Solar battery and photovoltaic power generation system

Abstract

To provide a high-efficiency solar battery.SOLUTION: A solar battery is a transmissive top cell and, when connected with a bottom cell, comprises: a support layer including a refraction index change layer or a refraction index change region on a bottom cell side of the top cell; and a clearance layer between the refraction index change layer and the bottom cell or between the support layer and the bottom cell. A refraction index of the refraction index change layer on a top cell side is high, a refraction index of the refraction index change layer on the bottom cell side is low, a refraction index of the refraction index change region on the top cell side is high and a refraction index of the refraction index change region on the bottom cell side is low. The clearance layer is capable of electrically insulating the top cell and the bottom cell.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solar cell and a solar power generation system. [Background technology]

[0002] Highly efficient solar cells are expected to be developed by combining a top cell (solar cell) with a wide bandgap light absorption layer and a bottom cell (solar cell) with a narrow bandgap light absorption layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-157176 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a highly efficient solar cell. [Means for solving the problem]

[0005] The solar cell of the embodiment is a transmissive top cell that, when connected to a bottom cell, has a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side of the refractive index change layer, a high refractive index on the top cell side of the refractive index change region, and a low refractive index on the bottom cell side of the refractive index change region. The gap layer can electrically insulate the top cell from the bottom cell. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram of a solar cell according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a solar cell according to an embodiment. [Figure 3] Figure 3 is a schematic diagram showing the positional relationship between the effective power generation area of ​​the top cell and the holding part. [Figure 4] Figure 4 is a schematic diagram showing the positional relationship between the effective power generation area of ​​the bottom cell and the holding part. [Figure 5] FIG. 5 is a schematic diagram of a solar cell according to an embodiment. [Figure 6] FIG. 6 is a schematic diagram of a solar cell according to an embodiment. [Figure 7] FIG. 7 is a schematic diagram of a solar cell according to an embodiment. [Figure 8] FIG. 8 is a schematic diagram of a solar cell according to an embodiment. [Figure 9] FIG. 9 is a schematic diagram of a solar cell according to an embodiment. [Figure 10] FIG. 10 is a schematic diagram of a solar cell according to an embodiment. [Figure 11] FIG. 11 is a schematic diagram of a solar cell according to an embodiment. [Figure 12] FIG. 12 is a configuration diagram of a solar power generation system according to an embodiment. [Figure 13] FIG. 13 is a schematic diagram of a vehicle according to an embodiment. [Figure 14] FIG. 14 is a schematic diagram of a flying object according to an embodiment. [Figure 15] FIG. 15 is a table relating to an embodiment. [Figure 16] FIG. 16 is a table relating to an embodiment. [Figure 17] FIG. 17 is a table relating to an embodiment. [Figure 18] FIG. 18 is a table relating to an embodiment. [Figure 19] FIG. 19 is a table relating to an embodiment. [Figure 20] FIG. 20 is a table relating to an embodiment. [Figure 21] FIG. 21 is a table relating to an embodiment. [Figure 22] FIG. 22 is a table relating to an embodiment. [Figure 23] FIG. 23 is a table relating to an embodiment. [Figure 24] FIG. 24 is a table relating to an embodiment. [Figure 25]FIG. 25 is a table relating to an embodiment. [Figure 26] FIG. 26 is a table relating to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] A preferred embodiment of the present invention will be described in detail below with reference to the drawings. Unless otherwise specified, the physical property values ​​are those at 25°C and 1 atmosphere (atmosphere). Averages indicate arithmetic mean values. Unless otherwise specified, each concentration is the average concentration of the target region or layer. In each layer, the inclusion of a specific element refers to, for example, an element whose presence is confirmed by SIMS (Secondary Ion Mass Spectrometry), and the absence of a specific element refers to, for example, an element whose presence cannot be confirmed by SIMS (an element below the detection limit).

[0008] In the specification, " / " represents a division symbol. However, the " / " in "or / and" means "or." In the specification, "·" represents a multiplication symbol. In the numerical values ​​in the specification, "." represents a decimal point.

[0009] (First embodiment) The first embodiment relates to a solar cell.

[0010] The solar cell of the embodiment includes a transparent top cell, a bottom cell, a support layer having a refractive index change layer or a refractive index change region between the top cell and the bottom cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side, a high refractive index on the top cell side, and a low refractive index on the bottom cell side of the refractive index change region. The gap layer electrically insulates the top cell and the bottom cell.

[0011] The solar cell of the embodiment is a transmissive top cell that, when connected to a bottom cell, has a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side of the refractive index change layer, a high refractive index on the top cell side of the refractive index change region, and a low refractive index on the bottom cell side of the refractive index change region. The gap layer can electrically insulate the top cell from the bottom cell.

[0012] The solar cell of the embodiment is a transmissive top cell that, when connected to a bottom cell, has a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side of the refractive index change layer, a high refractive index on the top cell side, and a low refractive index on the bottom cell side of the refractive index change region. The refractive index change layer and the bottom cell are not in direct contact, and the support layer and the bottom cell are not in direct contact.

[0013] The solar cell of the embodiment is a transmissive top cell that, when connected to a bottom cell, has a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side of the refractive index change layer, a high refractive index on the top cell side, and a low refractive index on the bottom cell side of the refractive index change region. The refractive index change layer and the bottom cell are not in direct contact, and the support layer and the bottom cell are not in direct contact.

[0014] The solar cell of the embodiment includes a transmissive top cell and a support layer having a refractive index change layer or a refractive index change region on the light-emitting surface side of the top cell, wherein the refractive index change layer has a high refractive index on the top cell side and a low refractive index on the side opposite to the top cell side, and the refractive index change region has a high refractive index on the top cell side and a low refractive index on the side opposite to the top cell side.

[0015] A schematic diagram of a solar cell is shown in Figure 1. The solar cell 100 shown in the schematic diagram of Figure 1 has a top cell 10, a bottom cell 20, a refractive index change layer 31, a gap layer 32, and a holding portion 33. The solar cell of the first embodiment is also a solar cell module.

[0016] The first embodiment includes a solar cell 101 shown in the schematic diagram of Fig. 2 as a modified example of the solar cell 100. The solar cell 101 shown in the schematic diagram of Fig. 2 has a top cell 10, a bottom cell 20, a support layer 34 including a refractive index change region 35, a gap layer 32, and a holding portion 33. The refractive index change region 35 corresponds to the refractive index change layer 31 of the solar cell 100.

[0017] The configuration of a solar cell when the top cell 10 is connected to the bottom cell 20 will be described.

[0018] The following description will mainly focus on solar cell 100, but the description of solar cell 100 corresponds to the description of solar cell 101. A submodule can be configured in which a plurality of top cells 10 are electrically connected. A submodule can be configured in which a plurality of bottom cells 20 are electrically connected. A solar cell can be configured to include submodules of a plurality of top cells 10, with the submodules connected to each other by bus bars. A solar cell can be configured to include submodules of a plurality of bottom cells 20, with the submodules connected to each other by bus bars.

[0019] The top cell 10 is a solar cell that has a light absorption layer with a wider band gap than the bottom cell 20. The top cell 10 is a transparent solar cell. A transparent solar cell is a solar cell that absorbs part of the incident light to generate electricity and transmits part of the incident light.

[0020] The light absorption layer of the top cell 10 may be made of one or more of a compound semiconductor, a perovskite compound, and amorphous silicon. The light absorption layer of the top cell 10 is preferably made of one of a compound semiconductor, a perovskite compound, and amorphous silicon. Preferred compound semiconductors include cuprous oxide (cuprous oxide compounds having a cuprite structure), compounds having a chalcopyrite structure (CIS, CIGS), compounds having a kesterite structure, compounds having a stannite structure, and transition metal chalcogenides.

[0021] In the solar cell 100, a cell not shown can be provided on the light incident side of the top cell 10. Solar cells configured so that light transmitted through a cell not shown is incident on the incident surface of the top cell are also included in the embodiments.

[0022] Light is incident on the top cell 10 from the side opposite to the bottom cell 20 side. The top cell 10 has an incident surface on the side opposite to the bottom cell 20 side.

[0023] Light that enters the top cell 10 from the incident surface on the side opposite to the bottom cell 20 side exits from the top cell 10 on the bottom cell 20 side.

[0024] The bottom cell 20 is a solar cell having a light absorption layer with a narrower band gap than the top cell 10. Light that has passed through the top cell 10 (transmitted light) enters the bottom cell 20, causing the bottom cell 20 to generate electricity. The bottom cell 20 is a non-transparent solar cell.

[0025] The bottom cell 20 has an anti-reflection coating 22 on the power generating element 21 and top cell 10 side. From the viewpoint of reducing reflection at the boundary between the gap layer 32 and the anti-reflection coating 22, the refractive index of the surface of the anti-reflection coating 22 on the top cell 10 side is preferably substantially 1.0 to 1.35, more preferably 1.0 to 1.30, more preferably 1.0 to 1.1, and more preferably 1.0 to 1.08. Alternatively, the bottom cell may have a structure in which the surface on the top cell side is uneven, thereby providing a continuously changing refractive index. Note that the refractive index in this specification refers to the refractive index of light having a wavelength in the range of 600 nm to 900 nm. The refractive index can be determined, for example, using a spectroscopic ellipsometer.

[0026] The light absorption layer of the bottom cell 20 is preferably polycrystalline or single-crystalline Si.

[0027] Light is incident on the top cell 10 side of the bottom cell 20. The bottom cell 20 has an incident surface on the top cell 10 side.

