Solar cell

Abstract

To provide a solar cell having improved photoelectric conversion efficiency.SOLUTION: A solar cell 100 includes a first cell 100A having a first light-absorbing layer 110, and a second cell 100B arranged on a light-receiving surface side of the first cell 100A and having a second light-absorbing layer 120 having a wider band gap than that of the first light-absorbing layer 110, in which the second light-absorbing layer 120 is provided with openings 122 penetrating the second light-absorbing layer 120, the openings 122 are dispersed over the entire second cell 100B, and an opening ratio OR of the openings 122 is 1% or more and 55% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a solar cell. [Background technology]

[0002] In recent years, there has been a strong demand for solar cells with higher photoelectric conversion efficiency. However, when a single-layer solar cell is used, the theoretical limit efficiency is about 30%, and the conversion efficiency of existing solar cells is approaching its limit. Therefore, tandem technology, which stacks multiple solar cells and raises the theoretical limit efficiency to 40% or more, has attracted attention.

[0003] For example, Patent Document 1 reports a two-terminal tandem solar cell in which a top cell on the light-receiving surface side and a bottom cell on the opposite side to the light-receiving surface are connected in series, with a perovskite solar cell being used for the top cell and a crystalline silicon solar cell or a chalcopyrite solar cell being used for the bottom cell. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6263186 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the solar cell described in Patent Document 1 is unable to fully utilize sunlight, and there is a demand for further improvement in photoelectric conversion efficiency.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solar cell with improved photoelectric conversion efficiency. [Means for solving the problem]

[0007] A solar cell according to one embodiment of the present invention includes a first cell having a first light absorbing layer, and a second cell arranged on the light receiving surface side of the first cell and having a second light absorbing layer having a wider band gap than the first light absorbing layer, the second light absorbing layer having openings penetrating the second light absorbing layer, the openings being dispersed throughout the second cell, and an aperture ratio of the openings being 1% or more and 55% or less.

[0008] In the solar cell according to one aspect of the present invention, the light transmittance of the second cell for light of a wavelength corresponding to the band gap of the first light absorbing layer is improved, and the amount of light absorbed by the second light absorbing layer is increased. This increases the short-circuit current density of the first cell, i.e., the photocurrent, and improves the photoelectric conversion efficiency of the entire solar cell. By setting the aperture ratio of the openings in the second light absorbing layer to 1% or more, the amount of light passing through the second cell and absorbed by the first light absorbing layer can be effectively increased. By setting the aperture ratio of the openings in the second light absorbing layer to 55% or less, excessive reduction in the amount of light absorbed in the second light absorbing layer can be suppressed. Since the openings are distributed throughout the second cell, it is possible to reduce unevenness in the amount of light in the in-plane direction of the light receiving surface in each of the first light absorbing layer and the second light absorbing layer, and to suppress unevenness in the photocurrent in the in-plane direction of the light receiving surface in each of the first cell and the second cell. Effect of the Invention

[0009] According to the present invention, it is possible to provide a solar cell with improved photoelectric conversion efficiency. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram showing an example of a cross-sectional structure of a solar cell according to a first embodiment. [Diagram 2] 4 is a diagram showing an example of a cross-sectional structure of a second light absorbing layer. FIG. [Diagram 3] FIG. 4 is a diagram showing an example of a planar structure of a second light absorbing layer. [Figure 4] 13 is a graph showing the performance of a comparative example. [Diagram 5] 4 is a graph showing the performance of the first embodiment. [Figure 6] 13 is a graph showing the performance of the first example and the comparative example at the summer solstice. [Figure 7] 11 is a graph showing the performance of the first example and the comparative example at the winter solstice. [Figure 8] FIG. 11 is a diagram showing an example of a cross-sectional structure of a second light absorbing layer according to a second embodiment. [Figure 9] 13 is a graph showing the performance of the second embodiment. [Figure 10] 13 is a diagram showing an example of a cross-sectional structure of a second light absorbing layer according to a third embodiment. FIG. [Figure 11] 13 is a diagram showing an example of a cross-sectional structure of a solar cell according to a fourth embodiment. FIG. [Figure 12] FIG. 13 is a diagram showing an example of a planar structure of a second light absorbing layer according to the fifth embodiment. [Figure 13] 1 is a graph showing the relationship between aperture ratio and photoelectric conversion efficiency. [Figure 14] 1 is a graph showing the relationship between aperture ratio and photoelectric conversion efficiency. [Figure 15] 1 is a graph showing the relationship between aperture ratio and photoelectric conversion efficiency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The following describes the embodiments of the present invention. In the following description of the drawings, the same or similar components are denoted by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic, and the technical scope of the present invention should not be interpreted as being limited to the embodiments.

[0012] In addition, in order to explain the positional relationships and the movement directions, etc., each figure may be conveniently illustrated with an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. The directions parallel to the X-axis, the Y-axis, and the Z-axis, respectively, are the X-axis direction, the Y-axis direction, and the Z-axis direction. The positive direction of the Z axis is the light receiving surface side.

[0013] First Embodiment First, the configuration of a solar cell 100 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the cross-sectional structure of the solar cell according to the first embodiment.

[0014] As shown in FIG. 1, the solar cell 100 is a two-terminal tandem solar cell in which a bottom cell 100A and a top cell 100B are connected in series. The bottom cell 100A and the top cell 100B are solar cells that convert light of different wavelengths into electricity. The top cell 100B is stacked on the light receiving surface side of the bottom cell 100A, and the bottom cell 100A and the top cell 100B are joined to each other. The absorption band of the bottom cell 100A is preferably located on the longer wavelength side than the absorption band of the top cell 100B. The bottom cell 100A corresponds to an example of a first cell, and the top cell 100B corresponds to an example of a second cell.

[0015] In this embodiment, a two-terminal tandem solar cell has been described as an example of one aspect of the present invention, but the embodiment of the present invention is not limited thereto. The solar cell according to one embodiment of the present invention may be a four-terminal tandem solar cell or a three-terminal tandem solar cell, which will be described later. The solar cell according to one embodiment of the present invention may be a multi-junction solar cell in which three or more solar cells each having a different absorption band are stacked and joined in the direction of incidence of sunlight. In the case of such a multi-junction solar cell, it is sufficient that an opening, which will be described later, penetrating the light absorption layer is formed in the light absorption layer of at least one cell provided on the light receiving surface side of the bottom cell. For example, in the case of a three-layer solar cell including a top cell, a middle cell, and a top cell, it is sufficient that an opening, which will be described later, is formed in at least one of the light absorption layers of the middle cell and the top cell.

[0016] The solar cell 100 has a substrate 101, a first electrode layer 102, a first hole transport layer 103, a first light absorption layer 110, a first electron transport layer 104, a second electrode layer 105, a second hole transport layer 106, a second light absorption layer 120, a second electron transport layer 107, a third electrode layer 108, and a grid electrode 109.

[0017] The first electrode layer 102 is provided on the substrate 101, the first hole transport layer 103 is provided on the first electrode layer 102, the first light absorption layer 110 is provided on the first hole transport layer 103, the first electron transport layer 104 is provided on the first light absorption layer 110, the second electrode layer 105 is provided on the first electron transport layer 104, the second hole transport layer 106 is provided on the second electrode layer 105, the second light absorption layer 120 is provided on the second hole transport layer 106, the second electron transport layer 107 is provided on the second light absorption layer 120, the third electrode layer 108 is provided on the second electron transport layer 107, and the grid electrode 109 is provided on the third electrode layer 108. The solar cell 100 receives light from the grid electrode 109 side to generate electricity. The solar cell 100 outputs a current from two terminals, the first electrode layer 102 and the grid electrode 109.

[0018] The first electrode layer 102 is the positive electrode of the bottom cell 100A, the first hole transport layer 103 is the hole transport layer of the bottom cell 100A, the first light absorption layer 110 is the light absorption layer of the bottom cell 100A, the first electron transport layer 104 is the electron transport layer of the bottom cell 100A, the second electrode layer 105 is the negative electrode of the bottom cell 100A and the positive electrode of the top cell 100B, the second hole transport layer 106 is the hole transport layer of the top cell 100B, the second light absorption layer 120 is the light absorption layer of the top cell 100B, the second electron transport layer 107 is the electron transport layer of the top cell 100B, and the third electrode layer 108 is the negative electrode of the top cell 100B.

[0019] (substrate) The substrate 101 is provided, for example, to support and handle the solar cell 100. The substrate 101 is provided, for example, by a glass substrate such as soda glass, low-alkali glass or non-alkali glass, a metal substrate such as stainless steel, aluminum or titanium, or a resin substrate such as polyimide or epoxy. The thickness of the substrate 101 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 20 μm or more and 250 μm or less, and more preferably 30 μm or more and 100 μm or less. When the thickness of the substrate 107 is within the above range, the solar cell tends to be lighter and more flexible.

[0020] (electrode layer) The first electrode layer 102 extracts a current caused by holes generated in the first light absorption layer 110. The material of the first electrode layer 102 is, for example, a metal material such as molybdenum (Mo), chromium (Cr), or titanium (Ti). The thickness of the first electrode layer 102 is, for example, 200 nm or more and 800 nm or less, and preferably 300 nm or more and 700 nm or less. By setting the thickness of the first electrode layer 102 within the above range, it is possible to make the solar cell lighter and more flexible while sufficiently extracting the current without loss.

[0021] When substrate 101 is a metal substrate, substrate 101 may function as the lower electrode of bottom cell 100A, and first electrode layer 102 may be omitted.

[0022] The material of the first electrode layer 102 is not limited to a metal material. The material of the first electrode layer 102 may be a conductive inorganic compound such as a conductive ceramic, or a conductive organic compound such as a conductive resin. However, from the viewpoint of reflecting sunlight and absorbing the reflected light in the first light absorption layer 110 and the second light absorption layer 120 to improve the conversion efficiency of the solar cell 100, it is preferable that either the substrate 101 or the first electrode layer 102 is made of a metal material with high reflectivity.

