indicated, it is intended to include both an upper and lower limit. In other words, unless otherwise specified, the expressions "XX to YY" or "XX to YY" representing a numerical range refer to a numerical range that includes both the lower and upper limits, which are the endpoints. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any combination.

[0021] By adopting the above-described configuration, this ionic compound exhibits the excellent reactivity due to the molecular cation and the effect due to the molecular anion. This effect is suitable for applications that utilize the excellent reactivity due to the molecular cation and / or the effect due to the molecular anion, such as the various applications described above. For example, this ionic compound serves as an additive to a hole transport material that is suitable for improving the performance and / or durability of perovskite solar cells. While the inventors do not wish to be bound by a particular theory, they speculate that the mechanism by which this perovskite solar cell achieves high performance and high durability is as follows.

[0022] First, at least one organic ammonium cation selected from the group consisting of primary organic ammonium cations, secondary organic ammonium cations, and tertiary organic ammonium cations, which are highly reactive cations derived from the ionic compound of this embodiment and added as a dopant to the hole transport material, spontaneously reacts with the surface of the perovskite layer, thereby reducing defects on the perovskite surface and / or improving the electrical junction interface with the hole transport material, thereby improving solar cell characteristics such as open-circuit voltage. Furthermore, the molecular anion containing a fluorinated bis(sulfonylimide) derived from the ionic compound of this embodiment can extract electrons from the hole transport material and oxidize it, thereby improving the hole mobility in the hole transport material. In particular, a concerted effect is expected due to the combination of these cations and anions. Due to its strong ionicity, the molecular anion containing the fluorinated bis(sulfonylimide) reacts effectively with the hole transport material, weakening the association between the organic ammonium cation and this anion, allowing the reaction between the organic ammonium cation and the perovskite to proceed spontaneously. Furthermore, as a result of the reaction of this organic ammonium cation with the perovskite, the negative charge of the anion becomes independent, and electrons are extracted from the hole transport material more effectively than when a cation is present. It is believed that the synergistic effect of either or both of these factors favorably improves the solar cell performance.

[0023] Furthermore, the spontaneous reaction of this highly reactive organic ammonium cation with the perovskite layer surface reduces defects on the perovskite surface and / or improves the electrical junction interface with the hole transport material, which is advantageous from the perspective of alleviating the need for strict control of the manufacturing environment. In the conventional process of depositing a hole transport layer on a perovskite layer, the perovskite surface is exposed to the atmosphere and reacts with solvents, particularly oxygen molecules in the atmosphere, forming defects on the perovskite surface, requiring strict control of the manufacturing environment, such as manufacturing in nitrogen. However, the spontaneous reaction of this highly reactive organic ammonium cation with the perovskite layer surface during deposition of the hole transport material prevents the defect-reduced perovskite surface from being directly exposed to the atmosphere, making it less susceptible to the effects of the manufacturing environment and reducing the need for manufacturing environment control. This makes it possible to suitably manufacture relatively high-performance perovskite solar cells even when manufactured in air, rather than in an inert atmosphere such as nitrogen.

[0024] (Organic Ammonium Cation) At least one organic ammonium cation (hereinafter also referred to as organic ammonium) selected from the group consisting of primary organic ammonium cations (hereinafter also referred to as primary organic ammonium), secondary organic ammonium cations (hereinafter also referred to as secondary organic ammonium), and tertiary organic ammonium cations (hereinafter also referred to as tertiary organic ammonium) has excellent reactivity. In addition, the raw materials are low-cost, relatively easy to obtain, and relatively safe. The primary organic ammonium cation is represented by the following formula (1), the secondary organic ammonium cation is represented by the following formula (5), and the tertiary organic ammonium cation is represented by the following formula (6). RNH ３ ＋ (1) (In formula (1), R is an organic moiety having 1 to 20 carbon atoms.) R ２ NH ２ ＋ (5) (In formula (5), each R is independently an organic moiety having 1 to 20 carbon atoms.) R ３ NH ＋(6) (In formula (6), each R is independently an organic moiety having 1 to 20 carbon atoms.) From the viewpoint of superior reactivity, the organic ammonium is more preferably a primary organic ammonium.

[0025] A small series number of the organic ammonium is preferred from the viewpoint of excellent reactivity. In particular, when used as an additive to perovskite solar cells, a small series number of the organic ammonium is preferred from the viewpoint of excellent reactivity with the perovskite. Specifically, from this viewpoint, the organic ammonium is preferably at least one organic ammonium selected from the group consisting of primary organic ammonium and secondary organic ammonium ions, and most preferably primary organic ammonium. On the other hand, from the viewpoint of reducing the viscosity of the ionic liquid and being advantageous for mixing and diffusion with other materials, a large series number of the organic ammonium is preferred. From this viewpoint, the organic ammonium is preferably at least one organic ammonium selected from the group consisting of secondary organic ammonium and tertiary organic ammonium ions, and most preferably tertiary organic ammonium.

[0026] The organic ammonium cation has an organic moiety having from 1 to 20 carbon atoms. Preferably, the organic ammonium cation has an organic moiety having from 2 to 20 carbon atoms. From the viewpoints of the low bulk of the organic ammonium cation, which can increase the density of the ionic compound itself, and the viewpoint of the ionic compound being able to be added more densely and effectively as a dopant, catalyst, gas adsorbent, and / or solvent on a molecular number basis, the number of carbon atoms in the organic moiety of the organic ammonium cation is 20 or less, and more preferably 12 or less. Furthermore, from the viewpoints of easily lowering the melting point of the ionic compound and making it advantageous for application as a liquid, the number of carbon atoms in the organic moiety of the organic ammonium cation is 1 or more, more preferably 2 or more, and even more preferably 4 or more. The number of carbon atoms in the organic moiety of the organic ammonium cation can be, for example, 2 to 12, 4 to 20, or 4 to 12.

[0027] In particular, when the ionic compound of this embodiment is used as a dopant for a hole transport material in a perovskite solar cell, it is preferable that the number of carbon atoms in the organic moiety of the organic ammonium cation be 7 or less, as this reduces the dopant concentration dependency and is advantageous for achieving a large surface area. From this perspective, the number of carbon atoms in the organic moiety of the organic ammonium cation is more preferably 4 or less, and even more preferably 2 or less. That is, from this perspective, the number of carbon atoms in the organic moiety of the organic ammonium cation may be, for example, 1 to 7, 1 to 4, or 1 to 2. Of these, 1 to 2 is particularly preferable. On the other hand, from the perspective of more effectively hydrophobizing the perovskite surface and being advantageous for improving durability, the number of carbon atoms in the organic ammonium cation is preferably 9 or more, and even more preferably 12 or more. That is, from this perspective, the number of carbon atoms in the organic moiety of the organic ammonium cation may be, for example, 9 to 20, or 12 to 20. On the other hand, it is also preferable that the number of carbon atoms in the organic ammonium cation is 1, from the viewpoints that the organic ammonium cation can be identical to the A site of the three-dimensional perovskite and therefore suffers little performance degradation even when it diffuses from the perovskite surface to the bulk, that it can be suitably applied as an additive to perovskite materials, that it can easily promote crystal growth of perovskite materials, and / or that it is advantageous for surface stabilization at perovskite grain boundaries.

[0028] Examples of the organic moiety having 1 to 20 carbon atoms include aliphatic and aromatic groups. Examples of aliphatic groups include saturated or unsaturated aliphatic hydrocarbons. That is, the organic moiety of ammonium may include saturated or unsaturated hydrocarbons. The saturated and unsaturated hydrocarbons may be cyclic, linear, or branched. Among these, when used as a dopant for a hole transport material, saturated hydrocarbons (e.g., alkyls) are preferred because of their high degree of freedom in the carbon chain and their ease of reaction with the perovskite surface. Saturated hydrocarbons include linear and cyclic saturated hydrocarbons. Furthermore, linear saturated hydrocarbons are preferred because they can react closely with the perovskite surface. Note that the same can be said for other applications due to their strong cationic properties and large electron orbital expansion.

[0029] Examples of aromatic groups include aromatic hydrocarbons and aromatic heterocycles. That is, the organic portion of the ammonium may contain an aromatic hydrocarbon or an aromatic heterocycle. From the viewpoint of enabling the arrangement of the organic ammonium on the perovskite through π-π interactions and advantageously improving the adhesion between the hole transport layer and the perovskite layer, it is preferable that the organic portion of the organic ammonium contain an aromatic group. Regarding the mechanism of this improved adhesion, the inventors do not wish to be bound by a particular theory, but speculate as follows: It is speculated that the aromatic group that can constitute the hole transport material and the aromatic group that constitutes the organic portion of the organic ammonium adsorbed on the perovskite surface improve adhesion through π-π interactions. It is also speculated that the induced dipole of the hole transport material solution has an affinity with the induced dipole of the aromatic group that constitutes the organic portion of the organic ammonium adsorbed on the perovskite surface, improving the wettability of the hole transport material solution to the perovskite surface and preventing the formation of vacancies, resulting in dense deposition of the hole transport layer on the perovskite layer. Examples of organic moieties containing an aromatic hydrocarbon or an aromatic heterocycle include aryl groups, heteroaryl groups, biphenyl groups, thienyl groups, pyridyl groups, pyrrolyl groups, furyl groups, etc. Among these, aryl groups are preferred from the viewpoints of effectively controlling the arrangement of organic ammonium on the perovskite and effectively improving the adhesion between the hole transport layer and the perovskite layer.

[0030] The organic moiety having 1 to 20 carbon atoms may include, for example, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, etc. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a neopentyl group, an n-hexyl group, an n-octyl group, an n-dodecyl group, and a cyclohexyl group. Specific examples of the alkenyl group include a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a 1-octenyl group, a 1-decenyl group, and a 1-octadecenyl group. Further, examples of the alkynyl group include ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 1-octynyl, 1-decynyl, 1-octadecynyl, phenyl, phenylmethyl, phenylethyl, phenylpropyl, phenylbutyl, trifluoroethyl, etc. Among these, methyl, ethyl, n-butyl, n-octyl, and n-dodecyl groups are more preferred from the viewpoint of excellent reactivity with the perovskite surface.

[0031] The organic moiety may have a functional group other than the organic ammonium. Examples of the functional group include an oxygen-containing group, a nitrogen-containing group, and a sulfur-containing group. The organic moiety may have a plurality of functional groups. That is, the organic moiety of the organic ammonium may contain at least one functional group selected from the group consisting of an oxygen-containing group, a nitrogen-containing group, and a sulfur-containing group. The carbon number of the organic moiety (1 to 20) includes the carbon number of the carbon atom contained in the functional group, if any. For example, if the functional group is a carboxy group (COOH), the carbon atom contained in the COOH is included in the carbon number of the organic moiety.