[0028] An electrode of the bottom cell 20 may be provided on the incident surface side of the bottom cell 20 in addition to the anti-reflection film 22 .

[0029] The refractive index change layer 31 (support layer 34 having a refractive index change region 35) is provided on the bottom cell 20 side of the top cell 10. The refractive index change layer 31 (support layer 34 having a refractive index change region 35) is provided between the top cell 10 and the bottom cell 20. The refractive index change layer 31 (support layer 34 having a refractive index change region 35) is preferably provided on the light exit surface side of the top cell 10. The refractive index change layer 31 (support layer 34 having a refractive index change region 35) is a light-transmitting member. Light transmitted through the top cell 10 exits from the refractive index change layer 31 (support layer 34 having a refractive index change region 35), passes through the gap layer 32, and strikes the bottom cell 20. The refractive index change layer 31 (refractive index change region 35) has a refractive index distribution. It is preferable that the refractive index of the support layer 34 in areas other than the refractive index change region 35 does not change significantly and is constant or approximately constant.

[0030] The refractive index changing layer 31 (support layer 34 having the refractive index changing region 35) and the bottom cell 20 are not in direct contact with each other.

[0031] The refractive index changing region 35 is not in direct contact with the bottom cell 20 .

[0032] The refractive index change layer 31 may include a region on the bottom cell 20 side where the refractive index is lowered and the refractive index is almost constant.

[0033] It should be noted that the refractive index change region 35 may include a region on the bottom cell 20 side where the refractive index is lowered and the refractive index is almost constant.

[0034] The refractive index changing region 35 of the support layer 34 is a region where the refractive index changes due to a difference in composition from the top cell 10 side of the support layer 34 and / or a difference in shape from the top cell 10 side of the support layer 34.

[0035] The refractive index of the refractive index change layer 31 (refractive index change region 35) on the top cell 10 side is high, and the refractive index of the refractive index change layer 31 (refractive index change region 35) on the bottom cell 20 side (gap layer 32 side) is low.

[0036] The thickness of the refractive index change layer 31 (the length of the refractive index change layer 31 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 0.01 μm or more and 2 mm or less, more preferably 0.02 μm or more and 1.5 mm or less, and even more preferably 0.03 μm or more and 1 mm or less.

[0037] The thickness of the refractive index change region 35 (the length of the refractive index change region 35 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 0.01 μm or more and 2 mm or less, more preferably 0.02 μm or more and 1.5 mm or less, and even more preferably 0.03 μm or more and 1 mm or less.

[0038] The thickness of the support layer 34 (the length of the support layer 34 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 0.01 μm or more and 2 mm or less, more preferably 0.02 μm or more and 1.5 mm or less, and even more preferably 0.03 μm or more and 1 mm or less.

[0039] The refractive index changing layer 31 (support layer 34 having the refractive index changing region 35) is preferably electrically insulating. The refractive index changing layer 31 (support layer 34 having the refractive index changing region 35) includes an inorganic material such as glass and / or a resin material. Examples of the glass include inorganic materials such as white plate glass, chemically strengthened glass, borosilicate glass, and quartz. Examples of the resin material include organic materials such as acrylic resin, epoxy resin, silicone resin, polyimide, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resins (such as polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), and perfluoroalkoxyalkane (PFA)), polyarylate, polysulfone, polyethersulfone, and polyetherimide.

[0040] The top cell 10 and the bottom cell 20 are not electrically connected via the refractive index change layer 31 (support layer 34 having refractive index change region 35). The top cell 10 and the bottom cell 20 are electrically insulated via the refractive index change layer 31 (support layer 34 having refractive index change region 35). The resistance of the refractive index change layer 31 (support layer 34 having refractive index change region 35) is 10 9 [Ω] or more is preferable, and 10 12 [Ω] or more is more preferable.

[0041] The top cell 10 preferably has an output terminal independent of the output terminal of the bottom cell 20. The bottom cell 20 preferably has an output terminal independent of the output terminal of the top cell 10. Because the top cell 10 is not connected to the bottom cell 20 in the stacking direction of the top cell 10 and the bottom cell 20, the voltage and / or current of the top cell 10 (submodule (multiple submodules) including the top cell 10) and the bottom cell 20 (submodule (multiple submodules) including the bottom cell 20) do not need to be identical to each other.

[0042] The refractive index change layer 31 (support layer 34 having refractive index change region 35) includes any of a laminate in which members with different refractive indices are stacked, a member whose refractive index changes gradually, and a member whose refractive index changes due to unevenness. The unevenness may have any shape, but may be, for example, a cone-shaped (needle-shaped), truncated cone-shaped, pyramidal (pyramid-shaped), or truncated pyramidal unevenness tapering toward the bottom cell 20 side, or a groove tapering toward the bottom cell 20 side. The groove pattern may be a line-shaped, mesh-shaped, or random pattern. The refractive index change layer 31 (support layer 34 having refractive index change region 35) may contain an inorganic material such as MgF2, SiN, TiO2, or SiO2, or carbon fine particles.

[0043] The refractive index of the surface of the refractive index change layer 31 (refractive index change region 35) on the bottom cell 20 side (the gap layer 32 side, the side opposite the top cell 10 side) is preferably 1.0 or more and 1.35 or less, preferably 1.0 or more and 1.30 or less, preferably 1.0 or more and 1.1 or less, and more preferably 1.0 or more and 1.08 or less. It is preferable that light of the wavelength used for power generation in the bottom cell 20 is not reflected when it is emitted from the top cell 10 side.

[0044] The refractive index of the refractive index change layer 31 (refractive index change region 35) on the top cell 10 side (the refractive index of a region from a position at a depth of 10% of the thickness of the refractive index change layer 31 in the direction from the surface of the refractive index change layer 31 in contact with the top cell 10 toward the bottom cell 20 to a position at a depth of 20% of the thickness of the refractive index change layer 31 in the direction from the surface of the refractive index change layer 31 in contact with the top cell 10 toward the bottom cell 20, and the refractive index of a region from a position at a depth of 10% of the thickness of the support layer 34 in the direction from the surface of the support layer 34 in contact with the top cell 10 toward the bottom cell 20 to a position at a depth of 20% of the thickness of the support layer 34 in the direction from the surface of the support layer 34 in contact with the top cell 1 ... toward the bottom cell 20) is The refractive index of the refractive index change layer 31 (refractive index change region 35) on the surface of the refractive index change layer 31 (on the top cell 10 side) is preferably higher than the refractive index of the region extending from a position at a depth of 80% of the thickness of the refractive index change layer 31 in the direction toward the bottom cell 20 to a depth of 90% of the thickness of the refractive index change layer 31 in the direction toward the bottom cell 20, and the refractive index of the region of the support layer 34 having the refractive index change region 35 extending from a position at a depth of 80% of the thickness of the support layer 34 in the direction toward the bottom cell 20 to a depth of 90% of the thickness of the support layer 34 in the direction toward the bottom cell 20. The absolute value of the difference between the refractive index of the member in contact with the refractive index change layer 31 of the top cell 10 and the refractive index of the refractive index change layer 31 on the top cell 10 side ([refractive index of the member in contact with the refractive index change layer 31 of the top cell 10] - [refractive index of the refractive index change layer 31 on the top cell 10 side]) is preferably 0.0 or more and 1.0 or less, and more preferably 0.0 or more and 0.5 or less. The absolute value of the difference between the refractive index of the member in contact with the support layer 34 of the top cell 10 and the refractive index of the region of the support layer 34 excluding the refractive index change region 35 on the top cell 10 side ([refractive index of the member in contact with the support layer 34 of the top cell 10] - [refractive index of the region of the support layer 34 excluding the refractive index change region 35 on the top cell 10 side]) is preferably 0.0 or more and 1.0 or less, and more preferably 0.0 or more and 0.5 or less.

[0045] The difference in refractive index between the member in contact with the refractive index change layer 31 of the top cell 10 and the refractive index of the refractive index change layer 31 on the top cell 10 side ([refractive index of the member in contact with the refractive index change layer 31 of the top cell 10] - [refractive index of the refractive index change layer 31 on the top cell 10 side]) is preferably -1.0 or more and 1.0 or less, and more preferably -0.5 or more and 0.5 or less. The difference in refractive index between the member in contact with the support layer 34 of the top cell 10 and the refractive index of the region of the support layer 34 excluding the refractive index change region 35 on the top cell 10 side ([refractive index of the member in contact with the support layer 34 of the top cell 10] - [refractive index of the region of the support layer 34 excluding the refractive index change region 35 on the top cell 10 side]) is preferably -1.0 or more and 1.0 or less, and more preferably -0.5 or more and 0.5 or less.

[0046] The refractive index of the refractive index change layer 31 side of the top cell 10 (the refractive index of the member in direct contact with the refractive index change layer 31 of the top cell 10) is preferably 1.3 or more and 2.2 or less, more preferably 1.4 or more and 2.0 or less.

[0047] The refractive index on the support layer 34 side of the top cell 10 (the refractive index of the member in direct contact with the support layer 34 of the top cell 10) is preferably 1.3 or more and 2.2 or less, and more preferably 1.4 or more and 2.0 or less.

