Solar cell and method for manufacturing a solar cell

Abstract

The present invention provides a solar cell that can reduce the resistance of the counter electrode without inhibiting the penetration of the perovskite precursor solution. [Solution] The solar cell (1) is provided with a substrate (2) in the following order: a first conductive layer (3), a photoelectric conversion layer (4), and a second conductive layer (5). The photoelectric conversion layer (4) includes a porous layer (6) and a light absorbing portion (9). The second conductive layer (5) includes a porous conductive layer (10) and a metal layer (11) located on the opposite side of the photoelectric conversion layer (4) from the porous conductive layer (10).

Description

[Technical Field]

[0001] The present disclosure relates to a solar cell and a method for manufacturing a solar cell. [Background Art]

[0002] Solar cells including a photoelectric conversion layer using a perovskite (PVSK) compound (perovskite solar cells) have attracted attention.

[0003] A conventional perovskite solar cell includes a base material, an underlayer laminated on the base material, and a light absorption layer containing an organic-inorganic perovskite compound formed inside the underlayer. The underlayer is formed by spraying at least one of N-type semiconductor fine particles and insulator fine particles, to which the organic-inorganic perovskite compound is adhered, onto the base material (Patent Document 1). [Prior Art Literature] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Publication No. 2016-178167 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] In a photoelectric conversion layer of a perovskite solar cell, a porous layer is formed in a region that will serve as the photoelectric conversion layer, and a precursor solution of a perovskite compound (hereinafter referred to as perovskite precursor solution) is dropped onto the porous layer and dried, whereby the perovskite compound can be formed in the voids of the porous layer.

[0006] In this type of multilayer porous layered electrode perovskite solar cell, a challenge is the high resistance of the carbon counter electrode. While increasing the carbon film thickness can reduce the carbon's resistance, this makes it difficult for the perovskite precursor solution to penetrate sufficiently into the underlying porous power generation layer when the solution is dropped. Insufficient filling of the perovskite precursor solution within the porous power generation layer leads to a decrease in the performance characteristics of the solar cell.

[0007] One aspect of this disclosure aims to realize a solar cell and a method for manufacturing a solar cell that can reduce the resistance of the counter electrode and does not inhibit the penetration of the perovskite precursor solution. [Means for solving the problem]

[0008] To solve the above problems, a solar cell according to one aspect of the present disclosure is a solar cell provided with a first conductive layer, a photoelectric conversion layer, and a second conductive layer in order from a substrate, wherein the photoelectric conversion layer includes a porous layer and a light absorbing portion, and the second conductive layer includes a porous conductive layer and a metal layer located on the opposite side of the photoelectric conversion layer from the porous conductive layer.

[0009] To solve the above problems, a method for manufacturing a solar cell according to one aspect of the present disclosure includes a lamination step of laminating a first conductive layer, a porous electron transport layer, a porous insulating layer, and a porous conductive layer in order from a substrate; a dropping step of dropping a perovskite precursor solution onto the porous conductive layer; and a metal layer step of forming a metal layer on the porous conductive layer. [Effects of the Invention]

[0010] According to one aspect of this disclosure, it is possible to realize a solar cell and a method for manufacturing a solar cell that can reduce the resistance of the counter electrode and does not inhibit the penetration of the perovskite precursor solution. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of a solar cell according to Embodiment 1. [Figure 2] The above is a flowchart showing the manufacturing method for the solar cell. [Figure 3] This is a cross-sectional view of a solar cell according to Comparative Example 1. [Figure 4] This is a cross-sectional view of a solar cell according to Comparative Example 2. [Figure 5] This is a cross-sectional view of a solar cell according to Embodiment 2. [Figure 6] The above is a flowchart showing the manufacturing method for the solar cell. [Modes for carrying out the invention]

[0012] (Embodiment 1) (Configuration of solar cell 1) Figure 1 is a cross-sectional view of a solar cell 1 according to Embodiment 1.

[0013] The solar cell 1 is provided with, in order from the substrate 2, a first conductive layer 3, a photoelectric conversion layer 4, and a second conductive layer 5 (counter electrode). The photoelectric conversion layer 4 includes a porous layer 6 and a light-absorbing portion 9. The second conductive layer 5 includes a porous conductive layer 10 and a metal layer 11 located on the opposite side of the photoelectric conversion layer 4 from the porous conductive layer 10. The light-absorbing portion 9 contains a perovskite compound.

[0014] The solar cell 1 includes a dense electron transport layer 12 located between the first conductive layer 3 and the photoelectric conversion layer 4.

[0015] The porous layer 6 includes a porous electron transport layer 7. The porous electron transport layer 7 includes at least one selected from titanium oxide, titanium dioxide, tin oxide, and aluminum oxide.

[0016] The porous layer 6 further includes a porous insulating layer 8 located on the opposite side of the first conductive layer 3 from the porous electron transport layer 7. The porous insulating layer 8 includes at least one selected from titanium oxide, zirconium dioxide, aluminum oxide, and silicon dioxide.

[0017] The porous conductive layer 10 contains a conductive carbon material. The porous conductive layer 10 preferably contains carbon.

[0018] The metal layer 11 contains at least one selected from the group consisting of nickel, gold, silver and platinum. The metal layer 11 preferably contains silver.

[0019] The substrate 2 is a substrate of the solar cell 1, and may be the same as or include a substrate or base material, may be hard and highly rigid, or may be flexible and have low rigidity. Examples of the shape of the substrate 2 include a flat plate shape and a film shape. When light is irradiated (light is incident) on the surface on the substrate 2 side of the solar cell 1 (the lower surface of the substrate 2 in FIG. 1), that is, when the substrate 2 side is the light-receiving surface side, the substrate 2 is preferably transparent. In this case, examples of the material of the substrate 2 include glass and a heat-resistant transparent resin. Note that when light is irradiated from the opposite side, the substrate 2 may be opaque. Transparent means transmitting light, but does not exclude materials that slightly reflect or absorb light; it is sufficient as long as light can be transmitted appropriately, and this can be considered synonymous with being provided on the light-receiving surface side of solar cell 1 (including the portion where light is incident, the same applies in the present disclosure). Therefore, the substrate can be regarded as transparent by being provided at least on the light-receiving surface side of the solar cell 1.

