Photoelectric conversion element

Abstract

A photoelectric conversion element capable of achieving current matching between a top cell and a bottom cell while suppressing non-uniformity in current density within the plane in a tandem solar cell is provided. [Solution] The photoelectric conversion element 10 in the tandem solar cell includes a top cell 11 arranged on the light-receiving surface side and a bottom cell 12 arranged on the back surface side, and an open groove portion 14 is formed in the top cell light-absorbing layer 114 so that a portion of the light incident from the light-receiving surface side can enter the bottom cell light-absorbing layer 122 without passing through the top cell light-absorbing layer 114.

Description

Technical Field

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

Background Art

[0002] In order to improve the power generation efficiency of solar cells, tandem solar cells in which different types of light absorption layers (photoelectric conversion layers) are stacked have been proposed. As an example of a tandem solar cell, a perovskite / silicon solar cell can be mentioned (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a tandem solar cell, different types of light absorption layers are connected in series. However, since the current-voltage characteristics are different for each light absorption layer, the current that can be extracted as a tandem solar cell is limited by the smallest current generated in each light absorption layer. Therefore, a tandem solar cell is designed so that the currents generated in each light absorption layer are equal, that is, current matching is achieved. <�

[0005] FIG. 7 is a cross-sectional view showing a 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, and the top cell 51 is disposed on the upper surface side and the bottom cell 52 is disposed on the back 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. Interconnectors 60 are connected to the top and back surfaces of the photoelectric conversion element 50.

[0007] Furthermore, when using expressions meaning "up" or "down" to describe direction, the expression "up" can be used to refer to the light-receiving side of the element, and the expression "down" can be used to refer to the back side of the element. Unless otherwise specified, this should be understood as such. In other words, the light-receiving 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 the case of a single-sided light-receiving solar cell, the light-receiving surface refers directly to the surface on which light enters the element. In the case of a double-sided light-receiving solar cell, either one of the two surfaces can be considered the light-receiving surface, and if one surface is considered the light-receiving surface, the opposite surface can be considered the back surface. In other words, if the configuration of the disclosure is present when at least one of the surfaces is considered the light-receiving surface, it can be considered to fall within the technical scope of the disclosure. To put it another way, even if the configuration of the disclosure is not present when one of the surfaces is considered the light-receiving surface, if the configuration of the disclosure is present when the other surface is considered the light-receiving surface, it can be considered to fall within the technical scope of the disclosure.

[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 and thereby changing 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. Figure 8 is a graph showing the results of a simulation of the change in photoelectric conversion efficiency (Pmax in Figure 8) when the ratio of the current generated in the top cell 51 with 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 the photoelectric conversion element structure shown in Figure 7. The results shown in Figure 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 the photoelectric conversion element structure shown in Figure 7, it may be necessary to adjust the band gap of the top cell to a specific value in order to match the current.

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

[0011] One method for achieving current matching without imposing a limit on the bandgap value of the top cell is to form the top cell slightly smaller than the bottom cell. In this case, the top cell does not exist on the periphery of the bottom cell. Therefore, at the periphery of the bottom cell, light incident from the light-receiving surface side 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 relative to the size of the top cell, the current generated at the periphery of the bottom cell will also reach the center, so there are few problems in current matching.

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

[0013] This disclosure has been made in view of the above-mentioned problems, and aims to provide a photoelectric conversion element that can match the current between the top cell and the bottom cell while suppressing non-uniformity of the current density in the plane of a tandem solar cell. [Means for solving the problem]

[0014] 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 includes a top cell disposed on the light-receiving surface side and a bottom cell disposed on the back side, characterized in that an opening 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. [Effects of the Invention]

[0015] The photoelectric conversion element disclosed herein offers excellent advantages, such as suppressing non-uniformity of current density within the plane of a tandem solar cell while achieving current matching between the top cell and the bottom cell. [Brief explanation of the drawing]