[0032] Specific examples of oxygen-containing groups include hydroxy groups, alkoxy groups, aryloxy groups, ester groups, acyl groups, carboxy groups, carbonyl groups, and epoxy groups. Of these, hydroxy groups and carboxy groups are preferred. Specific examples of nitrogen-containing groups include amino groups, imino groups, amido groups, imido groups, hydrazino groups, hydrazono groups, nitro groups, nitroso groups, cyano groups, isocyano groups, cyanate ester groups, amidino groups, diazo groups, secondary ammonium groups, tertiary ammonium groups, pyridyl groups, and imidazolyl groups. Of these, secondary ammonium and tertiary ammonium groups are preferred. From the viewpoint of reactivity, it is preferable that the organic moiety does not contain quaternary ammonium. Examples of sulfur-containing groups include thiol groups and sulfo groups. Of these, thiol groups are preferred.

[0033] The organic part of the organic ammonium cation may contain a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoint of strengthening the nucleophilicity of the organic ammonium cation by utilizing the electron-withdrawing properties of the halogen atom, the organic part of the organic ammonium cation preferably contains a halogen atom. Furthermore, from the viewpoint of reducing the surface energy of the ionic compound of this embodiment and / or a compound to which the ionic compound is added, a fluorine atom is more preferred. More specifically, examples of the organic ammonium cation include those containing a fluorocarbon containing a halogen atom such as a fluorine atom in the organic part. For example, the organic ammonium cation may contain a fluorocarbon in the organic part, and the carbon bonded to the nitrogen atom of the organic ammonium is CH ２ Those having the structure, and those containing a perfluoroalkyl group in the organic part of the organic ammonium (e.g., CF ３ , C ２ F ５ The bond here refers to a chemical bond, for example, a covalent bond. In particular, when the carbon atom bonded to the nitrogen atom of the organic ammonium cation is CH ２ It is preferable that the carbon bonded to the nitrogen atom of the organic ammonium cation is CH ２This is because the presence of the structure inhibits the fluorine atom of the perfluoroalkyl from reacting with the proton of the ammonium, thereby stabilizing the perfluoroalkyl. Examples of such structures include C ｎ F ２ｎ＋１ CH ２ NH ３ ＋ (n is an integer of 1 or more), and specifically, C ４ F ９ CH ２ NH ３ ＋ In addition, from the viewpoint of suppressing undesired side reactions, it is also a preferred embodiment that the organic ammonium cation does not contain any functional groups other than the organic ammonium. In particular, the organic moiety is preferably a linear alkyl group having 1 to 12 carbon atoms and no functional group, more preferably a linear alkyl group having 2 to 12 carbon atoms and no functional group. Furthermore, the organic moiety is even more preferably a linear alkyl group having 4 to 12 carbon atoms and no functional group.

[0034] Examples of cations of the ionic compound of this embodiment include methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, heptylammonium, octylammonium, nonylammonium, decylammonium, undecylammonium, dodecylammonium, anilinium, methylphenylammonium, phenylethylammonium, phenylpropylammonium, phenylbutylammonium, etc. When the ionic compound of this embodiment is used as a dopant for the hole transport material of a perovskite solar cell, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, heptylammonium, octylammonium, nonylammonium, decylammonium, undecylammonium, dodecylammonium, methylphenylammonium, phenylethylammonium, phenylpropylammonium, and phenylbutylammonium are preferred from the viewpoint of excellent reactivity between the organic ammonium and the perovskite. From the viewpoint of reducing the dopant concentration dependency and being advantageous for achieving a large area, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, and heptylammonium are more preferred, and methylammonium, ethylammonium, propylammonium, and butylammonium are even more preferred. From the viewpoint of more effectively hydrophobizing the perovskite surface and being advantageous for improving durability, nonylammonium, decylammonium, undecylammonium, and dodecylammonium are more preferred, and decylammonium, undecylammonium, and dodecylammonium are even more preferred. From the viewpoint of being able to control the arrangement of organic ammonium on the perovskite by π-π interactions and being advantageous for improving adhesion between the hole transport layer and the perovskite layer, methylphenylammonium, phenylethylammonium, phenylpropylammonium, and phenylbutylammonium are more preferred, and phenylethylammonium such as 2-phenylethylammonium is even more preferred.

[0035] (Molecular Anion Containing Fluorine-Containing Bisulfonylimide) The molecular anion contains a fluorine-containing bisulfonylimide. The fluorine-containing bisulfonylimide is represented by the following formula (2): RfSO ２ N - SO ２ Rf (2) (In formula (2), each Rf is independently fluorine or a fluorine-containing alkyl group having 1 to 10 carbon atoms (preferably 1 to 3 carbon atoms).)

[0036] The fluorine-containing bissulfonylimide anion has two sulfonyl groups. A functional group such as fluorine or fluorocarbon may be bonded to the sulfonyl group. The functional groups of the two sulfonyl groups may be the same or different, or may be cyclic. For example, when used as a dopant for a hole transport material, it is preferable that the functional groups of the two sulfonyl groups are the same, from the viewpoint of effectively withdrawing electrons from the hole transport material. More specifically, examples of fluorine-containing bissulfonylimides include those having perfluoroalkyl groups, such as bis(fluorosulfonyl)imide (FSI), bis(trifluoromethanesulfonyl)imide (TFSI), bis(pentafluoroethanesulfonyl)imide (PFSI), and bis(nonafluorobutanesulfonyl)imide (NFSI). Among these, bis(trifluoromethanesulfonyl)imide is preferred due to its high electronegativity and high affinity for solvents. For example, when used as a dopant for a hole transport material, it is preferred due to its effective electron withdrawal from the hole transport material. In addition, bis(fluorosulfonyl)imide anions are preferred from the viewpoint of reducing the viscosity of the ionic liquid and being advantageous for mixing with and diffusing other materials. Furthermore, bis(pentafluoroethanesulfonyl)imide and bis(nonafluorobutanesulfonyl)imide are preferred from the viewpoint of being advantageous for hydrophobizing the hole transport material in addition to hydrophobizing the perovskite layer.

[0037] The combination of organic ammonium cation and molecular anion is not particularly limited, but a combination that results in an ionic compound that becomes an ionic liquid is preferred from the perspective of its applicability as a liquid. When used as an additive, it is preferable from the perspective of shortening the time required for dissolution in a solvent compared to solid compounds, which is industrially advantageous. Ionic liquids are ionic compounds with a melting point of 100°C or less, and include those that are liquid at room temperature (5 to 35°C). These ionic liquids are nonvolatile, nonflammable, and have excellent thermal stability, making them easy to handle and usable under mild conditions. Therefore, in addition to electrical materials, they are also suitable as gas adsorbents, separation and extraction solvents, and reaction solvents. From the perspective of ease of use as an ionic liquid, ionic liquids that are liquid at room temperature are preferred. For example, if the organic moiety of the organic ammonium cation has 4 to 12 carbon atoms and the molecular anion is FSI, TFSI, or PFSI, the ionic compound is advantageous because its melting point is likely to be below room temperature, making it easy to use as an ionic liquid. For example, ionic compounds such as n-butylammonium TFSI, n-octylammonium TFSI, n-dodecylammonium TFSI, n-methyl-n-octylammonium TFSI, n,n-dimethyl-n-octylammonium TFSI, n-octylammonium FSI, and n-octylammonium PFSI are preferred because they are liquid even at room temperature. Here, a description such as "n-butylammonium TFSI" indicates that in an ionic compound composed of a molecular cation and a molecular anion, the molecular cation is n-butylammonium and the molecular anion is TFSI. In other words, it indicates a salt of n-butylammonium and TFSI.

[0038] When the ionic compound of this embodiment is the ionic liquid, a low viscosity of the ionic liquid is preferred from the viewpoint of advantageous mixing and diffusion with other materials. In particular, when the ionic compound is used as a dopant for a hole transport material, a low viscosity of the ionic compound is preferred from the viewpoint of advantageous rapid mixing of the hole transport material with the ionic compound. The viscosity is not particularly limited, but may be, for example, 1 to 2000 mPa·s at 25°C, preferably 10 to 600 mPa·s, and more preferably 15 to 400 mPa·s. Viscosity is measured by the method described below. Specifically, the viscosity is measured at 25°C using an E-type viscometer (TV-25, manufactured by TOKI SANGYO).

[0039] The ionic compound of this embodiment may contain an alkali metal cation. From the viewpoint of not inhibiting the reaction caused by the organic ammonium constituting the ionic compound, the concentration of the alkali metal contained in the ionic compound is preferably 100 ppm by mass or less, more preferably 10 ppm by mass or less. On the other hand, when the ionic compound is an ionic liquid, from the viewpoint of being advantageous in reducing viscosity, the alkali metal is preferably contained at a concentration of 1 ppb by mass or more, more preferably 10 ppb by mass or more, and even more preferably 100 ppb by mass or more. From the viewpoint of having a small ionic radius and being advantageous in diffusion, the alkali metal cation is preferably at least one selected from the group consisting of lithium cation, sodium cation, and potassium cation, and most preferably lithium cation.

[0040] Ionic compounds can be produced by the following ion exchange method or acid-base neutralization method. In the ion exchange method, an ionic compound can be easily produced by ion-exchanging an organic ammonium halide having an organic moiety having from 1 to 20 carbon atoms with an alkali metal salt of a fluorinated bissulfonylimide, followed by an extraction step. That is, the method for producing an ionic compound preferably includes a step of ion-exchanging an organic ammonium halide with an alkali metal salt of a fluorinated bissulfonylimide, and a step of extracting the ionic compound obtained by ion exchange. Compared to the neutralization method described below, the anion raw material for the ionic compound of this embodiment has excellent storage stability, so using the ion exchange method is a preferred embodiment. Specifically, the alkali metal salt of a fluorinated bissulfonylimide used in the ion exchange method is more stable than the acid of a fluorinated bissulfonylimide used in the neutralization method, so the ion exchange method is preferred from the perspective of excellent storage stability. Furthermore, the ion exchange method is preferred from the perspective of easily incorporating an alkali metal into the ionic compound, thereby easily reducing the viscosity of the ionic liquid.

[0041] Examples of halogen ions contained in the organic ammonium halide include fluorine ions, chlorine ions, bromine ions, and iodine ions. Of these, chlorine ions are preferred. As the organic ammonium halide, any of the organic ammonium halides listed in the organic ammonium column above can be used. Examples of alkali metal ions contained in the alkali metal salt of fluorinated bissulfonylimide include lithium ions, sodium ions, and potassium ions. Of these, lithium ions are preferred from the viewpoint of facilitating a reduction in the viscosity of the ionic liquid.

[0042] For example, an aqueous solution of lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) in an equimolar amount to the ammonium hydrochloride is slowly added dropwise to an aqueous solution of organic ammonium hydrochloride dissolved in pure water, followed by stirring at room temperature for a predetermined time (e.g., 2 or 24 hours). An extractant is then added, the solution is separated, and the extract phase is recovered. This extract phase is washed with ultrapure water and then vacuum dried to obtain an ionic liquid of organic ammonium TFSI with an organic moiety identical to that of the starting organic ammonium hydrochloride. Examples of extractants include chloroform and toluene, but chloroform is preferred due to its high vapor pressure and ease of removal.

