Photoelectric conversion element

Abstract

Provided is a photoelectric conversion element that, in a tandem solar cell, suppresses the occurrence of peeling between both a top cell light absorption layer and a bottom cell light absorption layer, by reducing shear stress between both light absorption layers generated by a temperature change or the like. The photoelectric conversion element includes a top cell (11) disposed on a light receiving surface side and a bottom cell (12) disposed on a rear surface side, and is configured such that a top cell light absorption layer (114) is divided into a plurality of regions by a gap portion (14) formed in the top cell light absorption layer (114).

Description

photoelectric conversion element

[0001] The present disclosure relates to a photoelectric conversion element in a tandem solar cell.

[0002] Tandem solar cells have been proposed in which different types of light absorption layers (photoelectric conversion layers) are stacked to increase the power generation efficiency of solar cells. One example of a tandem solar cell is a perovskite / silicon solar cell (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2022-910

[0004] In tandem solar cells, different types of light-absorbing layers are stacked, resulting in a difference in thermal expansion coefficients between the light-absorbing layer of the top cell and the light-absorbing layer of the bottom cell. When a temperature change occurs in a tandem solar cell, this difference in thermal expansion coefficients generates shear stress in the region between the light-absorbing layer of the top cell and the light-absorbing layer of the bottom cell. Repeated temperature changes can lead to delamination between the two light-absorbing layers. This problem is particularly pronounced in tandem solar cells that have a light-absorbing layer (perovskite layer) made of a perovskite compound, such as perovskite / silicon solar cells and perovskite / compound crystalline solar cells, due to the tendency for the thermal expansion coefficient difference between the perovskite layer and other light-absorbing layers to be weak. Furthermore, the adhesive strength between the layers constituting the cell (particularly the adhesive strength of the perovskite layer and the adhesive strength of the self-assembled monolayer serving as a hole-transport layer) tends to be weak.

[0005] Fig. 6 is a cross-sectional view showing the schematic configuration of a conventional photoelectric conversion element 50 in a tandem solar cell. As shown in Fig. 6, the photoelectric conversion element 50 has a configuration in which a top cell 51 and a bottom cell 52 are stacked, with the top cell 51 disposed on the upper surface side and the bottom cell 52 disposed on the lower surface side. Here, the top cell 51 is a perovskite solar cell, and the bottom cell 52 is a crystalline silicon solar cell.

[0006] The top cell 51 has, in order from the top side, a surface grid electrode 511, a surface transparent electrode 512, a top cell electron transport layer 513, a top cell light absorption layer 514, and a top cell hole transport layer 515. The bottom cell 52 has, in order from the top side, a bottom cell n-type doped layer 521, a bottom cell light absorption layer 522, a bottom cell p-type doped layer 523, a back surface transparent electrode 524, and a back surface grid electrode 525. An intermediate electrode (or intermediate layer) 53 is provided between the top cell 51 and the bottom cell 52, and the top cell 51 and the bottom cell 52 are connected in series by the intermediate electrode 53. An interconnector 60 is connected to the top and back surfaces of the photoelectric conversion element 50.

[0007] When expressions meaning "up" or "down" are used to describe directions, the expression "up" can refer to the light-receiving surface side of the element, and the expression "down" can refer to the back side of the element, and this is understood to be the case unless otherwise specified. In other words, it is understood that the light-receiving surface side and the top side basically mean the same thing, and the back side and the bottom side also mean the same thing.

[0008] Furthermore, in a monofacial solar cell, the light-receiving surface refers to the surface on which light is directly incident into the element. In a bifacial solar cell, either one of the surfaces can be considered the light-receiving surface, and when either one of the surfaces is considered as the light-receiving surface, the opposite surface can be considered as the back surface. In other words, as long as at least one of the surfaces has the configuration of the present disclosure when considered as the light-receiving surface, it can be considered to fall within the technical scope of the present disclosure. In other words, even if one of the surfaces does not have the configuration of the present disclosure when considered as the light-receiving surface, it can be considered to fall within the technical scope of the present disclosure as long as the other surface has the configuration of the present disclosure when considered as the light-receiving surface.

[0009] In the photoelectric conversion element 50, shear stress is particularly likely to occur at the interface of the top cell light absorption layer 514 on the bottom cell 52 side, and this shear stress can cause peeling from areas where the adhesive strength between the layers constituting the cell is weak, and as temperature changes are repeated, the cell itself can be damaged. S' in Figure 6 represents the region where shear stress is likely to occur (hereinafter referred to as the shear stress generation region), and the wider the shear stress generation region S', the greater the shear stress and the more likely peeling will occur.

[0010] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a photoelectric conversion element in a tandem solar cell in which shear stress between the light absorption layer of the top cell and the light absorption layer of the bottom cell, which occurs due to temperature changes or the like, is reduced, thereby suppressing the occurrence of delamination between the two light absorption layers.

[0011] In order to solve the above problems, the following photoelectric conversion element is provided: The photoelectric conversion element of the present disclosure is a photoelectric conversion element in a tandem solar cell, and is characterized in that it includes a top cell arranged on the light-receiving surface side and a bottom cell arranged on the back surface side, and the light-absorbing layer of the top cell is divided into multiple regions by voids formed in the light-absorbing layer of the top cell.

