WO2025135104A1 - Perovskite precursor solution, method for manufacturing solar cell, and solar cell - Google Patents

Abstract

A perovskite precursor solution according to one aspect of the present invention contains: a solvent; a perovskite precursor that forms a perovskite compound which performs photoelectric conversion; a hole transport layer-forming compound that forms a self-assembled monolayer which has hole-selective permeability; and an optionally substituted chain hydrocarbon group having 5 or more carbon atoms and an ionic functional group.

Description

Perovskite precursor liquid, solar cell manufacturing method, and solar cell

The present invention relates to a perovskite precursor liquid, a solar cell manufacturing method, and a solar cell.

The use of solar cells is expanding as an energy source with a small environmental impact. Perovskite solar cells, which have a photoelectric conversion layer mainly made of a perovskite compound, are known as one type of solar cell. A basic perovskite solar cell is formed by stacking a first electrode layer, a first charge transport layer, a perovskite photoelectric conversion layer, a second charge transport layer, and a second electrode layer in this order on a substrate. In addition, since perovskite solar cells have a different absorption wavelength from solar cells that use a crystalline silicon substrate as a photoelectric conversion layer, they can also be stacked on crystalline silicon solar cells for use. The charge transport layer is a layer that selectively passes electrons or holes, but it also has electrical resistance that causes internal losses. For this reason, in order to reduce electrical resistance, a technology has been proposed in which a thin charge transport layer is formed using a self-assembled monolayer made of a carbazole compound or the like that has a charge selection function (see, for example, Patent Document 1).

In general, the formation of a self-assembled monolayer requires that the material solution be applied thinly and evenly by spin coating or the like. When enlarging a solar cell, it is difficult to employ spin coating, and it is desirable to apply the material by a method such as die coating or bar coating. In addition, since the perovskite photoelectric conversion layer is generally also formed by coating, when the first charge transport layer is formed by coating, it is necessary to repeat coating and drying. In order to efficiently manufacture solar cells, it has been reported that by blending a carbazole compound that forms a hole-selective self-assembled monolayer into a perovskite precursor liquid and applying the mixture, the carbazole compound forms a self-assembled monolayer at the interface with the electrode layer of the coating film, thereby simultaneously forming a hole transport layer and a perovskite photoelectric conversion layer (for example, see Non-Patent Document 1).

JP 2023-46212 A

“Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells”, Nature Energy, 2023, vol. 8, p. 462-472

As in Non-Patent Document 1, when a carbazole compound is added to a perovskite precursor liquid, it is necessary to add an excess of the carbazole compound relative to the coating area in order to form a continuous hole transport layer. As a result of the inventors' verification, it was confirmed that an excess of the carbazole compound in the precursor solution can form a layer on the surface of the coating film and inhibit the transfer of electrons.

The objective of the present invention is to provide a perovskite precursor liquid that can simultaneously form a hole transport layer, a photoelectric conversion layer, and a passivation layer while suppressing the formation of a layer that inhibits electron transport, a solar cell manufacturing method, and a solar cell that can be easily manufactured.

(1) The perovskite precursor liquid according to the first aspect of the present invention includes a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer-forming compound that forms a self-assembled monolayer that has hole selective permeability, and an organic compound that has a chain hydrocarbon group having 5 or more carbon atoms that may be substituted and an ionic functional group.

(2) In the perovskite precursor liquid of (1), the ionic functional group may be any one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphonic acid group, a phosphoric acid group, a hydroxyl group, a carboxyl group, and a sulfonyl group.

(3) In the perovskite precursor liquid of (1), the organic compound may be a halide salt.

(4) In the perovskite precursor liquids of (1) to (3), the perovskite precursor may contain a metal halide including at least one of a lead halide and a tin halide, and an organic halide or an alkali metal halide, and the molar concentration of the metal portion of the metal halide may be in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal by 0.5 mol % to 10 mol %.

(5) The perovskite precursor liquids (1) to (4) may further contain an organic hydrochloride that promotes the growth of crystals of the perovskite compound.

(6) The perovskite precursor liquids (1) to (5) may further contain at least one of a fluorine-containing organic compound, piperazine, or a piperazine derivative, and a polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle.

(7) In the perovskite precursor liquid of (6), the fluorine-containing organic compound may have at least one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphate group, a phosphonic acid group, a hydroxyl group, a carboxyl group, a sulfonyl group, or an ionized form thereof at its terminal, and may have a carbon skeleton containing an alkyl chain or benzene in which hydrogen is replaced by fluorine or a trifluoromethyl group.

(8) A solar cell manufacturing method according to a second aspect of the present invention includes a step of applying the above-mentioned perovskite precursor liquid to a first electrode layer formed on one main surface of a substrate, and a step of volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound.

(9) A solar cell according to a third aspect of the present invention includes a plate- or sheet-shaped substrate, a first electrode layer laminated on one main surface of the substrate, a hole transport layer laminated on the first electrode layer and made of a film of a hole transport layer-forming compound having hole selective permeability, a photoelectric conversion layer laminated on the hole transport layer and containing a perovskite compound, an excess material layer partially laminated on the photoelectric conversion layer and containing the hole transport layer-forming compound, a passivation layer laminated in an area of the photoelectric conversion layer where the excess material layer is absent, the passivation layer containing an organic compound having a chain hydrocarbon group having 5 or more carbon atoms and an ionic functional group that may be substituted, and a second electrode layer laminated on the excess material layer and the one side of the passivation layer.

(10) In the solar cell of (8), the photoelectric conversion layer may have an impurity film containing a halide of a metal atom in the perovskite compound at the grain boundary of the crystal of the perovskite compound.

(11) The solar cell of (8) to (9) may further include an electron transport layer laminated between the excess material layer and the passivation layer and the second electrode layer.

(12) The perovskite precursor liquid according to the fourth aspect of the present invention includes a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer-forming compound that forms a self-assembled monolayer having hole selective permeability, and at least one of a piperazine derivative and a piperazine derivative.

(13) In the perovskite precursor liquid of (12), the piperazine derivative may be a halide salt.

(14) In the perovskite precursor liquid of (12) to (13), the piperazine derivative may have an alkyl chain or a fluorine-containing organic group bonded to one of the nitrogen atoms.

(15) The perovskite precursor liquids (12) to (14) may further contain a fluorine-containing organic compound.

(16) In the perovskite precursor liquids of (12) to (15), the fluorine-containing organic compound may have at least one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphate group, a phosphonic acid group, a hydroxyl group, a carboxyl group, a sulfonyl group, or an ionized form thereof at its terminal, and may have a carbon skeleton containing an alkyl chain or benzene in which hydrogen is replaced by fluorine or a trifluoromethyl group.

(17) In the perovskite precursor liquids of (11) to (16), the perovskite precursor may contain a metal halide including a lead halide, and an organic halide or an alkali metal halide, and the molar concentration of the metal may be in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal by 0.5 mol % or more and 10 mol % or less.

(18) (11) to (17) The above-mentioned perovskite precursor liquid may further contain a hydrochloride that promotes the growth of crystals of the perovskite compound.

(19) A solar cell manufacturing method according to a fifth aspect of the present invention includes the steps of applying the above-mentioned perovskite precursor liquid to a first electrode layer formed on one main surface of a substrate, and volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound.

(20) A solar cell according to a sixth aspect of the present invention includes a plate- or sheet-shaped substrate, a first electrode layer laminated on one main surface of the substrate, a hole transport layer laminated on the first electrode layer and made of a film of a hole transport layer-forming compound having hole selective permeability, a photoelectric conversion layer laminated on the hole transport layer and containing a perovskite compound, an excess material layer partially laminated on the photoelectric conversion layer and made of the hole transport layer-forming compound, a passivation layer containing at least one of piperazine and a piperazine derivative laminated in an area of the photoelectric conversion layer where the excess material layer is absent, and a second electrode layer laminated on the excess material layer and the one side of the passivation layer.

(21) In the solar cell of (19), the photoelectric conversion layer may have an impurity film containing a halide of a metal atom in the perovskite compound at the grain boundary of the crystal of the perovskite compound.

(22) The solar cell of (19) to (20) may further include an electron transport layer laminated between the excess material layer and the passivation layer and the second electrode layer.

(23) The perovskite precursor liquid according to the seventh aspect of the present invention includes a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer-forming compound that forms a self-assembled monolayer, and a polymer passivation compound that has a repeating unit having a nitrogen-containing heterocycle.

(24) In the perovskite precursor liquid of (23), the polymer passivation compound may have a polyvinyl skeleton.

(25) In the perovskite precursor liquids (23) to (24), the nitrogen-containing heterocycle may be any one of pyridine, pyrrolidone, phthalimide, caprolactam, imidazole, imidazolium, triazole, thiazole, piperidium, and derivatives thereof.

(26) In the perovskite precursor liquid of (23) to (25), the perovskite compound may have an _ABX3 structure in which X is a halogen atom, and the molar concentration of X may be higher than the molar concentration of at least one of A and B.

(27) A solar cell manufacturing method according to an eighth aspect of the present invention includes the steps of applying the above-mentioned perovskite precursor liquid to a first electrode layer formed on one main surface of a substrate, and volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound.

(28) A solar cell according to a ninth aspect of the present invention includes a plate- or sheet-shaped substrate, a first electrode layer laminated on one main surface of the substrate, a hole transport layer laminated on the first electrode layer and made of a film of a hole transport layer-forming compound, a photoelectric conversion layer laminated on the hole transport layer and containing a perovskite compound, an excess material layer partially laminated on the photoelectric conversion layer and made of the hole transport layer-forming compound, a passivation layer laminated in an area of the photoelectric conversion layer where the excess material layer is absent and containing a polymer passivation compound having a repeating unit having a nitrogen-containing heterocycle, and a second electrode layer laminated on the excess material layer and on the one side of the passivation layer.

(29) In the solar cell of (28), the passivation layer may contain a halide of the polymer passivation compound.

The present invention provides a perovskite precursor liquid that can simultaneously form a hole transport layer, a photoelectric conversion layer, and a passivation layer while suppressing the formation of a layer that inhibits electron transport, a solar cell manufacturing method, and a solar cell that can be easily manufactured.

1 is a schematic cross-sectional view showing a configuration of a solar cell according to a first embodiment of the present invention. 1 is a flowchart showing the steps of a solar cell manufacturing method according to a first embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing the configuration of a solar cell according to a second embodiment of the present invention. 10 is a flowchart showing the steps of a solar cell manufacturing method according to a second embodiment of the present invention. FIG. 11 is a schematic cross-sectional view showing the configuration of a solar cell according to a third embodiment of the present invention. 10 is a flowchart showing the steps of a solar cell manufacturing method according to a third embodiment of the present invention.

[First embodiment]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the configuration of a solar cell 1 according to a first embodiment of the present invention. For the sake of convenience, the dimensions of various members in the drawings have been adjusted for ease of viewing.

The solar cell 1 comprises a plate- or sheet-shaped substrate 10, a first electrode layer 20 laminated on one main surface of the substrate 10 (the lower side in FIG. 1), a hole transport layer 30 laminated on one surface of the first electrode layer 20, a photoelectric conversion layer 40 laminated on one surface of the hole transport layer 30, an excess material layer 50 partially laminated on one surface of the photoelectric conversion layer 40, a passivation layer 60 laminated in an area where the excess material layer 50 is absent on one surface of the photoelectric conversion layer 40, an electron transport layer 70 laminated on one side of the excess material layer 50 and the passivation layer 60, and a second electrode layer 80 laminated on one side of the electron transport layer 70.

The substrate 10 is a structure that supports the other layers and ensures the strength of the solar cell 1. When the solar cell 1 receives light from the substrate 10 side, the substrate 10 is formed from a transparent material. Specifically, the substrate 10 may be formed from glass, or a resin such as polyimide, polyamide, or polyethylene terephthalate. When the solar cell 1 receives light from the second electrode layer 80 side, the substrate 10 may be formed from a composite material including a metal layer.

The first electrode layer 20 collects holes generated in the photoelectric conversion layer 40 through the hole transport layer 30 and outputs them to the outside. The first electrode layer 20 can be formed of a transparent conductive oxide (TCO) having electrical conductivity and optical transparency. Examples of the transparent conductive oxide that forms the first electrode layer 20 include indium oxide, tin oxide, zinc oxide, titanium oxide, and composite oxides thereof. Among these, indium-based composite oxides mainly composed of indium oxide, zinc oxide, tungsten oxide, molybdenum oxide, etc., or fluorine-doped tin oxide are preferred. From the viewpoint of high electrical conductivity and transparency, indium oxide is particularly preferred. In order to improve the formability of the hole transport layer 30, the first electrode layer 20 is preferably subjected to a surface treatment such as ozone treatment, and may have a multilayer structure having a layer of a p-type oxide semiconductor mainly composed of nickel oxide, niobium oxide, etc. on the surface.

The hole transport layer 30 is formed from a film of a hole transport layer forming compound that forms a self-assembled monolayer (SAM). The hole transport layer 30 transmits only holes out of the positive and negative photocarriers (holes and electrons) generated in the photoelectric conversion layer 40 to the first electrode layer 20. The hole transport layer forming compound preferably has a highest occupied orbital close to the valence band of the perovskite compound that performs photoelectric conversion so as to facilitate the transmission of holes, and preferably has a lowest unoccupied orbital smaller than the conduction band in order to block electrons. The hole transport layer forming compound that forms the hole transport layer 30 preferably has a functional functional group capable of transporting holes, such as a carbazole system, a phenothiazine system, or a dimethylacridine system, and a self-assembled terminal group that chemically bonds to the substrate, such as phosphoric acid and carboxylic acid. In order to impart passivation properties to the hole transport layer 30, it is preferable that a linear structure such as an alkyl chain is present between the functional group and the self-organizing terminal group. The alkyl chain between the functional group and the self-organizing terminal group preferably has 4 or more carbon atoms. Specifically, examples of the hole transport layer forming compound that forms the hole transport layer 30 include Me-4PACz ([4-(3,6-Dimethyl-9H-carbazol-9-yl) butyl] phosphoric acid), MeO-4PACz ([4-(3,6-Dimethoxy-9H-carbazol-9-yl) butyl] phosphoric acid), DMAcPA ((4-(2,7-dibromo-9,9-dimethylacridin-10(9H)-yl) butyl) phosphoric acid), etc.

