Solar battery cell and solar battery module

Abstract

This solar battery cell (1) comprises: a cell body (10); a bypass diode (20); an interconnector (21) that electrically connects the cell body (10) and the bypass diode (20); and a cover glass (40) that covers light-receiving surfaces of the cell body (10) and the bypass diode (20). One end (21a) of the interconnector (21) is welded to the bypass diode (20), the other end (21b) of the interconnector (21) is welded to an opposite surface electrode (14) on the opposite surface to the light-receiving surface of the cell body (10), the cell body (10) is provided with a stress buffering part (13) at a portion of the light-receiving surface corresponding to a welded portion at which the other end (21b) of the interconnector (21) is welded on the opposite surface, and the stress buffering part (13) has the same height as a front surface electrode (grid line) (11) provided on the light-receiving surface of the cell body (10).

Description

Solar Cell and Solar Module

[0001] The present disclosure relates to a solar cell and a solar module including a cell body, a bypass diode, an interconnector that electrically connects the cell body and the bypass diode, and a cover glass that covers the light-receiving surfaces of the cell body and the bypass diode.

[0002] In recent years, as a solar cell that can be suitably used for space applications such as power sources for space equipment such as artificial satellites, for example, an example of using a triple-junction compound semiconductor solar cell having a structure of a top cell (InGaP layer), a middle cell (InGaAs layer), and a bottom cell (Ge layer) is increasing (see Patent Document 1).

[0003] Since it is very difficult to repair or replace parts of an artificial satellite once it is launched into orbit, the solar cell built into the artificial satellite is required to have high reliability to function stably even in a severe space environment. Therefore, a solar cell having a CIC (Connector and Coverglass Integrated Cell) structure is adopted for the solar cell. Since the solar cell with the CIC structure has a structure in which an interconnector is welded to the light-receiving surface and a cover glass is adhered, it has high characteristics for use in a special environment such as space different from the ground.

[0004] A plurality of such solar cells are connected via an interconnector and a bypass diode to form a solar module.

[0005] Japanese Patent Application Laid-Open No. 2005-136333

[0006] By the way, when connecting adjacent solar cells by an interconnector, since the surface of each solar cell is covered with a cover glass and there is no step that causes stress concentration, there is no risk of cell cracking when welding the interconnector to the back surface.

[0007] On the other hand, the bypass diode is attached by welding to the back electrode on the back of the light-receiving surface before the cover glass is bonded. During this welding process, stress concentration occurs at the step of the surface electrode on the surface of the solar cell, which may cause the solar cell to crack (hereinafter referred to as cell cracking). Therefore, a configuration that can suppress the risk of cell cracking was desired.

[0008] This disclosure has been made in view of the above-mentioned problems and aims to provide a solar cell in which the risk of cell cracking is suppressed.

[0009] To solve the above problems, the solar cell of the present disclosure is a solar cell comprising a cell body, a bypass diode, an interconnector for electrically connecting the cell body and the bypass diode, and a cover glass covering the light-receiving surfaces of the cell body and the bypass diode, wherein one end of the interconnector is welded to the bypass diode, and the other end of the interconnector is welded to a back electrode on the back surface of the light-receiving surface, and the cell body is provided with a stress buffer portion on the back surface of the light-receiving surface at a location corresponding to the welding location where the other end of the interconnector is welded, and the stress buffer portion has the same height as the surface electrode provided on the light-receiving surface.

[0010] According to the above configuration, when welding one end of the interconnector that electrically connects the cell body and the bypass diode to the back electrode of the cell body, a stress buffer portion is provided that is the same height as the surface electrode, making it less likely for stress concentration to occur at the step of the surface electrode. Therefore, the risk of cell cracking is suppressed. Note that the stress buffer portion being the same height as the surface electrode means that it is sufficient to be the same height to alleviate stress concentration during welding. Alternatively, the stress buffer portion may be the same height as the surface electrode that is in contact with the stress buffer portion, or the same height as the surface electrode adjacent to the stress buffer portion.

[0011] In this disclosure, the stress buffer portion may be characterized by being molded from the same material as the surface electrode.