[0043] In the acid-base neutralization method, the ionic compound can be easily produced by neutralizing an organic amine having an organic moiety having from 1 to 20 carbon atoms with the acid of a fluorinated bissulfonylimide. That is, the method for producing an ionic compound preferably includes a step of neutralizing an organic amine with the acid of a fluorinated bissulfonylimide. Here, the organic amine is preferably at least one organic amine selected from the group consisting of primary organic amines, secondary organic amines, and tertiary organic amines. Of these, a primary organic amine is more preferable. When the acid-base neutralization method is used, it is not necessary to use an alkali metal salt of a fluorinated bissulfonylimide as a raw material, and impurities derived from the alkali metal salt are less likely to be present in the hole transport layer. Therefore, using the acid-base neutralization method is a preferred embodiment. Here, impurities derived from the alkali metal salt include, for example, alkali metal ions.

[0044] In the acid-base neutralization method, a solvent can be added to the acid and / or base to be reacted. Adding a solvent is preferred from the viewpoint of increasing the heat capacity and reducing the temperature rise of the reaction product of the acid and base due to the heat generated by neutralization. That is, the method for producing an ionic compound preferably includes a step of neutralizing an organic amine and an acid of a fluorinated bissulfonylimide in the presence of a solvent. Furthermore, it is preferred that this solvent be an azeotrope with water, as this is advantageous for removing moisture contaminated from the raw materials or the humidity of the atmosphere. From these viewpoints, alcohols and ethers are preferred as solvents, and more specifically, ethanol, toluene, chloroform, and chlorobenzene are preferred, with ethanol being most preferred from the viewpoint of excellent affinity with the raw materials and the product. As described above, the method for producing an ionic compound preferably includes a solvent removal step.

[0045] The primary organic amine is represented by the following formula (1-1), the secondary organic amine is represented by the following formula (5-1), and the tertiary organic amine is represented by the following formula (6-1). As the organic moiety, the organic moiety described in the organic ammonium cation column can be used. RNH ２ (1-1) (In formula (1-1), R is an organic moiety having 1 to 20 carbon atoms.) R ２ NH (5-1) (In formula (5-1), each R is independently an organic moiety having 1 to 20 carbon atoms.) ３ N (6-1) (In formula (6-1), each R is independently an organic moiety having 1 to 20 carbon atoms.)

[0046] The acid of the fluorine-containing bissulfonylimide is represented by the following formula (2-1): RfSO ２ NHSO ２ Rf (2-1) (In formula (2-1), each Rf is independently fluorine or a fluorine-containing alkyl group having 1 to 10 carbon atoms.)

[0047] For example, examples of fluorine-containing bissulfonylimide acids include those having a perfluoroalkyl group, such as protonated bis(fluorosulfonyl)imide (H-FSI), protonated bis(trifluoromethanesulfonyl)imide (H-TFSI), protonated bis(pentafluoroethanesulfonyl)imide (H-PFSI), and protonated bis(nonafluorobutanesulfonyl)imide (H-NFSI).

[0048] An example of the acid-base neutralization method is shown below. For example, an aqueous solution of protonated bis(trifluoromethanesulfonyl)imide (H-TFSI), prepared by dissolving an equimolar amount of the organic amine in ethanol, is slowly added dropwise to a solution of an organic amine mixed in a solvent such as ethanol, and the mixture is stirred at room temperature for a predetermined time (e.g., 30 minutes or 2 hours) to obtain a product (neutralization step). The solution is then vacuum dried at a predetermined temperature (e.g., 60°C) for a predetermined time (e.g., 2 hours) to remove the solvent, thereby obtaining an ionic liquid of organic ammonium TFSI having the same organic moiety as the organic moiety of the starting organic amine. Solvent removal is preferably achieved by subjecting the product to conditions of reduced pressure (e.g., 10 Pa or less) below atmospheric pressure at a temperature of 30°C to 120°C, since this allows for efficient solvent removal without decomposing the ionic compound. That is, the solvent removal step preferably includes a step of subjecting the product produced in the neutralization step to conditions of reduced pressure (e.g., 10 Pa or less) below atmospheric pressure. Examples of the solvent include ethanol and butanol, but it is preferable to use ethanol because it is easy to remove the solvent.

[0049] Furthermore, the ionic compound of this embodiment has excellent reactivity of the molecular cations and / or molecular anions constituting it, making it applicable to a variety of uses, such as electrical materials, reagents, solvents for organic synthesis, and gas absorbents. As electrical materials, the compound is suitable for, for example, solar cell materials, photosensors, light-emitting materials, and lithium-ion secondary batteries. Because of its excellent electrical properties, it is particularly suitable as a battery material. For example, when used as a dopant for the hole transport material in organic EL panels or perovskite solar cells, it facilitates the movement of holes, resulting in high photoelectric conversion efficiency. In particular, when used as a dopant for the hole transport material contained in a hole transport layer laminated with a perovskite layer, it imparts hydrophobicity, i.e., high water resistance, to the perovskite layer, making it suitable for use in devices having a perovskite layer other than solar cells.

[0050] (Hole Transport Material) The hole transport material referred to here is a semiconductor in which the effective mass of holes is smaller than that of electrons, and is a material that is advantageous for transporting holes. Examples of hole transport materials include compounds that serve as raw materials for organic or inorganic substances. However, from the viewpoint that the material is flexible and therefore less likely to form defects in the film due to bending, the hole transport material preferably contains an organic substance. Specific examples of organic substances include aggregates of organic molecules and organic polymers. As described above, from the viewpoint of improving the adhesion of the hole transport layer to the perovskite layer, the organic substance preferably contains an aromatic compound. Furthermore, the hole transport material includes a reaction product of a raw material compound for the hole transport material and the ionic compound of the present disclosure, as described below. More specifically, the raw material compounds include 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), N,N-bis(3-methylphenyl)-N,N-diphenylbenzidine (TPD), N, Examples of the pyridine compound include N-di[(1-naphthyl)-N,N-diphenyl]-(1,1-biphenyl)-4,4-diamine (NPD), tris(4-carbazoyl-9-ylphenyl)amine (TCTA), poly(9-vinylcarbazole) (PVK), 4,4-bis(N-carbazolyl)-1,1-biphenyl (CBP), and pyridine compounds such as 4-tert-butylpyridine, and these compounds may be used alone or in combination of two or more. The pyridine compound refers to a compound containing a pyridine ring structure in its molecular structure. In particular, from the viewpoints of having a relatively deep HOMO level, being able to increase carrier density and be advantageous for hole transport, being able to further increase the adhesion of the hole transport layer to the perovskite layer, and being able to increase the electromotive force, at least one selected from the group consisting of Spiro-OMeTAD, PTAA, TPD, and PVK is preferred, and at least one selected from the group consisting of Spiro-OMeTAD and PTAA is more preferred. From the viewpoints of being able to interact particularly effectively with ionic compounds and being able to improve the performance of perovskite solar cells, Spiro-OMeTAD is more preferred.Furthermore, from the viewpoint of improving the heat resistance of the solar cell, 4-tert-butylpyridine is preferred.

[0051] From the viewpoint of improving the short-circuit current density, open circuit voltage, fill factor, and conversion efficiency of the cell, it is preferable that the hole transport material does not contain alkali metal ions. In order to prevent the hole transport material from containing alkali metal ions, for example, the acid-base neutralization method described above can be used.

[0052] (Use as a dopant for hole transport material) The hole transport material is formed on a substrate by a film formation method appropriate for the raw material compound, and the substrate can be appropriately selected depending on the type of electrical material and the purpose of forming a hole transport layer thereon. For example, when used as a hole transport layer for a perovskite solar cell, the substrate is a perovskite or an electrode. The doping treatment is performed by mixing an ionic compound with a raw material compound for the hole transport material. In this doping treatment, the ionic compound and the raw material compound for the hole transport material may be mixed in a solvent. For example, a dopant (ionic compound) may be dissolved in a solution in which a raw material compound for the hole transport material has been dissolved. Note that not only one type of ionic compound but also two or more types of ionic compounds may be used as the dopant.

[0053] By using the ionic compound of this embodiment as a dopant for the hole transport material, organic ammonium cations, which are highly reactive cations derived from the ionic compound, diffuse to the surface of the perovskite layer and react spontaneously. This reduces defects on the perovskite surface and / or improves the electrical junction interface with the hole transport material, thereby improving solar cell characteristics such as open circuit voltage. In addition, the reaction of the organic ammonium cations with the surface of the perovskite layer is facilitated by the NH ３ ＋This is thought to occur when cationic moieties such as ammonium cations orient toward the surface of the perovskite layer. As a result, the organic moieties in the ammonium cations orient toward the surface opposite the perovskite layer, i.e., toward the hole transport layer, at the interface between the hole transport layer and the perovskite layer. This orientation of the organic moieties makes it possible to hydrophobize the surface of the perovskite layer facing the hole transport layer. A hydrophobized surface is preferable because it improves water resistance and moisture resistance and provides long-life solar cell properties.

[0054] That is, in a perovskite solar cell including a perovskite layer and a hole transport layer on the perovskite, when the hole transport layer is removed and the water contact angle of the exposed perovskite layer is measured, the water contact angle is preferably 55.0° or more, more preferably 65.0° or more, and even more preferably 75.0° or more. There is no particular upper limit, but preferred examples include 55.0 to 110°, 65.0 to 100°, and 75.0 to 100°. The method for measuring the water contact angle will be described later. The water contact angle can be changed by adjusting the number of carbon atoms in the organic moiety.

[0055] Furthermore, as described above, the molecular anion containing a fluorine-containing bis(sulfonylimide) can improve the hole mobility in the hole transport material. In particular, the combination of these molecular cations and molecular anions is thought to favorably improve solar cell performance due to the concerted effects of either or both of the strong ionicity of the anion and the fact that the organic ammonium cation reacts with the perovskite, making the anion's negative charge independent and allowing electrons to be extracted from the hole transport material more effectively than when a cation is present. Therefore, the hole transport material can achieve high photoelectric conversion efficiency accompanied by a large open circuit voltage, thereby improving the electrical properties of the hole transport material. In particular, using an ionic liquid as a dopant has the following advantages.

[0056] For example, when a compound with a high melting point, such as Li-TFSI (melting point 232°C), is used as the dopant, high temperature conditions may be required when preparing a precursor solution for the hole transport material (film), or it may take time to dissolve the solid in the solvent. Furthermore, accurate weighing of the solid may be difficult due to factors such as static electricity. On the other hand, because ionic liquids have low melting points, they can be prepared as precursor solutions simply by mixing them with a solvent at room temperature or even under weak heating conditions below the boiling point of the solvent. This simplifies the precursor solution preparation process and is therefore preferable. For example, ionic liquids with a melting point below 35°C, preferably 25°C or below, are even more preferable because they remain liquid even at room temperature, allowing the precursor solution to be prepared under mild conditions. Examples of such ionic liquids include ionic liquids composed of TFSI and an organic ammonium cation having an alkyl group with a carbon number of, for example, 2 to 12, 4 to 20, or 4 to 12. Specific examples include n-butylammonium TFSI (melting point 23°C), n-octylammonium TFSI (melting point below -70°C), n-dodecanammonium TFSI (melting point below 10°C), n-octylammonium FSI (melting point below 0°C), n-methyl-n-octylammonium TFSI (melting point 1°C), n,n-dimethyl-n-octylammonium TFSI (melting point -35°C), n-octylammonium FSI (melting point -24°C), and n-octylammonium PFSI (melting point 7°C).