The photoelectric conversion layer 40 includes a perovskite compound that performs photoelectric conversion, and absorbs incident light to generate photocarriers. The perovskite compound included in the photoelectric conversion layer 40 includes an organic atom A that includes at least one of an alkali metal (Am), a monovalent organic ammonium ion, and an amidinium-based ion, a metal atom B that generates a divalent metal ion, and a halogen atom X that includes at least one of an iodide ion I, a bromide ion Br, a chloride ion Cl, and a fluoride ion F, and is represented by _ABX3 . Examples of the alkali metal at the A site include potassium K, cesium Cs, and rubidium Rb, and examples of the organic atom A include methylammonium MA (CH ₃ NH ₃ ), formamidinium FA (CH ₃ N ₂ ), and the like. Examples of the metal atom B include lead Pb and tin Sn. It is preferable to include at least one of lead Pb and tin Sn, and a mixture thereof may be used. The halogen atom X is preferably at least one of iodide I, bromide Br and chloride Cl.

Specifically, preferred perovskite compounds include methylammonium lead halides (MAPbX ₃ ) such as MAPbI ₃ , MAPbBr ₃ , and MAPbCl ₃ , and formamidinium lead halides (FAPbX ₃ ) such as FAPbI ₃ , FAPbBr ₃ , and FAPbCl _3. The halogen atom X may include multiple types. It may be FA _y MA _1-y PbX ₃ , which contains both methylammonium and formamidinium. In addition, when an alkali metal is included, examples include Am _y FA _z MA _1-y-z PbIX and Am _y FA _1-y PbIX. Am may be a single type of Cs, Rb, or K, or may include multiple types. (y and z are any positive integers).

The photoelectric conversion layer 40 preferably has an impurity film 41 containing a halide of a metal atom in the perovskite compound, such as Pb, PbI ₂ , PbBr ₂ , or PbCl ₂ , at the grain boundary of the crystal of the perovskite compound. In order to form such an impurity film 41, the metal B in the perovskite compound preferably contains at least one of lead (Pb) and tin (Sn). By the photoelectric conversion layer 40 having the impurity film 41 containing the metal atom B and the metal compound, the hole transport layer forming compound forming the hole transport layer 30 and the material forming the passivation layer 60 are prevented from being left behind at the grain boundary of the crystal of the perovskite compound when the photoelectric conversion layer 40 is formed, and the photoelectric conversion efficiency can be improved.

The excess material layer 50 is formed from a material containing the same hole transport layer forming compound as that forming the hole transport layer 30. The excess material layer 50 may be composed of only the hole transport layer forming compound, or may contain other materials contained in the perovskite precursor liquid. When the excess material layer contains a hole transport layer forming compound, the weight content of the hole transport layer forming compound in the excess material layer 50 is preferably 10% or more, and more preferably 30% or more. In addition, the weight content of the hole transport layer forming compound is preferably 90% or less, and more preferably 70% or less. The weight content in the excess material layer can be calculated based on the composition of the excess material layer measured by combining transmission electron microscope observation and energy dispersive X-ray analysis, etc. The hole transport layer forming compound used as the hole transport layer 30 has a lowest unoccupied orbital lower than the conduction band of the perovskite compound (close to the vacuum level) in order to block electron transport, so if it exists between the photoelectric conversion layer 40 and the electron transport layer, the excess material layer 50 may make it difficult for electrons generated in the photoelectric conversion layer 40 to reach the electron transport layer, and may act as a resistor. For this reason, it is necessary to ensure that the excess material layer 50 is formed in an appropriate state. For example, when the hole transport layer 30 and the photoelectric conversion layer 40 are formed by the same process, in order to form a seamless hole transport layer 30 that covers the entire surface of the first electrode layer 20, it is preferable to use a perovskite precursor liquid in which the concentration of the hole transport layer forming compound is adjusted to be slightly greater than the number of hole transport forming compounds required to densely cover the coating surface. In addition, a material contained in the perovskite precursor liquid may be included in the excess material layer 50 to make it difficult to hinder the transport of electrons passing through the excess material layer 50. A simple method for understanding the growth state of the hole transport layer-forming compound on the TCO surface is to assume that the molecular length is the unit (lattice constant) of the monolayer, estimate the number of hole transport-forming compounds per coating area, and determine the concentration so that the number of hole transport-forming compounds contained in the coating film is greater than that. In the case of a halide, the molecular length of an ion that does not contain a halogen can be used as the unit.

The passivation layer 60 prevents the recombination of photocarriers at the interface with the photoelectric conversion layer 40, and promotes the arrival of electrons at the electron transport layer 70. The passivation layer 60 is formed so as to compete with the surface of the excess material layer 50 and the photoelectric conversion layer 40, and prevents the excess material layer 50 from covering the entire surface of the photoelectric conversion layer 40, thereby preventing a decrease in photoelectric conversion efficiency. The passivation layer 60 includes an organic compound (hereinafter referred to as a "specific organic compound") having a chain hydrocarbon group having 5 or more carbon atoms that may be substituted and an ionic functional group. Note that the "chain hydrocarbon group that may be substituted" includes a chain hydrocarbon group in which the hydrogen atom is substituted with another atom or group. Specific examples of specific organic compounds include n-octylphosphocholine, 2,8-dimethyl-5-nonylphosphocholine, 10-undecylenyl-1-phosphocholine, n-octylammonium iodide, and L-α-phosphotidylcholine. The deposition of specific organic compounds on the surface can be confirmed by time-of-flight secondary ion mass spectrometry.

The specific organic compound is mixed in a solvent containing aprotic polar solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and acetonitrile, which are used to form the photoelectric conversion layer 40. Large-sized materials are less susceptible to the crystallization of the perovskite material and are pushed out to the surface and interface. At that time, by using alkyl chains that interact with each other and have an orientation effect, it becomes easier to arrange them two-dimensionally. In addition, by having ionic ends, it becomes easier to attach to defects on the surface of the perovskite material, and the orientation of the molecules can be controlled. If the orientation is poor, the coverage rate will be poor, such as growing by folding each other over, and the passivation will be poor or it will become resistance, making it difficult to transport electrons. The number of carbon atoms in the chain hydrocarbon is preferably 5 or more, and preferably 24 or less. It is important to have a size that is less susceptible to crystallization, and the longer the carbon number, the easier it will be oriented, and more preferably the number of carbons is 8 or more. On the other hand, the orientation will be poor if the number of carbons is large and the length is long. The chain hydrocarbon group may be linear or branched. Having a sufficient number of carbon atoms prevents incorporation into the crystals of the perovskite material, and the number of carbon atoms in one chain hydrocarbon is short, which reduces electrical resistance. It is preferable to partially have a double chain (alkene), triple chain (alkyne), or aromatic ring. By having a π bond such as a double chain, triple chain, or aromatic ring, the insulation property decreases even if the hydrocarbon group is long. For example, L-α-phosphatidylcholine is bifurcated and contains a chain hydrocarbon with 15 carbon atoms and a chain hydrocarbon with 17 carbon atoms. A chain hydrocarbon with 17 carbon atoms requires a partial double chain. In addition, by creating a halide, it is easy to ionize when dissolved in a solvent, and the halogen ions also act to fill in defects in the perovskite material, preventing a decrease in characteristics.

The ionic functional group binds to defects in the crystal of the perovskite compound, thereby preventing the recombination of photocarriers. Since defects in the crystal of the perovskite compound can be both positive and negative, the ionic functional group may form either a positive or negative ion. Specifically, the ionic functional group is preferably any of an amino group, a hydrazine group, a trialkylamino group, a phosphonic acid group, a phosphoric acid group, a hydroxyl group, a carboxyl group, and a sulfonyl group. In particular, it is more preferable to have an ionic functional group that has both a positive ion and an negative ion, such as a phosphocholine group, and that becomes a zwitterion, since this compensates for defects of both charges on the perovskite surface.

In addition to the specific organic compound, the passivation layer 60 may further contain at least one of a fluorine-containing organic compound, piperazine and piperazine derivatives, and a polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle. Since a single material alone may not be sufficiently deposited on the surface of the perovskite layer, mixing with a material having a different deposition method and different passivation properties can more reliably cover the surface and improve passivation properties.

Fluorine-containing organic compounds have high surface deposition properties and high electron transport capabilities. On the other hand, they have low surface energy and low adhesion to materials grown on them. In addition, when formed by coating, they tend to exhibit lyophobic properties, which can cause coating defects. Therefore, by combining them with specific organic compounds, it is possible to improve adhesion and coatability.

The fluorine-containing organic compound preferably has a carbon skeleton containing an alkyl chain or benzene, and has a structure in which hydrogen is partially replaced by fluorine or a trifluoromethyl group. It is more preferable that the carbon skeleton contains consecutive carbons to which fluorine is bonded. When the fluorine-containing organic compound has a benzene skeleton, it is preferable that any of the six hydrogens of benzene are replaced by fluorine or a trifluoromethyl group, and one is connected to a lyophilic group at the end. The greater the number of fluorine and trifluoromethyl group replacements, the higher the lyophobicity becomes, and the greater the effect of selectively orienting to the surface. Therefore, when replaced by fluorine, it is preferable to have a structure of pentafluorinated benzene in which all hydrogens except one connected to the end are replaced by fluorine. When the fluorine-containing organic compound has an alkyl chain skeleton, it is preferable that the tip is a trifluoromethyl group or a phenyl group containing fluorine or a trifluoromethyl group, and the end is a lyophilic group. The tip containing fluorine is oriented toward the electron transport layer side, and the end containing the lyophilic group is oriented toward the perovskite surface side. It is preferable that the straight chain skeleton excluding the tip and end has 1 to 17 carbon atoms. More preferably, the number of carbon atoms is 5 or more and 16 or less. In order to promote the formation of the passivation layer 60 by self-organization, the longer the alkyl chain, the better the orientation and the better the passivation, but the higher the insulating property and the lower the conductivity. Therefore, by providing an alkyl chain that is equal to or greater than the upper limit, it is possible to provide sufficient orientation, and by being equal to or less than the lower limit, it is possible to achieve both passivation and conductivity. When the fluorine-containing organic compound has an alkyl chain skeleton and the tip is a trifluoromethyl group, it is preferable that the alkyl chain continuing from the tip contains fluorinated carbons in succession. More preferably, it is preferable that all of the carbons except one or two carbons adjacent to the end are fluorinated. By continuously fluorinating, the lyophobicity is increased, and the formation of the passivation layer 60 can be promoted by selectively precipitating on the surface. Another example of a fluorine-containing organic compound having an alkyl chain skeleton is a polymer structure. The partially fluorinated polymer structure, unlike the one in which the tip containing fluorine is oriented on the electron transport layer side and the end containing lyophilic groups is oriented on the perovskite surface side by containing a lot of fluorine, tends to be oriented on the surface in a planar manner. In the case where the fluorine-containing organic compound has an alkyl chain skeleton and the tip is a phenyl group containing fluorine or trifluoromethyl group, the effect is greater as the number of substitutions of fluorine and trifluoromethyl group increases, as described above. Therefore, when hydrogen of the phenyl group is substituted with fluorine, pentafluorinated benzene is preferable. In addition, by having both a phenyl group having fluorine and a trifluoromethyl group and an alkyl chain, it is possible to promote deposition on the surface more selectively than in the case of only a benzene skeleton. In addition, it is preferable that the fluorine-containing organic compound has at least one or more lyophilic groups, specifically, amino groups, hydrazine groups, trialkylamino groups, phosphoric acid groups, phosphonic acid groups, hydroxyl groups, carboxyl groups, and sulfonyl groups, and ionized forms thereof, at the end. These have lyophilicity with respect to the aprotic polar solvent, which is the solvent for making the photoelectric conversion layer 40, and can be positioned on the surface of the photoelectric conversion layer 40 from a stage before the drying process by combining with a fluorine-containing skeleton that is lyophobic. By having a straight-chain skeleton or a lyophilic group, or both, each fluorine-containing organic compound is easy to align, a thin and uniform film can be formed, and series resistance can be reduced. By ionizing these ends, defects such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer can be compensated for, and the performance can be improved. In addition, the fluorine-containing organic compound may be of multiple types. In addition, these end groups may be ionized in the solvent. It is more preferable that the fluorine-containing organic compound has both a cationic end group and an anionic end group in order to compensate for defects that exist with different charges, such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer. Examples of ends that have both a cationic end group and an anionic end group include a phosphocholine group and a carbamic acid group. In addition, the specific organic compound and the fluorine-containing organic compound tend to be oriented due to interactions between the individual molecules and the film boundaries between the specific organic compound, which tends to be charged positively, and the fluorine-containing compound, which tends to be charged negatively, making it possible to form a dense passivation layer. In particular, by selecting a fluorine-containing organic compound that has a chain structure similar to the specific organic compound, orientation becomes easier.

Specific examples of fluorine-containing organic compounds include those having a benzene skeleton substituted with fluorine and a trifluoromethyl group, such as 4-fluorophenethylamine hydroiodide (FPEAI), 4-(trifluoromethyl)phenylammonium hydroiodide, 2,6-difluoroaniline, 3,4,5-trifluoroaniline, pentafluorophenylphosphonic acid (5FPAc), pentafluorophenylhydrazine (5FPHZ), and pentafluorobenzene-amino-carboxylic acid (carbamic acid) hydroiodide. When the fluorine-containing organic compound has an alkyl chain skeleton, examples of compounds having a trifluoromethyl group at the end and a lyophilic end include 1H,1H-undecafluorohexylamine ( _{CF3 ( CF2} ) _4CH2NH2 ) _, 1H,1H-pentadecafluorooctylamine ( _CF3 ( _CF2 ) _6CH2NH2 ), (fluorinated) Fos-Choline- ₈ (registered trademark: _{C13H17F13NO4P} ), _2,2,2 - _{trifluoroethylamine} ( _CF3CH2NH2 ), and 3,3,4,4,5,5,6,6 _{- nonafluorohexylphosphonic acid} (FHPA), and examples of compounds having _a polymer structure include polyvinylidene fluoride (PVDF). When the fluorine-containing organic compound has an alkyl chain skeleton, an example of a compound having a phenyl group containing fluorine or a trifluoromethyl group is 12-pentafluorophenoxydodecylphosphonic acid (C ₁₈ H ₂₆ F ₅ O ₄ P). It can be confirmed by observing the contact angle that the fluorine-containing organic compound is deposited on the surface as a passivation layer. For example, when evaluated with chlorobenzene, the contact angle increases with the addition of a small amount of a linear fluoroalkyl chain, 1H,1H-undecafluorohexylamine, (fluorinated)Fos-Choline-8, etc., which have high lyophilicity.