[0023] The second electrode layer 105 extracts a current due to electrons generated in the first light absorbing layer 110, and extracts a current due to holes generated in the second light absorbing layer 120. The second electrode layer 105 also electrically connects the bottom cell 100A and the top cell 100B in series. The third electrode layer 108 extracts a current due to electrons generated in the second light absorbing layer 120.

[0024] In the solar cell 100, the second light absorbing layer 120 absorbs the light that has passed through the third electrode layer 108, so in order to increase the amount of light absorbed in the second light absorbing layer 120, it is preferable that the third electrode layer 108 is a transparent electrode layer. Also, the first light absorbing layer 110 absorbs the light that has passed through the second electrode layer 105, so in order to increase the amount of light absorbed in the first light absorbing layer 110, it is preferable that the second electrode layer 105 is a transparent electrode. A transparent electrode is an electrode made of a material that has both high electrical conductivity and high visible light transmittance. There is no particular limitation on the high electrical conductivity, but it is preferable that the high electrical conductivity is, for example, a material having a specific resistance of 5.0×10 -3 It means that the transmittance is Ωcm or less. Although there is no particular limitation, high visible light transmittance means, for example, that the average transmittance in the wavelength region of 400 to 1300 nm is 80% or more. As the material for the transparent electrode, a known material can be used, and examples thereof include indium tin oxide (ITO), hydrogen-containing indium oxide (IOH), fluorine-containing tin oxide (FTO), boron-containing zinc oxide (ZnO:B), and aluminum-containing zinc oxide (ZnO:Al).

[0025] When the second electrode layer 105 is a transparent electrode, the content of the above-mentioned material is not particularly limited as long as the second electrode layer 105 functions as a transparent electrode. More specifically, although not particularly limited, the content of the above-mentioned material is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, more preferably 70% by mass or more and 100% by mass or less, more preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and more preferably 95% by mass or more and 100% by mass or less, based on the total mass of the second electrode layer 105. The same applies to the content of the above-mentioned material when the third electrode layer 108 is a transparent electrode.

[0026] For example, the thickness of the second electrode layer 105 is 0.1 μm or more and 0.3 μm or less, and the thickness of the third electrode layer 108 is 0.1 μm or more and 1.5 μm or less, but is not limited thereto. The thickness of the second electrode layer 105 is preferably 0.01 μm or more and 3.0 μm or less, more preferably 0.02 μm or more and 2.5 μm or less, more preferably 0.04 μm or more and 2.0 μm or less, more preferably 0.1 μm or more and 1.5 μm or less, more preferably 0.1 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.5 μm or less, and more preferably 0.1 μm or more and 0.3 μm or less. By having the thickness of the second electrode layer 105 within the above range, the solar cell tends to be lighter and more flexible while sufficiently extracting current without loss. The same applies to the thickness of the third electrode layer 108.

[0027] The materials of the second electrode layer 105 and the third electrode layer 108 may be the same or different. The thicknesses of the second electrode layer 105 and the third electrode layer 108 may be the same or different.

[0028] (Hole transport layer) The first hole transport layer 103 efficiently extracts holes generated in the first light absorbing layer 110 from the first light absorbing layer 110, and suppresses recombination of electrons and holes in the first light absorbing layer 110. The second hole transport layer 106 efficiently extracts holes generated in the second light absorbing layer 120 from the second light absorbing layer 120, and suppresses recombination of electrons and holes in the second light absorbing layer 120.

[0029] The material of the first hole transport layer 103 and the second hole transport layer 106 is preferably a p-type semiconductor. The substance contained in the p-type semiconductor is not particularly limited, but examples thereof include organic compounds such as polythiophene derivatives such as poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS), poly(3-hexylthiophene) (P3HT), and poly(3-octylthiophene) (P3OT), fluorene derivatives such as 2,2'-7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeO-TAD), carbazole derivatives such as polyvinylcarbazole, triphenylamine derivatives, diphenylamine derivatives, polysilane derivatives, and polyaniline derivatives, as well as inorganic compounds such as nickel oxide, molybdenum oxide, copper gallium oxide, copper aluminum oxide, molybdenum selenide, molybdenum sulfide selenide, and zinc telluride. The p-type semiconductor used in the first hole transport layer 103 and the second hole transport layer 106 may be of one type alone or may be of two or more types.

[0030] The first hole transport layer 103 and the second hole transport layer 106 are preferably substantially composed of the above-mentioned organic compounds or inorganic compounds, and more preferably are the above-mentioned organic compounds or inorganic compounds. The content of the above-mentioned organic compounds or inorganic compounds in the first hole transport layer 103 is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and even more preferably 99% by mass or more and 100% by mass or less, based on the total amount of the first hole transport layer 103. The content of the above-mentioned organic compounds or inorganic compounds in the second hole transport layer 106 is similar.

[0031] For example, the thickness of the first hole transport layer 103 is 10 nm or more and 50 nm or less, and the thickness of the second hole transport layer 106 is 5 nm or more and 20 nm or less, but is not limited thereto. The thickness of the first hole transport layer 103 is preferably 5 nm or more and 100 nm or less, more preferably 15 nm or more and 80 nm or less, and even more preferably 20 nm or more and 60 nm or less. By setting the thickness of the first hole transport layer 103 within the above range, it tends to be possible to efficiently extract holes generated in the first light absorption layer 110 from the first light absorption layer 110, while making the solar cell lighter and more flexible. The same applies to the thickness of the second hole transport layer 106.

[0032] The materials of the first hole transport layer 103 and the second hole transport layer 106 may be the same or different. The thicknesses of the first hole transport layer 103 and the second hole transport layer 106 may be the same or different. At least one of the first hole transport layer 103 and the second hole transport layer 106 may be omitted.

[0033] (Light absorbing layer) The first light absorbing layer 110 and the second light absorbing layer 120 absorb light such as near infrared light, visible light, and ultraviolet light to generate electrons and holes. The band gap of the first light absorbing layer 110 is different from the band gap of the second light absorbing layer 120. The band gap of the first light absorbing layer 110 is preferably smaller than the band gap of the second light absorbing layer 120. That is, the first light absorbing layer 110 absorbs light with a longer wavelength than the light absorbed by the second light absorbing layer 120. The light utilization efficiency of the entire solar cell 100 is improved by absorbing short-wavelength light that is easily scattered and has low transparency in the second light absorbing layer 120 close to the light receiving surface, and absorbing long-wavelength light that is difficult to scatter and has high transparency in the first light absorbing layer 110 far from the light receiving surface.

[0034] The photoelectric conversion material of the first light absorbing layer 110 and the second light absorbing layer 120 is not particularly limited, and may be, for example, a silicon-based photoelectric conversion material such as single crystal silicon, polycrystalline silicon, and amorphous silicon, a compound-based photoelectric conversion material such as a chalcopyrite compound such as CIGS, a III-V group compound such as a gallium arsenide (GaAs) compound, and a II-VI group compound such as a cadmium telluride (CaTe) compound, or an organic-based photoelectric conversion material such as an organic semiconductor, a dye-sensitized compound, and a perovskite. The photoelectric conversion material of the first light absorbing layer 110 and the second light absorbing layer 120 preferably contains, for example, a perovskite compound, a chalcopyrite compound, a kesterite compound, or a cadmium telluride compound. The photoelectric conversion material used in the first light absorbing layer 110 and the second light absorbing layer 120 may be one type alone, or two or more types.

[0035] However, in the solar cell 100, which is a two-terminal tandem solar cell, the bottom cell 100A and the top cell 100B are connected in series, so from the viewpoint of aligning the generated photocurrents and reducing current mismatch, there is a preferred combination of materials for the first light absorbing layer 110 and the second light absorbing layer 120. The material for the first light absorbing layer 110 is preferably a material having a band gap of about 1.00 eV or more and 1.15 eV or less, for example, a chalcopyrite compound having a band gap of about 1.00 eV, or crystalline silicon having a band gap of about 1.13 eV. The material for the second light absorbing layer 120 is preferably a perovskite compound, a chalcopyrite compound, or a cadmium tellurium compound having a band gap of about 1.40 eV or more and 1.70 eV or less.

[0036] A chalcopyrite compound suitable for the first light absorbing layer 110 contains a large amount of indium as a group III element and selenium as a group VI element. A perovskite compound suitable for the second light absorbing layer 120 contains a large amount of iodine as a group VII element. A chalcopyrite compound suitable for the second light absorbing layer 120 contains a large amount of indium as a group III element and sulfur as a group VI element.

[0037] The content of the photoelectric conversion material in the first light absorbing layer 110 is not particularly limited as long as the first light absorbing layer 110 has a function of absorbing light such as visible light and ultraviolet light to generate electrons and holes. More specifically, although not particularly limited, the content is 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less, relative to the total mass of the first light absorbing layer 110. The same applies to the content of the photoelectric conversion material in the second light absorbing layer 120.

[0038] For example, the thickness of the first light absorbing layer 110 is 1 μm or more and 3 μm or less, and the thickness of the second light absorbing layer 120 is 0.4 μm or more and 1 μm or less, but is not limited thereto. The thickness of the first light absorbing layer 110 is preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 4 μm or less, more preferably 0.3 μm or less and 3 μm or less, more preferably 0.4 μm or more and 2 μm or less, and more preferably 0.5 μm or more and 1 μm or less. By setting the thickness of the first light absorbing layer 110 within the above range, it tends to be possible to efficiently generate electrons and holes in the first light absorbing layer 110, while making the solar cell lighter and more flexible. The same applies to the thickness of the second light absorbing layer 120.

[0039] The first light absorbing layer 110 and the second light absorbing layer 120 may have the same thickness or may have different thicknesses.

[0040] The perovskite compound used as the photoelectric conversion material is represented by the general formula AMX 3 and those represented by the general formula A 2 MX 4 Here, M represents a divalent cation, A represents a monovalent cation, and X represents a monovalent anion.