[0012] The photoelectric conversion element of the present disclosure exhibits excellent effects in a tandem solar cell, such as reducing shear stress between the light absorption layer of the top cell and the light absorption layer of the bottom cell that occurs due to temperature changes or the like, thereby preventing peeling between the two light absorption layers.

[0013] Fig. 1 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element according to a first embodiment of the present disclosure. Fig. 2 is a plan view showing a portion of a photoelectric conversion module using the photoelectric conversion element of Fig. 1. Fig. 3 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element according to a second embodiment of the present disclosure. Fig. 4 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element according to a third embodiment of the present disclosure. Fig. 5 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element according to a fourth embodiment of the present disclosure. Fig. 6 is a cross-sectional view showing a schematic configuration of a conventional photoelectric conversion element in a tandem solar cell.

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Fig. 1 shows an embodiment of the present disclosure and is a cross-sectional view illustrating a schematic configuration of a photoelectric conversion element 10. As shown in Figs.

[0015] In the present disclosure, a tandem solar cell refers to a solar cell configured so that some or all of the light (more specifically, light having a certain wavelength band) incident from the light-receiving surface side of the photoelectric conversion element can be absorbed in sequence by two or more light-absorbing layers.

[0016] In terms of configuration, in the present disclosure, a tandem solar cell may refer to a solar cell in which two light absorbing layers are provided in order from the light receiving surface side to the back surface side of a photoelectric conversion element. It is not necessary for the two light absorbing layers to completely overlap when viewed from the light receiving surface side; at least a partial overlap is sufficient. It is also desirable for at least one light absorbing layer to completely overlap the other light absorbing layer. In other words, in the present disclosure, a tandem solar cell is one in which some or all of the light incident from the light receiving surface side of the photoelectric conversion element (specifically, light having a certain wavelength band) passes through one light absorbing layer and enters the other light absorbing layer. The light absorbing layer referred to here does not need to be a single layer, but may be multiple layers. The multiple layers referred to here may refer to, for example, a stacked structure consisting of a PN junction.

[0017] The light absorbing layer is a layer that can absorb light incident on a photoelectric conversion element and generate electrons and holes. It is self-evident that the light absorbing layer absorbs light and generates electrons and holes as long as the solar cell functions as a solar cell, and so as long as the light absorbing layer is made of an appropriate material, there is no need to confirm that it absorbs light and generates electron-hole pairs, which is very difficult to confirm.

[0018] Photoelectric conversion element 10 is a photoelectric conversion element in a tandem solar cell using a perovskite solar cell, and in Fig. 1, the upper surface side is the light-receiving surface. As shown in Fig. 1, photoelectric conversion element 10 has a configuration in which a top cell 11 and a bottom cell 12 are stacked, with top cell 11 disposed on the upper surface side and bottom cell 12 disposed on the back surface side.

[0019] The top cell 11 has, in order from the top side, a surface grid electrode 111, a surface transparent electrode 112, a top cell electron transport layer 113, a top cell light absorption layer 114, and a top cell hole transport layer 115. The bottom cell 12 has, in order from the top side, a bottom cell n-type doped layer 121, a bottom cell light absorption layer 122, a bottom cell p-type doped layer 123, a back surface transparent electrode 124, and a back surface grid electrode 125. In addition, in the photoelectric conversion element 10, an intermediate electrode 13 is provided between the top cell 11 and the bottom cell 12, and the top cell 11 and the bottom cell 12 are connected in series by the intermediate electrode 13.

[0020] In this embodiment, the top cell 11 is a perovskite solar cell, and a crystalline silicon solar cell is used as a silicon-based solar cell for the bottom cell 12. That is, the top cell light absorption layer 114 is a layer containing a perovskite compound, which is a photoelectric conversion material, and may be composed of a perovskite compound alone, or may contain a substance other than a perovskite compound.

[0021] Furthermore, in a solar cell (or photoelectric conversion module) using a photoelectric conversion element 10, a surface interconnector 20A is connected to the upper surface of the photoelectric conversion element 10 (i.e., the upper surface of the top cell 11), and a back surface interconnector 20B is connected to the back surface of the photoelectric conversion element 10 (i.e., the lower surface of the bottom cell 12).

[0022] 1 can be fabricated by forming each layer required for the top cell 11 on the bottom cell 12. However, the fabrication procedure for the photoelectric conversion element 10 of the present disclosure is not particularly limited. The photoelectric conversion element 10 may also be fabricated by other methods, such as fabricating the top cell 11 and the bottom cell 12 separately and then bonding these cells together.