[0020] The first conductive layer 3 is a member having conductivity. The first conductive layer 3 is formed on the base 2, on the surface of the base 2, or on the side of one surface of the base 2 (the upper side as an example), and functions as an electrode for extracting the photovoltaic power of the solar cell 1. As long as the solar cell 1 has a photoelectric conversion function as a solar cell, there is no need to confirm the conductive physical property values of the first conductive layer 3, and if the first conductive layer 3 is formed of a material considered to have conductivity, it can be identified as the first conductive layer 3. The first conductive layer 3 can be divided into a plurality of parts and arranged spaced apart in the short-side direction X in an island shape. The first conductive layer 3 is formed of a transparent conductive material, and examples thereof include conductive transparent materials such as FTO (fluorine-doped tin oxide), CuI (copper iodide), ITO (indium tin oxide), SnO₂ (tin oxide), AZO (aluminum zinc oxide), IZO (indium zinc oxide), GZO (gallium zinc oxide), and ATO (antimony-doped tin oxide), as well as conductive transparent polymers. It should be noted that chemical formulas are typical examples, and any material corresponding to the compound name is acceptable (the same applies in the present disclosure). In addition, although it is desirable that the composition ratio in the chemical formula is stoichiometric, it does not necessarily have to be stoichiometric (the same applies in the present disclosure). The first conductive layer 3 may have a structure in which a conductive metal such as silver or a fine wire thereof is formed on an oxide film such as a conductive transparent material. The term "film" does not define thickness or width, and includes films that are patterned or island-shaped and films having portions with different thicknesses. A film preferably has a substantially constant thickness. Unless otherwise specified, the terms "substantially" and "approximately" mean the range of manufacturing errors, and preferentially indicate that a variation of plus 15% and minus 15% of the numerical value is allowed.

[0021] The dense electron transport layer 12 is a layer capable of transporting electrons generated in the light-absorbing portion 9 (for example, a perovskite compound). The dense electron transport layer 12 naturally possesses this function as long as the solar cell 1 has the function of photoelectric conversion, and can be considered equivalent to being located on the electron transport side of the light-absorbing portion 9 of the solar cell 1. Therefore, as long as it is located on the electron transport side of the perovskite compound, it can be said to have an electron transport function. It is preferable that the dense electron transport layer 12 has the function of blocking the transport of holes. The dense electron transport layer 12 is dense. Details about the dense material are described below, but it is preferable that the layer has almost no pores or only a few pores. Furthermore, it is preferable that most of these pores are independent and not connected. The dense layer can function as a layer in which liquid hardly seeps into the dense layer even when a liquid is dropped onto it. In this embodiment, the dense electron transport layer 12 is formed of titanium oxide or tin oxide. Furthermore, the dense electron transport layer 12 is provided on top of the first conductive layer 3 and does not exist on the substrate 2.

[0022] A layer does not define thickness or width, and includes patterns, islands, or parts with different thicknesses. Preferably, a layer is a component with approximately constant thickness.

[0023] Compact matter, also known as compact or compact quality, can be the same as or contain the same as these.

[0024] Porous, also known as porous or mesoporous, can be the same as or include the same as these. In this disclosure, porous means a material that can contain light-absorbing portions 9 (for example, a perovskite compound) in its voids (which can be expressed in various ways, such as gaps, holes, or pores). The porous layer may include a porous electron transport layer 7 or a porous insulating layer 8, or both. Preferably, the porous electron transport layer 7 is located on one side of the thickness direction of the porous layer (for example, the bottom side), and the porous insulating layer 8 is located on the opposite side (for example, the top side). The porous layer may also include a second conductive layer 5.

[0025] Furthermore, dense material means material with extremely small voids. In other words, in this disclosure, dense material means material in which, upon observation, the light-absorbing portion 9 (in this embodiment, a perovskite compound as an example, and hereinafter described as a perovskite compound) is absent on one side in the thickness direction of the dense material (for example, the lower side). That is, even if a perovskite compound is present on the upper side of the dense material, it is possible to prevent it from penetrating and not being present on the lower side of the dense material. Preferably, dense material means material with extremely small voids. Preferably, dense material means material with a maximum void width of less than 5 nm. Preferably, dense material is one that suppresses the penetration of perovskite compounds and allows for a state in which perovskite compounds are absent on one side in the thickness direction of the dense material. Even more preferably, dense material means material in which perovskite compounds cannot be contained in the voids, or material that does not have a portion in which perovskite compounds exist continuously throughout the thickness of the dense material portion. In other words, if compaction cannot be confirmed by the maximum width of its voids, it is sufficient to confirm that there are no areas where the perovskite compound penetrates the layer thickness through observation using SEM (Scanning Electron Microscope) or EDX (Energy Dispersive X-ray spectroscopy). In this disclosure, unless otherwise contradictory, observation by SEM is sufficient if it is confirmed by observing a 400 nm wide cross-sectional SEM (or EDX) image. For example, if a single 400 nm wide cross-sectional SEM or EDX observation shows no areas where the perovskite compound penetrates the layer thickness, then that layer can be said to be compaction.

[0026] The porous electron transport layer 7 (an example of an electron transport layer) functions as an electron transport layer that transports electrons generated in the light absorption section 9 to the electrode (first conductive layer 3). The porous electron transport layer 7 naturally has this function as long as the solar cell 1 has the function of photoelectric conversion, and can be considered equivalent to being located on the electron transport side of the light absorption section 9 of the solar cell 1. Therefore, as long as it is located on the electron transport side of the perovskite compound, it can be said to have an electron transport function. As materials for the porous electron transport layer 7, for example, titanium oxide, tin oxide, aluminum oxide, etc. are used. Furthermore, the porous electron transport layer 7 is preferably an N-type inorganic oxide. As detailed above, the porous layer preferably has many pores in the layer, and these pores are connected. Because it is porous, when a liquid (one with good wettability) is dropped onto the porous layer (one with hollow pores), the liquid can function as a layer that seeps into the porous layer. Furthermore, the porous electron transport layer 7, like the dense electron transport layer 12, is a layer capable of transporting electrons generated by the perovskite compound, and naturally possesses this function as long as it functions as a solar cell 1. That is, as long as it is located on the electron transport side (or negative electrode side, similarly in this disclosure) of the perovskite compound of the solar cell 1, it can be said to have an electron transport function. The porous electron transport layer 7 may preferably be a mesoporous layer. Moreover, it is even better if the porous electron transport layer 7 is a mesoporous nanocrystalline layer.