[0041] The monovalent cation A is not particularly limited, and examples thereof include cations of Group 1 elements of the periodic table and organic cations. Among these, cesium ion, rubidium ion, ammonium ion (including amidinium ion) which may have a substituent, phosphonium ion which may have a substituent, or amidinium ion which may have a substituent are preferred. Examples of ammonium ions which may have a substituent include primary ammonium ions and secondary ammonium ions. Specific examples of ammonium ions which may have a substituent include alkylammonium ions, arylammonium ions, amidinium ions, and guanidium ions. In particular, in order to avoid steric hindrance, monoalkylammonium ions are preferred, and from the viewpoint of improving stability, it is preferred to use alkylammonium ions substituted with one or more fluorine atoms. In addition, a combination of two or more types of cations can be used as the cation A. Examples of the monovalent cation A include a methylammonium ion, a methylammonium monofluoride ion, a methylammonium difluoride ion, a methylammonium trifluoride ion, an ethylammonium ion, an isopropylammonium ion, an n-propylammonium ion, an isobutylammonium ion, an n-butylammonium ion, a t-butylammonium ion, a dimethylammonium ion, a diethylammonium ion, a phenylammonium ion, a benzylammonium ion, a phenethylammonium ion, a guanidinium ion, a formamidinium ion, an acetamidinium ion, and an imidazolium ion.

[0042] The divalent cation M is not particularly limited, and examples thereof include divalent metal cations and semimetal cations. Specific examples include cations of elements in Group 14 of the periodic table, and more specific examples include lead cations (Pb 2+ ), tin cation (Sn 2+ ), and germanium cation (Ge 2+ In addition, the cation M may be a combination of two or more kinds of cations.

[0043] The monovalent anion X is not particularly limited, and examples thereof include halide ions, acetate ions, nitrate ions, sulfate ions, borate ions, acetylacetonate ions, carbonate ions, citrate ions, sulfur ions, tellurium ions, thiocyanate ions, titanate ions, zirconate ions, 2,4-pentanedionate ions, and silicofluoride ions. X may be one type of anion or a combination of two or more types of anions. It is preferable to use a halide ion or a combination of a halide ion and another anion as X. Examples of halide ions X include chloride ions, bromide ions, and iodide ions.

[0044] The perovskite compound includes organic-inorganic perovskite compounds, particularly halide-based organic-inorganic perovskite compounds. Specific examples of perovskite compounds include CH 3 NH 3 PbI 3 , C.H. 3 NH 3 PbBr 3 , C.H. 3 NH 3 PbCl 3 , C.H. 3 NH 3 SnI 3 , C.H. 3 NH 3 SnBr 3 , C.H. 3 NH 3 SnCl 3 , C.H. 3 NH 3 PbI (3-x) Cl x , C.H. 3 NH 3 PbI (3-x) Br x , C.H. 3 NH 3 PbBr (3-x) Cl x , C.H. 3 NH 3 Pb (1-y) Sn yI 3 , C.H. 3 NH 3 Pb (1-y) Sn y Br 3 , C.H. 3 NH 3 Pb (1-y) Sn y Cl 3 , C.H. 3 NH 3 Pb (1-y) Sn y I (3-x) Cl x , C.H. 3 NH 3 Pb (1-y) Sn y I (3-x) Br x , and C.H. 3 NH 3 Pb (1-y) Sn y Br (3-x) Cl x , and CH in the above compounds 3 NH 3 Instead of CFH 2 NH 3 , C.F. 2 HNH 3 , C.F. 3 NH 3 , or NH 2 CH=NH 2 In the above formula, x is an arbitrary value of 0 or more and 3 or less, and y is an arbitrary value of 0 or more and 1 or less.

[0045] The chalcopyrite compound used as the photoelectric conversion material is preferably a compound of the I-III-VI 2 Group I-III-VI chalcopyrite compounds. 2 The group chalcopyrite compound is not particularly limited, but for example, CuAlS 2 , CuAlSe 2 , CuAlTe 2 , CuGaS 2 , CuGaSe 2 , CuGaTe 2 , CuInS 2 , CuInSe 2 , CuInTe2 , AgAlS 2 , AgAlSe 2 , AgAlTe 2 , AgGaS 2 , AgGaSe 2 , AgGaTe 2 , AgInS 2 , AgInSe 2 , AgInTe 2 , and combinations thereof. "Combinations thereof" is not particularly limited, but for example, CuGaS 2 and CuInSe 2 when combined, Cu(In x Ga 1-x )(Se y S 1-y )(0 < x < 1, 0 < y < 1) are included. Among these chalcopyrite compounds, CuGaS 2 , CuGaSe 2 , CuInS 2 , CuInSe 2 , Cu(In 2 Ga x )(Se 1-x )(Se y S 1-y )(0 < x < 1, 0 < y < 1) are preferred, and Cu(In 2 Ga x )(Se 1-x )(Se y S 1-y )(0 < x < 1, 0 < y < 1) are more preferred. In this embodiment, when referring to a CIS compound, it is a chalcopyrite compound containing Cu, In, and Se; when referring to a CIGS compound, it is a chalcopyrite compound containing Cu, In, Ga, and Se; when referring to a CIGSS compound, it is a chalcopyrite compound containing Cu, In, Ga, Se, and S. 2 (0 < x < 1, 0 < y < 1) are even more preferred. Note that in this embodiment, when referring to a kesterite compound used as a photoelectric conversion material, preferably, an I

[0046] -II-IV-VI 2 -family kesterite compound is included. I 4 -II-IV-VI 2 -family kesterite compound is included. I 4The family of kesterite compounds is not particularly limited, but for example, Cu 2 ZnSnS 4 、Cu 2 ZnSnSe 4 、Cu 2 ZnGeS 4 、Cu 2 ZnGeSe 4 、Cu 2 MnSnS 4 、Cu 2 MnSnSe 4 、Cu 2 MnGeS 4 、Cu 2 MnGeSe 4 、Ag 2 ZnSnS 4 、Ag 2 ZnSnSe 4 、Ag 2 ZnGeS 4 、Ag 2 ZnGeSe 4 、Ag 2 MnSnS 4 、Ag 2 MnSnSe 4 、Ag 2 MnGeS 4 、Ag 2 MnGeSe 4 、and combinations thereof. "Combinations thereof" is not particularly limited, but for example, when Cu 2 ZnSnS 4 and Ag 2 ZnSnSe 4 are combined, (Cu x Ag 1-x ) 2 ZnSn(S y Se 1-y ) 4 (0 < x < 1, 0 < y < 1), and when Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 are combined, Cu 2 ZnSn(S x Se 1-x ) 4 (0 < x < 1) are included. Among these kesterite compounds, Cu2 ZnSnS 4 、 Cu 2 ZnSnSe 4 、 Ag 2 ZnSnS 4 、 Ag 2 ZnSnSe 4 、 (Cu x Ag 1-x ) 2 ZnSn(S y Se 1-y ) 4 (0 < x < 1, 0 < y < 1) is preferable, and (Cu x Ag 1-x ) 2 ZnSn(S y Se 1-y ) 4 (0 < x < 1, 0 < y < 1) is more preferable. In this embodiment, when referring to the CZTS compound, it is a kesterite compound containing Cu, Zn, Sn, and S; when referring to the ACZTS compound, it is a kesterite compound containing Ag, Cu, Zn, Sn, and S; when referring to the ACZTSS compound, it is a kesterite compound containing Ag, Cu, Zn, Sn, S, and Se.

[0047] Note that the cadmium telluride compound used as the photoelectric conversion material is not particularly limited, and examples include CdTe, CdMgTe, CdZnTe, CdSe, CdMgSe, CdZnSe, CdS, CdMgS, CdZnS, and combinations thereof. "Combinations thereof" is not particularly limited, and for example, when combining CdMgTe and CdMgSe, (Cd x Mg 1-x )(Te y Se 1-y )(0 < x < 1, 0 < y < 1) is included.

[0048] (Electron transport layer) The first electron transport layer 104 efficiently extracts electrons generated in the first photoabsorbing layer 110 from the first photoabsorbing layer 110, and suppresses recombination of electrons and holes in the first photoabsorbing layer 110. The second electron transport layer 107 efficiently extracts electrons generated in the second photoabsorbing layer 120 from the second photoabsorbing layer 120, and suppresses recombination of electrons and holes in the second photoabsorbing layer 120.

[0049] The material of the first electron transport layer 104 and the second electron transport layer 107 is preferably an n-type semiconductor. The material contained in the n-type semiconductor is not particularly limited, but for example, C 60 Organic compounds such as fullerenes, phenanthroline derivatives such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine: BCP), phenylpyridine derivatives such as 4,6-bis(3,5-di-4-pyridinylphenyl)-2-methylpyrimidine (B4PymPm) and tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), as well as cadmium sulfide (CdS), indium sulfide (In 2 S 3 ), indium oxide sulfide (InOS), zinc oxide sulfide (ZnOS), zinc magnesium oxide (ZnMgO x ), zinc titanium oxide (ZnTiO x ), zinc tin oxide (ZnSnO x ), tin oxide (SnO 2 ), titanium dioxide (TiO 2 ), zinc oxide (ZnO 2 The p-type semiconductor used in the first electron transport layer 104 and the second electron transport layer 107 may be of one type alone or of two or more types.

[0050] The first electron transport layer 104 and the second electron transport layer 107 are preferably substantially composed of the above-mentioned n-type semiconductor, and more preferably are the above-mentioned n-type semiconductor. The content of the above-mentioned n-type semiconductor in the first electron transport layer 104 is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and even more preferably 99% by mass or more and 100% by mass or less, based on the total amount of the first electron transport layer 104. The content of the above-mentioned n-type semiconductor in the second electron transport layer 107 is similar.

[0051] The thickness of each of the first electron transport layer 104 and the second electron transport layer 107 is, for example, 20 nm or more and 140 nm or less, but is not limited thereto. The thickness of the first electron transport layer 104 is preferably 5 nm or more and 200 nm or less, more preferably 10 nm or more and 180 nm or less, and even more preferably 15 nm or more and 160 nm or less. By setting the thickness of the first electron transport layer 104 within the above range, it tends to be possible to efficiently extract holes generated in the first light absorption layer 110 from the first light absorption layer 110, while making the solar cell lighter and more flexible. The same applies to the thickness of the second electron transport layer 107.