[0048] It is preferable that unevenness is provided on the bottom cell 20 side of the refractive index change layer 31 (refractive index change region 35). The height of the unevenness is preferably 20 nm or more and less than 1000 nm, and preferably 60 nm or more and 800 nm or less. The unevenness pitch is preferably 20 nm or more and less than 1000 nm, and preferably 60 nm or more and 800 nm or less. The unevenness may be regular or irregular. It is preferable that the unevenness on the bottom cell 20 side of the refractive index change layer 31 (refractive index change region 35) is connected to the gap layer 32. The unevenness of the refractive index change layer 31 (refractive index change region 35) is a convex portion on the bottom cell 20 side and a concave portion on the top cell 10 side.

[0049] The refractive index of the refractive index change layer 31 (refractive index change region 35) preferably decreases stepwise or / and gradiently from the top cell 10 side toward the bottom cell 20 side (the side opposite to the top cell 10 side). When the refractive index of the refractive index change layer 31 (refractive index change region 35) changes stepwise or / and gradiently, the refractive index change layer 31 (refractive index change region 35) may include a portion where the refractive index increases from the top cell 10 side toward the bottom cell 20 side.

[0050] The gap layer 32 is a space that exists between the refractive index change layer 31 (the support layer 34 having the refractive index change region 35) and the bottom cell 20. The gap layer 32 is preferably electrically insulating. The gap layer 32 is formed by an air layer (for example, a pressure of 1 [Pa] or more and 10 [Pa] or less). 6 [Pa] or less), inert gas layer or vacuum layer (0 [Pa] or more 10 6 [Pa], less).

[0051] In the configuration in which the top cell 10 and the bottom cell 20 are connected, the gap layer 32 electrically insulates the top cell 10 and the bottom cell 20 .

[0052] When the top cell 10 is connected to the bottom cell 20 , the gap layer 32 can electrically isolate the top cell 10 and the bottom cell 20 .

[0053] The thickness of the gap layer 32 (the length of the gap layer 32 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 1 μm or more and 10 mm or less, more preferably 5 μm or more and 5 mm or less, and even more preferably 10 μm or more and 3 mm or less.

[0054] The minimum thickness of the gap layer 32 (the minimum length of the gap layer 32 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 0.1 μm to 10 mm, more preferably 1 μm to 5 mm, and even more preferably 5 μm to 3 mm. When the refractive index change layer 31 (the support layer 34 having the refractive index change region 35) is in direct contact with the bottom cell 20, the minimum thickness of the gap layer 32 is 0 μm, and the thickness of the gap layer 32 (the length of the gap layer 32 in the stacking direction of the top cell 10 and the bottom cell 20) is preferably 0.01 μm to 2 mm, more preferably 0.02 μm to 1.5 mm, and even more preferably 0.03 μm to 1 mm.

[0055] The refractive index of the gap layer 32 is about 1. The overall refractive index of the gap layer 32 is about 1. The overall refractive index of the gap layer 32 is preferably 1.0 or more and 1.2 or less, and the solar cell 100 of the embodiment has the refractive index change layer 31 (support layer 34 having the refractive index change region 35), the gap layer 32, and the anti-reflection film 22 so that light is less likely to be reflected at the boundary between the refractive index change layer 31 (support layer 34) and the gap layer 32 and at the boundary between the anti-reflection film 22 and the gap layer 32.

[0056] In the solar cell 100, it is preferable that the top cell 10 and the bottom cell 20 are not joined together by a layered adhesive layer covering the power generating element 21 of the bottom cell 20, and that the refractive index change layer 31 (support layer 34) and the bottom cell 20 are not joined together. That is, in the stacking direction of the top cell 10 and the bottom cell 20, it is preferable that no adhesive layer exists between the refractive index change layer 31 (support layer 34) and the power generating element 21 of the bottom cell 20. It is also preferable that only the gap layer 32 exists between the refractive index change layer 31 (support layer 34) and the bottom cell 20 in the stacking direction of the top cell 10 and the bottom cell 20. In the stacking direction of the top cell 10 and the bottom cell 20, members such as a holding portion 33 or an adhesive layer (not shown) may exist between the refractive index change layer 31 (support layer 34) and members other than the power generating element 21 of the bottom cell 20.

[0057] The anti-reflection coating 22 and the refractive index change layer 31 (support layer 34) of the solar cell 100 of the embodiment are configured to have a refractive index that reduces reflection at the interface with the gap layer 32. When the top cell 10 and the bottom cell 20 are joined together, for example, with an adhesive layer without the gap layer 32, the surface member of the top cell 10 facing the bottom cell 20 (e.g., a substrate or a transparent electrode) is in direct contact with the adhesive. Because the refractive index of the adhesive layer is, for example, approximately 1.5, the difference in refractive index between the adhesive layer and the bottom cell 20 is slightly large, which makes reflection more likely at the interface between the bottom cell 20 and the adhesive layer. In the embodiment, light transmitted through the top cell 10 passes through the refractive index change layer 31 (support layer 34) and the gap layer 32, allowing light transmitted through the top cell 10 side to reach the light incident surface of the bottom cell 20 with almost no reflection. Furthermore, by providing the anti-reflection coating 22 on the incident surface of the bottom cell 20, reflection occurring at the interface between the anti-reflection coating 22 and the gap layer 32 (e.g., an air layer), which is a medium with a refractive index of approximately 1, can be suppressed. By intentionally not using a configuration in which the top cell 10 and the bottom cell 20 are sealed with an adhesive and instead directing the light that passes through the top cell 10 through the air to the bottom cell 20 side, reflection at the component boundary from the top cell 10 to the bottom cell 20 can be effectively reduced.

[0058] When a configuration is adopted in which the space between the top cell 10 and the bottom cell 20 is sealed with an adhesive, if an anti-reflection film 22 whose refractive index on the top cell 10 side is close to 1 (for example, a refractive index of 1.1) is provided on the incident surface side of the bottom cell 20, reflection becomes more likely due to the difference in refractive index between the adhesive and the anti-reflection film 22. In the solar cell 100 of the embodiment, by making both the exit surface on the top cell 10 side and the incident surface on the bottom cell 20 side a medium with a refractive index of approximately 1, such as air, less reflective, the amount of power generated on the bottom cell 20 side can be increased.

[0059] The gap layer 32 is an insulating region. The top cell 10 and the bottom cell 20 are not electrically connected via the refractive index change layer 31 (support layer 34) and the gap layer 32. The top cell 10 and the bottom cell 20 are electrically insulated via the refractive index change layer 31 (support layer 34) and the gap layer 32. When the refractive index change layer 31 (support layer 34) is physically separated from the bottom cell 20, the glassy carbon may form irregularities or grooves on the surface of the refractive index change layer 31 (support layer 34).

[0060] If a sheet-like insulating film or organic material layer exists between the refractive index change layer 31 (support layer 34 having refractive index change region 35) and the gap layer 32, such that the refractive index is higher than that of the bottom cell 20 side (opposite the top cell 10 side) of the refractive index change layer 31 (support layer 34 having refractive index change region 35), reflection occurs at the interface between the sheet-like insulating film or organic material layer and the refractive index change layer 31 (support layer 34 having refractive index change region 35) or at the interface between the sheet-like insulating film or organic material layer and the bottom cell 20, reducing the amount of light reaching the bottom cell 20 side. Connecting the top cell 10 and the bottom cell 20 with a low-refractive index member and the gap layer 32 can reduce reflection from both the exit surface of the top cell 10 and the entrance surface on the bottom cell 20 side.

[0061] The retaining portion 33 is a member that retains the top cell 10 and / or the refractive index change layer 31 (support layer 34) and the bottom cell 20. The retaining portion 33 retains the top cell 10 and / or the refractive index change layer 31 (support layer 34) and the bottom cell 20, thereby providing the gap layer 32. The retaining portion 33 may be a protruding portion of the refractive index change layer 31 (support layer 34), or the like.

[0062] The holding portion 33 is preferably provided outside the power generation effective area of ​​the top cell 10 and the bottom cell 20. The outside of the power generation effective area of ​​the top cell 10 is an area that does not overlap with the light absorption layer of the top cell 10 in the stacking direction of the top cell 10 and the bottom cell 20. The outside of the power generation effective area of ​​the bottom cell 20 is an area that does not overlap with the light absorption layer of the bottom cell 20 in the stacking direction of the top cell 10 and the bottom cell 20.

[0063] FIG. 3 is a schematic diagram showing the positional relationship between the power generation effective area 11 of the top cell 10 and the retaining portion 33. The retaining portion 33 is preferably located in the hatched area 33a in FIG. 3. The power generation effective area 11 of the top cell 10 is, for example, the area where the light absorption layer of the top cell 10 is provided. In the stacking direction of the top cell 10 and the bottom cell 20, the retaining portion 33 preferably does not cover 95% to 100% of the power generation effective area 11 of the top cell 10, more preferably does not cover 98% to 100%, and even more preferably does not cover 99% to 100%. In the stacking direction of the top cell 10 and the bottom cell 20, the retaining portion 33 preferably does not cover 100% of the power generation effective area 11 of the top cell 10.

[0064] FIG. 4 is a schematic diagram showing the positional relationship between the power generation effective area 23 of the bottom cell 20 and the retaining portion 33. The retaining portion 33 is preferably located in the hatched area 33a in FIG. 4. The power generation effective area 23 of the bottom cell 20 is, for example, the area where the light absorption layer of the bottom cell 20 is provided. In the stacking direction of the top cell 10 and the bottom cell 20, the retaining portion 33 preferably does not cover 95% to 100% of the power generation effective area 23 of the bottom cell 20, more preferably does not cover 98% to 100%, and even more preferably does not cover 99% to 100%. In the stacking direction of the top cell 10 and the bottom cell 20, the retaining portion 33 preferably does not cover 100% of the power generation effective area 23 of the bottom cell 20.

