WO2025047796A1 - Solar cell and manufacturing method thereof - Google Patents

Abstract

This solar cell (1) is provided with, in order from a substrate (2), an electron transport layer (4), a spacer layer (6), and a hole transport layer (7). The spacer layer (6) is a porous layer having a gap. The electron transport layer (4) is a denser layer than the spacer layer (6).

Description

Solar cell and its manufacturing method

This disclosure relates to a solar cell using a perovskite compound and a method for manufacturing the same.

In recent years, solar cells have become popular as a way to utilize renewable energy. Solar cells using inorganic photoelectric conversion elements (e.g., silicon-based solar cells, CIGS-based solar cells, and CdTe-based solar cells) are in widespread use, but solar cells using organic photoelectric conversion elements (e.g., organic thin-film solar cells, dye-sensitized solar cells, and perovskite solar cells) are also being considered. Perovskite solar cells in particular have been actively researched because they can be produced at lower cost than conventional solar cells (see, for example, Patent Document 1).

JP 2016-178167 A

　A conventional solar cell has a substrate, an underlayer laminated on the substrate, and a light absorbing layer containing an organic-inorganic perovskite compound formed inside the underlayer. The underlayer is formed by spraying at least one of N-type semiconductor particles and insulating particles to which the organic-inorganic perovskite compound is attached onto the substrate.

In the solar cell described above, when forming the underlayer, the perovskite compound is sprayed onto the substrate, but there is a problem in that it is not possible to form a dense electron transport layer that does not contain the perovskite compound. Furthermore, no consideration has been given to the connectivity between the fine particles, and when only the fine particles are formed to form a porous film and then the perovskite compound is applied to the porous film, no consideration has been given to the permeability of the perovskite compound into the porous film in order to increase the connectivity between the fine particles, so there is a risk that the perovskite compound will not penetrate the entire underlayer.

The present disclosure has been made to solve the above problems, and aims to provide a solar cell with improved permeability of the perovskite solution and a method for manufacturing the same.

The solar cell according to the present disclosure is a solar cell having, in order from a substrate, an electron transport layer, a spacer layer, and a hole transport layer, the spacer layer being a porous layer having voids, and the electron transport layer being a layer denser than the spacer layer.

In the solar cell according to the present disclosure, the electron transport layer may be configured as a dense layer.

In the solar cell according to the present disclosure, the electron transport layer may be configured so that the maximum width of the void is less than 5 nm.

In the solar cell according to the present disclosure, the electron transport layer may be configured such that no perovskite compound is present on one side in the thickness direction of the electron transport layer.

In the solar cell according to the present disclosure, the electron transport layer may be configured so that there is no portion in which the perovskite compound is present throughout the layer thickness.

In the solar cell according to the present disclosure, the spacer layer may be insulating and may be arranged adjacent to and in contact with the electron transport layer.

In the solar cell according to the present disclosure, there may be no porous electron transport layer between the dense electron transport layer and the spacer layer.

In the solar cell according to the present disclosure, the electron transport layer may be formed of a metal oxide selected from titanium oxide, tin oxide, zirconium dioxide, aluminum oxide, and silicon dioxide, either alone or in combination, and with a particle size of 1 to 80 nm.

In the solar cell according to the present disclosure, the electron transport layer may be formed of tin oxide.

In the solar cell according to the present disclosure, the substrate may be a flexible film.

The method for manufacturing a solar cell according to the present disclosure includes the steps of providing, in order from a substrate, an electron transport layer, a spacer layer, and a hole transport layer, the spacer layer being a porous layer having voids, and the electron transport layer being a layer denser than the spacer layer.

According to the present disclosure, by laminating a spacer layer on top of the electron transport layer, the porous layer through which the perovskite solution permeates becomes thinner, improving permeability. This makes it possible to provide a solar cell with high conversion efficiency and improved variability.

1 is a schematic cross-sectional view showing a solar cell according to an embodiment of the present disclosure. FIG. 1 is a schematic explanatory diagram showing a structure of a perovskite compound. 1 is a characteristic diagram showing a result of comparing the characteristics of a solar cell according to an embodiment of the present disclosure with a comparative example. 1 is a cross-sectional SEM photograph of a spacer layer.