[0027] In this embodiment, the porous electron transport layer 7 can be provided on the dense electron transport layer 12, in a narrower area in the short-side direction X than the dense electron transport layer 12. Therefore, there can be areas on the upper surface of the dense electron transport layer 12 that are not covered by the porous electron transport layer 7. Furthermore, the porous electron transport layer 7 can be positioned closer to the edge of the dense electron transport layer 12 in the short-side direction X.

[0028] In this embodiment, the dense electron transport layer 12 is arranged on the first conductive layer 3 with the same width (width in the short-side direction X in Figure 1), but it is not necessarily required to be the same width. At the edges in the short-side direction X, a portion of the first conductive layer 3 may be formed to be exposed and not covered by the dense electron transport layer 12. Doing so improves the electrical connection between the first conductive layer 3 of one solar cell and the second conductive layer 5 of another adjacent solar cell (not shown).

[0029] The porous insulating layer 8 is made of a porous material. Examples of materials for the porous insulating layer 8 include metal oxides containing titanium oxide, zirconium dioxide, and aluminum oxide, and oxides containing silicon dioxide. It should be noted that insulation does not necessarily have to completely prevent the movement of charge; depending on its thickness and structure, it is acceptable if it can suppress, but not completely prevent, the movement of charge. Adding the porous insulating layer 8 increases the distance between the first conductive layer 3 (including the electron transport layer if present) and the second conductive layer 5 (including the hole transport layer if present), suppressing physical contact between the materials on both sides and preventing the recombination of electrons and holes generated in the light absorption section 9. In other words, adding the porous insulating layer 8 can improve the performance of the solar cell 1, contributing to its commercialization level of performance. Therefore, the porous insulating layer 8 exists between the first conductive layer 3 (including the electron transport layer if present) and the second conductive layer 5 (including the hole transport layer if present), contributing to increasing the distance between the two sides. As a result, if the solar cell is commercialized, verification is sufficient, and it is not necessary to verify the physical properties of the insulating performance. Furthermore, the porous insulating layer 8 is a porous layer containing voids, and it is preferable that it has many voids with a size of 20 nm or more. In other words, the porous insulating layer 8 is occupied by metal oxides that constitute it, and voids which are the gaps between the metal oxides. The porous insulating layer 8 also has voids with a size of less than 20 nm, and the porosity is defined to include these small voids as well. In addition, light absorbing parts 9 that absorb irradiated light are provided in the voids of the porous insulating layer 8.

[0030] In this embodiment, the porous insulating layer 8 is located on the porous electron transport layer 7 and can be provided over a wider area in the short-side direction X than the porous electron transport layer 7. Specifically, one end of the porous insulating layer 8 in the short-side direction X can cover a portion of the upper surface of the dense electron transport layer 12, and the other end in the short-side direction X can extend beyond the dense electron transport layer 12, covering the first conductive layer 3 and the sides of the dense electron transport layer 12. The other end of the porous insulating layer 8 in the short-side direction X can not reach the first conductive layer 3 and the dense electron transport layer 12 of the adjacent solar cell 1, and can be spaced apart.

[0031] The porous conductive layer 10 of the second conductive layer 5 is a conductive material. The porous conductive layer 10 functions as an electrode for extracting the photovoltaic power of the solar cell 1. The porous conductive layer 10 has the function of collecting holes photoexcited in the light absorption section 9, and preferably it is formed of a carbon material for the porous layer. As long as the solar cell 1 has the function of photoelectric conversion as a solar cell, it is not necessary to check the conductive physical properties of the second conductive layer 5, and it can be confirmed as the second conductive layer 5 if it is formed of a material that is considered to be conductive.

[0032] The porous conductive layer 10 may be made of porous oxide conductive materials other than carbon, such as tin-doped indium oxide, fluorine-doped tin oxide, or aluminum-doped zinc oxide. It is not limited to these. Other examples include metal films with a work function of 5 eV or higher. By making the porous conductive layer 10 from a metal with a deep work function (5 eV or higher), it becomes easier to generate a band structure bend that smooths the flow of holes at the interface between the light-absorbing layer or the light-absorbing section 9 or the layer on the light-absorbing section 9 side and the porous conductive layer 10. Examples of materials for the porous conductive layer 10 include metals such as Ni, Pt, and Pd. A porous layer can be formed from metal nanoparticles. In this case, a film thickness of approximately 50 nm to 150 nm is desirable for the porous conductive layer 10. The porous conductive layer 10 can be formed, for example, by sputtering or vacuum deposition. Furthermore, conductive carbon materials such as graphite, graphene, carbon nanowires, carbon nanofibers, carbon nanotubes, and carbon black can be used. In terms of materials, there are no exclusions from application as long as they are basically conductive.

[0033] The metal layer 11 of the second conductive layer 5 is added on top of the porous conductive layer 10. Examples of materials constituting the metal layer 11 include nickel, gold, silver, and platinum. The porous conductive layer 10 is preferably made of carbon. The thickness of the carbon film is 5 to 50 μm, preferably 15 to 30 μm, but is not limited to this example. The metal layer 11 is preferably made of silver.