[0065] As a specific example of the solar cell 100, a schematic diagram of a specific solar cell 102 is shown in Figure 5. The solar cell 102 shown in the schematic diagram of Figure 5 has, from the light incident side, an antireflection layer 17, a first n-electrode 16, an n-type layer 15, a p-type light absorbing layer 14, a first p-electrode 13, a substrate 12, a refractive index change layer 31, a gap layer 32, a second p-electrode 28, an antireflection film 22, a p-type layer 27, an n-type light absorbing layer 26, a BSF layer 25, and a second n-electrode 24. Figure 5 shows a top cell 10 that assumes the use of a compound semiconductor layer as the p-type light absorbing layer 14. A suitable configuration of the top cell 10 can be adopted depending on the material used for the p-type light absorbing layer 14.

[0066] The substrate 12 is a transparent substrate. The substrate 12 may be made of an organic substrate such as a light-transmitting acrylic, polyimide, polycarbonate, polyethylene terephthalate (PET), polypropylene (PP), fluorine-based resin (polytetrafluoroethylene (PTFE), perfluoroethylene propene copolymer (FEP), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), perfluoroalkoxyalkane (PFA)), polyarylate, polysulfone, polyethersulfone, or polyetherimide, or an inorganic substrate such as soda-lime glass, white plate glass, chemically strengthened glass, or quartz. The substrate 12 may be made by laminating the above-listed substrates.

[0067] The first p-electrode 13 is provided on the substrate 12 and is disposed between the substrate 12 and the p-type light absorbing layer 14. The first p-electrode 13 preferably forms an ohmic junction with the p-type light absorbing layer 14. The first p-electrode 13 is provided on the p-type light absorbing layer 14 side and is a conductive layer that is optically transparent to light with wavelengths from about 1200 nm to visible light. The thickness of the first p-electrode 13 is typically 50 nm to 2000 nm. In FIG. 5, the first p-electrode 13 is in direct contact with the p-type light absorbing layer 14. The first p-electrode 13 preferably includes one or more transparent conductive oxide films. Examples of the oxide transparent conductive film include semiconductor conductive films such as indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), boron-doped zinc oxide (BZO), gallium-doped zinc oxide (GZO), doped tin oxide, titanium-doped indium oxide (ITiO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), and hydrogen-doped indium oxide (IOH). The oxide transparent conductive film may be a laminated film having multiple films. The dopant for the tin oxide film or the like is not particularly limited as long as it is one or more elements selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. The first p-electrode 13 preferably includes a tin oxide film doped with one or more elements selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. In the doped tin oxide film, the one or more elements selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. are preferably contained in an amount of 10 atomic % or less relative to the tin contained in the tin oxide film. The first p-electrode 13 can be a laminated film formed by stacking a transparent conductive oxide film and a metal film.The metal film preferably has a thickness of 1 nm to 500 μm. The metal (including alloy) contained in the metal film is not particularly limited, and may be Mo, Au, Cu, Ag, Al, Ta, or W. The metal film is preferably a conductive layer with openings rather than a solid film. The first p-electrode 13 preferably includes a dot-, line-, or mesh-shaped electrode (one or more selected from the group consisting of metals, alloys, graphene, conductive nitrides, and conductive oxides) between the oxide transparent conductive film and the substrate 12, or between the oxide transparent conductive film and the p-type light absorbing layer 14. The dot-, line-, or mesh-shaped metal preferably has an opening ratio of 50% or more relative to the oxide transparent conductive film. The dot-, line-, or mesh-shaped metal may be Mo, Au, Cu, Ag, Al, Ta, or W, and is not particularly limited. When a metal film is used for the first p-electrode 13, the thickness is preferably approximately 5 nm or less from the viewpoint of light transparency. When a line-shaped or mesh-shaped metal film is used, the light transmittance is ensured by the openings, so the thickness of the metal film is not limited to the above. For example, by fabricating the top cell 10 using the refractive index change layer 31 as the substrate 12, the solar cell 104 can be obtained without using a separate refractive index change layer 31.

[0068] It is preferable that a doped tin oxide film be provided on the outermost surface of the oxide transparent conductive film on the side of the p-type light absorbing layer 14, forming an ohmic junction with the p-type light absorbing layer 14. It is preferable that at least a part of the doped tin oxide film provided on the outermost surface of the p-type light absorbing layer 14 of the oxide transparent conductive film be in direct contact with the p-type light absorbing layer 14.

[0069] The p-type light absorbing layer 14 is a light absorbing layer provided between the n-type layer 15 and the first p-electrode 13. The p-type light absorbing layer 14 preferably contains one selected from the group consisting of cuprous oxide (cuprous oxide compound having a cuprite structure), compounds having a chalcopyrite structure, compounds having a kesterite structure, compounds having a stannite structure, and transition metal chalcogenides. Depending on the type of compound semiconductor, an n-type semiconductor layer can be used for the p-type light absorbing layer 14, and a p-type semiconductor layer can be used for the n-type layer 15. An i-type semiconductor layer can be provided between the p-type light absorbing layer 14 and the n-type layer 15.

[0070] The area of ​​the p-type light absorbing layer 14 is the power generation effective area 11 of the top cell 10 .

[0071] The n-type layer 15 is a semiconductor layer that forms a pn junction or a pin junction with the p-type light absorbing layer 14. A suitable n-type layer 15 can be used depending on the p-type light absorbing layer 14. As the n-type layer 15, it is preferable to use, for example, a metal oxide, a metal sulfide, or a metal oxysulfide.

[0072] The first n-electrode 16 is an electrode on the n-type layer 15 side that is optically transparent in the wavelength range from about 1200 nm to the ultraviolet region. The first n-electrode 16 is preferably provided on the n-type layer 15. The n-type layer 15 is sandwiched between the first n-electrode 16 and the p-type light absorbing layer 14. An intermediate layer (not shown) can be provided between the n-type layer 15 and the first n-electrode 16. A transparent conductive oxide film is preferably used for the first n-electrode 16. The transparent conductive oxide film used for the first n-electrode 16 is preferably one or more semiconductor conductive films selected from the group consisting of indium tin oxide, aluminum-doped zinc oxide, boron-doped zinc oxide, gallium-doped zinc oxide, indium-doped zinc oxide, titanium-doped indium oxide, indium gallium zinc oxide, and hydrogen-doped indium oxide. The dopant for the tin oxide film or the like is not particularly limited as long as it is at least one selected from the group consisting of In, Si, Ge, Ti, Cu, Sb, Nb, Ta, W, Mo, F, Cl, etc. The first n-electrode 16 may include a mesh- or line-shaped electrode to reduce the resistance of the oxide transparent conductive film. The mesh- or line-shaped electrode may include, but is not limited to, Mo, Au, Cu, Ag, Al, Ta, and W. Graphene may also be used for the first n-electrode 16. Graphene is preferably stacked with silver nanowires.

[0073] The thickness of the first n-electrode 16 is determined by cross-sectional observation using an electron microscope or a step gauge, and is not particularly limited, but is typically 30 nm or more and 2 μm or less.

[0074] The first n-electrode 16 is preferably formed by, for example, ALD or sputtering.

[0075] When a perovskite compound is used as the light absorption layer of the top cell 10, the p-type light absorption layer 14 and the n-type layer 15 can be replaced with a hole transport layer (e.g., p-type PEDOT:PSS), a photoactive layer (e.g., perovskite compound and pyrrolidone derivative), and an electron transport layer (e.g., n-type TiO).

[0076] The antireflection layer 17 is an antireflection layer provided on the incident surface side of the top cell 10. The antireflection layer 17 suppresses reflection at the incident surface of the top cell 10. The antireflection layer 17 contains an inorganic material and / or an organic material. The refractive index of the surface of the antireflection layer 17 opposite the p-type light absorbing layer 14 is preferably 1.0 or more and 1.9 or less. The antireflection layer 17 can be multilayered depending on the refractive index of the first n-electrode 16. For example, the antireflection layer 17 can have a structure in which an Al2O3 layer provided on the first n-electrode 16 side is laminated with a film having a moth-eye surface structure, or a sputtered film of an inorganic material such as MgF2, SiN, TiO2, or SiO2. The incident surface side of the antireflection layer 17 preferably has irregularities. The irregularities of the antireflection layer 17 are convex on the incident surface side and concave on the bottom cell 20 side. The irregularities are needle-like irregularities or grooves tapering toward the bottom cell 20 side. The groove pattern may be a line pattern, a mesh pattern, or a random pattern.

[0077] The anti-reflection film 22 is an anti-reflection film provided on the incident surface side of the bottom cell 20. The anti-reflection film 22 is a layer that suppresses reflection on the incident surface of the bottom cell 20. The anti-reflection film 22 includes an inorganic material and / or an organic material. For example, a film with a moth-eye surface structure or a sputtered film of an inorganic material such as MgF2, SiN, TiO2, or SiO2 can be used as the anti-reflection film 22. The incident surface side of the anti-reflection film 22 preferably has irregularities. The irregularities of the anti-reflection film 22 have convex portions on the top cell 10 side and concave portions on the power generating element 21 side. The irregularities are needle-like irregularities or grooves that taper toward the bottom cell 20 side. The groove pattern may be line-shaped, mesh-shaped, random, or the like.

