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

Abstract

Provided is a perovskite precursor liquid with which it is possible to form a hole transport layer and a photoelectric conversion layer at the same time without forming a layer that hinders electron transport. A perovskite precursor liquid according to one embodiment of the present invention 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 monomolecular film having hole selective permeability; and a fluorine-containing organic compound.

Description

Technical Field

[0001] This invention relates to perovskite precursor liquid, a method for manufacturing solar cells, and solar cells. Background Technology

[0002] Solar cells, as an energy source with a low environmental impact, have seen their applications expand. One type of solar cell is the perovskite solar cell, which has a photoelectric conversion layer primarily composed of a perovskite compound. A basic perovskite solar cell is formed by sequentially 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 on a substrate. Furthermore, since the absorption wavelength of perovskite solar cells differs from that of solar cells with a crystalline silicon substrate as the photoelectric conversion layer, they can also be stacked on top of crystalline silicon solar cells. The charge transport layer is the layer that allows electrons or holes to selectively pass through, and it also contributes to internal losses due to its resistance. Therefore, to reduce resistance, techniques have been proposed to form a thin charge transport layer using a self-assembled monolayer composed of a carbazole compound with charge-selective properties (see, for example, Patent Document 1).

[0003] Generally, the formation of self-assembled monolayers requires the thin and uniform application of a material solution via spin coating or similar methods. However, spin coating is difficult to implement in the large-scale production of solar cells; therefore, methods such as die coating or rod coating are preferred. Furthermore, the perovskite photoelectric conversion layer is typically formed through coating, requiring repeated coating and drying processes to form the first charge transport layer. To efficiently manufacture solar cells, the following technique has been reported: by combining a carbazole compound, which forms a hole-selective self-assembled monolayer, with a perovskite precursor solution and then coating it, the carbazole compound forms a self-assembled monolayer at the interface between the coating and the electrode layer, enabling the simultaneous formation of both the hole transport layer and the perovskite photoelectric conversion layer (see, for example, Non-Patent Literature 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2023-46212

[0007] Non-patent literature

[0008] Non-patent document 1: "Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells", Nature Energy, 2023, vol.8, p.462-472 Summary of the Invention

[0009] In cases where a carbazole compound is incorporated into the perovskite precursor solution, as in Non-Patent Document 1, an excess of the carbazole compound relative to the coating area is required to form a crack-free hole transport layer. Through verification by the inventors, it has been confirmed that an excess of the carbazole compound in the precursor solution forms a layer on the surface of the coating, hindering electron transport.

[0010] The objective of this invention is to provide a perovskite precursor liquid capable of simultaneously forming a hole transport layer and a photoelectric conversion layer without forming a layer that hinders electron transport, a method for manufacturing solar cells, and an easily manufactured solar cell.

[0011] One aspect of the present invention relates to a perovskite precursor liquid comprising: a solvent, a perovskite precursor for forming a perovskite compound for photoelectric conversion, a hole transport layer forming compound for forming a self-assembled monolayer with hole selective permeability, and a fluorinated organic compound.

[0012] In the perovskite precursor liquid described above, the fluorinated organic compound may have at least one of the following at its terminal: amino, hydrazine, trialkylamino, phosphocholine, phosphate, phosphonic acid, hydroxyl, carboxyl, and sulfonyl groups, as well as their ionized forms.

[0013] In the perovskite precursor liquid described above, the fluorinated organic compound may have a carbon skeleton comprising an alkyl chain in which hydrogen is replaced by fluorine or trifluoromethyl or benzene.

[0014] In the perovskite precursor liquid described above, the alkyl chain or benzene may continuously contain carbons bonded by fluorine.

[0015] In the perovskite precursor liquid described above, the fluorinated organic compound may have cationized and anionized terminal groups.

[0016] The perovskite precursor liquid described above may contain a variety of the aforementioned fluorinated organic compounds.

[0017] In the perovskite precursor solution described above, the perovskite precursor may contain a metal halide, as well as an organic halide or an alkali halide, wherein the metal halide includes lead halide, and the molar concentration of the metal is 0.5 mol% to 10 mol higher than the sum of the molar concentrations of the organic compound and the alkali metal.

[0018] The perovskite precursor solution described above may further contain hydrochloride salts that promote the crystal growth of the perovskite compound described above.

[0019] One aspect of the present invention relates to a solar cell manufacturing method comprising the following steps: coating a first electrode layer formed on a main surface of a substrate with the aforementioned perovskite precursor liquid; and causing the solvent to evaporate from the coating of the perovskite precursor liquid and reacting the perovskite precursor to generate crystals of a perovskite compound.