[0057] (Perovskite solar cell) The doped hole transport material produced by the above method can be used as a material for the hole transport layer of organic EL panels, perovskite solar cells, and the like. For example, an example of its use as a material for the hole transport layer of a perovskite solar cell is shown below. FIG. 1 is a schematic diagram showing an example of the basic configuration of a perovskite solar cell 1. The perovskite solar cell 1 has an electron transport layer 5, a perovskite layer 7, and a hole transport layer 9 formed in this order between a conductive substrate 3 and an electrode 11, which is an electrode (positive electrode). In addition, an electrode (negative electrode) 11 is formed on the conductive substrate 3. That is, the perovskite solar cell 1 preferably includes a perovskite layer 7 and a hole transport layer 9 on the perovskite layer 7, and more preferably includes a conductive substrate 3, an electron transport layer 5 and an electrode 11 on the conductive substrate 3, a perovskite layer 7 on the electron transport layer 5, a hole transport layer 9 on the perovskite layer 7, and an electrode 11 on the hole transport layer. In the perovskite solar cell 1, light incident from below is absorbed by the perovskite layer 7, generating electrons and holes. The electrons and holes move to the electron transport layer 5 and the hole transport layer 9, respectively, generating photovoltaic power between the two electrodes and generating a current. Note that the conductive substrate 3 can also be made transparent, in which case electricity can be generated by irradiating light from above.

[0058] (Conductive Substrate) The conductive substrate 3 is a substrate made of a conductive material. Examples of conductive materials include metals such as platinum and gold, carbon, and conductive metal oxides such as fluorine-doped tin oxide (FTO) and indium tin oxide (ITO). Among these, FTO and ITO are preferred because of their transparency. Although not shown, a transparent support substrate such as a glass substrate or plastic substrate may be present below the conductive substrate 3. The thickness of the conductive substrate 3 is not particularly limited, but is preferably approximately 100 nm to 1000 nm. The conductive substrate 3 can be obtained, for example, by forming a conductive material into a flat plate. If a support substrate is present, the conductive substrate 3 can be obtained by stacking the conductive material on top of the support substrate.

[0059] (Electron Transport Layer) Then, an electron transport layer 5 is formed on the conductive substrate 3. The electron transport layer 5 contains an electron transport material. The electron transport material of the electron transport layer 5 may contain an organic or inorganic material, but it is preferable that the electron transport material contains an inorganic material because of its high strength. Furthermore, from the viewpoint of relatively easy adjustment of physical properties, the inorganic material is more preferably a metal compound. Furthermore, from the viewpoint of relatively easy production and storage in the atmosphere, it is even more preferable that the inorganic material is a metal oxide. That is, the electron transport layer is preferably a metal oxide layer. Specific examples of metal oxides include, but are not limited to, titanium oxide (TiO ２ ), zinc oxide (ZnO), niobium oxide (Nb ２ O ５ etc.), tungsten oxide (WO ２ , W.O. ３ , W ２ O ３ etc.), tin oxide (SnO ２ ), aluminum oxide (Al ２ O ３ ), silicon oxide (SiO ２ ), magnesium oxide (MgO), zirconium oxide (ZrO ２) are examples. Titanium oxide and niobium oxide are preferred from the viewpoint of small effective electron mass. Titanium oxide is particularly preferred from the viewpoint of abundant and inexpensive material. The thickness of the electron transport layer 5 is preferably approximately 10 to 1,000 nm, for example, from the viewpoint of being able to collect electrons more effectively from the overlying perovskite layer 7. The electron transport layer 5 can be obtained using a known film formation method depending on the material to be formed. For example, when tin oxide is used, the layer can be prepared by applying a colloidal solution of tin oxide to the conductive substrate 3, heating (e.g., 100 to 150°C), and drying. Titanium oxide can also be prepared by applying an alcohol solution of titanium oxide paste (e.g., an ethanol solution or an isopropanol solution). Aluminum oxide, zirconium oxide, niobium oxide, etc. can also be applied in a paste form. Known or commercially available tin oxide colloidal solutions and titanium oxide pastes can be used. Note that, from the viewpoint of reducing defects such as pinholes in the electron transport material, the electron transport material may be subjected to a process of adsorbing and reacting a precursor material of the electron transport material. Specifically, in the case of titanium oxide, titanium chloride species are adsorbed onto an electron transport material such as titanium oxide, and then hydrolyzed to bind the titanium oxide (TiCl ４ It is preferable to carry out a treatment.

[0060] (Perovskite Layer) A perovskite layer 7 functioning as a photoelectric conversion layer is formed on the electron transport layer 5. The perovskite layer 7 generates electrons and holes (positive holes) upon irradiation with light. The perovskite layer is a compound represented by the general formula ABX ３ (where A is an organic molecular cation (NH ３ or potassium, cesium, or rubidium, B is a metal atom, and X is a halogen atom), and perovskite complexes such as APbX ３ , ASnX ３ More specifically, CH ３ NH ３ PbI ３ , (CHN ２ H ４ ) PbI ３ , CsPbX ３ , RbPbX３ and a combination of multiple types of A. The film thickness of the perovskite layer 7 is preferably, for example, 100 to 600 nm from the viewpoint of the balance between light absorption efficiency and exciton diffusion length, and the absorption efficiency of light transmitted through the conductive substrate 3. The perovskite layer 7 can be produced by dissolving the components forming the perovskite layer 7 in a solvent, applying the solution to the electron transport layer 5, and drying the solution. Preferred solvents include esters such as γ-butyl lactone, methyl formate, and ethyl acetate; ketones such as acetone and dimethyl ketones; ethers such as diethyl ether and diisopropyl ether; alcohols such as methanol and ethanol; halogenated hydrocarbons such as ethylene chloride and chloroform; nitrile solvents such as acetonitrile and propionitrile; N,N-dimethylformamide, dimethyl sulfoxide, and the like. Among these, at least one selected from the group consisting of N,N-dimethylformamide and dimethyl sulfoxide is preferred. The perovskite layer 7 may be formed by applying a precursor of the perovskite layer 7 and then applying a poor solvent such as chlorobenzene or toluene.

[0061] (Hole Transport Layer) A hole transport layer 9 is formed on the perovskite layer 7. The hole transport layer 9 can be made using the hole transport material described above. That is, the hole transport layer 9 preferably contains the hole transport material of the present disclosure. The hole transport layer 9 can be produced by applying a solution in which a material for the hole transport layer 9, such as a hole transport material, is dissolved onto the perovskite layer 7 and drying the solution. The thickness of the layer is preferably approximately 10 to 1,000 nm. A thickness of approximately 50 to 500 nm is more preferable because a thickness sufficient to prevent pinholes from being formed and low resistance is desirable. The amount of dopant (ionic compound) is preferably an amount sufficient to sufficiently oxidize the hole transport material but not excessively oxidize it. For example, a concentration of 3 mM to 80 mM relative to the total solution is preferable. From the above viewpoint, the concentration of the dopant is preferably 4 mol % to 111 mol % relative to the hole transport material.

[0062] The average adhesion strength of the hole transport layer to the perovskite layer is 1.0 N cm －１Within this range, the adhesion between the hole transport layer and the perovskite layer is likely to be improved, and the durability of the perovskite solar cell is likely to be improved. The upper limit is not particularly limited, but may be, for example, 1.0 N cm －１ 10.0N・cm or more －１ Below, 1.0N・cm －１ 5.0N・cm or more －１ Below, 1.0N・cm －１ 2.0N・cm or more －１ The following can be mentioned. As mentioned above, the average adhesion can be adjusted by changing, for example, the structure of the organic ammonium or the material contained in the hole transport layer. The method for measuring the average adhesion will be described later; the measurement is carried out using a Tensilon UCT-5T model (manufactured by Orientec Co., Ltd.) and Kapton tape at a crosshead speed of 100 mm / min. The average adhesion is the arithmetic mean value of the adhesion per tape width within a crosshead length range of 10 to 50 mm.

[0063] Between the hole transport layer 9 and the perovskite layer 7, a treatment step (e.g., a step of applying a solution containing n-octylammonium iodide salt and then drying) may be required at the interface to stabilize the surface of the perovskite layer 7. However, according to this embodiment, such a treatment step is not required, and the interface condition between the perovskite and the hole transport material can be improved, which is industrially significantly advantageous. Therefore, perovskite solar cells can be manufactured by a simple method with a few steps. Furthermore, as described above, the organic ammonium cation in the hole transport layer reacts with the surface of the perovskite layer. In other words, the hole transport layer preferably contains a reaction product between the organic ammonium cation and the perovskite layer.

[0064] (Electrode) Finally, an electrode 11 is formed on each of the transparent conductive substrate 3 and the hole transport layer 9, thereby producing the solar cell 1 (solar cell element). The electrode 11 is formed of, for example, gold (Au). Alternatively, metal materials such as silver, copper, aluminum, and nickel may be used. The electrode 11 can be formed by known methods such as vapor deposition, sputtering, spraying, spin coating, and dip coating.

[0065] (Method for manufacturing perovskite solar cell) As described above, the method for manufacturing a perovskite solar cell according to the present disclosure is a method for manufacturing a perovskite solar cell in which an electron transport layer, a perovskite layer, and a hole transport layer are stacked between a conductive substrate and an electrode. The method for manufacturing a perovskite solar cell also includes a step of forming a hole transport layer. The step of forming the hole transport layer further includes a step of forming a film on the perovskite layer using the hole transport material of the present disclosure. The method for manufacturing a perovskite solar cell preferably also includes a step of preparing a conductive substrate, a step of forming an electron transport layer on the conductive substrate, a step of forming a perovskite layer on the electron transport layer, a step of forming a hole transport layer on the perovskite layer, and a step of forming electrodes on the conductive substrate and the hole transport layer.

[0066] The present embodiment will be described in more detail below with reference to specific examples and comparative examples, but the present embodiment is not limited to these examples and comparative examples as long as the gist of the present embodiment is not exceeded. The physical properties, reaction conditions, and product identification in the examples and comparative examples described below were measured and set by the methods shown below.

[0067] (Evaluation of solar cell characteristics) The solar cell characteristics of the cells prepared by the following method were evaluated using the following apparatus and evaluation method. [Apparatus] (Simulated sunlight) Simulated sunlight was generated using a solar simulator (manufactured by Seric) with a photodiode irradiated with an amount of 100 mW / cm. ２ The irradiation area of ​​the irradiation cell was adjusted to 0.119 cm for each cell. ２ (DC Power Source) The voltage application to the cell, the evaluation of the photocurrent value, and the sweep of the applied voltage were performed using a DC voltage / current generator (manufactured by ADVANTEST Co., Ltd., product number R6243), and the voltage was swept from the high potential side to the low potential side or from the low potential side to the high potential side.

[0068] [Evaluation Method] (Short-Circuit Current Density) The short-circuit current was determined from the photocurrent density that flowed when the prepared cell was irradiated with the above-mentioned simulated sunlight without applying a voltage to the cell.