[0052] The first electron transport layer 104 may be a single layer or a multilayer. Similarly, the second electron transport layer 107 may be a single layer or a multilayer. The materials of the first electron transport layer 104 and the second electron transport layer 107 may be the same or different. Furthermore, the thicknesses of the first electron transport layer 104 and the second electron transport layer 107 may be the same or different.

[0053] (Grid electrode) The grid electrode 109 is provided to extract electricity from the third electrode layer 108. The conductive material of the grid electrode 109 is not particularly limited as long as the grid electrode 109 exhibits a lower resistivity than the third electrode layer 108. The conductive material used for the grid electrode 109 is, for example, a metal such as Mo, Cr, Ag, Cu, Ni, Al, or Ti, but may also be a conductive inorganic compound or a conductive organic compound other than a metal. The conductive material used for the grid electrode 109 may be one type alone or two or more types.

[0054] The content of the conductive material in the grid electrode 109 is not particularly limited as long as the grid electrode 109 exhibits a lower resistivity than the third electrode layer 108. The content of the conductive material in the grid electrode 109 is preferably 50 mass % or more and 100 mass % or less, more preferably 60 mass % or more and 100 mass % or less, more preferably 70 mass % or more and 100 mass % or less, more preferably 80 mass % or more and 100 mass % or less, and more preferably 90 mass % or more and 100 mass % or less, based on the total mass of the grid electrode 109.

[0055] The thickness of grid electrode 109 is not particularly limited, but is, for example, 5 μm to 50 μm. When the thickness of grid electrode 109 is within the above range, it tends to be possible to make the solar cell lighter and more flexible while sufficiently extracting current without loss.

[0056] Next, the configuration of the second light absorbing layer 120 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a diagram showing an example of the cross-sectional structure of the second light absorbing layer. Fig. 3 is a diagram showing an example of the planar structure of the second light absorbing layer. Hereinafter, a cross-sectional view of a cross section intersecting with the light receiving surface as shown in Fig. 2 will be simply referred to as a "cross-sectional view". Also, a planar view from the light receiving surface side as shown in Fig. 3 will be simply referred to as a "planar view".

[0057] The second light absorbing layer 120 has an opening 122. As shown in FIG. 2, the opening 122 penetrates the second light absorbing layer 120 in the Z-axis direction intersecting with the light receiving surface. That is, the opening 122 is open on both sides of the second light absorbing layer 120, the bottom cell 100A side and the light receiving surface side. Also, as shown in FIG. 3, the opening 122 is distributed throughout the top cell 100B in the XY plane direction parallel to the light receiving surface. Here, when the ratio of the opening 122 to the second light absorbing layer 120 in a plan view is defined as the "aperture ratio CR," "the openings 122 are distributed throughout" means that the standard deviation of the aperture ratio OR within any number of 10 μm squares is within 5%. The aperture ratio OR of the opening 122 is, for example, 1% or more and 55% or less, preferably 1% or more and 70% or less, more preferably 5% or more and 60% or less, more preferably 10% or more and 60% or less, and even more preferably 15% or more and 50% or less.

[0058] A high-resistance transparent member is provided inside the opening 122. The transparent member is filled into the opening 122 without any gaps, for example. The light transmittance of the transparent member is preferably higher than that of the second light absorption layer 120 for a wavelength corresponding to the band gap of the first light absorption layer 110. The resistivity of the transparent member is also higher than that of the second light absorption layer 120, and the material of the transparent member is preferably an insulator. The refractive index of the transparent material is preferably lower than that of the second light absorption layer 120, and more preferably 2 or less. The refractive index of the transparent material is preferably closer to that of the second electron transport layer 107 than that of the second light absorption layer 120.

[0059] The material constituting the transparent member provided inside the opening 122 is, for example, zirconia (ZrO 2 ), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), yttrium oxide (Y 2 O 3 ), silicon oxide (SiO x ), calcium oxide (CaO), hafnium oxide (HfO 2), cerium oxide (CeO 2 ), cerium fluoride (CeF 3 ), lanthanum fluoride (LaF 3 ), calcium fluoride (CaF 2 ), Magnesium Fluoride (MgF 2 ) and the like, and combinations of these inorganic compounds, as well as resins such as silicone, epoxy, acrylic, polyolefin, and polyester.

[0060] The transparent member provided inside the opening 122 may extend outside the opening 122, but it is preferable that the upper base 121B of the convex portion 121 is exposed from the transparent member. From the viewpoint of suppressing the generation of a gap between the transparent member and the second light absorbing layer 120 due to thermal history, the thermal expansion coefficient of the transparent member is preferably closer to the thermal expansion coefficient of the second light absorbing layer 120 than the thermal expansion coefficient of the substrate 101, the second electrode layer 105, the third electrode layer 108, or the grid electrode 109.

[0061] As shown in FIG. 3, the openings 122 are provided in a lattice pattern, and the second light absorbing layer 120 has a plurality of convex portions 121 partitioned by the openings 122. The plurality of convex portions 121 are spaced apart from one another and surrounded by the openings 122. As shown in FIG. 3, the shape of the convex portion 121 when viewed in a plan view (hereinafter referred to as a "planar shape") is a square shape. As shown in FIG. 2, the shape of the convex portion 121 when viewed in a cross section (hereinafter referred to as a "cross-sectional shape") is a trapezoid. That is, the shape of the convex portion 121 is a quadrangular pyramid truncated shape with a square planar shape. When the "columnar degree CR" is used as an index showing how close the convex portion 121 is to a columnar shape, the columnar degree CR of the convex portion 121 that is a quadrangular pyramid truncated shape is not particularly limited, and is, for example, 1% to 99%, 5% to 90%, 10% to 80%, 15% to 70%, 20% to 60%, and 25% to 50%. It should be noted that the columnar degree CR is such that a columnar shape is obtained when it is 100% and a pyramidal shape is obtained when it is 0%.

[0062] In the plan view shown in FIG. 3, the multiple protrusions 121 are periodically provided in the X-axis direction and the Y-axis direction, and are arranged in a matrix. Each protrusion 121 has a pair of sides extending parallel to the X-axis direction and a pair of sides extending parallel to the Y-axis direction. The sides extending in the X-axis direction of each of the multiple protrusions 121 are parallel to each other, and the sides extending in the Y-axis direction of each of the multiple protrusions 121 are parallel to each other. Two protrusions 121 that are arranged closest to each other among the multiple protrusions 121 are adjacent to each other in the X-axis direction or the Y-axis direction. Hereinafter, such two protrusions 121 are simply referred to as "adjacent protrusions 121".

[0063] 3, the protrusions 121 are dispersed throughout the top cell 100B in the XY plane directions parallel to the light receiving surface. Here, "the protrusions 121 are dispersed throughout" means that the standard deviation of the projected area of ​​the protrusions 121 within any number of 10 μm squares in plan view is within 5%.

[0064] The number of openings is not limited to one, and the shape of the openings is not limited to a lattice shape. When a plurality of openings are provided, the shape of each of the plurality of openings may be, for example, a strip shape, an inverted polygonal pyramid shape, an inverted circular cone shape, an inverted elliptical cone shape, an inverted polygonal pyramid shape, an inverted cone shape, an inverted elliptical cone shape, a polygonal column shape, a cylinder shape, an elliptical cylinder shape, a polyhedron shape, a sphere shape, an elliptical sphere shape, or a combination thereof. When a plurality of openings are provided, the planar shape of the convex portion is not particularly limited, and may be, for example, a square shape, a rectangular shape, a polygonal shape other than a rectangle, a circular shape, an elliptical shape, or a combination thereof. Here, the inverted pyramid shape is a pyramid shape in which the area of ​​the upper base on the light receiving surface side is larger than the area of ​​the lower base on the opposite side to the light receiving surface, and the inverted pyramid shape is a pyramid shape with the light receiving surface side as the bottom surface. The plurality of openings may be, for example, arranged periodically in the X-axis direction and the Y-axis direction in a matrix shape, or may be arranged alternately in the X-axis direction and the Y-axis direction in a staggered shape.

[0065] In a plan view, the lower opening surface 121A and the upper opening surface 121B of the convex portion 121, which will be described later, overlap, but the shape of the convex portion is not limited to this. In a plan view, a part of the lower opening surface may overlap with the upper opening surface and a part may be located outside the upper opening surface, or the entire lower opening surface may be located outside the upper opening surface.

[0066] Note that the shape of the convex portion is not limited to a frustum of a square pyramid with a square planar shape. The shape of the convex portion may be, for example, a frustum of a polygonal pyramid, a frustum of a cone, a frustum of an elliptical cone, a polygonal pyramid, a cone, an elliptical cone, a polygonal prism, a cylinder, an elliptical cylinder, a polyhedron, a sphere, an ellipsoid, or a combination thereof. The planar shape of the convex portion is not limited to a square shape and may be, for example, a rectangular shape, a polygonal shape other than a rectangle, a circular shape, an elliptical shape, or a combination thereof. The shape of the convex portion may be, for example, a porous shape formed by aggregation of a plurality of particles. The convex portion may be provided, for example, in a lattice shape or a strip shape. The arrangement of the plurality of convex portions is not limited to a matrix shape, and the plurality of convex portions may be arranged in a staggered manner, for example, shifted alternately in the X-axis direction and the Y-axis direction.

[0067] The convex portion 121 has a lower base 121A located on the bottom cell 100A side and an upper base 121B located on the light-receiving surface side. When the area of the lower base 121A of the convex portion 121 is S1 and the area of the upper base 121B of the convex portion 121 is S2, the relationship S2 < S1 holds.

