Perovskite precursor solution, method for manufacturing solar cell, and solar cell

Abstract

The present invention provides a perovskite precursor solution which is capable of simultaneously forming a hole transport layer and a photoelectric conversion layer without forming a layer that inhibits transmission of electrons.　A perovskite precursor solution according to one aspect of the present invention includes: a solvent; a perovskite precursor which forms a perovskite compound that performs photoelectric conversion; a hole transport layer forming compound which forms a self-assembled monolayer that has hole-selective permeability; and a fluorine-containing organic compound.

Description

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

[0001] The present invention relates to a perovskite precursor liquid, a solar cell manufacturing method, and a solar cell.

[0002] The use of solar cells is expanding as an energy source with a low environmental impact. Perovskite solar cells, which have a photoelectric conversion layer primarily composed 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. Furthermore, because perovskite solar cells have a different absorption wavelength than solar cells that use a crystalline silicon substrate as a photoelectric conversion layer, they can also be stacked on crystalline silicon solar cells. The charge transport layer selectively passes electrons or holes, but also creates electrical resistance that generates internal losses. Therefore, to reduce electrical resistance, a technique has been proposed in which a thin charge transport layer is formed using a self-assembled monolayer composed of a carbazole compound with charge-selective properties (see, for example, Patent Document 1).

[0003] Generally, forming a self-assembled monolayer requires applying a material solution 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 methods such as die coating or bar coating. Furthermore, since perovskite photoelectric conversion layers are generally also formed by coating, forming the first charge transport layer by coating requires repeated coating and drying. It has been reported that, in order to efficiently manufacture solar cells, a carbazole compound that forms a hole-selective self-assembled monolayer is incorporated into a perovskite precursor solution and then applied, whereby the carbazole compound forms a self-assembled monolayer at the interface of the coating film with the electrode layer, thereby simultaneously forming a hole transport layer and a perovskite photoelectric conversion layer (see, for example, Non-Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2023-46212

[0005] "Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells", Nature Energy, 2023, vol. 8, p. 462-472

[0006] When a carbazole compound is blended into a perovskite precursor liquid as in Non-Patent Document 1, it is necessary to blend an excess amount of the carbazole compound relative to the coating area in order to form a continuous hole transport layer. As a result of the inventors' investigations, it was confirmed that an excess amount of the carbazole compound in the precursor solution forms a layer on the surface of the coating film and can inhibit electron transport.

[0007] An object of the present invention is to provide a perovskite precursor liquid that can simultaneously form a hole transport layer and a photoelectric conversion layer without forming a layer that inhibits electron transport, a solar cell manufacturing method, and a solar cell that can be easily manufactured.

[0008] A perovskite precursor liquid according to one 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 a fluorine-containing organic compound.

[0009] In the perovskite precursor liquid described above, the fluorine-containing organic compound may have at its terminal at least one of an amino group, a hydrazine group, a trialkylamino group, a phosphocholine group, a phosphate group, a phosphonate group, a hydroxyl group, a carboxyl group, a sulfonyl group, or an ionized form thereof.

[0010] In the perovskite precursor liquid described above, the fluorine-containing organic compound may have a carbon skeleton containing an alkyl chain or benzene in which hydrogen is substituted with fluorine or a trifluoromethyl group.

[0011] In the above-described perovskite precursor liquid, the alkyl chain or benzene may include successive carbons to which fluorine is bonded.

[0012] In the perovskite precursor liquid described above, the fluorine-containing organic compound may have a cationizable end group and an anionizable end group.

[0013] The perovskite precursor liquid may contain a plurality of types of the fluorine-containing organic compounds.

[0014] In the perovskite precursor liquid described above, the perovskite precursor may contain a metal halide including a lead halide, and a halogenated organic compound 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.

[0015] The above-mentioned perovskite precursor liquid may further contain hydrochloride, which promotes the growth of crystals of the perovskite compound.

[0016] A solar cell manufacturing method according to one aspect of the present invention includes the steps of: applying the 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 produce crystals of a perovskite compound.