[0069] (Open Circuit Voltage) The open circuit voltage was determined from the voltage applied to the cell at which the current value became zero when the cell was irradiated with the pseudo solar light.

[0070] (Fill Factor) The fill factor (hereinafter also referred to as "F.F.") was calculated from the following formula (3), which was obtained by dividing the value at which the power was maximized (maximum actual power value) by the product of the short-circuit current density and the open-circuit voltage when the applied voltage was swept while irradiating the simulated solar light: (F.F.)=(maximum actual power value) / ((short-circuit current density)×(open-circuit voltage)) (3)

[0071] (Solar Energy Conversion Efficiency) The solar energy conversion efficiency (hereinafter also referred to as conversion efficiency) was calculated from the following formula (4): (Conversion efficiency) = (Maximum actual power (mW cm －２ )) / 100mWcm －２ (4)

[0072] [Contact angle of water] The contact angle of water was determined by dropping 1 mL of distilled water onto the sample and measuring the contact angle between the sample and the water droplet after 2 seconds using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product number DMo-401). The method for preparing the sample will be described later.

[0073] Example 1 (Fabrication of Perovskite Solar Cell) Glass (manufactured by Nippon Sheet Glass Co., Ltd.) on which FTO (fluorine-doped tin oxide) was deposited was used as a conductive substrate, and a 50 nm thick TiO 3 film was deposited on the FTO surface as an electron transport material. ２ A dense layer of TiO with a particle diameter of 15 nm and a thickness of 200 nm was formed on the dense layer by spray pyrolysis. ２ A particle layer was deposited by spin coating to form an electron transport layer. On top of this, 1.8 mM formamidium lead iodide (FAPbI; FAI and PbI, manufactured by Tokyo Chemical Industry Co., Ltd.) was deposited. ２A single crystal of FTO (synthesized by recrystallization from FTO) was dissolved in a 4:1 volume ratio of N,N-dimethylformamide (manufactured by Aldrich) and dimethyl sulfoxide (manufactured by Aldrich), and the solution was spin-coated at 6000 rpm for 50 seconds. 10 seconds after the start of spin-coating, 1 mL of chlorobenzene (manufactured by Aldrich) was added dropwise. After this spin-coating, the sample was heated at 100°C for 10 minutes to form a thin film of a perovskite layer. A hole transport layer precursor solution containing the ionic compound as a dopant and based on Spiro-OMeTAD, as specified below, was spin-coated onto this thin film at 3000 rpm for 30 seconds to form a hole transport material, forming a hole transport layer. The preparation method for the hole transport layer precursor solution is described below. Finally, electrodes were fabricated by vacuum deposition of 200 nm of gold (manufactured by Nilaco Corporation) on the FTO and hole transport layer, respectively.

[0074] The ionic compound used as a dopant was prepared by the following method (ion exchange method). Under a nitrogen stream, 5.23 g (32 mmol) of octylamine hydrochloride (Tokyo Chemical Industry Co., Ltd.) was weighed into a 200 mL two-neck flask and dissolved in 50 mL of pure water. 50 mL of an aqueous solution containing 9.06 g (32 mmol) of lithium bis(trifluoromethanesulfonyl)imide (Tokyo Chemical Industry Co., Ltd.) was added to this solution and stirred at room temperature for 24 hours. After 24 hours, a chloroform solution (Kishida Chemical Industry Co., Ltd.) was added, and the solution was separated. The chloroform layer was washed twice with ultrapure water. The chloroform solution was then evaporated at 40 °C using an evaporator, followed by vacuum drying at room temperature to obtain an ionic liquid of n-octylammonium TFSI. n-Octylammonium TFSI was identified by H-NMR (Figure 2) and F-NMR (Figure 3) using deuterated chloroform. H-NMR and F-NMR were measured using a nuclear magnetic resonance spectrometer (Bruker, model number AVANCE400). A measurement sample was prepared by mixing 5 mg of the ionic liquid sample with 1 mL of deuterated chloroform. The melting point was determined by sweeping the temperature from 25°C to -70°C using a differential scanning calorimeter (Hitachi High-Tech Science Corporation, model number DSC7020). Since no change in calorific value attributable to the freezing point was observed, the melting point was confirmed to be less than -70°C. The amount of lithium contained in this ionic liquid was evaluated using a high-frequency inductively coupled plasma analyzer (Agilent, ICP-OES710). The result was 2.8 ppm by mass.

[0075] The hole transport layer precursor solution was prepared as follows: 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 12 mM of the above-obtained n-octylammonium TFSI, and 34 mM of t-butylpyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) were dissolved in chlorobenzene to prepare the hole transport layer precursor solution.

[0076] The solar cell characteristics were evaluated by irradiating the cell obtained above with simulated sunlight from the FTO glass side. The evaluation results are shown in Table 1. Fifteen perovskite solar cells were fabricated using the same process, and Table 1 shows their arithmetic mean values. Table 1 also shows these arithmetic mean values ​​together with errors calculated from the standard deviation. In the following examples and comparative examples, unless otherwise noted, the same methods and conditions as in Example 1 were used, and the same reagents were used for common compounds. Furthermore, unless otherwise noted, the same devices and conditions were used for measurements as in Example 1.

[0077] Example 2: TiO ２ A perovskite solar cell was fabricated using the same method and conditions as in Example 1, except that the average particle diameter of the particle layer was 30 nm, the ionic compound was prepared by the method described below, and the hole transport layer precursor solution was a solution of 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 24 mM n-octylammonium TFSI prepared by the method described below, and 102 mM t-butylpyridine dissolved in chlorobenzene. The ionic compound used as the dopant was prepared by the following method (acid-base neutralization method). Ethanol (93 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 13.06 g, 46.4 mmol) was added to the flask to prepare a homogeneous solution. Then, octylamine (manufactured by Tokyo Chemical Industry Co., Ltd., 6.03 g, 46.6 mmol) in ethanol (93 mL) was added dropwise using a funnel. After the entire content was added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then stirred for 2 hours while immersed in an ice bath. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure at 40°C, 50°C, and 60°C for 2 hours each to obtain a liquid ionic compound (n-octylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 4. 1H-NMR was measured using a nuclear magnetic resonance spectrometer (JEOL Ltd., model number JNM-ECZ400S / L1) on a solution of this ionic compound mixed with deuterated chloroform solvent. In the following Examples 3-6, 1H-NMR was measured using the same apparatus and under the same conditions as in Example 2.

[0078] Example 3: A perovskite solar cell was fabricated using the same method and conditions as in Example 2, except that an ionic compound was prepared using the following method, and a hole transport layer precursor solution was prepared by dissolving 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 48 mM n-dodecylammonium TFSI prepared using the following method, and 204 mM t-butylpyridine in chlorobenzene. The ionic compound used as a dopant was prepared using the following method (acid-base neutralization method). Ethanol (75 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 10.61 g, 37.7 mmol) was added to the flask to prepare a homogeneous solution. Then, dodecylamine (manufactured by Tokyo Chemical Industry Co., Ltd., 7.02 g, 37.7 mmol) in ethanol (75 mL) was added dropwise using a funnel. After the entire amount had been added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then stirred for 2 hours while immersed in an ice bath. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure for 2 hours at 40°C, 60°C, and 80°C, yielding a liquid ionic compound (n-dodecylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 5.

[0079] Example 4 A perovskite solar cell was fabricated using the same method and conditions as in Example 3, except that an ionic compound was prepared using the following method, and a hole transport layer precursor solution was used, in which 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 18 mM n-butylammonium TFSI prepared using the following method, and 77 mM t-butylpyridine were dissolved in chlorobenzene. The ionic compound used as a dopant was prepared using the following method (acid-base neutralization method). Ethanol (110 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 15.38 g, 54.7 mmol) was added to the flask to prepare a homogeneous solution. Then, butylamine (manufactured by Tokyo Chemical Industry Co., Ltd., 4.03 g, 54.7 mmol) in ethanol (110 mL) was added dropwise using a funnel. After the entire amount had been added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then stirred for 2 hours while immersed in an ice bath. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure for 2 hours at 40°C, 60°C, and 80°C, yielding a liquid ionic compound (n-butylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 6.

[0080] Example 5 A perovskite solar cell was fabricated using the same method and conditions as in Example 2, except that an ionic compound was prepared by the following method, and a hole transport layer precursor solution was used, in which 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 18 mM ethylammonium TFSI prepared by the following method, and 77 mM t-butylpyridine were dissolved in chlorobenzene. The ionic compound used as a dopant was prepared by the following method (acid-base neutralization method). Ethanol (102 mL) was added to a 500 mL four-neck flask, and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 14.37 g, 51.1 mmol) was added to prepare a homogeneous solution. Thereafter, ethylamine (Tokyo Chemical Industry Co., Ltd., 34.3 mass% ethylamine / ethanol solution (6.72 g, 51.1 mmol) / ethanol (96 mL) was added dropwise using a funnel. The entire amount was added dropwise over 30 minutes, and then the inside of the funnel was washed with a small amount of ethanol. The mixture was stirred for 2 hours while the flask was immersed in an ice bath. The reaction liquid was then transferred to an eggplant-shaped flask and concentrated under reduced pressure for 2 hours at temperatures of 40°C, 60°C, and 80°C, respectively, to obtain a solid ionic compound (ethylammonium TFSI). The 1H-NMR results of this ionic compound are shown in Figure 7. The melting point was found to be 45°C according to the results of measurement using a differential scanning calorimeter.

[0081] Example 6 A perovskite solar cell was fabricated using the same method and conditions as in Example 2, except that an ionic compound was prepared using the following method, and a hole transport layer precursor solution was prepared by dissolving 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 48 mM 2-phenylethylammonium TFSI prepared using the following method, and 204 mM t-butylpyridine in chlorobenzene. The ionic compound used as a dopant was prepared using the following method (acid-base neutralization method). Ethanol (83 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 11.6 g, 41.4 mmol) was added to the flask to prepare a homogeneous solution. Then, 2-phenylethylamine (5.02 g, 41.4 mmol) in ethanol (83 mL) was added dropwise using a funnel. After the entire amount had been added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then immersed in an ice bath and stirred for 2 hours. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure for 2 hours at 40°C, 60°C, and 80°C, yielding a solid ionic compound (2-phenylethylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 8. The melting point was determined to be 35°C using a differential scanning calorimeter.

[0082] Example 7 A perovskite solar cell was fabricated using the same method and conditions as in Example 2, except that an ionic compound was prepared using the following method, and a hole transport layer precursor solution was prepared by dissolving 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 48 mM n-methyl-n-octylammonium TFSI prepared using the following method, and 204 mM t-butylpyridine in chlorobenzene. The ionic compound used as a dopant was prepared using the following method (acid-base neutralization method). Ethanol (83 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 15.79 g, 56.2 mmol) was added to the flask to prepare a homogeneous solution. Then, n-methyl-n-octylamine (8.05 g, 56.2 mmol) / ethanol (100 mL) was added dropwise using a funnel. After the entire amount was added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then stirred for 2 hours while immersed in an ice bath. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure at 60°C for 12 hours to obtain a solid ionic compound (n-methyl-n-octylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 9. The melting point was 1°C as measured by a differential scanning calorimeter.

