Photoelectric conversion element

Abstract

Provided is a photoelectric conversion element which, in a tandem solar cell, can achieve current matching between a top cell and a bottom cell while suppressing non-uniformity of in-plane current density. 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 an opening groove (14) is formed in a top cell light-absorbing layer (114) so that a portion of the light incident from the light-receiving surface side can be incident on a bottom cell light-absorbing layer (122) without passing through the top cell light-absorbing 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 a tandem solar cell, different types of photoabsorption layers are connected in series, but because the current-voltage characteristics of each photoabsorption layer are different, the current that can be extracted from the tandem solar cell is limited by the smallest current generated in each photoabsorption layer. Therefore, tandem solar cells are designed so that the current generated in each photoabsorption layer is equal, i.e., current matching is achieved.

[0005] Fig. 7 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. 7, 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, for example, by changing the composition of the perovskite compound contained in the top cell light absorption layer 514 to change its band gap, it is possible to match the current generated in the top cell 51 with the current generated in the bottom cell 52. FIG. 8 is a graph showing the results of a simulation of the change in photoelectric conversion efficiency (Pmax in FIG. 8) when the ratio of the current generated in the top cell 51 to the current generated in the bottom cell 52 is changed by changing the band gap of the top cell 51 in a tandem solar cell having a photoelectric conversion element with the structure shown in FIG. 7. The results shown in FIG. 8 show that the photoelectric conversion efficiency peaks when the band gap of the top cell light absorption layer 514 is around 1.7 eV. Thus, in a tandem solar cell having a photoelectric conversion element with the structure shown in FIG. 7, it may be necessary to adjust the band gap of the top cell to around a specific value in order to achieve current matching.

[0010] However, when current matching is achieved by changing the composition, etc., of the perovskite compound, a wide range of design changes are required, such as the design of the interface between the light absorbing layer and an adjacent layer in the photoelectric conversion element, the design of the method for forming the light absorbing layer in the manufacturing method, the design of the thermal history in the formation process and the resulting impact on other layers, etc. Therefore, changing the design of the band gap value of the top cell by changing the composition, etc. of the perovskite compound has an excessive impact on the design of the entire photoelectric conversion element, which is problematic.

[0011] One possible method for achieving current matching without limiting the bandgap value of the top cell is to make the top cell slightly smaller than the bottom cell. In this case, the top cell is not present above the bottom cell at the periphery of the bottom cell. Therefore, at the periphery of the bottom cell, light incident from the light-receiving surface directly enters the bottom cell without passing through the top cell. This increases the amount of light received by the bottom cell, making it possible to achieve current matching between the top and bottom cells. If the in-plane electrical resistance of the intermediate layer (or intermediate electrode) between the top and bottom cells is sufficiently small compared to the size of the top cell, the current generated at the periphery of the bottom cell will reach the center, making current matching less of a problem.

[0012] However, when the top cell is large and there is a distance between its periphery and the center, or when the in-plane electrical resistance of the intermediate layer (or intermediate electrode) between the top cell and the bottom cell cannot be reduced, there is a problem that the current generated at the periphery of the bottom cell does not reach the center. In other words, there is a problem that the current density becomes non-uniform within the plane of the solar cell. In particular, in perovskite / silicon solar cells, current matching using this method is difficult to achieve because it is difficult to significantly reduce the resistance of the intermediate layer (or intermediate electrode) and because, although it is difficult to improve photoelectric conversion efficiency by current matching unless the width of the top cell is several centimeters or less, silicon wafers for solar cells have recently become large, with widths of 18 cm or more.

[0013] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a photoelectric conversion element in a tandem solar cell that can achieve current matching between the top cell and the bottom cell while suppressing uneven current density within the plane.

[0014] 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 an open groove portion is formed in the light-absorbing layer of the top cell so that a portion of light incident from the light-receiving surface side can be incident on the light-absorbing layer of the bottom cell without passing through the light-absorbing layer of the top cell.

