Solar cell manufacturing methods

Abstract

This invention provides a method for manufacturing a perovskite solar cell having a photoelectric conversion layer that does not have pinholes. [Solution] A method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound comprises, in this order, applying a precursor solution of the perovskite compound to a coating surface to form a coating, blowing an inert gas with a flow rate of 40 m / s or more perpendicularly onto the coating which is heated to 35°C to 45°C, and drying the coating by heating to form the photoelectric conversion layer.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing solar cells. [Background technology]

[0002] One type of solar cell known is the perovskite solar cell, in which the main component of the photoelectric conversion layer is a perovskite compound.

[0003] Non-patent document 1 describes how a uniform and dense perovskite film was formed by blowing 120°C air onto a wet film of a precursor solution of a perovskite compound formed by ultrasonic spray coating for 15 seconds, and then annealing it. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Jian Su et al., “Efficient Perovskite Solar Cells Prepared by Hot Air Blowing to Ultrasonic Spraying in Ambient Air”, ACS Applied Materials & Interfaces, 2019, Vol. 11, Issue 11, pp. 10689-10696 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Perovskite solar cells are desirable to have high power generation efficiency, and for this to be desirable, it is known that the photoelectric conversion layer is free of pinholes. This disclosure provides a novel method for manufacturing a perovskite solar cell having a photoelectric conversion layer free of pinholes. [Means for solving the problem]

[0006] Aspects of the present disclosure include the following. [Aspect 1] The following formula (1) ABX3 (1) (wherein, A represents a monovalent cation containing at least one cation selected from the group consisting of Cs , , , + , + , , , 2+ , , , , , 2+ , + , 2+ , , , , , , CH3NH3 + , and HC(NH2)2 + ), and B represents a divalent cation containing at least one cation selected from the group consisting of Pb 2+ and Sn 2+ ), and X represents a monovalent anion containing at least one anion selected from the group consisting of halide anions). A method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound represented by applying a precursor solution containing A, B, and X to a coating surface to form a coating; spraying an inert gas with a flow rate of 40 m / s or more perpendicularly to the coating onto the coating heated at 35°C to 45°C; drying the coating by heating to form the photoelectric conversion layer; The method including the above steps in this order. [Aspect 2] A is at least one cation selected from the group consisting of Cs + , CH3NH3 + , and HC(NH2)2 + , B is at least one cation selected from the group consisting of Pb 2+ and Sn 2+ , X is at least one anion selected from the group consisting of halide anions, the method according to Aspect One. [Aspect 3] The method according to Aspect 1 or 2, wherein the flow rate of the inert gas sprayed onto the coating is within the range of 40 m / s to 70 m / s. [Aspect 4]​The method according to any one of Aspects 1 to 3, wherein the heating temperature of the coating for drying the coating is 70°C to 200°C. [Aspect 5] The solar cell further includes a substrate, a first electrode layer, a first carrier transport layer, a second carrier transport layer, and a second electrode layer in this order. The method according to any one of Aspects 1 to 4, wherein the photoelectric conversion layer is disposed between the first carrier transport layer and the second carrier transport layer. [Advantages of the Invention]

[0007] By the manufacturing method of the present disclosure, a perovskite solar cell having a photoelectric conversion layer without pinholes can be manufactured. [Brief Description of the Drawings]

[0008] [Figure 1] It is a schematic cross-sectional view showing an example of the structure of a solar cell. [Figure 2] It is a schematic diagram showing a perovskite crystal structure. [Figure 3] It is a flowchart showing a method for manufacturing a solar cell according to an embodiment. [Figure 4] Figures 4(a) to (f) are optical microscope images of the photoelectric conversion layers of Experimental Examples 1 to 6. [Figure 5] Figures 5(a) to (f) are optical microscope images of the photoelectric conversion layers of Experimental Examples 7 to 12. [Figure 6] Figures 6(a) and (b) are plan SEM images of the photoelectric conversion layers of Experimental Examples 5 and 6. [Modes for Carrying Out the Invention]

