Solar cell, battery module, and photovoltaic system

Abstract

The present application relates to the technical field of solar cells, and provides a solar cell, a battery module, and a photovoltaic system. The solar cell comprises a silicon wafer, first doped layers, and second doped layers; leakage current composite contact structures are formed by means of composite contact between the second doped layers and the first doped layers at preset positions; when a reverse voltage applied to two ends of the solar cell is 17 V or less than 17 V, the leakage current per unit length of each leakage current composite contact structure is greater than Impp / S / N, wherein Impp is the maximum power point current of the solar cell, S is the area of the solar cell, N is the length of the leakage current composite contact structure within the unit area in the solar cell, and N is smaller than or equal to 4.32 cm / cm2. The risk of hot spots can be reduced while it is ensured that no significant conversion efficiency loss of the solar cell is caused; in addition, the defect management and control requirements for solar cells can be lowered or even eliminated, and the solar cell manufacturing capacity is improved.

Description

Solar cells, battery modules and photovoltaic systems Technical Field

[0001] The present disclosure relates to the technical field of solar cells, and in particular to a solar cell sheet, a solar cell assembly and a photovoltaic system. Background Art

[0002] In related technologies, photovoltaic cell modules are usually composed of a cell array consisting of multiple cells. In order to effectively control the risk of hot spots, solar cells usually adopt a low leakage characteristic + bypass diode design to reduce the leakage current of the cell, thereby controlling the heating power of the leakage point.

[0003] However, in order to mitigate the risk of hot spot failure, such a technical solution requires that the leakage current of the cell be kept to a low value, which places high demands on the control of leakage current. However, this is a difficult problem for the photovoltaic industry's manufacturing capabilities. During the manufacturing process of solar cells, any defect introduced may cause the leakage current to exceed the control value, resulting in poor resistance to the risk of hot spots and low manufacturing capabilities.

[0004] Therefore, how to develop a new anti-hot spot technology with higher manufacturing capability, thereby improving the ability of battery cells to resist the risk of hot spots, has become a technical issue that technicians are studying.

[0005] Summary of the Invention

[0006] The present disclosure provides a solar cell, a cell assembly and a photovoltaic system, aiming to solve the technical problem of how to improve the manufacturing capacity of solar cells and enhance the ability of cells to resist hot spot risks.

[0007] The present disclosure is implemented as follows: a solar cell according to an embodiment of the present disclosure comprises:

[0008] silicon wafers;

[0009] a first doping layer stacked on the silicon wafer; and

[0010] a second doped layer stacked on the silicon wafer, the second doped layer having a polarity opposite to that of the first doped layer, the second doped layer being in composite contact with the first doped layer at a preset position to form a leakage composite contact structure, wherein when a reverse voltage applied across the solar cell is 17V or less than 17V, a leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N, where Impp is the maximum power point current of the solar cell, S is the area of ​​the solar cell, N is the length per unit area of ​​the leakage composite contact structure in the solar cell, and N is less than or equal to 4.32 cm / cm 2 .

[0011] Furthermore, N is less than or equal to 3.45 cm / cm 2 .

[0012] Furthermore, N is less than or equal to 2.59 cm / cm 2 .

[0013] Furthermore, when the reverse voltage applied across the solar cell is 9V, the leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N.

[0014] Furthermore, when the reverse voltage applied across the solar cell is 6V, the leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N.

[0015] Furthermore, the solar cell is a double-sided solar cell, the silicon wafer has a first surface and a second surface relative to each other, the first doped layer is stacked on the first surface, the second doped layer is stacked on the second surface, and the second doped layer and the first doped layer form a composite contact at a preset position on the edge of the silicon wafer, thereby forming the leakage composite contact structure.

[0016] Furthermore, the solar cell is a back-contact solar cell, the silicon wafer has a relative front side and back side, a plurality of the first doped layers and a plurality of the second doped layers are stacked on the back side, the plurality of the first doped layers and the plurality of the second doped layers are alternately arranged in sequence, and a spacing region is provided between the first doped layers and the second doped layers. At a preset position of the spacing region, the first doped layers and the second doped layers are in composite contact to form the leakage composite contact structure.

[0017] The present disclosure also provides a battery assembly, which includes any of the solar cell sheets described above.

[0018] Furthermore, the battery assembly includes a plurality of battery strings, the battery strings include a plurality of solar cells connected in series, and bypass diodes are connected in parallel at both ends of the battery strings;

[0019] The reverse bias voltage at both ends of the solar cell that is blocked <D*Voc*(M-1)+L:

[0020] The reverse bias voltage is the voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current; Voc is the open circuit voltage of the solar cell, M is the number of solar cells in the battery string connected in parallel with the bypass diode, D is a constant less than 1, and L is the startup voltage of the bypass diode.

