Photoelectric conversion element

Abstract

In tandem solar cells, the passivation properties are maintained even when using TOPCon type solar cells as the photoelectric conversion element. [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 side. The top cell 11 has a top cell light absorption layer 114 containing a perovskite compound, and the bottom cell 12 has a bottom cell light absorption layer 123 containing silicon. Between the bottom cell light absorption layer 123 and the top cell 11, there is an n-type polysilicon dopant layer 121 and a first tunnel oxide layer 122. Between the bottom cell light absorption layer 123 and the lower electrode 126, there is a p-type polysilicon dopant layer 125 and a second tunnel oxide layer 124.

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. A perovskite / silicon solar cell is an example of a tandem solar cell. As a crystalline silicon solar cell constituting such a tandem solar cell, silicon heterojunction (HJT) solar cells with good passivation properties are widely used (for example, Patent Document 1).

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of Invention

Problem to be Solved by the Invention

[0004] As described above, it is also conceivable to use a lower-cost TOPCon (Tunnel Oxide Passivated Contact) solar cell as the crystalline silicon solar cell of a tandem solar cell. A TOPCon solar cell has a configuration including a polysilicon layer and a tunnel oxide layer on the surface of a silicon-containing photoelectric conversion layer. However, when a TOPCon solar cell is arranged on the light-receiving surface side, there is a concern that the amount of light absorbed by the polysilicon layer increases, making it impossible to ensure passivation properties.

[0005] The present disclosure has been made in view of the above problems, and an object of the present disclosure is to enable good passivation properties to be maintained even when a TOPCon solar cell is used in a photoelectric conversion element of a tandem solar cell. [Means for solving the problem]

[0006] 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, comprising a top cell disposed on the light-receiving surface side and a bottom cell disposed on the back side, wherein the top cell has a first photoelectric conversion layer containing a perovskite compound, the bottom cell has a second photoelectric conversion layer containing silicon, the bottom cell has a first thin-film silicon compound layer and a first polycrystalline silicon layer between the second photoelectric conversion layer and the top cell, and the bottom cell has a second thin-film silicon compound layer and a second polycrystalline silicon layer between the second photoelectric conversion layer and the lower electrode.

[0007] In this disclosure, the first polycrystalline silicon layer may be an n-type polysilicon dopant layer, and the second polycrystalline silicon layer may be a p-type polysilicon dopant layer.

[0008] In this disclosure, the first polycrystalline silicon layer may be a p-type polysilicon dopant layer, and the second polycrystalline silicon layer may be an n-type polysilicon dopant layer.

[0009] In this disclosure, a transparent conductive oxide layer may be provided between the top cell and the bottom cell.

[0010] In this disclosure, the top cell may have a configuration in which the first photoelectric conversion layer is sandwiched between an electron transport layer and a hole transport layer. [Effects of the Invention]

[0011] According to this disclosure, even when using a TOPCon type solar cell in the photoelectric conversion element of a tandem solar cell, good passivation properties can be maintained. [Brief explanation of the drawing]

[0012] [Figure 1]This is a cross-sectional view showing the schematic configuration of a photoelectric conversion element according to the present disclosure. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Figure 1 shows one embodiment of the present disclosure and is a cross-sectional view showing the schematic configuration of the photoelectric conversion element 10.