[0012] According to the above configuration, since the stress buffer and the surface electrode are molded from the same material, there is no need to prepare a separate material for forming the stress buffer from the surface electrode.

[0013] In this disclosure, the stress buffer portion may be characterized by being integrally molded with the surface electrode.

[0014] According to the above configuration, the manufacturing process is simplified because the stress buffer and the surface electrode are molded integrally. Furthermore, since the stress buffer and the surface electrode are continuous, the stress buffer can also function as an electrode.

[0015] In this disclosure, the stress buffer portion may be characterized by being large enough to cover the welded area in a plan view.

[0016] Furthermore, the size of the stress buffer covering the welded area refers to a size equal to or greater than the welded area at the other end of the interconnect. With the above configuration, the stress buffer covers the welded area in a plan view, further suppressing the risk of cell cracking.

[0017] In this disclosure, the stress buffer portion may be characterized by being flattened.

[0018] Furthermore, the term "flat" for the stress buffering section means that it should be flat enough to alleviate stress concentration during welding. With the above configuration, because the stress buffering section is flat, stress concentration during welding is further alleviated, and the risk of cell cracking is further suppressed.

[0019] To solve the above problems, the solar cell module of this disclosure is characterized by including a string to which solar cells having any of the above characteristics are connected.

[0020] According to the above configuration, a solar cell module can be obtained that includes a string of solar cells connected in series, with a reduced risk of cell breakage.

[0021] The solar cells and solar modules related to this disclosure are highly reliable for use in the unique environment of outer space, which differs from that of Earth.

[0022] Figure 1 is a plan view of the light-receiving surface side of the solar cell according to this disclosure. Figure 2 is a plan view of the back side of the light-receiving surface of the solar cell according to Figure 1. Figure 3 is a plan view of the light-receiving surface side of the cell body. Figure 4 is an explanatory diagram of welding a bypass diode to the back side of the cell body. Figure 5 is a plan view of the light-receiving surface side of the cell body with the bypass diode welded to it. Figure 6 is an explanatory diagram of the main part of the cell body. Figure 7 is a cross-sectional view taken along line A-A in Figure 6. Figure 8 is a cross-sectional view taken along line B-B in Figure 6. Figure 9 is a schematic diagram of the configuration of the solar cell. Figure 10 is a front view of the string. Figure 11 is a back view of the string. Figure 12 is an explanatory diagram of the interconnector.

[0023] The embodiments of this disclosure will be described in detail below with reference to the drawings.

[0024] Figures 1 and 2 show a solar cell 1. This solar cell 1 is a multi-junction compound semiconductor solar cell. Multi-junction solar cells extend the usable wavelength range of sunlight and achieve high power generation efficiency by forming a multi-junction structure in which materials with different band gaps are stacked. In this embodiment, the solar cell 1 is a three-junction compound semiconductor solar cell.

[0025] The solar cell 1 comprises a cell body 10, a bypass diode 20 electrically connected to the cell body 10, an interconnector 21 attached to the bypass diode 20 and the cell body 10, an interconnector 30 attached to the cell body 10 and the bypass diode 20 for connecting to adjacent solar cells, and a cover glass 40 mounted to cover the light-receiving surfaces of the cell body 10 and the bypass diode 20. The cover glass 40 is provided for each combination of one cell body 10 and one bypass diode 20. Thus, the solar cell 1 has a CIC structure.