[0021] Furthermore, the battery assembly includes a plurality of battery strings, and the battery strings include a plurality of solar cells connected in series;

[0022] The two ends of the solar cell that is blocked are reverse biased <D*Voc*(P-1);

[0023] The reverse bias voltage is the voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current; Voc is the open circuit voltage of the solar cell, P is the number of solar cells connected in series with the blocked solar cell, and D is a constant less than 1.

[0024] Furthermore, the value range of D is 0.1-0.5.

[0025] Furthermore, when the solar cell is shielded, the heating power of a single leakage composite contact structure in the solar cell is less than 8.85W.

[0026] Furthermore, the number S of the leakage composite contact structures in the solar cell satisfies the following condition: S>(Impp*V Impp ) / 8.85W;

[0027] Wherein, Impp is the maximum power point current of the solar cell, V Impp is the reverse bias voltage across the shaded solar cell when the solar cell is shaded and the leakage current of the shaded solar cell reaches the maximum power point current, and S is a positive integer.

[0028] Furthermore, when the solar cell is blocked, in any 4cm*4cm square area of ​​the solar cell, the leakage current I 漏 The following conditions are met: I 漏 <8.85W / V Impp ;

[0029] Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within a 4cm*4cm square, VImpp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

[0030] Furthermore, when the solar cell is blocked, in any 4cm*4cm square area of ​​the solar cell, the leakage current I 漏 The following conditions are met: I 漏 <4.54W / V Impp ;

[0031] Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within the square range, V Impp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

[0032] Furthermore, when the solar cell is blocked, in any 4cm*4cm square area of ​​the solar cell, the leakage current I 漏 The following conditions are met: I 漏 <2.26W / V Impp ;

[0033] Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within the square range, V Impp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

[0034] Furthermore, in the solar cell, the distance between two adjacent leakage composite contact structures is greater than or equal to 4 cm.

[0035] The present disclosure also provides a photovoltaic system, which includes the above-mentioned battery assembly.

[0036] In the solar cell, battery module, and photovoltaic system of the embodiments of the present disclosure, by introducing a leakage composite contact structure formed by two doping layers of different polarities at a preset position and rationally designing the leakage current per unit length of the leakage composite contact structure, the leakage capacity of the solar cell can be improved, so that the leakage composite contact structure has a high reverse leakage characteristic. Thus, with the improvement of the leakage capacity, at the module end, when the solar cell is blocked, when the leakage current of the solar cell reaches the maximum power point current, the voltage across the blocked solar cell will decrease, and the heat generation power of the solar cell will decrease, thereby achieving the purpose of controlling the risk of hot spots. At the same time, the technical solution of the present disclosure, by deliberately introducing the leakage composite contact structure at a preset position, has a protective effect against hot spots caused by defects in the silicon wafer itself, which can reduce or even eliminate the requirements for defect control, while reducing the risk of hot spots caused by defects and improving the manufacturing capacity of the solar cell. Furthermore, in the present disclosure, by rationally designing the length of the leakage composite contact structure per unit area, it is possible to avoid excessive efficiency loss, thereby ensuring the conversion efficiency of the solar cell.

[0037] Additional aspects and advantages of the present disclosure will be given in part in the description that follows and, in part, will be obvious from the description that follows, or will be learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is a schematic diagram of a module of a photovoltaic system provided by an embodiment of the present disclosure;

[0039] FIG2 is a schematic diagram of a module of a battery assembly provided by an embodiment of the present disclosure;

[0040] FIG3 is a schematic diagram of a planar structure of a back-contact solar cell provided by an embodiment of the present disclosure;

[0041] FIG4 is a schematic cross-sectional view of the back contact solar cell along line IV-IV in FIG3 ;

[0042] FIG5 is another schematic cross-sectional view of the back contact solar cell along line IV-IV in FIG3 ;

[0043] FIG6 is another schematic cross-sectional view of the back contact solar cell along line IV-IV in FIG3 ;

[0044] FIG7 is a schematic diagram of the planar structure of a double-sided solar cell provided in an embodiment of the present disclosure;

[0045] FIG8 is a schematic cross-sectional view of the bifacial solar cell along line VIII-VIII in FIG7 ;

[0046] FIG9 is another cross-sectional schematic diagram of the bifacial solar cell along line VIII-VIII in FIG7 ;

[0047] FIG10 is a graph showing the relationship between the hot spot temperature of a solar cell and the heating power it carries;

[0048] FIG. 11 is an equivalent circuit diagram of a battery pack in the related art.