[0014] The photoelectric conversion element 10 is a photoelectric conversion element in a tandem solar cell using a perovskite solar cell, and in Figure 1, the top side is the light-receiving surface. As shown in Figure 1, the photoelectric conversion element 10 has a stacked configuration of a top cell 11 and a bottom cell 12, with the top cell 11 on the top side and the bottom cell 12 on the back side. In this disclosure, when simply referred to as the light-receiving surface, it means the light-receiving surface or the side mainly used as the light-receiving surface. Similarly, when simply referred to as the back side, it means the back side or the side mainly used as the back side. Furthermore, when using expressions meaning "up" or "down" regarding direction, the expression meaning "up" can be used for the light-receiving surface side of the element, and the expression meaning "down" can be used for the back side of the element, and unless otherwise specified, it will be understood as such. In other words, basically, the light-receiving surface and the top side mean the same thing, and the back side and the bottom side also mean the same thing. Furthermore, in a photoelectric conversion element with single-sided light reception, the light-receiving surface refers to the surface on which light enters the element directly. However, in a photoelectric conversion element capable of receiving light from both sides, one of the two sides may be considered the light-receiving surface, and if one side is considered the light-receiving surface, the opposite side may be considered the back surface. In other words, if the configuration of the present disclosure is present when at least one side is considered the light-receiving surface, it can be considered to fall within the technical scope of the present disclosure. To put it another way, even if the configuration of the present disclosure is not present when one side is considered the light-receiving surface, if the configuration of the present disclosure is present when the other side is considered the light-receiving surface, it can be considered to fall within the technical scope of the present disclosure. Furthermore, in this disclosure, a layer or film preferably refers to a component with a substantially constant film thickness, but is not limited thereto, and may have parts with different thicknesses, or be in the shape of a pattern or islands.

[0015] In this disclosure, a tandem solar cell means a solar cell in which 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 is sequentially absorbed by two or more light-absorbing layers.

[0016] In terms of configuration, in this disclosure, a tandem solar cell may mean a solar cell in which two light-absorbing layers are provided in order from the light-receiving side to the back side of the photoelectric conversion element, starting from the light-receiving side. It is not necessary for the two light-absorbing layers to be completely superimposed when viewed from the light-receiving side; at least a portion of them should be superimposed. Furthermore, it is desirable that at least one light-absorbing layer is completely superimposed on the other. In other words, in this disclosure, a tandem solar cell is one in which some or all of the light (specifically, light having a certain wavelength band) incident from the light-receiving side of the photoelectric conversion element can pass through one light-absorbing layer and then enter the other light-absorbing layer. The light-absorbing layers referred to here do not need to be single layers; they may consist of multiple layers. These multiple layers can refer to, for example, a laminated structure consisting of PN junctions.

[0017] Furthermore, a light-absorbing layer (including the top cell light-absorbing layer or the bottom cell light-absorbing layer) is a layer that absorbs light incident on the 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 has the function of photoelectric conversion as a solar cell, and as long as the light-absorbing layer is made of appropriate materials, it is not necessary to confirm that it absorbs light and generates electron-hole pairs, which is extremely difficult to confirm.

[0018] The top cell 11 of the photoelectric conversion element 10 has, in order from the top side, an upper electrode (first electrode) 111, a transparent conductive oxide layer 112, an electron transport layer 113, a top cell light absorption layer (first photoelectric conversion layer) 114, and a hole transport layer 115. The bottom cell 12 has, in order from the top side, an n-type first polysilicon dopant layer 121, a first tunnel oxide layer 122, a bottom cell light absorption layer (second photoelectric conversion layer) 123, a second tunnel oxide layer 124, a p-type polysilicon dopant layer 125, and a lower electrode (second electrode) 126. Adjacent layers from the upper electrode 111 of the top cell 11 to the lower electrode 126 of the bottom cell 12 are electrically connected to each other.

[0019] 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 of the top cell 11 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 the perovskite compound.

[0020] 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. Regarding the materials and film deposition methods for each layer in the photoelectric conversion element 10, known technologies can be applied, so a detailed explanation is omitted here.

[0021] The photoelectric conversion element 10 shown in FIG. 1 exemplifies a configuration (Example 1 described below) in which current flows from the top to the bottom of the figure (that is, electrons flow upward and holes flow downward). However, the direction of current is not limited thereto, and a configuration in which current flows from the bottom to the top may be employed. In the case of the configuration in which current flows from the bottom to the top (Example 2 described below), the positions of the electron transport layer 113 and the hole transport layer 115 are swapped in the top cell 11, and the positions of the n-type first polysilicon dopant layer 121 and the p-type polysilicon dopant layer 125 are swapped in the bottom cell 12. The photoelectric conversion element 10 shown in FIG. 1 may also be used as a double-sided light-receiving type. The photoelectric conversion element 10 may be configured to be capable of receiving light not only from the light-receiving surface side (the top cell 11 side) but also from the back surface side (the bottom cell 12 side). For example, light such as sunlight is incident on the light-receiving surface side of the photoelectric conversion element 10, and reflected light or the like according to the environment where the solar cell is installed is incident on the back surface side. In a double-sided light-receiving solar cell, either one of the surfaces may be considered as the light-receiving surface, and when either one surface is considered as the light-receiving surface, the opposite surface may be considered as the back surface. That is, when at least one of the surfaces is considered as a light-receiving surface, it may be considered to fall within the technical scope of the present disclosure as long as it has the configuration of the present disclosure. In other words, even if it does not have the configuration of the present disclosure when one surface is considered as the light-receiving surface, it may be considered to fall within the technical scope of the present disclosure as long as it has the configuration of the present disclosure when the other surface is considered as the light-receiving surface.