[0015] The photoelectric conversion element of the present disclosure exhibits excellent effects in a tandem solar cell, such as being able to suppress uneven current density within the plane while achieving current matching between the top cell and the bottom cell.

[0016] 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 plan view showing a portion of a photoelectric conversion module using the photoelectric conversion element according to a second embodiment of the present disclosure. FIG. 4 is a plan view showing a portion of a photoelectric conversion module using the photoelectric conversion element according to a third embodiment of the present disclosure. FIG. 5 is a plan view showing a portion of a photoelectric conversion module using the 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 photoelectric conversion element according to a fifth embodiment of the present disclosure. FIG. 7 is a cross-sectional view showing a schematic configuration of a conventional photoelectric conversion element in a tandem solar cell. FIG. 8 is a graph showing the relationship between the band gap of the light absorption layer of a top cell and photoelectric conversion efficiency in a tandem solar cell. FIG. 9 is a graph showing the relationship between the aperture ratio of the top cell and photoelectric conversion efficiency.

[0017] [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.

[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] 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.

[0020] 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 can refer to, for example, a stacked structure consisting of a PN junction.

[0021] 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.

[0022] The top cell 11 in the photoelectric conversion element 10 has, from the top surface 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, from the top surface 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.

[0023] 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.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] As shown in Fig. 1 , in the photoelectric conversion element 10, an open groove 14 is formed in the top cell light absorption layer 114 so that a portion of light incident from the light-receiving surface side (the upper side in Fig. 1 ) can be incident on the bottom cell light absorption layer 122 without passing through the top cell light absorption layer 114. Note that in this embodiment, a photoelectric conversion element 10 in which the open groove 14 is formed in the top cell 11 so that a portion of light incident from the light-receiving surface side can be incident on the bottom cell 12 without passing through the top cell 11 is described as an example, but this configuration is not limited to this. That is, this does not exclude a configuration in which the open groove 14 does not penetrate through a portion of the layers constituting the top cell 11, in other words, a configuration in which a portion of the layers constituting the top cell 11 is provided in the region where the open groove 14 in Fig. 1 is located.

[0028] In this embodiment, a plurality of open grooves 14 are provided in the top cell 11, and the top cell 11 is divided into a plurality of regions by these open grooves 14. Note that, as will be exemplified later as a fourth embodiment, a configuration in which the open grooves 14 are provided in a manner that does not divide the top cell 11 into a plurality of regions may also be used.

[0029] Note that "a portion of light incident from the light-receiving surface side can be incident on component B without passing through component A" specifically means, for example, "a configuration in which, when components A and B are provided in order from the light-receiving surface side to the back surface side of a photoelectric conversion element, at least a portion of component B does not overlap with component A when viewed from the light-receiving surface side." Note that other configurations are not excluded. For example, the definition is not necessarily limited to a view at an angle perpendicular to the light-receiving surface, and in the case of a structure in which light is incident at a certain angle, cases in which the above configuration is satisfied when viewed at that certain angle are not excluded.

[0030] The opening groove 14 can be formed by removing a part of the top cell 11 by a scribing method (laser scribing method or mechanical scribing method). Alternatively, a mask may be used when forming the top cell 11 so that the top cell 11 is not formed in the region that will become the opening groove 14 from the beginning.

[0031] 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.

[0032] 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.

[0033] As shown in Fig. 2, the opening grooves 14 are formed in a direction parallel to the interconnector 20. That is, the opening grooves 14 in the photoelectric conversion element 10 are all formed to be parallel to each other. Fig. 2 illustrates a configuration in which two opening grooves 14 are provided in the photoelectric conversion element 10, but the number of opening grooves 14 is not particularly limited, as will be illustrated later as a second embodiment and a third embodiment.

[0034] At least one interconnector 20 is connected to each of the divided regions of the top cell 11 of the photoelectric conversion element 10. In this embodiment, one interconnector 20 is connected to one divided region of the top cell 11, but as exemplified later as a third embodiment, two or more interconnectors 20 may be connected to one divided region.