[0023] 1 illustrates a configuration in which current flows from top to bottom in the photoelectric conversion element 10. However, the direction of current flow is not limited thereto, and the current may flow from bottom to top. In a configuration in which current flows from bottom to top, the positions of the top cell electron transport layer 113 and the top cell hole transport layer 115 are interchanged in the top cell 11, and the positions of the bottom cell n-type doped layer 121 and the bottom cell p-type doped layer 123 are interchanged in the bottom cell 12. The type of doped layer (bottom cell n-type doped layer 121 or bottom cell p-type doped layer 123) in the bottom cell 12 is not particularly limited, and may be any of a PERC (Passivated Emitter and Rear Cell) type, a TOPCon (Tunnel Oxide Passivated Contact) type, or a heterojunction type. In addition to the doped layer, a PERC portion, a TOPCon portion, or a heterojunction portion may be provided.

[0024] 1 , in the photoelectric conversion element 10, the top cell light absorption layer 114 is divided into multiple regions. In this embodiment, the void 14 is formed as an open groove that opens on the upper surface side of the top cell 11 and penetrates from the surface grid electrode 111 to the top cell hole transport layer 115, and this open groove divides the entire top cell 11 into multiple regions. The void 14 as this open groove can be formed by removing a portion of the top cell 11 by a scribing method (laser scribing method or mechanical scribing method). Alternatively, a mask may be used during the formation of the top cell 11 so that the top cell 11 is not formed in the region that will become the void 14 from the beginning.

[0025] That is, in the photoelectric conversion element 10, the interface of the top cell light absorbing layer 114 on the bottom cell 12 side is divided into multiple regions. In other words, as shown in Fig. 1, the shear stress generation region S in the photoelectric conversion element 10 is divided into multiple regions. Therefore, compared to the shear stress generation region S' in the conventional photoelectric conversion element 50 shown in Fig. 6, the shear stress generated per divided region of the shear stress generation region S is smaller. Consequently, the shear stress generated throughout the entire area between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122 is smaller, thereby suppressing the occurrence of delamination between the two light absorbing layers.

[0026] In this embodiment, the void 14 is formed as an opening groove that penetrates all the way to the top cell hole transport layer 115. However, when the void 14 is formed as an opening groove, it is sufficient that it penetrates at least from the upper surface of the top cell 11 to the top cell light absorbing layer 114. Specifically, as exemplified later as a second embodiment, the void 14 as an opening groove may be configured to penetrate all the way to the top cell light absorbing layer 114 but not the top cell hole transport layer 115. Furthermore, the void 14 may not be configured to open to the upper surface of the top cell 11. Specifically, as exemplified later as a third embodiment, the void 14 may be configured to divide only the top cell light absorbing layer 114 into multiple regions. This is because, as long as the shear stress generation region S is divided into multiple regions, the generated shear stress can be reduced, and thus peeling between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122 can be suppressed. In consideration of ease of cell fabrication, it is preferable that the void portion 14 be formed as an open groove that divides the entire top cell 11 into a plurality of regions, as in this embodiment.

[0027] FIG. 2 is a plan view showing a portion of a photoelectric conversion module 100 using a photoelectric conversion element 10. The photoelectric conversion module 100 has at least one photoelectric conversion string in which a plurality of photoelectric conversion elements 10 are connected in series. Alternatively, the photoelectric conversion module 100 may be a photoelectric conversion array in which a plurality of photoelectric conversion strings are connected in parallel. In FIG. 2, two adjacent photoelectric conversion elements 10 in the photoelectric conversion string are shown. Here, the photoelectric conversion element 10 on the upper side in the Y direction in the drawing is referred to as the first element 10A, and the photoelectric conversion element 10 on the lower side in the Y direction in the drawing is referred to as the second element 10B. The cross-sectional view of FIG. 1 is a cross-sectional view of the photoelectric conversion element 10 shown in FIG. 2 taken along the A-A plane.

[0028] The first element 10A and the second element 10B are electrically connected via an interconnector 20. The interconnector 20 is a connection member in which a front surface interconnector 20A and a back surface interconnector 20B are integrally connected. In the interconnector 20 connecting the first element 10A and the second element 10B, the front surface interconnector 20A is connected to the front surface grid electrode 111 of the first element 10A, and the back surface interconnector 20B is connected to the back surface grid electrode 125 of the second element 10B. Note that although an interconnector is used as an example of the connection member here, it is not limited to an interconnector and broadly refers to a member capable of electrically connecting elements to each other.

[0029] As shown in FIG. 2 , the bottom cell 12 in the photoelectric conversion element 10 can be a substantially rectangular silicon wafer (e.g., a substantially square silicon wafer cut in half). While the shape of the bottom cell 12 is not limited to this, when the bottom cell 12 is substantially rectangular, the void 14 is preferably formed along a direction perpendicular to the long side of the bottom cell 12. Without the void 14, the long side of the bottom cell 12 is the long side of the shear stress generation region S. Therefore, dividing the shear stress generation region S along a direction perpendicular to the long side effectively reduces shear stress generated by temperature changes and the like. This in turn prevents delamination between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122.