The solar cell according to the embodiment of the present disclosure will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing a solar cell according to an embodiment of the present disclosure.

The solar cell 1 according to the embodiment of the present disclosure has an electron transport layer 4, a spacer layer 6, and a hole transport layer 7 laminated on a substrate 2 having a transparent electrode layer 3 formed on its surface.

The base 2 is the base of the solar cell 1, and is the same as or includes the substrate or base material. The shape of the base 2 can be, for example, a flat plate or a film. When light is irradiated to the surface of the solar cell 1 facing the base 2 (the lower surface of the base 2 in FIG. 1), the base 2 is preferably transparent. In this case, examples of the material for the base 2 include transparent glass and transparent resins having heat resistance. When light is irradiated from the opposite side, the base 2 may be opaque. Note that transparency means that light is transmitted, but does not exclude materials that reflect or absorb even a little, and it is sufficient to transmit light appropriately, and can be considered to be synonymous with being provided on the light receiving surface side of the solar cell (including the part where light is incident, as in this disclosure). Therefore, it can be considered transparent if it is provided at least on the light receiving surface side of the solar cell.

The transparent electrode layer 3 is formed on the substrate 2 or on the surface of the substrate 2, and functions as an electrode for extracting the photovoltaic power of the solar cell 1. The transparent electrode layer 3 is formed of a transparent conductive material, such as FTO (fluorine-doped tin oxide), CuI (copper iodide), ITO (indium tin oxide), SnO ₂ (tin oxide), AZO (aluminum zinc oxide), IZO (indium zinc oxide), GZO (gallium zinc oxide), ATO (antimony-doped tin oxide), and conductive transparent polymers. The chemical formula is a representative example, and may be any compound name (same in the present disclosure). In addition, the composition ratio of the chemical formula is preferably stoichiometric, but does not necessarily have to be stoichiometric (same in the present disclosure).

In this embodiment, the transparent electrode layer 3 is divided into two parts, and for the sake of explanation, one of the transparent electrode layers 3 may be referred to as the first electrode portion 3a (the right side in FIG. 1) and the other may be referred to as the second electrode portion 3b (the left side in FIG. 1). The film or layer does not specify the thickness or width, and includes patterned or island-shaped ones and ones having parts of different thicknesses. The film or layer preferably has an approximately constant thickness. Unless otherwise specified, approximately means that a variation within the range of manufacturing error is allowed, and preferentially indicates that a variation of plus or minus 15% of the numerical value is allowed. In this disclosure, the thickness, width, etc. are confirmed by cross-sectional observation unless otherwise specified, and for example, SEM observation is performed on a cross-sectional SEM image with a width of 400 nm, and it is sufficient to confirm the thickness, width, etc. within that range, and it is not necessary to confirm all cross sections. That is, for example, "approximately constant thickness" can be said to be "approximately constant thickness" if the thickness is within a range of plus or minus 15% of the average thickness in a cross-sectional SEM image with a width of 400 nm.

The electron transport layer 4 is a layer capable of transporting electrons generated in the perovskite compound, and naturally has this function insofar as it functions as a solar cell, and can be considered to be synonymous with being disposed on the electron transport side of the perovskite compound of the solar cell. Therefore, as long as it is disposed at least on the electron transport side of the perovskite compound, it can be said to have an electron transport function. The electron transport layer 4 preferably has a function of blocking the transport of holes. The electron transport layer 4 is preferably dense. In this embodiment, the electron transport layer 4 is formed of tin oxide, and is provided only on the first electrode portion 3a, and is not present on the second electrode portion 3b.

The term "layer" does not specify thickness or width, and includes patterns or islands, and layers with parts of different thicknesses. A layer is preferably a member with a roughly constant thickness.

Dense is also called dense, compact, compact quality, etc., and is the same as or includes these.