[0049] Explanation of main component symbols: 1000, photovoltaic system; 200, battery assembly; 100, solar cell; 101, preset position; 10, silicon wafer; 11, first surface; 12, second surface; 13, front surface; 14, back surface; 20, first doped layer; 30, second doped layer; 40, leakage composite contact structure; 50, spacer; 60, first dielectric layer; 70, second dielectric layer; 80, third dielectric layer; 90, fourth dielectric layer; 110, fifth dielectric layer; 120, sixth dielectric layer. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present disclosure and are not to be construed as limiting the present disclosure. In addition, it should be understood that the specific embodiments described herein are only used to explain the present disclosure and are not intended to limit the present disclosure.

[0051] In the description of the present disclosure, it should be understood that the terms "length", "width", "up", "down", "horizontal", "longitudinal", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present disclosure.

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the described features. Throughout the present disclosure, "plurality" means two or more, unless otherwise specifically defined.

[0053] In the description of this disclosure, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections, electrical connections, or mutual communication; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this disclosure based on specific circumstances.

[0054] In the present disclosure, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Moreover, a first feature being "above," "above," and "above" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature includes the first feature being directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0055] The disclosure below provides many different embodiments or examples for realizing different structures of the present disclosure. In order to simplify the disclosure of the present disclosure, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present disclosure. In addition, the present disclosure may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present disclosure provides examples of various specific processes and materials, but those of ordinary skill in the art will recognize the application of other processes and / or the use scenarios of other materials.

[0056] Referring to Figures 1 and 2, the photovoltaic system 1000 in the embodiment of the present disclosure may include the battery assembly 200 in the embodiment of the present disclosure, and the battery assembly 200 in the embodiment of the present disclosure may include multiple solar cells 100 in the embodiment of the present disclosure. In the embodiment of the present disclosure, the multiple solar cells 100 in the battery assembly 200 can be connected in series to form multiple battery strings. The battery strings can be connected in series, in parallel, or in a combination of series and parallel to achieve current bus output. For example, the connection between the battery cells can be achieved by welding welding strips, and the connection between the battery strings can be achieved by bus bars. In some embodiments, the battery strings can form a battery array, which is then packaged together by a front plate, a front adhesive film, a rear adhesive film, and a back plate to form a battery assembly 200.

[0057] Referring to Figures 3 to 8, the solar cell 100 in the embodiment of the present disclosure may include a silicon wafer 10, a first doping layer 20, and a second doping layer 30. The silicon wafer 10 may be a P-type silicon wafer or an N-type silicon wafer, and is not specifically limited here. The first doping layer 20 is stacked on the silicon wafer 10, and the second doping layer 30 is also stacked on the silicon wafer 10, and the second doping layer 30 has an opposite polarity to the first doping layer 20. Specifically, in the embodiment of the present disclosure, the first doping layer 20 may be an N-type doping layer, and the second doping layer 30 may be a P-type doping layer, or the first doping layer 20 may be a P-type doping layer, and the second doping layer 30 may be a P-type doping layer, and is not specifically limited here, as long as the polarities of the two are opposite.

[0058] As shown in FIG3 and FIG7 , in the present disclosure, the second doped layer 30 of the solar cell 100 is in composite contact with the first doped layer 20 at a predetermined position 101 to form a leakage composite contact structure 40. When the reverse voltage applied across the solar cell 100 is 17 V or less, the leakage current per unit length of the leakage composite contact structure 40 is greater than Impp / S / N.

[0059] Wherein, Impp is the maximum power point current of the solar cell 100, S is the area of ​​the solar cell 100 (i.e., the area of ​​the light-receiving surface and the backlight surface of the silicon wafer 10), and N is the length of the leakage composite contact structure 40 per unit area in the solar cell 100, and N is less than or equal to 4.32 cm / cm 2 .

[0060] It should be noted that the maximum power point current of the solar cell 100 is: the current when the cell is at maximum power under standard test conditions, wherein the standard test conditions are common and well-known standard test technologies in the field of solar cell technology and are not described in detail here.

[0061] Referring to Figures 3 and 4 , in some embodiments, a solar cell 100 may be a back-contact solar cell. In this case, the silicon wafer 10 may include a front side 13 and a back side 14 facing each other. A plurality of first doped layers 20 and a plurality of second doped layers 30 may be stacked on the back side 14. The plurality of first doped layers 20 and the plurality of second doped layers 30 are alternately arranged in sequence, with a spacer 50 between the first doped layers 20 and the second doped layers 30. At a predetermined position 101 of the spacer 50, the first doped layers 20 and the second doped layers 30 are in composite contact to form a leaky composite contact structure 40. Specifically, as shown in Figure 3 , in a back-contact solar cell, the plurality of first doped layers 20 and the plurality of second doped layers 30 may be alternately arranged in sequence along a lateral direction and extend along a longitudinal direction, with a spacer between adjacent first doped layers 20 and second doped layers 30.