[0034] The light-absorbing portion 9 described above contains a perovskite compound. In this embodiment, the porous electron transport layer 7 and the porous insulating layer 8 also have light-absorbing portions 9. That is, the light-absorbing portions 9 are arranged in the voids (which can be expressed in various ways, such as gaps, holes, or pores) of these layers. Preferably, these layers are filled with light-absorbing portions 9. It is desirable that the voids in the porous electron transport layer 7 and the porous insulating layer 8 be filled with light-absorbing portions 9. As long as the solar cell 1 has a photoelectric conversion function, it naturally includes light-absorbing portions 9 as a component. The light-absorbing portion 9 generates electrons and holes by absorbing light, the electrons generated in the light-absorbing portion 9 move to the electron transport layer, and the holes generated in the light-absorbing portion 9 move to the second conductive layer 5, where the charge is separated. As long as the solar cell 1 has a photoelectric conversion function, it can be confirmed that electrons and holes are generated by absorbing light in the parts with appropriate materials, and it is not necessary to check the physical properties of the photoelectric conversion of the light-absorbing portion 9 in order to confirm that it is a light-absorbing portion 9.

[0035] The light-absorbing portion 9 refers to a specific part that absorbs light (for example, a perovskite compound), and this portion can be collectively described as a light-absorbing layer. Here, the light-absorbing portion 9 can mean a specific region or part of the light-absorbing layer. Furthermore, the light-absorbing layer can mean a collection of light-absorbing portions 9 that exist discretely in a region in a certain direction with a thickness (which does not need to be constant).

[0036] The perovskite compound contained in the light-absorbing section 9 is composed of a compound represented by the general formula: ABX3···(1). However, while the composition ratio of each is preferably 1:1:3, it is not necessarily 1:1:3, the content of each element may be adjusted as appropriate, and each constituent element does not need to be of only one type. As long as the solar cell 1 has a photoelectric conversion function, the perovskite compound contained in the light-absorbing section 9 is performing the photoelectric conversion function, and therefore it is reasonable to assume that it is performing that function even with the degree of freedom in composition as described in terms of composition ratio and type of constituent element. In general formula (1), A is an organic molecule (including an organic group or organic cation, as is the case in this disclosure) or an inorganic atom or molecule (including an inorganic group or inorganic cation, as is the case in this disclosure) or a combination thereof, B is a metal atom or molecule (including a metal cation, as is the case in this disclosure), and X is a halogen atom or molecule or a chalcogen atom or molecule (including a halogen anion or chalcogen anion, as is the case in this disclosure). In general formula (1), the three X's may be the same or different from each other. As long as the solar cell 1 has a photoelectric conversion function, the perovskite compound contained in the light-absorbing section 9 is exhibiting a photoelectric conversion function, and this should be taken into consideration. That is, if it can be confirmed that a compound has A, B, and X, it is reasonable to consider it a perovskite compound that exhibits a photoelectric conversion function. For example, it is sufficient if it is found to have an organic molecule, a metal atom, and a halogen atom. Furthermore, as long as the solar cell 1 has a photoelectric conversion function, it can be confirmed that a compound has a photoelectric conversion function if elements corresponding to A, B, and X are detected. For example, as organic molecules, molecules containing carbon, nitrogen, and hydrogen are suitable, and therefore, it is sufficient if carbon, nitrogen, hydrogen, a metal element, and a halogen or chalcogen are detected. Alternatively, a compound can be considered to have A, B, and X if it is found to have an inorganic atom, a metal atom, and a halogen atom. Furthermore, the fact that it is a perovskite compound can be confirmed if elements corresponding to A, B, and X are detected, as long as solar cell 1 has a photoelectric conversion function.For example, cesium or rubidium are preferred as inorganic atoms; therefore, it is sufficient if cesium or rubidium, a metallic element, and a halogen or chalcogen are detected. Furthermore, the fact that it is a perovskite compound is not required because it is a natural consequence that the solar cell 1 has a crystalline structure as long as it has a photoelectric conversion function. The light-absorbing portion 9 may contain substances other than perovskite compounds.

[0037] The light-absorbing section 9 may contain an organic-inorganic hybrid compound. An organic-inorganic hybrid compound means a compound containing both an inorganic material and an organic material. Perovskite compounds are also included in organic-inorganic hybrid compounds, and a solar cell 1 using a perovskite compound is also called an organic-inorganic hybrid solar cell. "Organic" typically means something composed of multiple carbon atoms as constituent elements. However, carbon materials such as graphite, graphene, carbon nanowires, carbon nanofibers, carbon nanotubes, and carbon or carbon black that function as electrodes are not specifically considered organic materials. In other words, organic refers to anything that has multiple carbon atoms as one of its constituent elements, excluding the above-mentioned carbon materials such as graphite. "Inorganic" means something that is not organic.

[0038] The light-absorbing section 9 may include quantum dots. A quantum dot is a dot with a maximum width of 100 nm or less. The shape of the quantum dot is not particularly restricted as long as it satisfies the above maximum width, and is not limited to a spherical three-dimensional shape (circular cross-sectional shape). For example, it may have a polygonal cross-sectional shape, a rod-shaped three-dimensional shape, a branch-shaped three-dimensional shape, a three-dimensional shape with irregularities on the surface, or a combination thereof. The quantum dot is typically made of a semiconductor. A semiconductor is any material that can absorb light, and may include at least the materials described below. The semiconductor includes, for example, at least one selected from the group consisting of group II-VI compounds, group III-V compounds, chalcogenides, and perovskite compounds. Group II-VI compounds mean compounds containing group II and group VI elements, and group III-V compounds mean compounds containing group III and group V elements. Furthermore, Group II elements include Group 2 and Group 12 elements, Group III elements include Group 3 and Group 13 elements, Group V elements include Group 5 and Group 15 elements, and Group VI elements may include Group 6 and Group 16 elements. Here, the group numbering of elements using Roman numerals is based on the old IUPAC or old CAS system, and the group numbering of elements using Arabic numerals is based on the current IUPAC system. Semiconductors include, for example, at least one selected from the group consisting of MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, GaAs, GaP, InN, InAs, InP, and InSb.

[0039] Examples of organic molecules represented by A in general formula (1) include alkylamines, alkylammonium compounds, and nitrogen-containing heterocyclic compounds. In perovskite compound (1), the organic molecule represented by A may be only one type of organic molecule, or it may be two or more types of organic molecules.