Porous is also called porous, mesoporous, or mesoporous, and includes the same or all of these. In addition, porous means something that can contain perovskite compounds in the voids. When we say "denser than porous," the denseness means that it is denser than other things, and specifically, it means that it has less porosity than the voids in porous things and is denser. It is important to note that the evaluation criteria for "density" are different between absolute "density" without comparison with others, that is, not relative, and relative "density."

Here, "dense material", that is, "dense" used without comparison with others, means that the voids are extremely small. For example, dense specifically means that the maximum width of the voids is less than 5 nm in cross-sectional observation by SEM. Here, the maximum width of the voids refers to the maximum part of the width of the voids in cross-sectional observation by SEM. For example, it is sufficient to observe a cross-sectional SEM image with a width of 400 nm and confirm that the maximum width of the voids in that range is less than 5 nm. Preferably, dense means that the intrusion of the perovskite compound is suppressed and that the perovskite compound is not present on one side of the thickness direction of the dense layer. More preferably, dense means that the perovskite compound cannot be contained in the voids, or that there is no part where the perovskite compound is continuously present throughout the thickness of the dense part. That is, when the dense layer cannot be confirmed at the maximum width of the void, it is sufficient to confirm the absence of the perovskite compound on one side of the thickness direction by SEM and EDX observation. The absence of the perovskite compound can be, for example, observed in a cross-sectional SEM (or EDX) image with a width of 400 nm by SEM and EDX observation, and when the perovskite compound does not exist within that range, it can be determined that the perovskite compound does not exist. Alternatively, when the absence of the perovskite compound cannot be confirmed, it is sufficient to confirm that there is no part where the perovskite compound exists through the layer thickness by SEM and EDX observation. In addition, in the present disclosure, unless there is a particular contradiction, the observation by SEM can be confirmed by observing a cross-sectional SEM (or EDX) image with a width of 400 nm. For example, when a 400 nm wide cross-section is observed by SEM or EDX, if there is no part where the perovskite compound exists throughout the thickness of the layer, the layer can be said to be a dense layer. Note that the definition of denseness as being one with extremely small voids takes precedence, and if this is not possible, the above preferred definition (e.g., a state in which the perovskite compound is not present on one side in the thickness direction) can be applied, and if this is still not possible, the above more preferred definition (e.g., there is no part where the perovskite compound exists continuously throughout the thickness of the dense part) can be applied.

The spacer layer 6 is made of a porous material and is preferably an insulator. That is, it is preferably an insulating porous spacer layer. Examples of materials for the spacer layer 6 include metal oxides such as titanium oxide, zirconium dioxide, aluminum oxide, and silicon dioxide. Furthermore, examples of materials for the insulating spacer layer 6 include insulating metal oxides such as insulating titanium oxide, insulating zirconium dioxide, insulating aluminum oxide, and insulating silicon dioxide. The spacer layer 6 is a porous layer including voids. The spacer layer 6 preferably has a large number of voids with a size of 20 nm or more. In other words, the spacer layer 6 is occupied by, for example, the metal oxide 6c that constitutes the spacer layer itself and the voids that are the gaps between the metal oxides 6c. The porous layer has a large number of pores in the layer, and these pores are connected. Porous means that when a liquid (with good wettability) is dropped onto a porous layer (a layer with hollow pores), the liquid seeps into the porous layer.

It is preferable that the spacer layer is formed directly on the dense electron transport layer. That is, the spacer layer is not formed on the dense electron transport layer after a porous electron transport layer is formed on the dense electron transport layer, but is formed directly on the dense electron transport layer. The structure can be explained as the spacer layer being arranged adjacent to the dense electron transport layer. Or, from another perspective, the spacer layer is arranged adjacent to the dense electron transport layer, and there is no porous electron transport layer between the dense electron transport layer and the spacer layer. This structure can be confirmed by observing a cross-sectional SEM (or EDX) image with a width of 400 nm in cross-sectional observation using SEM or the like. In other words, it is sufficient to confirm that the spacer layer is arranged adjacent to the dense electron transport layer in a cross-sectional SEM image with a width of 400 nm. Or, from another cut, it is sufficient to confirm that there is no porous electron transport layer between the dense electron transport layer and the spacer layer in the range of a cross-sectional SEM image with a width of 400 nm.