[0020] One aspect of the present invention relates to a solar cell comprising: a plate-shaped or sheet-shaped substrate; a first electrode layer formed on a main surface of one side of the substrate; a hole transport layer stacked on the first electrode layer, comprising a film of a hole transport layer forming compound having hole selective permeability; a photoelectric conversion layer stacked on the hole transport layer, comprising a perovskite compound; an excess material layer stacked on a portion of the photoelectric conversion layer, comprising the hole transport layer forming compound; a passivation layer stacked on a region of the photoelectric conversion layer where the excess material layer is absent, comprising a fluorinated organic compound; and a second electrode layer stacked on the excess material layer and the passivation layer.

[0021] In the above-described solar cell manufacturing process, the photoelectric conversion layer may have an impurity film at the grain boundaries of the perovskite compound crystal, the impurity film containing halides of metal atoms in the perovskite compound.

[0022] According to the present invention, a perovskite precursor liquid capable of simultaneously forming a hole transport layer and a photoelectric conversion layer without forming a layer that hinders electron transport, a method for manufacturing solar cells, and an easily manufactured solar cell can be provided. Attached Figure Description

[0023] Figure 1 This is a cross-sectional schematic diagram showing the configuration of a solar cell according to one embodiment of the present invention.

[0024] Figure 2 This is a flowchart illustrating the steps of a solar cell manufacturing method according to one embodiment of the present invention. Detailed Implementation

[0025] The embodiments of the present invention will be described below with reference to the accompanying drawings. Figure 1 This is a cross-sectional schematic diagram showing the configuration of a solar cell 1 according to one embodiment of the present invention. It should be noted that, for ease of explanation, the dimensions of the various components in the drawings have been adjusted to a level that is easily observable.

[0026] Solar cell 1 comprises: a plate-shaped or sheet-shaped substrate 10, and a layer of material stacked on one side of the substrate 10. Figure 1The first electrode layer 20 on the main surface of the lower side of the first electrode layer 20, the hole transport layer 30 on one side of the first electrode layer 20, the photoelectric conversion layer 40 on one side of the hole transport layer 30, the excess material layer 50 on a portion of one side of the photoelectric conversion layer 40, the passivation layer 60 on a portion of one side of the photoelectric conversion layer 40 where the excess material layer 50 is not present, the electron transport layer 70 on one side of the excess material layer 50 and the passivation layer 60, and the second electrode layer 80 on the electron transport layer 70.

[0027] The substrate 10 is a structure that supports the other layers to ensure the strength of the solar cell 1. When the solar cell 1 receives light from the substrate 10 side, the substrate 10 is formed of a transparent material. Specifically, the substrate 10 can be formed of glass, resins such as polyimide, polyamide, and polyethylene terephthalate. Alternatively, when the solar cell 1 receives light from the second electrode layer 80 side, the substrate 10 can be formed of a composite material including a metal layer.

[0028] 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) that has conductivity and light transmittance. Examples of transparent conductive oxides 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 with indium oxide, zinc oxide, tungsten oxide, molybdenum oxide, etc., as the main components, or fluorine-doped tin oxide, are preferred. Indium oxide is particularly preferred from the viewpoint of high conductivity and transparency. To improve the formability of the hole transport layer 30, the first electrode layer 20 is preferably subjected to surface treatments such as ozone treatment, and the first electrode layer 20 can have a multilayer structure with layers of p-type oxide semiconductors with, for example, nickel oxide, niobium oxide, etc., as the main components on its surface.

[0029] The hole transport layer 30 is formed from a film of a hole transport layer forming compound that forms self-assembled monolayers (SAM). The hole transport layer 30 transports only holes from 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 for forming the hole transport layer 30 preferably has functional groups capable of transporting holes, such as carbazole-based, phenothiazine-based, or dimethylacridine-based compounds, and self-assembly end groups that are chemically bonded to a substrate, such as phosphoric acid or carboxylic acid. Passivation is preferably achieved by using a straight-chain material, such as an alkyl chain, between the functional groups and the self-assembly end groups. The alkyl chain preferably has four or more carbon atoms. Specifically, examples of hole transport layer forming compounds that form the hole transport layer 30 include Me-4PACz ([4-(3,6-dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid), MeO-4PACz ([4-(3,6-dimethoxy-9H-carbazole-9-yl)butyl]phosphonic acid), Me-PhpPACz ([4-(3,6-dimethyl-9H-carbazole-9-yl)phenyl]phosphonic acid), and DMAcPA ((4-(2,7-dibromo-9,9-dimethylacridin-10(9H)-yl)butyl)phosphonic acid).