[0022] Hereinafter, the configuration of each layer in the photoelectric conversion element 10 will be described by way of example. Since known techniques can be applied to the materials and film formation methods of each layer in the photoelectric conversion element 10, the configuration of each layer applicable to the present embodiment is not limited to this example. That is, as long as it has a function as a photoelectric conversion element in a tandem solar cell, any omittable layer may be omitted, layers other than those described below may be included, and one layer may also serve as another layer.

[0023] (Upper Electrode, Lower Electrode) The upper electrode 111 of the top cell 11 serves as the cathode of the photoelectric conversion element 10 and is connected to the transparent conductive oxide layer 112 of the top cell 11. The lower electrode 126 of the bottom cell 12 serves as the anode of the photoelectric conversion element 10 and is connected to the p-type polysilicon dopant layer 125 of the bottom cell 12. As materials for the upper electrode 111 and the lower electrode 126, materials having conductivity and light transmittance can be employed; examples thereof 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). One of these may be used alone, or two or more thereof may be used in combination.

[0024] (Transparent Conductive Oxide Layer) The transparent conductive oxide layer 112 of the top cell 11 is a thin-film conductive layer having conductivity and light transmittance disposed on the light-receiving surface side of the photoelectric conversion element 10. Examples of materials for the transparent conductive oxide layer 112 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). One of these may be used alone, or two or more thereof may be used in combination. In the present disclosure, the terms "transparent" and "light-transmissive" mean that light is transmitted through the layer, but do not exclude materials that reflect or absorb a small amount of light. These terms mean that the layer is provided on the light-receiving surface side (including the site where light is incident; the same applies in the present disclosure) relative to the light absorption layer (either the top cell light absorption layer or the bottom cell light absorption layer) of the photoelectric conversion element 10. Therefore, a layer provided at least on the light-receiving surface side can be regarded as transparent. Further, in the present disclosure, the terms "conductive" or "conductivity" mean that electricity can be conducted. However, it is self-evident that the transparent conductive oxide layer 112 has conductivity as long as the solar cell functions as a solar cell to perform photoelectric conversion, and it is not necessary to confirm that electricity can be conducted as long as the conductive layer is formed of an appropriate material.

[0025] (Electron Transport Layer) The electron transport layer 113 of the top cell 11 is a layer that transports electrons generated in the top cell light absorption layer 114 to the transparent conductive oxide layer 112. Preferably, the 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 transparent conductive oxide layer 112. Examples of materials for the electron transport layer 113 include tin oxide, titanium oxide, and zinc oxide. For the formation of the electron transport layer 113, for example, sputtering, die coating, or screen printing can be used.

[0026] Furthermore, as long as the photoelectric conversion element 10 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 as the electron transport layer 113.

[0027] Furthermore, the electron transport layer 113 can also perform the function of the transparent conductive oxide layer 112, and vice versa. Therefore, the photoelectric conversion element 10 does not necessarily have to be configured to include both the transparent conductive oxide layer 112 and the electron transport layer 113; it may be configured to include only one of them, with one layer performing the function of the other.

[0028] (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 be composed of a perovskite compound alone, or it may contain substances other than perovskite compounds. The top cell light absorption layer 114 can be deposited using known film deposition methods such as spin coating, die coating, and inkjet.

[0029] 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.