Also, a light absorbing layer that absorbs irradiated light is provided in the gaps of the spacer layer 6. In this embodiment, the spacer layer 6, like the electron transport layer 4, has an insulating layer laminate portion 6a formed on the first electrode portion 3a, and an interelectrode portion 6b that covers the side surface of the electron transport layer 4 and fills between the first electrode portion 3a and the second electrode portion 3b. In the spacer layer 6, it is preferable that the particles of the metal oxide 6c are formed so as to be continuously connected.

The hole transport layer 7 is a layer that collects holes photoexcited in the light absorption layer, and is formed of a carbon electrode material that forms a porous layer. The hole transport layer 7 has a collection layer laminate 7a that covers the insulating layer laminate 6a on the spacer layer 6, and an electrode connection portion 7b that covers the side of the interelectrode portion 6b and is laminated on the second electrode portion 3b.

The light absorbing layer described above is a layer containing a perovskite compound. As long as the solar cell has a photoelectric conversion function, the light absorbing layer naturally generates electrons and holes by photoexcitation, the electrons generated in the light absorbing layer move to the electron transport layer, and the holes generated in the light absorbing layer move to the hole transport layer 7, and the charges are separated. As long as the solar cell has a photoelectric conversion function, it can be said that electrons and holes are generated by photoexcitation. The hole transport layer 7 also has a layer filled with a perovskite compound. In other words, the voids in the hole transport layer 7 also contain a perovskite compound. It is desirable that the voids in the hole transport layer 7 are filled with a perovskite compound. The thickness of the light absorbing layer is preferably 500 nm or more and 2 μm or less, and more preferably 700 nm or more and 800 nm or less.

The perovskite compound contained in the light absorbing layer is composed of a compound represented by the general formula: ABX ₃ ... (1). However, although the composition ratio of each is preferably 1:1:3, it is not necessarily 1:1:3, the content of each element may be appropriately increased or decreased, and each constituent element does not necessarily have to be one type. As long as the solar cell has a photoelectric conversion function, the perovskite compound contained in the light absorbing layer exerts a photoelectric conversion function, and therefore, even if it has the degree of freedom of composition as explained in the composition ratio and the type of constituent element, it is reasonable to consider that it exerts its function. In the general formula (1), A is an organic molecule (including an organic group or an organic cation, the same in this disclosure) or an inorganic atom or molecule (including an inorganic group or an inorganic cation, the same in this disclosure) or a combination thereof, B is a metal atom or molecule (including a metal cation, the same in this disclosure), and X is a halogen atom or molecule or a chalcogen atom or molecule (including a halogen anion or a chalcogen anion, the same in this disclosure). In the general formula (1), the three Xs may be the same or different from each other. As long as the solar cell has a photoelectric conversion function, the perovskite compound contained in the light absorbing layer exhibits a photoelectric conversion function, and this should be taken into consideration. That is, if it is confirmed that the compound is a perovskite compound, it is appropriate to consider it as a perovskite compound exhibiting a photoelectric conversion function, and it is sufficient to know that it has, for example, an organic molecule, a metal atom, and a halogen atom. Furthermore, as long as the solar cell has a photoelectric conversion function, it can be confirmed that the compound is a perovskite compound if elements corresponding to A, B, and X are detected. For example, molecules containing carbon, nitrogen, and hydrogen are suitable as organic molecules, and therefore, it is sufficient to detect carbon, nitrogen, hydrogen, a metal element, and a halogen or chalcogen. Alternatively, it is sufficient to know that the compound is a perovskite compound if it has A, B, and X, and it is sufficient to know that the compound has, for example, an inorganic atom, a metal atom, and a halogen atom. Furthermore, the presence of a perovskite compound can be confirmed by detecting elements corresponding to A, B, and X as long as the solar cell has a photoelectric conversion function. For example, cesium or rubidium is suitable as an inorganic atom, and therefore, it is sufficient to detect cesium or rubidium, a metal element, and a halogen or chalcogen. Furthermore, the presence of a perovskite compound does not require confirmation of a crystal structure, since it is a natural consequence that a solar cell has a crystal structure as long as the solar cell has a photoelectric conversion function. The light absorption layer may include compounds other than perovskite compounds.