[0040] Examples of alkylamines include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, and ethylbutylamine.

[0041] Alkylammonium compounds are ionized compounds of the alkylamines mentioned above. Examples of alkylammonium compounds include methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, dimethylammonium, diethylammonium, dipropylammonium, dibutylammonium, dipentylammonium, dihexylammonium, trimethylammonium, triethylammonium, tripropylammonium, tributylammonium, tripentylammonium, trihexylammonium, ethylmethylammonium, methylpropylammonium, butylmethylammonium, methylpentylammonium, hexylmethylammonium, ethylpropylammonium, and ethylbutylammonium.

[0042] Examples of nitrogen-containing heterocyclic compounds include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, and carbazole. Nitrogen-containing heterocyclic compounds may also be ionized. Phenethylammonium is preferred as an ionized nitrogen-containing heterocyclic compound.

[0043] In general formula (1), the organic molecule represented by A is preferably methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, or phenethylammonium, more preferably methylamine, ethylamine, propylamine, methylammonium, ethylammonium, or propylammonium, and even more preferably methylammonium.

[0044] In general formula (1), examples of metal atoms represented by B include lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, and europium. In perovskite compounds, the metal atom represented by B may be only one type of metal atom, or it may be two or more types of metal atoms. From the viewpoint of improving the light absorption and charge generation characteristics of perovskite compounds, lead atoms or tin atoms are preferred as the metal atom represented by B. From the viewpoint of reducing lead, tin atoms are preferred.

[0045] In general formula (1), examples of halogen atoms represented by X include fluorine, chlorine, bromine, and iodine atoms, while examples of chalcogen atoms include oxygen, sulfur, selenium, and tellurium atoms. In a perovskite compound, the halogen atom or chalcogen atom represented by X may be one or two or more. From the viewpoint of enabling the perovskite compound to utilize light in a broad wavelength range, iodine is preferred as the halogen atom represented by X. More specifically, it is preferable that at least one of the three Xs represents an iodine atom, and more preferably that all three Xs represent iodine atoms.

[0046] As the perovskite compound, compounds represented by the general formula "CH3NH3PbX3 (where X represents a halogen atom)" are preferred, and CH3NH3PbI3 is more preferred. By using a compound represented by the general formula "CH3NH3PbX3" (especially CH3NH3PbI3) as the perovskite compound, electrons and holes can be generated more efficiently in the perovskite compound, and as a result, the photoelectric conversion efficiency of the solar cell 1 can be further improved.

[0047] The photoelectric conversion layer 4 is a layer that has the function of converting light into electricity. It can include a porous layer 6 and a light-absorbing portion 9, and refers to the layer located between the first conductive layer 3 and the second conductive layer 5. The light-absorbing portion 9 is often located between the first conductive layer 3 and the second conductive layer 5, in which case the photoelectric conversion layer 4 is also located only between the first conductive layer 3 and the second conductive layer 5. However, if the first conductive layer 3 and the second conductive layer 5 have a special shape such as being porous, the light-absorbing portion 9 may include the region encompassing the first conductive layer 3 and the second conductive layer 5 themselves, and in such cases, the photoelectric conversion layer 4 can include the portion of the first conductive layer 3 and the second conductive layer 5 in which the light-absorbing portion 9 is located. Even in that case, the photoelectric conversion layer 4 is located at least between the first conductive layer 3 and the second conductive layer 5. In other words, in any case, the solar cell 1 is provided with a first conductive layer 3, a photoelectric conversion layer 4, and a second conductive layer 5 in that order from the substrate 2, and this does not exclude the first conductive layer 3 and the second conductive layer 5 themselves from being included, nor does it exclude the presence of the photoelectric conversion layer 4 in a part other than the space between the first conductive layer 3 and the second conductive layer 5. As long as the solar cell 1 has the function of photoelectric conversion as a solar cell, it is not necessary to confirm the function of the photoelectric conversion layer 4 to convert light into electricity, and it can be confirmed as a photoelectric conversion layer 4 if it contains a material that is thought to have a photoelectric conversion function (for example, a light absorbing part 9 containing a perovskite compound).

[0048] In this embodiment, the hole transport layer (same as the positive electrode layer) may be placed between the perovskite compound, which is the light-absorbing portion 9, and the second conductive layer 5. The hole transport layer is a layer that has the function of moving holes generated in the light-absorbing portion 9 to the second conductive layer 5. It is self-evident that, as long as the solar cell 1 has a photoelectric conversion function, the hole transport layer located on the hole transport side of the light-absorbing portion 9 or on the hole transport side of the light-absorbing portion 9 has the function of transporting holes, and no confirmation is required. That is, as long as the solar cell 1 functions as a solar cell, the layer located on the hole transport side of the light-absorbing portion 9 (or on the positive electrode side, similarly in this disclosure) or on the hole transport side of the light-absorbing portion 9 is called the hole transport layer. The hole transport layer may be made of a material with, for example, a band gap of 2 eV or more and an ionization potential smaller than 5.4 eV (shallow). The hole transport layer may be made of an inorganic material. The thickness of the hole transport layer can be, for example, about 30 nm to 100 nm. Specific materials that constitute the hole transport layer include oxides and sulfides such as copper oxide (Cu2O), zinc sulfide (ZnS), and nickel oxide. Fine particles of oxides or sulfides may also be used. Organic materials may also be used. Furthermore, the hole transport layer may inhibit electron transport (electron blocking). The hole transport layer may also be accompanied by a separate electron blocking layer. Alternatively, the hole transport layer may be absent, and instead, an electron blocking layer may be present.

[0049] (Manufacturing method for solar cell 1) Next, the manufacturing method of solar cell 1 will be explained. Figure 2 is a flowchart showing the manufacturing method of solar cell 1.

[0050] The manufacturing method for the solar cell 1 includes a lamination step (S1) in which a first conductive layer 3, a dense electron transport layer 12, a porous electron transport layer 7, a porous insulating layer 8, and a porous conductive layer 10 are laminated in that order from a substrate 2; a dropping step (S2) in which a perovskite precursor solution 14 is dropped onto the porous conductive layer 10; and a metal layer step (S3) in which a metal layer 11 is formed on the porous conductive layer 10. The metal layer 11 includes at least one selected from nickel, gold, silver, and platinum.