While piperazine compounds exhibit a high passivation effect on the perovskite surface, they have low solubility in solvents, making it difficult to dissolve a sufficient amount to cover the surface, and if there are any undissolved areas, they become impurities and are likely to cause poor solar cell characteristics. Therefore, by combining them with specific compounds, a synergistic effect can be produced.

Piperazine compounds tend to be poorly soluble at room temperature in solvents including aprotic polar solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and acetonitrile, which are used to form the photoelectric conversion layer 40. Therefore, compared to the excess material layer 50, the piperazine compounds are less likely to be involved in the crystal growth of the perovskite material, and precipitate on the surface and grain boundaries of the photoelectric conversion layer 40. It is known that the crystallization process occurs from the surface, and the poorly soluble piperazine compounds precipitate on the surface first, followed by the perovskite compounds containing the hole transport forming compounds. By precipitating on the surface, the piperazine compounds are more likely to transport electrons while maintaining passivation properties. In particular, by forming a halide salt of the piperazine compound and making it an ionic material, it becomes more poorly soluble and more likely to precipitate on the surface. In addition, by having a hydrophobic group such as an alkyl chain or a fluorine-containing organic group bonded to one of the nitrogen groups, precipitation on the surface can be further promoted. The fluorine-containing organic group is preferably a fluorinated alkyl group. Here, the "piperazine compound" refers to at least one of piperazine and piperazine derivatives (including halogenated salts) represented by the following chemical formulas 1 to 3, and may be a mixture of two or more of these. In the formulas, R1 to R8 are hydrogen or any substituent, RA1 to RA4 are hydrogen or an alkyl group, and X is a halogen. The deposition of the piperazine compound on the surface can be confirmed by time-of-flight secondary ion mass spectrometry.

Specific examples of piperazine derivatives include piperazine-1,4-diium iodide, piperazineinium iodide, pentylpiperazine hydrochloride, and 1-(2-fluoroethyl) piperazine dihydrochloride.

Polymer passivation compounds with repeating units that have nitrogen-containing heterocycles have the advantage that nitrogen ions easily combine with halogen ions to form polymer passivation halides, which play a role in compensating for halogen defects that occur on the surface when perovskite compounds are formed. These compounds have the unique effect of being polymers. On the other hand, they can be difficult to control, such as by causing aggregation, so by combining them with specific organic compounds that are monomolecular, a denser passivation layer can be created.

Since the polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle is a polymer and has a large size, when the photoelectric conversion layer 40 is formed using the perovskite precursor liquid described later, it is not incorporated into the perovskite crystal and is preferentially precipitated on the surface. Therefore, the formation of the excess material layer 50 can be suppressed to form the passivation layer 60. In order to ensure the formation of the passivation layer 60, the molecular weight of the polymer passivation compound is preferably 5,000 to 5,000,000 in weight average. In order to ensure that it is not incorporated into the perovskite compound, it is more preferable that it is 10,000 or more, and in order to maintain solubility in the solvent, it is more preferable that it is 2.5 million or less. In addition, the polymer passivation compound has a nitrogen-containing heterocycle in the repeating unit, which prevents recombination and allows electrons to pass efficiently. It may also be a polymer passivation halide. A polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle is easy to form a polymer passivation compound with halogen ions in the precursor liquid. By creating a polymer passivation halide, it is possible to compensate for halogen defects that occur due to aging on the surface of perovskite compounds, thereby improving the reliability of solar cell characteristics.

The nitrogen-containing heterocycle of the polymer passivation compound is preferably pyridine, pyrrolidone, phthalimide, caprolactam, imidazole, imidazolium, triazole, thiazole, piperidium, and derivatives thereof. The polymer passivation compound preferably has a larger band gap than the perovskite compound. More preferably, the highest occupied molecular orbital of the polymer passivation compound is larger than the valence band of the perovskite compound (farther than the vacuum level), and the lowest unoccupied molecular orbital of the polymer passivation compound is smaller than the conduction band of the perovskite compound (closer to the vacuum level). In addition, by using a heterocycle having an alkyl chain composed of locally highly insulating vinyl groups and having high conductivity, carriers can be transported efficiently while maintaining passivation properties.

In addition, pyrrolidone, phthalimide, and caprolactam have oxygen in the skeleton, and in skeletons that have hydrogen halide ions and pyridine, imidazole, imidazolium, triazole, and thiazole, nitrogen ions are likely to combine with halogen ions to form polymer passivation halides. Therefore, when forming the passivation layer from the precursor liquid, halogen ions that are not used in the formation of the perovskite compound are taken in to partially form polymer passivation halides. Polymer passivation halides play a role in compensating for halogen defects that occur on the surface during the formation of the perovskite compound, improving the passivation properties of the perovskite compound surface. In addition, in completed solar cells, polymer passivation halides can also compensate for halogen defects on the surface of the perovskite compound that occur due to aging, improving the reliability of the solar cell characteristics. Therefore, if the molar concentration of halogen ions X in the precursor liquid is 1% or more in excess of at least one of the molar concentrations of the materials related to the A site and the B site of the perovskite compound, it is possible to effectively form a halide with the polymer passivation compound. If it is 3% or more in excess, it is possible to more effectively incorporate halogen ions. In addition, it is preferable that the excess amount is 20% or less, and the formation of defects occurring in the perovskite compound can be suppressed. If the excess amount is 10% or less, it can be more effectively suppressed. In addition, a precursor liquid containing excess halogen can be formed by adding a halide of the polymer passivation compound to the precursor. It is preferable that the polymer passivation halide in the passivation layer after the solar cell is formed is formed in 1% or more of the total number of repeating structures of the polymer passivation compound from the viewpoint of improving reliability. Furthermore, by forming 5% or more, it is possible to more effectively compensate for defects occurring in the perovskite compound. In addition, by making the polymer passivation halide 90% or less of the total number of repeating structures of the polymer passivation compound, the stable state of the polymer passivation compound can be maintained without steric hindrance. Furthermore, by keeping it below 80%, a more stable state can be maintained.

The repeating unit of the polymer passivation compound may be an alkyl unit. That is, the repeating unit of the polymer passivation compound may be an alkyl unit substituted with a nitrogen-containing heterocycle. As a typical example, the polymer passivation compound may be a compound having a polyvinyl skeleton obtained by vinyl polymerization of a monomer having a nitrogen-containing heterocycle and a vinyl group. That is, the polymer passivation compound may be a compound in which a nitrogen-containing heterocycle is bonded to every two carbons of the alkyl chain. In this way, since the polymer passivation compound is a compound having an alkyl chain as the main chain, the polymer can be synthesized relatively easily and the desired molecular weight can be obtained, so that the passivation layer 60 can be formed more reliably. In addition, the presence of the alkyl chain makes it easy to control the orientation, and the arrangement of the heterocycles can be aligned. Furthermore, the polymer passivation compound may include a repeating structure of other skeletons, such as a fluorinated alkyl chain skeleton, in addition to a structure having a nitrogen-containing heterocycle or a vinyl skeleton. For example, the polymer passivation compound may have a skeleton having a fluorinated alkyl chain as a branch of the alkyl chain between the skeletons of poly(vinylimidazole). Fluorinated alkyl chains tend to exhibit lyophobic properties and can be more selectively deposited on the surface of perovskite compounds.

Examples of polymeric passivation compounds with repeating units of alkyl units substituted with nitrogen-containing heterocycles include poly(vinylpyrrolidone), poly(4-vinylpyridine), poly(2-vinylpyridine), poly(1-vinylimidazole), poly(2-vinylimidazole), poly(4-vinylimidazole), poly(vinylazole), poly(vinylphthalimide), poly(vinylimidazole), poly(vinylcaprolactam), poly(vinyltriazole), poly(5-vinylthiazole), and poly(4-methyl-5-vinylthiazole). Examples of halides include poly(vinylpyrrolidone) iodine complexes.

In addition to the specific organic compound, the passivation layer 60 may contain two or more types of fluorine-containing organic compounds, piperazine and piperazine derivatives, and polymeric passivation compounds having repeating units with nitrogen-containing heterocycles. By using appropriate combinations, it is possible to obtain a higher effect than if one type were used alone.

If the coverage of the photoelectric conversion layer 40 by the passivation layer 60 is 50% or more, electron transport can be performed effectively. Furthermore, if it is 90% or more, the effect is enhanced, which is preferable. Furthermore, if it is 99% or less, the resistance loss caused by partial thickening of the polymer passivation compound can be reduced. Furthermore, if it is 95% or less, the resistance loss can be suppressed more effectively.

The electron transport layer 70 selectively transmits electrons and transfers them to the second electrode layer 80. The electron transport layer 70 is formed of a material mainly composed of fullerene, for example. Examples of fullerene include C60, C70, their hydrides, oxides, metal complexes, and derivatives with alkyl groups added thereto, for example PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester). In addition, a hole blocking layer such as pasocuproine (BCP), lithium fluoride (LiF), tin oxide (SnO ₂ ), aluminum-doped zinc oxide (ZnO), or titanium oxide (TiO ₂ ) may be included between the electron transport layer 70 and the second electrode layer 80. The inorganic oxide layer may be doped with another metal material.

When the solar cell 1 receives light from the substrate 10 side, the second electrode layer 80 preferably includes a metal layer made of, for example, copper, in order to reduce electrical resistance. When the solar cell 1 receives light from the second electrode layer 80 side, the second electrode layer 80 may be made of a transparent conductive oxide.

The solar cell 1 having the above configuration is manufactured by a solar cell manufacturing method according to one embodiment of the present invention shown in Figure 2. The solar cell manufacturing method of this embodiment includes a first electrode layer forming step (step S1), a precursor liquid application step (step S2), a crystallization step (step S3), an electron transport layer forming step (step S4), and a second electrode layer forming step (step S5).

In the first electrode layer forming process of step S1, the first electrode layer 20 is formed on one main surface of the substrate 10. The first electrode layer 20 can be laminated using a vacuum film forming technique such as sputtering. In the first electrode layer process, it is preferable to modify the surface of the formed first electrode layer 20 in order to promote the formation of the hole transport layer 30 in the next process. Specific methods for modifying the surface of the first electrode layer 20 include, for example, hydroxylation of the surface by ultraviolet-ozone treatment or ozone water washing, film formation by vacuum film forming techniques such as sputtering of oxides such as nickel oxide, which is prone to grow a self-assembled film, film formation by coating technology of oxide nanoparticles, and heat treatment to activate the surface and remove impurities so that a self-assembled film can easily grow.

In the precursor liquid application process of step S2, the perovskite precursor liquid is applied to the first electrode layer 20. The perovskite precursor liquid can be applied using, for example, a die coater, a bar coater, or the like. The perovskite precursor liquid applied in the precursor liquid application process is itself one embodiment of the perovskite precursor liquid according to the present invention.

The perovskite precursor liquid contains a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer forming compound that forms a self-assembled monolayer that has hole selective permeability, and a specific organic compound. In addition, it is preferable that the perovskite precursor liquid further contains an organic hydrochloride that promotes the growth of crystals of the perovskite compound.

The solvent may be a polar aprotic solvent such as DMF, DMSO, NMP, GBL, or acetonitrile, either alone or in a mixture of multiple types, and may further contain other types of solvents.

As the perovskite precursor, a metal halide BX and AX composed of an organic halide or an alkali metal halide are used in a predetermined ratio. The molar concentration of the metal atom B (the metal part of the metal halide) is preferably 0.5 mol% to 10 mol% in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal. This expels other materials to the front and back interfaces of the perovskite precursor liquid in the crystallization process, suppresses other materials from being left behind in the impurity film 41 formed between the crystals of the perovskite compound being generated, and suppresses a decrease in photoelectric conversion efficiency due to the remaining other materials.

As described above, the hole transport layer forming compound is a material that forms a self-assembled monolayer having hole selective permeability. When the perovskite precursor liquid is applied onto the first electrode layer 20, the hole transport layer forming compound preferentially self-assembles at the interface with the first electrode layer 20 to form a film (hole transport layer 30). The remaining hole transport layer forming compound that has formed a film at the interface with the first electrode layer 20 also self-assembles on the surface of the coating of the perovskite precursor liquid (the side opposite to the first electrode layer 20) to form a film (excess material layer 50). The concentration of the hole transport layer forming compound in the perovskite precursor liquid can be 0.1 mmol/L or more and 5.0 mmol/L or less. A concentration of 0.5 mmol/L or more and 2.0 mmol/L or more is more preferable. Within the range in which the substrate surface can be covered, a lower concentration can suppress the formation of the excess material layer 50.

The specific organic compound aggregates in a film shape on the surface of the coating film of the perovskite precursor liquid, and partially covers the surface of the layer of the perovskite compound (photoelectric conversion layer 40) generated from the perovskite precursor, thereby forming a passivation layer 60 that suppresses the recombination of photocarriers (holes and electrons) at the interface of the photoelectric conversion layer 40. In addition, the specific organic compound inhibits the growth of the film of the hole transport layer forming compound on the surface of the coating film of the perovskite precursor liquid, thereby reliably forming a region where the excess material layer 50 does not exist and the passivation layer 60 exists. The concentration of the specific organic compound in the perovskite precursor liquid can be 1 μmol/L or more and 5 mmol/L or less. A more preferable range is 50 μmol/L or more and 2 mmol/L or less. In order to obtain high performance, it is preferable that the coverage rate of the specific organic compound on the surface is high, and more preferably, the specific organic compound is made to cover almost the entire surface (for example, 90% or more of the region, etc.), thereby suppressing the inhibition of electron transport by the hole transport layer forming compound. On the other hand, if the concentration of the specific organic compound is increased to improve the coverage, it may be taken into the perovskite compound and act as an impurity, making it easier for recombination to occur, or forming multiple layers may cause resistance, which may result in a decrease in performance. Therefore, as with the hole transport layer forming compound, the molecular length is assumed to be the unit (lattice constant) of the monomolecular film, the number of specific organic compounds per coating area is estimated, and the concentration is determined so that the number of specific organic compounds contained in the coating film is smaller than that. If the specific organic compound is an ionic material, the molecular weight is determined by the ions containing the specific organic compound.
There are cases where the passivation layer 60 and the excess material layer 50 do not cover the entire surface of the photoelectric conversion layer 40. In that case, a separate passivation layer may be formed as an additional layer. The additional passivation layer may be formed from an organic compound in a solution, or may be formed by vapor deposition of an inorganic material such as lithium fluoride or magnesium difluoride.