[0030] In general formula (1), A is an organic molecule (including an organic group or an organic cation, as is done in this disclosure), an inorganic atom or molecule (including an inorganic group or an inorganic cation, as is done in this disclosure), or a combination thereof; B is a metal atom or molecule (including a metal cation, as is done 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 done in this disclosure). In general formula (1), the three Xs may be the same or different from one another.

[0031] 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.

[0032] Furthermore, it is possible to determine that a perovskite compound is present if it is confirmed that the photoelectric conversion element 10 possesses 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 if A, B, and X contain organic molecules, metal atoms, and halogen atoms, or if A, B, and X contain inorganic atoms, metal atoms, and halogen atoms. Moreover, as long as the photoelectric conversion element 10 possesses a photoelectric conversion function, it can be confirmed if the elements corresponding to A, B, and X are detected. For example, molecules containing carbon, nitrogen, and hydrogen are suitable as organic molecules; therefore, it is sufficient if carbon, nitrogen, hydrogen, metal elements, and halogens or chalcogens are detected. Alternatively, it is sufficient if it contains A, B, and X, for example, if it contains inorganic atoms, metal atoms, and halogen atoms. Furthermore, the presence of a perovskite compound can be confirmed by detecting elements corresponding to A, B, and X, as long as the photoelectric conversion element 10 has a photoelectric conversion function. For example, cesium or rubidium are suitable as inorganic atoms; therefore, it is sufficient if cesium or rubidium, a metallic element, and a halogen or chalcogen are detected.

[0033] The term "light-absorbing region" can refer to any portion that absorbs light (for example, a region containing a perovskite compound). If there are other light-absorbing regions besides the indicated light-absorbing region, they can be collectively described as a light-absorbing layer. In other words, the light-absorbing region can mean any portion of the light-absorbing layer. Furthermore, the light-absorbing layer can mean a collection of light-absorbing regions that exist discretely or continuously in a region mainly in a certain direction, having a thickness (similar to the definition of "layer," which does not need to be constant, for example). In this embodiment, the light-absorbing region means a perovskite compound. However, this does not exclude the inclusion of components other than perovskite compounds in the light-absorbing region.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] As a method for forming the top cell light-absorbing layer 114 containing the perovskite compound, an example can be described as a method of forming a film by coating 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.

[0043] (Hole transport layer) The hole transport layer 115 of the top cell 11 is a layer that transports holes generated in the top cell light absorption layer 114 to the bottom cell 12. Preferably, the 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 bottom cell 12. For example, sputtering, die coating, screen printing, etc., can be used to form the hole transport layer 115.

[0044] The hole transport layer 115 is composed mainly of a hole transport material. Specifically, the 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.

[0045] Furthermore, as long as the photoelectric conversion element 10 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 photoelectric conversion element 10 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 hole transport layer 115.

[0046] (Bottom cell light absorption layer) The bottom cell light absorption layer 123 can employ a configuration used in known TOPCon type solar cells. The bottom cell light absorption layer 123 is made of, for example, an n-type single-crystal silicon substrate. The light-receiving surface of the bottom cell light absorption layer 123 is formed as a substantially flat surface, while the back surface of the bottom cell light absorption layer 123 has a textured structure with numerous pyramidal (square pyramidal or truncated square pyramidal) irregularities of various sizes and shapes. The textured structure can be formed by anisotropic etching on the surface of the crystalline silicon substrate, and the irregularities include overlapping and deformed ones.

[0047] In this disclosure, silicon is an example of a semiconductor, and semiconductors other than silicon may be used. In this disclosure, a semiconductor means a material that has a certain band gap and can absorb light, and typically includes silicon.

[0048] (First tunnel oxide layer, second tunnel oxide layer) The first tunnel oxide layer 122 and the second tunnel oxide layer 124 of the bottom cell 12 can employ configurations used in known TOPCon type solar cells. The first tunnel oxide layer 122 and the second tunnel oxide layer 124 are formed to be thin enough to increase the probability that electrons will pass directly through the first tunnel oxide layer 122 and the second tunnel oxide layer 124. The first tunnel oxide layer 122 and the second tunnel oxide layer 124 may be formed, for example, by thermal growth or chemical deposition (e.g., plasma chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD)). Alternatively, the first tunnel oxide layer 122 and the second tunnel oxide layer 124 may be formed, for example, by ozone oxidation treatment.