[0051] In this manner, a porous electron transport layer 7 (porous TiO2), a porous insulating layer 8 (porous ZrO2), and a porous conductive layer 10 (porous carbon) are sequentially layered on the substrate 2. Each layer is formed by screen printing. Then, a perovskite precursor solution 14 (Figures 3 and 4) is dropped onto the uppermost porous conductive layer 10 (porous carbon) and dried. In this embodiment, a metal layer 11 (metal (Ag)) is then added to the upper side of the porous conductive layer 10 (porous carbon). The metal layer 11 may be formed by vapor deposition or sputtering.

[0052] The fabricated laminated substrate has a porous layer, and a solar cell 1 is fabricated by dropping a perovskite precursor solution 14 containing a perovskite compound onto the top of the laminated substrate and firing it. In this embodiment, the perovskite precursor solution 14 is prepared by mixing and stirring methylamine iodide (1.14 M), lead iodide (1.2 M), 5-aminovaleric acid hydroiodide (0.06 M), and γ-butyrolactone (solvent).

[0053] The perovskite precursor solution 14, dropped onto the laminated substrate, penetrates the porous conductive layer 10, the porous insulating layer 8, and the porous electron transport layer 7.

[0054] Subsequently, by firing and evaporating the perovskite precursor solution 14, light-absorbing portions 9 are formed in the pores of the porous conductive layer 10, the porous insulating layer 8, and the porous electron transport layer 7.

[0055] (Comparative Example 1) Figure 3 is a cross-sectional view of a solar cell according to Comparative Example 1. Components similar to those described above are denoted by the same reference numerals. A detailed explanation of these components will not be repeated.

[0056] In the solar cell according to Comparative Example 1 shown in Figure 3, a porous electron transport layer 7 and a porous insulating layer 8 are formed on the photoelectric conversion layer 4. A perovskite precursor solution 14 is dropped onto this porous layer and dried to form a light-absorbing portion 9 containing a perovskite compound in the voids of the porous layer.

[0057] In such multilayer porous layered electrode type perovskite solar cells, there is a problem in that the high resistance of the porous conductive layer 10 containing carbon, which serves as the counter electrode, induces a decrease in the performance of the solar cell.

[0058] In the solar cell according to Comparative Example 1, the carbon film thickness is small, 5 to 40 μm, preferably 5 to 30 μm, so the carbon resistance increases and the FF (Fill Factor) decreases. Because the carbon film thickness is small, the dropped perovskite precursor solution 14 easily penetrates into the interior of the lower porous electron transport layer 7, and there is no shortage of filling with the perovskite precursor solution 14. As a result, the Jsc (short-circuit current density) improves.

[0059] [Table 1] (Comparative Example 2) Figure 4 is a cross-sectional view of a solar cell according to Comparative Example 2.

[0060] Therefore, as shown in Figure 4, if the carbon film thickness of the porous conductive layer 10 is increased to more than 40 μm, the lateral resistance of the porous conductive layer 10, which is the counter electrode containing carbon, will decrease.

[0061] However, as the carbon film thickness increases, the penetration of the perovskite precursor solution 14 into the internal porous layer becomes more difficult. For example, the perovskite precursor solution 14 may not adequately fill the porous electron transport layer 7 containing TiO2, leading to a problem of reduced performance in the solar cell.

[0062] In the solar cell according to Comparative Example 2 in Figure 4, the carbon film thickness of the porous conductive layer 10 is large, so the carbon resistance is reduced and the flip-flop (FF) is improved.

[0063] However, because the carbon film thickness is large, the dropped perovskite precursor solution 14 does not easily penetrate into the porous electron transport layer 7 below, resulting in insufficient filling of the perovskite precursor solution 14. Consequently, Jsc decreases.

[0064] (Mechanism and effects of solar cell 1) In contrast, the solar cell 1 according to this embodiment, as shown in Figure 1, has a two-electrode structure formed by coating a silver-containing metal layer 11 on a carbon-containing porous conductive layer 10. As a result, the lateral conductivity of the second conductive layer 5, which includes the porous conductive layer 10, is improved, making it possible to reduce the resistance of the counter electrode (second conductive layer 5).

[0065] Furthermore, by attaching metal to the carbon to create a two-layer electrode structure, not only is lateral conductivity improved, but moisture intrusion into the solar cell 1 can also be prevented. This prevents moisture damage to the perovskite compound, leading to improved reliability of the solar cell 1.

[0066] Furthermore, the light that has passed through the porous layer, including the porous electron transport layer 7 and the porous insulating layer 8, from the light-receiving surface is reflected by the Ag in the metal layer 11, which is the outermost layer on the non-light-receiving side, thereby increasing the current extracted from the solar cell 1.

[0067] Thus, in solar cell 1, the carbon film thickness of the porous conductive layer 10 is small, so the perovskite precursor solution 14 easily penetrates into the interior of the lower porous electron transport layer 7, and there is no shortage of perovskite precursor solution 14 filling. As a result, Jsc is improved.

[0068] Furthermore, since the metal is added to the carbon after the perovskite precursor solution 14 is dropped, the lateral conductivity of the second conductive layer 5, which is the counter electrode containing carbon, is improved, and the resistance is reduced. As a result, the FF (fastness flip-flop) is improved.

[0069] (Embodiment 2) (Configuration of solar cell 1A) Figure 5 is a cross-sectional view of a solar cell 1A according to Embodiment 2. Components similar to those described above are denoted by the same reference numerals. A detailed description of these components will not be repeated.

[0070] The solar cell 1A comprises a second conductive layer 5A. The second conductive layer 5A further includes an intermediate layer 13 located between the metal layer 11 and the porous conductive layer 10. The intermediate layer 13 includes at least one selected from a hole transport layer, a protective layer, and a conductive layer. The intermediate layer 13 includes at least one of PEDOT:PSS (a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS)) and Spiro-MeOTAD (Spiro-OMeTAD).