[0083] Example 8: A perovskite solar cell was fabricated using the same method and conditions as in Example 2, except that an ionic compound was prepared using the following method, and the hole transport layer precursor solution was a solution of 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 24 mM n-octylammonium FSI prepared using the following method, and 204 mM t-butylpyridine dissolved in chlorobenzene. The ionic compound used as the dopant was prepared using the following method (ion exchange method). Under a nitrogen stream, 6.63 g (40 mmol) of octylamine hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was weighed into a 200 mL two-neck flask and dissolved in 20 mL of pure water. To this solution, 20 mL of an aqueous solution of 7.48 g (40 mmol) of lithium bis(fluorosulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was stirred at room temperature for 2 hours. After 2 hours, a chloroform solution (Kishida Chemical Co., Ltd.) was added, and the layers were separated. The chloroform layer was washed twice with ultrapure water. The chloroform solution was then evaporated at 40°C using an evaporator, and the mixture was then vacuum dried at room temperature to obtain an ionic liquid of n-octylammonium FSI. The 1H-NMR results for this ionic compound are shown in Figure 10. The melting point was found to be -24°C using a differential scanning calorimeter. The lithium content was 6.7 ppm by mass.

[0084] Comparative Example 1 A perovskite solar cell was fabricated and evaluated in the same manner as in Example 1, except that a solution of 70 mM Spiro-OMeTAD dissolved in chlorobenzene was used as the hole transport material precursor solution.

[0085] Comparative Example 2 A perovskite solar cell was fabricated and evaluated in the same manner as in Example 1, except that a hole transport material precursor solution prepared by dissolving 70 mM Spiro-OMeTAD, 48 mM Li-TFSI (manufactured by Aldrich Chemical Co.), and 272 mM t-butylpyridine in chlorobenzene was used.

[0086] Comparative Example 3 A perovskite solar cell was fabricated and evaluated in the same manner as in Example 1, except that a hole transport material precursor solution prepared by dissolving 70 mM Spiro-OMeTAD, 34 mM methyltri-n-octylammonium TFSI, and 10 mM t-butylpyridine in chlorobenzene was used.

[0087] Comparative Example 4 A perovskite solar cell was fabricated and evaluated in the same manner as in Example 1, except that a hole transport material precursor solution prepared by dissolving 70 mM Spiro-OMeTAD, 24 mM 1-ethyl-3-methylimidazolium TFSI, and 64 mM t-butylpyridine in chlorobenzene was used. The evaluation results are shown in Tables 1 and 2.

[0088] According to the present example, as can be seen from the results in Tables 1 and 2, almost all of the short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency were higher than those of the comparative example, particularly in the open-circuit voltage and conversion efficiency, which are important performance factors of solar cells. In other words, an improvement in solar cell characteristics was observed. In particular, the effect on the open-circuit voltage was remarkable, which is thought to be due to the high reactivity of the organic ammonium cation that constitutes the ionic compound.

[0089] Example 9 A methylammonium lead iodide solution, prepared by dissolving 1.50 mM methylamine hydroiodide and 1.58 mM lead iodide in a 4:1 volume ratio of N,N-dimethylformamide (manufactured by Aldrich) and dimethyl sulfoxide (manufactured by Aldrich), was spin-coated at 6000 rpm for 10 seconds onto a substrate on which an electron transport layer had been deposited in the same manner as in Example 1. 4 seconds after the start of spin-coating, 0.2 mL of chlorobenzene (manufactured by Aldrich) was added dropwise. After this spin-coating, the sample was heated at 100°C for 10 minutes, and then heated at 110°C for 10 minutes to form a thin film of a perovskite layer. Next, 4.8 mM of methylammonium TFSI, synthesized by the method described below, was added as a dopant to a solution prepared by adding 14 mM 4-tertbutylpyridine to a 10 mg / mL PTAA-toluene solution. The solution was then deposited on the perovskite layer at 3,000 rpm. Au was then deposited in the same manner as in Example 1, completing a solar cell. The results are shown in Tables 3-1 and 3-2. The ionic compound used as the dopant was prepared by the following method (acid-base neutralization method). Ethanol (85 mL) was added to a 300 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (Tokyo Chemical Industry Co., Ltd., 12.0 g, 42.6 mmol) was added to the flask to prepare a homogeneous solution. Then, methylamine (16.5 mL, 42.6 mmol) / ethanol (85 mL) was added dropwise using a funnel. After the entire amount had been added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then immersed in an ice bath and stirred for 2 hours. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure at 40°C for 12 hours and then at 60°C for 2 hours, yielding a solid ionic compound (methylammonium TFSI). The 1H-NMR results for this ionic compound are shown in Figure 11. The melting point was found to be 43°C as measured by a differential scanning calorimeter.

[0090] Comparative Example 5 A perovskite solar cell was fabricated in the same manner as in Example 9, except that the ionic compound dopant was Li-TFSI. The results are shown in Tables 3-1 and 3-2.

[0091] According to this example, the results in Tables 3-1 and 3-2 show that almost all of the short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency were higher than those of the comparative examples, particularly the open-circuit voltage and conversion efficiency, which are important performance factors for solar cells. In other words, improvements in solar cell characteristics were observed. The effect was particularly significant in the open-circuit voltage, which is thought to be due to the high reactivity of the primary organic ammonium cation that constitutes the ionic compound. In particular, in Example 9, performance was improved by the methylammonium cation, which is the same as the cation that constitutes the perovskite material. Even if this cation diffuses into the bulk of the perovskite layer during continued use as a solar cell, it is found that there is little significant performance degradation and is also advantageous for improving durability.

[0092] Example 10 A perovskite solar cell was fabricated in the same manner as in Example 1, except for the following points: The perovskite layer of Example 1 was formed by spin-coating a cesium formamidium lead iodide solution obtained by dissolving 0.07 mM cesium iodide, 1.0 mM formamidine hydroiodide, and 1.15 mM lead iodide in a volume ratio of 4:1 between N,N-dimethylformamide (manufactured by Aldrich) and dimethyl sulfoxide (manufactured by Aldrich) at 6000 rpm for 30 seconds, and then dropping 0.5 mL of diethyl ether (manufactured by Wako Co., Ltd.) 10 seconds after the start of spin-coating. A perovskite solar cell was fabricated in the same manner as in Example 1, except that a hole transport material film was formed by spin coating the hole transport material solution, which was a toluene solution containing 10 mg / mL PTAA, 9.6 mM of n-octylammonium TFSI synthesized in Example 2, and 7 mM 4-tert-butylpyridine, on the perovskite layer at 3000 rpm for 3 seconds. The results are shown in Tables 4-1 and 4-2.

[0093] Example 11 A perovskite solar cell was fabricated in the same manner as in Example 10, except that the hole transport material solution in Example 10 was a toluene solution containing 10 mg / mL PTAA, 4.8 mM of the phenylethylammonium synthesized in Example 6, and 7 mM 4-tert-butylpyridine. The results are shown in Tables 4-1 and 4-2.

[0094] Comparative Example 6 A perovskite solar cell was fabricated in the same manner as in Example 10, except that the hole transport material solution in Example 10 was a toluene solution containing 10 mg / mL PTAA, 4.8 mM Li-TFSI, and 7 mM 4-tert-butylpyridine. The results are shown in Tables 4-1 and 4-2.

[0095] According to the results of Tables 4-1 and 4-2, this example achieved higher values ​​than the comparative examples in almost all of the short-circuit current density, open-circuit voltage, fill factor, and conversion efficiency, particularly in the open-circuit voltage and conversion efficiency, which are important performance factors for solar cells. That is, improvements in solar cell characteristics were observed. The effect was particularly remarkable in the open-circuit voltage, which is thought to be due to the high reactivity of the organic ammonium cation that constitutes the ionic compound. In particular, Example 11 was found to exhibit superior characteristics to Example 10, which is thought to be due to the improved adhesion between the hole transport material and the perovskite layer caused by the organic portion of the organic ammonium containing an aromatic group.

[0096] Examples 12 to 21 (Water Contact Angle) In Example 12, the perovskite layer of Example 1 and the hole transport layer of Example 1 were deposited on an alkali-free glass substrate in the same manner as in the preparation of the perovskite solar cell. The sample surface was then rinsed 40 times with 1 mL of chlorobenzene, and then dried with dry air to obtain a perovskite layer sample from which the hole transport layer had been removed. The water contact angle of this sample was measured. In Example 13, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was replaced with that of Example 3, and the water contact angle of the perovskite layer was measured. In Example 14, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was replaced with that of Example 4, and the water contact angle of the perovskite layer was measured. In Example 15, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was replaced with that of Example 5, and the water contact angle of the perovskite layer was measured. In Example 16, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was changed to that of Example 7, and the water contact angle of the perovskite layer was measured. In Example 17, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was changed to that of Example 8, and the water contact angle of the perovskite layer was measured. The results are shown in Table 5.

[0097] In Example 18, an ionic compound was prepared by the following method. A sample was prepared in the same manner as in Example 12, except that the hole transport layer precursor solution was a solution of 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 24 mM n-octylammonium PFSI prepared by the following method, and 204 mM t-butylpyridine dissolved in chlorobenzene. The water contact angle of the perovskite layer was measured. The results are shown in Table 5. The ionic compound used as a dopant was prepared by the following method (ion exchange method). Under a nitrogen stream, 3.31 g (20 mmol) of octylamine hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was weighed into a 200 mL two-neck flask and dissolved in 20 mL of pure water. To this solution, 20 mL of an aqueous solution of 7.74 g (20 mmol) of lithium bis(pentafluoroethanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was stirred at room temperature for 2 hours. After 2 hours, a chloroform solution (Kishida Chemical Co., Ltd.) was added, and the layers were separated. The chloroform layer was washed twice with ultrapure water. The chloroform solution was then evaporated at 40°C using an evaporator, and the mixture was then vacuum dried at room temperature to obtain an ionic liquid of n-octylammonium PFSI. The 1H-NMR results for this ionic compound are shown in Figure 12. The melting point was 7°C as measured by a differential scanning calorimeter. The lithium content was less than 0.2 ppm by mass.

[0098] In Example 19, an ionic compound was prepared by the following method, and a sample was prepared in the same manner as in Example 12, except that the hole transport layer precursor solution was a solution of 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 24 mM n-octylammonium NFSI prepared by the following method, and 204 mM t-butylpyridine dissolved in chlorobenzene. The water contact angle of the perovskite layer was then measured. The results are shown in Table 5. The ionic compound used as a dopant was prepared by the following method (ion exchange method). Under a nitrogen stream, 3.31 g (20 mmol) of octylamine hydrochloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was weighed into a 200 mL two-neck flask and dissolved in 20 mL of pure water. To this solution, 20 mL of an aqueous solution of 11.74 g (20 mmol) of lithium bis(nonafluorobutanesulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was stirred at room temperature for 2 hours. After 2 hours, a chloroform solution (Kishida Chemical Co., Ltd.) was added, and the layers were separated. The chloroform layer was washed twice with ultrapure water. The chloroform solution was then evaporated at 40°C using an evaporator, and the mixture was then vacuum dried at room temperature to obtain an ionic liquid of n-octylammonium NFSI. The 1H-NMR results for this ionic compound are shown in Figure 13. The melting point was 141°C, as measured using a differential scanning calorimeter. The lithium content was 0.79 ppm by mass.