[0030] As shown in FIG. 2, the voids 14 are formed in a direction parallel to the interconnectors 20. That is, all of the voids 14 in the photoelectric conversion element 10 are formed to be parallel. While FIG. 2 illustrates a configuration in which the voids 14 are provided as two open grooves in the photoelectric conversion element 10, the number of voids 14 is not particularly limited. Furthermore, the number of interconnectors 20 is not particularly limited. For example, when voids 14 are provided so that the top cell light absorption layer 114 is divided between all of the adjacent interconnectors 20, if the number of interconnectors 20 on the top cell 11 is n, then n-1 voids 14 may be formed in a direction parallel to the interconnectors 20.

[0031] By forming the void portion 14 in a direction parallel to the interconnector 20, the area without the top cell light absorption layer 114 and the area where the interconnector 20 is located do not overlap, so that the void portion 14 does not hinder the cell current collection by the interconnector 20, and ultimately, the impact of providing the void portion 14 on the battery characteristics can be minimized.

[0032] Furthermore, by forming the void portion 14 in a direction parallel to the interconnector 20, an area can be effectively created on the bottom cell 12 that is free of the top cell light absorption layer 114 and is capable of receiving light, which has the advantage of not reducing the current collection efficiency of the interconnector 20.

[0033] In the top cell 11 of the photoelectric conversion element 10, at least one interconnector 20 is connected to each of the divided regions. In this embodiment, one interconnector 20 is connected to one divided region of the top cell 11 (i.e., one divided region of the top cell light absorbing layer 114), but two or more interconnectors 20 may be connected to one divided region. In other words, instead of providing gaps 14 so that the top cell light absorbing layer 114 is divided between all adjacent interconnectors 20, gaps 14 may be provided so that the top cell light absorbing layer 114 is divided between every other interconnector 20 or every third other interconnector 20.

[0034] In this embodiment, an intermediate electrode 13 is provided on the bottom cell 12, but a modified example of this embodiment can include a configuration in which the intermediate electrode 13 is not provided between the top cell 11 and the bottom cell 12 (a configuration in which the top cell 11 and the bottom cell 12 are directly bonded).

[0035] In the following, the configuration of each layer in the photoelectric conversion element 10 will be described as an example, but known techniques can be applied to the materials and film formation methods of each layer in the photoelectric conversion element 10, and therefore the configuration of each layer that can be applied to this embodiment is not limited to this example. In other words, as long as the function of a photoelectric conversion element in a tandem solar cell is maintained, optional layers may be omitted, layers other than those described below may be included, and one layer may also serve the function of another layer.

[0036] (Front surface grid electrode, rear surface grid electrode) The front surface grid electrode 111 and the rear surface grid electrode 125 are composed of a plurality of conductive members that are parallel to one another. These conductive members extend in a first direction (the X direction shown in FIGS. 1 and 2 ) and are arranged parallel to one another at intervals in a second direction (the Y direction shown in FIGS. 1 and 2 ). The conductive members in the front surface grid electrode 111 (rear surface grid electrode 125) are connected by the interconnector 20 or a grid electrode arranged below the interconnector 20. Specifically, the interconnector 20 extends in the second direction and is arranged so as to be perpendicular to the conductive members. Because the second direction is a direction along the short sides of the photoelectric conversion element 10, the electrical resistance of the interconnector 20 can be reduced by arranging the interconnector 20 to extend in this direction.

[0037] The front surface grid electrode 111 (rear surface grid electrode 125) is also called a finger electrode, and the interconnector 20 is also called a bus bar electrode. The material of the conductive member is not particularly limited, but examples include metals such as silver, copper, and aluminum. The conductive member in the front surface grid electrode 111 (rear surface grid electrode 125) is narrower than the interconnector 20, and light is incident into the interior of the photoelectric conversion element 10 through gaps between adjacent conductive members. Note that the rear surface grid electrode 125 is on the opposite side to the light-receiving surface, so it may be configured so that light does not pass through it.

[0038] (Front transparent electrode, rear transparent electrode) The front transparent electrode 112 and the rear transparent electrode 124 are thin-film electrodes that are conductive and light-transmitting. Examples of materials include conductive transparent materials such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO). These may be used alone or in combination of two or more. Note that the rear transparent electrode 124 is on the opposite side to the light-receiving surface, and therefore may not be light-transmitting.

[0039] (Top Cell Electron Transport Layer) The top cell electron transport layer 113 is a layer that transports electrons generated in the top cell light absorption layer 114 to the surface transparent electrode 112. The top cell electron transport layer 113 preferably also functions as a hole blocking layer that inhibits holes generated in the top cell light absorption layer 114 from migrating to the surface transparent electrode 112. Examples of materials for the top cell electron transport layer 113 include tin oxide, titanium oxide, and zinc oxide.

[0040] Note that, as long as the top cell 11 has a photoelectric conversion function, it is self-evident that a portion located on the electron transport side (or on the negative electrode side, similarly in the present disclosure) of the top cell light absorbing layer 114 or on the electron transport side within the top cell light absorbing layer 114 has an electron transport function, and there is no need to confirm the electron transport function, which is difficult to confirm in practice. In other words, as long as the top cell 11 has a photoelectric conversion function, a layer located on the electron transport side of the top cell light absorbing layer 114 or on the electron transport side within the top cell light absorbing layer 114 and made of an appropriate material can be considered to be the top cell electron transport layer 113.