[0049] In this disclosure, the first tunnel oxide layer 122 and the second tunnel oxide layer 124 are examples of thin-film silicon compound layers, and other thin-film silicon compound layers (e.g., tunnel nitride layers) may also be used. In this disclosure, a thin film is preferably a film thickness that allows tunnel conduction, meaning a film thickness of 0.1 nm or more and 5 nm or less, preferably 1 nm or more and 3 nm or less, and even more preferably 1.5 nm or more and 2 nm or less. For example, in the case of silicon, a film thickness of 0.1 nm or more and 2 nm or less is preferred.

[0050] (n-type polysilicon dopant layer, p-type polysilicon dopant layer) The n-type polysilicon dopant layer 121 and the p-type polysilicon dopant layer 125 of the bottom cell 12 can adopt configurations used in known TOPCon type solar cells. For example, by adding dopant impurities to the surface of a crystalline silicon substrate, an n-type polysilicon dopant layer 121 can be formed on one side (light-receiving side) of the crystalline silicon substrate, and a p-type polysilicon dopant layer 125 can be formed on the other side (back side). By adding phosphorus, arsenic, etc. as dopant impurities, the n-type polysilicon dopant layer 121 can be formed, and by adding boron, gallium, etc., the p-type polysilicon dopant layer 125 can be formed.

[0051] In this disclosure, the n-type polysilicon dopant layer 121 and the p-type polysilicon dopant layer 125 are examples of polycrystalline silicon layers, and other polycrystalline silicon layers may be used. Polycrystalline silicon is preferred as the material for the polycrystalline silicon layer. However, microcrystalline silicon, which is difficult to distinguish clearly, can be mentioned or included. Examples of materials for the polycrystalline silicon layer include amorphous silicon, microcrystalline silicon, amorphous silicon alloys, microcrystalline silicon alloys, etc. 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. In this disclosure, polycrystalline silicon is preferred. However, microcrystalline silicon, which is difficult to distinguish clearly, can be mentioned or included. Non-monocrystalline silicon such as amorphous silicon and microcrystalline silicon can also be mentioned or included. Polycrystalline silicon does not necessarily mean silicon with relatively large grain boundaries on the μm order on its surface; it can also include, or be defined as, silicon with relatively small grain boundaries on the nm order. Furthermore, polycrystalline silicon can also include, or be defined as, silicon with grain boundaries so small that they cannot be observed. At the very least, if the material can be confirmed to be silicon, and in addition, at least grain boundaries can be observed, that portion can be considered polycrystalline silicon.

[0052] (Example 1) In this disclosure, the photoelectric conversion element 10 in a tandem solar cell has an n-type polysilicon dopant layer and a first tunnel oxide layer 122 between the bottom cell light absorption layer 123 of the bottom cell 12 and the top cell 11, and a p-type polysilicon dopant layer 125 and a second tunnel oxide layer 124 between the bottom cell light absorption layer 123 of the bottom cell 12 and the lower electrode 126. In the photoelectric conversion element 10, the polysilicon dopant layer and the tunnel oxide layer are laminated on both the light-receiving side and the back side of the bottom cell light absorption layer 123 of the bottom cell 12, respectively, forming a TOPCon type structure. The bottom cell light absorption layer 123 is sandwiched between the polysilicon dopant layer and the tunnel oxide layer from both the light-receiving side and the back side.

[0053] The photoelectric conversion element 10 disclosed herein can maintain good passivation even when using a TOPCon type solar cell. Specifically, in the photoelectric conversion element 10, photoelectric conversion is performed by the top cell light absorption layer 114 of the top cell 11 when light incident from the light-receiving surface side. In addition, light transmitted through the top cell 11 is incident on the bottom cell 12, and photoelectric conversion is also performed by the bottom cell light absorption layer 123 of the bottom cell 12. Therefore, the overall photoelectric conversion efficiency of the photoelectric conversion element 10 can be improved.