Some organic hydrochlorides have the function of promoting the crystallization of the perovskite compound and increasing the grain size of the perovskite crystal. Examples include methylammonium hydrochloride (MACl), formamidinium hydrochloride (FACl), and methylenediaminium hydrochloride (MDACl ₂ ). In these organic hydrochlorides, only the organic portion remains in the perovskite crystal, and the hydrochloric acid portion functions to bond the crystal grains. This reduces the area of the grain boundaries in the photoelectric conversion layer 40, suppresses the generation of impurities between the perovskite crystals, and achieves high photoelectric conversion efficiency. The portion other than the hydrochloride is preferably equal to or smaller than the crystal lattice of the perovskite crystal and has an amino group. The concentration of the hydrochloride in the perovskite precursor liquid can be 0.05 mol% or more and 40 mol% or less with respect to the molar concentration of the metal ion located at the center (B site) of the crystal of the perovskite compound. Chlorides containing alkyl metals may also have a similar effect. For example, cesium chloride (CsCl) and rubidium chloride (RbCl) can be mentioned.

In the crystallization process of step S3, the solvent is evaporated from the coating of the perovskite precursor liquid to dry the coating, and the perovskite precursor is reacted to generate crystals of the perovskite compound. This forms a photoelectric conversion layer 40 mainly composed of the perovskite compound, and fixes the hole transport layer 30, the excess material layer 50, and the passivation layer 60. In addition, when the crystals of the perovskite compound grow, an impurity film 41 containing excess metal B and metal compounds is formed between the crystal grains of the perovskite compound. Since the crystals of the perovskite compound grow from the surface side (the side opposite to the first electrode layer 20), the impurity film 41 also grows from the surface side toward the first electrode layer 20. As a method for promoting the generation of crystals of the perovskite compound in the film of the perovskite precursor liquid, for example, poor solvent quenching, vacuum quenching, gas quenching, laser processing, etc. can be adopted. If the crystallization of the perovskite compound is too fast, the crystal growth of the specific organic compound will end before it reaches the surface, so it is preferable to slow down the crystallization of the perovskite compound so that it can grow sufficiently on the surface. From this perspective, vacuum quenching or gas quenching is more preferable. In the crystallization process of step S3, the dried coating film of the perovskite precursor liquid may be further heated. Heating is a preferable method for removing the hydrochloric acid portion of the organic hydrochloride salt.

In the electron transport layer formation step S4, the electron transport layer 70 is formed by a method such as a coating method or a vacuum deposition method. A hole blocking layer may be formed on the electron transport layer 70 by a vacuum deposition method or an atomic deposition method.

In the second electrode formation process of step S5, the second electrode layer 80 is formed by a method such as sputtering, vacuum deposition, plating, or coating, depending on the material used.

As described above, the perovskite precursor liquid according to one embodiment of the present invention contains a perovskite precursor, a hole transport layer forming compound, and a specific organic compound, and therefore a hole transport layer 30 and a photoelectric conversion layer 40 can be simultaneously formed on the first electrode layer 20 by a single coating, while a passivation layer 60 is formed on the surface of the photoelectric conversion layer 40, preventing the photoelectric conversion layer 40 from being completely covered with an excess material layer 50 that inhibits the transfer of electrons. Therefore, the solar cell manufacturing method according to one embodiment of the present invention can easily manufacture a solar cell 1 having a relatively high photoelectric conversion efficiency.

[Second embodiment]
3 is a schematic cross-sectional view showing the configuration of a solar cell 101 according to a second embodiment of the present invention. The solar cell 101 includes a plate-like or sheet-like base material 110, a first electrode layer 120 laminated on one main surface (the lower side of FIG. 3) of the base material 110, a hole transport layer 130 laminated on one side of the first electrode layer 120, a photoelectric conversion layer 140 laminated on one side of the hole transport layer 130, an excess material layer 150 partially laminated on one side of the photoelectric conversion layer 140, a passivation layer 160 laminated in an area where the excess material layer 150 is absent on one side of the photoelectric conversion layer 140, an electron transport layer 170 laminated on one side of the excess material layer 150 and the passivation layer 160, and a second electrode layer 180 laminated on one side of the electron transport layer 170.

The substrate 110 is a structure that supports the other layers and ensures the strength of the solar cell 101. When the solar cell 101 receives light from the substrate 110 side, the substrate 110 is formed from a transparent material. Specifically, the substrate 110 may be formed from glass, or a resin such as polyimide, polyamide, or polyethylene terephthalate. When the solar cell 101 receives light from the second electrode layer 180 side, the substrate 110 may be formed from a composite material including a metal layer, or the like.

The first electrode layer 120 collects holes generated in the photoelectric conversion layer 140 through the hole transport layer 130 and outputs them to the outside. The first electrode layer 120 can be formed of a transparent conductive oxide (TCO) having electrical conductivity and optical transparency. Examples of the transparent conductive oxide that forms the first electrode layer 120 include indium oxide, tin oxide, zinc oxide, titanium oxide, and composite oxides thereof. Among these, indium-based composite oxides mainly composed of indium oxide, zinc oxide, tungsten oxide, molybdenum oxide, etc., or fluorine-doped tin oxide are preferred. In terms of high electrical conductivity and transparency, indium oxide is particularly preferred. In order to improve the formability of the hole transport layer 130, the first electrode layer 120 is preferably subjected to a surface treatment such as ozone treatment, and may have a multilayer structure having a layer of a p-type oxide semiconductor mainly composed of nickel oxide, niobium oxide, etc. on the surface.

The hole transport layer 130 is formed from a film of a hole transport layer forming compound that forms a self-assembled monolayer (SAM). The hole transport layer 130 transmits only holes out of the positive and negative photocarriers (holes and electrons) generated in the photoelectric conversion layer 140 to the first electrode layer 120. In order to facilitate the transmission of holes, the highest occupied orbital of the hole transport layer forming compound is preferably close to the valence band of the perovskite compound that performs photoelectric conversion, and in order to block electrons, the lowest unoccupied orbital is preferably smaller than the conduction band. The hole transport layer forming compound that forms the hole transport layer 130 preferably has a functional functional group capable of transporting holes, such as a carbazole system, a phenothiazine system, or a dimethylacridine system, and a self-assembled terminal group that chemically bonds to the substrate, such as phosphoric acid and carboxylic acid. In order to impart passivation properties to the hole transport layer 130, it is preferable that a linear structure such as an alkyl chain is present between the functional group and the self-assembled terminal group. The alkyl chain preferably has four or more carbon atoms. Specifically, examples of the hole transport layer forming compound that forms the hole transport layer 130 include Me-4PACz ([4-(3,6-Dimethyl-9H-carbazol-9-yl) butyl] phosphoric acid), MeO-4PACz ([4-(3,6-Dimethoxy-9H-carbazol-9-yl) butyl] phosphoric acid), DMAcPA ((4-(2,7-dibromo-9,9-dimethylacridin-10(9H)-yl) butyl) phosphoric acid), etc.

The photoelectric conversion layer 140 contains a perovskite compound that performs photoelectric conversion, and absorbs incident light to generate photocarriers. The perovskite compound contained in the photoelectric conversion layer 140 includes an organic atom A containing at least one of an alkali metal (Am), a monovalent organic ammonium ion, and an amidinium-based ion, a metal atom B that generates a divalent metal ion, and a halogen atom X containing at least one of an iodide ion I, a bromide ion Br, a chloride ion Cl, and a fluoride ion F, and can be a compound represented by ABX3. Examples of the alkali metal at the A site include potassium K, cesium Cs, and rubidium Rb, and examples of the organic atom A include methylammonium MA (CH ₃ NH ₃ ), formamidinium FA (CH ₃ N ₂ ), and the like. Examples of the metal atom B include lead Pb and tin Sn, and it is preferable that the main component is lead. The halogen atom X is preferably at least one of iodide I, bromide Br, and chloride Cl.

Specifically, preferred perovskite compounds include methylammonium lead halides (MAPbX ₃ ) such as MAPbI ₃ , MAPbBr ₃ , and MAPbCl ₃ , and formamidinium lead halides (FAPbX ₃ ) such as FAPbI ₃ , FAPbBr ₃ , and FAPbCl _3. The halogen atom X may include multiple types. It may be FA _y MA _1-y PbX ₃ , which contains both methylammonium and formamidinium. In addition, when an alkali metal is included, examples include Am _y FA _z MA _1-y-z PbIX and Am _y FA _1-y PbIX. Am may be a single type of Cs, Rb, or K, or may include multiple types. (y and z are any positive integers).

The photoelectric conversion layer 140 preferably has an impurity film 141 containing a halide of a metal atom in the perovskite compound, such as Pb, PbI ₂ , PbBr ₂ , or PbCl ₂ , at the grain boundary of the crystal of the perovskite compound. In order to form such an impurity film 141, the metal B in the perovskite compound is preferably lead (Pb). By the photoelectric conversion layer 140 having the impurity film 141 containing the metal atom B and a metal compound, the hole transport layer forming compound forming the hole transport layer 130 and the material forming the passivation layer 160 are prevented from being left behind at the grain boundary of the crystal of the perovskite compound when the photoelectric conversion layer 140 is formed, and the photoelectric conversion efficiency can be improved.

The excess material layer 150 is formed from the same hole transport layer forming compound as that forming the hole transport layer 130. The hole transport layer forming compound used as the hole transport layer 130 has the lowest unoccupied orbital below the conduction band of the perovskite compound in order to block electron transport, making it difficult for electrons to reach the electron transport layer and acting as a resistor. Ideally, it is preferable that the excess material layer 150 is not formed, but when the hole transport layer 130 and the photoelectric conversion layer 140 are formed in the same process, it is necessary to mix a slightly larger amount of the hole transport layer forming compound in order to form a seamless hole transport layer 130 that covers the entire surface of the first electrode layer 120, and the excess of the hole transport layer forming compound forms the excess material layer 150. Because it is difficult to accurately grasp the growth state of the hole transport layer-forming compound on the TCO surface, we simply assume that the molecular length is the unit (lattice constant) of the monolayer, estimate the number of hole transport-forming compounds per coating area, and determine the concentration so that the number of hole transport-forming compounds contained in the coating film is greater than that.

The passivation layer 160 prevents the recombination of photocarriers at the interface with the photoelectric conversion layer 140 and promotes the arrival of electrons at the electron transport layer 170. The passivation layer 160 is formed so as to compete with the surface of the excess material layer 150 and the photoelectric conversion layer 140, and prevents the excess material layer 150 from covering the entire surface of the photoelectric conversion layer 140 and reducing the photoelectric conversion efficiency. The passivation layer 160 contains a piperazine compound and is prone to exhibiting poor solubility at room temperature in solvents including aprotic polar solvents such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and acetonitrile, which are used to form the photoelectric conversion layer 140. Therefore, compared to the excess material layer 150, the passivation layer 160 is less likely to be involved in the crystal growth of the perovskite material and precipitates on the surface and grain boundaries of the photoelectric conversion layer 140. It is known that the crystallization process occurs from the surface, and the poorly soluble piperazine compound is first precipitated on the surface, followed by the perovskite compound containing the hole transport forming compound. By precipitating on the surface, the piperazine compound is more likely to transport electrons while maintaining passivation properties. In particular, by forming a halogenated salt of the piperazine compound and making it an ionic material, the piperazine compound becomes more poorly soluble and more likely to precipitate on the surface. In addition, by having a hydrophobic group such as an alkyl chain or a fluorine-containing organic group bonded to one of the nitrogen groups, it is possible to further promote deposition on the surface. The fluorine-containing organic group is preferably a fluorinated alkyl group. Here, the "piperazine compound" refers to at least one of piperazine and piperazine derivatives (including halogenated salts) represented by the following chemical formulas 1 to 3, and may be a mixture of multiple types of these. In addition, R1 to R8 in the formula are hydrogen or any substituent, RA1 to RA4 are hydrogen or an alkyl group, and X is a halogen. The deposition of piperazine compounds on surfaces can be confirmed by time-of-flight secondary ion mass spectrometry.

Specific examples of piperazine derivatives include piperazine-1,4-diium iodide, piperazineinium iodide, pentylpiperazine hydrochloride, and 1-(2-fluoroethyl) piperazine dihydrochloride.

The passivation layer 160 preferably further contains a fluorine-containing organic compound. Fluorine-containing organic compounds have high surface deposition properties and high electron transport capabilities. On the other hand, they have low surface energy and low adhesion to materials grown on them. In addition, when formed by coating, they tend to exhibit lyophobicity, which can cause coating defects. Therefore, by combining them with specific organic compounds, it is possible to improve adhesion and coating properties.