[0030] The photoelectric conversion layer 40 contains a perovskite compound that performs photoelectric conversion, absorbing incident light to generate photocarriers. As the perovskite compound contained in the photoelectric conversion layer 40, a compound represented by ABX3 can be used, comprising an organic atom A, a metal atom B, and a halogen atom X, wherein the organic atom A comprises an alkali metal (Am), a monovalent organic ammonium ion, and an amidine. The metal atom B is a divalent metal ion, and the halogen atom X comprises at least one of the following: iodide ion I, bromide ion Br, chloride ion Cl, and fluoride ion F. Examples of alkali metals as sites A include potassium K, cesium Cs, and rubidium Rb; examples of organic atoms A include methylammonium MA (CH3NH3) and formamidinium. Examples of metal atoms include FA (CH3N2). Examples of metal atoms B include lead (Pb) and tin (Sn), with lead being the preferred predominant. Examples of halogen atoms X include at least one of iodide I, bromide Br, and chloride Cl.

[0031] Specifically, preferred perovskite compounds include, for example, methylammonium lead halide (MAPbX3) such as MAPbI3, MAPbBr3, and MAPbCl3, and formamidinium such as FAPbI3, FAPbBr3, and FAPbCl3. Lead halide (FAPbX3). It should be noted that the halogen atom X can be of various types. It can include methylammonium, formamidinium, etc. The FA of these two forms y MA 1-y PbX3. Additionally, when alkali metals are present, Am can be cited as an example. y FA z MA 1-y-z PbX3, Am y FA 1-y PbX3, etc. Am can be a single type of Cs, Rb, or K, or it can contain multiple types. (y and z are arbitrary positive integers). Halogen atoms X can also contain multiple types.

[0032] The photoelectric conversion layer 40 preferably has an impurity film 41 at the grain boundaries of the perovskite compound crystal. This impurity film 41 contains halides of metal atoms in the perovskite compound, such as Pb, PbI2, PbBr2, and PbCl2. For the formation of such an impurity film 41, the metal B in the perovskite compound is lead (Pb). By having an impurity film 41 containing metal atoms B and metal compounds, the photoelectric conversion layer 40 can suppress the residue of hole transport layer forming compounds (forming the hole transport layer 30) and fluorine-containing organic compounds (forming the passivation layer 60) at the grain boundaries of the perovskite compound crystal during the formation of the photoelectric conversion layer 40, thereby improving the photoelectric conversion efficiency.

[0033] The excess material layer 50 is formed from the same hole transport layer forming compound as the compound forming the hole transport layer 30. Since the hole transport layer forming compound used as the hole transport layer 30 has a lowest unoccupied molecular orbital (close to the vacuum level) lower than the conduction band of the perovskite compound, it blocks electron transport, making it difficult for electrons to reach the electron transport layer, resulting in resistance. Ideally, the excess material layer 50 should not be formed. However, when forming the hole transport layer 30 and the photoelectric conversion layer 40 using the same process, a slightly larger amount of hole transport layer forming compound is needed to form a crack-free hole transport layer 30 covering the entire surface of the first electrode layer 20. The excess portion of the hole transport layer forming compound forms the excess material layer 50. Furthermore, the excess material layer 50 can also function as an anchoring agent to improve the adhesion with the electron transport layer 70. In other words, fluorinated organic compounds with low surface free energy generally have poor adhesion with the electron transport layer 70; therefore, forming the excess material layer 50 can compensate for this deficiency. The excess material layer 50 may consist solely of a hole transport layer forming compound, or it may contain other materials contained in the perovskite precursor liquid. The weight percentage 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 percentage of the hole transport layer forming compound in the excess material layer 50 is preferably 90% or less, more preferably 70% or less. In other words, in areas where the passivation layer is not formed, a portion of the perovskite compound directly contacts the electron transport layer 70 and can transport electrons. However, compared to forming a surface containing many defects, it is more preferable to form the hole transport layer forming compound on the surface of the perovskite compound, thereby driving electrons back into the perovskite compound layer. The weight percentage 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 obtained by combined transmission electron microscopy observation and energy-dispersive X-ray analysis, etc.

[0034] The passivation layer 60 prevents the recombination of photocarriers at the interface with the photoelectric conversion layer 40, promoting the arrival of electrons to the electron transport layer 70. Furthermore, the passivation layer 60 is formed to compete with the excess material layer 50 for the surface of the photoelectric conversion layer 40, thereby 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 composed of a fluorinated organic compound. Because it readily exhibits lipolytic properties to solvents used to form the photoelectric conversion layer 40, such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and acetonitrile, it preferentially precipitates onto the surface of the photoelectric conversion layer 40 compared to the excess material layer 50. Additionally, fluorine, which has electron-withdrawing properties, preferentially transports electrons.