[0078] A PERC (Passivated Emitter and Rear Cell) type Si solar cell is exemplified as the bottom cell 20. The bottom cell 20 may also be a back-contact type, a TOPCon (Tunnel Oxide Passivated Contacts) type, or an SHJ (Silicon Heterojunction) type Si solar cell. In addition to a Si solar cell, a solar cell using a light absorption layer with a narrower band gap than the light absorption layer of the top cell 10 can also be used as the bottom cell 20. A transparent solar cell can also be used as the bottom cell 20.

[0079] The second n-electrode 24 is, for example, a solid metal film. As the metal film, an opaque electrode such as Al can be used.

[0080] The n-type light absorbing layer 26 is an n-type Si layer.

[0081] The area of ​​the n-type light absorbing layer 26 is the power generation effective area 23 of the bottom cell 20 .

[0082] The BSF layer 25 is, for example, an AlO / SiN layer.

[0083] The p-type layer 27 is a p-type Si layer.

[0084] The second p-electrode 28 is an electrode that penetrates the anti-reflection film 22 and is, for example, an Ag extraction electrode.

[0085] As a specific example of solar cell 100, a schematic diagram of a specific solar cell 103 is shown in Fig. 6. Solar cell 103 shown in the schematic diagram of Fig. 6 has, from the light incident side, an antireflection layer 17, a first n-electrode 16, an n-type layer 15, a p-type light absorbing layer 14, a first p-electrode 13, a substrate 12, a support layer 34 having a refractive index change region 35, a gap layer 32, a second p-electrode 28, an antireflection film 22, a p-type layer 27, an n-type light absorbing layer 26, a BSF layer 25, and a second n-electrode 24. Solar cell 103 shown in the schematic diagram of Fig. 6 uses a support layer 34 having a refractive index change region 35 instead of the refractive index change layer 31 of solar cell 102 shown in the schematic diagram of Fig. 5.

[0086] As a specific example of the solar cell 100, a schematic diagram of a specific solar cell 104 is shown in FIG. 7. The solar cell 104 shown in the schematic diagram of FIG. 7 includes, from the light incident side, an antireflection layer 17, a first n-electrode 16, an n-type layer 15, a p-type light absorbing layer 14, a first p-electrode 13, a support layer 34 having a refractive index change region 35, a gap layer 32, a second p-electrode 28, an antireflection film 22, a p-type layer 27, an n-type light absorbing layer 26, a BSF layer 25, and a second n-electrode 24. The solar cell 104 shown in the schematic diagram of FIG. 7 does not use the substrate 12 of the solar cell 103 shown in the schematic diagram of FIG. 6, but instead has a top cell 10 provided on the surface of the support layer 34 opposite the refractive index change region 35. The solar cell 104 shown in the schematic diagram of FIG. 7 uses the support layer 34 as the substrate for the top cell 10. For example, by fabricating the top cell 10 using the support layer 34 as the substrate 12, the solar cell 104 can be obtained without using a separate support layer 34.

[0087] As a specific example of the solar cell 100, a schematic diagram of a specific solar cell 105 is shown in FIG. 8. The solar cell 105 shown in the schematic diagram of FIG. 8 has three top cells 10 and one bottom cell 20. The multiple top cells 10 are electrically connected by wiring (not shown). The multiple top cells 10 are provided on one or more refractive index change layers 31.

[0088] As a specific example of the solar cell 100, FIG. 9 shows a schematic diagram of a specific solar cell 106. The solar cell 106 shown in the schematic diagram of FIG. 9 has four top cells 10 and two bottom cells 20. The multiple top cells 10 are electrically connected by wiring (not shown). The multiple top cells 10 are provided on one or more refractive index change layers 31. The multiple bottom cells 20 are electrically connected by wiring (not shown). The multiple bottom cells 20 can be held by a holding layer 36. The holding layer 36 may be a member that functions as wiring that electrically connects the bottom cells 20.

[0089] An insulating member 37 having a refractive index similar to that of the refractive index change layer 31 may be provided in the region between adjacent top cells 10. The refractive index of the insulating member 37 present in the region between adjacent top cells 10 is preferably 0.8 to 1.2 times, and more preferably 0.9 to 1.1 times, that of the refractive index change layer 31. The insulating member 37 is preferably made of, for example, resin or oil.

[0090] Moreover, instead of the insulating member 37, an antireflection film 38 similar to the antireflection layer 17 may be provided. Moreover, an antireflection film 38 may be further provided on the incident surface side of the insulating member 37.

[0091] The holding portion 33 of the solar cell 106 is preferably made of a light-transmitting material. The region of the holding portion 33 facing the gap layer 32 preferably has a refractive index of 1.0 or more and 1.1 or less on the surface facing the gap layer 32, similar to the refractive index change layer 31 or the refractive index change region 35. By setting the refractive index of the surface of the region of the holding portion 33 facing the gap layer 32 to 1.0 or more and 1.1 or less, the holding portion 33 also functions as the refractive index change layer 31 (refractive index change region 35). Furthermore, when the holding portion 33 covers the effective power generation region 23 of the bottom cell 20, the holding portion 33 may have light diffusibility to diffuse light and increase the amount of light introduced into the bottom cell 20. Alternatively, a protrusion of the refractive index change layer 31 (support layer 34) may serve as the holding portion 33.

[0092] By adopting the configuration of the first embodiment, in various forms, light that has passed through the top cell 10 reaches the bottom cell 20 with little reflection, contributing to an improvement in the amount of power generated by the bottom cell 20. In addition to providing an anti-reflection film on the light incident surface of the solar cell, providing one on the light exit surface of the top cell 10 can improve the conversion efficiency of the entire solar cell.

[0093] (Second embodiment) The second embodiment relates to a solar cell.

[0094] The solar cell of the embodiment includes a transparent top cell, a bottom cell, a support layer having a refractive index change layer or a refractive index change region between the top cell and the bottom cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side, a high refractive index on the top cell side, and a low refractive index on the bottom cell side of the refractive index change region. The gap layer electrically insulates the top cell and the bottom cell.

[0095] The solar cell of the embodiment is a transmissive top cell that, when connected to a bottom cell, has a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell, and a gap layer between the refractive index change layer and the bottom cell or between the support layer and the bottom cell. The refractive index change layer has a high refractive index on the top cell side, a low refractive index on the bottom cell side of the refractive index change layer, a high refractive index on the top cell side of the refractive index change region, and a low refractive index on the bottom cell side of the refractive index change region. The gap layer can electrically insulate the top cell from the bottom cell.

[0096] FIG. 10 shows a schematic diagram of a solar cell. The solar cell 107 shown in the schematic diagram of FIG. 10 has a top cell 10, a bottom cell 20, a refractive index change layer 31, a gap layer 32, and a holding portion 33. The solar cell of the second embodiment is also a solar cell module. The solar cell 107 of the second embodiment is a modified example of the solar cells (100 to 106) of the first embodiment. Descriptions of the content common to the first and second embodiments will be omitted.

[0097] The configuration of a solar cell when the top cell 10 is connected to the bottom cell 20 will be described.

[0098] The refractive index change layer 31 (support layer 34) has irregularities on the bottom cell 20 side. At least a part of the tip of the convex part of the irregularities on the bottom cell 20 side of the refractive index change layer 31 (refractive index change region 35) is in direct contact with the incident surface side of the bottom cell 20.

[0099] The convex portion of the refractive index change layer 31 (refractive index change region 35) comes into contact with the bottom cell 20, thereby dividing the gap layer 32.

[0100] Even when the convex portion of the refractive index change layer 31 (refractive index change region 35) is in contact with the bottom cell 20, the surface of the refractive index change layer 31 (refractive index change region 35) has a low refractive index, and the incident surface on the bottom cell 20 side also has a low refractive index, so reflection at the interface between the refractive index change layer 31 (refractive index change region 35) and the anti-reflection film 22 is suppressed, and the amount of light introduced to the bottom cell 20 side can be increased, as in the first embodiment. Increasing the amount of light introduced to the bottom cell 20 side contributes to improving the amount of power generation on the bottom cell 20 side. In addition to providing an anti-reflection film on the incident surface side of the solar cell, providing one on the light exit surface side of the top cell 10 can improve the conversion efficiency of the entire solar cell.

[0101] (Third embodiment) The third embodiment relates to a solar cell.

[0102] The solar cell of the embodiment includes a transmissive top cell and a support layer having a refractive index change layer or a refractive index change region on the light-emitting surface side of the top cell, wherein the refractive index change layer has a high refractive index on the top cell side and a low refractive index on the side opposite to the top cell side, and the refractive index change region has a high refractive index on the top cell side and a low refractive index on the side opposite to the top cell side.

[0103] A schematic diagram of a solar cell is shown in Figure 11. Solar cell 108 of the third embodiment is a modified example of the solar cells (100 to 106) of the first embodiment or solar cell 107 of the second embodiment. Descriptions of the content common to the first to third embodiments will be omitted.

[0104] The solar cell 108 shown in the schematic diagram of FIG. 11 has a top cell 10 and a refractive index change layer 31 (a support layer 34 having a refractive index change region 35). Of the light incident on the top cell 10, the light that is not absorbed or reflected by the top cell 10 passes through the air outside the refractive index change layer 31 (a support layer 34 having a refractive index change region 35). By providing the refractive index change layer 31 (a support layer 34 having a refractive index change region 35) on the light output surface side of the top cell 10, reflection at the boundary between the air on the light output surface side and the refractive index change layer 31 (a support layer 34 having a refractive index change region 35) can be reduced. Compared to a solar cell 108 without the refractive index change layer 31 (a support layer 34 having a refractive index change region 35), the solar cell 108 has excellent light transmittance, and therefore can increase the amount of light output from the light output surface side of the top cell 10. Furthermore, by changing the shape of the irregularities or grooves on the surface opposite to the top cell 10 of the refractive index change layer 31 (support layer 34 having the refractive index change region 35), it is possible to make the solar cell 108 highly transparent or to make it into privacy glass such as frosted glass.