[0071] Thus, a hole transport layer, protective layer, and conductive layer such as PEDOT or Spiro may be provided between the metal layer 11 containing metal and the porous conductive layer 10 containing carbon.

[0072] (Manufacturing method for solar cell 1A) Figure 6 is a flowchart showing the manufacturing method of solar cell 1A. The manufacturing method for solar cell 1A includes a lamination step (S1) in which a first conductive layer 3, a porous electron transport layer 7, a porous insulating layer 8, and a porous conductive layer 10 are laminated in that order from a substrate 2; a dropping step (S2) in which a perovskite precursor solution 14 is dropped onto the porous conductive layer 10; and a metal layer step (S3) in which a metal layer 11 is formed on the porous conductive layer 10. The metal layer 11 contains at least one selected from nickel, gold, silver, and platinum.

[0073] The method for manufacturing the solar cell 1A further includes an intermediate layer step (S4) in which an intermediate layer 13 is formed on the porous conductive layer 10 after the dropping step (S2) and before the metal layer step (S3). The intermediate layer 13 includes at least one selected from a hole transport layer, a protective layer, and a conductive layer. Preferably, the intermediate layer 13 includes at least one of PEDOT and Spiro.

[0074] Thus, when PEDOT or Spiro is used as the intermediate layer 13, the intermediate layer 13 is added after dropping the perovskite precursor solution 14, but before adding the metal layer 11. The metal layer 11 may be formed by a spin coating method or the like.

[0075] If the intermediate layer 13 is a hole transport layer and this hole transport layer allows the perovskite precursor solution 14 to permeate, the perovskite precursor solution 14 may be added dropwise to the intermediate layer 13 after it has been formed. In this disclosure, the first conductive layer side or the light-receiving surface side is described as the electron transport side, and the second conductive layer side or the back surface side is described as the hole transport side. However, the disclosure can also be applied when the conductivity types are reversed, i.e., when the first conductive layer side or the light-receiving surface side is the hole transport side and the second conductive layer side or the back surface side is the electron transport side. In that case, the terms "hole" and "electron" can be reversed as appropriate, as long as there is no contradiction.

[0076] [Note] A solar cell according to Embodiment 1 of the present disclosure is a solar cell provided with, in order from a substrate, a first conductive layer, a photoelectric conversion layer, and a second conductive layer, wherein the photoelectric conversion layer includes a porous layer and a light absorbing portion, and the second conductive layer includes a porous conductive layer and a metal layer located on the opposite side of the photoelectric conversion layer from the porous conductive layer.

[0077] According to the above configuration, since the second conductive layer, which is the counter electrode, contains a metal layer, the resistance of the counter electrode can be reduced. Furthermore, since it is not necessary to thicken the porous conductive layer to reduce the resistance of the counter electrode, the penetration of the perovskite precursor solution is not inhibited. As a result, it is possible to realize a solar cell in which the resistance of the counter electrode can be reduced and the penetration of the perovskite precursor solution is not inhibited.

[0078] In the solar cell according to aspect 2 of this disclosure, it is preferable that the porous layer in aspect 1 includes a porous electron transport layer.

[0079] According to the above configuration, electrons generated in the photoelectric conversion layer can be transported to the first conductive layer by the porous electron transport layer.

[0080] In the solar cell according to embodiment 3 of this disclosure, it is preferable that the porous layer further includes a porous insulating layer located on the opposite side of the first conductive layer from the porous electron transport layer, in embodiment 2.

[0081] According to the above configuration, by adding a porous insulating layer, the distance between the first conductive layer and the second conductive layer can be increased, physical contact between the materials on both sides can be suppressed, and the recombination of electrons and holes generated in the photoelectric conversion layer can be suppressed.

[0082] In the solar cell according to aspect 4 of this disclosure, it is preferable that the porous conductive layer includes a carbon material in any one of the above aspects 1 to 3.

[0083] According to the above configuration, holes photoexcited in the photoelectric conversion layer can be collected by electrodes containing a conductive porous carbon material.

[0084] In any one embodiment of embodiments 1 to 4, the solar cell according to aspect 5 of the present disclosure preferably comprises at least one selected from nickel, gold, silver, and platinum in the metal layer.

[0085] According to the above configuration, holes photoexcited in the photoelectric conversion layer can be collected by an electrode containing at least one selected from nickel, gold, silver, and platinum.

[0086] In the solar cell according to aspect 6 of this disclosure, it is preferable that the metal layer in aspect 5 contains silver.

[0087] According to the above configuration, holes photoexcited in the photoelectric conversion layer can be collected by an electrode containing silver.

[0088] In the solar cell according to aspect 7 of this disclosure, it is preferable that the light-absorbing portion includes a perovskite compound in any one of the above aspects 1 to 6.

[0089] According to the above configuration, the light-absorbing portion containing the perovskite compound can excite the light incident on the photoelectric conversion layer.

[0090] In the solar cell according to embodiment 8 of this disclosure, in embodiment 2, 3, or 9 above, it is preferable that the porous electron transport layer comprises at least one selected from titanium oxide, titanium dioxide, tin oxide, and aluminum oxide.

[0091] According to the above configuration, electrons generated in the photoelectric conversion layer can be transported to the first conductive layer by a porous electron transport layer containing at least one selected from titanium oxide, titanium dioxide, tin oxide, and aluminum oxide.

[0092] In the solar cell according to aspect 9 of this disclosure, in aspect 3 above, it is preferable that the porous insulating layer includes at least one selected from titanium oxide, zirconium dioxide, aluminum oxide, and silicon dioxide.

[0093] According to the above configuration, a porous insulating layer containing at least one selected from titanium oxide, zirconium dioxide, aluminum oxide, and silicon dioxide can increase the distance between the first conductive layer and the second conductive layer, suppressing physical contact between the materials on both sides and preventing the recombination of electrons and holes generated in the photoelectric conversion layer.