[0054] In this way, the photoelectric conversion element 10 uses light that has passed through the top cell 11 and entered the bottom cell 12 to generate electricity in the bottom cell 12. The bottom cell 12 is formed in a double-sided TOPCon type structure, but compared to the case of a single-cell TOPCon type structure, the amount of light absorbed by the n-type polysilicon dopant layer 121 can be kept to a minimum, and good passivation properties can be maintained. As a result, a decrease in photoelectric conversion efficiency due to light absorption by the n-type polysilicon dopant layer 121 can be suppressed. In addition, since the amount of light incident on the bottom cell 12 is reduced compared to the amount of light incident on the top cell 11, the degradation of the bottom cell 12 due to light absorption can be suppressed compared to the case of a single-cell TOPCon type structure. Therefore, since the n-type polysilicon dopant layer 121 and the first tunnel oxide layer 122 of the bottom cell 12, which is a TOPCon type solar cell, are provided adjacent to the back side of the top cell 11, which is a perovskite solar cell, the disadvantages of the TOPCon type solar cell (light absorption by the n-type polysilicon dopant layer 121) can be suppressed, and the photoelectric conversion efficiency of the top cell 11 and the bottom cell 12 can be improved.

[0055] (Intermediate connection layer) Furthermore, an intermediate connecting layer may be provided between the top cell 11 and the bottom cell 12. The intermediate connecting layer is a transparent conductive oxide layer that can be used between the top cell 11 and the bottom cell 12, and is a thin conductive layer having conductivity and light transmittance. Examples of materials for the transparent conductive oxide layer of the intermediate connecting layer 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 conductivity of the intermediate connecting layer is self-evident as long as the solar cell has the function of photoelectric conversion as a solar cell, and as long as it is properly arranged, it is not necessary to confirm that it can conduct electricity.

[0056] (Example 2) In this disclosure, the photoelectric conversion element 10 in a tandem solar cell has a p-type polysilicon dopant layer and a first tunnel oxide layer 122 between the bottom cell light absorption layer 123 of the bottom cell 12 and the top cell 11, and an n-type polysilicon dopant layer and a second tunnel oxide layer 124 between the bottom cell light absorption layer 123 of the bottom cell 12 and the lower electrode 126. In the photoelectric conversion element 10, the polysilicon dopant layer and the tunnel oxide layer are laminated on both the light-receiving side and the back side of the bottom cell light absorption layer 123 of the bottom cell 12, respectively, forming a TOPCon type structure. The bottom cell light absorption layer 123 is sandwiched between the polysilicon dopant layer and the tunnel oxide layer from both the light-receiving side and the back side. For example, the bottom cell light absorption layer 123 is made of a p-type single crystal silicon substrate. An intermediate connecting layer may also be provided between the top cell 11 and the bottom cell 12. Example 2 is a modified version of Example 1 in which the p-type polysilicon dopant layer and the n-type polysilicon dopant layer are swapped.

[0057] The photoelectric conversion element 10 disclosed herein can maintain good passivation even when using a TOPCon type solar cell. Specifically, in the photoelectric conversion element 10, photoelectric conversion is performed by the top cell light absorption layer 114 of the top cell 11 when light incident from the light-receiving surface side. In addition, light transmitted through the top cell 11 is incident on the bottom cell 12, and photoelectric conversion is also performed by the bottom cell light absorption layer 123 of the bottom cell 12. Therefore, the overall photoelectric conversion efficiency of the photoelectric conversion element 10 can be improved.

[0058] In this way, the photoelectric conversion element 10 uses light that has passed through the top cell 11 and entered the bottom cell 12 to generate electricity in the bottom cell 12. The bottom cell 12 is formed in a double-sided TOPCon type structure, but compared to the case of a single-cell TOPCon type structure, the amount of light absorbed by the p-type polysilicon dopant layer can be kept to a minimum, and good passivation properties can be maintained. As a result, a decrease in photoelectric conversion efficiency due to light absorption by the p-type polysilicon dopant layer can be suppressed. In addition, since the amount of light incident on the bottom cell 12 is reduced compared to the amount of light incident on the top cell 11, the degradation of the bottom cell 12 due to light absorption can be suppressed compared to the case of a single-cell TOPCon type structure. Therefore, since the p-type polysilicon dopant layer and the first tunnel oxide layer 122 of the bottom cell 12, which is a TOPCon type solar cell, are provided adjacent to the back side of the top cell 11, which is a perovskite solar cell, the disadvantages of the TOPCon type solar cell (light absorption by the p-type polysilicon dopant layer) can be suppressed, and the photoelectric conversion efficiency of the top cell 11 and the bottom cell 12 can be improved.