The fluorine-containing organic compound preferably has a carbon skeleton containing an alkyl chain or benzene, and has a structure in which hydrogen is partially replaced by fluorine or a trifluoromethyl group. It is more preferable that the carbon skeleton contains consecutive carbons to which fluorine is bonded. When the fluorine-containing organic compound has a benzene skeleton, it is preferable that any of the six hydrogens of benzene are replaced by fluorine or a trifluoromethyl group, and one is connected to a lyophilic group at the end. The greater the number of fluorine and trifluoromethyl group replacements, the higher the lyophobicity becomes, and the greater the effect of selectively orienting to the surface. Therefore, when replaced by fluorine, it is preferable to have a structure of pentafluorinated benzene in which all hydrogens except one connected to the end are replaced by fluorine. When the fluorine-containing organic compound has an alkyl chain skeleton, it is preferable that the tip is a trifluoromethyl group or a phenyl group containing fluorine or a trifluoromethyl group, and the end is a lyophilic group. The tip containing fluorine is oriented toward the electron transport layer side, and the end containing the lyophilic group is oriented toward the perovskite surface side. It is preferable that the straight chain skeleton excluding the tip and end has 1 to 17 carbon atoms. More preferably, the number of carbon atoms is 5 or more and 16 or less. In order to promote the formation of the passivation layer 160 by self-organization, the longer the alkyl chain, the better the orientation and the better the passivation, but the higher the insulation and the lower the conductivity. Therefore, by providing an alkyl chain that is equal to or greater than the upper limit, sufficient orientation can be achieved, and by being equal to or less than the lower limit, both passivation and conductivity can be achieved. When the fluorine-containing organic compound has an alkyl chain skeleton and the tip is a trifluoromethyl group, it is preferable that the alkyl chain continuing from the tip contains fluorinated carbons in succession. More preferably, all of the carbons except for one or two carbons adjacent to the end are fluorinated. By continuously fluorinating, the lyophobicity is increased, and the formation of the passivation layer 160 can be promoted by selectively precipitating on the surface. Another example of a fluorine-containing organic compound having an alkyl chain skeleton is a polymer structure. The partially fluorinated polymer structure, unlike the one in which the tip containing fluorine is oriented on the electron transport layer side and the end containing lyophilic groups is oriented on the perovskite surface side by containing a lot of fluorine, tends to be oriented on the surface in a planar manner. In the case where the fluorine-containing organic compound has an alkyl chain skeleton and the tip is a phenyl group containing fluorine or trifluoromethyl group, the effect is greater as the number of substitutions of fluorine and trifluoromethyl group increases, as described above. Therefore, when hydrogen of the phenyl group is substituted with fluorine, pentafluorinated benzene is preferable. In addition, by having both a phenyl group having fluorine and a trifluoromethyl group and an alkyl chain, it is possible to promote deposition on the surface more selectively than in the case of only a benzene skeleton. In addition, it is preferable that the fluorine-containing organic compound has at least one or more lyophilic groups, specifically, amino groups, hydrazine groups, trialkylamino groups, phosphoric acid groups, phosphonic acid groups, hydroxyl groups, carboxyl groups, and sulfonyl groups, and ionized forms thereof, at the end. These have lyophilicity with respect to the aprotic polar solvent, which is the solvent for making the photoelectric conversion layer 140, and can be positioned on the surface of the photoelectric conversion layer 140 from a stage before the drying process by combining with a fluorine-containing skeleton that is lyophobic. By having a straight-chain skeleton or a lyophilic group, or both, each fluorine-containing organic compound is easy to align, a thin and uniform film can be formed, and series resistance can be reduced. By ionizing these ends, defects such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer are compensated for, thereby improving performance. In addition, there may be multiple types of fluorine-containing organic compounds. In addition, these end groups may be ionized in the solvent. It is more preferable that the fluorine-containing organic compound has both a cationic end group and an anionic end group in order to compensate for defects that exist with different charges, such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer. Examples of ends that have both a cationic end group and an anionic end group include phosphocholine groups and carbamic acid groups.

Specific examples of fluorine-containing organic compounds include those having a benzene skeleton substituted with fluorine and a trifluoromethyl group, such as 4-fluorophenethylamine hydroiodide (FPEAI), 4-(trifluoromethyl)phenylammonium hydroiodide, 2,6-difluoroaniline, 3,4,5-trifluoroaniline, pentafluorophenylphosphonic acid (5FPAc), pentafluorophenylhydrazine (5FPHZ), and pentafluorobenzene-amino-carboxylic acid (carbamic acid) hydroiodide. When the fluorine-containing organic compound has an alkyl chain skeleton, examples of compounds having a trifluoromethyl group at the end and a lyophilic end include 1H,1H-undecafluorohexylamine ( _{CF3 ( CF2} ) _4CH2NH2 ) _, 1H,1H-pentadecafluorooctylamine ( _CF3 ( _CF2 ) _6CH2NH2 ), (fluorinated) Fos-Choline- ₈ (registered trademark: _{C13H17F13NO4P} ), _2,2,2 - _{trifluoroethylamine} ( _CF3CH2NH2 ), and 3,3,4,4,5,5,6,6 _{- nonafluorohexylphosphonic acid} (FHPA), and examples of compounds having _a polymer structure include polyvinylidene fluoride (PVDF). When the fluorine-containing organic compound has an alkyl chain skeleton, an example of a compound having a phenyl group containing fluorine or a trifluoromethyl group is 12-pentafluorophenoxydodecylphosphonic acid (C ₁₈ H ₂₆ F ₅ O ₄ P). It can be confirmed by observing the contact angle that the fluorine-containing organic compound is deposited on the surface as a passivation layer. For example, when evaluated with chlorobenzene, the contact angle increases with the addition of a small amount of a linear fluoroalkyl chain, 1H,1H-undecafluorohexylamine, (fluorinated)Fos-Choline-8, etc., which have high lyophilicity.

The electron transport layer 170 selectively transmits electrons and transfers them to the second electrode layer 180. The electron transport layer 170 is formed of a material mainly composed of fullerene, for example. Examples of fullerene include C60, C70, their hydrides, oxides, metal complexes, and derivatives with alkyl groups added thereto, for example PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester). In addition, a hole blocking layer such as pasocuproine (BCP), lithium fluoride (LiF), aluminum-doped zinc oxide (ZnO), or titanium oxide (TiO ₂ ) may be included between the electron transport layer 170 and the second electrode layer 180. The inorganic oxide layer may be doped with another metal material.

When the solar cell 101 receives light from the substrate 110 side, the second electrode layer 180 preferably includes a metal layer made of, for example, copper, in order to reduce electrical resistance. When the solar cell 101 receives light from the second electrode layer 180 side, the second electrode layer 180 may be made of a transparent conductive oxide.

The solar cell 101 having the above configuration is manufactured by a solar cell manufacturing method according to one embodiment of the present invention shown in Figure 4. The solar cell manufacturing method of this embodiment includes a first electrode layer forming step (step S11), a precursor liquid application step (step S12), a crystallization step (step S13), an electron transport layer forming step (step S14), and a second electrode layer forming step (step S15).

In the first electrode layer forming process of step S11, the first electrode layer 120 is formed on one main surface of the substrate 110. The first electrode layer 120 can be laminated using a vacuum film forming technique such as sputtering. In the first electrode layer process, it is preferable to modify the surface of the formed first electrode layer 120 in order to promote the formation of the hole transport layer 130 in the next process. Specific methods for modifying the surface of the first electrode layer 120 include, for example, hydroxylation of the surface by ultraviolet-ozone treatment or ozone water washing, film formation by vacuum film forming techniques such as sputtering of oxides such as nickel oxide, which is prone to grow a self-assembled film, film formation by coating technology of oxide nanoparticles, and heat treatment to activate the surface and remove impurities so that a self-assembled film can easily grow.

In the precursor liquid application process of step S12, the perovskite precursor liquid is applied to the first electrode layer 120. The perovskite precursor liquid can be applied using, for example, a die coater, a bar coater, or the like. The perovskite precursor liquid applied in the precursor liquid application process is itself one embodiment of the perovskite precursor liquid according to the present invention.

The perovskite precursor liquid contains a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer forming compound that forms a self-assembled monolayer that has hole selective permeability, and a piperazine compound. In addition, the perovskite precursor liquid preferably further contains a hydrochloride that promotes the growth of crystals of the perovskite compound.

The solvent may be a polar aprotic solvent such as DMF, DMSO, NMP, GBL, or acetonitrile, either alone or in a mixture of multiple types, and may further contain other types of solvents.

As the perovskite precursor, a metal halide BX and AX composed of an organic halide or an alkali metal halide are used in a predetermined ratio. The molar concentration of the metal atom B is preferably 0.5 mol% to 10 mol% in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal. This expels other materials to the front and back interfaces of the perovskite precursor liquid in the crystallization process, suppresses other materials from being left behind in the impurity film 141 formed between the crystals of the perovskite compound being generated, and suppresses a decrease in photoelectric conversion efficiency due to the remaining other materials.

As described above, the hole transport layer forming compound is a material that forms a self-assembled monolayer having hole selective permeability. When the perovskite precursor liquid is applied onto the first electrode layer 120, the hole transport layer forming compound preferentially self-assembles at the interface with the first electrode layer 120 to form a film (hole transport layer 130). The remaining hole transport layer forming compound that has formed a film at the interface with the first electrode layer 120 also self-assembles on the surface of the coating of the perovskite precursor liquid (the side opposite to the first electrode layer 120) to form a film (excess material layer 150). The concentration of the hole transport layer forming compound in the perovskite precursor liquid can be 0.1 mmol/L or more and 5.0 mmol/L or less. A concentration of 0.5 mmol/L or more and 2.0 mmol/L or less is more preferable. Within the range in which the substrate surface can be covered, a lower concentration can suppress the formation of the excess material layer 150.

The piperazine compound aggregates in a film on the surface of the coating of the perovskite precursor liquid, partially covering the surface of the layer of the perovskite compound (photoelectric conversion layer 140) generated from the perovskite precursor, thereby forming a passivation layer 160 that suppresses the recombination of photocarriers (holes and electrons) at the interface of the photoelectric conversion layer 140. In addition, the piperazine compound preferentially precipitates on the surface of the coating of the perovskite precursor liquid, and by inhibiting the growth of the film of the hole transport layer forming compound, it reliably forms an area where there is no excess material layer 150 and where there is a passivation layer 160. The concentration of the piperazine compound in the perovskite precursor liquid can be 1 μmol/L or more and 5 mmol/L or less. A more preferable range is 50 μmol/L or more and 2 mmol/L or less. In order to obtain high performance, it is preferable that the coverage rate of the piperazine compound on the surface is high, and more preferably, the piperazine compound is applied to almost the entire surface (for example, 90% or more of the area), so that the inhibition of electron transport by the hole transport layer can be suppressed. On the other hand, if the concentration of the piperazine compound is increased to improve the coverage rate, it may be taken into the perovskite compound and act as an impurity, making recombination more likely to occur, and if multiple layers are formed, it may become a resistance, which may reduce performance. Therefore, as with the hole transport layer forming compound, the molecular length is assumed to be the unit unit (lattice constant) of the monomolecular film, the number of piperazine compounds per coating area is estimated, and the concentration is determined so that the number of piperazine compounds contained in the coating film is smaller than that. When the piperazine compound is an ionic material, the molecular weight is determined by the ions containing the piperazine ring.

The hydrochloride promotes the crystallization of the perovskite compound and increases the grain size of the perovskite crystal. This reduces the area of the grain boundaries in the photoelectric conversion layer 140 and suppresses the decrease in photoelectric conversion efficiency due to impurities between the perovskite crystals. Examples of hydrochloride include methylammonium hydrochloride (MACl), formamidinium hydrochloride (FACl), and methylenediaminium hydrochloride (MDACl ₂ ). The portion other than the hydrochloride is preferably equal to or smaller than the crystal lattice of the perovskite crystal and has an amino group. The concentration of the hydrochloride in the perovskite precursor liquid can be 0.05 mol% or more and 40 mol% or less with respect to the molar concentration of the metal ion located at the center (B site) of the crystal of the perovskite compound. Chlorides containing alkyl metals may also have a similar effect. For example, cesium chloride (CsCl) and rubidium chloride (RbCl) can be mentioned.

In the crystallization process of step S13, the film of the perovskite precursor liquid is dried (the solvent is evaporated) to react the perovskite precursor to generate crystals of the perovskite compound. This forms a photoelectric conversion layer 140 mainly composed of the perovskite compound, which fixes the hole transport layer 130, the excess material layer 150, and the passivation layer 160. In addition, when the crystals of the perovskite compound grow, an impurity film 141 containing excess metal B and metal compounds is formed between the crystal grains of the perovskite compound. Since the crystals of the perovskite compound grow from the surface side (the side opposite to the first electrode layer 120), the impurity film 141 also grows from the surface side toward the first electrode layer 120. As a method for promoting the generation of crystals of the perovskite compound in the film of the perovskite precursor liquid, for example, poor solvent quenching, vacuum quenching, gas quenching, laser processing, etc. are preferably adopted. Poor solvent quenching, vacuum quenching, and gas quenching, in which crystallization begins from the surface, are more preferred. Furthermore, in order to facilitate uniform growth of the passivation layer on the surface side of the coating film of the perovskite precursor liquid, it is preferable to cause the crystallization of the perovskite compound to proceed slowly relative to the precipitation of the passivation layer. From this perspective, vacuum quenching and gas quenching are more preferred. In the crystallization process of step S13, the dried coating film of the perovskite precursor liquid may be further heated.

In step S14, the electron transport layer formation process, the electron transport layer 170 is formed by a method such as a coating method or a vacuum deposition method. A hole blocking layer may be formed on the electron transport layer 170 by a vacuum deposition method or an atomic deposition method.

In the second electrode layer formation process of step S15, the second electrode layer 180 is formed by a method such as sputtering, vacuum deposition, plating, or coating, depending on the material used.

As described above, the perovskite precursor liquid according to one embodiment of the present invention contains a perovskite precursor, a hole transport layer forming compound, and a piperazine compound, and therefore a hole transport layer 130 and a photoelectric conversion layer 140 can be simultaneously formed on the first electrode layer 120 by a single coating, while a passivation layer 160 is formed on the surface of the photoelectric conversion layer 140, thereby preventing the photoelectric conversion layer 140 from being completely covered with an excess material layer 150 that inhibits the transport of electrons. Therefore, the solar cell manufacturing method according to one embodiment of the present invention can easily manufacture a solar cell 101 having a relatively high photoelectric conversion efficiency.

[Third embodiment]
5 is a schematic cross-sectional view showing the configuration of a solar cell 101 according to a third embodiment of the present invention. The solar cell 201 includes a plate-like or sheet-like base material 210, a first electrode layer 220 laminated on one main surface (the lower side of FIG. 5) of the base material 210, a hole transport layer 230 laminated on one side of the first electrode layer 220, a photoelectric conversion layer 240 laminated on one side of the hole transport layer 230, an excess material layer 250 partially laminated on one side of the photoelectric conversion layer 240, a passivation layer 260 laminated in an area where the excess material layer 250 is absent on one side of the photoelectric conversion layer 240, an electron transport layer 270 laminated on one side of the excess material layer 250 and the passivation layer 260, and a second electrode layer 280 laminated on one side of the electron transport layer 270.

The substrate 210 is a structure that supports the other layers and ensures the strength of the solar cell 201. When the solar cell 201 receives light from the substrate 210 side, the substrate 210 is formed from a transparent material. Specifically, the substrate 210 may be formed from glass, or a resin such as polyimide, polyamide, or polyethylene terephthalate. When the solar cell 201 receives light from the second electrode layer 280 side, the substrate 210 may be formed from a composite material including a metal layer.