[0016] [Figure 1] This is a cross-sectional view showing the schematic configuration of a photoelectric conversion element according to the first embodiment of this disclosure. [Figure 2] Figure 1 is a plan view showing a part of a photoelectric conversion module using the photoelectric conversion element. [Figure 3] This is a plan view showing a part of a photoelectric conversion module using a photoelectric conversion element according to the second embodiment of this disclosure. [Figure 4] This is a plan view showing a part of a photoelectric conversion module using a photoelectric conversion element according to the third embodiment of this disclosure. [Figure 5] This is a plan view showing a part of a photoelectric conversion module using a photoelectric conversion element according to the fourth embodiment of this disclosure. [Figure 6] This is a cross-sectional view showing the schematic configuration of a photoelectric conversion element according to the fifth embodiment of this disclosure. [Figure 7] This is a cross-sectional view showing the schematic configuration of a conventional photoelectric conversion element in a tandem solar cell. [Figure 8] This graph shows the relationship between the bandgap of the top cell's light-absorbing layer and the photoelectric conversion efficiency in a tandem solar cell. [Figure 9]It is a graph showing the relationship between the aperture ratio of the top cell and the photoelectric conversion efficiency.

Embodiments for Carrying out the Invention

[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 showing a schematic configuration of a photoelectric conversion element 10.

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

[0019] In the present disclosure, the tandem solar cell means a solar cell configured such that part or all of the light (specifically, light having a certain wavelength band) incident from the light-receiving surface side of the photoelectric conversion element can be sequentially absorbed by two or more light absorption layers.

[0020] Explaining in terms of the configuration, in the present disclosure, the tandem solar cell may also mean a solar cell provided with two light absorption layers in order from the light-receiving surface side to the back surface side of the photoelectric conversion element. Note that, in the form seen from the light-receiving surface side, the two light absorption layers do not necessarily have to completely overlap, and it is sufficient if at least a part thereof overlaps. Also, it is desirable that at least one of the light absorption layers completely overlaps the other light absorption layer. That is, in the present disclosure, the tandem solar cell only needs to be configured such that part or all of the light (specifically, light having a certain wavelength band) incident from the light-receiving surface side of the photoelectric conversion element can enter the other light absorption layer via one light absorption layer. Note that the light absorption layer here does not necessarily have to be a single layer and may be composed of a plurality of layers. The plurality of layers here can mean, for example, a stacked structure composed of a PN junction.

[0021] A light-absorbing layer is a layer that absorbs light incident on a photoelectric conversion element and generates electrons and holes. The fact that a light-absorbing layer absorbs light and generates electrons and holes is self-evident as long as the solar cell functions as a solar cell, and as long as the light-absorbing layer is made of appropriate materials, it is not necessary to verify that it absorbs light and generates electron-hole pairs, which is extremely difficult to verify.

[0022] In the photoelectric conversion element 10, 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.

[0023] In this embodiment, the top cell 11 is a perovskite solar cell, and the bottom cell 12 is a crystalline silicon solar cell as a silicon-based solar cell. That is, the top cell light absorption layer 114 is a layer containing a perovskite compound, which is a photoelectric conversion material, and may consist of a perovskite compound alone, or it may contain substances other than perovskite compounds.

[0024] Furthermore, in a solar cell (or photoelectric conversion module) using the 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] The photoelectric conversion element 10 shown in Figure 1 can be fabricated by depositing the necessary layers for the top cell 11 onto the bottom cell 12. However, the fabrication procedure for the photoelectric conversion element 10 of this 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] The photoelectric conversion element 10 shown in Figure 1 illustrates a configuration in which current flows from top to bottom in the figure, but the direction of the current is not limited to this, and it may also be configured in which the current flows from bottom to top. In the configuration in which the 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 swapped 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 swapped in the bottom cell 12. Furthermore, the type of doped layer in the bottom cell 12 (bottom cell n-type doped layer 121 or bottom cell p-type doped layer 123) is not particularly limited, and may be any of PERC (Passivated Emitter and Rear Cell) type, TOPCon (Tunnel Oxide Passivated Contact) type, or heterojunction type, and in addition to the doped layer, a PERC section, TOPCon section, or heterojunction section may also be provided.