[0035] In the photoelectric conversion element 10, the open groove 14 is formed in the top cell 11, thereby reducing the amount of light received by the top cell 11. Furthermore, light that passes through the open groove 14 is incident directly on the bottom cell 12 without passing through the top cell 11, thereby increasing the amount of light received by the bottom cell 12. In other words, the current generated in the top cell 11 decreases and the current generated in the bottom cell 12 increases, and thus, by adopting this configuration, current matching between the top cell 11 and the bottom cell 12 can be achieved. Furthermore, since there is no need to change the composition of the perovskite compound in the top cell light absorption layer 114 during the design stage of the photoelectric conversion element 10, the problem of a design change to the top cell light absorption layer 114 having an excessive impact on the design of the entire photoelectric conversion element 10 is resolved.

[0036] Furthermore, by forming the opening groove portion 14 in a direction parallel to the interconnector 20, an area can be effectively created above the bottom cell 12 where there is no top cell 11 and where light can be received, which has the advantage that the current collection efficiency by the interconnector 20 is not reduced.

[0037] Furthermore, since the interconnectors 20 are connected to each of the divided regions of the top cell 11, it is possible to equalize the current flowing through each interconnector 20. In other words, it is possible to prevent the current-voltage characteristics from deteriorating due to the formation of the open groove portions 14 in the top cell 11.

[0038] In this embodiment, since the intermediate electrode 13 is provided on the bottom cell 12, strictly speaking, light incident on the open groove 14 passes through the intermediate electrode 13 before reaching the bottom cell 12. A variation 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).

[0039] Next, a description will be given of a preferred aperture ratio of the top cell 11 due to the open groove portion 14 in the photoelectric conversion element 10. Here, the aperture ratio of the top cell 11 in the present disclosure is a value calculated as the ratio of the open area of ​​the top cell 11 due to the open groove portion 14 to the area of ​​one face of the bottom cell 12 (or the area of ​​one face of the top cell 11 in a state before the opening groove portion 14 is formed). An example of the aperture ratio of the top cell 11 is 3% or more and 20% or less. A specific calculation example will be described later using the second embodiment as an example.

[0040] Figure 9 is a graph showing a simulation of the relationship between the aperture ratio of the top cell and the photoelectric conversion efficiency (Pmax) for three cells with a bandgap of 1.7 eV or less out of the six cells (six plots) with different bandgaps shown in Figure 8. Figure 9 shows that the smaller the bandgap, the stronger the tendency for the cell output to increase as the aperture ratio of the top cell increases.

[0041] The results show that for cells with a bandgap of 1.65 eV, the cell output is maximized when the aperture ratio is around 5% (e.g., 2% to 8%, more preferably 3% to 7%), and for cells with a bandgap of 1.55 eV, the cell output is maximized when the aperture ratio is around 15% (e.g., 2% to 30%, more preferably 3% to 20%, even more preferably 6% to 15%). Also, for cells with a bandgap of 1.46 eV, the cell output is estimated to be maximized at aperture ratios significantly greater than 15%.

[0042] These results show that when a top cell with a band gap of 1.7 eV or less is used and the current generated in the bottom cell is smaller than the current generated in the top cell, the cell output can be improved by adopting a photoelectric conversion element 10 configuration in which an open groove portion 14 is formed in the top cell 11.

[0043] For example, CH3NH3PbI3 is known as a perovskite compound used in perovskite solar cells, but its band gap is 1.55 eV to 1.6 eV, which is somewhat narrow for the top cell of a tandem solar cell, making it difficult to increase photoelectric conversion efficiency. Even when CH3NH3PbI3 is used as the photoelectric conversion material for the top cell light absorption layer 114, by forming the opening groove 14 so that the aperture ratio of the top cell 11 is about 10% (e.g., 5% to 15%), it is possible to increase the cell output compared to when the opening groove 14 is not formed.