[0041] Furthermore, the top cell electron transport layer 113 may also function as the surface transparent electrode 112, or vice versa. Therefore, the photoelectric conversion element 10 does not necessarily have to have both the surface transparent electrode 112 and the top cell electron transport layer 113, and may have only one of them, with one layer also functioning as the other.

[0042] (Top Cell Light-Absorbing Layer) The top cell light-absorbing layer 114 can be a layer containing a perovskite compound, which is a photoelectric conversion material. The top cell light-absorbing layer 114 is a layer that can absorb at least a portion of light incident on the photoelectric conversion element 10 and generate electrons and holes. Of these, the electrons move to the top cell electron transport layer 113, and the holes move to the top cell hole transport layer 115. The top cell light-absorbing layer 114 may be composed of a perovskite compound alone, or may contain a substance other than a perovskite compound.

[0043] The perovskite compound is composed of compounds represented by the general formula: ABX3 (1). The composition ratio of each element is preferably 1:1:3, but it does not necessarily have to be 1:1:3, and the content of each element may be increased or decreased as appropriate.

[0044] In general formula (1), A is an organic molecule (including an organic group or an organic cation, the same applies in this disclosure), an inorganic atom or molecule (including an inorganic group or an inorganic cation, the same applies in this disclosure), or a combination thereof, B is a metal atom or molecule (including a metal cation, the same applies in this disclosure), and X is a halogen atom or molecule or a chalcogen atom or molecule (including a halogen anion or a chalcogen anion, the same applies in this disclosure). In general formula (1), the three Xs may be the same or different from one another.

[0045] In the general formula (1), the organic molecule represented by A is preferably a molecule containing carbon, nitrogen, and hydrogen, and the inorganic atom represented by A is preferably cesium or rubidium.

[0046] Note that a perovskite compound can be identified by knowing that the top cell light absorbing layer 114 has a photoelectric conversion function and contains A, B, and X, and it is not necessary to confirm that it has a crystalline structure. For example, it can be identified by knowing that A, B, and X contain organic molecules, metal atoms, and halogen atoms, or that A, B, and X contain inorganic atoms, metal atoms, and halogen atoms.

[0047] In general formula (1), examples of the organic molecule represented by A include alkylamine, alkylammonium, and nitrogen-containing heterocyclic compounds. In the perovskite compound (1), the organic molecule represented by A may be only one type of organic molecule, or may be two or more types of organic molecules.

[0048] Examples of alkylamines include methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, and ethylbutylamine.

[0049] The alkylammonium is an ionized product of the alkylamine. Examples of the alkylammonium include methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, dimethylammonium, diethylammonium, dipropylammonium, dibutylammonium, dipentylammonium, dihexylammonium, trimethylammonium, triethylammonium, tripropylammonium, tributylammonium, tripentylammonium, trihexylammonium, ethylmethylammonium, methylpropylammonium, butylmethylammonium, methylpentylammonium, hexylmethylammonium, ethylpropylammonium, and ethylbutylammonium.

[0050] Examples of the nitrogen-containing heterocyclic compound include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, and carbazole. The nitrogen-containing heterocyclic compound may be an ionized compound. As the ionized nitrogen-containing heterocyclic compound, phenethylammonium is preferred.

[0051] In general formula (1), the organic molecule represented by A is preferably methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, methylammonium, ethylammonium, propylammonium, butylammonium, pentylammonium, hexylammonium, or phenethylammonium, more preferably methylamine, ethylamine, propylamine, methylammonium, ethylammonium, or propylammonium, and even more preferably methylammonium.

[0052] In general formula (1), examples of the metal atom represented by B include lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, and europium. In the perovskite compound, the metal atom represented by B may be only one type of metal atom, or may be two or more types of metal atoms. From the viewpoint of improving the light absorption properties and charge generation properties of the perovskite compound, the metal atom represented by B is preferably a lead atom or a tin atom. From the viewpoint of reducing lead, a tin atom is preferred.

[0053] In general formula (1), examples of halogen atoms represented by X include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Examples of chalcogen atoms include oxygen atoms, sulfur atoms, selenium atoms, and tellurium atoms. In the perovskite compound, the halogen atoms or chalcogen atoms represented by X may be one type or two or more types. As the halogen atom represented by X, an iodine atom is preferred from the viewpoint of enabling the perovskite compound to utilize light in a wide wavelength range. Specifically, of the three Xs, it is preferred that at least one X represents an iodine atom, and it is more preferred that all three Xs represent iodine atoms.

[0054] As the perovskite compound, a compound represented by the general formula "CH3NH3PbX3 (wherein X represents a halogen atom)" is preferred, with CH3NH3PbI3 being more preferred. By using a compound represented by the general formula "CH3NH3PbX3" (particularly CH3NH3PbI3) as the perovskite compound, electrons and holes can be generated more efficiently in the perovskite compound, and as a result, the photoelectric conversion efficiency of the solar cell can be further improved.