The first electrode layer 220 collects holes generated in the photoelectric conversion layer 240 through the hole transport layer 230 and outputs them to the outside. The first electrode layer 220 may be formed of a transparent conductive oxide (TCO) having electrical conductivity and optical transparency. Examples of the transparent conductive oxide that can be used to form the first electrode layer 220 include indium oxide, tin oxide, zinc oxide, titanium oxide, and composite oxides thereof. Among these, indium-based composite oxides mainly composed of indium oxide, zinc oxide, tungsten oxide, molybdenum oxide, etc., or fluorine-doped tin oxide are preferred. In terms of high electrical conductivity and transparency, indium oxide is particularly preferred. In order to improve the formability of the hole transport layer 230, the first electrode layer 220 is preferably subjected to a surface treatment such as ozone treatment, and may have a multilayer structure having a layer of a p-type oxide semiconductor mainly composed of nickel oxide, niobium oxide, etc. on the surface.

The hole transport layer 230 is formed from a film of a hole transport layer forming compound that forms a self-assembled monolayer (SAM) that can transport (selectively transmit) holes. The hole transport layer 230 transmits the holes of the positive and negative photocarriers (holes and electrons) generated in the photoelectric conversion layer 240 to the first electrode layer 220. In order to facilitate the transport of holes, the highest occupied orbital of the hole transport layer forming compound is preferably close to the valence band of the perovskite compound that performs photoelectric conversion, and in order to block electrons, the lowest unoccupied orbital is preferably smaller than the conduction band (close to the vacuum level). The hole transport layer forming compound that forms the hole transport layer 230 preferably has a functional functional group capable of transporting holes, such as a carbazole system, a phenothiazine system, or a dimethylacridine system, and a self-assembled terminal group that chemically bonds to the substrate, such as phosphoric acid and carboxylic acid. In order to impart passivation properties to the hole transport layer 230, it is preferable that there is a linear structure such as an alkyl chain between the functional group and the self-assembled terminal group. The alkyl chain preferably has four or more carbon atoms. Specifically, examples of hole transport layer forming compounds that form the hole transport layer 230 include Me-4PACz ([4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid) and Me-6PACz ([6-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid)).

The photoelectric conversion layer 240 contains a perovskite compound that performs photoelectric conversion, and absorbs incident light to generate photocarriers. As the perovskite compound contained in the photoelectric conversion layer 240, a compound represented by ABX3 can be used, which contains an organic atomic group A containing at least one of monovalent organic ammonium ions and amidinium ions, a metal atom B that generates a divalent metal ion, and a halogen atom X containing at least one of iodide ions I, bromide ions Br, chloride ions Cl, and fluoride ions F. In addition, perovskite compounds in which a part _or all of the organic atomic group A is replaced with an alkali metal Am are not excluded from the present invention.

Examples of the organic atomic group A include methylammonium MA (CH ₃ NH ₃ ) and formamidinium FA (CH ₃ N ₂ ). Examples of the alkali metal Am include potassium K, cesium Cs, and rubidium Rb. Among them, when the power generation efficiency of the solar cell 201 is important, cesium Cs and rubidium Rb are preferable as the alkali metal Am, and cesium Cs is particularly preferable from the viewpoint of cost and availability. Examples of the metal atom B include lead Pb and tin Sn. The amount of lead and tin is adjusted according to the required band gap. The halogen atom X is preferably at least one of iodide I, bromide Br, and chloride Cl.

Specifically, preferred perovskite compounds include methylammonium lead halides (MAPbX ₃ ) such as MAPbI ₃ , MAPbBr ₃ , and MAPbCl ₃ , and formamidinium lead halides (FAPbX 3 ) such as FAPbI ₃ , FAPbBr ₃ , and FAPbCl ₃ . The halogen atom X may include multiple types, and may be FA _y MA _1-y PbX ₃ containing both methylammonium and formamidinium as the organic atomic group A. In addition, when the alkali metal Am is included, examples include Am _y FA _z MA _1-y-z PbI _X and _{Am y} FA _1-y PbI _X. Am may be a single type of Cs, Rb, or K, or may include multiple types (y and z are any positive integers).

The excess material layer 250 is formed from the same hole transport layer forming compound as that forming the hole transport layer 230. The hole transport layer forming compound used as the hole transport layer 230 has a lowest unoccupied orbital lower than the conduction band of the perovskite compound (close to the vacuum level), so that electron transport is blocked, making it difficult for electrons to reach the electron transport layer, and it behaves as a resistor. Ideally, it is preferable that the excess material layer 250 is not formed, but when the hole transport layer 230 and the photoelectric conversion layer 240 are formed in the same process, in order to form a continuous hole transport layer 230 that covers the entire surface of the first electrode layer 220, it is necessary to mix a slightly larger amount of the hole transport layer forming compound, and the excess of the hole transport layer forming compound forms the excess material layer 250. The excess material layer 250 may be composed of only the hole transport layer forming compound, or may contain other materials contained in the perovskite precursor liquid. The weight content of the hole transport layer forming compound in the excess material layer 250 is preferably 10% or more, more preferably 30% or more. The weight content of the hole transport layer forming compound in the excess material layer 250 is preferably 90% or less, more preferably 70% or less. In other words, in the region where the passivation layer is not formed, the perovskite compound is partially in direct contact with the electron transport layer, which enables electron transport. However, it is preferable that the hole transport layer forming compound is formed on the perovskite compound surface to repel the electrons again into the perovskite compound layer, rather than forming a surface containing many defects. The weight content of the hole transport layer forming compound in the excess material layer can be calculated based on the composition of the excess material layer measured by combining transmission electron microscope observation and energy dispersive X-ray analysis. Because it is difficult to accurately grasp the growth state of the hole transport layer-forming compound on the TCO surface, we simply assume that the molecular length is the unit (lattice constant) of the monolayer, estimate the number of hole transport-forming compounds per coating area, and determine the concentration so that the number of hole transport-forming compounds contained in the coating film is greater than that.

The passivation layer 260 prevents the recombination of photocarriers at the interface with the photoelectric conversion layer 240 and promotes the arrival of electrons at the electron transport layer 270. The passivation layer 260 is formed so as to compete with the surface of the excess material layer 250 and the photoelectric conversion layer 240, and prevents the excess material layer 250 from covering the entire surface of the photoelectric conversion layer 240 and reducing the photoelectric conversion efficiency. The passivation layer 260 contains a polymer passivation compound having a repeating unit having a heterocycle containing nitrogen. Since the polymer passivation compound is a polymer and has a large size, when the photoelectric conversion layer 240 is formed using the perovskite precursor liquid described later, it is not incorporated into the perovskite crystal and is preferentially precipitated on the surface. Therefore, the formation of the excess material layer 250 can be suppressed to form the passivation layer 260. In order to ensure the formation of the passivation layer 260, the molecular weight of the polymer passivation compound is preferably 5,000 to 5,000,000 in weight average. A molecular weight of 10,000 or more is more preferable to ensure that the compound is not incorporated into the perovskite compound, and a molecular weight of 2.5 million or less is more preferable to maintain solubility in the solvent. The polymer passivation compound has a nitrogen-containing heterocycle in the repeating unit, which prevents recombination and allows electrons to pass efficiently. A polymer passivation halide may also be used. A polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle is easy to form a polymer passivation compound with halogen ions in the precursor liquid. By forming a polymer passivation halide, halogen defects caused by aging on the surface of the perovskite compound can be compensated for, improving the reliability of the solar cell characteristics.

If the coverage of the photoelectric conversion layer 240 by the passivation layer 260 is 50% or more, electron transport can be performed effectively. Furthermore, if it is 90% or more, the effect is enhanced, which is preferable. Furthermore, if it is 99% or less, the resistance loss caused by partial thickening of the polymer passivation compound can be reduced. Furthermore, if it is 95% or less, the resistance loss can be suppressed more effectively.

The nitrogen-containing heterocycle of the polymer passivation compound is preferably pyridine, pyrrolidone, phthalimide, caprolactam, imidazole, imidazolium, triazole, thiazole, piperidium, and derivatives thereof. The polymer passivation compound preferably has a larger band gap than the perovskite compound. More preferably, the highest occupied molecular orbital of the polymer passivation compound is larger than the valence band of the perovskite compound (farther than the vacuum level), and the lowest unoccupied molecular orbital of the polymer passivation compound is smaller than the conduction band of the perovskite compound (closer to the vacuum level). In addition, by using a heterocycle having an alkyl chain composed of locally highly insulating vinyl groups and having high conductivity, carriers can be transported efficiently while maintaining passivation properties.

In addition, pyrrolidone, phthalimide, and caprolactam have oxygen in the skeleton, and in skeletons that have hydrogen halide ions and pyridine, imidazole, imidazolium, triazole, and thiazole, nitrogen ions are likely to combine with halogen ions to form polymer passivation halides. Therefore, when forming the passivation layer from the precursor liquid, halogen ions that are not used in the formation of the perovskite compound are taken in to partially form polymer passivation halides. Polymer passivation halides play a role in compensating for halogen defects that occur on the surface during the formation of the perovskite compound, improving the passivation properties of the perovskite compound surface. In addition, in completed solar cells, polymer passivation halides can also compensate for halogen defects on the surface of the perovskite compound that occur due to aging, improving the reliability of the solar cell characteristics. Therefore, if the molar concentration of halogen ions X in the precursor liquid is 1% or more in excess of at least one of the molar concentrations of the materials related to the A site and the B site of the perovskite compound, it is possible to effectively form a halide with the polymer passivation compound. If it is 3% or more in excess, it is possible to more effectively incorporate halogen ions. In addition, it is preferable that the excess amount is 20% or less, and the formation of defects occurring in the perovskite compound can be suppressed. If the excess amount is 10% or less, it can be more effectively suppressed. In addition, a precursor liquid containing excess halogen can be formed by adding a halide of the polymer passivation compound to the precursor. It is preferable that the polymer passivation halide in the passivation layer after the solar cell is formed is formed in 1% or more of the total number of repeating structures of the polymer passivation compound from the viewpoint of improving reliability. Furthermore, by forming 5% or more, it is possible to more effectively compensate for defects occurring in the perovskite compound. In addition, by making the polymer passivation halide 90% or less of the total number of repeating structures of the polymer passivation compound, the stable state of the polymer passivation compound can be maintained without steric hindrance. Furthermore, by keeping it below 80%, a more stable state can be maintained.

The repeating unit of the polymer passivation compound may be an alkyl unit. That is, the repeating unit of the polymer passivation compound may be an alkyl unit substituted with a nitrogen-containing heterocycle. As a typical example, the polymer passivation compound may be a compound having a polyvinyl skeleton obtained by vinyl polymerization of a monomer having a nitrogen-containing heterocycle and a vinyl group. That is, the polymer passivation compound may be a compound in which a nitrogen-containing heterocycle is bonded to every two carbons of the alkyl chain. In this way, since the polymer passivation compound is a compound having an alkyl chain as the main chain, the polymer can be synthesized relatively easily and the desired molecular weight can be obtained, so that the passivation layer 260 can be formed more reliably. In addition, the presence of the alkyl chain makes it easy to control the orientation, and the arrangement of the heterocycles can be aligned. Furthermore, the polymer passivation compound may include a repeating structure of other skeletons, such as a fluorinated alkyl chain skeleton, in addition to a structure having a nitrogen-containing heterocycle or a vinyl skeleton. For example, the polymer passivation compound may have a skeleton having a fluorinated alkyl chain as a branch of the alkyl chain between the skeletons of poly(vinylimidazole). Fluorinated alkyl chains tend to exhibit lyophobic properties and can be more selectively deposited on the surface of perovskite compounds.

Examples of polymeric passivation compounds with repeating units of alkyl units substituted with nitrogen-containing heterocycles include poly(vinylpyrrolidone), poly(4-vinylpyridine), poly(2-vinylpyridine), poly(1-vinylimidazole), poly(2-vinylimidazole), poly(4-vinylimidazole), poly(vinylazole), poly(vinylphthalimide), poly(vinylimidazole), poly(vinylcaprolactam), poly(vinyltriazole), poly(5-vinylthiazole), and poly(4-methyl-5-vinylthiazole). Examples of halides include poly(vinylpyrrolidone) iodine complexes.

The electron transport layer 270 transports electrons and transfers them to the second electrode layer 280. The electron transport layer 270 may be formed of a material mainly composed of fullerene, for example. Examples of fullerene include C60, C70, their hydrides, oxides, metal complexes, and derivatives with alkyl groups added thereto, for example PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester). In addition, a hole blocking layer such as pasocuproine (BCP), lithium fluoride (LiF), tin oxide (SnO ₂ ), aluminum-doped zinc oxide (ZnO), or titanium oxide (TiO ₂ ) may be included between the electron transport layer 270 and the second electrode layer 280. The inorganic oxide layer may be doped with another metal material.

When the solar cell 201 receives light from the substrate 210 side, the second electrode layer 280 preferably includes a metal layer made of, for example, copper, in order to reduce electrical resistance. When the solar cell 201 receives light from the second electrode layer 280 side, the second electrode layer 280 may be made of a transparent conductive oxide.

The solar cell 201 having the above configuration is manufactured by a solar cell manufacturing method according to one embodiment of the present invention shown in Figure 6. The solar cell manufacturing method of this embodiment includes a first electrode layer forming step (step S21), a precursor liquid application step (step S22), a crystallization step (step S23), an electron transport layer forming step (step S24), and a second electrode layer forming step (step S25).

In the first electrode layer forming process of step S21, the first electrode layer 220 is formed on one main surface of the substrate 210. The first electrode layer 220 can be laminated using a vacuum film forming technique such as sputtering. In the first electrode layer process, it is preferable to modify the surface of the formed first electrode layer 220 in order to promote the formation of the hole transport layer 230 in the next process. Specific methods for modifying the surface of the first electrode layer 220 include, for example, hydroxylation of the surface by ultraviolet light-ozone treatment or ozone water washing, film formation by vacuum film forming techniques such as sputtering of oxides such as nickel oxide, which is prone to growing a self-assembled film, film formation by coating technology of oxide nanoparticles, and heat treatment for activating the surface and removing impurities so that a self-assembled film is likely to grow.

In the precursor liquid application process of step S22, the perovskite precursor liquid is applied to the first electrode layer 220. The perovskite precursor liquid can be applied using, for example, a die coater, a bar coater, or the like. The perovskite precursor liquid applied in the precursor liquid application process is itself one embodiment of the perovskite precursor liquid according to the present invention.