[0105] (Fourth embodiment) The fourth embodiment relates to a solar power generation system. The solar cells of the first to third embodiments can be used as generators to generate electricity in the solar power generation system of the fourth embodiment. The solar power generation system of the embodiment generates electricity using solar cells, and specifically includes a solar cell that generates electricity, a means for converting the generated electricity, and a storage means for storing the generated electricity or a load for consuming the generated electricity. FIG. 12 shows a configuration diagram of a solar power generation system 200 of the embodiment. The solar power generation system of FIG. 11 includes a solar cell 201 (100-107), a converter 202, a storage battery 203, and a load 204. The solar cell 201 is, for example, a solar cell module including multiple sub-modules each electrically connected with a large number of top cells 10 of the solar cells 100-106, and multiple bottom cells 20, or a solar cell module including multiple sub-modules each electrically connected with a large number of top cells 10 of the solar cell 107. Either the storage battery 203 or the load 204 may be omitted. The load 204 may be configured to be able to utilize electrical energy stored in the storage battery 203. The converter 202 is a device including circuits or elements that perform power conversion such as voltage transformation and DC-AC conversion, such as a DC-DC converter, a DC-AC converter, or an AC-AC converter. The converter 202 may be configured in a suitable manner depending on the power generation voltage and the configurations of the storage battery 203 and the load 204. A converter 202 for the top cell 10 and a converter 202 for the bottom cell 20 may be used separately. A common converter 202 for the top cell 10 and the bottom cell 20 may be used in the solar power generation system.

[0106] The top cell 10 and bottom cell 20 included in the solar cell 201 receive light and generate electricity, and the electrical energy is converted by the converter 202 and stored in the storage battery 203 or consumed by the load 204. The solar cell 201 is preferably provided with a solar tracking drive device for always directing the solar cell 201 toward the sun, a concentrator for concentrating sunlight, or other devices for improving power generation efficiency.

[0107] The solar power generation system 200 is preferably used in real estate such as residences, commercial facilities, factories, etc., or in movable property such as vehicles, aircraft, electronic devices, etc. By using the solar cell with excellent conversion efficiency of the embodiment in a solar cell module, an increase in the amount of power generation is expected.

[0108] A vehicle is shown as an example of the use of the solar power generation system 200. FIG. 13 shows a conceptual diagram of the configuration of the vehicle 300. The vehicle 300 in FIG. 13 includes a vehicle body 301, a solar cell 302 (201), a power converter 303, a storage battery 304, a motor 305, and tires (wheels) 306. The power generated by the solar cell 302 provided on the top of the vehicle body 301 is converted by the power converter 303 and charged in the storage battery 304, or the power is consumed by loads such as the motor 305. The vehicle 300 can be moved by rotating the tires (wheels) 306 using the power supplied from the solar cell 302 or the storage battery 304 with the motor 305. When optically transparent solar cells 302 are used as the solar cells 302, it is also preferable to use the solar cells 302 as power-generating windows on the sides of the vehicle body 301 in addition to the top of the vehicle body 301.

[0109] An air vehicle (drone) is shown as an example of use of the solar power generation system 200. The air vehicle uses a solar cell 201. The configuration of the air vehicle according to this embodiment will be briefly described using the schematic diagram of an air vehicle 400 in FIG. 14. The air vehicle 400 has a solar cell 401 (201), a body frame 402, a motor 403, rotors 404, and a control unit 405. The solar cell 401, the motor 403, the rotors 404, and the control unit 405 are arranged on the body frame 402. The control unit 405 converts the power output from the solar cell 401 and adjusts the output. The motor 403 uses the power output from the solar cell 401 to rotate the rotors 404. By using the air vehicle 400 with this configuration that includes the solar cell 401 of the embodiment, a air vehicle that can fly using more power is provided.

[0110] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0111] Example A (Example A1) ITO (In:Sn=80:20, film thickness 150 nm) and ATO (Sn:Sb=98:2, film thickness 100 nm) are deposited on the top surface of a glass substrate 12, the side that contacts the glass, to form a first p-electrode 13 on the rear side. A 6 μm-thick CuO layer is formed on the ATO by sputtering in an oxygen and argon gas atmosphere as a p-type light absorbing layer 14. After the p-type light absorbing layer 14 is formed, a 10 nm-thick GaO film is formed as an n-type layer 15. A 0.1 μm-thick AZO (ZnO:Al) film is then formed by ALD as a first n-electrode 16, and a refractive index change layer 31 is formed on the side of the substrate 12 opposite the first p-electrode 13, thereby completing the top cell 10. The refractive index changing layer 31 of Example A1 has pyramidal irregularities on the surface of an acrylic resin layer having a refractive index of 1.49 as a base material, with the diameter of the protrusions being 800 nm, the pitch of the protrusions being 800 nm, and the height of the protrusions (≈ the thickness of the refractive index changing layer 31) being 1000 nm. The refractive index of the refractive index changing layer 31 on the side opposite to the top cell 10 side is 1.05.

[0112] A solar simulator simulating an AM1.5G light source is used, and a reference Si cell is used under that light source, with the light intensity adjusted to achieve 1 sun. Measurements are taken at atmospheric pressure with the temperature of the measurement room at 25°C. The voltage is swept and the short-circuit current density Jsc (current divided by cell area) is measured. With the horizontal axis representing voltage and the vertical axis representing current density, the point where they intersect is the open-circuit voltage Voc. On the measurement curve, multiply the voltage and short-circuit current density, and the points at which they are maximum are designated Vmpp and Jmpp (maximum power point), respectively. The fill factor can be calculated as FF = (Vmpp * Jmpp) / (Voc * Jsc). Conversion efficiency can also be calculated as Eff. = Voc * Jsc * FF.

[0113] (Examples A2 to A14, Comparative Examples A1 and A2) A top cell is prepared in the same manner as in Example A1, except that the refractive index change layer 31 shown in the table of Fig. 15 is formed, and evaluation is performed in the same manner as in Example A1. Note that in Comparative Example A1, the refractive index change layer 31 is not formed. When the refractive index change layer 31 is multilayered, the material on the top cell 10 side is written on the left side in the column for base material in Fig. 15, and the material on the opposite side to the top cell 10 side is written on the right side.

[0114] The light transmittance is evaluated as A when the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less is more than 102% and 130% or less of the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less of the comparative sample. The light transmittance is evaluated as B when the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less is 98% or more and 102% or less of the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less of the comparative sample. The light transmittance is evaluated as C when the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less is less than 98% of the light intensity (cd) in the wavelength band of 700 nm or more and 1000 nm or less of the comparative sample. The evaluation of light transmittance is common to Example A and Examples other than Example A.

[0115] When Jsc is 0.95 to 1.05 times the conversion efficiency of the comparison target, it is evaluated as A, and when it is less than 0.95 times the Jsc of the comparison target, it is evaluated as B. The evaluation of Jsc is common to Example A and examples other than Example A.

[0116] When Voc is 0.95 to 1.05 times the conversion efficiency of the comparison target, it is evaluated as A, and when it is less than 0.95 times the Voc of the comparison target, it is evaluated as B. The evaluation of Voc is common to Example A and examples other than Example A.

[0117] FF is evaluated as A when it is 0.95 to 1.05 times the conversion efficiency of the comparison target, and is evaluated as B when it is less than 0.95 times the conversion efficiency of the comparison target. The evaluation of FF is common to Example A and examples other than Example A.

[0118] Conversion efficiency greater than 1.05 times the conversion efficiency of the comparison target was evaluated as A. Conversion efficiency between 0.95 and 1.05 times was evaluated as B, and conversion efficiency less than 0.95 times the conversion efficiency of the comparison target was evaluated as C. The evaluation of conversion efficiency is common to Example A and examples other than Example A.

[0119] The evaluation results of Example A are shown in the table of FIG.

[0120] In samples of various shapes using multiple materials, the light transmittance was improved. Although the amount of light transmitted to the bottom cell increased, there was almost no change in the amount of light absorbed by the top cell, so no significant differences were observed in Jsc, Voc, FF, or conversion efficiency. From these results, it can be seen that introducing a refractive index change layer on the bottom cell side of the top cell does not have a negative impact on the top cell side. In Example A, a solar cell was used that used a compound semiconductor as the p-type light absorption layer 14, but the transmittance of the top cell 10 also improved in other solar cells that use perovskite compounds, etc.

[0121] Example B Example B1 A multi-junction solar cell is fabricated by using a RERC-type polycrystalline Si solar cell as the bottom cell 20 and combining it with the top cell 10 with the refractive index change layer 31 of Example A1. An air gap layer 32 is provided between the refractive index change layer 31 and the bottom cell 20 so that the distance from the tip of the refractive index change layer 31 to the second p-electrode 28 of the bottom cell 20 is 100 μm. The same light source as in Example A is used to irradiate the cells, and the total conversion efficiency of the top cell 10 and bottom cell 20 is determined, and the difference in conversion efficiency from a comparison target is evaluated.