[0055] An example of a method for forming the top cell light absorbing layer 114 containing a perovskite compound is a method in which a precursor solution obtained by dissolving a precursor compound of the perovskite compound in an organic solvent is applied by a known method such as spin coating or bar coating to form a film.

[0056] (Top Cell Hole Transport Layer) The top cell hole transport layer 115 is a layer that transports holes generated in the top cell light absorption layer 114 to the intermediate electrode 13. The top cell hole transport layer 115 preferably also functions as an electron blocking layer that suppresses the movement of electrons generated in the top cell light absorption layer 114 to the intermediate electrode 13.

[0057] The top cell hole transport layer 115 is primarily composed of a hole transport material. Specifically, the top cell hole transport layer 115 preferably contains 70% by mass or more of the hole transport material, and more preferably 85% by mass or more and 100% by mass or less. Examples of hole transport materials include P-type organic semiconductors, conductive polymers, metal oxides, and metal sulfides (e.g., CuO, NiO, and ZnS), and spiro-OMeTAD is preferred.

[0058] Note that, as long as the top cell 11 has a photoelectric conversion function, it is self-evident that a portion located on the hole transport side (or on the positive electrode side, similarly in the present disclosure) of the top cell light absorbing layer 114 or on the hole transport side within the top cell light absorbing layer 114 has a hole transport function, and there is no need to confirm the hole transport function, which is difficult to confirm in practice. In other words, as long as the top cell 11 has a photoelectric conversion function, a layer located on the hole transport side of the top cell light absorbing layer 114 or on the hole transport side within the top cell light absorbing layer 114 and made of an appropriate material can be considered to be the top cell hole transport layer 115.

[0059] (Intermediate Layer) In this embodiment, an intermediate electrode 13 is exemplified as the intermediate layer. The intermediate electrode 13 is an electrode that electrically connects the top cell and the bottom cell, and is configured so that light not absorbed by the top cell 11 can reach the bottom cell 12. That is, a material that is conductive and optically transparent can be used as the material for the intermediate electrode 13, and examples of such materials include conductive transparent materials such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium zinc oxide (IZO), and gallium-doped zinc oxide (GZO). These materials may be used alone or in combination of two or more.

[0060] Furthermore, the intermediate layer is not limited to the intermediate electrode 13, but may be any other structure that is disposed between a known tandem top cell and a bottom cell, such as a highly doped impurity-doped layer, a highly doped PN junction layer, or a tunnel junction layer.

[0061] The intermediate layer may be any structure disposed between the top cell and the bottom cell in a tandem solar cell. It is obvious that such a structure functions as an intermediate layer, as long as the solar cell functions as a solar cell, without waiting for confirmation of the physical properties, such as the conductivity and transmittance, of the intermediate layer. Furthermore, an intermediate layer is not necessarily required; a layer on the bottom cell side of the top cell and a layer on the top cell side of the bottom cell can be substituted for the intermediate layer by having a similar configuration to the intermediate layer. It is obvious that these layers function as a substitute for an intermediate layer, as long as a tandem solar cell having the top cell and bottom cell functions as a tandem solar cell, without waiting for confirmation of the physical properties, such as the conductivity and transmittance, of these layers.

[0062] (Bottom Cell N-Type Doped Layer, Bottom Cell Light Absorption Layer, Bottom Cell P-Type Doped Layer) The bottom cell n-type doped layer 121, bottom cell light absorption layer 122, and bottom cell p-type doped layer 123 may have structures used in known silicon solar cells. For example, by adding doping impurities to the surface of a crystalline silicon substrate, the bottom cell n-type doped layer 121 may be formed on one side of the bottom cell light absorption layer 122, which is a crystalline silicon substrate, and the bottom cell p-type doped layer 123 may be formed on the other side. The bottom cell n-type doped layer 121 may be formed by adding phosphorus, arsenic, or the like as a doping impurity, and the bottom cell p-type doped layer 123 may be formed by adding boron, gallium, or the like.

[0063] Furthermore, in a configuration using heterojunction silicon, for example, a configuration can be adopted in which a non-single-crystal silicon-based thin film such as amorphous silicon or microcrystalline silicon is formed as the bottom cell n-type doped layer 121 and the bottom cell p-type doped layer 123 on a single-crystal silicon substrate as the bottom cell light absorption layer 122. Examples of materials for the silicon-based thin films as the bottom cell n-type doped layer 121 and the bottom cell p-type doped layer 123 include amorphous silicon, microcrystalline silicon, amorphous silicon alloys, and microcrystalline silicon alloys. Examples of silicon alloys include silicon oxide, silicon carbide, silicon nitride, and silicon germanium. These may be used alone or in combination of two or more.

[0064] 3 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 10 according to a second embodiment of the present disclosure. The photoelectric conversion element 10 according to this embodiment can have the same configuration as that of the first embodiment, except as described below.

[0065] In the photoelectric conversion element 10 according to this embodiment, the voids 14 serving as opening grooves that open on the upper surface side of the top cell 11 penetrate all the way to the top cell light absorbing layer 114 but do not penetrate the top cell hole transport layer 115. Even with this configuration, the voids 14 divide the top cell light absorbing layer 114 into multiple regions, reducing the shear stress generated between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122 and preventing peeling between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122.