[0017] A solar cell according to one aspect of the present invention includes a plate- or sheet-like 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 made of a fluorine-containing organic compound laminated in an area of ​​the photoelectric conversion layer where the excess material layer is not present, and a second electrode layer laminated on the excess material layer and the passivation layer.

[0018] In the above-described method for manufacturing a solar cell, 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.

[0019] The present invention provides a perovskite precursor liquid that can simultaneously form a hole transport layer and a photoelectric conversion layer without forming a layer that inhibits electron transport, a solar cell manufacturing method, and a solar cell that can be easily manufactured.

[0020] 1 is a schematic cross-sectional view showing the configuration of a solar cell according to one embodiment of the present invention; 2 is a flowchart showing the steps of a solar cell manufacturing method according to one embodiment of the present invention;

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described below with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view showing the configuration of a solar cell 1 according to one embodiment of the present invention. The dimensions of various components in the drawings have been adjusted for clarity and convenience.

[0022] The solar cell 1 comprises a plate- or sheet-shaped substrate 10, a first electrode layer 20 laminated on one main surface (the lower side in Figure 1) of the substrate 10, 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 of ​​the one surface of the photoelectric conversion layer 40 where the excess material layer 50 is not present, 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 the electron transport layer 70.

[0023] 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.

[0024] 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 may be formed of a transparent conductive oxide (TCO) having electrical conductivity and optical transparency. Examples of transparent conductive oxides that can be used to form the first electrode layer 20 include indium oxide, tin oxide, zinc oxide, titanium oxide, and composite oxides thereof. Among these, indium-based composite oxides containing indium oxide, zinc oxide, tungsten oxide, molybdenum oxide, or the like as their main components, and fluorine-doped tin oxide are preferred. From the viewpoints of high electrical conductivity and transparency, indium oxide is particularly preferred. The first electrode layer 20 is preferably subjected to a surface treatment, such as ozone treatment, to improve the formability of the hole transport layer 30. The first electrode layer 20 may have a multilayer structure having a p-type oxide semiconductor layer, for example, containing nickel oxide, niobium oxide, or the like as its main component, on its surface.

[0025] 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 transports only the holes 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 that forms the hole transport layer 30 preferably has a functional group capable of transporting holes, such as a carbazole, phenothiazine, or dimethylacridine compound, and a self-assembled terminal group that chemically bonds to the substrate, such as phosphoric acid or carboxylic acid. A linear material, such as an alkyl chain, is preferably used to provide passivation 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 for forming the hole transport layer 30 include Me-4PACz ([4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid), MeO-4PACz ([4-(3,6-Dimoxy-9H-carbazol-9-yl)butyl]phosphonic Acid), Me-PhpPACz ([4-(3,6-Dimethyl-9H-carbazol-9-yl)phenyl]phosphonic Acid), Acid), DMAcPA ((4-(2,7-dibromo-9,9-dimethylacridin-10(9H)-yl)butyl)phosphonic acid), and the like.

[0026] The photoelectric conversion layer 40 contains a perovskite compound that performs photoelectric conversion and absorbs incident light to generate photocarriers. The perovskite compound contained in the photoelectric conversion layer 40 contains an organic atom A containing at least one of an alkali metal (Am), a monovalent organic ammonium ion, and an amidinium 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 the perovskite compound contains an ABX ３The alkali metal at the A site may be potassium K, cesium Cs, rubidium Rb, or the like, and the organic atom A may be methylammonium MA (CH ３ NH ３ ), Formamidinium FA (CH ３ N ２ The metal atom B may be lead (Pb) or tin (Sn), and preferably is mainly lead. The halogen atom X is preferably at least one of iodide (I), bromide (Br), and chloride (Cl).