[0068] The aperture ratio OR of the opening 122 is expressed as "(unit area - projected area of the convex portion 121) / unit area" using the unit area in a plan view and the projected area of the convex portion 121. Therefore, when the number of convex portions 121 included in the unit area is N and the unit area is S, the aperture ratio OR of the opening 122 is defined as {(S - S1×N) / S}×100% = (1 - S1×N / S)×100 (%). The columnarity CR of the convex portion 121 is expressed as "area of the upper base 121B / area of the lower base 121A". Therefore, the columnarity CR of the convex portion 121 is defined as (S2 / S1)×100 (%).

[0069] The opening 122 has a lower opening surface 122A that opens the second light absorption layer 120 toward the bottom cell 100A side and an upper opening surface 122B that opens the second light absorption layer 120 toward the light receiving surface side. When the width of the lower opening surface 122A side of the opening 122 between two adjacent convex portions 121 is defined as G1 and the width of the upper opening surface 122B side of the opening 122 between two adjacent convex portions 121 is defined as G2, the relationship G1 < G2 holds.

[0070] The width of the interval between the two convex portions arranged closest to each other corresponds to the width G1 in the present embodiment where the shape of the convex portion 121 is a frustum of a square pyramid. The width of the interval between two adjacent convex portions 121, that is, the width G1 on the lower opening surface 122A side, is, for example, 1 nm or more and 980 nm or less, preferably 1 nm or more and 2000 nm or less, more preferably 10 nm or more and 1800 nm or less, still more preferably 20 nm or more and 1600 nm or less, still more preferably 50 nm or more and 1400 nm or less, still more preferably 100 nm or more and 1200 nm or less, and still more preferably 150 nm or more and 1000 nm or less.

[0071] The width G2 on the upper opening surface 122B side is, for example, 10 nm or more and 3000 nm or less, 50 nm or more and 2500 nm or less, 100 nm or more and 2000 nm or less, and 150 nm or more and 1500 nm or less.

[0072] When the sides or surfaces of two adjacent convex portions facing each other are not provided in parallel, the width of the interval between the two adjacent convex portions is the shortest distance between the two convex portions. Even in such a case, the width of the interval between two adjacent convex portions is preferably 1 nm or more and 2000 nm or less, more preferably 10 nm or more and 1800 nm or less, still more preferably 20 nm or more and 1600 nm or less, still more preferably 50 nm or more and 1400 nm or less, still more preferably 100 nm or more and 1200 nm or less, and still more preferably 150 nm or more and 1000 nm or less.

[0073] When the width of one side of the lower base 121A of the convex portion 121 is L1 and the width of one side of the upper base 121B of the convex portion 121 is L2, the relationship L1>L2 is established. In the present embodiment in which the shape of the convex portion 121 is a quadrangular pyramid, the width of the convex portion 121 is, for example, width L1. The width of the convex portion 121, i.e., the width L1 of one side of the lower base 121A, is, for example, 400 nm or more and 1000 nm or less, preferably 200 nm or more and 3000 nm or less, more preferably 250 nm or more and 2500 nm or less, more preferably 300 nm or more and 2000 nm or less, more preferably 350 nm or more and 1500 nm or less, more preferably 400 nm or more and 1000 nm or less, and more preferably 450 nm or more and 800 nm or less.

[0074] The width L2 of one side at the upper base 121B is preferably 200 nm or more and 3000 nm or less, more preferably 250 nm or more and 2500 nm or less, even more preferably 300 nm or more and 2000 nm or less, even more preferably 350 nm or more and 1500 nm or less, even more preferably 400 nm or more and 1000 nm or less, and even more preferably 450 nm or more and 800 nm or less.

[0075] In addition, when the planar shape of the convex portion is not a square, the width of the convex portion is the length of one side when the projection surface of the convex portion in plan view is deformed into a square shape while maintaining the same area. Even in such a case, the width of the convex portion is preferably 200 nm to 3000 nm, more preferably 250 nm to 2500 nm, more preferably 300 nm to 2000 nm, more preferably 350 nm to 1500 nm, more preferably 400 nm to 1000 nm, and more preferably 450 nm to 800 nm.

[0076] When the height of the convex portion 121 along the Z-axis direction is T, the lower base 121A of the convex portion 121 forms the lower surface of the second light absorbing layer 120, and the upper base 121B of the convex portion 121 forms the upper surface of the second light absorbing layer 120, and therefore the height T corresponds to the thickness of the second light absorbing layer 120. The thickness of the second light absorbing layer 120, i.e., the height T, is, for example, 400 nm, and is preferably 0.1 μm or more and 5 μm or less, more preferably 0.2 μm or more and 4 μm or less, even more preferably 0.3 μm or more and 3 μm or less, even more preferably 0.4 μm or more and 2 μm or less, and even more preferably 0.5 μm or more and 1 μm or less.

[0077] When the period in which the convex portions 121 are arranged in the X-axis or Y-axis direction is P, the period P is, for example, 400 nm to 1000 nm, preferably 200 nm to 3000 nm, more preferably 250 nm to 2500 nm, more preferably 300 nm to 2000 nm, more preferably 350 nm to 1500 nm, more preferably 400 nm to 1000 nm, and more preferably 450 nm to 800 nm. Here, the period P is the distance between the centers of two convex portions 121 adjacent to each other in the X-axis or Y-axis direction in a plan view.

[0078] Next, the effects of the present embodiment will be described with reference to Figs. 4 to 7. Fig. 4 is a graph showing the performance of a comparative example. Fig. 5 is a graph showing the performance of the first embodiment. Fig. 6 is a graph showing the performance of the first embodiment and the comparative example at the summer solstice. Fig. 7 is a graph showing the performance of the first embodiment and the comparative example at the winter solstice. Fig. 4 is a graph showing the external quantum efficiency EQE and the photoelectric conversion efficiency Eff (%) of the comparative example in a standard state. Fig. 5 is a graph showing the external quantum efficiency EQE and the photoelectric conversion efficiency Eff (%) of the first embodiment in a standard state. In Figs. 4 and 5, the vertical axis shows the external quantum efficiency EQE, and the horizontal axis shows the wavelength (nm) of light. Figs. 6 and 7 are graphs showing the change in the photoelectric conversion efficiency Eff (%) due to the change in the sunshine conditions. Fig. 6 is a graph showing the change in the photoelectric conversion efficiency Eff (%) from sunrise to sunset on June 21, which is the summer solstice in Japan, when the solar cell is installed on a horizontal surface. Fig. 7 is a graph showing the change in photoelectric conversion efficiency Eff (%) from sunrise to sunset on November 22, which is the winter solstice in Japan, when the solar cell is installed on a horizontal surface. In Figs. 6 and 7, the horizontal axis represents time, and the vertical axis represents photoelectric conversion efficiency Eff (%).

[0079] The configuration of the first example is based on the first embodiment, and the materials and thicknesses of the layers are as follows: First electrode layer: Molybdenum (Mo), 200-800 nm First hole transport layer: Molybdenum selenide (MoSe), 10 to 50 nm First light absorbing layer: Chalcopyrite compound (Cu(In,Ga)(Se,S) 2 ), 1~3μm First electron transport layer: Zinc titanium oxide (ZnTiO x ), 20~140nm Second electrode layer: hydrogen-containing indium oxide (IOH), 0.1 to 0.3 μm Second hole transport layer: Nickel oxide (NiO x ), 5~20nm Second light absorbing layer: Perovskite compound ((Cs,FA)PbI 3 ), 0.4~1.0μm Second electron transport layer: Tin oxide (SnO 2 ), 20~140nm Third electrode layer: hydrogen-containing indium oxide (IOH), 0.1 to 0.3 μm Grid electrode: Silver (Ag), 5 to 25 μm

[0080] In the first embodiment, the band gap of the first light absorption layer is Eg = 1.01 eV, and the band gap of the second light absorption layer is Eg = 1.55 eV. As described above, the aperture ratio OR is defined as {(S-S1 x N) / S} x 100% = (1-S1 x N / S) x 100 (%), and the columnar ratio CR is defined as (S2 / S1) x 100 (%), and the aperture ratio OR of the second light absorption layer is 23%, and the columnar ratio CR is 22%.

[0081] The configuration of the comparative example is similar to that of the example, except that no opening is provided in the second light absorbing layer.

[0082] As shown in FIG. 4, in the comparative example, the short circuit current density of the top cell was J SC =24.2mA / cm 2 and the short circuit current density of the bottom cell is J SC =17.6mA / cm 2 As shown in FIG. 5, in the first embodiment, the short-circuit current density of the top cell is J SC =21.7mA / cm 2 and the short circuit current density of the bottom cell is J SC =21.6mA / cm 2 The overall photoelectric conversion efficiency is Eff = 32.4%.

[0083] In the comparative example, the short circuit current density J of the top cell SC is the short circuit current density of the bottom cell, J SC Since the photocurrent of the top cell is too large compared to the photocurrent of the bottom cell, a current mismatch occurs between the photocurrent of the top cell and the photocurrent of the bottom cell. Because the top cell and the bottom cell are connected in series, the bottom cell becomes a bottleneck in the current that can be extracted as a whole, and the overall photoelectric conversion efficiency Eff is small.

[0084] In contrast, the short circuit current density J of the top cell in the first embodiment SC is the short circuit current density J of the comparative example SC Although the short circuit current density J of the bottom cell in the first embodiment is smaller than SC is the short circuit current density J of the comparative example SC This is because the provision of an opening in the second light absorbing layer reduces the amount of light absorbed in the second light absorbing layer and increases the amount of light that passes through the top cell and reaches the bottom cell, thereby increasing the amount of light absorbed in the first light absorbing layer. As a result, the current mismatch is reduced in the first embodiment, and the overall photoelectric conversion efficiency Eff in the first embodiment is greater than the overall photoelectric conversion efficiency Eff in the comparative example. Note that the short-circuit current density J of the top cell is SC can be appropriately adjusted by changing the shape and size of the opening of the second light absorbing layer.