[0122] (Examples B2 to B14, Comparative Examples B1 and B2) The top cell 10 was replaced, and the total conversion efficiency of the top cell 10 and the bottom cell 20 was determined in the same manner as in Example B1, and the difference in conversion efficiency from the comparison target was evaluated. The top cell 10 used in Example B is shown in the table of FIG.

[0123] The evaluation results of Example B are shown in the table of FIG.

[0124] As described above, there is no significant difference in the conversion efficiency of the top cell. However, compared to Comparative Example A1, the improved light transmittance leads to an improvement in the Jsc of the bottom Si cell, and thus to an improvement in conversion efficiency. Simply introducing an acrylic resin, as in Comparative Example B2, provides a slight anti-reflection effect and improves conversion efficiency, but not as much as in the other examples. These results confirm that the introduction of a refractive index-changing layer improves the efficiency of the bottom cell. In Example B14, although the two layers are flat, the addition of two layers provides an anti-reflection effect, resulting in improved conversion efficiency compared to Comparative Example B2. These results further support the effect of gradually lowering the refractive index from the glass substrate side. Comparative Example B2 uses a top cell 10 in which the refractive index-unchanging acrylic resin of Comparative Example A2 is used instead of the refractive index-unchanging layer 31, and no improvement in conversion efficiency is observed compared to Comparative Example B1.

[0125] Example C Example C1 ITO (In:Sn=80:20, film thickness 150 nm) and ATO (Sn:Sb=98:2, film thickness 100 nm) are deposited on the top surface of a glass substrate 12, on the side in contact with the glass, to form the first p-electrode 13 on the rear side. A 6 μm-thick CuO layer is formed on the ATO by sputtering in an oxygen and argon gas atmosphere as the p-type light absorbing layer 14. After the p-type light absorbing layer 14 is formed, a 10 nm-thick GaO film is formed as the n-type layer 15. A 0.1 μm-thick AZO (ZnO:Al) film is then formed by ALD as the first n-electrode 16, and a support layer 34 is formed on the side of the substrate 12 opposite the first p-electrode 13, to obtain the top cell 10. The support layer 34 in Example C1 is an acrylic resin layer with a refractive index of 1.49 and a thickness of 50 μm. A refractive index change region 35 is formed on the surface of the support layer 34. The refractive index change region 35 has pyramidal irregularities with a diameter of 800 nm, a pitch of 800 nm, and a height of 1000 nm. The refractive index of the refractive index change region 35 on the side opposite to the top cell 10 is 1.05.

[0126] (Examples C2 to C16, Comparative Examples C1 and C2) A top cell is prepared in the same manner as in Example C1, except that the support layer 34 shown in the table of Figure 19 is formed, and evaluation is performed in the same manner as in Example A1. Note that in Comparative Example C1, no support layer 34 is formed. When the support layer 34 is multi-layered, in Figure 15, the material on the top cell 10 side and the like are written on the left side in the column for support layer 34, and the material on the opposite side from the top cell 10 side and the like are written on the right side.

[0127] The evaluation results of Example C are shown in the table of FIG.

[0128] As with Example A, in which the texture was formed directly on the glass substrate, Example C also showed improved light transmittance in samples of various shapes using multiple materials. Although the amount of light transmitted to the bottom cell increased, the amount of light absorbed by the top cell remained almost unchanged, resulting in no significant differences in Jsc, Voc, FF, or conversion efficiency. These findings suggest that introducing a refractive index change layer on the bottom cell side of the top cell does not adversely affect the top cell. Examples C14 and C15 were designed to test the effects of a film with a moth-eye surface structure, and like the other examples, they demonstrated improved light transmittance. Example C16 was designed to test the effects of a laminated resin. While its light transmittance was superior to that of Comparative Examples C1 and C2, its improvement in light transmittance was less than that of the other examples due to the larger refractive index difference with the gap layer 32. Comparative Example C2, which uses an acrylic resin with a constant refractive index, is thought to have reduced light transmittance compared to Comparative Example C1 due to the light absorption of the acrylic resin itself. In Example C, the solar cell used a compound semiconductor as the p-type light absorbing layer 14, but the transmittance of the top cell 10 also improves in other solar cells using perovskite compounds and the like.

[0129] Example D Example D1 A multi-junction solar cell is fabricated by using a back-contact type polycrystalline Si solar cell as the bottom cell 20 and combining it with the top cell 10 with the support layer 34 of Example C1. The surface of the support layer 34 on the refractive index change region 35 side is in contact with the bottom cell 20. A gap layer 32 is provided in the gap between the recess of the refractive index change region 35 and the surface of the anti-reflection film 22 of the bottom cell 20. Air is present in the gap layer 32. The same light source as in Example A is used to irradiate the cells, and the total conversion efficiency of the top cell 10 and bottom cell 20 is determined to evaluate the difference in conversion efficiency from a comparison target.

[0130] (Examples D2 to D16, Comparative Examples D1 and D2) The top cell 10 was replaced, and the total conversion efficiency of the top cell 10 and the bottom cell 20 was determined in the same manner as in Example D1, and the difference in conversion efficiency from the comparison target was evaluated. The top cell 10 used in Example D is shown in the table of FIG.

[0131] The evaluation results of Example D are shown in the table of FIG.

[0132] As with Example B, improved light transmittance was observed compared to the state of Comparative Example C1, resulting in improved Jsc of the bottom cell and improved conversion efficiency. Comparative Example D2, in which an acrylic resin with a constant refractive index was used instead of the support layer 34, showed almost no effect on the improvement in conversion efficiency compared to Comparative Example D1. Even with the presence of these substrates, the presence of a region on the surface that changes the refractive index confirmed an improvement in the efficiency of the bottom cell. Similar efficiency improvements were observed in Examples D14, D15, and D16, which had two thick resin layers. It is believed that this effect was due to the fact that the refractive index was not significantly different from the glass substrate used as the top cell.

[0133] Example E Example E1 On the surface of a glass support layer 34 with a refractive index of 1.52 and a refractive index change region 35 on the back surface, ITO (In:Sn=80:20, film thickness 150 nm) and ATO (Sn:Sb=98:2, film thickness 100 nm) are deposited on the upper surface, in contact with the glass, as the first p-electrode 13 on the back surface side. A 6 μm-thick CuO layer is formed on the ATO by sputtering in an oxygen and argon gas atmosphere as the p-type light absorbing layer 14. After the p-type light absorbing layer 14 is formed, a 10 nm-thick GaO film is formed as the n-type layer 15. Then, a 0.1 μm-thick AZO (ZnO:Al) film is formed by ALD as the first n-electrode 16, obtaining the top cell 10. The substrate of Example E1 is the support layer. The refractive index change region 35 of Example E1 has irregularities on the side opposite the top cell 10 side. The unevenness of the refractive index changing region 35 of Example E1 is pyramidal, with a diameter of 500 nm, a pitch of 500 nm, and a height of 1000 nm. The refractive index of the refractive index changing region 35 on the side opposite to the top cell 10 is 1.06.

[0134] (Examples E2 to E16, Comparative Examples E1 to E2) A top cell is prepared in the same manner as in Example E1, except that the support layer 34 shown in the table of Fig. 23 is formed, and evaluation is performed in the same manner as in Example A1. Note that in Comparative Example E1, no support layer 34 is formed. When the support layer 34 is multi-layered, in Fig. 15, the material on the top cell 10 side and the like are written on the left side in the column for support layer 34, and the material on the opposite side from the top cell 10 side and the like are written on the right side.

[0135] The evaluation results of Example E are shown in the table of FIG.

[0136] In Example E, the light transmittance was improved in all samples of various shapes using multiple materials. Although the amount of light transmitted to the bottom cell increased, the amount of light absorbed by the top cell remained almost unchanged, so no significant differences were observed in Jsc, Voc, FF, or conversion efficiency. These findings demonstrate that introducing a refractive index change layer on the bottom cell side of the top cell does not adversely affect the top cell. Examples E15 and E16 were designed to verify the effects of refractive index changes due to nanoimprinting and a multilayer structure, and, like the other examples, showed improved light transmittance. In Example E, a solar cell was used that used a compound semiconductor as the p-type light absorption layer 14. However, the transmittance of the top cell 10 also improved in other solar cells that use perovskite compounds, etc.

[0137] Example F Example F1 A multi-junction solar cell is fabricated by using a PERC-type polycrystalline Si solar cell as the bottom cell 20 and combining it with the top cell 10 with the refractive index change layer 31 of Example E1. An air gap layer 32 is provided between the refractive index change layer 31 and the bottom cell 20 so that the distance from the tip of the refractive index change layer 31 to the second p-electrode 28 of the bottom cell 20 is 100 μm. Air exists in the gap layer 32. The same light source as in Example A is used to irradiate the cells, and the total conversion efficiency of the top cell 10 and bottom cell 20 is determined, and the difference in conversion efficiency with that of a comparison target is evaluated.

[0138] (Examples F2 to F16, Comparative Examples F1 to F2) The top cell 10 was replaced, and the total conversion efficiency of the top cell 10 and bottom cell 20 was determined in the same manner as in Example F1, and the difference in conversion efficiency from the comparison target was evaluated. The top cell 10 used in Example F is shown in the table of FIG.

[0139] The evaluation results of Example F are shown in the table of FIG.