[0026] As shown in Figure 9, the cell body 10 is arranged such that the band gap decreases sequentially from the light-receiving surface side that receives sunlight, with the top cell 50, middle cell 60, and bottom cell 70 connected in series vertically. As shown in Figure 9, the cell body 10 has a semiconductor layer and electrodes formed on the semiconductor layer. The semiconductor layer is formed in the following order on a bottom cell 70 consisting of a p-type Ge layer and an n-type Ge layer: a buffer layer 19 consisting of an InGaP layer and an n-type InGaAs layer; a tunnel junction layer 18 consisting of a p-type GaAs layer and an n-type GaAs layer; a middle cell 60 consisting of a back field layer which is a p-type InGaP layer, a base layer which is a p-type InGaAs layer, an emitter layer which is an n-type InGaAs layer, and a window layer which is an n-type InGaP layer; a tunnel junction layer 17 consisting of a p-type AlGaAs layer and an n-type InGaP layer; a top cell 50 consisting of a back field layer which is a p-type AlInP layer, a base layer which is a p-type InGaP layer, an emitter layer which is an n-type InGaP layer, and a window layer which is an n-type AlInP layer; and a contact layer 15 consisting of an n-type GaAs layer. Then, a surface electrode 11 is formed on the contact layer 15 and a back electrode 14 is formed on the bottom cell 70. The surface electrode 11 and the back electrode 14 are silver electrodes. Furthermore, an anti-reflective coating (AR coating) 16 is formed on the top cell 50. Note that the materials and composition of the cell body 10 are merely examples and are not limited to these.

[0027] Sunlight incident on the light-receiving surface of solar cell 1 is absorbed sequentially by the top cell 50, middle cell 60, and bottom cell 70, starting with the shortest wavelength (highest energy) light. The carriers generated by this sunlight are separated at the junction of the emitter layer and the base layer, collected by the surface electrode 11, and extracted to the outside.

[0028] The cell body 10 is obtained by using Ge (germanium) of the bottom cell 70 as a substrate, thinly flowing GaAs (gallium arsenide) constituting the middle cell 60 in gaseous form onto it and crystallizing it, and then similarly crystallizing and stacking InGaP (indium gallium phosphide) constituting the top cell 50 on top of that to form the surface electrode 11 and the back electrode 14.

[0029] A contact layer 15 is provided between the top cell 50 and the surface electrode 11 to reduce current loss due to series resistance such as electrode contact resistance. A tunnel junction layer 17 is provided between the top cell 50 and the middle cell 60 to improve the connection between them using tunnel current. A tunnel junction layer 18 and a buffer layer 19 are provided between the middle cell 60 and the bottom cell 70.

[0030] The bypass diode 20 is provided to prevent malfunctions in the cell body 10. As shown in Figures 7 and 8, the bypass diode 20 has a thickness similar to that of the cell body 10. One end 21a of the interconnector 21 is connected to the bypass diode 20, and the other end 21b of the interconnector 21 is connected to the back electrode 14 of the cell body 10 (see Figure 2). Note that one end 21a and the other end 21b of the interconnector 21 are connected to the bypass diode 20 and the back electrode 14, respectively, by welding.

[0031] As shown in Figure 3, the light-receiving surface of the cell body 10 is provided with a surface electrode (grid line) 11, a surface electrode (busbar electrode) 12A, and a connecting pad 12B. The busbar electrode 12A and the connecting pad 12B are formed in the same way as the surface electrode 11. The busbar electrode 12A has a tapered shape, being thicker on the side of the connecting pad 12B and becoming thinner as it moves away from the connecting pad 12B. On the side connected to the connecting pad 12B, where the current is large, the busbar electrode 12A is thick, resulting in low resistance. On the other hand, on the tip side, where the current is small, the busbar electrode 12A is thin, which suppresses the decrease in power generation due to the shadow of the electrode.

[0032] The connection pad 12B is provided for welding one end of two interconnectors 30 to the light-receiving surface of the cell body 10, excluding one interconnector 30 whose one end is connected to the surface of the bypass diode 20. As will be described later, the other end of the interconnector 30 is welded to the back electrode 14 of the adjacent cell body 10.

[0033] As shown in Figures 3 and 4, a stress buffer portion 13 is further provided on the light-receiving surface of the cell body 10. Specifically, the stress buffer portion 13 is provided on the back surface of the back electrode 14 where the other end 21b of the interconnector 21 for connecting the bypass diode 20 is welded, i.e., at a predetermined location on the light-receiving surface. In a plan view, the area where the stress buffer portion 13 is provided and part or all of the area where the other end 21b is welded overlap.