The perovskite precursor liquid contains a solvent, a perovskite precursor that forms a perovskite compound that performs photoelectric conversion, a hole transport layer forming compound that forms a self-assembled monolayer, and a polymer passivation compound. In addition, the perovskite precursor liquid preferably further contains a hydrochloride that promotes the growth of crystals of the perovskite compound.

The solvent may be, for example, an amide solvent such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP), a sulfoxide such as dimethyl sulfoxide (DMSO), diethyl sulfoxide, or dibutyl sulfoxide, an ester such as γ-valerolactone (GBL), or an aprotic polar solvent such as acetonitrile, used alone or as a mixture of multiple types, or may further contain other types of organic solvents. The boiling points of these organic solvents are preferably as low as possible because they need to be distilled off when forming the perovskite crystals. Specific boiling points under atmospheric pressure are preferably 300°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower. The polymer passivation compound may be different from the solvent that dissolves the perovskite compound. In order to grow the polymer passivation compound uniformly on the surface of the perovskite compound, it is preferable that the polymer passivation compound is dispersed in the solvent. Therefore, it is preferable to add a small amount of a non-polar solvent in addition to the polar solvent and mix them. By adding a small amount of a non-polar solvent, it is possible to disperse the polymer passivation compound while preventing the perovskite compound from crystallizing in the liquid. In addition, after dissolving the polymer passivation compound in a non-polar solvent, it can be added to the solvent in which the perovskite compound and the hole transport layer forming compound are dissolved. Examples of non-polar solvents include isopropanol.

As described above, a material that forms a self-assembled monolayer is used as the hole transport layer forming compound. When the perovskite precursor liquid is applied onto the first electrode layer 220, the hole transport layer forming compound preferentially self-assembles at the interface with the first electrode layer 220 to form a film (hole transport layer 230). The remaining hole transport layer forming compound that has formed a film at the interface with the first electrode layer 220 also self-assembles on the surface of the coating of the perovskite precursor liquid (the side opposite to the first electrode layer 220) to form a film (excess material layer 250). The concentration of the hole transport layer forming compound in the perovskite precursor liquid can be 0.1 mmol/L or more and 5.0 mmol/L or less. A concentration of 0.5 mmol/L or more and 2.0 mmol/L or less is more preferable. Within the range in which the substrate surface can be covered, a lower concentration can suppress the formation of the excess material layer 250.

The polymer passivation compound aggregates in a film on the surface of the coating of the perovskite precursor liquid, partially covering the surface of the layer of perovskite compound (photoelectric conversion layer 240) generated from the perovskite precursor, forming a passivation layer 260 that suppresses the recombination of photocarriers (holes and electrons) at the interface of the photoelectric conversion layer 240. The polymer passivation compound has a larger molecular weight than other materials, and because it is a polymer and has a large size, it is not incorporated into the perovskite crystal and precipitates preferentially on the surface of the photoelectric conversion layer 240. Therefore, by inhibiting the growth of the film of the hole transport layer-forming compound, the precipitation of the excess material layer 250 is suppressed, and the area where the passivation layer 260 exists is reliably formed.

In the crystallization process of step S23, the film of the perovskite precursor liquid is dried (the solvent is evaporated) to react with the perovskite precursor to generate crystals of the perovskite compound. This forms a photoelectric conversion layer 240 mainly made of the perovskite compound, which fixes the hole transport layer 230, the excess material layer 250, and the passivation layer 260. Furthermore, if the passivation layer 260 contains a polymer passivation halide, halogen ions are released from the polymer passivation compound and bond to defects on the surface of the perovskite compound, suppressing carrier recombination.

As a method for promoting the formation of crystals of the perovskite compound in the perovskite precursor liquid film, for example, poor solvent quenching, vacuum quenching, gas quenching, laser treatment, etc. are preferably adopted. Poor solvent quenching, vacuum quenching, and gas quenching, in which crystallization starts from the surface, are more preferable. Furthermore, in order to facilitate the uniform growth of the passivation layer on the surface side of the perovskite precursor liquid coating film, it is preferable to cause the crystallization of the perovskite compound to proceed slowly relative to the precipitation of the passivation layer. From this viewpoint, vacuum quenching and gas quenching are more preferable. In the crystallization process of step S23, the dried coating film of the perovskite precursor liquid may be further heated.

In the electron transport layer formation process of step S24, the electron transport layer 270 is formed by a method such as a coating method or a vacuum deposition method. A hole blocking layer may be formed on the electron transport layer 270 by a vacuum deposition method or an atomic deposition method.

In the second electrode layer formation process of step S25, the second electrode layer 280 is formed by a method such as sputtering, vacuum deposition, plating, or coating, depending on the material used.

As described above, the perovskite precursor liquid according to one embodiment of the present invention contains a perovskite precursor, a hole transport layer forming compound, and a polymer passivation compound, and therefore a hole transport layer 230 and a photoelectric conversion layer 240 can be simultaneously formed on the first electrode layer 220 by a single coating, while a passivation layer 260 is formed on the surface of the photoelectric conversion layer 240, thereby preventing the photoelectric conversion layer 240 from being completely covered with an excess material layer 250 that inhibits the transfer of electrons. Therefore, the solar cell manufacturing method according to one embodiment of the present invention can easily manufacture a solar cell 201 having a relatively high photoelectric conversion efficiency.

The above describes the embodiments of the present invention, but the present invention is not limited to the above-mentioned embodiments, and various modifications and variations are possible. The solar cell according to the present invention may include an additional functional layer, and for example, may include a second passivation layer between the excess material layer and the passivation layer and the electron transport layer, covering one side of the excess material layer and the passivation layer. This second passivation layer may be formed from the same material as the first passivation layer that is laminated in the area where the excess material layer is not present. In the solar cell according to the present invention, the electron transport layer may be omitted. In the solar cell according to the invention, a photoelectric converter such as a crystalline silicon solar cell may be used as a substrate to form a tandem solar cell.

The present invention will be specifically explained below based on examples, but the present invention is not limited to the following examples.

Example 1
A commercially available glass/ITO substrate (glass substrate with a first electrode laminated thereon in advance) was used as the substrate. First, NiOx was formed as an electron blocking layer. Next, a perovskite precursor liquid was applied, and a crystallization process and heating were performed to generate crystals of a perovskite compound to form a hole transport layer, a photoelectric conversion layer, an excess material layer, and a passivation layer. The crystallization process used a vacuum quench method. Furthermore, an electron transport layer was formed by coating PCBM, a hole blocking layer was formed by vapor deposition of BCP, and a second electrode was formed by vapor deposition of Ag, thereby creating Example 1 of a solar cell. The perovskite precursor liquid was prepared by dissolving 1.2 mol/L of perovskite precursor (PbI ₂ , CsI, FAI), 1.0 mmol/L of Me-4PACz (hole transport layer forming compound), and 0.2 mmol/L of n-Octylphosphocholine (specific organic compound) in a mixed solvent of DMF and NMP in a volume ratio of 90:10. The perovskite precursor contained FA and Cs in a molar ratio of 90:10 for the formation of the A site, Pb for the formation of the B site, and I as a halogen atom for the formation of the X site. Here, the molecular lengths of Me-4PACz and n-Octylphosphocholine can be estimated to be 1 nm and 1.8 nm, respectively, by molecular orbital calculation. Assuming that these are grown densely on the substrate as unit lattices, Me-4PACz and n-Octylphosphocholine should grow at 9.0×10 ¹⁴ and 5.0×10 ¹⁴ , respectively (these numbers of molecules are the standard close-packed molecular number). Assuming that the perovskite layer is 500 nm, the number of molecules precipitated from the concentration of Me-4PACz selected here is 1.3×10 ¹⁵ , and the number of precipitates calculated from the concentration of n-Octylphosphocholine is 2.6×10 ¹⁴ . Therefore, the concentration of Me-4PACz is determined so that it is equal to or greater than the standard close-packed molecular number and equal to or less than the standard close-packed molecular number of n-Octylphosphocholine.

(Examples 2 to 5)
A solar cell of Example 2 was produced under the same conditions as Example 1, except that 0.2 mmol/L of 2,8-Dimethyl-5-Nonylphosphocholine was used as the specific organic compound. A solar cell of Example 3 was produced under the same conditions as Example 1, except that 0.2 mmol/L of 10-Undecylenyl-1-phosphocholine was used as the specific organic compound. A solar cell of Example 4 was produced under the same conditions as Example 1, except that 0.2 mol/L of n-Octylammonium Iodide was used as the specific organic compound. A solar cell of Example 5 was produced under the same conditions as Example 1, except that 0.13 mol/L of L-α-Phosphatidylcholine was used as the specific organic compound.

(Examples 6 to 7)
A solar cell of Example 5 was produced under the same conditions as Example 1, except that 10 mol % of MACl was mixed in the perovskite precursor liquid. A solar cell of Example 6 was produced under the same conditions as Example 1, except that the hole transport layer forming compound Me-4PACz was replaced with DMAcPA.

(Example 8)
A solar cell of Example 8 was produced under the same conditions as in Example 5, except that MeO-4PACz was used as the hole transport layer forming material.

(Comparative Example 1)
A solar cell of Comparative Example 1 was produced under the same conditions as in Example 1, except that a perovskite precursor liquid not containing an organic compound having a chain hydrocarbon group was used.

The photoelectric conversion efficiency was measured for Examples 1 to 8 and Comparative Example 1, and the ratio to the photoelectric conversion efficiency of Comparative Example 1 was calculated. As a result, Example 1 had a photoelectric conversion efficiency of 1.15, Example 2 had a photoelectric conversion efficiency of 1.16, Example 3 had a photoelectric conversion efficiency of 1.18, Example 4 had a photoelectric conversion efficiency of 1.17, Example 6 had a photoelectric conversion efficiency of 1.16, Example 7 had a photoelectric conversion efficiency of 1.18, and Example 8 had a photoelectric conversion efficiency of 1.18. The photoelectric conversion efficiency of the solar cell was calculated by measuring the current-voltage characteristics at ²⁵ °C and 1000 W/m2. Specifically, the photoelectric conversion efficiency was calculated by dividing the maximum output determined from the current-voltage characteristics measurement by the power generation area.

Example 9
The perovskite precursor liquid contained FA and Cs in a molar ratio of 80:20 for the formation of the A site, Pb for the formation of the B site, and I and Br in a molar ratio of 90:10 as halogen atoms for the formation of the X site. Except for using 1.0 mmol/L Me-4PACz (a hole transport layer forming compound) and 0.13 mmol/L L-α-Phosphatidylcholine as a specific organic compound, a solar cell of Example 9 was produced under the same conditions as Example 1.

Example 10
A solar cell of Example 10 was produced under the same conditions as in Example 9, except that 0.3 mmol/L of piperazine-1,4-diium iodide was further added as the piperazine compound.

(Examples 11 and 12)
Example 11 of a solar cell was produced under the same conditions as Example 10, except that ₂ mM of MDACl2 was further added to the perovskite precursor liquid. Example 12 of a solar cell was produced under the same conditions as Example 10, except that 2 mM of RbCl was further added to the perovskite precursor liquid.

Example 13
A solar cell of Example 13 was produced under the same conditions as in Example 10, except that 0.5 mmol/L of piperazine compound, piperazine iodide, was added to the perovskite precursor liquid instead of piperazine-1,4-diium iodide.

(Example 14)
A solar cell of Example 15 was produced under the same conditions as in Example 10, except that 0.4 mmol/L of 4-fluorophenethylamine hydroiodide, which is a fluorine-containing organic compound, was used instead of piperazine-1,4-diium iodide.

(Examples 15 and 16)
Furthermore, a solar cell of Example 15 was produced under the same conditions as Example 10, except that 0.4 mmol/L of 4-fluorophenethylamine hydroiodide, a fluorine-containing organic compound, was additionally blended. Further, a solar cell of Example 16 was produced under the same conditions as Example 13, except that 0.4 mM of 4-fluorophenethylamine hydroiodide, a fluorine-containing organic compound, was additionally blended.

(Example 17)
A solar cell of Example 17 was produced under the same conditions as in Example 10, except that 0.4 mmol of pentafluorophenylphosphonic acid, a fluorine-containing organic compound, was used in place of piperazine-1,4-diium iodide.

(Example 18)
Furthermore, a solar cell of Example 18 was prepared under the same conditions as Example 17, except that ₂ mM of MDAC12 was additionally blended.

Example 19
Furthermore, a solar cell of Example 19 was produced under the same conditions as Example 10, except that 0.4 mmol of pentafluorophenylphosphonic acid, a fluorine-containing organic compound, was additionally blended.

(Example 20)
A solar cell of Example 20 was produced under the same conditions as in Example 10, except that 0.2 mmol of (fluorinated) Fos-Choline-8, a fluorine-containing organic compound, was used in place of piperazine-1,4-diium iodide.

(Example 21)
Furthermore, a solar cell of Example 21 was produced under the same conditions as Example 10, except that 0.2 mmol of (fluorinated)Fos-Choline-8 was additionally blended.
(Example 22)
A solar cell of Example 22 was produced under the same conditions as in Example 12, except that 0.1 mg/mL of poly(vinylpyrrolidone)-iodine complex, which is a polymer passivation compound having a repeating unit having a nitrogen-containing heterocycle, was added instead of piperazine-1,4-diium iodide.

(Example 23)
A solar cell of Example 23 was produced under the same conditions as in Example 19, except that MeO-4PACz was used instead of Me-4PACz as the hole transport layer forming material.

(Comparative Example 2)
A solar cell of Comparative Example 11 was produced under the same conditions as those of Example 11, except that a perovskite precursor liquid not containing the specific organic compound and other passivation materials, and not containing an excess of a perovskite compound-forming material, was used.

The photoelectric conversion efficiency was measured for Examples 9 to 23 and Comparative Example 2, and the ratio to the photoelectric conversion efficiency of Comparative Example 2 was calculated. As a result, Example 9 was 1.05, Example 10 was 1.07, Example 11 was 1.08, Example 12 was 1.09, Example 13 was 1.08, Example 14 was 1.07, Example 15 was 1.11, Example 16 was 1.13, Example 17 was 1.04, Example 18 was 1.06, Example 19 was 1.11, Example 20 was 1.07, Example 21 was 1.13, Example 24 was 1.06, and Example 23 was 1.07.