[0027] As shown in Figure 1, in the photoelectric conversion element 10, an aperture groove 14 is formed in the top cell light absorption layer 114 so that a portion of the light incident from the light-receiving surface side (upper side in Figure 1) can enter the bottom cell light absorption layer 122 without passing through the top cell light absorption layer 114. In this embodiment, a photoelectric conversion element 10 in which an aperture groove 14 is formed in the top cell 11 so that a portion of the light incident from the light-receiving surface side can enter the bottom cell 12 without passing through the top cell 11 is described as an example, but the configuration is not limited to this. That is, a configuration in which the aperture groove 14 does not penetrate 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 aperture groove 14 is located in Figure 1 is not excluded.

[0028] In this embodiment, the top cell 11 is provided with a plurality of opening grooves 14, and the top cell 11 is divided into multiple regions by these opening grooves 14. However, as illustrated later in the fourth embodiment, the top cell 11 can also be configured in which the opening grooves 14 are provided without dividing it into multiple regions.

[0029] Furthermore, the statement that "a portion of the light incident from the light-receiving surface can enter component B without passing through component A" means, for example, specifically, that "when component A and component B are arranged sequentially from the light-receiving surface to the back surface of the photoelectric conversion element, at least a portion of component B does not overlap with component A when viewed from the light-receiving surface." This does not exclude other configurations. For example, it is not necessarily limited to viewing at an angle perpendicular to the light-receiving surface; in cases where the structure has light incident at a certain angle, cases where the above configuration is satisfied when viewed at that certain angle are also excluded.

[0030] The opening groove 14 can be formed by removing a portion of the top cell 11 using a scribing method (laser scribing method or mechanical scribing method). Alternatively, a mask can 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 opening groove 14 from the beginning.

[0031] Figure 2 is a plan view showing a part of a photoelectric conversion module 100 using photoelectric conversion elements 10. The photoelectric conversion module 100 has at least one row of photoelectric conversion strings in which multiple photoelectric conversion elements 10 are connected in series. Alternatively, the photoelectric conversion module 100 may be a photoelectric conversion array in which multiple rows of photoelectric conversion strings are connected in parallel. In Figure 2, two adjacent photoelectric conversion elements 10 in the photoelectric conversion string are shown separately, with the upper photoelectric conversion element 10 in the Y direction in the figure being referred to as the first element 10A, and the lower photoelectric conversion element 10 in the Y direction in the figure being referred to as the second element 10B. Note that the cross-sectional view in Figure 1 is a cross-sectional view of the photoelectric conversion element 10 shown in Figure 2, cut across plane AA.

[0032] The first element 10A and the second element 10B are electrically connected via an interconnector 20. The interconnector 20 is a connecting member in which a front interconnector 20A and a back interconnector 20B are integrally connected. In the interconnector 20 connecting the first element 10A and the second element 10B, the front interconnector 20A is connected to the front grid electrode 111 of the first element 10A, and the back interconnector 20B is connected to the back grid electrode 125 of the second element 10B. Note that while an interconnector is used as an example here, the term "connecting member" is not limited to interconnectors and broadly refers to any member capable of electrically connecting elements.

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

[0034] 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, but as illustrated later in the third embodiment, two or more interconnectors 20 may be connected to one divided region.

[0035] In the photoelectric conversion element 10, the formation of an aperture groove 14 in the top cell 11 reduces the amount of light received by the top cell 11. Also, since the light that passes through the aperture groove 14 is directly incident on the bottom cell 12 without passing through the top cell 11, the amount of light received by the bottom cell 12 increases. In other words, the current generated in the top cell 11 decreases and the current generated in the bottom cell 12 increases, so 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 excessive impact on the overall design of the photoelectric conversion element 10 due to design changes in the top cell light absorption layer 114 is eliminated.

[0036] Furthermore, by forming the opening groove 14 along a direction parallel to the interconnector 20, an area can be effectively provided on the bottom cell 12 where there is no top cell 11 and light can be received, which has the advantage of not reducing the current collection efficiency of the interconnector 20.

[0037] Furthermore, since an interconnector 20 is connected to each of the divided regions of the top cell 11, the current flowing through each interconnector 20 can be equalized. In other words, the deterioration of the current-voltage characteristics caused by the formation of the opening groove 14 on the top cell 11 can be suppressed.

[0038] In this embodiment, since the intermediate electrode 13 is provided on the bottom cell 12, light incident on the opening groove 14 strictly passes through the intermediate electrode 13 before reaching the bottom cell 12. As a variation of this embodiment, 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 joined) can be included.