[0009] Embodiments will be described below with reference to drawings as appropriate. In the drawings referenced in the following description, the dimensional ratios and shapes of each component may be exaggerated for illustrative purposes and may differ from the actual dimensional ratios and shapes. In this application, "on ~" includes both "directly on ~" and "indirectly on ~" unless otherwise specified in the context. In this application, "perpendicular" includes not only exact perpendicularity but also substantial perpendicularity. In this application, numerical ranges represented by the symbol "~" include the numerical values ​​before and after the symbol "~" as the lower and upper limits, respectively, unless otherwise specified. The upper and lower limits stated in this application may be used alone or in any combination. In this application, "including ~" and "containing ~" mean that additional components or elements may be included unless otherwise specified, and include "essentially made from ~" and "consisting of ~". "Essentially made from ~" means that additional components or elements may be included that do not substantially adversely affect the product. "Consisting of ~" means that only the described material or element is included, but does not exclude the inclusion of unavoidable impurities.

[0010] I. Solar cells First, we will describe a perovskite solar cell (hereinafter also simply referred to as "solar cell") manufactured by the manufacturing method according to the embodiment described later. Figure 1 is a schematic cross-sectional view showing an example of the structure of a solar cell.

[0011] As shown in Figure 1, in one embodiment, the solar cell C has a substrate 1, a first electrode layer 2a, a first carrier transport layer 3a, a photoelectric conversion layer 4, a second carrier transport layer 3b, and a second electrode layer 2b in this order.

[0012] (a) Photoelectric conversion layer 4 The photoelectric conversion layer 4 is located between the first carrier transport layer 3a and the second carrier transport layer 3b. When the photoelectric conversion layer 4 receives light, it generates charge carriers. The charge carriers generated in the photoelectric conversion layer 4 move to either the first carrier transport layer 3a or the second carrier transport layer 3b.

[0013] Specifically, positive charge carriers, i.e., holes, generated in the photoelectric conversion layer 4 are transported to the first electrode layer 2a or the second electrode layer 2b via either the first carrier transport layer 3a or the second carrier transport layer 3b, which are hole transport layers. Negative charge carriers, i.e., electrons, generated in the photoelectric conversion layer 4 are transported to the first electrode layer 2a or the second electrode layer 2b via either the first carrier transport layer 3a or the second carrier transport layer 3b, which are electron transport layers.

[0014] The photoelectric conversion layer 4 contains a perovskite compound. The photoelectric conversion layer 4 may contain a perovskite compound as its main component. The perovskite compound content in the photoelectric conversion layer 4 may be 60% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 100% by weight. The thickness of the photoelectric conversion layer 4 may be 100 nm to 1000 nm.

[0015] Generally, perovskite compounds are represented by the following formula (1) ABX3(1) (In the formula, A represents a monovalent cation, B represents a divalent cation, and X represents a monovalent anion.) It is represented as follows.

[0016] Perovskite compounds have a perovskite-type crystal structure. Figure 2 is a schematic diagram showing a perovskite-type crystal structure. As shown in Figure 2, the perovskite-type crystal structure has a cubic unit cell, with A at each vertex of the cubic crystal, B at the body center, and X at each face center. The fact that a compound has a perovskite-type crystal structure can be confirmed, for example, by X-ray diffraction (XRD) analysis.

[0017] In one embodiment, in formula (1), A is a cesium cation (Cs + ), methylammonium (MA) cation (CH3NH3 + ), and formamidinium (FA) cation (HC(NH2)2 + B represents a monovalent cation containing at least one cation selected from the group consisting of ), where B is a lead(II) cation (Pb 2+) and tin(II) cation (Sn 2+ X represents a divalent cation containing at least one cation selected from the group consisting of ), and X represents a monovalent anion containing at least one anion selected from the group consisting of halide anions.

