Solar cell

Abstract

A solar cell (100) of the present application includes a substrate (1), a first electrode (6), an electron transport layer (2), a first photoelectric conversion layer (3), and a cover layer (5). The first photoelectric conversion layer (3) is provided between the first electrode (6) and the substrate (1). The substrate (1) has a first main surface and a second main surface, and the second main surface has a concavo-convex structure. The electron transport layer (2) has a first main surface and a second main surface, and the first and second main surfaces have a concavo-convex structure. The first photoelectric conversion layer (3) has a first main surface and a second main surface. The second main surface of the substrate (1) faces the first main surface of the electron transport layer (2). The second main surface of the electron transport layer (2) faces the first main surface of the first photoelectric conversion layer (3). The second main surface of the electron transport layer (2) has a first region (21) not covered by the first photoelectric conversion layer (3), and a second region (22) covered by the first photoelectric conversion layer (3). The first photoelectric conversion layer (3) contains a perovskite compound. The first region (21) is covered by the cover layer (5). The cover layer (5) contains an oxide semiconductor.

Description

TECHNICAL FIELD

[0001] The present application relates to a solar cell. BACKGROUND

[0002] In recent years, research and development of organic thin-film solar cells or perovskite solar cells as new solar cells to replace existing silicon-based solar cells have been progressing.

[0003] In perovskite solar cells, a perovskite compound represented by the chemical formula ABX3(wherein A is a 1-valent cation, B is a 2-valent cation, and X is a halide anion) is used as a photoelectric conversion material.

[0004] Non-Patent Literature 1 discloses a perovskite solar cell in which a perovskite compound represented by the chemical formula CH3NH3PbI3 (hereinafter, referred to as "MAPbI3") is used as a photoelectric conversion material of the perovskite solar cell. In the perovskite solar cell disclosed in Non-Patent Literature 1, a perovskite compound represented by MAPbI3, TiO2, and Spiro-OMeTAD are used as a photoelectric conversion material, an electron transporting material, and a hole transporting material, respectively.

[0005] Non-Patent Literature 2 discloses a perovskite solar cell in which CH3NH3 + (hereinafter, referred to as "MA"), CH(NH2)2 + (hereinafter, referred to as "FA"), and a polycation perovskite compound in which Cs is used as a 1-valent cation are used as a photoelectric conversion material of the perovskite solar cell. In the perovskite solar cell disclosed in Non-Patent Literature 2, a polycation perovskite compound, TiO2, and Spiro-OMeTAD are used as a photoelectric conversion material, an electron transporting material, and a hole transporting material, respectively.

[0006] Patent Literature 1 discloses an organic thin-film solar cell. The organic thin-film solar cell disclosed in Patent Literature 1 has a fine structure of a concave-convex shape at the interface of a photoelectric conversion layer and an electrode. By this configuration, the organic thin-film solar cell disclosed in Patent Literature 1 can improve photoelectric energy conversion efficiency.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2014 / 208713

[0010] NON-PATENT LITERATURE

[0011] Non-Patent Literature 1: Julian Burschka et al., "Sequential deposition as a route to high-performance perovskite-sensitized solar cells", Nature, vol. 499, pp. 316-319, 18 July 2013 [DOI: 10.1038 / nature12340]

[0012] Non-Patent Literature 2: Taisuke Matsui et al., "Room-Temperature Formation of Highly Crystalline Multication Perovskites for Efficient, Low-Cost Solar Cells", Advanced Materials, Volume 29, Issue 15, April 18, 2017, 1606258 [DOI: 10.1002 / adma.201606258] SUMMARY

[0013] PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] An object of the present application is to provide a solar cell having a high voltage, which is a perovskite solar cell provided with a photoelectric conversion layer disposed on a surface having a concavo-convex structure.

[0015] MEANS FOR SOLVING THE PROBLEMS

[0016] The solar cell of the present application is provided with: a substrate, a first electrode, an electron transport layer, a first photoelectric conversion layer, and a cover layer,

[0017] The first photoelectric conversion layer is disposed between the first electrode and the substrate,

[0018] The substrate has a first main surface and a second main surface, and the second main surface of the substrate has a concavo-convex structure,

[0019] The electron transport layer has a first main surface and a second main surface, and the first main surface and the second main surface of the electron transport layer have a concavo-convex structure,

[0020] The first photoelectric conversion layer has a first main surface and a second main surface,

[0021] The second main surface of the substrate faces the first main surface of the electron transport layer,

[0022] the second main surface of the electron-transporting layer faces the first main surface of the first photoelectric conversion layer,

[0023] the second main surface of the electron-transporting layer has a first region not covered by the first photoelectric conversion layer and a second region covered by the first photoelectric conversion layer,

[0024] the first photoelectric conversion layer contains a perovskite compound,

[0025] the first region is covered by the covering layer,

[0026] the covering layer contains an oxide semiconductor.

[0027] Effects of Invention

[0028] The present application provides a solar cell having a high voltage, which is a perovskite solar cell provided with a photoelectric conversion layer disposed on a surface having a concavo-convex structure. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1A A cross-sectional view of a solar cell of Embodiment 1 is shown.

[0030] Figure 1B An enlarged cross-sectional view of a first region of a solar cell of Embodiment 1 is shown.

[0031] Figure 1C An enlarged cross-sectional view of a second region of a solar cell of Embodiment 1 is shown.

[0032] Figure 2A A view illustrating a convex portion of a concavo-convex structure in a solar cell of Embodiment 1 is shown.

[0033] Figure 2B A view illustrating a concave portion of a concavo-convex structure in a solar cell of Embodiment 1 is shown.

[0034] Figure 3A A cross-sectional view of a solar cell of Embodiment 2 is shown.

[0035] Figure 3B An enlarged cross-sectional view of a first region of a solar cell of Embodiment 2 is shown.

[0036] Figure 3C An enlarged cross-sectional view of a second region of a solar cell of Embodiment 2 is shown.

[0037] Figure 4A A dark field scanning transmission electron microscope (hereinafter, referred to as "STEM") image of a cross section of a solar cell of Example 1 is shown.

[0038] Figure 4Bis a bright field STEM image of a cross section of the solar cell of Example 1.

[0039] Figure 5 is a mapping image of various elements obtained from the cross-sectional STEM image obtained in Figure 4A DETAILED DESCRIPTION

[0040] <Definitions of Terms>

[0041] The term "perovskite compound" used in the present specification means a perovskite crystal structure represented by the chemical formula ABX3(wherein A is a 1-valent cation, B is a 2-valent cation, and X is a halogen anion) and a structure having a similar crystal to it.

[0042] The term "perovskite solar cell" used in the present specification means a solar cell containing a perovskite compound as a photoelectric conversion material.

[0043] The term "lead-based perovskite compound" used in the present specification means a perovskite compound containing lead.

[0044] The term "lead-based perovskite solar cell" used in the present specification means a solar cell containing a lead-based perovskite compound as a photoelectric conversion material.

[0045] <Insights that became the basis of the present application>

[0046] Hereinafter, the insights that became the basis of the present application will be described.

[0047] A perovskite compound has a high light absorption coefficient and a long diffusion length as characteristic physical properties. By such physical properties, a perovskite solar cell can generate electricity with high efficiency with a thickness of several hundred nanometers. Furthermore, a perovskite solar cell has features such as use of a small amount of material, no need for a high temperature in a formation process, and formation by coating, compared to a conventional silicon solar cell. Due to the features, a perovskite solar cell is lightweight, and can also be formed on a substrate formed of a flexible material like plastic. Therefore, a perovskite solar cell becomes capable of being disposed on a portion that has had a weight restriction so far. For example, regarding a perovskite solar cell, it is possible to extend to a building material integrated solar cell combined with a conventional member, such as a building material or the like. In the case where a perovskite solar cell is configured by combination with a building material like this, it is necessary to use a member having a relatively large concave-convex structure on a surface as a substrate, and form a perovskite solar cell on the substrate.

[0048] ​Further, in order to further improve the photoelectric conversion efficiency, a laminated solar cell, that is, a tandem solar cell in which a perovskite solar cell and a silicon solar cell are overlapped, has been studied. The silicon solar cell sometimes has a texture structure in which a concavo-convex is provided on the surface in order to effectively use the incident light. Therefore, in the case where the silicon solar cell has the texture structure, the perovskite solar cell needs to be formed on the surface having the concavo-convex structure.