[0066] 4 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 10 according to a third embodiment of the present disclosure. The photoelectric conversion element 10 according to this embodiment can have the same configuration as that of the first embodiment, except as described below.

[0067] In the photoelectric conversion element 10 according to this embodiment, the void 14 is formed as a void located inside the top cell 11, and in this example, only the top cell light absorbing layer 114 is configured to be divided into a plurality of regions. The void 14 can be formed by using a mask when forming the top cell light absorbing layer 114 so that the top cell light absorbing layer 114 is not initially formed in the region that will become the void 14. Alternatively, the void 14 may be formed by removing the top surface side of the top cell 11 up to the top cell light absorbing layer 114 by a scribing method (laser scribing method or mechanical scribing method), and then refilling with layers other than the top cell light absorbing layer 114.

[0068] Even with this configuration, the top cell light absorbing layer 114 is divided into multiple regions by the voids 14, so the shear stress generated between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122 is reduced, and peeling between the top cell light absorbing layer 114 and the bottom cell light absorbing layer 122 can be suppressed.

[0069] Fourth Embodiment FIG. 5 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 10 according to a fourth embodiment of the present disclosure. While the first to third embodiments illustrate a two-junction photoelectric conversion element 10 in which two types of light absorbing layers are stacked, this embodiment illustrates a three-junction photoelectric conversion element 10 in which three types of light absorbing layers are stacked. In this disclosure, the term "two-junction" refers to a tandem solar cell in which the number of light absorbing layers capable of sequentially absorbing light is two, and the description of the light absorbing layer configuration can be applied to the description of the tandem solar cell. Similarly, the term "three-junction" refers to a tandem solar cell in which the number of light absorbing layers capable of sequentially absorbing light is three, and the description of the light absorbing layer configuration can be applied to the description of the tandem solar cell. Note that the term "junction" here does not literally mean "junction," but is a term commonly used to describe the number of light absorbing layers in a tandem solar cell. Therefore, the term "junction" can be essentially understood as "light absorbing layer."

[0070] The photoelectric conversion element 10 in FIG. 5 has a configuration in which a middle cell 15 is stacked in addition to a top cell 11 and a bottom cell 12. Specifically, the top cell 11 is disposed on the upper surface side, the bottom cell 12 is disposed on the back surface side, and the middle cell 15 is disposed between the top cell 11 and the bottom cell 12. The configurations of the top cell 11 and the bottom cell 12 in this embodiment can be similar to those of the top cell 11 and the bottom cell 12 in the first to third embodiments. Furthermore, as intermediate layers, an intermediate electrode 131 is provided between the top cell 11 and the middle cell 15, and an intermediate electrode 132 is provided between the middle cell 15 and the bottom cell 12. The intermediate electrodes 131 and 132 can be configured similarly to the intermediate layer or intermediate electrode 13 in the first to third embodiments.

[0071] The middle cell 15 has, in order from the top side, a middle cell electron transport layer 151, a middle cell light absorbing layer 152, and a middle cell hole transport layer 153. The middle cell 15 is a perovskite solar cell like the top cell 11, but preferably has at least a portion of a different material from the top cell 11, and preferably has a different wavelength of light to be photoelectrically converted from the top cell 11. That is, more specifically, it is preferable that the wavelength range of light that can be absorbed by the top cell light absorbing layer 114 and the middle cell light absorbing layer 152 differ. In particular, if the wavelength range of light that can be absorbed by the middle cell light absorbing layer 152 is longer than the wavelength range of light that can be absorbed by the top cell light absorbing layer 114, the photoelectric conversion efficiency of the element can be further improved.

[0072] In the photoelectric conversion element 10 according to this embodiment, the void 14 is formed as an open groove that opens on the upper surface side of the top cell 11 and penetrates from the surface grid electrode 111 in the top cell 11 to the middle cell hole transport layer 153 in the middle cell 15. That is, in addition to the top cell light absorbing layer 114, the middle cell light absorbing layer 152 is also divided into a plurality of regions, and the divided regions of the top cell light absorbing layer 114 and the divided regions of the middle cell light absorbing layer 152 correspond to each other.

[0073] In the photoelectric conversion element 10 according to this embodiment, the top cell light absorbing layer 114 and the middle cell light absorbing layer 152 have the same number of segment regions, and the arrangement direction of the segment regions is the same in the top cell light absorbing layer 114 and the middle cell light absorbing layer 152. In this case, segment regions that are arranged in the same order along the arrangement direction in the top cell light absorbing layer 114 and the middle cell light absorbing layer 152 correspond to each other. Corresponding segment regions only need to overlap each other in at least a portion of their area in a planar view, in which case it can be said that "the segment regions of the top cell light absorbing layer 114 and the segment regions of the middle cell light absorbing layer 152 correspond to each other." Note that it is preferable that corresponding segment regions completely overlap each other in a planar view.