[0059] The present invention can be implemented in various other forms without departing from its spirit, purpose, or main features. Therefore, the embodiments described above are merely illustrative in all respects and should not be constrained. The scope of the invention is defined by the claims, and the text of the specification is not restrictive. Furthermore, any modifications or changes within the equivalent scope of the claims are all within the scope of the invention.

[0060] [Note]

[0061] (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, The top cell has a first photoelectric conversion layer containing a perovskite compound, The bottom cell has a second photoelectric conversion layer containing silicon, Between the second photoelectric conversion layer in the bottom cell and the top cell, there is a first thin-film silicon compound layer and a first polycrystalline silicon layer. A photoelectric conversion element characterized in that a second thin-film silicon compound layer and a second polycrystalline silicon layer are provided between the second photoelectric conversion layer and the lower electrode in the bottom cell.

[0062] (Aspect 2) In the photoelectric conversion element described in Embodiment 1, The first polycrystalline silicon layer is an n-type polysilicon dopant layer, A photoelectric conversion element characterized in that the second polycrystalline silicon layer is a p-type polysilicon dopant layer.

[0063] (Aspect 3) In the photoelectric conversion element described in Embodiment 1, The first polycrystalline silicon layer is a p-type polysilicon dopant layer, A photoelectric conversion element characterized in that the second polycrystalline silicon layer is an n-type polysilicon dopant layer.

[0064] (Aspect 4) In the photoelectric conversion element described in any one of the three embodiments, A photoelectric conversion element characterized by having a transparent conductive oxide layer between the top cell and the bottom cell.

[0065] (Appendix 5) In the photoelectric conversion element described in any one of the embodiments 1 to 4, The top cell is a photoelectric conversion element characterized in that the first photoelectric conversion layer is sandwiched between an electron transport layer and a hole transport layer. [Explanation of symbols]

[0066] 10 Photoelectric conversion element 11 Top Cells 114. Top cell light absorption layer (first photoelectric conversion layer) 12 bottom cells 121 n-type polysilicon dopant layer (first polycrystalline silicon layer) 122 First tunnel oxide layer (first thin-film silicon compound layer) 123 Bottom cell light absorption layer (second photoelectric conversion layer) 124 Second tunnel oxide layer (second thin-film silicon compound layer) 125 p-type polysilicon dopant layer (second polycrystalline silicon layer) 126 Lower electrode

Claims

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, The top cell has a first photoelectric conversion layer containing a perovskite compound, The bottom cell has a second photoelectric conversion layer containing silicon, Between the second photoelectric conversion layer in the bottom cell and the top cell, there is a first thin-film silicon compound layer and a first polycrystalline silicon layer. A photoelectric conversion element characterized in that a second thin-film silicon compound layer and a second polycrystalline silicon layer are provided between the second photoelectric conversion layer and the lower electrode in the bottom cell.

2. In the photoelectric conversion element according to claim 1, The first polycrystalline silicon layer is an n-type polysilicon dopant layer, A photoelectric conversion element characterized in that the second polycrystalline silicon layer is a p-type polysilicon dopant layer.

3. In the photoelectric conversion element according to claim 1, The first polycrystalline silicon layer is a p-type polysilicon dopant layer, A photoelectric conversion element characterized in that the second polycrystalline silicon layer is an n-type polysilicon dopant layer.

4. In the photoelectric conversion element according to any one of claims 1 to 3, A photoelectric conversion element characterized by having a transparent conductive oxide layer between the top cell and the bottom cell.

5. In the photoelectric conversion element according to any one of claims 1 to 3, The top cell is a photoelectric conversion element characterized in that the first photoelectric conversion layer is sandwiched between an electron transport layer and a hole transport layer.

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