[0039] Next, we will explain what aperture ratio of the top cell 11 formed by the opening groove 14 is preferable in the photoelectric conversion element 10. Here, the aperture ratio of the top cell 11 in this disclosure is a value calculated as the ratio of the opening area of ​​the top cell 11 formed by the opening groove 14 to the area of ​​one surface of the bottom cell 12 (or the area of ​​one surface of the top cell 11 before the opening groove 14 is formed). An example of an aperture ratio of the top cell 11 is 3% or more and 20% or less. A specific calculation example will be explained later using the second embodiment as an example.

[0040] Figure 9 is a graph showing the relationship between the aperture ratio of the top cell and the photoelectric conversion efficiency (Pmax) for three of the six cells (six plots) shown in Figure 8 with varying band gaps, where the band gap is 1.7 eV or less. As can be seen in Figure 9, the smaller the band gap, the stronger the tendency for the cell output to increase as the aperture ratio of the top cell increases.

[0041] These results show that for a cell with a band gap of 1.65 eV, the cell output is maximized at an aperture ratio of around 5% (e.g., 2% to 8%, more preferably 3% to 7%), and for a cell with a band gap of 1.55 eV, the cell output is maximized at an aperture ratio of around 15% (e.g., 2% to 30%, more preferably 3% to 20%, and even more preferably 6% to 15%). Furthermore, it is estimated that for a cell with a band gap of 1.46 eV, the cell output is maximized at an aperture ratio considerably larger than 15%.

[0042] These results show that when using a top cell with a band gap of 1.7 eV or less, and the current generated in the bottom cell is smaller than the current generated in the top cell, the output of the photoelectric conversion element 10 can be improved by adopting a configuration in which an opening groove 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 1.55eV to 1.6eV, which is a relatively narrow band gap for a top cell in 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, it is possible to increase the cell output compared to when the opening groove 14 is not formed by forming an opening groove 14 such that the aperture ratio of the top cell 11 is about 10% (for example, 5% to 15%).

[0044] In the following description, the configuration of each layer in the photoelectric conversion element 10 will be explained using examples. However, since known technologies can be applied to the materials and film deposition methods of each layer in the photoelectric conversion element 10, the configuration of each layer applicable to this embodiment is not limited to these examples. That is, as long as it functions as a photoelectric conversion element in a tandem solar cell, any optional layers may be omitted, and there may be layers other than those described below, and one layer may also perform the function of another layer.

[0045] (Front grid electrode, back grid electrode) The surface grid electrode 111 and the back grid electrode 125 are composed of multiple conductive members that are parallel to each other. These multiple conductive members extend in a first direction (the X direction shown in Figures 1 and 2) and are arranged parallel to each other with spacing between them in a second direction (the Y direction shown in Figures 1 and 2). The multiple conductive members in the surface grid electrode 111 (back grid electrode 125) are connected by the interconnector 20 or a grid electrode located below the interconnector 20. Specifically, the interconnector 20 extends in the second direction and is arranged to be perpendicular to these multiple conductive members. Since the second direction is along the short side of the photoelectric conversion element 10, arranging the interconnector 20 to extend in this direction can reduce its electrical resistance.

[0046] The front grid electrode 111 (back grid electrode 125) is also called a finger electrode, and the interconnector 20 is also called a busbar 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 grid electrode 111 (back grid electrode 125) is narrower than the interconnector 20, and light is incident into the interior of the photoelectric conversion element 10 through the gap between adjacent conductive members. Note that the back grid electrode 125 is on the opposite side from the light-receiving surface, so it may be configured so that light does not pass through it.