[0085] In addition, in the first embodiment, the convex portions of the second light absorbing layer are periodically provided in the Z-axis direction and the Y-axis direction, the shape of the convex portions is a quadrangular pyramid shape, and the dimensions of the convex portions are on the order of nm, so that the second light absorbing layer has a moth-eye structure in which the average refractive index changes continuously in the Z-axis direction. Therefore, the interfacial reflection at the interface between the second light absorbing layer and the second electron transport layer is reduced, so that the decrease in the amount of light absorbed in the second light absorbing layer due to the openings is suppressed, and the overall photoelectric conversion efficiency Eff is increased.

[0086] The reduction in interface reflection caused by providing the second light absorbing layer with periodic convex portions does not depend on the angle of incidence of light to the solar cell. As shown in Figs. 6 and 7, the photoelectric conversion efficiency Eff of the first embodiment is higher than that of the comparative example throughout the entire daytime period when the height of the sun changes. Moreover, from the summer solstice, when the sun's nadir altitude is the highest, to the winter solstice, when the sun's nadir altitude is the lowest, the first embodiment maintains a higher photoelectric conversion efficiency than the comparative example. This shows that the low reflectance exhibited in the first embodiment over a wide range of angles of incidence of sunlight contributes to the improvement of photoelectric conversion efficiency.

[0087] As described above, as one embodiment of the present invention, the solar cell 100 includes a bottom cell 100A having a first light absorbing layer 110, and a top cell 100B having a second light absorbing layer 120 having a band gap wider than that of the first light absorbing layer 110, the second light absorbing layer 120 is provided with openings 122 penetrating the second light absorbing layer 120 in the Z-axis direction, the openings 122 are dispersed throughout the top cell 100B, and the aperture ratio OR of the openings 122 is 1% or more and 55% or less.

[0088] This improves the light transmittance of the top cell 100B for light of a wavelength corresponding to the band gap of the first light absorbing layer 110, and increases the amount of light absorbed by the second light absorbing layer 120. This increases the short-circuit current density, i.e., the photocurrent, of the bottom cell 100A, and improves the photoelectric conversion efficiency of the entire solar cell 100. By setting the aperture ratio OR of the opening 122 in the second light absorbing layer 120 to 1% or more, it is possible to effectively increase the amount of light that passes through the top cell 100B and is absorbed by the first light absorbing layer 110. By setting the aperture ratio OR of the opening 122 in the second light absorbing layer 120 to 55% or less, it is possible to suppress an excessive decrease in the amount of light absorbed in the second light absorbing layer 120. Since the openings 122 are dispersed throughout the top cell 100B, it is possible to reduce unevenness in the amount of light in the in-plane direction of the light receiving surface in each of the first light absorbing layer 110 and the second light absorbing layer 120, and to suppress unevenness in the photocurrent in the in-plane direction of the light receiving surface in each of the bottom cell 100A and the top cell 100B.

[0089] The aperture ratio OR of the openings 122 in the second light absorbing layer 120 is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. This can more effectively increase the amount of light that passes through the top cell 100B and is absorbed by the first light absorbing layer 110. The aperture ratio OR of the openings 122 in the second light absorbing layer 120 is preferably 70% or less, more preferably 60% or less, and even more preferably 50% or less. This can further suppress an excessive decrease in the amount of light absorbed in the second light absorbing layer 120.

[0090] As one embodiment of the above, the second light absorbing layer 120 has a plurality of convex portions 121 partitioned by openings 122, and the interval G1 between adjacent convex portions 121 is not less than 1 nm and not more than 980 nm.

[0091] According to this, by setting the width G1 of the gap between adjacent convex portions 121 to 1 nm or more, it is possible to effectively increase the amount of light that passes through the top cell 100B and is absorbed by the first light absorbing layer 110. In addition, it is possible to reduce the possibility that the opening 122 is blocked due to manufacturing variations, and to reduce the possibility that the amount of light that passes through the top cell 100B and is absorbed by the first light absorbing layer 110 is reduced. By setting the width G1 of the gap between adjacent convex portions 121 to 980 nm or less, it is possible to suppress an excessive decrease in the amount of light absorbed in the second light absorbing layer 120.

[0092] In one embodiment, the width L1 of the protrusion 121 in a plan view is not less than 400 nm and not more than 1000 nm.

[0093] According to this, by setting the width L1 to 400 nm or more, it is possible to suppress an excessive decrease in the amount of light absorbed in the second light absorption layer 120. By setting the width L1 to 1000 nm or less, it is possible to effectively improve the amount of light absorbed in the first light absorption layer 110. In addition, it is possible to reduce unevenness in the amount of light in the in-plane direction of the light receiving surface in the first light absorption layer 110, and to suppress unevenness in the photocurrent in the in-plane direction of the light receiving surface in the bottom cell 100A.

[0094] As one embodiment of the above, the thickness of the second light absorbing layer 120, that is, the height T of the protrusions 121, is not less than 300 nm and not more than 1000 nm.

[0095] According to this, by setting the height T to 300 nm or more, it is possible to suppress a decrease in the photoelectric conversion efficiency in the second light absorbing layer 120. Furthermore, when the convex portion is frustum-shaped or pyramidal-shaped, it is possible to ensure an inclined surface of sufficient length and effectively form a moth-eye structure. By setting the height T to 1000 nm or less, it is possible to suppress a decrease in the light transmittance of the top cell 100B for light of a wavelength corresponding to the band gap of the first light absorbing layer 110, and to suppress a decrease in the amount of light absorbed by the second light absorbing layer 120. Furthermore, it is possible to suppress damage to the convex portion 121.

[0096] As one aspect of the above, the convex portions 121 are provided periodically. Also, the area S2 of the upper base 121B on the light receiving surface side of the convex portion 121 is larger than the area S1 of the lower base 121A on the opposite side to the light receiving surface.

[0097] This allows the second light absorbing layer 120 to have a moth-eye structure, which reduces the reflectance and suppresses changes in reflectance depending on the incident angle of light, thereby suppressing fluctuations in photoelectric conversion efficiency due to time and season.

[0098] As one aspect of the above, a transparent member is provided in the opening 122, and the refractive index of the transparent member is lower than the refractive index of the second light absorbing layer 120, and the resistivity of the transparent member is higher than the resistivity of the second light absorbing layer 120.

[0099] According to this, by filling the opening 122 with a transparent member, it is possible to suppress a decrease in mechanical strength caused by providing the opening 122. By providing the transparent member with a material having a lower refractive index than the second light absorbing layer 120, it is possible to suppress the interface reflection at the interface between the transparent member and the second hole transport layer 106 and the interface between the transparent member and the second electron transport layer 107. By providing the transparent member with a material having a higher resistance than the second light absorbing layer 120, it is possible to suppress the leakage current.

[0100] In one embodiment of the above, the bottom cell 100A and the top cell 100B are electrically connected in series.

[0101] According to this, the solar cell 100 has a two-terminal tandem structure, and the manufacturing process can be simplified by the number of electrodes being smaller than that of a four-terminal tandem structure, and the number of power conditioners and wiring can also be reduced. Therefore, the manufacturing cost and system cost can be reduced. The photocurrent of the bottom cell 100A and the top cell 100B can be appropriately adjusted by the shapes and dimensions of the convex portion 121 and the opening 122. Therefore, the current mismatch between the bottom cell 100A and the top cell 100B, which is a factor that reduces the photoelectric conversion efficiency in a two-terminal tandem structure, can be reduced, and the photoelectric conversion efficiency can be improved.

[0102] As one embodiment of the above, the material of the first light absorbing layer 110 is a chalcopyrite compound or silicon having a band gap Eg of 1.00 eV or more and 1.15 eV or less, and the material of the second light absorbing layer 120 is a perovskite compound, a chalcopyrite compound, or a cadmium tellurium compound having a band gap of 1.40 eV or more and 1.70 eV or less.

[0103] This makes it possible to easily adjust the photocurrents of the bottom cell 100A and the top cell 100B by adjusting the shape and dimensions of the convex portion 121 and the opening 122, since the current mismatch between the bottom cell 100A and the top cell 100B is small when the opening 122 is omitted.

[0104] The configuration of a solar cell according to another embodiment of the present invention will be described below. In the following embodiment, the description of the matters common to the first embodiment will be omitted, and only the differences will be described. In particular, the same effects and advantages due to the same configuration will not be mentioned one by one.

[0105] <Second embodiment> Next, the configuration of the second light absorbing layer 220 in the solar cell according to the second embodiment will be described with reference to Figs. 8 and 9. Fig. 8 is a diagram showing an example of the cross-sectional structure of the second light absorbing layer according to the second embodiment. Fig. 9 is a graph showing the performance of the second example. Fig. 9 is a graph showing the external quantum efficiency (EQE) and photoelectric conversion efficiency (Eff) of the second example in the standard state. In Fig. 9, the vertical axis indicates the external quantum efficiency (EQE) and the horizontal axis indicates the wavelength of light.

[0106] In the second light absorbing layer 220 according to the second embodiment, the planar shape of the convex portion 221 is a square shape, and the shape of the convex portion 221 is a quadrangular prism shape. That is, a relationship of G1=G2 is established between a width G1 on the lower opening surface 222A side of the opening 222 between two adjacent convex portions 221 and a width G2 on the upper opening surface 222B side of the opening 222 between two adjacent convex portions 221. Also, a relationship of L1=L2 is established between a width L1 of one side of the lower base 221A of the convex portion 221 and a width L2 of one side of the upper base 221B of the convex portion 221. Also, a relationship of S2=S1 is established between an area S1 of the lower base 221A of the convex portion 221 and an area S2 of the upper base 221B of the convex portion 221.

[0107] When the number of convex portions 221 included in a unit area is N and the unit area is S, the aperture ratio OR of the opening 222 is defined as {(S-S1×N) / S}×100%=(1-S1×N / S)×100(%). The configuration of the second example is based on the second embodiment. In the second example, the aperture ratio OR of the second light absorbing layer is 53%. The second example is similar to the first example, except for the shapes of the convex portions and openings in the second light absorbing layer.