[0027] Specifically, preferred perovskite compounds include, for example, MAPbI ３ , MAPbBr ３ , MAPbCl ３ Methylammonium lead halides (MAPbX) such as ３ ), and FAPbI ３ , FAPbBr ３ , FAPbCl ３ Formamidinium lead halide (FAPbX) ３ The halogen atom X may contain multiple types. FA, which contains both methylammonium and formamidinium, is also suitable. ｙ MA 1-ｙ PbX ３ In addition, when an alkali metal is contained, Am ｙ FA ｚ MA １－ｙ－ｚ PbX ３ , Am ｙ FA １－ｙ PbX ３ Am may be a single type of Cs, Rb, or K, or may contain multiple types of Am (y and z are any positive integers). The halogen atom X may also contain multiple types.

[0028] The photoelectric conversion layer 40 contains Pb, PbI, and the like at the grain boundaries of the crystals of the perovskite compound. ２ , PbBr ２ , PbCl ２, or the like. In order to form such an impurity film 41, the metal B in the perovskite compound is preferably lead (Pb). By having the photoelectric conversion layer 40 have the impurity film 41 containing the metal atom B and a metal compound, it is possible to prevent the hole transport layer-forming compound that forms the hole transport layer 30 and the fluorine-containing organic compound that forms the passivation layer 60 from being left behind at the grain boundaries of the crystals of the perovskite compound during the formation of the photoelectric conversion layer 40, thereby improving the photoelectric conversion efficiency.

[0029] The excess material layer 50 is formed from the same hole transport layer-forming compound as that forming the hole transport layer 30. The hole transport layer-forming compound used for the hole transport layer 30 has a lowest unoccupied molecular orbital (LOW) lower than the conduction band of the perovskite compound (close to the vacuum level), which blocks 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 50 not be formed. However, when the hole transport layer 30 and the photoelectric conversion layer 40 are formed using the same process, a slightly larger amount of hole transport layer-forming compound must be blended to form a seamless hole transport layer 30 that covers the entire surface of the first electrode layer 20, and the excess hole transport layer-forming compound forms the excess material layer 50. The excess material layer 50 can also function as an anchor that improves adhesion to the electron transport layer 70. In other words, fluorine-containing organic compounds, which generally have low surface free energy, have poor adhesion to the electron transport layer 70, so forming the excess material layer 50 can compensate for this drawback. The excess material layer 50 may be composed solely of 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 50 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 50 is preferably 90% or less, more preferably 70% or less. That is, in the region where the passivation layer is not formed, the perovskite compound is in direct contact with the electron transport layer 70 partially, enabling electron transport. However, rather than forming a surface containing many defects, it is preferable for the hole transport layer-forming compound to be formed on the perovskite compound surface, thereby repelling electrons back into the perovskite compound layer. The weight content of the hole transport layer-forming compound in the excess material layer 50 can be calculated based on the composition of the excess material layer measured by a combination of transmission electron microscope observation and energy dispersive X-ray analysis.

[0030] The passivation layer 60 prevents photocarrier recombination at the interface with the photoelectric conversion layer 40 and promotes electrons reaching the electron transport layer 70. The passivation layer 60 is formed so as to share the surface of the excess material layer 50 and the photoelectric conversion layer 40, preventing the excess material layer 50 from covering the entire surface of the photoelectric conversion layer 40 and reducing the photoelectric conversion efficiency. The passivation layer 60 is made of a fluorine-containing organic compound and is likely to exhibit lyophobicity to solvents used to form the photoelectric conversion layer 40, including aprotic polar solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and acetonitrile. Therefore, the passivation layer 60 deposits preferentially on the surface of the photoelectric conversion layer 40 compared to the excess material layer 50. Furthermore, the passivation layer 60 contains electron-withdrawing fluorine, allowing it to preferentially transport electrons.