[0049] However, the photoelectric conversion layer, that is, the layer containing the perovskite compound in the perovskite solar cell has a thin film thickness, and the film is formed by coating. Due to these facts, in the case where the photoelectric conversion layer in the perovskite solar cell is formed on the surface having the concavo-convex structure, the covering of the concavo-convex following the shape of the concavo-convex structure becomes insufficient. In particular, the covering of the photoelectric conversion layer with respect to the apex of the convex portion and the peripheral portion thereof becomes insufficient. As a result, the solar cell is short-circuited due to the upper electrode and the lower electrode contacting each other, and the power generation voltage of the solar cell is reduced.

[0050] In view of these findings, the present inventors have found a structure of a solar cell having a high voltage in a perovskite solar cell having a photoelectric conversion layer provided on a surface having a concavo-convex structure.

[0051] <Embodiments of the Present Application>

[0052] Hereinafter, the embodiments of the present application will be described in detail while referring to the accompanying drawings.

[0053] (First Embodiment)

[0054] Figure 1A A cross-sectional view of the solar cell 100 of the first embodiment is shown. Figure 1B An enlarged cross-sectional view of the first region 21 of the solar cell 100 of the first embodiment is shown. Figure 1C An enlarged cross-sectional view of the second region 22 of the solar cell 100 of the first embodiment is shown.

[0055] As Figure 1AAs shown, the solar cell 100 of this embodiment includes a substrate 1, an electron transport layer 2, a first photoelectric conversion layer 3, a hole transport layer 4, a capping layer 5, and a first electrode 6. The first photoelectric conversion layer 3 is disposed between the substrate 1 and the first electrode 6. Specifically, the substrate 1, electron transport layer 2, first photoelectric conversion layer 3, hole transport layer 4, capping layer 5, and first electrode 6 are disposed sequentially. However, in the solar cell 100, there are also regions where the substrate 1, electron transport layer 2, capping layer 5, and first electrode 6 are disposed sequentially. In other words, there are regions in the electron transport layer 2 that are not covered by the first photoelectric conversion layer 3 and the hole transport layer 4. The first photoelectric conversion layer 3 contains a perovskite compound. The capping layer 5 contains an oxide semiconductor. It should be noted that the hole transport layer 4 may not be provided in the solar cell 100. The following also includes the differences in regions, and each configuration of the solar cell 100 will be described in detail.

[0056] like Figure 1B and 1C As shown, substrate 1 has a first main surface 1a and a second main surface 1b. Electron transport layer 2 has a first main surface 2a and a second main surface 2b. First photoelectric conversion layer 3 has a first main surface 3a and a second main surface 3b. Hole transport layer 4 has a first main surface 4a and a second main surface 4b. Cover layer 5 has a first main surface 5a and a second main surface 5b. First electrode 6 has a first main surface 6a and a second main surface 6b. Wherein, in Figures 1A-1C In the middle, the first principal surface of each component is equivalent to the lower surface, and the second principal surface is equivalent to the upper surface.

[0057] The second main surface 1b of the substrate 1 faces the first main surface 2a of the electron transport layer 2. The second main surface 2b of the electron transport layer 2 faces the first main surface 3a of the first photoelectric conversion layer 3.

[0058] The second main surface 1b of the substrate 1 has an uneven structure. The first main surface 2a and the second main surface 2b of the electron transport layer 2 have uneven structures.

[0059] The first region 21 of the solar cell 100 corresponds to the region not covered by the first photoelectric conversion layer 3 in the second main surface 2b of the electron transport layer 2. The first region 21 of the second main surface 2b of the electron transport layer 2 is covered by a cover layer 5. By providing the cover layer 5, the solar cell 100 of the first embodiment can prevent short circuits caused by the first electrode 6 contacting the electron transport layer 2. As a result, the solar cell 100 of the first embodiment can have a high voltage. In the uneven structure of the second main surface 2b of the electron transport layer 2, the apex of the protrusion is the part where it is difficult to form the first photoelectric conversion layer 3. Therefore, the first region 21, for example, includes the apex of the protrusion in the uneven structure of the second main surface 2b of the electron transport layer 2.

[0060] Figure 1BThe enlarged view of the first region 21 of the solar cell 100 shown in FIG. 1 specifically shows a convex portion of the second main surface lb of the substrate 1 and the second main surface 2b of the electron transporting layer 2, and a peripheral portion of the convex portion. Hereinafter, the second main surface lb of the substrate 1 and the second main surface 2b of the electron transporting layer 2 will be collectively referred to as a second region 22. Figure 1B The configuration of the solar cell 100 shown in FIG. 1 will be described in detail. As described above, the second main surface lb of the substrate 1 has a concavo-convex structure. The second main surface lb of the substrate 1 is in contact with the first main surface 2a of the electron transporting layer 2. The second main surface 2b of the electron transporting layer 2 is covered with the cover layer 5, and is in contact with the first main surface 5a of the cover layer 5. The second main surface 5b of the cover layer 5 is in contact with the first main surface 6a of the first electrode 6. Note that, between at least one of the second main surface lb of the substrate 1 and the first main surface 2a of the electron transporting layer 2, and the second main surface 5b of the cover layer 5 and the first main surface 6a of the first electrode 6, a layer having another function can be provided.

[0061] The second region 22 of the solar cell 100 corresponds to a region other than the first region 21, i.e., a region covered with the first photoelectric conversion layer 3, in the second main surface 2b of the electron transporting layer 2. The second region 22, for example, includes a bottom of a concave portion in the concavo-convex structure of the second main surface 2b of the electron transporting layer 2. On the second region of the electron transporting layer 2, the first photoelectric conversion layer 3 and the hole transporting layer 4 can be provided in this order, or the first photoelectric conversion layer 3, the hole transporting layer 4, and the cover layer 5 can be provided in this order.

[0062] Figure 1C The enlarged view of the second region 22 of the solar cell 100 shown in FIG. 1 specifically shows a concave portion of the second main surface lb of the substrate 1 and the second main surface 2b of the electron transporting layer 2, and a peripheral portion of the concave portion. Hereinafter, the second main surface lb of the substrate 1 and the second main surface 2b of the electron transporting layer 2 will be collectively referred to as a second region 22. Figure 1CThe configuration of the solar cell 100 shown in FIG. 1 is described in detail. As described above, the second principal surface lb of the substrate 1 has a concavo-convex structure. The second principal surface lb of the substrate 1 is in contact with the first principal surface 2a of the electron transporting layer 2. The second principal surface 2b of the electron transporting layer 2 is in contact with the first principal surface 3a of the first photoelectric conversion layer 3. The second principal surface 3b of the first photoelectric conversion layer 3 is in contact with the first principal surface 4a of the hole transporting layer 4. The second principal surface 4b of the hole transporting layer 4 is in contact with the first principal surface 5a of the cover layer 5. The second principal surface 5b of the cover layer 5 is in contact with the first principal surface 6a of the first electrode 6. Note that, between at least one of the second principal surface lb of the substrate 1 and the first principal surface 2a of the electron transporting layer 2, the second principal surface 2b of the electron transporting layer 2 and the first principal surface 3a of the first photoelectric conversion layer 3, the second principal surface 3b of the first photoelectric conversion layer 3 and the first principal surface 4a of the hole transporting layer 4, and the second principal surface 5b of the cover layer 5 and the first principal surface 6a of the first electrode 6, a layer having another function can be provided. In other words, the second principal surface lb of the substrate 1 and the first principal surface 2a of the electron transporting layer 2 can face each other without necessarily being in contact with each other. Further, the second principal surface 2b of the electron transporting layer 2 and the first principal surface 3a of the first photoelectric conversion layer 3 can face each other without necessarily being in contact with each other. Further, the second principal surface 3b of the first photoelectric conversion layer 3 and the first principal surface 4a of the hole transporting layer 4 can face each other without necessarily being in contact with each other. Further, the second principal surface 5b of the cover layer 5 and the first principal surface 6a of the first electrode 6 can face each other without necessarily being in contact with each other. Note that, as the "layer having another function" described above, a porous layer can be given.

[0063] Here, in the present specification, the "concavo-convex structure" is a structure in which the average of the height difference between the convex portions and the concave portions exceeds 0.1 μm, as observed in a cross-sectional image of STEM. Here, the average of the height difference between the convex portions and the concave portions is calculated as follows. First, using a cross-sectional image of STEM, an arbitrary region having a length of 20 μm is extracted in the cross-sectional image. Next, the height difference between all the adjacent convex portions and concave portions is measured with respect to the surface concavo-convex structure of the region. The average of the height difference is calculated from the obtained measurement values. By performing such an operation, the average of the height difference between the convex portions and the concave portions is calculated.