[0108] As shown in FIG. 9, in the second embodiment, the short circuit current density of the top cell is J SC =21.3mA / cm 2 and the short circuit current density of the bottom cell is J SC =21.2mA / cm 2 The overall photoelectric conversion efficiency Eff is 31.6%. In the second example based on the second embodiment, similar to the first example based on the first embodiment, the short-circuit current density JSC is the short circuit current density J of the comparative example SC is smaller than the short circuit current density J of the bottom cell. SC is the short circuit current density J of the comparative example SC Moreover, the overall photoelectric conversion efficiency Eff in the second embodiment is greater than the overall photoelectric conversion efficiency Eff in the comparative example.

[0109] <Third embodiment> Next, the configuration of the second light absorbing layer 320 in the solar cell according to the third embodiment will be described with reference to Fig. 10. Fig. 10 is a diagram showing an example of the cross-sectional structure of the second light absorbing layer according to the third embodiment.

[0110] In the third embodiment, the shape of the convex portion 321 is granular, and the shape of the third light absorbing layer 320 is porous formed by aggregation of a plurality of granular convex portions 321. Between the plurality of convex portions 321, there is a continuous gap that opens on both the light receiving portion side and the opposite side and connects the light receiving portion side and the opposite side. The gap corresponds to an example of an opening. The upper opening surface of the gap on the light receiving surface side and the lower opening surface of the gap on the opposite side to the light receiving surface overlap, for example, in the Z axis direction, but may be shifted in at least one direction of the X axis direction and the Y axis direction. The plurality of convex portions 321 may be aligned in the X axis direction and the Y axis direction, or may be arranged in a complicated manner in the X axis direction, the Y axis direction, and the Z axis direction. Even when the plurality of convex portions 321 are arranged in a complicated manner, at least a part of the plurality of gaps formed between the plurality of convex portions 321 opens on both the light receiving portion side and the opposite side and connects the light receiving portion side and the opposite side.

[0111] <Fourth embodiment> Next, the configuration of a solar cell 400 according to a fourth embodiment will be described with reference to Fig. 11. Fig. 11 is a diagram showing an example of a cross-sectional structure of the solar cell according to the fourth embodiment.

[0112] As shown in FIG. 11, the solar cell 400 is a four-terminal tandem solar cell in which the bottom cell 400A and the top cell 400B are connected in parallel. The solar cell 400 includes an electrode layer 451, an insulating layer 452, and an electrode layer 453 between the first electron transport layer 104 and the second hole transport layer 106 instead of the second electrode layer 105. The electrode layer 451 is provided on the first electron transport layer 104, the electrode layer 453 is provided under the second hole transport layer 106, and the insulating layer 452 is provided between the electrode layer 451 and the electrode layer 543. The electrode layer 451 is the negative electrode of the bottom cell 400A, and the electrode layer 453 is the positive electrode of the top cell 400B. The material and thickness of the insulating layer 452 are not particularly limited as long as it electrically insulates the bottom cell 400A and the top cell 400B. The electrode layers 451 and 453 are preferably transparent electrode layers, and are provided, for example, in the same manner as the second electrode layer 105 in the first embodiment. The insulating layer 452 is preferably a transparent insulating layer.

[0113] Solar cell 400 outputs current from four terminals, namely, first electrode layer 102, electrode layers 451 and 453, and grid electrode 109. Specifically, solar cell 400 outputs current of bottom cell 400A from two terminals, namely, first electrode layer 102 and electrode layer 451, and outputs current of top cell 400B from two terminals, namely, electrode layer 453 and grid electrode 109.

[0114] The openings and protrusions periodically provided in the second light absorbing layer 120 suppress interface reflection inside the top cell 400B, so that the decrease in the amount of light absorbed by the top cell 400B caused by providing the openings in the second light absorbing layer 120 can be suppressed. In addition, the openings provided in the second light absorbing layer 120 increase the amount of light absorbed by the bottom cell 400A through the top cell 400B. Therefore, even if the openings are provided in the second light absorbing layer 120, the decrease in the photoelectric conversion efficiency of the top cell 400B is suppressed, and the photoelectric conversion efficiency of the bottom cell 400A is improved. Therefore, the overall photoelectric conversion efficiency can be improved even in the solar cell 400, which is a four-terminal tandem solar cell in which it is not necessary to consider the current mismatch between the bottom cell 400A and the top cell 400B.

[0115] <Fifth embodiment> Next, the configuration of the second light absorbing layer 520 in the solar cell according to the fifth embodiment will be described with reference to Fig. 12. Fig. 12 is a diagram showing an example of the planar structure of the solar cell according to the fifth embodiment.

[0116] In the second light absorbing layer 520, the convex portions 521 are provided in a lattice pattern and define a plurality of openings 522. The openings 522 are surrounded by the convex portions 521. The shape of the openings 522 is an inverted quadrangular pyramid shape, and the planar shape of the openings 522 is a square shape. The plurality of openings 522 are provided periodically in the X-axis direction and the Y-axis direction, and are arranged in a matrix pattern. The lower opening surface 522A and the upper opening surface 522B of each opening 522 have a pair of sides extending parallel to each other along the X-axis direction and a pair of sides extending parallel to each other along the Y-axis direction. The sides extending in the X-axis direction of each of the plurality of lower opening surfaces 522A and the upper opening surface 522B are parallel to each other, and the sides extending in the Y-axis direction of each of the plurality of lower opening surfaces 522A and the upper opening surface 522B are parallel to each other.

[0117] <Evaluation of aperture ratio and columnar degree> Next, with reference to Figs. 13 to 15, the influence of the aperture ratio OR and the columnar degree CR on the photoelectric conversion efficiency Eff(%) in a two-terminal tandem solar cell and a four-terminal tandem solar cell will be described. Fig. 13 is a graph showing the relationship between the aperture ratio and the photoelectric conversion efficiency. Fig. 14 is a graph showing the relationship between the aperture ratio and the photoelectric conversion efficiency. Fig. 15 is a graph showing the relationship between the aperture ratio and the photoelectric conversion efficiency. In Figs. 13 to 15, the horizontal axis indicates the aperture ratio OR(%), and the vertical axis indicates the photoelectric conversion efficiency Eff(%). As described above, the aperture ratio OR is defined as {(S-S1×N) / S}×100%=(1-S1×N / S)×100(%), and the columnar degree CR is defined as (S2 / S1)×100(%).

[0118] FIG. 13 shows the photoelectric conversion efficiency Eff(%) in a two-terminal tandem solar cell and a four-terminal tandem solar cell when the height T of the convex portion corresponding to the thickness of the second light absorbing layer is set to 490 nm or 980 nm, the columnar degree CR is fixed to 100%, and the aperture ratio OR is changed from 0% to 75%.

[0119] In the case of a two-terminal tandem solar cell, the photoelectric conversion efficiency Eff increases as the aperture ratio OR increases from 0%. When T=490 nm, the aperture ratio OR at which the photoelectric conversion efficiency Eff is maximized (hereinafter referred to as the "optimum aperture ratio") is about 55%. When OR=0%, i.e., when no aperture is provided, the photoelectric conversion efficiency Eff (hereinafter referred to as the "conventional photoelectric conversion efficiency") is about 27.6%, and when the photoelectric conversion efficiency Eff is at the optimal aperture ratio (hereinafter referred to as the "optimum photoelectric conversion efficiency") is about 31.6%. When T=980 nm, the optimal aperture ratio is greater than 75%. The conventional photoelectric conversion efficiency is about 26.9%, and the optimal photoelectric conversion efficiency is greater than 31.7%. When T increases, the conventional photoelectric conversion efficiency decreases, but the optimal aperture ratio and the optimal photoelectric conversion efficiency increase.

[0120] In the case of a four-terminal tandem solar cell, as in the case of a two-terminal tandem solar cell, the photoelectric conversion efficiency Eff increases as the aperture ratio OR increases from 0%. When T=490 nm, the optimal aperture ratio is about 10%, the conventional photoelectric conversion efficiency is about 33.1%, and the optimal photoelectric conversion efficiency is about 33.2%. When T=980 nm, the optimal aperture ratio is about 45%, the conventional photoelectric conversion efficiency is about 33.4%, and the optimal photoelectric conversion efficiency is about 33.9%. As T increases, the conventional photoelectric conversion efficiency increases, unlike the two-terminal tandem solar cell, and the optimal aperture ratio and optimal photoelectric conversion efficiency increase, similar to the two-terminal tandem solar cell. The optimal aperture ratio in a four-terminal tandem solar cell is smaller than the optimal aperture ratio in a two-terminal tandem solar cell. The amount of change from the conventional photoelectric conversion efficiency to the optimum photoelectric conversion efficiency in a four-terminal tandem solar cell is smaller than the amount of change from the conventional photoelectric conversion efficiency to the optimum photoelectric conversion efficiency in a two-terminal tandem solar cell.

[0121] FIG. 14 shows the photoelectric conversion efficiency Eff (%) in a two-terminal tandem solar cell when the height T of the convex portion corresponding to the thickness of the second light absorbing layer is set to 490 nm or 980 nm, the columnar degree CR is set to 12.5%, 25%, 50%, and 100%, and the aperture ratio OR is changed from 0% to 75%.

[0122] For T=490nm, when the columnar degree CR=100%, the conventional photoelectric conversion efficiency is approximately 27.6%, the optimal aperture ratio is approximately 55%, and the optimal photoelectric conversion efficiency is approximately 31.6%; when the columnar degree CR=50%, the optimal aperture ratio is approximately 35%, and the optimal photoelectric conversion efficiency is approximately 32.1%; when the columnar degree CR=25%, the optimal aperture ratio is approximately 20%, and the optimal photoelectric conversion efficiency is approximately 32.4%; and when the columnar degree CR=12.5%, the optimal aperture ratio is approximately 8%, and the optimal photoelectric conversion efficiency is approximately 32.4%.

[0123] In the case of T=980 nm, when the columnar degree CR=100%, the conventional photoelectric conversion efficiency is approximately 26.9%, the optimal aperture ratio is 75% or more, and the optimal photoelectric conversion efficiency is 31.7% or more; when the columnar degree CR=50%, the optimal aperture ratio is approximately 65% ​​and the optimal photoelectric conversion efficiency is approximately 32.0%; when the columnar degree CR=25%, the optimal aperture ratio is approximately 57% and the optimal photoelectric conversion efficiency is approximately 32.2%; and when the columnar degree CR=12.5%, the optimal aperture ratio is approximately 50% and the optimal photoelectric conversion efficiency is approximately 32.5%.