[0099] In Example 20, an ionic compound was prepared by the following method, and a sample was prepared in the same manner as in Example 12, except that the hole transport layer precursor solution was a solution of 70 mM Spiro-OMeTAD (manufactured by Nippon Fine Chemicals Co., Ltd.), 24 mM n,n-dimethyl-n-octylammonium TFSI prepared by the following method, and 204 mM t-butylpyridine dissolved in chlorobenzene. The water contact angle of the perovskite layer was measured. The results are shown in Table 5. The ionic compound used as a dopant was prepared by the following method (acid-base neutralization method). Ethanol (83 mL) was added to a 500 mL four-neck flask and the flask was immersed in an ice bath. H-TFSI (manufactured by Tokyo Chemical Industry Co., Ltd., 14.30 g, 50.9 mmol) was added to the flask to prepare a homogeneous solution. Then, n,n-dimethyl-n-octylamine (8.00 g, 50.9 mmol) in ethanol (100 mL) was added dropwise using a funnel. After the entire amount was added dropwise over 30 minutes, the funnel was rinsed with a small amount of ethanol. The flask was then stirred for 2 hours while immersed in an ice bath. The reaction mixture was then transferred to a recovery flask and concentrated under reduced pressure at 60°C for 12 hours to obtain the ionic liquid n,n-dimethyl-n-octylammonium TFSI. The 1H-NMR results for this ionic compound are shown in Figure 14. The melting point was determined to be -35°C using a differential scanning calorimeter.

[0100] In Example 21, the perovskite layer of Example 11 and the hole transport layer of Example 11 were deposited on an alkali-free glass substrate in the same manner as in the fabrication of the perovskite solar cell. The hole transport layer was then removed by peeling it off with tape, and the water contact angle of the perovskite layer was evaluated in the same manner as in Example 12. The results are shown in Table 5.

[0101] (Comparative Examples 7 to 9) In Comparative Example 7, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was changed to that of Comparative Example 2, and the water contact angle of the perovskite layer was measured. In Comparative Example 8, a sample was prepared in the same manner as in Example 12, except that the hole transport layer was changed to that of Comparative Example 4, and the water contact angle of the perovskite layer was measured. In Comparative Example 9, a sample was prepared in the same manner as in Example 12, except that the hole transport material was changed to that of Comparative Example 6, and the water contact angle of the perovskite layer was measured. The results are shown in Table 5.

[0102] The larger the water contact angle value, the more hydrophobic the material and the higher its water resistance. The results in Table 5 show that the dopant of this example exhibited higher water resistance than the comparative example. It was shown that adding an ionic compound to the hole transport material precursor solution can suitably hydrophobize the surface of the perovskite layer, i.e., impart water resistance. Therefore, weather resistance, moisture resistance, etc. are improved, and the product can be used in a wide range of applications, such as solar cells and optical sensors.

[0103] Examples 22 to 25 In Example 22, the remaining solar cell performance after a 500-hour durability test was conducted on the perovskite solar cell fabricated in Example 1 under conditions of a temperature of 30°C and humidity of 50% was examined. The remaining capacity was calculated by dividing the solar cell's ...

[0104] Comparative Example 10 The same test as in Example 22 was carried out on the perovskite solar cell fabricated in Comparative Example 2. The results are shown in Table 6.

[0105] Examples 26 to 28 In Example 26, the perovskite solar cell produced in Example 1 was subjected to a durability test for 1000 hours under conditions of a temperature of 30°C and a humidity of 50%, after which the remaining solar cell performance was examined, and the remaining solar cell performance was calculated in the same manner as in Example 22. In Example 27, a solar cell was produced in the same manner as in Example 3, and sample evaluation after the durability test was carried out in the same manner as in Example 26. In Example 28, a solar cell was produced in the same manner as in Example 11, and sample evaluation after the durability test was carried out in the same manner as in Example 26. Table 7 shows the evaluation results.

[0106] (Comparative Examples 11 and 12) In Comparative Example 11, the same test as in Example 26 was carried out on the perovskite solar cell produced in Comparative Example 2. In Comparative Example 12, the same test as in Example 26 was carried out on the perovskite solar cell produced in Comparative Example 6. The results are shown in Table 7.

[0107] The results in Tables 6 and 7 indicate that solar cells using the dopants of this example exhibited higher residual solar cell performance than those in the comparative examples. Furthermore, those using n-dodecylammonium (C12), which has a higher carbon number than n-octylammonium (C8), exhibited higher residual solar cell performance. A comparison of Examples 22 and 24 in Table 6 demonstrates that using a PFSI anion, which has a higher carbon number and fluorine atom number than the TFSI anion, to make the hole transport material more hydrophobic is effective in improving the durability of solar cells. Furthermore, a comparison of Examples 22 and 25 in Table 6 demonstrates that increasing the series of the organic ammonium from primary and / or increasing the carbon number of the organic moiety is effective in improving durability. In addition, the results of Example 28 and Comparative Example 12 in Table 7 demonstrate that compounds containing aromatic phenylethyl groups are also effective in improving the durability of perovskite solar cells. In other words, it can be said that these compounds provide solar cell properties with improved weather resistance, moisture resistance, and other properties, resulting in longer-life solar cells. This is thought to be because the hydrophilic perovskite surface was hydrophobized by the ionic compound of this example, imparting water resistance. Therefore, the ionic compound of this example improves weather resistance, moisture resistance, etc., and is applicable to a wide range of applications such as solar cells and optical sensors.

[0108] Examples 29-32 In Example 29, the viscosity of n-octylammonium TFSI synthesized by the ion exchange method in Example 1 was measured at 25°C using an E-type viscometer (TV-25, manufactured by TOKI SANGYO Co., Ltd.). In Example 30, the viscosity of n-octylammonium TFSI synthesized by the neutralization method in Example 2 was evaluated in the same manner as in Example 29. In Example 31, the viscosity of n-methyl-n-octylammonium TFSI synthesized in Example 7 was evaluated in the same manner as in Example 29. In Example 32, the viscosity of n-octylammonium FSI synthesized in Example 8 was evaluated in the same manner as in Example 29. In Example 33, the viscosity of n,n-dimethyl-n-octylammonium TFSI synthesized in Example 20 was evaluated in the same manner as in Example 29. The results are shown in Table 8.

[0109] From the results in Table 8, comparing the results of Examples 29 and 30, the ion exchange method showed a lower viscosity than the neutralization method. This indicated that more rapid mixing was possible during the preparation process of the raw solution and that it was advantageous for mixing and diffusion with other materials. This is thought to be due to the presence of lithium cations in the ion exchange method. It was shown that including alkali metal cations in the ionic compound was advantageous for the manufacturing process. Furthermore, comparing Examples 30, 31, and 33, it was shown that increasing the organic ammonium series of the cation in the ionic liquid reduced the viscosity, enabling more rapid mixing during the preparation process of the raw solution and being advantageous for mixing and diffusion with other materials. Furthermore, comparing Examples 29 and 32, it was shown that changing the anion from TFSI to FSI reduced the viscosity, enabling more rapid mixing during the preparation process of the raw solution and being advantageous for mixing and diffusion with other materials.

[0110] Examples 34 to 36 In Example 34, a perovskite solar cell was fabricated in the same manner as in Example 2, except that the dopant amount was 48 mM, twice that of Example 2. The performance was compared with that of Example 2 as a reference, and the relative performance when doped at twice the amount was calculated as follows: (Relative performance when doped at twice the amount) = (Solar energy conversion efficiency when doped at twice the amount) / (Solar energy conversion efficiency in the reference example). In Example 35, a solar cell was fabricated in the same manner as in Example 4, except that the dopant amount was 36 mM. Evaluation was performed in the same manner as in Example 34, except that the performance of Example 4 was used as a reference. In Example 36, a solar cell was fabricated in the same manner as in Example 5, except that the dopant amount was 36 mM. Evaluation was performed in the same manner as in Example 34, except that the performance of Example 5 was used as a reference. The results are shown in Table 9.

[0111] The low dependency of solar cell performance on dopant concentration is industrially advantageous, as it allows for excellent uniformity in cell production and allows for larger cell areas, etc. The results in Table 6 show that the dependency of solar cell performance on dopant concentration is further reduced by reducing the number of carbon atoms in the organic moiety from 8 to 4, or even to 2.

[0112] Examples 37 and 38 In Example 37, a perovskite layer and a hole transport layer were deposited in the same manner as in Example 10, and the adhesion of the hole transport layer to the perovskite layer was evaluated by a 180° tape peel test of the hole transport layer. A Tensilon UCT-5T (manufactured by Orientec Co., Ltd.) and Kapton tape were used, and measurements were performed at a crosshead speed of 100 mm / min. The average adhesion was defined as the arithmetic mean value of the adhesion per tape width within a crosshead length range of 10 to 50 mm. In Example 38, a perovskite layer and a hole transport layer were deposited in the same manner as in Example 11, and the sample was evaluated in the same manner as in Example 37. The results are shown in Table 10.

[0113] The results in Table 10 show that the organic portion containing an aromatic group is advantageous in improving the adhesion between the hole transport material and the perovskite layer.

[0114] Example 39 A perovskite solar cell was fabricated in the same manner as in Example 10, except that 4-tert-butylpyridine was not added to the hole transport material solution, and the fabricated solar cell was subjected to a heat resistance test at 85°C in nitrogen for 68 hours, after which the solar cell performance was evaluated in the same manner as for the initial performance, and the relative performance from the initial performance was calculated. The results are shown in Table 11.

[0115] Example 40 A perovskite solar cell was fabricated in the same manner as in Example 10, except that 4 mM of 4-tert-butylpyridine was added to the solution of the hole transport material, and evaluated in the same manner as in Example 39. The results are shown in Table 11.

[0116] Example 41 A perovskite solar cell was fabricated in the same manner as in Example 10 and evaluated in the same manner as in Example 39. The results are shown in Table 11.

[0117] Example 42 A perovskite solar cell was fabricated in the same manner as in Example 10, except that 14 mM of 4-tert-butylpyridine was added to the solution of the hole transport material, and evaluated in the same manner as in Example 39. The results are shown in Table 11.

[0118] Example 43 A perovskite solar cell was fabricated in the same manner as in Example 10, except that 28 mM of 4-tert-butylpyridine was added to the solution of the hole transport material, and evaluated in the same manner as in Example 39. The results are shown in Table 11.

[0119] The results in Table 11 show that the heat resistance of solar cells is improved by adding 4-tert-butylpyridine to the hole transport material together with the ionic compound of this embodiment. This is a surprising result, as it contradicts previous findings.

[0120] These examples demonstrate that the ionic compound of this embodiment can improve solar cell performance and / or water resistance due to the high reactivity of its organic ammonium cation. Therefore, it can be said that the ionic compound of this embodiment can be used in a wide range of applications that utilize its reactivity, such as electrical materials, reagents, solvents for organic synthesis, separation and extraction solvents, gas absorbents, and catalysts.