[0064] Next, the "convex portion" and the "concave portion" of the concavo-convex structure of the present specification are described. Figure 2A FIG. 2 is a diagram for explaining the convex portion of the concavo-convex structure in the solar cell 100 of the first embodiment. Figure 2B FIG. 3 is a diagram for explaining the concave portion of the concavo-convex structure in the solar cell 100 of the first embodiment. The convex portion is a portion that protrudes from the surface of the solar cell 100, as shown in FIG. 3. Figure 2AThe apex of the convex shape and the peripheral portion thereof refer to the apex of the convex shape of the concavo-convex structure and the peripheral portion thereof as shown in FIG. 1. The peripheral portion of the apex, for example, is a region including a height above the middle between the adjacent bottoms of the concave shape, with the apex as a reference. The concave portion, for example, is a region including a height below the middle between the adjacent apexes of the convex shape, with the bottom of the concave shape as a reference. Figure 2B The bottom of the concave shape and the peripheral portion thereof refer to the bottom of the concave shape of the concavo-convex structure and the peripheral portion thereof as shown in FIG. 1. The peripheral portion of the bottom of the concave shape, for example, is a region including a height below the middle between the adjacent apexes of the convex shape, with the bottom of the concave shape as a reference.

[0065] Note that, in the case where the substrate 1 has the concavo-convex structure, the apex of the convex shape and the peripheral portion thereof refer to the apex of the convex shape of the concavo-convex structure and the peripheral portion thereof as shown in FIG. 1. The peripheral portion of the apex, for example, is a region including a height above the middle between the adjacent bottoms of the concave shape, with the apex as a reference. The concave portion, for example, is a region including a height below the middle between the adjacent apexes of the convex shape, with the bottom of the concave shape as a reference. Figures 1A-1C In the case where the second main surface 5b of the cover layer 5 and the first main surface 6a and the second main surface 6b of the first electrode 6 have the concavo-convex structure, the average value of the height difference of the surface concavo-convexity observed in the cross-sectional image of the STEM is preferably 0.1 μm or less.

[0066] In the case where the other main surface 1b of the substrate 1 has the concavo-convex structure, the average value of the height difference of the surface concavo-convexity observed in the cross-sectional image of the STEM is preferably 0.1 μm or less. Figures 1A-1C In the case where the other main surface 1b of the substrate 1 has the concavo-convex structure, the average value of the height difference of the surface concavo-convexity observed in the cross-sectional image of the STEM is preferably 0.1 μm or less. Figure 1A In the case where the first photoelectric conversion layer 3 does not cover the apexes of all the convex portions of the electron-transport layer 2, the apexes of a part of the convex portions can be covered with the first photoelectric conversion layer 3. Further, the surface roughness of the first main surface and the second main surface of each layer can be the same as or different from each other.

[0067] Hereinafter, the details will be described for each layer.

[0068] (Substrate 1)

[0069] The substrate 1 is, for example, an electrode having conductivity. In the case where the substrate 1 is an electrode, the electrode can or can not have light-transmitting property. At least one selected from the group consisting of the substrate 1 and the first electrode 6 has light-transmitting property. The substrate 1 holds the electron-transport layer 2, the first photoelectric conversion layer 3, the hole-transport layer 4, the cover layer 5, and the first electrode 6. In the case where the substrate 1 functions as an electrode, the substrate 1 can have a structure in which a layer having conductivity is provided on a base material formed of a material having no conductivity. In this case, the base material formed of a material having no conductivity can be a transparent material.

[0070] Light in the visible region to the near-infrared region can be transmitted through the electrode having light-transmitting property. The electrode having light-transmitting property can be formed of a material that is transparent and has conductivity.

[0071] Examples of such a material are:

[0072] (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine,

[0073] (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon,

[0074] (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen,

[0075] (iv) indium-tin complex oxide,

[0076] (v) tin oxide doped with at least one selected from the group consisting of antimony and fluorine,

[0077] (vi) zinc oxide doped with at least one of boron, aluminum, gallium, and indium, or

[0078] (vii) a composite thereof.

[0079] The electrode having light-transmitting properties can be formed using an opaque material provided with a light-transmissive pattern. Examples of the light-transmissive pattern are a linear pattern, a wavy linear pattern, a lattice pattern, or a pattern of a punched metal in which a plurality of fine through-holes are regularly or irregularly arranged. If the electrode having light-transmitting properties has such a pattern, light can transmit through the portions where the electrode material is not present. Examples of the opaque material are platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of them. A carbon material having electrical conductivity can also be used as the opaque material.

[0080] The solar cell 100 can have no barrier property against holes from the first photoelectric conversion layer 3 because the electron transport layer 2 is provided between the first photoelectric conversion layer 3 and the substrate 1. Therefore, the material of the substrate 1 can be a material capable of ohmic contact with the first photoelectric conversion layer 3.

[0081] (Electron transport layer 2)

[0082] As described above, the electron transport layer 2 has the first main surface 2a and the second main surface 2b having a concavo-convex structure. The concavo-convex structure of the first main surface 2a and the second main surface 2b can also be a concavo-convex structure formed by following the shape of the concavo-convex structure of the second main surface lb of the substrate 1 in the case where the electron transport layer 2 is formed on the second main surface lb of the substrate 1. The first main surface 2a of the electron transport layer 2 faces the second main surface lb of the substrate 1. The first main surface la of the electron transport layer 2 can also be in contact with the second main surface lb of the substrate 1.

[0083] As described above, the second main surface 2b of the electron transport layer 2 has the first region 21 and the second region 22. The first region 21 is not covered with the first photoelectric conversion layer 3 and is covered with the cover layer 5. Note that, in the case where the hole transport layer 4 is provided, the first region 21 is also not covered with the hole transport layer 4. The second region 22 is covered with the first photoelectric conversion layer 3.

[0084] The electron-transporting layer 2 transports electrons. The electron-transporting layer 2 contains a semiconductor. The electron-transporting layer 2 is preferably formed of a semiconductor having a band gap of 3.0 eV or more. By forming the electron-transporting layer 2 of a semiconductor having a band gap of 3.0 eV or more, it is possible to transmit visible light and infrared light to the first photoelectric conversion layer 3. As examples of the semiconductor, there can be mentioned n-type semiconductors of organic or inorganic.

[0085] Examples of the n-type semiconductor of organic are imide compounds, quinone compounds, fullerene or a derivative of fullerene. Examples of the n-type semiconductor of inorganic are metal oxides, metal nitrides or perovskite oxides. Examples of the metal oxide are oxides of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si or Cr. TiO2 is preferable. An example of the metal nitride is GaN. Examples of the perovskite oxide are SrTiO3, CaTiO3 and ZnTiO3.

[0086] The electron-transporting layer 2 can also be formed of a substance having a band gap of more than 6.0 eV. Examples of the substance having a band gap of more than 6.0 eV are:

[0087] (i) halides of alkali metals or alkaline earth metals such as lithium fluoride or barium fluoride, or

[0088] (ii) oxides of alkaline earth metals such as magnesium oxide.

[0089] In this case, in order to ensure the electron-transporting property of the electron-transporting layer 2, the thickness of the electron-transporting layer 2 can also be, for example, 10 nm or less.

[0090] The electron-transporting layer 2 can also contain a plurality of layers formed of different materials from each other.

[0091] (First photoelectric conversion layer 3)

[0092] The first photoelectric conversion layer 3 contains a perovskite compound. That is, the first photoelectric conversion layer 3 contains a perovskite compound composed of a monovalent cation, a divalent cation and a halide anion as a photoelectric conversion material. The photoelectric conversion material is a light-absorbing material.

[0093] In the present embodiment, the perovskite compound can be a compound represented by the chemical formula ABX3(wherein A is a monovalent cation, B is a divalent cation, and X is a halide anion).

[0094] In the present specification, A, B and X are also referred to as A site, B site and X site, respectively, in accordance with the expression conventionally used for perovskite compounds.

[0095] In the first embodiment, the perovskite compound can have a perovskite-type crystal structure represented by the chemical formula ABX3. As one example, a monovalent cation is located at the A site, a divalent cation is located at the B site, and a halide anion is located at the X site.

[0096] (A site)

[0097] The monovalent cation located at the A site is not limited. Examples of the monovalent cation are an organic cation or an alkali metal cation. Examples of the organic cation are a methylammonium cation (i.e., CH3NH3 + ), a formamidinium cation (i.e., NH2CHNH2 + ), a phenylethylammonium cation (i.e., C6H5C2H4NH3 + ), or a guanidinium cation (i.e., CH6N3 + ). Examples of the alkali metal cation are a cesium cation (i.e., Cs + ).