[0047] (Surface transparent electrode, back transparent electrode) The front transparent electrode 112 and the back transparent electrode 124 are thin-film electrodes that are conductive and light-transmitting. Examples of materials for these electrodes 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 individually or in combination of two or more. The back transparent electrode 124 is on the opposite side from the light-receiving surface, so it may be configured not to 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. Preferably, the top cell electron transport layer 113 also functions as a hole blocking layer that suppresses the movement of holes generated in the top cell light absorption layer 114 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] Furthermore, as long as the top cell 11 has a photoelectric conversion function, it is self-evident that the portion located on the electron transport side (or negative electrode side, similarly in this disclosure) of the top cell light absorption layer 114 or on the electron transport side within the top cell light absorption layer 114 has an electron transport function, and there is no need to verify the electron transport function, which is difficult to actually confirm. In other words, as long as the top cell 11 has a photoelectric conversion function, any layer located on the electron transport side of the top cell light absorption layer 114 or on the electron transport side within the top cell light absorption layer 114 and made of an appropriate material can be considered the top cell electron transport layer 113.

[0050] Furthermore, the top cell electron transport layer 113 can also function as the surface transparent electrode 112, and vice versa. Therefore, the photoelectric conversion element 10 does not necessarily have to be configured to include both the surface transparent electrode 112 and the top cell electron transport layer 113; it may be configured to include only one of them, with one of them performing the function of the other.

[0051] (Top cell light absorption layer) The top cell light absorption layer 114 can be a layer containing a perovskite compound, which is a photoelectric conversion material. The top cell light absorption layer 114 is a layer that absorbs at least a portion of the light incident on the photoelectric conversion element 10 and can generate electrons and holes. Of these, electrons move to the top cell electron transport layer 113, and holes move to the top cell hole transport layer 115. The top cell light absorption layer 114 may consist of a perovskite compound alone, or it may contain substances other than perovskite compounds.

[0052] The perovskite compound is composed of compounds represented by the general formula: ABX3···(1). While the compositional ratio is preferably 1:1:3, it does not necessarily have to be 1:1:3, and the content of each element may be adjusted as appropriate.

[0053] In general formula (1), A is an organic molecule (including an organic group or an organic cation, as is the case in this disclosure), an inorganic atom or molecule (including an inorganic group or an inorganic cation, as is the case in this disclosure), or a combination thereof; B is a metal atom or molecule (including a metal cation, as is the case 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, as is the case in this disclosure). In general formula (1), the three Xs may be the same or different from one another.

[0054] In 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] Furthermore, it is possible to determine that a compound is a perovskite compound if it is known that the top cell light-absorbing layer 114 has a photoelectric conversion function and contains A, B, and X; confirmation of the presence of a crystalline structure is not required. For example, it is possible to determine this by knowing that A, B, and X contain organic molecules, metal atoms, and halogen atoms, or by knowing that A, B, and X contain inorganic atoms, metal atoms, and halogen atoms.

[0056] Examples of organic molecules represented by A in general formula (1) include alkylamines, alkylammonium compounds, and nitrogen-containing heterocyclic compounds. In perovskite compound (1), the organic molecule represented by A may be only one type of organic molecule, or it 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] Alkylammonium compounds are ionized compounds of the alkylamines mentioned above. Examples of alkylammonium compounds 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 nitrogen-containing heterocyclic compounds include imidazole, azole, pyrrole, aziridine, azirine, azetidine, azeto, azole, imidazoline, and carbazole. Nitrogen-containing heterocyclic compounds may also be ionized. Phenethylammonium is preferred as an ionized nitrogen-containing heterocyclic compound.

[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 metal atoms 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 perovskite compounds, the metal atom represented by B may be only one type of metal atom or two or more types of metal atoms. From the viewpoint of improving the light absorption and charge generation characteristics of perovskite compounds, lead atoms or tin atoms are preferred as the metal atom represented by B. From the viewpoint of reducing lead, tin atoms are preferred.

[0062] Examples of halogen atoms represented by X in general formula (1) include fluorine, chlorine, bromine, and iodine atoms. Examples of chalcogen atoms include oxygen, sulfur, selenium, and tellurium atoms. In a perovskite compound, the halogen atom or chalcogen atom represented by X may be one or two or more. From the viewpoint of enabling the perovskite compound to utilize light in a wide wavelength range, iodine is preferred as the halogen atom represented by X. More specifically, it is preferable that at least one of the three Xs represents an iodine atom, and it is more preferable that all three Xs represent iodine atoms.

[0063] As the perovskite compound, compounds represented by the general formula "CH3NH3PbX3 (where X represents a halogen atom)" are preferred, and CH3NH3PbI3 is more preferred. By using a compound represented by the general formula "CH3NH3PbX3" (especially 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 solar cells can be further improved.