The light absorbing layer may contain an organic-inorganic hybrid compound. An organic-inorganic hybrid compound means a compound containing an inorganic material and an organic material. Organic-inorganic hybrid compounds also include perovskite compounds, and solar cells using perovskite compounds are also called organic-inorganic hybrid solar cells. "Organic" typically means something that is composed of multiple carbons as constituent elements. Note that graphite, graphene, carbon nanowires, carbon nanofibers, carbon nanotubes, and carbon materials such as carbon and carbon black that function as electrodes are not considered to be organic materials. In other words, organic means something that has multiple carbons as one of its constituent elements, excluding the above carbon materials such as graphite. "Inorganic" means something that is not organic.

In general formula (1), examples of the organic molecule represented by A include alkylamines, alkylammoniums, and nitrogen-containing heterocyclic compounds. In the perovskite compound (1), the organic molecule represented by A may be only one type of organic molecule, or may be two or more types of organic molecules.

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.

Alkylammonium is an ionized product of the above-mentioned alkylamine. Examples of alkylammonium 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.

Examples of the nitrogen-containing heterocyclic compound include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, and carbazole. The nitrogen-containing heterocyclic compound may be an ionized compound. Phenethylammonium is a preferred example of the nitrogen-containing heterocyclic compound that is an ionized compound.

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.

In general formula (1), examples of the metal atom 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 the perovskite compound, the metal atom represented by B may be only one type of metal atom, or may be two or more types of metal atoms. From the viewpoint of improving the light absorption characteristics and charge generation characteristics of the perovskite compound, the metal atom represented by B is preferably a lead atom or a tin atom. From the viewpoint of reducing lead, a tin atom is preferred.

In general formula (1), examples of halogen atoms represented by X include fluorine, chlorine, bromine, and iodine atoms, and 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 type or two or more types. As the halogen atom represented by X, an iodine atom is preferred from the viewpoint of enabling the perovskite compound to utilize light in a wide wavelength range. In more detail, it is preferred that at least one of the three Xs represents an iodine atom, and it is more preferred that the three Xs represent iodine atoms.

As the perovskite compound, _a compound represented by the general formula " _CH3NH3PbX3 (wherein _X represents a halogen atom) _" is preferred, and _CH3NH3PbI3 is more preferred. By using a compound represented by the general formula _{" CH3NH3PbX3 "} (particularly _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.

When manufacturing the solar cell 1, first, a base is prepared using a general photolithography process, screen printing process, or the like, with the appropriate areas set for each layer of the solar cell 1. The prepared base has a porous layer as described above, and the solar cell 1 is produced by dripping a perovskite precursor solution containing a perovskite compound (described below) from the top of the base and firing it.

In the process of manufacturing the solar cell 1, after each layer is formed on the substrate 2, a perovskite precursor solution containing an organic onium salt is dripped onto the substrate and baked to form a light absorbing layer. In this embodiment, the organic onium salt-containing perovskite precursor solution is made by adding 5% 5-aminovaleric acid hydroiodide (5-AVAI) to 100% Pb.

In FIG. 1, a configuration in which an electrode layer is provided only on the substrate 2 is shown, but this is not limited thereto, and a configuration in which a new electrode layer is provided on the hole transport layer 7 may also be used.

As described above, the electron transport layer 4 is a denser layer than the spacer layer 6. In this way, by stacking the spacer layer 6 on the electron transport layer 4, the porous layer through which the perovskite solution permeates becomes thinner, and the permeability can be improved. This makes it possible to provide a solar cell with high conversion efficiency and improved variability.