[0098] In order to have high photoelectric conversion efficiency, the A site can also contain at least one selected from the group consisting of Cs + , a formamidinium cation, and a methylammonium cation.

[0099] The cation constituting the A site can also mix a plurality of the above-described organic cations. The cation constituting the A site can also mix at least one of the above-described organic cations and at least one of the metal cations.

[0100] (B site)

[0101] The divalent cation located at the B site is not limited. Examples of the divalent cation are divalent cations of Group 13 to Group 15 elements. For example, the B site contains a Pb cation, i.e., Pb 2+ .

[0102] (X site)

[0103] The halide anion located at the X site is not limited.

[0104] The X site can also mainly contain iodide ions. The halide anion mainly containing iodide ions means that the proportion of the number of moles of iodide ions with respect to the total number of moles of halide ions is the highest. The X site can also be substantially composed of only iodide ions. The phrase “the X site is substantially composed of only iodide ions” means that the molar ratio of the number of moles of iodide ions with respect to the total number of moles of anions is 90% or more, preferably 95% or more.

[0105] The elements, i.e., ions, located at each of the A, B, and X sites can be a plurality or one.

[0106] The first photoelectric conversion layer 3 can also contain a material other than the photoelectric conversion material. For example, the first photoelectric conversion layer 3 can further contain a quencher substance for reducing the defect density of the perovskite compound. The quencher substance is a fluorine compound such as tin fluoride. The molar ratio of the quencher substance to the photoelectric conversion material can also be 5 to 20%.

[0107] The first photoelectric conversion layer 3 can also mainly contain a perovskite compound composed of a monovalent cation, a divalent cation, and a halogen anion.

[0108] The phrase "the first photoelectric conversion layer 3 mainly contains a perovskite compound composed of a monovalent cation, a divalent cation, and a halogen anion" means that the first photoelectric conversion layer 3 contains 70% by mass or more (preferably 80% by mass or more) of a perovskite compound composed of a monovalent cation, a divalent cation, and a halogen anion.

[0109] The first photoelectric conversion layer 3 can contain impurities. The first photoelectric conversion layer 3 can also further contain a compound other than the above-described perovskite compound.

[0110] The first photoelectric conversion layer 3 can have a thickness of 100 nm to 10 μm, and preferably a thickness of 100 nm to 1000 nm. The thickness of the first photoelectric conversion layer 3 depends on the magnitude of its light absorption.

[0111] The perovskite layer contained in the first photoelectric conversion layer 3 can be formed using a coating method using a solution or a co-evaporation method, or the like.

[0112] The first photoelectric conversion layer 3 can have a first main surface 3a and a second main surface 3b having a concave-convex structure. The concave-convex structure of the first main surface 3a and the second main surface 3b can also be a concave-convex structure formed by following the shape of the concave-convex structure of the second main surface 2b of the electron transport layer 2 in the case where the first photoelectric conversion layer 3 is formed on the second main surface 2b of the electron transport layer 2.

[0113] The first photoelectric conversion layer 3 can be in contact with the above-described electron transport layer 2 or the later-described hole transport layer 4, and can also be in a state of being mixed with the electron transport layer 2 or the hole transport layer 4 in a part thereof. The first photoelectric conversion layer 3 can also be in a state of having a plurality of interfaces with the electron transport layer 2 or the hole transport layer 4 within the film.

[0114] (Hole transport layer 4)

[0115] The hole transport layer 4 contains a hole transport material. The hole transport material is a material that transports holes. Examples of the hole transport material are organic substances or inorganic semiconductors.

[0116] Examples of the representative organic substance used as the hole-transporting material are 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine) 9,9'-spirobifluorene (hereinafter, referred to as "spiro-OMeTAD"), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (hereinafter, referred to as "PTAA"), poly(3-hexylthiophene-2,5-diyl) (hereinafter, referred to as "P3HT"), poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (hereinafter, referred to as "PEDOT:PSS"), or copper phthalocyanine (hereinafter, referred to as "CuPc").

[0117] The inorganic semiconductor is a semiconductor of p-type. Examples of the inorganic semiconductor are Cu2O, CuGaO2, CuSCN, CuI, NiO x x , MoO x , V2O5, or a carbon material such as graphene oxide.

[0118] The hole-transporting layer 4 can also include a plurality of layers formed of different materials from each other.

[0119] The thickness of the hole-transporting layer 4 is preferably 1 nm to 1000 nm, more preferably 10 nm to 500 nm, and further preferably 10 nm to 50 nm. If the thickness of the hole-transporting layer 4 is 1 nm to 1000 nm, sufficient hole-transporting property can be exhibited. Furthermore, if the thickness of the hole-transporting layer 4 is 1 nm to 1000 nm, the resistance of the hole-transporting layer 4 is low, and thus light can be efficiently converted into electricity.

[0120] The hole-transporting layer 4 can also contain an additive and a solvent. The additive and the solvent, for example, have an effect of increasing the hole conductivity in the hole-transporting layer 4.

[0121] Examples of the additive are an ammonium salt or an alkali metal salt. Examples of the ammonium salt are tetrabutylammonium perchlorate, tetraethylammonium hexafluorophosphate, an imidazolium salt, or a pyridinium salt. Examples of the alkali metal salt are lithium bis(pentafluoroethanesulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide (hereinafter referred to as "LiTFSI"), LiPF6, LiBF4, lithium perchlorate, or potassium tetrafluoroborate.

[0122] The solvent contained in the hole-transport layer 4 can also have high ionic conductivity. The solvent can be an aqueous solvent or an organic solvent. From the viewpoint of stabilization of the solute, an organic solvent is preferable. Examples of the organic solvent are a heterocyclic compound such as t-butylpyridine (hereinafter referred to as "t-BP"), pyridine, or n-methylpyrrolidone.

[0123] The solvent contained in the hole-transport layer 4 can also be an ionic liquid. The ionic liquid can be used alone or in combination with another solvent. The ionic liquid is preferable from the viewpoints of low volatility and high flame retardancy.

[0124] Examples of the ionic liquid are an imidazolium compound such as 1-ethyl-3-methylimidazolium tetracyanoborate, a pyridine compound, an alicyclic amine compound, an aliphatic amine compound, or an azinium amine compound.

[0125] The method for forming the film can employ a publicly known various coating method or printing method. Examples of the coating method are a doctor blade method, a bar coater method, a spray method, a dip coating method, or a spin coating method. Examples of the printing method are a screen printing method.

[0126] (Cover layer 5)

[0127] As described above, the cover layer 5 covers the first region 21 of the second main surface 2b of the electron-transport layer 2. The cover layer 5 contains an oxide semiconductor. The oxide semiconductor can also be at least one selected from the group consisting of tungsten oxide, molybdenum oxide, copper oxide, nickel oxide, and vanadium oxide.

[0128] By providing the cover layer 5, the solar cell 100 of the first embodiment can prevent a short circuit due to contact of the first electrode 6 with the electron-transport layer 2. Thus, the solar cell 100 of the first embodiment forms the first photoelectric conversion layer 3 on the second main surface 2b of the electron-transport layer 2 having a concavo-convex structure. Therefore, even in the case where part or all of the convex portion of the electron-transport layer 2 is not covered with the first photoelectric conversion layer 3, a short circuit is prevented by preventing contact of the first electrode 6 with the electron-transport layer 2 by the cover layer 5, and thus the solar cell 100 of the first embodiment can achieve a high voltage.

[0129] The cover layer 5 preferably has a wide band gap that prevents ohmic contact between the first electrode 6 and the electron transport layer 2.

[0130] The cover layer 5 can also be provided on the second region 22 of the second main surface 2b of the electron transport layer 2 in a state in which the first photoelectric conversion layer 3 and the hole transport layer 4 are provided therebetween. In this case, the cover layer 5 preferably has hole transport properties.

[0131] The cover layer 5 can contain at least one selected from the group consisting of tungsten oxide and molybdenum oxide. The cover layer 5 containing at least one selected from the group consisting of tungsten oxide and molybdenum oxide can more reliably prevent short-circuiting between the first electrode 6 and the electron transport layer, and also has excellent hole transport properties. Therefore, by providing the cover layer 5 having such a configuration, the solar cell 100 can achieve a higher voltage.