[0064] As a method for forming the top cell light-absorbing layer 114 containing the perovskite compound, an example is to coat a precursor solution, obtained by dissolving a precursor compound of the perovskite compound in an organic solvent, using known methods such as spin coating or bar coating to form the 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. Preferably, the top cell hole transport layer 115 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 composed mainly 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 contains 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, metal sulfides (e.g., Cu2O, NiO, ZnS), and spiro-OMeTAD is preferred.

[0067] Furthermore, as long as the top cell 11 has a photoelectric conversion function, it is self-evident that the portion located on the hole transport side (or positive electrode side, similarly in this disclosure) of the top cell light absorption layer 114 or on the hole transport side within the top cell light absorption layer 114 has a hole transport function, and there is no need to verify the hole transport function, which is difficult to actually confirm. In other words, as long as the top cell 11 has a photoelectric conversion function, any layer located on the hole transport side of the top cell light absorption layer 114 or on the hole transport side within the top cell light absorption layer 114 and made of an appropriate material can be considered as the top cell hole transport layer 115.

[0068] (Middle class) In this embodiment, an intermediate electrode 13 is exemplified as an 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, the material of the intermediate electrode 13 can be a material that has conductivity and light transmittance, and examples of conductive transparent materials include 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 individually or in combination of two or more.

[0069] Furthermore, the intermediate layer is not limited to the intermediate electrode 13, but can also be any other known structure placed between the tandem top cell and 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 can be any structure placed between the top cell and the bottom cell in a tandem solar cell. As long as the solar cell is functioning as a solar cell, it is self-evident that such a structure functions as an intermediate layer without needing to verify its physical properties such as conductivity and transmittance. Furthermore, an intermediate layer is not necessarily required; the layer on the bottom cell side of the top cell and the layer on the top cell side of the bottom cell can serve as a substitute, having a similar configuration. As long as the tandem solar cell containing these top and bottom cells is functioning as a tandem solar cell, it is self-evident that these layers function as a substitute for the intermediate layer without needing to verify their physical properties such as conductivity and transmittance.

[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, the bottom cell light-absorbing layer 122, and the bottom cell p-type doped layer 123 can employ configurations used in known silicon solar cells. For example, by adding doping impurities to the surface of a crystalline silicon substrate, a configuration can be achieved in which the bottom cell n-type doped layer 121 is formed on one side of the bottom cell light-absorbing layer 122, which is a crystalline silicon substrate, and the bottom cell p-type doped layer 123 is formed on the other side. The bottom cell n-type doped layer 121 can be formed by adding phosphorus, arsenic, etc., as doping impurities, and the bottom cell p-type doped layer 123 can be formed by adding boron, gallium, etc.

[0072] Furthermore, when using a heterojunction silicon configuration, for example, a non-single-crystal silicon-based thin film, such as amorphous silicon or microcrystalline silicon, can be deposited on a single-crystal silicon substrate as the bottom cell light absorption layer 122, forming the bottom cell n-type doping layer 121 and the bottom cell p-type doping layer 123. Examples of materials for the silicon-based thin film as the bottom cell n-type doping layer 121 and the bottom cell p-type doping layer 123 include amorphous silicon, microcrystalline silicon, amorphous silicon alloy, and microcrystalline silicon alloy. Examples of silicon alloys include silicon oxide, silicon carbide, silicon nitride, and silicon germanium. These may be used individually or in combination of two or more.

[0073] [Second Embodiment] Figure 3 is a plan view showing a part of a photoelectric conversion module 100 using the photoelectric conversion element 10 according to the second embodiment of this 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 with eight opening grooves 14. The opening 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] If the top cell 11 is configured such that one interconnector 20 is connected to each of the divided regions, and the number of interconnectors 20 on the top cell 11 is n, then the top cell 11 will be divided by n-1 opening grooves 14.