[0035] Fluorinated organic compounds preferably have a carbon skeleton containing an alkyl chain and benzene, and a portion of which has a structure in which hydrogen atoms are substituted by fluorine, trifluoromethyl, or the like. More preferably, the carbon skeleton continuously comprises carbon atoms bonded by fluorine. When a fluorinated organic compound has a benzene skeleton, it is preferable that any 5 of the 6 hydrogen atoms of benzene are substituted by fluorine or trifluoromethyl, and the remaining 1 is connected to a hydrophilic group that becomes the terminal. The more fluorine and trifluoromethyl substitutions there are, the higher the hydrophilicity and the greater the effect of surface selective orientation. Therefore, when fluorine is substituted, it is preferable to have a structure of pentafluorinated benzene in which all hydrogen atoms except the 1 connected to the terminal are substituted by fluorine. When a fluorinated organic compound has an alkyl chain skeleton, it is preferable that the leading end is trifluoromethyl or a phenyl group containing fluorine or trifluoromethyl, and the terminal is a hydrophilic group. The leading end containing fluorine is oriented on the electron transport layer side, and the terminal end containing the hydrophilic group is oriented on the perovskite surface side. The number of carbon atoms in the skeleton of the straight chain other than the leading and terminal ends is preferably 1 to 17. The number of carbon atoms is further preferably 5 to 16. To facilitate the formation of passivation layer 60 through self-assembly of fluorinated organic compounds, longer alkyl chains result in higher orientation and passivation, but also higher insulation and lower conductivity. Therefore, sufficient orientation can be achieved by imparting alkyl chains above the upper limit, while passivation and conductivity can be achieved by imparting alkyl chains below the lower limit. Preferably, the fluorinated organic compound has an alkyl chain backbone, with a trifluoromethyl end, where the alkyl chain from the end continuously contains fluorinated carbons. More preferably, all carbons except for one or two adjacent to the end are fluorinated. Continuous fluorination improves hydrophilicity, allowing for further selective precipitation onto the surface, thereby promoting the formation of passivation layer 60. Another example of a fluorinated organic compound having an alkyl chain backbone is a polymer structure. Partially fluorinated polymer structures, due to their high fluorine content, tend to align planarly on the surface, unlike cases where the fluorinated end is oriented on the electron transport layer side and the hydrophilic end is oriented on the perovskite surface side. Similar to the case described above where fluorinated organic compounds have an alkyl chain backbone and a phenyl group containing fluorine and trifluoromethyl groups at the leading end, the greater the number of fluorine and trifluoromethyl substitutions, the greater the effect. Therefore, when the hydrogen of the phenyl group is substituted with fluorine, pentafluorobenzene is preferred. Furthermore, by having both phenyl and alkyl chains containing fluorine and trifluoromethyl groups, surface precipitation can be promoted more selectively compared to the case with only a benzene backbone.

[0036] Furthermore, the fluorinated organic compounds preferably have a hydrophilic group at their ends, specifically at least one of amino, hydrazine, trialkylamino, phosphate, phosphonic, hydroxyl, carboxyl, and sulfonyl groups, and their ionized forms. These groups are hydrophilic to the solvent forming the photoelectric conversion layer 40, i.e., an aprotic polar solvent, and by combining with a hydrophobic fluorinated backbone, they can be located on the surface of the photoelectric conversion layer 40 from a stage before the drying process. By having a linear backbone, a hydrophilic group, or both, the fluorinated organic compounds can easily align, forming a thin and uniform film, and reducing series resistance. By ionizing their ends, defects such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer can be compensated, thereby improving performance. Additionally, various fluorinated organic compounds can be used. Furthermore, their end groups can be ionized in a solvent. To compensate for defects such as iodine defects, lead defects, and halogen defects on the surface of the perovskite layer that exist due to different charges, it is more preferable that the fluorinated organic compounds have both cationic and anionic end groups. Examples of terminals that can be either cationic or anionic include phosphocholine and carbamate.