[0031] The fluorine-containing organic compound preferably has a carbon skeleton containing an alkyl chain or benzene, with some hydrogen atoms substituted with fluorine, trifluoromethyl groups, or the like. The carbon skeleton more preferably contains consecutive carbon atoms bonded to fluorine. When the fluorine-containing organic compound has a benzene skeleton, it is preferable that five of the six hydrogen atoms in the benzene are substituted with fluorine or trifluoromethyl groups, with one hydrogen atom connected to a terminal lyophilic group. The greater the number of fluorine and trifluoromethyl group substitutions, the higher the lyophobicity and the greater the effect of selectively orienting the compound toward the surface. Therefore, when substituted with fluorine, it is preferable to have a pentafluorobenzene structure in which all hydrogen atoms except one connected to the terminal are substituted with fluorine. When the fluorine-containing organic compound has an alkyl chain skeleton, it is preferable that the end of the alkyl chain has a trifluoromethyl group or a phenyl group containing fluorine or trifluoromethyl groups, and the end of the alkyl chain has a lyophilic group. The fluorine-containing end faces the electron transport layer, and the end containing the lyophilic group faces the perovskite surface. The linear skeleton, excluding the end and terminal, preferably has from 1 to 17 carbon atoms. More preferably, the number of carbon atoms is 5 or more and 16 or less. To promote the formation of the passivation layer 60 by self-organization, the longer the alkyl chain, the better the orientation and passivation properties. However, the longer the alkyl chain, the higher the insulating properties and the lower the conductivity. Therefore, by adding an alkyl chain longer than the upper limit, sufficient orientation can be achieved, and by keeping the alkyl chain length below the lower limit, both passivation properties and conductivity can be achieved. When the fluorine-containing organic compound has an alkyl chain skeleton and a trifluoromethyl group at the end, it is preferable that the alkyl chain continuing from the end contains consecutive fluorinated carbons. More preferably, all carbons except for one or two adjacent to the end are fluorinated. Continuous fluorination enhances lyophobicity and allows for more selective deposition on the surface, promoting the formation of the passivation layer 60. Another example of a fluorine-containing organic compound having an alkyl chain skeleton is a polymer structure.The partially fluorinated polymer structure, containing a large amount of fluorine, is more likely to be oriented planarly on the surface, unlike structures in which the fluorine-containing end faces the electron transport layer and the lyophilic end faces the perovskite surface. When the fluorine-containing organic compound has an alkyl chain skeleton and a phenyl group at the end containing fluorine or trifluoromethyl groups, the greater the number of fluorine and trifluoromethyl group substitutions, as described above. Therefore, when the hydrogen atoms of the phenyl group are substituted with fluorine, pentafluorobenzene is preferred. Furthermore, the combination of the phenyl group containing fluorine and trifluoromethyl groups with the alkyl chain can promote more selective deposition on the surface than when the compound has only a benzene skeleton. Furthermore, the fluorine-containing organic compound preferably has at least one lyophilic group at the end, specifically, an amino group, a hydrazine group, a trialkylamino group, a phosphate group, a phosphonate group, a hydroxyl group, a carboxyl group, a sulfonyl group, or an ionized form thereof. These compounds are lyophilic and lyophobic in the aprotic polar solvent used to form the photoelectric conversion layer 40. By combining them with a fluorine-containing skeleton, which is lyophilic and lyophobic, they can be positioned on the surface of the photoelectric conversion layer 40 even before the drying process. Having a linear skeleton, lyophilic groups, or both facilitates alignment of the fluorine-containing organic compounds, allowing for the formation of thin, uniform films and reduced series resistance. Ionization of these terminal groups improves performance by compensating for defects such as iodine defects, lead defects, and halogen defects on the perovskite layer surface. Multiple types of fluorine-containing organic compounds may also be used. These terminal groups may also be ionized in the solvent. It is more preferable for the fluorine-containing organic compound to have both cationic and anionic terminal groups to compensate for defects with different charges, such as iodine defects, lead defects, and halogen defects, on the perovskite layer surface. Examples of terminal groups with both cationic and anionic terminal groups include phosphocholine groups and carbamic acid groups. Examples of polymers include:

[0032] 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 (CF ３ (CF ２ ) ４ CH ２ NH ２ ), 1H,1H-pentadecafluorooctylamine (CF ３ (CF ２ ) ６ CH ２ NH ２ ), Fos-Choline-8 (fluoride) (registered trademark: C １３ H １７ F １３ NO ４ P), 2,2,2-trifluoroethylamine (CF ３ CH ２ NH ２ Examples of fluorine-containing organic compounds include 12-pentafluorophenoxydodecylphosphonic acid (C ), 3,3,4,4,5,5,6,6-nonafluorohexylphosphonic acid (FHPA), and polyvinylidene fluoride (PVDF) as a polymer structure. When the fluorine-containing organic compound has an alkyl chain skeleton, examples of fluorine-containing organic compounds having a phenyl group containing fluorine or a trifluoromethyl group include 12-pentafluorophenoxydodecylphosphonic acid (C ). １８ H ２６ F ５ O ４P), etc. The deposition of fluorine-containing organic compounds on the surface as a passivation layer can be confirmed by observing the contact angle. For example, when evaluated with chlorobenzene, the contact angle increases with the addition of a small amount of linear fluoroalkyl chains, highly lyophilic 1H,1H-undecafluorohexylamine, (fluorinated) Fos-Choline-8, etc.

[0033] 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, and their hydrides, oxides, metal complexes, and derivatives with alkyl groups added thereto, such as PCBM ([6,6]-Phenyl-C61-Butyric Acid Methyl Ester). In addition, a hole blocking layer made of pasocuproine (BCP), lithium fluoride (LiF), tin oxide (SnO ２ ), aluminum-doped zinc oxide (ZnO), titanium oxide (TiO ２ The inorganic oxide layer may be doped with another metallic material.

[0034] When the solar cell 1 receives light from the side of the substrate 10, 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 side of the second electrode layer 80, the second electrode layer 80 can be made of a transparent conductive oxide.

[0035] The solar cell 1 having the above configuration is manufactured by a solar cell manufacturing method according to one embodiment of the present invention, as shown in Fig. 2. The solar cell manufacturing method of this embodiment includes a first electrode layer forming step (step S1), a precursor liquid applying step (step S2), a crystallization step (step S3), an electron transport layer forming step (step S4), and a second electrode forming step (step S5).

[0036] In the first electrode layer formation process of step S1, a first electrode layer 20 is formed on one main surface of the substrate 10. The first electrode layer 20 can be deposited using a vacuum film-forming technique such as sputtering. Furthermore, in the first electrode layer process, it is preferable to modify the surface of the deposited first electrode layer 20 in order to facilitate 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, surface hydroxylation by ultraviolet-ozone treatment or ozone water washing, deposition of oxides such as nickel oxide, which are prone to grow self-assembled monolayers, using vacuum film-forming techniques such as sputtering, deposition using a coating technique for oxide nanoparticles, and heat treatment to activate the surface and remove impurities to facilitate the growth of self-assembled monolayers.

[0037] In the precursor liquid application step 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 step is itself one embodiment of the perovskite precursor liquid according to the present invention.

[0038] 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 fluorine-containing organic compound. The perovskite precursor liquid preferably further contains hydrochloride that promotes crystal growth of the perovskite compound.

[0039] As the solvent, for example, polar aprotic solvents such as DMF, DMSO, NMP, GBL, acetonitrile, etc. may be used alone or as a mixture of two or more kinds, and may further contain other kinds of solvents.

[0040] The perovskite precursor is a mixture of a metal halide BX and an AX composed of an organic halide compound or an alkali metal halide, in a predetermined ratio. The molar concentration of the metal atom B is preferably 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 %. This expels other materials to the interfaces between the front and back of the perovskite precursor liquid during the crystallization process, preventing other materials from being left behind in the impurity film 41 formed between the crystals of the perovskite compound, and suppressing a decrease in photoelectric conversion efficiency due to the remaining other materials.