[0132] In order to increase the voltage of the solar cell 100, the cover layer 5 can also have a thickness of 5 nm to 40 nm. The cover layer 5 can preferably have a thickness of 5 nm to 30 nm.

[0133] (First electrode 6)

[0134] The first electrode 6 can have light transmittance or can not have light transmittance. At least one selected from the group consisting of the substrate 1 and the first electrode 6 has light transmittance.

[0135] In the case where the first electrode 6 is an electrode having light transmittance, light in the visible region to the near-infrared region can be transmitted through the first electrode 6. The electrode having light transmittance can be formed of a material that is transparent and has electrical conductivity.

[0136] Examples of such a material are:

[0137] (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine,

[0138] (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon,

[0139] (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen,

[0140] (iv) indium-tin composite oxide,

[0141] (v) tin oxide doped with at least one selected from the group consisting of antimony and fluorine,

[0142] (vi) zinc oxide doped with at least one of boron, aluminum, gallium, and indium, or

[0143] (vii) a composite thereof.

[0144] The electrode having light transmittance can be formed using an opaque material provided with a light-transmissive pattern. Examples of the light-transmissive pattern are a linear pattern, a wavy pattern, a lattice pattern, or a pattern of a plurality of fine through-holes arranged regularly or irregularly in a punched metal shape. If the electrode having light transmittance has such a pattern, light can transmit through the portion where the electrode material is not present. Examples of the opaque material are platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of them. A carbon material having electrical conductivity can also be used as the opaque material.

[0145] In a case where the solar cell 100 does not have the hole-transport layer 4, the first electrode 6 is formed of a material having a barrier property to electrons from the first photoelectric conversion layer 3, for example. In this case, the first electrode 6 does not have an ohmic contact with the first photoelectric conversion layer 3. The barrier property to electrons is a property of passing only the holes generated in the first photoelectric conversion layer 3 and not passing the electrons. The Fermi level of the material having the barrier property to electrons is lower than the energy level of the lower end of the conduction band of the first photoelectric conversion layer 3. The Fermi level of the material having the barrier property to electrons can also be lower than the Fermi level of the first photoelectric conversion layer 3. Examples of the material having the barrier property to electrons are a carbon material such as graphene.

[0146] In a case where the solar cell 100 has the hole-transport layer 4 between the first photoelectric conversion layer 3 and the first electrode 6, the first electrode 6 can also not have a barrier property to electrons from the first photoelectric conversion layer 3. In this case, the first electrode 6 can also have an ohmic contact with the first photoelectric conversion layer 3.

[0147] The material having the barrier property to electrons from the first photoelectric conversion layer 3 sometimes does not have light transmittance. Therefore, when the first electrode 6 is formed using such a material, the first electrode 6 has the above-described pattern such that light transmits through the first electrode 6.

[0148] The transmittance of light of the first electrode 6 can be 50% or more, or 80% or more. The wavelength of light that transmits through the first electrode 6 depends on the absorption wavelength of the first photoelectric conversion layer 3. The thickness of the first electrode 6 is in the range of 1 nm to 1000 nm, for example.

[0149] (Layer having other functions)

[0150] Examples of the "layer having another function" described above are a porous layer. The porous layer is, for example, provided between the electron-transporting layer 2 and the first photoelectric conversion layer 3. The porous layer contains a porous body. The porous body contains pores. The pores contained in the porous layer provided between the electron-transporting layer 2 and the first photoelectric conversion layer 3 can also be connected from a portion in contact with the electron-transporting layer 2 to a portion reaching the first photoelectric conversion layer 3. The pores are typically filled with a material constituting the first photoelectric conversion layer 3. Electrons can move directly from the first photoelectric conversion layer 3 to the electron-transporting layer 2.

[0151] The porous layer described above can function as a pedestal when the first photoelectric conversion layer 3 is formed on the substrate 1 and the electron-transporting layer 2. The porous layer does not hinder light absorption by the first photoelectric conversion layer 3 and movement of electrons from the first photoelectric conversion layer 3 to the electron-transporting layer 2.

[0152] The porous body constituting the porous layer described above is, for example, formed by connection of particles of an insulator or a semiconductor. Examples of the insulating particles are alumina particles or silica particles. Examples of the semiconductor particles are inorganic semiconductor particles. Examples of the inorganic semiconductor are an oxide of a metal element, a perovskite oxide of a metal element, a sulfide of a metal element, or a metal chalcogenide. Examples of the oxide of a metal element are oxides of each of Cd, Zn, In, Pb, Mo, W, Sb, Bi, Cu, Hg, Ti, Ag, Mn, Fe, V, Sn, Zr, Sr, Ga, Si, and Cr. A specific example of the oxide of a metal element is TiO2. Examples of the perovskite oxide of a metal element are SrTiO3, CaTiO3, and ZnTiO3. Examples of the sulfide of a metal element are CdS, ZnS, In2S3, PbS, Mo2S, WS2, Sb2S3, Bi2S3, ZnCdS2, and Cu2S. Examples of the metal chalcogenide are CdSe, In2Se3, WSe2, HgS, PbSe, and CdTe.

[0153] The thickness of the porous layer described above can also be 0.01 μm to 10 μm, and can also be 0.1 μm to 1 μm. The porous layer can also have a large surface roughness. Specifically, the surface roughness coefficient of the porous layer given as a value of an effective area / projection area can also be 10 or more, and can also be 100 or more. Note that the projection area is the area of a shadow formed on the back of an object when the object is irradiated with light from the front. The effective area is the actual surface area of the object. The effective area can be calculated from the volume calculated from the projection area and the thickness of the object, and the specific surface area and the bulk density of the material constituting the object.

[0154] (Action effects of the solar cell 100)

[0155] Next, the basic operation of the solar cell 100 will be described. In the solar cell 100, at least one selected from the group consisting of the substrate 1 and the first electrode 6 has a light-transmitting property. Light is incident into the solar cell 100 from the surface having the light-transmitting property. If light is irradiated to the solar cell 100, the first photoelectric conversion layer 3 absorbs the light, and generates excited electrons and holes. The excited electrons move to the electron transport layer 2. On the other hand, the holes generated in the first photoelectric conversion layer 3 move to the hole transport layer 4. The electron transport layer 2 and the hole transport layer 4 are electrically connected to the substrate 1 and the first electrode 6, respectively. Electric current is extracted from the substrate 1 and the first electrode 6 which function as a negative electrode and a positive electrode, respectively. Note that, with respect to the direction of incidence of light, there is also a case where the hole transport layer 4 is opposite to the electron transport layer 2.

[0156] (One example of the method of manufacturing the solar cell 100)

[0157] The solar cell 100 can be manufactured, for example, by the following method.

[0158] First, as the substrate 1, an electrode having a concavo-convex structure on at least one main surface (i.e., the second main surface lb) is prepared. Then, on the second main surface lb of the substrate 1, the electron transport layer 2 is formed using a sputtering method or a spray pyrolysis method. On the electron transport layer 2, the first photoelectric conversion layer 3 is formed using a coating method such as a spin coating method, a die coating method, or an inkjet method. On the first photoelectric conversion layer 3, the hole transport layer 4 is formed using a coating method such as a spin coating method, a die coating method, or an inkjet method. On the hole transport layer 4, the cover layer 5 is formed by a vacuum heating evaporation method. Finally, on the cover layer 5, the first electrode 6 is formed by a sputtering method.

[0159] (Second Embodiment)

[0160] Figure 3A A cross-sectional view of the solar cell 200 according to the second embodiment is shown. Figure 3B An enlarged cross-sectional view of the first region 21 of the solar cell 200 according to the second embodiment is shown. Figure 3C An enlarged cross-sectional view of the second region 22 of the solar cell 200 according to the second embodiment is shown.

[0161] As Figure 3AAs shown, the solar cell 200 of the second embodiment has a configuration that further includes a second photoelectric conversion layer 7 and a second electrode 8 compared to the solar cell 100 of the first embodiment. That is, the solar cell 200 is a stacked solar cell with two photoelectric conversion layers. The second photoelectric conversion layer 7 faces the first main surface 1a of the substrate 1. In other words, the second photoelectric conversion layer 7 is provided on the underside of the substrate 1. Further, the second photoelectric conversion layer 7 is provided between the second electrode 8 and the substrate 1. The second photoelectric conversion layer 7 has a first main surface 7a and a second main surface 7b. The second electrode 8 has a first main surface 8a and a second main surface 8b. Here, in... Figures 3A-3C In, with Figures 1A-1C Similarly, the first principal surface of each component corresponds to the lower surface, and the second principal surface corresponds to the upper surface.