[0044] 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.

[0045] (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.

[0046] 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.

[0047] (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.

[0048] (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.

[0049] 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.

[0050] 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.

[0051] (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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] (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.

[0066] 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.

[0067] 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.

[0068] (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.

[0069] 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.

[0070] 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.

[0071] (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.

[0072] 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.

[0073] 3 is a plan view showing a portion of a photoelectric conversion module 100 using 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 the first embodiment, except as described below.

[0074] The photoelectric conversion element 10 according to this embodiment has a configuration in which eight open grooves 14 are provided. The open grooves 14 formed in the top cell 11 are formed in a direction parallel to the interconnector 20, and the interconnector 20 is connected to each of the divided regions of the top cell 11, as in the first embodiment.

[0075] In a configuration in which one interconnector 20 is connected to each of the divided regions of the top cell 11, if the number of interconnectors 20 on the top cell 11 is n, the top cell 11 will be divided by n-1 open groove portions 14.

[0076] 3, the photoelectric conversion element 10 is a half-size cell made from a 166 mm square silicon wafer, and the width of the open groove 14 is 2 mm. Using this example, the aperture ratio of the top cell 11 is calculated using the following formula: Opening ratio of top cell = [Width of open groove 14] × [Short side of cell] × [Number of open grooves 14] ÷ ([Long side of cell] × [Short side of cell] - [Area of ​​C-face of cell (chip at corner)] × 2) = 2 × 83 × (9 - 1) ÷ (166 × 83 - 8.55 × 8.55 ÷ 2 × 2) = 9.69%

[0077] The aperture ratio of the top cell 11 can be adjusted by changing the width of the open groove portion 14. As described above, the suitable range of the aperture ratio of the top cell 11 varies depending on the band gap of the cell, and therefore, by adjusting the aperture ratio in accordance with the band gap of the top cell 11, a photoelectric conversion element 10 with high output can be obtained.

[0078] 4 is a plan view showing a portion of a photoelectric conversion module 100 using 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 the first embodiment, except as described below.

[0079] The photoelectric conversion element 10 according to this embodiment has a configuration in which two interconnectors 20 are connected to each of the divided regions of the top cell 11. In other words, instead of providing an open groove 14 between all of the adjacent interconnectors 20 as in the first and second embodiments, an open groove 14 is provided between every other interconnector 20. Even in this configuration, an equal number of interconnectors 20 are provided in each of the divided regions of the top cell 11, so that the current flowing per interconnector 20 can be equalized. In other words, it is possible to prevent the formation of open grooves 14 in the top cell 11 from deteriorating the current-voltage characteristics.

[0080] 5 is a plan view showing a portion of a photoelectric conversion module 100 using a photoelectric conversion element 10 according to a fourth 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.

[0081] In the photoelectric conversion element 10 according to this embodiment, the opening groove 14 formed in the top cell 11 is formed along a direction parallel to the interconnector 20, as in the first to third embodiments, but the opening groove 14 is not formed to the end (long side of the cell) of the top cell 11. As such, even if the opening groove 14 is provided in a manner that does not divide the top cell 11 into multiple regions, the amount of light received by the top cell 11 decreases and the amount of light received by the bottom cell 12 increases, as in the first embodiment. Therefore, the photoelectric conversion element 10 according to this embodiment can also achieve current matching between the top cell 11 and the bottom cell 12.

[0082] Furthermore, according to the configuration of the opening groove portion 14 of this embodiment, even if the opening groove portion 14 is not formed to the edge of the top cell 11, it has essentially the same effect as if the top cell 11 were divided into multiple regions by the opening groove portion 14, and therefore it is possible to maintain uniformity in the current density within the surface of the solar cell.

[0083] 6 is a cross-sectional view showing a schematic configuration of a photoelectric conversion element 10 according to a fifth 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.