[0034] As shown in Figure 12, the interconnector 21 is composed of a conductive strip. The strip is configured in an S-shape, and this S-shape allows for the reduction of stress between the welding points 21W corresponding to the welding points on the cell body 10 and the welding points 21W corresponding to the welding points on the bypass diode 20. However, the strip does not have to be S-shaped.

[0035] Furthermore, the strip is provided with multiple openings 21H along its curved longitudinal direction, which helps to alleviate the stress generated between the welded joint 21W on the cell body 10 side and the welded joint 21W on the bypass diode 20 side. However, the number of openings 21H is illustrative, and the openings 21H may not be provided at all.

[0036] The interconnector 12 has a bifurcated shape at one end 21a and the other end 21b, which are welded to the bypass diode 20 and the back electrode 14, respectively. Specifically, two points on the one end 21a are welded to the back surface of the bypass diode 20, and two points on the other end 21b are welded to the back electrode 14. The stress buffer portion 13 is provided in two locations corresponding to the other end 21b of the interconnector 21.

[0037] Because one end 21a and the other end 21b of the interconnector 12 are bifurcated, the stress of expansion and contraction in the width direction of the strip constituting the interconnector 21 caused by temperature changes during use can be distributed. However, the one end 21a and the other end 2 of the interconnector 12 are not limited to being bifurcated; they may be divided into three or more branches.

[0038] In this case, the welding points 21W may be spot welded to the bypass diode 20 or back electrode 14 at one or more locations in the width direction of each branch of the strip constituting the interconnector 21, or they may be welded to the bypass diode 20 or back electrode 14 over the entire width direction of each branch. The stress buffer portion 13 only needs to be provided at a position corresponding to at least the welding points 21W. In any case, the stress buffer portion 13 only needs to be provided at a position corresponding to at least the welding points 21W. Therefore, one stress buffer portion 13 may be large enough to span multiple welding points 21W.

[0039] Furthermore, one end 21a and the other end 21b of the interconnector 12 do not have to be branched. In this case, the welding points 21W may be spot welded to the bypass diode 20 or back electrode 14 at one or more locations in the width direction of the strip constituting the interconnector 21, or they may be welded to the bypass diode 20 or back electrode 14 over the entire width direction of the strip. In this case as well, the stress buffer portion 13 only needs to be provided at positions corresponding to at least the welding points 21W. Therefore, one stress buffer portion 13 may be large enough to span multiple welding points 21W.

[0040] The stress buffer portion 13 is formed when the surface electrodes 11 of the cell body 10 are formed. In this embodiment, the stress buffer portion 13 is formed simultaneously in the process of forming the surface electrodes (11, 12A) and the connecting pad 12B by vapor deposition. However, the stress buffer portion 13 may be formed in a process separate from the process of forming the surface electrodes (11, 12A). The stress buffer portion 13 is made of the same material as the surface electrodes 11. In this embodiment, the materials constituting the surface electrodes 11 and the stress buffer portion 13 include silver. Note that the stress buffer portion 13 may be made of a different material than the surface electrodes 11.

[0041] As shown in Figure 3, the stress buffer portion 13 is wider than the surface electrode 11. As shown in Figures 7 and 8, the stress buffer portion 13 is flat. Also, as shown in Figures 7 and 8, the height of the stress buffer portion 13 is the same as that of the surface electrode 11. As shown in Figure 3, the shape of the stress buffer portion 13 is rectangular. However, the shape of the stress buffer portion 13 is not limited to rectangular. Preferably, the stress buffer portion 13 is sized and shaped to cover the welding area 21W corresponding to the location where the other end 21b of the interconnector 21 for connecting the bypass diode 20 is welded on the back electrode 14.

[0042] As described above, a bypass diode 20 is connected to the cell body 10 via an interconnector 21, and as shown in Figures 5 and 6, an interconnector 30 is attached to the light-receiving side of the cell body 10 and the bypass diode 20. Furthermore, as shown in Figures 7 and 8, a cover glass 40 with an OCA (Optical Clear Adhesive) 41 pre-attached to it is bonded to the light-receiving side of the cell body 10 and the bypass diode 20. The cover glass 40 is shaped to cover the cell body 10 and the bypass diode 20 in a plan view. The OCA 41 is also shaped to cover the cell body 10 and the bypass diode 20 in a plan view. The OCA 41 is configured to have a shape corresponding to the cover glass 40. In this embodiment, the OCA 41 is configured to have the same shape as the cover glass 40.