[0037] Examples of polymers

[0038] Specific examples of fluorinated organic compounds, specifically those with a benzene skeleton substituted with fluorine and trifluoromethyl groups, include 4-fluorophenylethylamine hydroiodate (FPEAI), 4-(trifluoromethyl)phenylammonium hydroiodate, 2,6-difluoroaniline, 3,4,5-trifluoroaniline, pentafluorophenylphosphonic acid (5FPAc), pentafluorophenylhydrazine (5FPHZ), and pentafluorophenyl-amino-carboxylic acid (carbamic acid) hydrogen iodide. When fluorinated organic compounds have an alkyl chain skeleton, examples of compounds with a trifluoromethyl group at the front and a lyophilic end include 1H,1H-undecanohexylamine (CF3(CF2)4CH2NH2), 1H,1H-pentadecafluorooctylamine (CF3(CF2)6CH2NH2), and (fluorinated)Fos-Choline-8 (registered trademark: C...). 13 H 17 F 13 Examples of compounds with polymeric structures include NO4P, 2,2,2-trifluoroethylamine (CF3CH2NH2), and 3,3,4,4,5,5,6,6-nonafluorohexylphosphonic acid (FHPA), such as polyvinylidene fluoride (PVDF). When fluorinated organic compounds have an alkyl chain backbone, examples of compounds containing a phenyl group including fluorine and a trifluoromethyl group include pentafluorophenoxydodecyl phosphonic acid (C4P). 18 H 26Fluorinated organic compounds (F5O4P), etc., are deposited on the surface as a passivation layer, which can be confirmed by observing the contact angle. For example, when evaluating with chlorobenzene, the contact angle increases by adding small amounts of linear fluoroalkyl chains, highly hydrophilic 1H,1H-undecylfluorohexylamine, (fluorinated) Fos-Choline-8, etc.

[0039] The electron transport layer 70 allows electrons to selectively pass through and be transferred to the second electrode layer 80. The electron transport layer 70 is formed, for example, of a material primarily composed of fullerenes. Examples of fullerenes include C60, C70, their hydrides, oxides, metal coordination compounds, and derivatives of added alkyl groups, such as PCBM ([6,6]-phenyl-C61-butyrate). Furthermore, a hole-blocking layer such as copper hydroxide (BCP), lithium fluoride (LiF), tin oxide (SnO2), aluminum-doped zinc oxide (ZnO), or titanium oxide (TiO2) can be included between the electron transport layer and the second electrode layer. The inorganic oxide layer can be doped with other metallic materials.

[0040] When the solar cell 1 receives light from the substrate 10 side, in order to reduce resistance, the second electrode layer 80 preferably includes a metal layer formed of, for example, copper. Alternatively, when the solar cell 1 receives light from the second electrode layer 80 side, the second electrode layer 80 may be formed of a transparent conductive oxide.

[0041] The solar cell 1 with the above configuration can be used Figure 2 The solar cell manufacturing method according to one embodiment of the present invention is shown. The solar cell manufacturing method of this embodiment includes: a first electrode layer formation step (step S1), a precursor liquid coating step (step S2), a crystallization step (step S3), an electron transport layer formation step (step S4), and a second electrode formation step (step S5).

[0042] In the first electrode layer formation step S1, a first electrode layer 20 is formed on the main surface of one side of the substrate 10. The first electrode layer 20 can be laminated using vacuum film deposition techniques such as sputtering. Furthermore, in the first electrode layer formation step, to facilitate the formation of the hole transport layer 30 in the subsequent step, it is preferable to modify the surface of the already formed first electrode layer 20. Specific methods for surface modification of the first electrode layer 20 include, for example, hydroxylation of the surface using ultraviolet-ozone treatment or ozone water cleaning; film formation using vacuum film deposition techniques such as sputtering with oxides, which are easy to grow self-assembled films; film formation using oxide nanoparticle coating techniques; and surface activation and impurity removal heat treatment in a manner conducive to self-assembled film growth.

[0043] In the precursor liquid coating step S2, a perovskite precursor liquid is coated onto the first electrode layer 20. The coating of the perovskite precursor liquid can be performed using, for example, a die coater or a bar coater. The perovskite precursor liquid coated in the precursor liquid coating step is itself an embodiment of the perovskite precursor liquid of the present invention.

[0044] The perovskite precursor solution comprises: a solvent, a perovskite precursor for forming a perovskite compound that performs photoelectric conversion, a hole transport layer forming compound for forming a self-assembled monolayer with hole selective permeability, and a fluorinated organic compound. Preferably, the perovskite precursor solution further comprises a hydrochloride salt that promotes crystal growth of the perovskite compound.

[0045] As solvents, polar aprotic solvents such as DMF, DMSO, NMP, GBL, and acetonitrile can be used alone or in the form of a mixture of various solvents, and may also include other types of solvents.

[0046] As a perovskite precursor, a metal halide BX, an organic halide, or an alkali metal halide AX are used in a specified proportion. The molar concentration of metal B atoms is preferably 0.5 mol% to 10 mol% higher than the sum of the molar concentrations of the organic compound and the alkali metal. This allows other materials to be expelled from the interface between the surface and interior of the perovskite precursor liquid during the crystallization process, suppressing the retention of other materials in the impurity film 41 formed between the crystals of the generated perovskite compound, and suppressing the decrease in photoelectric conversion efficiency caused by the residue of other materials.