[0041] 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 perovskite precursor liquid coating (the side opposite the first electrode layer 20) to form a film (excess material layer 50). Because it is difficult to accurately grasp the growth state of the hole transport layer-forming compound on the surface of the first electrode layer 20 (TCO), here, for simplicity, the molecular length is assumed to be the unit (lattice constant) of the monolayer, the number of hole transport-forming compounds per coating area is estimated, and the concentration is determined so that the number of hole transport-forming compounds contained in the coating film is greater than this. Specifically, the concentration of the hole transport layer-forming compound in the perovskite precursor liquid can be 0.1 mmol / L or more and 10 mmol / L or less. The hole transport layer-forming compound film formed on the surface of the perovskite precursor liquid coating provides a pathway for moisture volatilizing from the perovskite precursor liquid coating. In other words, the fluorine-containing organic compound layer is hydrophobic, preventing water from entering the perovskite compound, which is a photoelectric conversion layer vulnerable to moisture, thereby improving reliability. On the other hand, if only the fluorine-containing compound precipitates on the surface during coating of the perovskite precursor liquid, the moisture contained in the perovskite precursor liquid is prevented from escaping to the outside, reducing the reliability of the perovskite layer. Therefore, forming a hole transport layer-forming compound, which is less hydrophobic than the fluorine-containing compound, on the surface of the coating provides a pathway for moisture and improves the quality of the photoelectric conversion layer 40. This is particularly effective when coating is performed in the atmosphere, where the inflow of moisture into the perovskite precursor is unavoidable.

[0042] Due to the lyophobicity derived from fluorine, the fluorine-containing organic compound aggregates into a film on the surface of the coating film of the perovskite precursor liquid, partially covering the surface of the layer of 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. Furthermore, the fluorine-containing organic compound inhibits the growth of a 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 is absent and where the passivation layer 60 is present. The concentration of the fluorine-containing organic compound in the perovskite precursor liquid may be 1 μmol / L or more and 5 mmol / L or more. To achieve high performance, a high surface coverage of the fluorine-containing organic compound is preferable, and more preferably, the fluorine-containing organic compound covers substantially the entire surface (e.g., 90% or more of the region), thereby suppressing the inhibition of electron transport by the hole transport layer-forming compound. On the other hand, if the concentration of the fluorine-containing organic compound is increased to improve the coverage, it may be incorporated into the perovskite compound and act as an impurity, making recombination more likely. Furthermore, forming multiple layers may cause resistance, potentially reducing performance. Therefore, when the fluorine-containing organic compound is a low-molecular-weight compound, as with the hole transport layer-forming compound, the molecular length is assumed to be the unit (lattice constant) of a monomolecular film, and the number of fluorine-containing organic compounds per coating area is estimated. The concentration is then determined so that the number of fluorine-containing organic compounds contained in the coating film is smaller than this. Note that the passivation layer 60 and excess material layer 50 may not be able to cover the entire surface of the photoelectric conversion layer 40. In such cases, an additional passivation layer may be formed separately. The additional passivation layer may be formed using a solution of an organic compound, or may be formed using a vapor deposition method using an inorganic material such as lithium fluoride or magnesium difluoride.

[0043] The hydrochloride promotes the crystallization of the perovskite compound and increases the grain size of the perovskite crystals. This reduces the area of ​​the grain boundaries in the photoelectric conversion layer 40 and suppresses a decrease in photoelectric conversion efficiency due to impurities between the perovskite crystals. Examples of hydrochlorides include methylammonium hydrochloride (MACl), formamidinium hydrochloride (FACl), and methylenediaminium hydrochloride (MDACl). ２ The portion other than the hydrochloride salt preferably has a size equal to or smaller than the crystal lattice of the perovskite crystal and has an amino group. The concentration of the hydrochloride salt in the perovskite precursor liquid may be 1 mol % or more and 40 mol % or less relative to the molar concentration of the B site of the photoelectric conversion layer 40.