[0162] The solar cell 200 of the second embodiment includes a substrate 1, an electron transport layer 2, a first photoelectric conversion layer 3, a hole transport layer 4, a capping layer 5, a first electrode 6, a second photoelectric conversion layer 7, and a second electrode 8. Specifically, the second electrode 8, the second photoelectric conversion layer 7, the substrate 1, the electron transport layer 2, the first photoelectric conversion layer 3, the hole transport layer 4, the capping layer 5, and the first electrode 6 are arranged sequentially. However, in the solar cell 200, there are also regions where the second electrode 8, the second photoelectric conversion layer 7, the substrate 1, the electron transport layer 2, the capping layer 5, and the first electrode 6 are arranged sequentially. In other words, similar to the solar cell 100, the solar cell 200 has regions where the electron transport layer 2 is not covered by the first photoelectric conversion layer 3 and the hole transport layer 4.

[0163] The following is a detailed description of the structure of the solar cell 200.

[0164] Figure 3B The enlarged view of the first region 21 of the solar cell 200 shown specifically shows the protrusion of the second main surface 1b of the substrate 1 with an uneven structure and the second main surface 2b of the electron transport layer 2, and the peripheral portion of the protrusion.

[0165] like Figure 3B As shown, the second main surface 8b of the second electrode 8 is disposed in contact with the first main surface 7a of the second photoelectric conversion layer 7. Furthermore, the second main surface 7b of the second photoelectric conversion layer 7 is in contact with the first main surface 1a of the substrate 1. The first main surface 7a and the second main surface 7b of the second photoelectric conversion layer 7 have an uneven structure. Each layer above the substrate 1 has the same configuration as each layer of the solar cell 100 of the first embodiment. It should be noted that layers with other functions may also be disposed between the second main surface 8b of the second electrode 8 and the first main surface 7a of the second photoelectric conversion layer 7, and between the second main surface 7b of the second photoelectric conversion layer 7 and the first main surface 1a of the substrate 1.

[0166] The second principal surface 7b of the second photoelectric conversion layer 7 can face the first principal surface la of the substrate 1, and can not necessarily be in contact. Note that as a layer having another function, a porous layer can be cited.

[0167] Next, a configuration different from the solar cell 100 of the first embodiment will be described.

[0168] (Substrate 1)

[0169] In the case of a stacked solar cell like the solar cell 200, the substrate 1 is, for example, a recombination layer. The recombination layer has a function of taking in and recombining carriers generated in the first photoelectric conversion layer 3 and the second photoelectric conversion layer 7. Therefore, the recombination layer preferably has a certain degree of electrical conductivity.

[0170] The recombination layer can also have light transmittance, for example. Light in the visible region to the near-infrared region can be transmitted through the recombination layer having light transmittance. The recombination layer having light transmittance can be formed of a material that is transparent and has electrical conductivity.

[0171] Examples of such a material are:

[0172] (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine,

[0173] (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon,

[0174] (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen,

[0175] (iv) indium-tin composite oxide,

[0176] (v) tin oxide doped with at least one selected from the group consisting of antimony and fluorine,

[0177] (vi) zinc oxide doped with at least one of boron, aluminum, gallium, and indium, or

[0178] (vii) a composite thereof.

[0179] Further, as examples of the material of the recombination layer, metal oxides such as ZnO, WO3, MoO3, or MoO2, or electron-accepting organic compounds can be given. Examples of the electron-accepting organic compound are organic compounds having a CN group on a substituent. Examples of the organic compound having a CN group on a substituent are benzo-phenanthrene derivatives, tetracyanoquinodimethane derivatives, or indenofluorene derivatives, and the like. An example of the benzo-phenanthrene derivative is hexacyanohexaazabenzo-phenanthrene. Examples of the tetracyanoquinodimethane derivative are tetracyanoquinodimethane or dicyanoquinodimethane. Note that the electron-accepting substance can be used as a single substance, or can be mixed with other organic compounds.

[0180] (2nd photoelectric conversion layer 7)

[0181] The photoelectric conversion material used in the 2nd photoelectric conversion layer 7 has a smaller band gap than the photoelectric conversion material used in the 1st photoelectric conversion layer 3. Examples of the photoelectric conversion material used in the 2nd photoelectric conversion layer 7 are silicon, a perovskite compound, a chalcopyrite compound such as CIGS, or a Group III-V compound such as GaAs. The 2nd photoelectric conversion layer 7 can also contain silicon. In the case where the 2nd photoelectric conversion layer 7 contains silicon, the solar cell 200 becomes a laminated solar cell in which a silicon solar cell and a perovskite solar cell are overlapped. However, the photoelectric conversion material used in the 2nd photoelectric conversion layer 7 is not limited to this as long as it is a material having a smaller band gap than the photoelectric conversion material used in the 1st photoelectric conversion layer 3.

[0182] (2nd electrode 8)

[0183] The 2nd electrode 8 can have light-transmitting properties or can not have light-transmitting properties. At least one selected from the group consisting of the 2nd electrode 8 and the 1st electrode 6 has light-transmitting properties.

[0184] Light in the visible region to the near-infrared region can transmit through the electrode having light-transmitting properties. The electrode having light-transmitting properties can be formed of a material that is transparent and has conductivity.

[0185] Examples of such a material are:

[0186] (i) titanium oxide doped with at least one selected from the group consisting of lithium, magnesium, niobium, and fluorine,

[0187] (ii) gallium oxide doped with at least one selected from the group consisting of tin and silicon,

[0188] (iii) gallium nitride doped with at least one selected from the group consisting of silicon and oxygen,

[0189] (iv) indium-tin composite oxide,

[0190] (v) tin oxide doped with at least one selected from the group consisting of antimony and fluorine,

[0191] (vi) zinc oxide doped with at least one of boron, aluminum, gallium, indium, or

[0192] (vii) a composite thereof.

[0193] The electrode having light-transmitting property can be formed using an opaque material provided with a light-transmissive pattern. Examples of the light-transmissive pattern are a linear pattern, a wavy line pattern, a lattice pattern, or a pattern of a punched metal in which a plurality of fine through-holes are regularly or irregularly arranged. If the electrode having light-transmitting property has such a pattern, light can be transmitted through a portion where the electrode material is not present. Examples of the opaque material are platinum, gold, silver, copper, aluminum, rhodium, indium, titanium, iron, nickel, tin, zinc, or an alloy containing any of them. A carbon material having electrical conductivity can also be used as the opaque material.

[0194] The transmittance of light with respect to the second electrode 8 can be 50% or more, or 80% or more. The wavelength of light transmitted through the second electrode 8 depends on the absorption wavelength of the second photoelectric conversion layer 7 and the first photoelectric conversion layer 3. The thickness of the second electrode 8 is, for example, in the range of 1 nm to 1000 nm.

[0195] (Action effect of solar cell 200)

[0196] Next, a basic action effect of the solar cell 200 will be described. In the solar cell 200, at least one selected from the group consisting of the second electrode 8 and the first electrode 6 has light-transmitting property. In the case where the first electrode 6 has light-transmitting property, in the solar cell 200, for example, light is incident into the solar cell 200 from the surface of the first electrode 6. If light is irradiated onto the solar cell 200, the first photoelectric conversion layer 3 absorbs the light, generating excited electrons and holes. The excited electrons move to the electron transport layer 2. On the other hand, the holes generated in the first photoelectric conversion layer 3 move to the hole transport layer 4. Further, light not absorbed by the first photoelectric conversion layer 3 passes through the electron transport layer 2 and the substrate 1, and is absorbed by the second photoelectric conversion layer 7. The second photoelectric conversion layer 7 absorbs the light, generating excited electrons and holes. The excited electrons move to the second electrode 8. On the other hand, the holes generated in the second photoelectric conversion layer 7 move to the substrate 1. The electrons moving from the first photoelectric conversion layer 3 to the substrate 1 and the holes moving from the second photoelectric conversion layer 7 to the substrate 1 recombine in the substrate 1. Electric current is extracted from the second electrode 8 and the first electrode 6 which function as a negative electrode and a positive electrode, respectively.

[0197] (One example of a method for manufacturing solar cell 200)

[0198] The solar cell 100 can be manufactured, for example, by the following method.