[0084] In the photoelectric conversion element 10 according to this embodiment, dividing grooves 1251 are formed in the rear grid electrode 125, dividing the rear grid electrode 125 into a plurality of regions. As in the first embodiment, the top cell 11 is divided into a plurality of regions by the open grooves 14. The divided regions in the rear grid electrode 125 correspond to the divided regions in the front grid electrode 111 (top cell 11).

[0085] In the photoelectric conversion element 10 according to this embodiment, the number of divided regions is the same in the front grid electrode 111 and the back grid electrode 125, and the arrangement direction of the divided regions is the same in the front grid electrode 111 and the back grid electrode 125. In this case, divided regions that are arranged in the same order along the arrangement direction in the front grid electrode 111 and the back grid electrode 125 are considered to be corresponding divided regions. Corresponding divided regions have at least a partial overlap in a planar view, and preferably completely overlap in a planar view. Here, "corresponding" does not specifically mean being physically connected, but rather refers to a relationship in which the divided regions are physically connected to a portion of an adjacent element. That is, if a component (e.g., XA) in the first element 10A is at least physically connected to a component (e.g., YB) in the adjacent second element 10B by a connecting member, and the first element 10A includes a component (e.g., YA) corresponding to the component YB, then the component XA and the component YA may be said to "correspond." Here, for example, the component XA indicates one divided element of the front grid electrode 111 , and the components YA and YB indicate one divided element of the rear grid electrode 125 .

[0086] According to this configuration, the area collected by one interconnector 20 is divided into corresponding areas of the front grid electrode 111 and the back grid electrode 125, so that the current flowing through each interconnector 20 can be more clearly equalized.

[0087] 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.

[0088] [Note] The present disclosure includes the following aspects.

[0089] (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 an open groove portion is formed in the light-absorbing layer of the top cell so that a portion of light incident from the light-receiving surface side can be incident on the light-absorbing layer of the bottom cell without passing through the light-absorbing layer of the top cell.

[0090] (Aspect 2) The photoelectric conversion element according to Aspect 1, wherein the open groove is formed so as to divide the top cell into a plurality of regions.

[0091] (Aspect 3) The photoelectric conversion element according to Aspect 1 or Aspect 2, wherein the opening groove is formed so that a portion of the light incident from the light receiving surface side can be incident on the bottom cell without passing through the top cell.

[0092] (Aspect 4) A photoelectric conversion element according to any one of aspects 1 to 3, 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 opening groove portion is formed along a direction parallel to the interconnector.

[0093] (Aspect 5) The photoelectric conversion element according to any one of Aspects 1 to 4, wherein the top cell has a light absorption layer containing a perovskite compound.

[0094] (Aspect 6) A photoelectric conversion element according to any one of aspects 1 to 5, characterized in that the aperture ratio of the top cell, calculated as the ratio of the opening area of ​​the opening groove portion in the top cell to the area of ​​one side of the bottom cell, is 3% or more and 20% or less.

[0095] 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 Opening groove 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 an open groove is formed in the light-absorbing layer of the top cell so that a portion of the light incident from the light-receiving surface side can be incident on the light-absorbing layer of the bottom cell without passing through the light-absorbing layer of the top cell.

2. A photoelectric conversion element according to claim 1, wherein the open groove is formed so as to divide the top cell into a plurality of regions.

3. A photoelectric conversion element according to claim 1 or claim 2, characterized in that the opening groove is formed so that a portion of the light incident from the light-receiving surface side can enter the bottom cell without passing through the top cell.

4. A photoelectric conversion element according to any one of claims 1 to 3, 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 open groove portion is formed along a direction parallel to the interconnector.

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

6. A photoelectric conversion element according to any one of claims 1 to 5, characterized in that the aperture ratio of the top cell, calculated as the ratio of the opening area of ​​the opening groove portion in the top cell to the area of ​​one side of the bottom cell, is 3% or more and 20% or less.

Images