[0076] In the example shown in Figure 3, the photoelectric conversion element 10 is a half-size cell fabricated from a 166 mm square silicon wafer, and the width of the opening groove 14 is 2 mm. Using this example, the aperture ratio of the top cell 11 can be calculated using the following formula. Top cell aperture ratio =[Width of opening groove 14] × [Short side of cell] × [Number of opening grooves 14] ÷ ([Long side of cell] × [Short side of cell] - [Area of ​​C-face (corner cutout) of cell] × 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 aperture groove 14. As described above, the optimal range for the aperture ratio of the top cell 11 varies depending on the band gap of the cell. By adjusting the aperture ratio according to the band gap of the top cell 11, a photoelectric conversion element 10 with high output can be obtained.

[0078] [Third Embodiment] Figure 4 is a plan view showing a part of a photoelectric conversion module 100 using the photoelectric conversion element 10 according to the third embodiment of this 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 opening grooves 14 between all adjacent interconnectors 20 as in the first and second embodiments, opening grooves 14 are provided every other one. Even with this configuration, since the same number of interconnectors 20 are provided in each of the divided regions of the top cell 11, the current flowing through each interconnector 20 can be equalized. That is, the deterioration of the current-voltage characteristics due to the formation of opening grooves 14 on the top cell 11 can be suppressed.

[0080] [Fourth Embodiment] Figure 5 is a plan view showing a part of a photoelectric conversion module 100 using the photoelectric conversion element 10 according to the fourth embodiment of this disclosure. The photoelectric conversion element 10 according to this embodiment can have the same configuration as the first embodiment, except as described below.

[0081] In this embodiment, the photoelectric conversion element 10 has an opening groove 14 formed in the top cell 11 that is aligned parallel to the interconnector 20, similar to the first to third embodiments. However, the opening groove 14 does not extend to the end of the top cell 11 (the long side of the cell). Even though the opening groove 14 is provided in a way 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, similar to the first embodiment. Therefore, current matching between the top cell 11 and the bottom cell 12 can be achieved in the photoelectric conversion element 10 according to this embodiment.

[0082] Furthermore, according to the configuration of the opening groove 14 in this embodiment, even if the opening groove 14 is not formed all the way to the edge of the top cell 11, it has substantially the same effect as if the top cell 11 were divided into multiple regions by the opening groove 14, thus maintaining uniformity in the current density within the plane of the solar cell.

[0083] [Fifth Embodiment] Figure 6 is a cross-sectional view showing the schematic configuration of a photoelectric conversion element 10 according to the fifth embodiment of this disclosure. In the photoelectric conversion element 10 according to this embodiment, the configuration can be the same as that of the first embodiment, except as described below.

[0084] In the photoelectric conversion element 10 according to this embodiment, a dividing groove 1251 is formed on the back grid electrode 125, and the back grid electrode 125 is divided into multiple regions. The top cell 11 is divided into multiple regions by an opening groove 14, as in the first embodiment. The divided regions in the back grid electrode 125 and the divided regions in the front grid electrode 111 (top cell 11) correspond to each other.

[0085] In the photoelectric conversion element 10 according to this embodiment, the number of divided regions is the same for the front grid electrode 111 and the back grid electrode 125, and the arrangement direction of the divided regions is the same for the front grid electrode 111 and the back grid electrode 125. In this case, divided regions that have the same arrangement order along the arrangement direction for the front grid electrode 111 and the back grid electrode 125 are considered to be corresponding divided regions. In a plan view, at least a portion of the regions of the corresponding divided regions overlap, and it is preferable that they completely overlap in a plan view. Furthermore, "corresponding" here does not mean that they are physically connected, but rather that they are physically connected to parts of adjacent elements, and therefore have such a relationship. That is, if a certain component (for example, XA) in the first element 10A is at least physically connected by a connecting member to a component (for example, YB) in the adjacent element, the second element 10B, and the first element 10A has a component (for example, YA) that corresponds to component YB, then component XA and component YA are said to "correspond". Here, for example, component XA refers to one of the divided elements of the surface grid electrode 111, and components YA and YB refer to one of the divided elements of the back surface grid electrode 125.

[0086] With this configuration, the area from which current is collected by a single interconnector 20 is divided into corresponding regions by the front grid electrode 111 and the back grid electrode 125, thus allowing for a clearer equalization of the current flowing through each interconnector 20.

[0087] The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined by the claims. This includes all modifications within the meaning and scope of the claims.