[0074] As in the photoelectric conversion element 10 according to this embodiment, if the voids 14 are formed as opening grooves that open on the upper surface of the top cell 11 and penetrate at least to the middle cell light absorption layer 152, then the corresponding divided regions will necessarily overlap at least partially in a planar view. Furthermore, if the voids 14 as opening grooves are formed along a direction perpendicular to the upper surface of the top cell 11 (i.e., the Z direction shown in FIG. 5 ), then it can be said that the corresponding divided regions will completely overlap in a planar view.

[0075] Even in such a three-junction photoelectric conversion element 10, the top cell light absorption layer 114 and the middle cell light absorption layer 152 are each divided into multiple regions by the voids 14, which makes it possible to prevent peeling from occurring between the top cell light absorption layer 114 and the bottom cell light absorption layer 122 (for example, at the interface of the top cell light absorption layer 114 on the middle cell 15 side, or the interface of the middle cell light absorption layer 152 on the bottom cell 12 side).

[0076] While this embodiment is an example in which the two-junction photoelectric conversion element 10 according to the first embodiment is applied to a three-junction type, modifications of this embodiment may include examples in which the two-junction photoelectric conversion element 10 according to the second and third embodiments is applied to a three-junction type. That is, the void 14 serving as an opening groove opening on the upper surface side of the top cell 11 may penetrate all the way to the middle cell light absorption layer 152 but not through the middle cell hole transport layer 153. Alternatively, the void 14 may be provided as a gap located inside the top cell 11 and the middle cell 15 rather than as an opening groove.

[0077] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included.

[0078] [Note] The present disclosure includes the following aspects.

[0079] (Aspect 1) A photoelectric conversion element in a tandem solar cell, comprising a top cell arranged on the light-receiving surface side and a bottom cell arranged on the back surface side, wherein the light-absorbing layer of the top cell is divided into multiple regions by a void formed in the light-absorbing layer of the top cell.

[0080] (Aspect 2) The photoelectric conversion element according to Aspect 1, wherein the void portion is formed along a direction perpendicular to a long side of the bottom cell.

[0081] (Aspect 3) A photoelectric conversion element according to Aspect 1 or Aspect 2, wherein the top cell has a grid electrode composed of a plurality of conductive members parallel to each other, an interconnector is provided on the top cell to connect the plurality of conductive members in the grid electrode, and the void portion is formed along a direction parallel to the interconnector.

[0082] (Aspect 4) A photoelectric conversion element according to any one of Aspects 1 to 3, characterized in that the void portion is formed as a groove that penetrates at least from the upper surface side of the top cell to the light absorption layer of the top cell.

[0083] (Aspect 5) The photoelectric conversion element according to any one of Aspects 1 to 4, wherein the light absorption layer of the top cell contains a perovskite compound.

[0084] (Aspect 6) A photoelectric conversion element according to any one of aspects 1 to 5, comprising a middle cell arranged between the top cell and the bottom cell, wherein the light absorption layer of the middle cell is divided into a plurality of regions, and the divided regions of the light absorption layer of the top cell correspond to the divided regions of the light absorption layer of the middle cell.

[0085] REFERENCE SIGNS LIST 10 Photoelectric conversion element 100 Photoelectric conversion module 11 Top cell 111 Surface grid electrode 112 Surface transparent electrode 113 Top cell electron transport layer 114 Top cell light absorption layer 115 Top cell hole transport layer 12 Bottom cell 121 Bottom cell n-type doped layer 122 Bottom cell light absorption layer 123 Bottom cell p-type doped layer 124 Rear transparent electrode 125 Rear grid electrode 13 Intermediate electrode 14 Air gap 15 Middle cell 151 Middle cell electron transport layer 152 Middle cell light absorption layer 153 Middle cell hole transport layer 20 Interconnector 20A Front interconnector 20B Rear interconnector

Claims

1. A photoelectric conversion element in a tandem solar cell, comprising a top cell arranged on the light-receiving surface side and a bottom cell arranged on the back surface side, wherein the light absorption layer of the top cell is divided into multiple regions by voids formed in the light absorption layer of the top cell.

2. A photoelectric conversion element according to claim 1, wherein the gap is formed along a direction perpendicular to the long side of the bottom cell.

3. A photoelectric conversion element according to claim 1 or claim 2, wherein the top cell has a grid electrode made up of a plurality of conductive members parallel to each other, an interconnector is provided on the top cell to connect the plurality of conductive members in the grid electrode, and the void portion is formed along a direction parallel to the interconnector.

4. A photoelectric conversion element according to any one of claims 1 to 3, characterized in that the void portion is formed as a groove that penetrates at least from the upper surface side of the top cell to the light absorption layer of the top cell.

5. A photoelectric conversion element according to any one of claims 1 to 4, wherein the light absorption layer of the top cell contains a perovskite compound.

6. A photoelectric conversion element according to any one of claims 1 to 5, comprising a middle cell disposed between the top cell and the bottom cell, wherein the light absorption layer of the middle cell is divided into a plurality of regions, and the divided regions of the light absorption layer of the top cell and the divided regions of the light absorption layer of the middle cell correspond to each other.

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