[0047] As described above, the hole transport layer forming compound can be a material that forms a self-assembled monolayer with hole selective permeability. If a perovskite precursor liquid is coated 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 after forming 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 to the first electrode layer 20) to form a film (excess material layer 50). Since it is difficult to accurately determine the growth state of the hole transport layer forming compound on the surface of the first electrode layer 20 (TCO), the molecular length is simply assumed to be the unit cell (lattice constant) of the monolayer, and the number of hole transport layer forming compounds per unit coating area is estimated. The concentration is then determined by increasing the number of hole transport layer forming compounds contained in the coating film. Specifically, the concentration of the hole transport layer forming compound in the perovskite precursor liquid can be set to 0.1 mmol / L to 10 mmol / L. The hole transport layer formed on the surface of the perovskite precursor liquid coating provides a channel for moisture to evaporate from the coating. In other words, because the fluorinated organic compound layer is hydrophobic, it hinders the inflow of water from the outside into the perovskite compound, which is weakly resistant to moisture, thus improving reliability. On the other hand, if only the fluorinated compound precipitates to the surface during perovskite precursor liquid coating, it will hinder the drainage of moisture encapsulated within the perovskite precursor liquid, reducing the reliability of the perovskite layer. Therefore, by utilizing a fluorinated compound to form a low-hydrophobic hole transport layer on the surface of the coating, a channel for moisture can be provided, improving the quality of the photoelectric conversion layer 40. This is particularly effective for coatings applied in the atmosphere where moisture inflow into the perovskite precursor cannot be avoided.

[0048] Fluorinated organic compounds, utilizing the hydrophobic properties of fluorine, condense into a film on the surface of a coating of perovskite precursor liquid, covering a portion of the surface of the perovskite compound layer (photoelectric conversion layer 40) formed from the perovskite precursor. This forms a passivation layer 60 that suppresses the recombination of photocarriers (holes and electrons) at the interface of the photoelectric conversion layer 40. Furthermore, by hindering the growth of a hole transport layer forming compound film on the surface of the perovskite precursor liquid coating, the fluorinated organic compound reliably forms a region where the passivation layer 60 is present without an excess material layer 50. The concentration of the fluorinated organic compound in the perovskite precursor liquid can be set from 1 μmol / L to 5 mmol / L. For high performance, a higher surface coverage of the fluorinated organic compound is preferable; more preferably, the fluorinated organic compound covers approximately the entire surface (e.g., more than 90%), thereby suppressing the obstruction of electron transport by the hole transport layer forming compound. On the other hand, if the concentration of fluorinated organic compounds is increased to improve the coating rate, they may enter the perovskite compound and act as impurities, easily recombinizing and becoming resistive when forming multilayers, thus degrading performance. Therefore, when the fluorinated organic compound is of low molecular weight, similar to the hole transport layer forming compound, the molecular length is assumed to be the unit cell (lattice constant) of a monolayer, and the amount of fluorinated organic compound per unit coating area is estimated. The concentration is thus determined by reducing the amount of fluorinated organic compound contained in the coating film. It should be noted that there are cases where the entire surface of the photoelectric conversion layer 40 cannot be coated using the passivation layer 60 and the excess material layer 50. In this case, an additional passivation layer can be formed. As the additional passivation layer, an organic compound can be formed using solution deposition, or inorganic materials such as lithium fluoride or magnesium difluoride can be formed using vapor deposition.

[0049] Hydrochloride promotes the crystallization of perovskite compounds, increasing the grain size of perovskite crystals. This reduces the area of ​​grain boundaries in the photoelectric conversion layer 40, suppressing the decrease in photoelectric conversion efficiency caused by impurities between perovskite crystals. Methylammonium hydrochloride (MACl) and formamidinium can be used as hydrochloride. Hydrochloride (FACl), methylenediamine hydrochloride (MDACl2), etc. Regarding the portion other than hydrochloride, it is preferably a size below the lattice of the perovskite crystal and contains amino groups. The concentration of hydrochloride in the perovskite precursor solution, relative to the molar concentration of the B sites in the photoelectric conversion layer 40, can be set to 1 mol% to 40 mol%.

[0050] In the crystallization step S3, the perovskite precursor liquid film is dried, causing the perovskite precursor to react and form crystals of the perovskite compound. This forms a photoelectric conversion layer 40 primarily composed of the perovskite compound, fixing the hole transport layer 30, excess material layer 50, and passivation layer 60. Furthermore, if the perovskite compound crystals grow, an impurity film 41 containing excess metal B and metal compounds is formed between the perovskite compound grains. Since the perovskite compound crystals grow from the surface side (the side opposite to the first electrode layer 20), the impurity film 41 also grows from the surface side towards the first electrode layer 20. Methods to promote 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 step S3, the dried perovskite precursor liquid coating can be further heated.