[0018] Preferably, in formula (1), A is a cesium cation (Cs + ), methylammonium (MA) cation (CH3NH3 + ), and formamidinium (FA) cation (HC(NH2)2 + B represents at least one cation selected from the group consisting of ), where B is a lead(II) cation (Pb 2+ ) and tin(II) cation (Sn 2+ X represents at least one cation selected from the group consisting of ), and X represents at least one anion selected from the group consisting of halide anions. B is more preferably Pb 2+ This represents X, more preferably a fluoride anion (F - ), chloride anion (Cl - ), bromide anion (Br - ) and iodide anions (I - Represents at least one anion selected from the group consisting of ), in particular, Br - and I - Represents at least one anion selected from the group consisting of [the specified elements].

[0019] (b) First carrier transport layer 3a and second carrier transport layer 3b The first carrier transport layer 3a accepts charge carriers generated in the photoelectric conversion layer 4 and transports these charge carriers to the first electrode layer 2a. If the first carrier transport layer 3a is a hole transport layer, it transports holes to the first electrode layer 2a. If the first carrier transport layer 3a is an electron transport layer, it transports electrons to the first electrode layer 2a.

[0020] The second carrier transport layer 3b accepts charge carriers generated in the photoelectric conversion layer 4 and transports these charge carriers to the second electrode layer 2b. If the second carrier transport layer 3b is a hole transport layer, it transports holes to the second electrode layer 2b. If the second carrier transport layer 3b is an electron transport layer, it transports electrons to the second electrode layer 2b.

[0021] The hole transport layer transports holes generated by photoelectric conversion in the photoelectric conversion layer 4 to the first electrode layer 2a or the second electrode layer 2b. As the material for the hole transport layer, known organic or inorganic materials suitable for use in hole transport layers can be used.

[0022] Examples of organic materials that can be used as materials for the hole transport layer include 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (Spiro-OMeTAD), polyethylenedioxythiophene:polystyrene sulfonic acid (PEDOT:PSS), and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA).

[0023] Examples of inorganic materials that can be used as materials for hole transport layers include nickel oxide and copper oxide.

[0024] The electron transport layer transports electrons generated by photoelectric conversion in the photoelectric conversion layer 4 to the first electrode layer 2a or the second electrode layer 2b. As the material for the electron transport layer, known organic or inorganic materials suitable for use in electron transport layers can be used.

[0025] Examples of organic materials that can be used as materials for electron transport layers include fullerene compounds, phenanthroline derivatives (e.g., bathocuproine), and polyethyleneimines. Examples of fullerene compounds include fullerenes (e.g., C60 fullerene, C70 fullerene) and derivatives of fullerenes with substituents (e.g., [6,6]-phenyl-C 61-Methyl butyrate (also known as PCBM or

[60] PCBM), [6,6]-phenyl-C 71 - Methyl butyrate (also known as PCBM or

[70] PCBM) is an example.

[0026] Examples of inorganic materials that can be used as materials for electron transport layers include titanium oxide, tin oxide, and zinc oxide.

[0027] In one embodiment, the first carrier transport layer 3a is an electron transport layer, and the second carrier transport layer 3b is a hole transport layer. In this embodiment, the solar cell C has a substrate 1, a cathode, an electron transport layer, a photoelectric conversion layer 4, a hole transport layer, and an anode in this order. In this embodiment, the material of the hole transport layer may be Spiro-OMeTAD, PTAA, or nickel oxide. In this embodiment, the material of the electron transport layer may be fullerene, PCBM, bathocuproine, polyethyleneimines, titanium oxide, or tin oxide.

[0028] In another embodiment, the first carrier transport layer 3a is a hole transport layer, and the second carrier transport layer 3b is an electron transport layer. In this embodiment, the solar cell C comprises a substrate 1, an anode, a hole transport layer, a photoelectric conversion layer 4, an electron transport layer, and a cathode in this order. In this embodiment, the material of the hole transport layer may be PEDOT:PSS, PTAA, or nickel oxide. In this embodiment, the material of the electron transport layer may be fullerene, PCBM, bathocuproine, or polyethyleneimines.