[0124] In both cases where T=490 nm and 980 nm, regardless of the magnitude of the columnar degree CR, the photoelectric conversion efficiency Eff increases as the aperture ratio OR increases from 0%, and the photoelectric conversion efficiency Eff is maximum at the optimal aperture ratio. As the columnar degree CR decreases and the shape of the convex portion approaches a pyramidal shape, the optimal aperture ratio decreases. Also, as the columnar degree CR decreases and the shape of the convex portion approaches a pyramidal shape, the optimal photoelectric conversion efficiency increases. As T increases, the optimal aperture ratio increases, but the optimal photoelectric conversion efficiency remains almost unchanged.

[0125] FIG. 15 shows the photoelectric conversion efficiency Eff (%) in a four-terminal tandem solar cell when the height T of the convex portion corresponding to the thickness of the second light absorbing layer is set to 490 nm or 980 nm, the columnar degree CR is set to 12.5%, 25%, 50%, and 100%, and the aperture ratio OR is changed from 0% to 75%.

[0126] In the case of T=490 nm, when the columnar ratio CR=100%, the conventional photoelectric conversion efficiency is about 33.1%, and the optimal aperture ratio is 10% or more, and the optimal photoelectric conversion efficiency is about 33.2%. When the columnar ratio CR=50%, 25%, 12.5%, the photoelectric conversion efficiency Eff decreases as the aperture ratio OR increases from 0%, and there is no optimal aperture ratio or optimal photoelectric conversion efficiency.

[0127] In the case of T=980nm, when the columnar ratio CR=100%, the conventional photoelectric conversion efficiency is about 33.4%, the optimal aperture ratio is 45% or more, and the optimal photoelectric conversion efficiency is about 33.9%, and when the columnar ratio CR=50%, the optimal aperture ratio is 20% or more, and the optimal photoelectric conversion efficiency is about 34.5%. When the columnar ratio CR=25%, 12.5%, the photoelectric conversion efficiency Eff decreases as the aperture ratio OR increases from 0%, and there is no optimal aperture ratio or optimal photoelectric conversion efficiency.

[0128] In both cases where T=490 nm and 980 nm, when the columnar degree CR is large, the photoelectric conversion efficiency Eff increases as the aperture ratio OR increases from 0%, and the photoelectric conversion efficiency Eff is maximized at the optimal aperture ratio. When T increases, the optimal aperture ratio increases and the optimal photoelectric conversion efficiency also increases. As the columnar degree CR decreases and the shape of the convex portion approaches a pyramidal shape, the optimal aperture ratio decreases and the optimal photoelectric conversion efficiency increases. When the columnar degree CR is smaller than a certain value (hereinafter referred to as the "minimum columnar degree"), the optimal aperture ratio and the optimal photoelectric conversion efficiency do not exist. In other words, when the columnar degree CR is smaller than the minimum columnar degree, even if the opening 122 is provided in the second light absorption layer 120, the overall photoelectric conversion efficiency does not improve. As T increases, the minimum columnar degree decreases.

[0129] Although two-terminal tandem solar cells and four-terminal tandem solar cells have been described as examples, the present invention may be applied to three-terminal tandem solar cells. For example, a solar cell according to one embodiment of the present invention may be an intermediate electrode type three-terminal tandem solar cell in which the first electrode layer 102, the second electrode layer 105, and the grid electrode 109 of the solar cell 100 according to the first embodiment function as three terminals. That is, a current generated in the first light absorbing layer 110 may be output from the first electrode layer 102 and the second electrode layer 105, and a current generated in the second light absorbing layer 120 may be output from the second electrode layer 105 and the grid electrode 109.

[0130] The solar cell according to an embodiment of the present invention may be a back-contact three-terminal tandem solar cell. For example, the light absorbing layer of the bottom cell may be made of crystalline silicon, and an n-type silicon region (n-Si) and a p-type silicon region (p-Si) may be provided on the opposite side of the light absorbing layer of the bottom cell to the top cell, and the n-Si and p-Si of the bottom cell and the grid electrode of the top cell may function as three terminals. That is, the current generated in the light absorbing layers of the bottom cell and the top cell may be output from the n-Si and the grid electrode, and also from the p-Si and n-Si.

[0131] Some or all of the embodiments of the present invention will be described below. Note that the present invention is not limited to the following descriptions.

[0132] [1] a first cell having a first light absorbing layer; a second cell disposed on the light receiving surface side of the first cell and having a second light absorbing layer having a band gap wider than that of the first light absorbing layer; Equipped with the second light absorbing layer is provided with an opening penetrating the second light absorbing layer, the openings are distributed throughout the second cells; The aperture ratio of the opening is 1% or more and 55% or less. Solar cell.

[0133] [2] the second light absorbing layer has a plurality of convex portions defined by the openings, The interval between adjacent protrusions is 1 nm or more and 980 nm or less. The solar cell according to [1].

[0134] [3] the second light absorbing layer has a plurality of convex portions defined by the openings, Each of the plurality of protrusions has a width of 400 nm or more and 1000 nm or less in a plan view. The solar cell according to [1] or [2].

[0135] [4] the second light absorbing layer has a continuous convex portion that defines at least a portion of the opening; A solar cell according to any one of [1] to [3].

[0136] [5] The thickness of the second light absorbing layer is 300 nm or more and 1000 nm or less. A solar cell according to any one of [1] to [4].

[0137] [6] the second light absorbing layer has a plurality of convex portions defined by the openings, The plurality of protrusions are provided periodically. A solar cell according to any one of [1] to [5].

[0138] [7] The area of ​​the plurality of convex portions on the light receiving surface side is smaller than the area of ​​the opposite side to the light receiving surface. The solar cell according to [6].

[0139] [8] The plurality of protrusions are columnar. The solar cell according to [6] or [7].

[0140] [9] The second light absorbing layer is porous and formed by aggregation of a plurality of particles. A solar cell according to any one of [1] to [8].

[0141]

[10] A transparent member is provided inside the opening, the refractive index of the transparent member is lower than the refractive index of the second light absorbing layer, The resistivity of the transparent member is higher than the resistivity of the second light absorbing layer. A solar cell according to any one of [1] to [9].

[0142]

[11] The first cell and the second cell are electrically connected in series. [1] The solar cell according to any one of [1] to

[10] .

[0143]

[12] The material of the first light absorption layer is a chalcopyrite compound or silicon having a band gap of 1.00 eV or more and 1.15 eV or less. [1] The solar cell according to any one of [1] to

[11] .

[0144]

[13] The material of the second light absorption layer is a perovskite compound, a chalcopyrite compound, or a cadmium tellurium compound having a band gap of 1.40 eV or more and 1.70 eV or less. [1] The solar cell according to any one of [1] to

[12] .

[0145] As described above, according to one aspect of the present invention, a solar cell with improved photoelectric conversion efficiency can be provided.

[0146] The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangements, materials, conditions, shapes, sizes, etc., are not limited to those illustrated, and can be changed as appropriate. In addition, configurations shown in different embodiments can be partially substituted or combined with each other. [Explanation of symbols]

[0147] 100…Solar cell 100A…Bottleneck 100B…Top cell 101...Substrate 102...First electrode layer 103...first hole transport layer 104...first electron transport layer 105...Second electrode layer 106...Second hole transport layer 107...Second electron transport layer 108…Third electrode layer 109...Grid electrode 110...first light absorbing layer 120...Second light absorbing layer 121…Convex part 121A…lower bottom 121B…Top bottom 122…Opening 122A…Lower opening surface 122B…Top opening surface

Claims

1. a first cell having a first light absorbing layer; a second cell disposed on the light receiving surface side of the first cell and having a second light absorbing layer having a band gap wider than that of the first light absorbing layer; Equipped with the second light absorbing layer is provided with an opening penetrating the second light absorbing layer, the openings are distributed throughout the second cells; The aperture ratio of the opening is 1% or more and 55% or less. Solar cell.

2. the second light absorbing layer has a plurality of convex portions defined by the openings, The width of the interval between adjacent convex portions is 1 nm or more and 980 nm or less. The solar cell according to claim 1 .

3. the second light absorbing layer has a plurality of convex portions defined by the openings, Each of the plurality of protrusions has a width of 400 nm or more and 1000 nm or less in a plan view. The solar cell according to claim 1 .

4. the second light absorbing layer has a continuous convex portion that defines at least a part of the opening; The solar cell according to claim 1 .

5. The thickness of the second light absorbing layer is 300 nm or more and 1000 nm or less. The solar cell according to claim 1 .

6. the second light absorbing layer has a plurality of convex portions defined by the openings, The plurality of protrusions are provided periodically. The solar cell according to claim 1 .

7. The area of ​​the plurality of convex portions on the light receiving surface side is smaller than the area of ​​the opposite side to the light receiving surface. The solar cell according to claim 6.

8. The plurality of protrusions are columnar. The solar cell according to claim 6.

9. The second light absorbing layer is porous and formed by agglomeration of a plurality of particles. The solar cell according to claim 1 .

10. A transparent member is provided inside the opening, the refractive index of the transparent member is lower than the refractive index of the second light absorbing layer, The resistivity of the transparent member is higher than the resistivity of the second light absorbing layer. The solar cell according to claim 1 .

11. The first cell and the second cell are electrically connected in series. The solar cell according to claim 1 .

12. The material of the first light absorbing layer is a chalcopyrite compound or silicon having a band gap of 1.00 eV or more and 1.15 eV or less. The solar cell according to claim 1 .

13. The material of the second light absorbing layer is a perovskite compound, a chalcopyrite compound, or a cadmium tellurium compound having a band gap of 1.40 eV or more and 1.70 eV or less. The solar cell according to claim 1 .

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