[0121] As described above, an ionic compound according to one embodiment, a hole transport material according to one embodiment, and a perovskite solar cell according to one embodiment are as follows: (1) An ionic compound comprising a molecular cation and a molecular anion, wherein the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium, the organic ammonium having an organic moiety having from 1 to 20 carbon atoms, and the molecular anion comprises a fluorinated bissulfonylimide. (2) The ionic compound according to (1), wherein the molecular cation comprises a primary organic ammonium. (3) The ionic compound according to (1) or (2), wherein the fluorinated bissulfonylimide is bis(trifluoromethanesulfonyl)imide. (4) The ionic compound according to any one of (1) to (3), wherein the organic moiety of the organic ammonium has from 2 to 12 carbon atoms. (5) The ionic compound according to any one of (1) to (4), wherein the organic moiety of the organic ammonium comprises a saturated hydrocarbon. (6) The ionic compound according to (5), wherein the saturated hydrocarbon is a linear saturated hydrocarbon. (7) The ionic compound according to any one of (1) to (5), wherein the organic moiety of the organic ammonium contains a cyclic aliphatic hydrocarbon. (8) The ionic compound according to any one of (1) to (4), wherein the organic moiety of the organic ammonium contains an aromatic hydrocarbon. (9) The ionic compound according to any one of (1) to (4) and (8), wherein the organic ammonium is 2-phenylethylammonium. (10) The ionic compound according to any one of (1) to (8), wherein the organic moiety of the organic ammonium contains at least one functional group selected from the group consisting of secondary ammonium, tertiary ammonium, quaternary ammonium, a thiol group, a carboxy group, and a hydroxy group. (11) The ionic compound according to any one of (1) to (8) and (10), wherein the organic moiety of the organic ammonium contains a fluorocarbon. (12) The carbon bonded to the nitrogen atom of the organic ammonium is CH ２The ionic compound according to (11), having a structure. (13) The ionic compound according to (11), wherein the organic moiety of the organic ammonium contains a perfluoroalkyl group. (14) The ionic compound according to any one of (1) to (13), which is an ionic liquid having a melting point of 100°C or less. (15) A hole transport material comprising the ionic compound according to any one of (1) to (14). (16) The hole transport material according to (15), which contains a pyridine compound. (17) The hole transport material according to (16), wherein the pyridine compound is 4-tert-butylpyridine. (18) The hole transport material according to any one of (15) to (17), which contains Spiro-OMeTAD. (19) A perovskite solar cell comprising a perovskite layer and a hole transport layer on the perovskite layer, wherein the hole transport layer comprises the hole transport material according to any one of (15) to (19). (20) The perovskite solar cell according to (19), wherein, when the hole transport layer is removed and the contact angle of water on the exposed perovskite layer is measured, the contact angle of water is 55.0° or more. (21) The perovskite solar cell according to (19) or (20), wherein the hole transport material comprises poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], and the average adhesion strength of the hole transport layer to the perovskite layer is 1.0 N cm －１A perovskite solar cell as described above. (22) A method for producing an ionic compound according to any one of (1) to (14), comprising the steps of: subjecting a halide of organic ammonium having an organic moiety having from 1 to 20 carbon atoms to ion exchange with an alkali metal salt of a fluorinated bis-sulfonylimide; and extracting the ionic compound obtained by ion exchange. (23) A method for producing an ionic compound according to (22), wherein the extraction step uses chloroform for extraction. (24) A method for producing an ionic compound according to (22) or (23), wherein the halogen ion contained in the halide of the organic ammonium is a chloride ion. (25) A method for producing an ionic compound according to any one of (22) to (24), wherein the alkali metal contained in the alkali metal salt of a fluorinated bis-sulfonylimide is lithium. (26) A method for producing the ionic compound according to any one of (1) to (14), comprising a step of neutralizing an organic amine having an organic moiety containing 1 to 20 carbon atoms with an acid of a fluorinated bissulfonylimide. (27) A method for producing the ionic compound according to any one of (22) to (26), wherein the organic moiety of the organic amine has 2 to 12 carbon atoms. (28) A method for producing a hole transport material, comprising a step of mixing the ionic compound according to any one of (1) to (14) with a raw material compound for a hole transport material. (29) A method for producing the hole transport material according to (28), wherein at least Spiro-OMeTAD is used as the raw material compound for the hole transport material. (30) A method for manufacturing a perovskite solar cell, which comprises stacking an electron transport layer, a perovskite layer, and a hole transport layer between a conductive substrate and an electrode, the method comprising forming the hole transport layer, and the step of forming the hole transport layer comprises forming a film on the perovskite layer using the hole transport material according to any one of (15) to (18).

[0122] The present disclosure has potential applications in various fields, such as electrical materials, reagents, solvents for organic synthesis, separation and extraction solvents, gas absorbents, catalysts, etc. As electrical materials, the present disclosure has potential applications in various fields, such as solar cell materials, photosensors, luminescent materials, and lithium ion secondary batteries.

[0123] 1 Perovskite solar cell 3 Conductive substrate 5 Electron transport layer 7 Perovskite layer 9 Hole transport layer 11 Electrode

Claims

1. It is composed of a molecular cation and a molecular anion, the molecular cation comprises a primary organic ammonium; The primary organic ammonium is methylammonium, An ionic compound wherein the molecular anion comprises bis(trifluoromethanesulfonyl)imide.

2. It is composed of a molecular cation and a molecular anion, the molecular cation comprises a primary organic ammonium; The primary organic ammonium includes at least one aromatic hydrocarbon selected from the group consisting of methylphenylammonium, phenylethylammonium, phenylpropylammonium, and phenylbutylammonium; An ionic compound wherein the molecular anion comprises bis(trifluoromethanesulfonyl)imide.

3. It is composed of a molecular cation and a molecular anion, the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium; the organic ammonium has a linear saturated hydrocarbon having 4 to 20 carbon atoms, the molecular anion comprises a fluorine-containing bis-sulfonylimide; Ionic compounds containing alkali metal cations.

4. 4. The ionic compound of claim 3, wherein the alkali metal cation is a lithium cation.

5. 5. The ionic compound according to claim 3, wherein the saturated hydrocarbon has 4 or more and 12 or less carbon atoms.

6. 6. The ionic compound according to claim 3, wherein the molecular cation comprises a primary organic ammonium.

7. (delete)

8. (delete)

9. It is composed of a molecular cation and a molecular anion, the molecular cation comprises a primary organic ammonium; the primary organic ammonium is 2-phenylethylammonium; An ionic compound, wherein the molecular anion comprises a fluorine-containing bis-sulfonylimide.

10. The ionic compound according to any one of claims 3 to 6 and 9, wherein the fluorine-containing bissulfonylimide is bis(trifluoromethanesulfonyl)imide.

11. (delete)

12. (delete)

13. (delete)

14. (delete)

15. (delete)

16. (delete)

17. (delete)

18. The ionic compound according to any one of claims 1 to 6 and 9 to 10, which is an ionic liquid having a melting point of 100°C or less.

19. A hole transport material comprising an ionic compound, the hole transport material comprises 4-tert-butylpyridine and Spiro-OMeTAD; the ionic compound is composed of a molecular cation and a molecular anion, the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium; the organic ammonium has a saturated hydrocarbon having 1 to 20 carbon atoms, A hole transport material wherein the molecular anion comprises a fluorine-containing bis-sulfonylimide.

20. A hole transport material comprising the ionic compound according to any one of claims 1 to 6, 9 to 10, and 18.

21. A hole transport material comprising an ionic compound, the ionic compound being composed of a molecular cation and a molecular anion; the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium; the organic ammonium has a saturated hydrocarbon having 1 to 2 carbon atoms, A hole transport material wherein the molecular anion comprises a fluorine-containing bis-sulfonylimide.

22. 22. The hole transport material according to claim 20 or 21, comprising a pyridine compound.

23. 23. The hole transport material according to claim 22, wherein the pyridine compound is 4-tert-butylpyridine.

24. The hole transport material according to any one of claims 20 to 23, comprising Spiro-OMeTAD.

25. The hole transport material according to any one of claims 19 to 24, comprising PTAA.

26. 1. A perovskite solar cell comprising a perovskite layer and a hole transport layer on the perovskite layer, A perovskite solar cell, wherein the hole transport layer comprises the hole transport material according to any one of claims 19 to 25.

27. 27. The perovskite solar cell of claim 26, a perovskite solar cell, wherein, when the hole transport layer is removed and the contact angle of water on the exposed perovskite layer is measured, the contact angle of water is 55.0° or greater.

28. 28. The perovskite solar cell according to claim 26 or 27, the hole transport material contains poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], and the average adhesion strength of the hole transport layer to the perovskite layer is 1.0 N cm －１ That's it for perovskite solar cells.

29. A method for producing an ionic compound, comprising: the ionic compound is composed of a molecular cation and a molecular anion, the molecular cation comprises at least one organic ammonium selected from the group consisting of primary organic ammonium, secondary organic ammonium, and tertiary organic ammonium; the organic ammonium has a saturated hydrocarbon having 1 to 20 carbon atoms, the molecular anion comprises a fluorine-containing bis-sulfonylimide; The production method includes a step of ion-exchanging an organic ammonium halide having a saturated hydrocarbon having from 1 to 20 carbon atoms with an alkali metal salt of a fluorinated bis-sulfonylimide; extracting the ionic compounds obtained by ion exchange; A method for producing an ionic compound comprising:

30. The method for producing an ionic compound according to claim 29, wherein the extraction is performed using chloroform in the extraction step.

31. The method for producing an ionic compound according to claim 29 or 30, wherein the halogen ion contained in the organic ammonium halide is a chloride ion.

32. The method for producing an ionic compound according to any one of claims 29 to 31, wherein the alkali metal contained in the alkali metal salt of the fluorinated bis(sulfonylimide) is lithium.

33. A method for producing the ionic compound according to any one of claims 1 to 6, 9 to 10, and 18, comprising: A method for producing an ionic compound, comprising a step of neutralizing an organic amine having a saturated hydrocarbon having from 1 to 20 carbon atoms with an acid of a fluorinated bissulfonylimide.

34. The method for producing an ionic compound according to any one of claims 29 to 33, wherein the saturated hydrocarbon of the organic amine has 2 or more and 12 or less carbon atoms.

35. A method for producing a hole transport material, comprising a step of mixing the ionic compound according to any one of claims 1 to 6, 9 to 10, and 18 with a raw material compound for the hole transport material.

36. 36. The method for producing a hole transport material according to claim 35, wherein at least Spiro-OMeTAD is used as a raw material compound for the hole transport material.

37. A method for manufacturing a perovskite solar cell, comprising laminating an electron transport layer, a perovskite layer, and a hole transport layer between a conductive substrate and an electrode, the method comprising: The method for manufacturing a perovskite solar cell includes a step of forming the hole transport layer, A method for producing a perovskite solar cell, wherein the step of forming the hole transport layer comprises a step of forming a film on the perovskite layer using the hole transport material according to any one of claims 19 to 25.