[0199] First, as the second photoelectric conversion layer 7, for example, an n-type silicon single crystal having a concavo-convex structure on one main surface (i.e., a main surface corresponding to the second main surface 7b) is prepared. Then, on the first main surface 7a of the second photoelectric conversion layer 7, a second electrode 8 is formed using a sputtering method or vacuum heat evaporation. On the second main surface 7b of the second photoelectric conversion layer 7, a substrate 1 functioning as a recombination layer is formed using a sputtering method or vacuum heat evaporation method. Then, on the second main surface 1b of the substrate 1, an electron transport layer 2 is formed using a sputtering method or spray pyrolysis method. On the electron transport layer 2, a first photoelectric conversion layer 3 is formed using a coating method such as a spin coating method, a die coating method, or an inkjet method. On the first photoelectric conversion layer 3, a hole transport layer 4 is formed using a coating method such as a spin coating method, a die coating method, or an inkjet method. On the hole transport layer 4, a cover layer 5 is formed by vacuum heat evaporation method. Finally, on the cover layer 5, a first electrode 6 is formed by a sputtering method.

[0200] The solar cell 200 of the second embodiment has two photoelectric conversion layers. That is, the solar cell 200 is a two-layered stacked solar cell in which two solar cells are joined. However, the number of joined solar cells is not limited to two, and three or more solar cells can be joined to each other.

[0201] (Example)

[0202] The present application is described in more detail with reference to the following examples.

[0203] (Example 1)

[0204] In Example 1, the solar cell 100 shown in FIG. 1 was produced as follows. Each element of the solar cell 100 of Example 1 is as follows.

[0205] Substrate 1: A silicon substrate having a 2.0-μm textured surface (i.e., the average of the height difference between the convex portions and the concave portions of the textured surface is 2.0 μm. Sometimes described as "2.0-μm texture.") on which a tin-doped indium oxide layer is formed

[0206] Electron transport layer 2: TiO2 layer (thickness: 15 nm)

[0207] First photoelectric conversion layer 3: Layer mainly containing CH(NH2)2PbI3 as a perovskite compound

[0208] Hole transport layer 4: Layer containing PTAA (wherein LiN(SO2CF3)2 and 4-tert-butylpyridine (hereinafter, referred to as "t-BP") are contained as an additive and a solvent, respectively)

[0209] Cover layer 5: Molybdenum oxide layer (thickness: 10 nm)

[0210] First electrode 6: Tin-doped indium oxide layer (thickness: 200 nm)

[0211] The following shows a specific production method.

[0212] First, as the substrate 1, a silicon substrate having a texture size of 2.0 μm with a tin-doped indium oxide layer formed on the surface was prepared.

[0213] Next, on the tin-doped indium oxide layer of the substrate 1, a TiO2 film having a thickness of 15 nm was formed as the electron transport layer 2 by a sputtering method.

[0214] Next, on the electron transport layer 2, the first raw material solution was applied by spin coating to form the first photoelectric conversion layer 3. The first raw material solution was a solution containing 0.92 mol / L of PbI2(Tokyo Chemical Industry Co., Ltd.), 0.17 mol / L of PbBr2(Tokyo Chemical Industry Co., Ltd.), 0.83 mol / L of formamidinium iodide (GreatCell Solar) (hereinafter, referred to as "FAI"), 0.17 mol / L of methylammonium bromide (GreatCell Solar) (hereinafter, referred to as "MABr"), and 0.05 mol / L of CsI(Iwai Chemical Industry Co., Ltd.). The solvent of the solution was a mixture of dimethyl sulfoxide (acros) and N,N-dimethylformamide (acros). The mixing ratio of dimethyl sulfoxide and N,N-dimethylformamide in the first raw material solution (dimethyl sulfoxide:N,N-dimethylformamide) was 1:4 (volume ratio).

[0215] Next, on the first photoelectric conversion layer 3, the second raw material solution was applied by spin coating to form the hole transport layer 4. The second raw material solution was a toluene (acros) solution containing 10 mg of PTAA (Aldrich), 5 μL of t-BP (Aldrich), and 4 μL of a LiN(SO2CF3)2(Tokyo Chemical Industry Co., Ltd.) acetonitrile solution (concentration: 1.8 mol / L) in 1 mL.

[0216] Next, on the hole transport layer 4, a layer of molybdenum oxide having a thickness of 10 nm was formed by vacuum evaporation under a vacuum degree of 1.5 x 10 -5 Pa. The molybdenum oxide layer functions as the cover layer 5.

[0217] Finally, on the cover layer 5, a tin-doped indium oxide layer having a thickness of 200 nm was deposited by a sputtering method. The tin-doped indium oxide layer functions as the first electrode 6. The sputtering was performed using an In2O3 target containing 10 wt% SnO2 at a back pressure of 3.8 x 10 -4 Pa, a substrate-target distance of 100 mm, a substrate temperature of room temperature, a power of 60 W, a pressure of 0.5 Pa, and an oxygen concentration of 1%.

[0218] By operating like this, the solar cell 100 of Example 1 was obtained. Note that in the above procedure, the procedure of the first electrode 6 was performed in a dry room under a dry atmosphere having a dew point of -40°C or less.

[0219] (Example 2)

[0220] A solar cell was produced by the same method as in Example 1, except for the following.

[0221] (i) As the substrate 1, a silicon substrate having a 0.6-μm textured surface (i.e., the average of the height difference between the convex portions and the concave portions of the textured surface was 0.6 μm. Sometimes written as "0.6-μm texture.") on which a tin-doped indium oxide layer was formed on the surface was prepared.

[0222] (Example 3)

[0223] A solar cell was produced by the same method as in Example 1, except for the following.

[0224] (i) As the cover layer 5, instead of molybdenum oxide, tungsten oxide having a thickness of 10 nm was formed by vacuum evaporation.

[0225] (Example 4)

[0226] A solar cell was produced by the same method as in Example 1, except for the following.

[0227] (i) As the substrate 1, a silicon substrate having a 0.6-μm textured surface (i.e., the average of the height difference between the convex portions and the concave portions of the textured surface was 0.6 μm. Sometimes written as "0.6-μm texture.") on which a tin-doped indium oxide layer was formed on the surface was prepared.

[0228] (ii) As the cover layer 5, instead of molybdenum oxide, tungsten oxide having a thickness of 10 nm was formed by vacuum evaporation.

[0229] (Comparative Example 1)

[0230] A solar cell was produced by the same method as in Example 1, except for the following.

[0231] (i) The cover layer 5 was not formed.

[0232] (Comparative Example 2)

[0233] A solar cell was produced by the same method as in Example 1, except for the following.

[0234] (i) As the substrate 1, a 0.6-μm textured surface (i.e., the average of the height difference between the convex portions and the concave portions of the textured surface was 0.6 μm) of a silicon substrate on which a tin-doped indium oxide layer was formed on the surface was prepared.

[0235] (ii) The overcoat layer 5 was not formed.

[0236] (Comparative Example 3)

[0237] A solar cell was produced by the same method as in Example 1, except for the following.

[0238] (i) As the overcoat layer 5, instead of the molybdenum oxide, a copper phthalocyanine having a thickness of 10 nm was formed by vacuum evaporation.

[0239] (Reference Example 1)

[0240] A solar cell was produced by the same method as in Example 1, except for the following.

[0241] (i) As the substrate 1, a flat glass substrate (purchased from GEOMATEC Corporation) on which a tin-doped indium oxide layer was formed on the surface was prepared.

[0242] (Reference Example 2)

[0243] A solar cell was produced by the same method as in Example 1, except for the following.

[0244] (i) As the substrate 1, a flat glass substrate (purchased from GEOMATEC Corporation) on which a tin-doped indium oxide layer was formed on the surface was prepared.

[0245] (ii) As the overcoat layer 5, instead of the molybdenum oxide, a silicon dioxide having a thickness of 10 nm was formed by a sputtering method.

[0246] (Evaluation of the cross-sectional structure of the solar cell)

[0247] The cross-sectional structure of the solar cell of Example 1 was evaluated. The cross-sectional structure of the solar cell of Example 1 produced was thinned and processed by a focused ion beam processing device (NX5000 manufactured by Hitachi High-Tech Science Corporation). Then, the cross-section of the solar cell of Example 1 was analyzed by STEM (JEM-F200 manufactured by JEOL Ltd.). In the observation, an electron beam having an acceleration voltage of 200 kV was used. Figure 4A is a dark-field STEM image of the cross-section of the solar cell of Example 1. Figure 4B is a bright-field STEM image of the cross-section of the solar cell of Example 1. As Figure 4A and Figure 4BAs shown in FIG. 1, the two main surfaces of the electron transport layer 2 have a concave-convex structure following the shape of the concave-convex structure of the surface of the substrate 1. The first photoelectric conversion layer 3 formed on the electron transport layer 2 does not completely cover the electron transport layer 2. The region of the second main surface 2b of the electron transport layer 2 including the apexes of the convex portions is a first region which is not covered by the first photoelectric conversion layer 3. The cover layer 5 covers the first region of the second main surface 2b of the electron transport layer 2. The cover layer 5 also covers the first photoelectric conversion layer 3 and the hole transport layer 4.