As described above, it was confirmed that the photoelectric conversion efficiency can be improved by blending a hole transport layer-forming compound and a specific organic substance into the perovskite precursor liquid. It was also confirmed that the photoelectric conversion efficiency can be improved by adding a fluorine-containing organic compound, a piperazine compound, and a polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle in addition to the specific organic compound.

(Example 24)
A commercially available glass/ITO substrate (a substrate with a first electrode layer laminated thereon, 3 cm square) was used as the substrate. First, NiOx was formed as an electron blocking layer. Next, a perovskite precursor liquid was applied, and a crystallization process and heating were performed to generate crystals of a perovskite compound to form a hole transport layer, a photoelectric conversion layer, an excess material layer, and a passivation layer. The crystallization process used a vacuum quenching method. Furthermore, an electron transport layer was formed by coating PCBM, BCP was formed by deposition as a hole blocking layer, and Ag was laminated by deposition to form a second electrode layer, thereby creating Example 1 of a solar cell. The perovskite precursor liquid was prepared by dissolving 1.2 mol/L of perovskite precursor (PbI ₂ , CsI, FAI), 1.0 mmol/L of Me4PACz (hole transport layer forming compound), and 0.3 mmol/L of piperazine-1,4-diium iodide in a mixed solvent of DMF and NMP in a volume ratio of 90:10. The perovskite precursor contained FA and Cs in a molar ratio of 90:10 for the formation of the A site, Pb for the formation of the B site, and I as a halogen atom for the formation of the X site. Here, the molecular lengths of Me-4PACz and piperazine (only the piperazine skeleton is considered) can be estimated to be 1 nm and 0.3 nm, respectively, by molecular orbital calculation. Assuming that these are grown densely on the substrate as a unit lattice, Me-4PACz and piperazine should grow at 9.0x1014 and ^1.0x1016 , respectively (these numbers of molecules are the standard close-packed molecular number). Assuming that the perovskite layer is 500 nm, the number of molecules precipitated from the concentration of Me-4PACz selected here is ^1.3x1015 , and the number of piperazine precipitated from the concentration of piperazine-1,4-diium iodide is ^1.5x1015 . Therefore, the concentration of Me-4PACz is determined to be equal to ^or greater than the standard close-packed molecular number, and the concentration of piperazine-1,4-diium iodide is determined to be equal to or less than the standard close-packed molecular number.

(Examples 25 to 30)
Solar cell Example 25 was prepared under the same conditions as Example 24, except that 0.5 mM piperazine iodide was used as the piperazine compound. Solar cell Example 26 was prepared under the same conditions as Example 24, except that 0.15 mM piperazine was used as the piperazine compound. Solar cell Example 27 was prepared under the same conditions as Example 24, except that 0.5 mM pentylpiperazine hydrochloride was added as the piperazine compound. Solar cell Example 28 was prepared under the same conditions as Example 24, except that 0.5 mM 1-(Trifluoromethyl)piperazine hydrochloride was added as the piperazine compound. Solar cell Example 29 was prepared under the same conditions as Example 24, except that 10 mol% MACl was further added to the perovskite precursor. A solar cell of Example 30 was produced under the same conditions as in Example 29, except that DMAcPA was used as the hole transport layer-forming compound.

(Comparative Example 3)
Example 24, except that the perovskite precursor liquid did not contain a piperazine compound.
A solar cell of Comparative Example 3 was prepared under the same conditions as those in the above.

The photoelectric conversion efficiency was measured for Examples 24 to 30 and Comparative Example 3, and the ratio to the photoelectric conversion efficiency of Comparative Example 3 was calculated. As a result, Example 24 was 1.12, Example 25 was 1.14, Example 26 was 1.06, Example 27 was 1.15, Example 28 was 1.17, Example 29 was 1.14, and Example 30 was 1.10.

(Example 31)
A solar cell of Example 31 was produced under the same conditions as Example 24, except that the perovskite precursor used contained FA and Cs in a molar ratio of 80:20 for the A site formation, Pb for the B site formation, and I and Br in a molar ratio of 90:10 as halogen atoms for the X site formation.

(Example 32)
Furthermore, a solar cell of Example 32 was produced under the same conditions as Example 31, except that 0.4 mM of pentafluorophenylphosphonic acid was used.

(Comparative Example 4)
A solar cell of Comparative Example 4 was prepared under the same conditions as in Example 31, except that the piperazine compound and other passivation materials were not included.

The photoelectric conversion efficiency was measured for Examples 31 and 32 and Comparative Example 4, and the ratio to the photoelectric conversion efficiency of Comparative Example 4 was calculated. As a result, Example 31 was 1.04, and Example 32 was 1.09.

As described above, it was confirmed that the photoelectric conversion efficiency can be further improved by blending a hole transport layer-forming compound and a piperazine compound in the perovskite precursor liquid. It was also confirmed that the photoelectric conversion efficiency can be further improved by adding a fluorine-containing organic compound in addition to the piperazine compound.

(Example 33)
A commercially available glass/ITO substrate (a substrate with a first electrode layer laminated thereon, 3 cm square) was used as the substrate. First, NiOx was formed as an electron blocking layer. Next, a perovskite precursor liquid was applied, and a crystallization process and heating were performed to generate crystals of a perovskite compound to form a hole transport layer, a photoelectric conversion layer, an excess material layer, and a passivation layer. The crystallization process used a vacuum quenching method. Furthermore, an electron transport layer was formed by coating PCBM, BCP was formed by deposition as a hole blocking layer, and Ag was laminated by deposition to form a second electrode layer, thereby creating Example 61 of a solar cell. The perovskite precursor liquid was prepared by dissolving 1.2 mol/L of perovskite precursor (PbI ₂ , CsI, FAI) containing 5 mol% excess iodine, 1.0 mmol/L of Me4PACz (a hole transport layer forming compound), and 0.1 mg/mL of poly(vinylpyrrolidone)-iodine complex in a mixed solvent of DMF and NMP at a volume ratio of 90:10. The perovskite precursor contained FA and Cs at a molar ratio of 90:10 for the formation of the A site, Pb for the formation of the B site, and I as a halogen atom for the formation of the X site.

(Comparative Example 5)
A solar cell of Comparative Example 5 was produced under the same conditions as in Example 33, except that a perovskite precursor liquid not containing a poly(vinylpyrrolidone)-iodine complex was used.

The photoelectric conversion efficiency of Example 33 and Comparative Example 5 was measured, and the ratio to the photoelectric conversion efficiency of Comparative Example 5 was calculated. As a result, the photoelectric conversion efficiency of Example 33 was 1.17. The photoelectric conversion efficiency of the solar cell was calculated by measuring the current-voltage characteristics at 25°C and 1000 W/ ^m2 . Specifically, the photoelectric conversion efficiency was calculated by dividing the maximum output determined from the current-voltage characteristic measurement by the power generation area.

As described above, it was confirmed that photoelectric conversion efficiency can be improved by blending a hole transport layer-forming compound and a poly(vinylpyrrolidone)-iodine complex, which is a polymer passivation compound having a repeating unit with a nitrogen-containing heterocycle, into the perovskite precursor liquid.

Reference Signs List 1, 101, 201 Solar cell 10, 110, 210 Substrate 20, 120, 220 First electrode layer 30, 130, 230 Hole transport layer 40, 140, 240 Photoelectric conversion layer 41, 141 Impurity film 50, 150, 250 Excess material layer 60, 160, 260 Passivation layer 70, 170, 270 Electron transport layer 80, 180, 280 Second electrode layer

Claims (29)

A solvent;
A perovskite precursor that forms a perovskite compound that performs photoelectric conversion;
a hole transport layer forming compound that forms a self-assembled monolayer having hole selective permeability;
an organic compound having a chain hydrocarbon group having 5 or more carbon atoms which may be substituted and an ionic functional group;
A perovskite precursor liquid comprising: The perovskite precursor liquid according to claim 1, wherein the ionic functional group is any one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphonic acid group, a phosphoric acid group, a hydroxyl group, a carboxyl group, and a sulfonyl group. The perovskite precursor liquid according to claim 1, wherein the organic compound is a halide salt. The perovskite precursor liquid according to any one of claims 1 to 3, wherein the perovskite precursor contains a metal halide including at least one of a lead halide and a tin halide, and an organic halide or an alkali metal halide, and the molar concentration of the metal portion of the metal halide is in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal by 0.5 mol % to 10 mol %. The perovskite precursor liquid according to any one of claims 1 to 3, further comprising an organic hydrochloride that promotes the growth of crystals of the perovskite compound. The perovskite precursor liquid according to any one of claims 1 to 3, further comprising at least one of a fluorine-containing organic compound, piperazine and a piperazine derivative, and a polymer passivation compound having a repeating unit having a nitrogen-containing heterocycle. The perovskite precursor liquid according to claim 6, wherein the fluorine-containing organic compound has at least one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphoric acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, a sulfonyl group, and ionized forms thereof at its terminal, and has a carbon skeleton containing an alkyl chain or benzene in which hydrogen is replaced by fluorine or a trifluoromethyl group. A step of applying the perovskite precursor liquid according to any one of claims 1 to 3 to a first electrode layer formed on one main surface of a substrate;
volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound;
A solar cell manufacturing method comprising: A plate-shaped or sheet-shaped substrate;
A first electrode layer laminated on one main surface of the substrate;
a hole transport layer formed on the first electrode layer and made of a film of a hole transport layer-forming compound having hole selective permeability;
a photoelectric conversion layer that is laminated on the hole transport layer and contains a perovskite compound;
an excess material layer that is partially laminated on the photoelectric conversion layer and contains the hole transport layer-forming compound;
a passivation layer that is laminated on an area of the photoelectric conversion layer where the excess material layer is not present, the passivation layer including an organic compound having a chain hydrocarbon group having 5 or more carbon atoms that may be substituted and an ionic functional group;
a second electrode layer disposed on the one side of the excess material layer and the passivation layer;
A solar cell comprising: The solar cell according to claim 9, wherein the photoelectric conversion layer has an impurity film containing a halide of a metal atom in the perovskite compound at the grain boundaries of the crystals of the perovskite compound. The solar cell of claim 9 or 10, further comprising an electron transport layer laminated between the excess material layer and the passivation layer and the second electrode layer. A solvent;
A perovskite precursor that forms a perovskite compound that performs photoelectric conversion;
a hole transport layer forming compound that forms a self-assembled monolayer having hole selective permeability;
At least one of piperazine and a piperazine derivative,
A perovskite precursor liquid comprising: The perovskite precursor liquid according to claim 12, wherein the piperazine derivative is a halide salt. The perovskite precursor liquid according to claim 12, wherein the piperazine derivative has an alkyl chain or a fluorine-containing organic group bonded to one of the nitrogen atoms. The perovskite precursor liquid according to any one of claims 12 to 14, further comprising a fluorine-containing organic compound. The perovskite precursor liquid according to claim 15, wherein the fluorine-containing organic compound has at least one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphoric acid group, a phosphonic acid group, a hydroxyl group, a carboxyl group, a sulfonyl group, and ionized forms thereof at its terminal, and has a carbon skeleton containing an alkyl chain or benzene in which hydrogen is replaced by fluorine or a trifluoromethyl group. The perovskite precursor liquid according to any one of claims 12 to 14, wherein the perovskite precursor contains a metal halide including a lead halide, and an organic halide or an alkali metal halide, and the molar concentration of the metal is in excess of the sum of the molar concentration of the organic compound and the molar concentration of the alkali metal by 0.5 mol % or more and 10 mol % or less. The perovskite precursor liquid according to any one of claims 12 to 14, further comprising a hydrochloride salt that promotes crystal growth of the perovskite compound. A step of applying the perovskite precursor liquid according to any one of claims 12 to 14 to a first electrode layer formed on one main surface of a substrate;
volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound;
A solar cell manufacturing method comprising: A plate-shaped or sheet-shaped substrate;
A first electrode layer laminated on one main surface of the substrate;
a hole transport layer formed on the first electrode layer and made of a film of a hole transport layer-forming compound having hole selective permeability;
a photoelectric conversion layer that is laminated on the hole transport layer and contains a perovskite compound;
an excess material layer formed of the hole transport layer-forming compound and partially laminated on the photoelectric conversion layer;
a passivation layer including at least one of piperazine and a piperazine derivative, the passivation layer being laminated on an area of the photoelectric conversion layer where the excess material layer is not present;
a second electrode layer disposed on the one side of the excess material layer and the passivation layer;
A solar cell comprising: The solar cell according to claim 20, wherein the photoelectric conversion layer has an impurity film containing a halide of a metal atom in the perovskite compound at the grain boundaries of the crystals of the perovskite compound. The solar cell of claim 20 or 21, further comprising an electron transport layer laminated between the excess material layer and the passivation layer and the second electrode layer. A solvent;
A perovskite precursor that forms a perovskite compound that performs photoelectric conversion;
a hole transport layer forming compound that forms a self-assembled monolayer;
a polymeric passivation compound having a repeating unit having a nitrogen-containing heterocycle;
A perovskite precursor liquid comprising: The perovskite precursor liquid of claim 23, wherein the polymeric passivation compound has a polyvinyl backbone. The perovskite precursor liquid according to claim 23 or 24, wherein the nitrogen-containing heterocycle is any one of pyridine, pyrrolidone, phthalimide, caprolactam, imidazole, imidazolium, triazole, thiazole, piperidium, and derivatives thereof. 25. The perovskite precursor liquid according to claim 24, wherein the perovskite compound has an _ABX3 structure in which X is a halogen atom, and the molar concentration of X is higher than the molar concentration of at least one of A and B. A step of applying the perovskite precursor liquid according to claim 23 or 24 to a first electrode layer formed on one main surface of a substrate;
volatilizing the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound;
A solar cell manufacturing method comprising: A plate-shaped or sheet-shaped substrate;
A first electrode layer laminated on one main surface of the substrate;
a hole transport layer formed on the first electrode layer and made of a film of a hole transport layer-forming compound;
a photoelectric conversion layer that is laminated on the hole transport layer and contains a perovskite compound;
an excess material layer that is partially laminated on the photoelectric conversion layer and contains the hole transport layer-forming compound;
a passivation layer that is laminated on an area of the photoelectric conversion layer where the excess material layer is not present and that contains a polymer passivation compound having a nitrogen-containing heterocycle;
a second electrode layer disposed on the one side of the excess material layer and the passivation layer;
A solar cell comprising: The solar cell of claim 28, wherein the passivation layer includes a halide of the polymeric passivation compound.

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