[0051] In the electron transport layer formation process of step S4, the electron transport layer 70 is formed by methods such as coating or vacuum evaporation. A hole blocking layer can be formed on the electron transport layer 70 by vacuum evaporation or atomic deposition.

[0052] In the second electrode formation process of step S5, the second electrode layer 80 is formed by sputtering, vacuum evaporation, plating, coating or other methods according to the forming material.

[0053] As described above, since the perovskite precursor liquid according to one embodiment of the present invention contains a perovskite precursor, a hole transport layer forming compound, and a fluorinated organic compound, a hole transport layer 30 and a photoelectric conversion layer 40 can be simultaneously formed on the first electrode layer 20 in a single coating process. Furthermore, a passivation layer 60 is formed on the surface of the photoelectric conversion layer 40 to prevent the photoelectric conversion layer 40 from being completely covered by an excess material layer 50 that hinders electron transport. Therefore, the solar cell manufacturing method according to one embodiment of the present invention can easily manufacture a solar cell 1 with high photoelectric conversion efficiency.

[0054] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments and various modifications and variations are possible. The solar cell of the present invention may further include a functional layer. As an example, a second passivation layer covering one side of the excess material layer and passivation layer may be provided between the excess material layer and the passivation layer and the electron transport layer. This second passivation layer may be formed of the same material as the first passivation layer stacked in the region where there is no excess material layer. Furthermore, the electron transport layer may be omitted in the solar cell of the present invention. Additionally, in the solar cell of the present invention, a photoelectric converter such as a crystalline silicon solar cell can be used as a substrate to form a tandem solar cell.

[0055] Example

[0056] The present invention will be specifically described below based on the embodiments, but the present invention is not limited to the following embodiments.

[0057] (Example 1)

[0058] A commercially available glass / ITO substrate (first electrode) was used as the substrate. First, NiOx was deposited as an electron blocking layer. Next, a perovskite precursor solution was coated, and a crystallization process was performed, followed by 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. The crystallization process employed a vacuum quenching method. Further, an electron transport layer was formed by coating with PCBM, a hole blocking layer was formed by vapor deposition of BCP, and a second electrode was formed by stacking Ag using vapor deposition, thus fabricating Example 1 of a solar cell. The perovskite precursor solution was a substance prepared by dissolving 1.2 mol / L of perovskite precursors (PbI2, CsI, and FAI), 1.5 mmol / L of Me-4PACz (hole transport layer forming compound), and 1.0 mmol / L of 5FPAc (fluorine-containing organic compound) in a mixed solvent of DMF and NMP at a volume ratio of 90:10. The perovskite precursor comprises: FA and Cs in a molar ratio of 90:10 for forming site A, Pb for forming site B, and I as a halogen atom for forming site X.

[0059] (Examples 2-5)

[0060] Example 2: A solar cell was prepared under the same conditions as in Example 1, except that 1.0 mmol / L of 5FPHZ was used as the fluorinated organic compound. Example 3: A solar cell was prepared under the same conditions as in Example 1, except that 0.1 mmol / L of perfluorooctane was used as the fluorinated organic compound. Example 4: A solar cell was prepared under the same conditions as in Example 1, except that 0.2 mmol / L of (fluorinated) Fos-Choline-8 was used as the fluorinated organic compound. Example 5: A solar cell was prepared under the same conditions as in Example 1, except that 1 μmol / L of PVDF (molecular weight 180,000) was used as the fluorinated organic compound.

[0061] (Examples 6-7)

[0062] Example 6: A solar cell was fabricated under the same conditions as in Example 1, except that the perovskite precursor solution was made with a 1 mol% excess of PbI2. Example 7: A solar cell was fabricated under the same conditions as in Example 1, except that the perovskite precursor solution was made with a 15 mol% excess of MACl.

[0063] (Comparative Example 1)

[0064] Comparative Example 1: A solar cell was fabricated under the same conditions as in Example 1, except that a perovskite precursor liquid containing no fluorine-containing organic compounds was used.

[0065] The photoelectric conversion efficiency was measured for Examples 1-5 and Comparative Example 1, and the ratio of the photoelectric conversion efficiency to that of Comparative Example 1 was calculated. The results are uniformly shown in Table 1 below: Example 1: 1.05; Example 2: 1.01; Example 3: 1.04; Example 4: 1.15; Example 5: 1.10; Example 6: 1.09; Example 7: 1.08. This confirms that by combining a hole transport layer formation compound and a fluorinated organic compound in the perovskite precursor fluid, the photoelectric conversion efficiency can be improved.