[0044] In the crystallization process of step S3, the perovskite precursor liquid film is dried, causing the perovskite precursor to react and produce crystals of the perovskite compound. This forms a photoelectric conversion layer 40 primarily composed of the perovskite compound, which fixes the hole transport layer 30, the excess material layer 50, and the passivation layer 60. Furthermore, as the perovskite compound crystals grow, an impurity film 41 containing excess metal B and metal compounds is formed between the perovskite compound crystal grains. Because the perovskite compound crystals grow from the surface side (the side opposite the first electrode layer 20), the impurity film 41 also grows from the surface side toward the first electrode layer 20. Methods for promoting the formation of perovskite compound crystals in the perovskite precursor liquid film include, for example, poor solvent quenching, vacuum quenching, gas quenching, and laser treatment. In the crystallization process of step S3, the dried coating film of the perovskite precursor liquid may be further heated.

[0045] In the electron transport layer forming step S4, the electron transport layer 70 is formed by a method such as coating or vacuum deposition. A hole blocking layer may be formed on the electron transport layer 70 by vacuum deposition or atomic deposition.

[0046] In the second electrode forming step S5, the second electrode layer 80 is formed by a method such as sputtering, vacuum deposition, plating, or coating depending on the forming material.

[0047] 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 fluorine-containing organic compound, and therefore can simultaneously form the hole transport layer 30 and the photoelectric conversion layer 40 on the first electrode layer 20 by a single coating operation, while also forming a passivation layer 60 on the surface of the photoelectric conversion layer 40, thereby preventing the photoelectric conversion layer 40 from being completely covered with an excess material layer 50 that inhibits electron transport. 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.

[0048] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and various modifications and variations are possible. The solar cell according to the present invention may include an additional functional layer. For example, a second passivation layer may be provided 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 region where the excess material layer is absent. Furthermore, the electron transport layer may be omitted from the solar cell according to the present invention. Furthermore, the solar cell according to the present invention may be used to form a tandem solar cell using a photoelectric conversion body such as a crystalline silicon solar cell as a substrate.

[0049] The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples.

[0050] Example 1 A commercially available glass / ITO substrate (first electrode) was used as the substrate. First, a NiOx film was formed as an electron blocking layer. Next, a perovskite precursor liquid was applied, followed by a crystallization process and heating to generate crystals of the perovskite compound, thereby forming a hole transport layer, a photoelectric conversion layer, an excess material layer, and a passivation layer. A vacuum quenching method was used for the crystallization process. Furthermore, an electron transport layer was formed by application of PCBM, a hole blocking layer was formed by vapor deposition of BCP, and a second electrode was formed by laminating Ag by vapor deposition, thereby producing Example 1 of the solar cell. The perovskite precursor liquid was prepared by dissolving 1.2 mol / L of a perovskite precursor (PbI) in a mixed solvent of DMF and NMP in a volume ratio of 90:10. ２ The perovskite precursor contained FA and Cs in a molar ratio of 90:10 to form the A site, Pb to form the B site, and I as a halogen atom to form the X site.

[0051] Examples 2 to 5 Solar cell Example 2 was produced under the same conditions as Example 1, except that 1.0 mmol / L of 5FPHZ was used as the fluorine-containing organic compound. Solar cell Example 3 was produced under the same conditions as Example 1, except that 0.1 mmol / L of perfluorooctane was used as the fluorine-containing organic compound. Solar cell Example 4 was produced under the same conditions as Example 1, except that 0.2 mmol / L of (fluorinated) Fos-Choline-8 was used as the fluorine-containing organic compound. Solar cell Example 5 was produced under the same conditions as Example 1, except that 1 μmol / L of PVDF (molecular weight 180,000) was used as the fluorine-containing organic compound.

[0052] (Examples 6 to 7) PbI in perovskite precursor liquid ２ A solar cell of Example 6 was produced under the same conditions as Example 1, except that MACl in the perovskite precursor solution was in excess of 1 mol %. A solar cell of Example 7 was produced under the same conditions as Example 1, except that MACl in the perovskite precursor solution was in excess of 15 mol %.

[0053] 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 containing no fluorine-containing organic compound was used.