[0043] As shown in Figures 7 and 8, the cover glass 40 is larger than the OCA 41. In a plan view, the edge of the OCA 41 is located outside the edges of the cell body 10 and bypass diode 20, and the edge of the cover glass 40 is located outside the OCA 41. Thus, in a plan view, the edge of the cover glass 40 surrounds one pair of cell body 10 and bypass diode 20. Similarly, in a plan view, the edge of the OCA 41 surrounds one pair of cell body 10 and bypass diode 20. Furthermore, in a plan view, the edge of the cover glass 40 surrounds the OCA 41.

[0044] The OCA 41 is slightly larger than the cell body 10 and the bypass diode 20, and the cover glass 40 is designed to be slightly larger than the OCA 41. By designing in this way, even if the position is displaced due to assembly tolerance, the cell body 10 and the bypass diode 20 can be surely covered by the cover glass 40 and the OCA 41.

[0045] And, as shown in FIG. 8, a curvature portion 31 is formed in the interconnector 30, and the solar cell 1 is obtained.

[0046] The interconnector 30 is used when connecting adjacent solar cells 1. That is, as shown in FIGS. 10 and 11, the interconnector 30 of a certain solar cell 1 is welded to the back electrode 14 of the adjacent solar cell 1, and the adjacent solar cells 1 are connected to form a string, and a plurality of such strings are included to obtain a solar cell module. In addition, since the curvature portion 31 is provided in the interconnector 30, there is an advantage that even if the distance between adjacent solar cells 1 changes, it can be absorbed, but the curvature portion 31 may not be provided in the interconnector 30.

[0047] Note that the cover glass 40 may be made of quartz that does not discolor due to radiation or glass to which cerium (Ce) is added to prevent discoloration. The OCA 41 that adheres the cover glass 40 is made of a silicone resin that hardly emits outgas even under the high-temperature vacuum of the space environment.

[0048] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

[0049] This application claims priority based on Japanese Patent Application No. 2024-204548 filed in Japan on November 25, 2024. By referring to this, all of its contents are incorporated into this application.

[0050] This disclosure can be applied to applications aimed at suppressing the risk of cell cracking.

[0051] 1: Solar cell 10: Cell body 11: Surface electrode 12A: Busbar electrode 12B: Connection pad 13: Stress buffer section 14: Back electrode 15: Contact layer 17: Tunnel junction layer 18: Tunnel junction layer 19: Buffer layer 20: Bypass diode 21: Interconnector 21H: Opening 21W: Welding point 21a: One end 21b: Other end 30: Interconnector 31: Curved section 40: Cover glass 50: Top cell 60: Middle cell 70: Bottom cell

Claims

1. A solar cell comprising a cell body, a bypass diode, an interconnector for electrically connecting the cell body and the bypass diode, and a cover glass covering the light-receiving surfaces of the cell body and the bypass diode, wherein one end of the interconnector is welded to the bypass diode, and the other end of the interconnector is welded to a back electrode on the back surface of the light-receiving surface, and the cell body is provided with a stress buffer portion on the back surface of the light-receiving surface at a location corresponding to the welding location where the other end of the interconnector is welded, and the stress buffer portion has the same height as the surface electrode provided on the light-receiving surface.

2. The solar cell according to claim 1, characterized in that the stress buffer portion is molded from the same material as the surface electrode.

3. The solar cell according to claim 2, characterized in that the stress buffer portion is integrally molded with the surface electrode.

4. The solar cell according to claim 1, characterized in that the stress buffer portion is sized to cover the welded area in a plan view.

5. The solar cell according to claim 4, characterized in that the stress buffer portion is flattened.

6. A solar cell module characterized by including a string in which a plurality of solar cells according to any one of claims 1 to 5 are connected.

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