[0066]

[0067] (Examples 11-30, Comparative Example 2)

[0068] As shown in Table 2 below, solar cells of Examples 11-30 and Comparative Example 2 were fabricated by using compounds forming the hole transport layer of the perovskite precursor liquid, fluorinated organic compounds, and excess materials different from those in Example 1. Table 2 also shows the ratio of photoelectric conversion efficiency of Examples 11-20 and Comparative Example 2 to Comparative Example 2. It should be noted that in Examples 25 and 27, two fluorinated organic compounds were incorporated into the perovskite precursor liquid.

[0069] [Table 2]

[0070]

[0071] (Examples 31-40, Comparative Example 3)

[0072] Examples 31-40 and Comparative Example 3 included FA and Cs in a molar ratio of 80:20 for forming site A, Pb for forming site B, and I and Br in a molar ratio of 90:10 for forming halogen atoms at site X. Furthermore, as shown in Table 3 below, the hole transport layer forming compound, fluorinated organic compound, and excess material of the perovskite precursor liquid were different from those in Example 1, and solar cells of Examples 31-40 and Comparative Example 3 were fabricated. Table 3 also shows the ratio of the photoelectric conversion efficiency of Examples 31-40 and Comparative Example 3 to that of Comparative Example 3.

[0073] [Table 3]

[0074]

[0075] In summary, it has been confirmed that by combining hole transport layer compounds and fluorine-containing organic compounds in various perovskite precursor fluids, photoelectric conversion efficiency can be improved.

[0076] Symbol Explanation

[0077] 1. Solar cell

[0078] 10 Substrate

[0079] 20 First electrode layer

[0080] 30 Hole transport layer

[0081] 40 Photoelectric conversion layer

[0082] 41 Impurity Membrane

[0083] 50 Excess Material Layers

[0084] 60 passivation layer

[0085] 70 Electron Transport Layer

[0086] 80 Second electrode layer

Claims

1. A perovskite precursor liquid, comprising: Solvent, Perovskite precursors that form perovskite compounds that undergo photoelectric conversion. Hole transport layer forming compounds that form self-assembled monolayers with hole selective permeability, and Fluorine-containing organic compounds.

2. The perovskite precursor liquid according to claim 1, wherein, The fluorinated organic compound has at least one of the following at its terminal: amino, hydrazine, trialkylamino, phosphocholine, phosphate, phosphonic acid, hydroxyl, carboxyl, and sulfonyl groups, as well as their ionized compounds.

3. The perovskite precursor liquid according to claim 1 or 2, wherein, The fluorinated organic compound has a carbon skeleton comprising an alkyl chain in which hydrogen is replaced by fluorine or trifluoromethyl or benzene.

4. The perovskite precursor liquid according to claim 3, wherein, The alkyl chain or benzene continuously comprises carbon atoms bonded by fluorine.

5. The perovskite precursor liquid according to claim 1 or 2, wherein, The fluorinated organic compound has cationized and anionized terminal groups.

6. The perovskite precursor liquid according to claim 1 or 2, wherein, It contains a variety of the aforementioned fluorinated organic compounds.

7. The perovskite precursor liquid according to claim 1 or 2, wherein, The perovskite precursor comprises a metal halide and an organic halide or an alkali halide, wherein the metal halide comprises lead halide, and the molar concentration of the metal is 0.5 mol% to 10 mol higher than the sum of the molar concentrations of the organic compound and the alkali metal.

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

9. A method for manufacturing a solar cell, comprising the following steps: The process of coating a first electrode layer formed on a main surface of a substrate with the perovskite precursor liquid of claim 1 or 2, and The process of evaporating the solvent from the coating of the perovskite precursor liquid and reacting the perovskite precursor to form crystals of the perovskite compound.

10. A solar cell, comprising: Plate-shaped or sheet-shaped substrate, The first electrode layer is stacked on one side of the main surface of the substrate. A hole transport layer, stacked on the first electrode layer, is composed of a film of a hole transport layer forming compound with hole selective permeability. A photoelectric conversion layer, stacked on top of the hole transport layer, comprises a perovskite compound. An excess material layer, stacked on a portion of the photoelectric conversion layer, is composed of a compound formed from the hole transport layer. A passivation layer, stacked on the region of the photoelectric conversion layer where the excess material layer is absent, is composed of a fluorinated organic compound, and The second electrode layer is stacked on top of 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 at the grain boundary of the perovskite compound crystal, the impurity film containing halides of metal atoms in the perovskite compound.

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