[0054] The photoelectric conversion efficiencies of Examples 1 to 5 and Comparative Example 1 were measured, and the ratios to the photoelectric conversion efficiency of Comparative Example 1 were calculated. As a result, as summarized in Table 1 below, the values ​​were 1.05 for Example 1, 1.01 for Example 2, 1.04 for Example 3, 1.15 for Example 4, 1.10 for Example 5, 1.09 for Example 6, and 1.08 for Example 7. In this way, it was confirmed that the photoelectric conversion efficiency could be improved by blending a hole transport layer-forming compound and a fluorine-containing organic compound into the perovskite precursor liquid.

[0055]

[0056] (Examples 11 to 30, Comparative Example 2) As summarized in Table 2 below, solar cells were fabricated in Examples 11 to 30 and Comparative Example 2 by changing the hole transport layer-forming compound, fluorine-containing organic compound, and excess material in the perovskite precursor liquid from those in Example 1. Table 2 also shows the ratio of the photoelectric conversion efficiency of Examples 11 to 20 and Comparative Example 2 to that of Comparative Example 2. In Examples 25 and 27, two types of fluorine-containing organic compounds were blended into the perovskite precursor liquid.

[0057]

[0058] Examples 31 to 40, Comparative Example 3 For Examples 31 to 40 and Comparative Example 3, FA and Cs were used in a molar ratio of 80:20 to form the A site, Pb was used to form the B site, and I and Br were used as halogen atoms to form the X site in a molar ratio of 90:10. Furthermore, as summarized in the following Table 3, the hole transport layer-forming compound, fluorine-containing organic compound, and excess material in the perovskite precursor liquid were changed from those in Example 1, and solar cells were fabricated in Examples 31 to 40 and Comparative Example 3. Table 3 also shows the ratio of the photoelectric conversion efficiency of Examples 31 to 40 and Comparative Example 3 to that of Comparative Example 3.

[0059]

[0060] As described above, it was confirmed that the photoelectric conversion efficiency can be improved by blending a hole transport layer-forming compound and a fluorine-containing organic compound into various perovskite precursor liquids.

[0061] REFERENCE SIGNS LIST 1 solar cell 10 substrate 20 first electrode layer 30 hole transport layer 40 photoelectric conversion layer 41 impurity film 50 excess material layer 60 passivation layer 70 electron transport layer 80 second electrode layer

Claims

1. A perovskite precursor liquid comprising: 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 a fluorine-containing organic compound.

2. The perovskite precursor liquid according to claim 1, wherein the fluorine-containing organic compound has 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 a terminal thereof.

3. The perovskite precursor liquid according to claim 1 or 2, wherein the fluorine-containing organic compound has a carbon skeleton containing an alkyl chain or benzene in which hydrogen is substituted with fluorine or a trifluoromethyl group.

4. The perovskite precursor liquid according to claim 3, wherein the alkyl chain or benzene contains successive carbons to which fluorine is bonded.

5. The perovskite precursor liquid according to claim 1 or 2, wherein the fluorine-containing organic compound has a cationizable end group and a anionizable end group.

6. The perovskite precursor liquid according to claim 1 or 2, comprising a plurality of types of said fluorine-containing organic compounds.

7. The perovskite precursor liquid according to claim 1 or 2, wherein the perovskite precursor contains a metal halide including a lead halide, and a halogenated organic compound 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.

8. The perovskite precursor liquid according to claim 1 or 2, further comprising a hydrochloride salt that promotes crystal growth of the perovskite compound.

9. A solar cell manufacturing method comprising the steps of: applying the perovskite precursor liquid according to claim 1 or 2 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 produce crystals of a perovskite compound.

10. A solar cell comprising: a plate-like or sheet-like 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 made of a fluorine-containing organic compound laminated on an area of ​​the photoelectric conversion layer where the excess material layer is not present; and a second electrode layer laminated on the excess material layer and the passivation layer.

11. The solar cell according to claim 10, 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.

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