[0248] (Map images of various elements obtained from cross-sectional STEM images)

[0249] For obtaining the map images of the elements, an energy dispersive X-ray spectrometer attached to a scanning transmission electron microscope (JED 2300T) was used. The results are shown in FIG. 6. Figure 5

[0250] (Measurement of solar cell characteristics (voltage))

[0251] The open-circuit voltage of the solar cells of Examples 1 to 4, Comparative Examples 1 to 3, Reference Example 1 and Reference Example 2 was evaluated by a solar simulator (manufactured by BAS, ALS440B). The evaluation was performed using a pseudo sunlight having an illuminance of 100 mW / cm 2 .

[0252] Table 1

[0253]

[0254] (Investigation of experimental results)

[0255] ​The solar cells of Embodiments 1 to 4, which have the first photoelectric conversion layer 3 on the surface having the uneven structure by using the substrate 1 having the uneven structure, and which have the cover layer 5 containing molybdenum oxide or tungsten oxide, showed a high open-circuit voltage compared with the solar cells of Comparative Examples 1 and 2 not having the cover layer 5. Note that the solar cell of Comparative Example 3 has the cover layer 5, but the cover layer 5 does not contain at least one selected from the group consisting of tungsten oxide, molybdenum oxide, copper oxide, nickel oxide, and vanadium oxide, and is formed of copper phthalocyanine. Therefore, the solar cell of Comparative Example 3 has a lower open-circuit voltage than the solar cells of Embodiments 1 to 4. In the solar cells of Reference Examples 1 and 2, the first photoelectric conversion layer 3 is not provided on the surface having the uneven structure because a flat substrate 1 is used. However, it is confirmed from the results of these Reference Examples 1 and 2 that the open-circuit voltage differs depending on the material of the cover layer 5. It is confirmed from the comparison of the solar cells of Reference Examples 1 and 2 that, in the configuration in which the cover layer 5 is provided, the solar cell having the cover layer 5 formed of molybdenum oxide has a much higher open-circuit voltage than the solar cell having the cover layer 5 formed of silicon dioxide having no hole-transporting property.

[0256] As shown in the cross-sectional STEM images of Figure 4A and 4B , it is found that in the region including the apex of the unevenness, the electron-transporting layer 2 provided on the substrate 1 is prevented from contacting the first electrode 6 by the cover layer 5.

[0257] Figure 5 The mapping images of various elements obtained from the cross-sectional STEM images of Figure 4A (from the upper left of Figure 5 , the entire STEM image, C, O, Si, Ti. Next, from the lower left of Figure 5 , Mo, In, Sn, Pb) are shown. The mapping images of C and Pb correspond to the first photoelectric conversion layer 3. The mapping image of Si corresponds to the substrate 1. The mapping image of Ti corresponds to the electron-transporting layer 2. The mapping images of In and Sn correspond to the first electrode 6.

[0258] In the region (indicated by the dotted circle) of the substrate 1 including the apex of the convex portion of the uneven structure, Figure 5 Figure 5 , Ti element originating from TiO2 of the electron-transporting layer 2 and Mo element originating from molybdenum oxide of the cover layer 5 are observed. The molybdenum oxide of the cover layer 5 covers TiO2 of the electron-transporting layer 2 on ITO of the substrate 1, and prevents contact with the first electrode 6.

[0259] Industrial applicability

[0260] The solar cell of the present application is useful, for example, as a solar cell integrated with a building material.

[0261] Explanation of symbols

[0262] 1 substrate

[0263] 2 electron transport layer

[0264] 3 first photoelectric conversion layer

[0265] 4 hole transport layer

[0266] 5 cover layer

[0267] 6 first electrode

[0268] 7 second photoelectric conversion layer

[0269] 8 second electrode

[0270] 21 first region

[0271] 22 second region

[0272] 100, 200 solar cell

Claims

1. A solar cell comprising: a substrate, a first electrode, an electron transport layer, a first photoelectric conversion layer, a hole transport layer, and a cover layer, the first photoelectric conversion layer being provided between the first electrode and the substrate, the hole transport layer being provided between the first photoelectric conversion layer and the first electrode, the substrate having a first main surface and a second main surface, the second main surface of the substrate having a concavo-convex structure, the electron transport layer having a first main surface and a second main surface, the first main surface and the second main surface of the electron transport layer having a concavo-convex structure, the first photoelectric conversion layer having a first main surface and a second main surface, the second main surface of the substrate facing the first main surface of the electron transport layer, the second main surface of the electron transport layer facing the first main surface of the first photoelectric conversion layer, the second main surface of the electron transport layer having a first region not covered by the first photoelectric conversion layer and a second region covered by the first photoelectric conversion layer, the first photoelectric conversion layer containing a perovskite compound, the first region being covered by and in contact with the cover layer, the cover layer containing an oxide semiconductor, the hole transport layer containing poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], the oxide semiconductor being at least one selected from the group consisting of tungsten oxide, molybdenum oxide, copper oxide, nickel oxide, and vanadium oxide, the oxide semiconductor being at least one selected from the group consisting of tungsten oxide and molybdenum oxide, the first region including apexes of convex portions in the concavo-convex structure of the second main surface of the electron transport layer, the second region including bottoms of concave portions in the concavo-convex structure of the second main surface of the electron transport layer, the cover layer having a thickness of 5 nm to 40 nm, the first photoelectric conversion layer and the hole transport layer being provided in this order on the second region, the first photoelectric conversion layer, the hole transport layer, and the cover layer being provided in this order on the second region, the solar cell further comprising a second electrode and a second photoelectric conversion layer, the second photoelectric conversion layer being provided between the first main surface of the substrate and the second electrode, the second photoelectric conversion layer containing silicon, the second photoelectric conversion layer having a first main surface and a second main surface, the second main surface of the second photoelectric conversion layer having a concavo-convex structure, the second main surface of the second photoelectric conversion layer facing the first main surface of the substrate, the electron transport layer containing TiO2.

2. The solar cell according to claim 1, wherein the oxide semiconductor is at least one selected from the group consisting of tungsten oxide and molybdenum oxide.

3. The solar cell according to claim 1, wherein the oxide semiconductor is at least one selected from the group consisting of tungsten oxide and molybdenum oxide.

4. The solar cell according to claim 1, wherein the first region includes apexes of convex portions in the concavo-convex structure of the second main surface of the electron transport layer.

5. The solar cell according to claim 1, wherein the second region includes bottoms of concave portions in the concavo-convex structure of the second main surface of the electron transport layer.

6. The solar cell according to claim 1, wherein the cover layer has a thickness of 5 nm to 40 nm.

7. The solar cell according to claim 1, wherein the first photoelectric conversion layer and the hole transport layer are provided in this order on the second region.

8. The solar cell according to claim 1, wherein the first photoelectric conversion layer, the hole transport layer, and the cover layer are provided in this order on the second region.

9. The solar cell according to claim 1, further comprising a second electrode and a second photoelectric conversion layer, the second photoelectric conversion layer being provided between the first main surface of the substrate and the second electrode.

10. The solar cell according to claim 9, wherein the second photoelectric conversion layer contains silicon.

11. The solar cell according to claim 9, wherein the second photoelectric conversion layer has a first main surface and a second main surface, the second main surface of the second photoelectric conversion layer has a concavo-convex structure, and the second main surface of the second photoelectric conversion layer faces the first main surface of the substrate.

12. The solar cell according to claim 9, wherein the electron transport layer contains TiO2. ​ ​ ​ ​ ​ ​ ​ 2. The solar cell of claim 1, wherein, ​ 3. The solar cell of claim 2, wherein, ​ 4. The solar cell of claim 1, wherein, ​ 5. The solar cell according to any one of claims 1 to 4, wherein ​ 6. The solar cell of claim 1, wherein, ​ 7. The solar cell of claim 1, wherein, ​ 8. The solar cell of claim 7, wherein, ​ ​ ​ 10. The solar cell of claim 9, wherein, ​ 11. The solar cell according to claim 9 or 10, wherein ​ ​ ​ 12. The solar cell of claim 1, wherein, ​

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