The electron transport layer 4 is preferably made of a metal oxide selected from titanium oxide, tin oxide, zirconium dioxide, aluminum oxide, and silicon dioxide, either alone or in combination, and has a particle size of 1 to 80 nm, and more preferably has a particle size of 1 to 20 nm. In this way, a dense electron transport layer 4 can be obtained by using a metal oxide with an appropriate particle size.

The particle diameter in the electron transport layer 4 can be determined by calculating the diameter of a circle with an area equivalent to the cross-sectional area of 10 adjacent particles in SEM cross-section observation of the electron transport layer 4, and averaging these values.

The electron transport layer 4 is formed by depositing particles of various sizes, and is a layer with uneven thickness. The particle diameter of the metal oxide may be larger than the average film thickness of the electron transport layer 4. In other words, there may be particles that occupy the electron transport layer 4 from the bottom to the top.

By the way, it is possible to form a porous electron transport layer on the dense electron transport layer 4. Then, a porous spacer layer can be formed on the porous electron transport layer. By doing so, there is no problem with the electrical connectivity of the electron transport layer and the hole transport layer, and good photoelectric conversion function can be achieved. However, in this case, after forming the porous electron transport layer and the porous spacer layer, it is necessary to form the precursor of the perovskite compound so that it penetrates into both porous layers by coating or the like, and problems may arise in penetrating both layers evenly. As a result, some perovskite does not penetrate, resulting in resistance parts without perovskite compound, which may cause variation and performance degradation.

However, in this embodiment, a porous electron transport layer is not formed on the dense electron transport layer 4, but a porous spacer layer is formed directly on the dense electron transport layer. In this way, after forming only a porous spacer layer without a porous electron transport layer on the dense electron transport layer, it is only necessary to form a precursor of the perovskite compound so that it penetrates into the porous spacer layer by coating or the like, which makes it easy to penetrate the porous spacer layer evenly and the liquid penetrates evenly. As a result, the perovskite compound is formed evenly throughout the layer, which leads to improved conversion efficiency and improved variation.

As described above, in this embodiment, a film-shaped substrate 1 or a flexible film-shaped substrate 1 may be used. However, a problem with the film-shaped substrate 1 is that it cannot withstand high temperatures. When forming a mesoporous nanocrystal layer, as in conventional solar cells, firing is performed at 500°C, but there is a risk that the film-shaped substrate 1 will not be able to withstand this temperature.

In contrast, in the present embodiment, since there is no need to form a mesoporous nanocrystal layer, the material can be fired at a low temperature, for example, below 150°C, and the solar cell 1 can be formed without damaging the film-like substrate 1.

Next, the results of a comparison of the characteristics of the solar cell 1 according to the embodiment of the present disclosure and a comparative example produced under different conditions will be described with reference to Figures 2 and 3.

Figure 2 is a characteristic diagram that explains the electron mobility in the comparative example.

Figure 2 shows the relationship between the energy bands of the electron transport layer 4 and the perovskite compound (light absorbing layer) in the comparative example, where "La1" corresponds to the electron transport layer 4 and "La2" corresponds to the perovskite compound. In the comparative example, the electron transport layer 4 is formed of titanium oxide. In Figure 2, the energy level represented by EL1 or EL2 indicates the energy level of the lower end of the conduction band, and the energy level shown below with a dashed line indicates the upper end of the valence band. The upper end of the valence band is sometimes called the VBM (Valence band maximum), and the lower end of the conduction band is sometimes called the CBM (Conduction band minimum). Furthermore, the absolute value of the difference between the vacuum level and the CBM can be rephrased as the electron affinity (or its absolute value), and the absolute value of the difference between the vacuum level and the VBM can be rephrased as the ionization potential (or its absolute value). "Deep" or "low" for CBM or VBM means that the corresponding electron affinity or ionization energy is large or far from the vacuum level, and "shallow" or "high" for CBM or VBM means that the corresponding electron affinity or ionization energy is small or close to the vacuum level.