[0088] [Note] This disclosure includes the following aspects:

[0089] (Aspect 1) A photoelectric conversion element in a tandem solar cell, It includes a top cell located on the light-receiving side and a bottom cell located on the back side, A photoelectric conversion element characterized in that an aperture groove is formed in the light absorption 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 absorption layer of the bottom cell without passing through the light absorption layer of the top cell.

[0090] (Aspect 2) A photoelectric conversion element according to Aspect 1, The photoelectric conversion element is characterized in that the opening groove portion is formed to divide the top cell into multiple regions.

[0091] (Aspect 3) A photoelectric conversion element according to Aspect 1 or Aspect 2, The photoelectric conversion element is characterized in that 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, The top cell has grid electrodes composed of a plurality of conductive members parallel to each other, An interconnector for connecting the plurality of conductive members in the grid electrode is provided on the top cell. The photoelectric conversion element is characterized in that the opening groove is formed along a direction parallel to the interconnector.

[0093] (Aspect 5) A photoelectric conversion element according to any one of aspects 1 to 4, The top cell is a photoelectric conversion element characterized by having a light-absorbing layer containing a perovskite compound.

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

[0095] 10 Photoelectric conversion element 100 Photoelectric Conversion Modules 11 Top Cells 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 cells 121 Bottom cell n-type doped layer 122 Bottom cell light absorption layer 123 Bottom cell p-type doped layer 124 Back side transparent electrode 125 Backside grid electrode 13 Intermediate electrode 14 Open groove section 20 interconnectors 20A Surface Interconnector 20B Rear Interconnector

Claims

1. A photoelectric conversion element in a tandem solar cell, It includes a top cell positioned on the light-receiving surface side, a bottom cell positioned on the back side, and an intermediate layer positioned between the top cell and the bottom cell, An opening 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 enter the light-absorbing layer of the bottom cell without passing through the light-absorbing layer of the top cell. The aforementioned opening groove is formed to divide the top cell into multiple regions, The upper surface of the intermediate layer is in contact with each of the multiple regions into which the top cell is divided. The back surface of the intermediate layer is in contact with the bottom cell, The photoelectric conversion element is characterized in that the intermediate layer is made of a conductive transparent material, and the top cell is electrically connected integrally to a plurality of divided regions and the bottom cell.

2. A photoelectric conversion element in a tandem solar cell, It includes a top cell positioned on the light-receiving surface side, a bottom cell positioned on the back side, and an intermediate layer positioned between the top cell and the bottom cell, An opening 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 enter the light-absorbing layer of the bottom cell without passing through the light-absorbing layer of the top cell. The aforementioned opening groove is formed to divide the top cell into multiple regions, The intermediate layer is made of a conductive transparent material and electrically connects the multiple regions into which the top cell is divided with the bottom cell. A photoelectric conversion element characterized in that the top cell and the bottom cell are connected in series.

3. A photoelectric conversion element according to claim 1 or claim 2, The photoelectric conversion element is characterized in that 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.

4. A photoelectric conversion element according to claim 1 or claim 2, The top cell has a surface grid electrode composed of a plurality of conductive members parallel to each other, A surface interconnector is provided on the top cell for connecting the plurality of conductive members in the surface grid electrode. The photoelectric conversion element is characterized in that the opening groove portion is formed along a direction parallel to the surface interconnector.

5. A photoelectric conversion element according to Claim 4, The bottom cell has a back grid electrode composed of a plurality of conductive members parallel to each other, A back surface interconnector is provided on the back surface of the bottom cell for connecting the plurality of conductive members in the back surface grid electrode. The back grid electrode is divided into multiple regions by the dividing grooves formed on the back grid electrode. A photoelectric conversion element characterized in that the divided region in the back grid electrode and the divided region in the top cell correspond to each other.

6. A photoelectric conversion element according to claim 1 or claim 2, The top cell is a photoelectric conversion element characterized by having a light-absorbing layer containing a perovskite compound.

7. A photoelectric conversion element according to claim 1 or claim 2, A photoelectric conversion element characterized in that the aperture ratio of the top cell, calculated as the ratio of the aperture area due to the aperture groove in the top cell to the area of ​​one surface of the bottom cell, is 3% or more and 20% or less.

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