[0094] In any one embodiment of embodiments 1 to 9, the solar cell 1A further comprises an intermediate layer located between the metal layer and the porous conductive layer, wherein the intermediate layer preferably includes at least one selected from a hole transport layer, a protective layer, and a conductive layer.

[0095] According to the above configuration, a hole transport layer located between the metal layer and the porous conductive layer can transport holes generated in the photoelectric conversion layer to the second conductive layer, a protective layer located between the metal layer and the porous conductive layer can protect the photoelectric conversion layer, and a conductive layer located between the metal layer and the porous conductive layer can extract holes generated in the photoelectric conversion layer.

[0096] In the solar cell according to aspect 11 of this disclosure, it is preferable that the intermediate layer in aspect 10 includes at least one of PEDOT and Spiro.

[0097] According to the above configuration, a conductive layer can be formed between the metal layer and the porous conductive layer by the intermediate layer containing PEDOT, and a hole transport layer can be formed between the metal layer and the porous conductive layer by the intermediate layer containing Spiro.

[0098] A method for manufacturing a solar cell according to aspect 12 of this disclosure includes a lamination step of laminating a first conductive layer, a porous electron transport layer, a porous insulating layer, and a porous conductive layer in that order from a substrate; a dropping step of dropping a perovskite precursor solution onto the porous conductive layer; and a metal layer step of forming a metal layer on the porous conductive layer.

[0099] According to the above configuration, a metal layer serving as a counter electrode is formed on top of a porous conductive layer. This allows for low resistance of the counter electrode. Furthermore, since it is not necessary to thicken the porous conductive layer to reduce the resistance of the counter electrode, the penetration of the perovskite precursor solution is not inhibited. As a result, a method for manufacturing solar cells can be realized that allows for low resistance of the counter electrode without inhibiting the penetration of the perovskite precursor solution.

[0100] In the method for manufacturing a solar cell according to aspect 13 of this disclosure, it is preferable that the metal layer in aspect 12 comprises at least one selected from nickel, gold, silver, and platinum.

[0101] According to the above configuration, holes photoexcited in the photoelectric conversion layer can be collected by an electrode containing at least one selected from nickel, gold, silver, and platinum.

[0102] A method for manufacturing a solar cell according to aspect 14 of the present disclosure further includes, in aspect 12 or 13, an intermediate layer step of forming an intermediate layer on the porous conductive layer after the dropping step and before the metal layer step, wherein the intermediate layer 13 preferably includes at least one selected from a hole transport layer, a protective layer, and a conductive layer.

[0103] According to the above configuration, the hole transport layer formed on the porous conductive layer can transport holes generated in the photoelectric conversion layer to the second conductive layer, the protective layer formed on the porous conductive layer can protect the photoelectric conversion layer, and the conductive layer formed on the porous conductive layer can extract the holes generated in the photoelectric conversion layer.

[0104] The method for manufacturing a solar cell according to aspect 15 of this disclosure preferably includes at least one of PEDOT and Spiro in aspect 14.

[0105] According to the above configuration, a conductive layer can be formed between the metal layer and the porous conductive layer by the intermediate layer containing PEDOT, and a hole transport layer can be formed between the metal layer and the porous conductive layer by the intermediate layer containing Spiro.

[0106] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. [Explanation of symbols]

[0107] 1 solar cell 2 Base 3. First conductive layer 4. Photoelectric conversion layer 5. Second conductive layer 6. Porous layer 7 Porous electron transport layer 8. Porous insulating layer 9 Light-absorbing section 10 Porous conductive layer 11 Metal layer 13. Middle Class 14 Perovskite precursor solution

Claims

1. A solar cell having a substrate, in which a first conductive layer, a photoelectric conversion layer, and a second conductive layer are provided in that order, The photoelectric conversion layer includes a porous layer and a light-absorbing portion. A solar cell in which the second conductive layer includes a porous conductive layer and a metal layer located on the opposite side of the photoelectric conversion layer from the porous conductive layer.

2. The solar cell according to claim 1, wherein the porous layer includes a porous electron transport layer.

3. The solar cell according to claim 2, wherein the porous layer further comprises a porous insulating layer located on the opposite side of the first conductive layer from the porous electron transport layer.

4. The solar cell according to any one of claims 1 to 3, wherein the porous conductive layer comprises a carbon material.

5. The solar cell according to any one of claims 1 to 3, wherein the metal layer comprises at least one selected from nickel, gold, silver, and platinum.

6. The solar cell according to claim 5, wherein the metal layer contains silver.

7. The solar cell according to any one of claims 1 to 3, wherein the light-absorbing portion comprises a perovskite compound.

8. The solar cell according to claim 2, wherein the porous electron transport layer comprises at least one selected from titanium oxide, titanium dioxide, tin oxide, and aluminum oxide.

9. The solar cell according to claim 3, wherein the porous insulating layer comprises at least one selected from titanium oxide, zirconium dioxide, aluminum oxide, and silicon dioxide.

10. The second conductive layer further includes an intermediate layer located between the metal layer and the porous conductive layer, The solar cell according to any one of claims 1 to 3, wherein the intermediate layer includes at least one selected from a hole transport layer, a protective layer, and a conductive layer.

11. The solar cell according to claim 10, wherein the intermediate layer comprises at least one of PEDOT and Spiro.

12. The lamination process involves stacking a first conductive layer, a porous electron transport layer, a porous insulating layer, and a porous conductive layer in that order, starting from the substrate. A dropping step of dropping a perovskite precursor solution onto the porous conductive layer, A method for manufacturing a solar cell, comprising a metal layer step of forming a metal layer on the porous conductive layer.

13. The method for manufacturing a solar cell according to claim 12, wherein the metal layer comprises at least one selected from nickel, gold, silver, and platinum.

14. The process further includes an intermediate layer step, which is performed after the dropping step and before the metal layer step, in which an intermediate layer is formed on the porous conductive layer. The method for manufacturing a solar cell according to claim 12 or 13, wherein the intermediate layer includes at least one selected from a hole transport layer, a protective layer, and a conductive layer.

15. The method for manufacturing a solar cell according to claim 14, wherein the intermediate layer comprises at least one of PEDOT and Spiro.

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