[0029] (c) First electrode layer 2a and second electrode layer 2b The first electrode layer 2a is the electrode in contact with the first carrier transport layer 3a. The second electrode layer 2b is the electrode in contact with the second carrier transport layer 3b.

[0030] As the materials for the first electrode layer 2a and the second electrode layer 2b, known materials usable for electrodes of a solar cell C can be used. Examples of materials usable for the first electrode layer 2a and the second electrode layer 2b include metallic materials such as aluminum (Al), silver (Ag), and gold (Au), transparent conductive materials such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum-doped zinc oxide (AZO), and fluorine-doped tin oxide (FTO), and carbon nanotubes. The materials for the first electrode layer 2a and the second electrode layer 2b may be ITO, IZO, or FTO. When light is incident on the solar cell C through the surface of the substrate 1, the first electrode layer 2a may be transparent, and the second electrode layer 2b may be transparent or opaque. When light is incident on the solar cell C through the surface of the second electrode layer 2b, the first electrode layer 2a may be transparent or opaque, and the second electrode layer 2b may be transparent.

[0031] (d) Substrate 1 The substrate 1 supports a first electrode layer 2a, a first carrier transport layer 3a, a photoelectric conversion layer 4, a second carrier transport layer 3b, and a second electrode layer 2b.

[0032] The substrate 1 may be in the form of a plate or a film. Examples of materials for the substrate 1 include inorganic materials such as glass, organic materials such as polyethylene, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide-imide, liquid crystal polymer, and cycloolefin polymer, and metallic materials such as stainless steel and silicon.

[0033] The substrate 1 may be transparent or opaque. A transparent substrate is used when light is incident on the solar cell C through the surface of the substrate 1. Examples of transparent substrates include substrates made of glass, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide, or cycloolefin polymer. An opaque substrate can be used when light is incident on the solar cell C through the surface of the second electrode layer 2b.

[0034] II. Manufacturing Methods for Solar Cells Next, a method for manufacturing a solar cell according to the embodiment will be described. As shown in Figure 3, the method for manufacturing a solar cell according to the embodiment includes applying a precursor solution to a coating surface to form a coating (S1), blowing an inert gas onto the coating (S2), and drying the coating by heating to form a photoelectric conversion layer (S3).

[0035] In one embodiment, the method for manufacturing a solar cell optionally further includes forming a laminate comprising a substrate, a first electrode layer, and a first carrier transport layer in that order before coating a precursor solution, and optionally further including forming a second carrier transport layer and a second electrode layer on the photoelectric conversion layer in that order after forming the photoelectric conversion layer. In this embodiment, the precursor solution may be coated on the first carrier transport layer. The first electrode layer, the first carrier transport layer, the second carrier transport layer, and the second electrode layer can be formed in the same manner as in conventional photoelectric conversion elements. Therefore, a detailed explanation of the methods for forming these layers is omitted.

[0036] (a) Application of precursor solution (S1) A precursor solution is applied to the coating surface to form a coating. The coating surface may be the surface of the first carrier transport layer. If the solar cell does not have a first carrier transport layer, the coating surface may be the surface of the first electrode layer. If the solar cell has other layers between the photoelectric conversion layer and the first carrier transport layer, the coating surface may be the surface of those other layers. In other words, the coating surface is appropriately selected according to the configuration of the solar cell being manufactured.

[0037] The precursor solution contains a solute that is a precursor of the perovskite compound represented by formula (1) above. The precursor solution contains A, B, and X in a molar ratio of approximately 1:1:3.

[0038] In one embodiment, the precursor solution comprises at least one compound represented by the following formula (2) and at least one compound represented by the following formula (3). AX (2) BX2(3) (In the formula, A, B, and X are as defined above.) It can be prepared by dissolving it in a suitable solvent.

[0039] The solvent in the precursor solution may be a polar solvent from the viewpoint of solute solubility. Alternatively, the solvent in the precursor solution may be an aprotic solvent from the viewpoint of solute stability. Examples of solvents that can be used as the solvent for the precursor solution include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone, and mixed solvents containing one or more of these.