In the comparative example, the energy level of the CBM of the electron transport layer 4 (first energy level EL1) is higher than the energy level of the CBM of the perovskite compound (second energy level EL2), making it difficult to inject electrons from the perovskite compound. Therefore, unless a porous electron transport layer is provided between the electron transport layer 4 and the perovskite compound to increase the contact area, a suitable current cannot be obtained.

FIG. 3 is a characteristic diagram illustrating the mobility of electrons in an embodiment of the present disclosure.

FIG. 3 shows the relationship between the energy bands of the electron transport layer 4 and the perovskite compound (light absorbing layer) in an embodiment of the present disclosure, where "La3" corresponds to the electron transport layer 4 and "La4" corresponds to the perovskite compound. In this embodiment, the electron transport layer 4 is formed of tin oxide.

In this embodiment, the energy level of the CBM of the electron transport layer 4 (third energy level EL3) is lower than the energy level of the CBM of the perovskite compound (third energy level EL3), so electron injection from the perovskite compound is advantageous, and a suitable current can be obtained without providing a porous electron transport layer.

Figure 4 is a cross-sectional SEM photograph of a solar cell according to this embodiment.

FIG. 4 is an SEM photograph of a cross section of a solar cell 1 according to this embodiment. The lower region of the SEM photograph (first region AR1) corresponds to the electron transport layer 4, and appears dark overall. If the electron transport layer 4 is not porous, perovskite is not contained within, and therefore lead is not detected by EDX analysis or the like.

The central region of the SEM photograph (second region AR2) corresponds to the spacer layer 6, and in cross-sectional SEM observation, white areas are visible here and there because the layer is insulating and electrons are less likely to escape.

The embodiments disclosed herein are illustrative in all respects and are not intended to be a basis for restrictive interpretation. Therefore, the technical scope of this disclosure is not to be interpreted solely by the embodiments described above, but is defined based on the claims. Furthermore, all modifications that are equivalent in meaning and scope to the claims are included.

This application claims priority based on Japanese Patent Application No. 2023-140871, filed on August 31, 2023, the contents of which are incorporated herein by reference. In addition, all documents cited in this specification are specifically incorporated herein by reference in their entirety.

REFERENCE SIGNS LIST 1 Solar cell 2 Substrate 3 Transparent electrode layer 4 Electron transport layer 6 Spacer layer 7 Hole transport layer

Claims (11)

A solar cell comprising a substrate, an electron transport layer, a spacer layer, and a hole transport layer in this order,
the spacer layer is a porous layer having voids,
The solar cell according to claim 1, wherein the electron transport layer is denser than the spacer layer. The solar cell according to claim 1 ,
The solar cell according to claim 1, wherein the electron transport layer is a dense layer. The solar cell according to claim 2 ,
The electron transport layer has a maximum void width of less than 5 nm. The solar cell according to claim 2 or 3,
The solar cell is characterized in that the electron transport layer does not contain a perovskite compound on one side in a thickness direction of the electron transport layer. The solar cell according to any one of claims 2 to 4,
The solar cell, wherein the electron transport layer has no portion where the perovskite compound exists throughout the thickness of the layer. The solar cell according to any one of claims 2 to 5,
The spacer layer has insulating properties,
the spacer layer is disposed adjacent to and in contact with the electron transport layer. The solar cell according to claim 6,
13. A solar cell comprising: a spacer layer and a dense electron transport layer; and a porous electron transport layer between the spacer layer and the dense electron transport layer. The solar cell according to any one of claims 1 to 7,
The solar cell is characterized in that the electron transport layer is formed of a metal oxide selected from titanium oxide, tin oxide, zirconium dioxide, aluminum oxide, and silicon dioxide, either alone or in combination of two or more of these, and has a particle size of 1 to 80 nm. The solar cell according to claim 8,
The solar cell, wherein the electron transport layer is made of tin oxide. The solar cell according to any one of claims 1 to 9,
The solar cell, wherein the substrate is a flexible film. The method includes providing, in order from the substrate, an electron transport layer, a spacer layer, and a hole transport layer;
the spacer layer is a porous layer having voids,
The method for manufacturing a solar cell, wherein the electron transport layer is denser than the spacer layer.

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