[0140] As with Examples B and D, improved light transmittance was observed compared to the state of Comparative Example F1, resulting in improved Jsc of the bottom cell and improved conversion efficiency. Comparative Example F2, in which an acrylic resin with a constant refractive index was used instead of the support layer 34, showed almost no effect on the improvement of conversion efficiency compared to Comparative Example F1. Even when the structure was formed directly on the glass substrate, the presence of a region that changes the refractive index on the surface confirmed an improvement in the efficiency of the bottom cell. Similar efficiency improvements were observed for Examples F15 and F16 as a result of changing the refractive index using nanoimprinting (Example F15) and a multilayer structure (Example F16).

[0141] Although the embodiments of the present invention have been described above, the present invention should not be construed as being limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiments. For example, components from different embodiments may be appropriately combined, as in modified examples.

[0142] In the specification, some elements are shown only by their element symbols.

[0143] The technical solutions of the embodiments are described below. Technical proposal 1 A transmissive top cell, When connected to the bottom cell, a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The interstitial layer is capable of electrically insulating the top cell and the bottom cell. Technical proposal 2 A transmissive top cell, When connected to the bottom cell, a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The refractive index change layer and the bottom cell are not in direct contact with each other, A solar cell in which the support layer and the bottom cell are not in direct contact with each other. Technical proposal 3 A transparent top cell and a support layer having a refractive index change layer or a refractive index change region on the light exit surface side of the top cell, the refractive index of the refractive index change layer on the side opposite to the top cell side is high, and the refractive index of the refractive index change layer on the side opposite to the top cell side is low, A solar cell in which the refractive index change region has a high refractive index on the side of the top cell, and the refractive index change region has a low refractive index on the side opposite to the top cell. Technical proposal 4 the refractive index change layer is electrically insulating, The solar cell according to any one of Technical Schemes 1 to 3, wherein the support layer is electrically insulating. Technical proposal 5 The solar cell according to Technical Scheme 1 or 2, wherein the gap layer is electrically insulating. Technical proposal 6 the refractive index changing layer is in direct contact with the top cell, the refractive index change layer is provided on the light exit surface side of the top cell, the support layer is in direct contact with the top cell; The solar cell according to any one of technical proposals 1 to 4, wherein the support layer is provided on the light-emitting surface side of the top cell. Technical proposal 7 the refractive index of the surface of the refractive index change layer opposite to the top cell side is 1.0 or more and 1.1 or less; The solar cell according to any one of Technical Solutions 1 to 4 and 6, wherein the refractive index of the surface of the refractive index change region opposite to the top cell side is 1.0 or more and 1.1 or less. Technical proposal 8 the refractive index of the top cell on the refractive index change layer side is 1.3 or more and 2.2 or less; The solar cell according to any one of Technical Schemes 1 to 3, 6 and 7, wherein the refractive index of the support layer side of the top cell is 1.3 or more and 2.2 or less. Technical proposal 9 a refractive index of a member of the top cell that is in direct contact with the refractive index change layer is 1.3 or more and 2.2 or less; A solar cell according to any one of technical proposals 1 to 3 and 6 to 8, wherein the refractive index of the member in direct contact with the support layer of the top cell is 1.3 or more and 2.2 or less. Technical proposal 10 an absolute value of the difference between the refractive index of a member of the top cell that is in contact with the refractive index change layer and the refractive index of the refractive index change layer on the top cell side is 0.0 or more and 1.0 or less; A solar cell described in any one of technical proposals 1 to 3 and 6 to 9, wherein the absolute value of the difference between the refractive index of the member in contact with the support layer of the top cell and the refractive index of the region of the support layer excluding the refractive index change region on the top cell side is 0.0 or more and 1.0 or less. Technical proposal 11 The solar cell according to Technical Scheme 1, 2 or 5, wherein the gap layer is an air layer, an inert gas layer or a vacuum layer. Technical proposal 12 The solar cell according to Technical Scheme 1 or 2, wherein the top cell has a light absorbing layer with a wider band gap than the light absorbing layer of the bottom cell. Technical proposal 13 The solar cell according to Technical Scheme 1, 2, 5 or 12, wherein the top cell and the bottom cell are held by a holding portion. Technical proposal 14 the refractive index of the refractive index change layer decreases stepwise and / or gradiently from the top cell side toward the opposite side to the top cell side, A solar cell described in any one of technical proposals 1 to 3 and 6 to 10, wherein the refractive index of the refractive index change region decreases stepwise or / and gradiently from the top cell side toward the opposite side of the top cell side. Technical proposal 15 A solar power generation system that generates electricity using a solar cell described in any one of technical proposals 1 to 4. Technical proposal 16 A transparent top cell and A bottom cell; a support layer having a refractive index changing layer or a refractive index changing region between the top cell and the bottom cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The interstitial layer electrically insulates the top cell from the bottom cell. Technical proposal 17 A transparent top cell and A bottom cell; a support layer having a refractive index changing layer or a refractive index changing region between the top cell and the bottom cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The refractive index change layer and the bottom cell are not in direct contact with each other, A solar cell in which the support layer and the bottom cell are not in direct contact with each other. [Explanation of symbols]

[0144] 10: Top cell 11: Effective power generation area 12: Circuit board 13: 1st p electrode 14: p-type light absorbing layer 15:n-type layer 16: 1st n electrode 17: Anti-reflection layer 20: Bottom cell 21: Power generating element 22: Anti-reflection film 23: Effective power generation area 24: 2nd n electrode 25:BSF layer 26: n-type light absorbing layer 27:p-type layer 28: 2nd p electrode 31: Refractive index change layer 32: Interstitial layer 33: Holding part 33a: area 34:Support layer 35: Refractive index change region 36: Retention layer 37: Insulating material 38:Anti-reflective coating 100~108: Solar cells 200: Solar power generation system 201: Solar cells 202: Converter 203: Storage battery 204: Load 300: Vehicle 301: Body 302: Solar cells 303: Power conversion equipment 304: Storage battery 305: Motor 400: Projectile object 401: Solar cell 402: Aircraft frame 403: Motor 404: Rotor 405: Control unit

Claims

1. A transmissive top cell, When connected to the bottom cell, a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The spacer layer can electrically insulate the top cell from the bottom cell.

2. A transmissive top cell, When connected to the bottom cell, a support layer having a refractive index change layer or a refractive index change region on the bottom cell side of the top cell; a gap layer between the refractive index change layer and the bottom cell, or between the support layer and the bottom cell; the refractive index of the refractive index change layer on the top cell side is high, and the refractive index of the refractive index change layer on the bottom cell side is low, the refractive index of the refractive index change region on the top cell side is high, and the refractive index of the refractive index change region on the bottom cell side is low, The refractive index change layer and the bottom cell are not in direct contact with each other, A solar cell in which the support layer and the bottom cell are not in direct contact with each other.

3. A transparent top cell and a support layer having a refractive index change layer or a refractive index change region on the light exit surface side of the top cell, the refractive index of the refractive index change layer on the side opposite to the top cell side is high, and the refractive index of the refractive index change layer on the side opposite to the top cell side is low, A solar cell in which the refractive index change region has a high refractive index on the side of the top cell, and the refractive index change region has a low refractive index on the side opposite to the top cell.

4. the refractive index change layer is electrically insulating, 4. The solar cell according to claim 1, wherein the support layer is electrically insulating.

5. 3. The solar cell according to claim 1, wherein the interstitial layer is electrically insulating.

6. the refractive index changing layer is in direct contact with the top cell, the refractive index change layer is provided on the light exit surface side of the top cell, the support layer is in direct contact with the top cell; The solar cell according to claim 1 , wherein the support layer is provided on the light-emitting surface side of the top cell.

7. the refractive index of the surface of the refractive index change layer opposite to the top cell side is 1.0 or more and 1.1 or less; 4. The solar cell according to claim 1, wherein the refractive index of the surface of the refractive index change region opposite to the top cell side is 1.0 or more and 1.1 or less.

8. the refractive index of the top cell on the refractive index change layer side is 1.3 or more and 2.2 or less; 4. The solar cell according to claim 1, wherein the refractive index of the top cell on the support layer side is 1.3 or more and 2.2 or less.

9. a refractive index of a member of the top cell that is in direct contact with the refractive index change layer is 1.3 or more and 2.2 or less; 4. The solar cell according to claim 1, wherein a refractive index of a member of the top cell that is in direct contact with the support layer is 1.3 or more and 2.2 or less.

10. an absolute value of a difference between a refractive index of a member of the top cell that is in contact with the refractive index change layer and a refractive index of the refractive index change layer on the top cell side is 0.0 or more and 1.0 or less; 4. The solar cell according to claim 1, wherein the absolute value of the difference between the refractive index of the member in contact with the support layer of the top cell and the refractive index of the region of the support layer excluding the refractive index change region on the top cell side is 0.0 or more and 1.0 or less.

11. 3. The solar cell according to claim 1, wherein the gap layer is an air layer, an inert gas layer, or a vacuum layer.

12. 3. The solar cell according to claim 1, wherein the top cell has a light absorbing layer with a wider band gap than the light absorbing layer of the bottom cell.

13. The solar cell according to claim 1 or 2, wherein the top cell and the bottom cell are held by a holding portion.

14. the refractive index of the refractive index change layer decreases stepwise and / or gradiently from the top cell side toward the opposite side to the top cell side, 4. The solar cell according to claim 1, wherein the refractive index of the refractive index changing region decreases stepwise and / or gradually from the top cell side toward the opposite side to the top cell side.

15. A photovoltaic power generation system that generates power using the solar cell according to any one of claims 1 to 3.

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