[0040] The precursor solution may be applied by any coating method that can form a uniform coating. Examples of applicable coating methods include spin coating, inkjet coating, spray coating, blade coating, and die coating.

[0041] The application of the precursor solution may be carried out in a dry air atmosphere, and more particularly in an inert gas atmosphere, from the viewpoint of the stability of the precursor solution. The inert gas may be any gas that does not react with the solute of the precursor solution. Examples of inert gases include nitrogen and argon.

[0042] (b) Inert gas spraying (S2) Next, the coating is heated, and an inert gas is blown perpendicularly to the heated coating (i.e., in the direction of the coating's thickness). This causes the solvent in the coating to evaporate, and the coating to crystallize, forming a perovskite compound with a perovskite-type crystalline structure. The duration for blowing the inert gas is not particularly limited as long as it is sufficient for the coating to crystallize sufficiently, and may be set as appropriate depending on other conditions.

[0043] The heating temperature of the coating is within the range of 35°C to 45°C, and the flow rate of the inert gas sprayed onto the coating is 40 m / s or higher. By spraying the inert gas onto the coating under these conditions, a pinhole-free photoelectric conversion layer can be formed, as shown in the experimental examples described later. The inventors believe that the above heating temperature and flow rate conditions allow the nucleation and growth of perovskite crystals in the coating to proceed at an appropriate rate, thereby preventing the formation of pinholes.

[0044] The coating can be heated by any means, such as a hot plate, oven, infrared radiation, or semiconductor laser. For example, the coating can be heated by placing the laminate with the coating on it on a hot plate set to 35°C to 45°C.

[0045] The inert gas flow velocity is measured at a distance of 50 mm perpendicular to the coating (i.e., in the thickness direction of the coating) from the surface of the coating. The inert gas flow velocity is measured using a flowmeter appropriately selected according to the flow velocity (e.g., a thermal flowmeter, a vane flowmeter, a Pitot tube flowmeter, or a laser Doppler flowmeter). An inert gas outlet may be provided at a distance of 50 mm perpendicular to the coating from the surface of the coating. In this case, the flow rate of the gas just before it is discharged from the outlet can be measured with an ultrasonic flowmeter, and the inert gas flow velocity can be determined from the measured gas flow rate and the area of ​​the outlet. The inert gas flow velocity may be in the range of 40 m / s to 70 m / s. By setting the inert gas flow velocity to 70 m / s or less, it is possible to prevent the coating from scattering due to the sprayed inert gas. The temperature of the inert gas may be the ambient temperature, for example, 25°C to 60°C.

[0046] The inert gas may be any gas that does not react with the solute in the precursor solution. Examples of inert gases include nitrogen and argon.

[0047] (c) Drying by heating (S3) Next, the coating is further heated and dried. This removes the solvent from the coating and forms a photoelectric conversion layer. This heating may cause the grains of the perovskite crystals in the coating to become larger. The heating to dry the coating may be carried out by heating the coating at a temperature of, for example, between 70°C and 200°C.

[0048] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above, and various design modifications can be made without departing from the technical scope described in the claims. [Examples]

[0049] The present disclosure will be further explained below with reference to experimental examples. However, the scope of this disclosure is not limited by these experimental examples.

[0050] (a) Fabrication of the photoelectric conversion layer A laminate measuring 25 mm in length and 25 mm in width was prepared, comprising a poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) layer (hereinafter referred to as the "hole transport layer"), an indium tin oxide (ITO) layer, and a glass substrate in that order.

[0051] A precursor solution for a perovskite compound was prepared by dissolving 112 mg of cesium iodide (CsI), 1144 mg of formamidinium iodide (FAI), 156 mg of lead(II) bromide (PbBr2), and 3636 mg of lead(II) iodide (PbI2) in a mixed solvent of 5.778 mL of dimethylformamide (DMF) and 1.444 mL of dimethyl sulfoxide (DMSO).

[0052] A 190 μL precursor solution was applied to the hole transport layer by spin coating at 1000 rpm for 10 seconds, followed by 4000 rpm for 20 seconds, to form a coating.

[0053] The substrate was placed on a hot plate at the temperature shown in Table 1, and Ar gas at ambient temperature was blown from a gas outlet located 50 mm perpendicular to the surface of the coating. The Ar gas was then blown perpendicularly onto the heated coating for 30 seconds. The flow rate of the Ar gas measured at the gas outlet was as shown in Table 1.

[0054] Next, the substrate was placed on a hot plate at 120°C and heated for 10 minutes to dry the coating. This formed a photoelectric conversion layer on the hole transport layer.

[0055] (b) Structural evaluation of the photoelectric conversion layer The portion of the photoelectric conversion layer located directly below the gas outlet was observed using an optical microscope and a scanning electron microscope (SEM). Optical microscope images of the photoelectric conversion layers in Experimental Examples 1-12 are shown in Figures 4(a)-(f) and 5(a)-(f), while planar SEM images of the photoelectric conversion layers in Experimental Examples 5 and 6 are shown in Figures 6(a) and (b), respectively. Pinholes were formed in the photoelectric conversion layers of Experimental Examples 1-4 and 7-12. No pinholes were observed in the photoelectric conversion layers of Experimental Examples 5 and 6.

[0056] At all heating temperatures, a tendency was observed for the number of pinholes to decrease as the gas flow rate increased (Figures 4(a)-(f) and 5(a)-(f)). The inventors believe this is because, as the gas flow rate increases, the rate at which the solvent in the coating is removed increases, and the rate at which the solute concentration in the coating increases increases, leading to an increase in the number of crystal nucleations in the coating and the formation of denser crystals. In experimental examples 7-12, where the heating temperature was 50°C or higher, the inventors believe that the reason why pinholes did not disappear even when the gas flow rate was increased is that the increase in crystal growth rate due to the high heating temperature exceeded the increase in crystal nucleation rate due to the increase in gas flow rate, and as a result, crystals were not formed densely enough.

[0057] [Table 1] [Explanation of symbols]

[0058] 1:Substrate 2a: First electrode layer 2b: Second electrode layer 3a: First Carrier Transport Layer 3b: Second Carrier Transport Layer 4: Photoelectric conversion layer C: Solar Cell

Claims

1. The following formula (1) ABX ３ (1) (In the formula, A is Cs ＋ ,CH ３ NH ３ ＋ , and HC(NH ２ ) ２ ＋ Represents a monovalent cation containing at least one cation selected from the group consisting of, B represents a divalent cation containing at least one cation selected from the group consisting of Pb ２＋ and Sn ２＋ and is represented by X represents a monovalent anion containing at least one anion selected from the group consisting of halide anions. A method for manufacturing a solar cell having a photoelectric conversion layer containing a perovskite compound represented by, The process involves applying a precursor solution containing A, B, and X to the surface to form a coating, The coating, which is heated to 35°C to 45°C, is subjected to a flow rate of 40 m / s or more, which is then sprayed perpendicularly onto the coating. The coating is dried by heating to form the photoelectric conversion layer, A method that includes these elements in this order.

2. The above A is Cs ＋ ,CH ３ NH ３ ＋ , and HC(NH ２ ) ２ ＋ Represents at least one cation selected from the group consisting of, The aforementioned B is Pb ２＋ and Sn ２＋ Represents at least one cation selected from the group consisting of, The method according to claim 1, wherein X represents at least one anion selected from the group consisting of halide anions.

3. The method according to claim 1 or 2, wherein the flow velocity of the inert gas sprayed onto the coating is in the range of 40 m / s to 70 m / s.

4. The method according to claim 1 or 2, wherein the heating temperature of the coating for drying the coating is 70°C to 200°C.

5. The solar cell further comprises a substrate, a first electrode layer, a first carrier transport layer, a second carrier transport layer, and a second electrode layer in this order. The method according to claim 1 or 2, wherein the photoelectric conversion layer is disposed between the first carrier transport layer and the second carrier transport layer.

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