[0062] That is, as shown in FIG4 , at the preset position 101, a portion of the first doped layer 20 may extend to the spacer region 50, thereby forming a composite contact with the second doped layer 30, thereby forming a leakage composite contact structure 40. It will be understood that FIG4 merely illustrates one embodiment, and in other embodiments, at the preset position 101, a portion of the second doped layer 30 may extend to the spacer region 50, thereby forming a composite contact with the first doped layer 20, thereby forming a leakage composite contact structure 40. Furthermore, in some embodiments, at the preset position 101, both the first doped layer 20 and the second doped layer 30 may extend along the spacer region 50, thereby forming a composite contact within the spacer region 50, thereby forming a leakage composite contact structure 40. The specific details are not limited here.

[0063] As shown in FIG5 , in some embodiments, in a back-contact solar cell, the back surface 14 may have a plurality of spaced grooves. The first doped layer 20 and the second doped layer 30 may be stacked on a surface without grooves, and the grooves correspond to the aforementioned spacer 50. The first doped layer 20 and the second doped layer 30 are located on either side of the grooves, and the first doped layer 20 and the second doped layer 30 are isolated by the grooves. Of course, it is understood that in some embodiments, the width of the grooves may also be set wider. In such a case, the first doped layer 20 may be disposed on a surface without grooves, and the second doped layer 30 may be disposed within the grooves. In this way, the groove portion between the second doped layer 30 and the first doped layer 20 is the spacer 50 herein.

[0064] It should be noted that, in the present disclosure, “the first doped layer 20 and the second doped layer 30 are in composite contact to form a leakage composite contact structure 40” refers to the fact that at the preset position 101, there is no insulation between the first doped layer 20 and the second doped layer 30, and the two are composited at the preset position 101. It can be that the two are in direct contact to form a composite contact, or it can be that the composite contact is achieved through a dielectric layer to form a leakage point (i.e., the leakage composite contact structure 40), preferably, the composite contact is achieved through a dielectric layer. For example, as shown in FIG6 , in some embodiments, the first doped layer 20 and the second doped layer 30 form a composite contact by having a first dielectric layer 60 therebetween. The first dielectric layer 60 can be a film layer such as a tunneling oxide layer, such as a silicon oxide film layer or the like having a passivation function. At least part of the first dielectric layer 60 has a tunneling function to achieve composite contact between the first doped layer 20 and the second doped layer 30. In this way, the first dielectric layer 60 can achieve composite contact between the two while passivating the surfaces in contact with each other.

[0065] Furthermore, referring to Figures 4-6, in some embodiments, the back-contact solar cell may further include a second dielectric layer 70 stacked between the first doped layer 20 and the back surface 14 of the silicon wafer 10, and a third dielectric layer 80 stacked between the second doped layer 30 and the back surface 14 of the silicon wafer 10. Both the second dielectric layer 70 and the third dielectric layer 80 may be tunneling layers, such as silicon oxide tunneling layers or other films with passivation and tunneling functions. The specific type of these layers can be selected based on actual conditions and is not specifically limited herein. In other words, in the entire solar cell 100, wherever there is a location for the first doped layer 20, there is a second dielectric layer 70, and wherever there is a location for the second doped layer 30, there is a third dielectric layer 80. That is, if the first doped layer 20 extends to the spacer region 50, then the portion of the first doped layer 20 extending to the spacer region 50 also has a second dielectric layer 70 (not shown in the figure) underneath; if the second doped layer 30 extends to the spacer region 50, then the portion of the second doped layer 30 extending to the spacer region 50 also has a third dielectric layer 80 (not shown in the figure) underneath.

[0066] As shown in FIG3 , it is readily understood that in a back-contact solar cell, the length L of the leaky composite contact structure 40 refers to the length of the leaky composite contact structure 40 in the longitudinal direction of the spacer 50 (i.e., the longitudinal direction in FIG3 , i.e., the direction in which the first doped layer 20 and the second doped layer 30 extend). This refers to the length of the leaky composite contact structure 40 in the longitudinal direction in FIG3 , i.e., the length of the surface where the first doped layer 20 and the second doped layer 30 make composite contact. The "unit length of the leaky composite contact structure 40" refers to the length of the leaky composite contact structure per unit area, i.e., the ratio of the total length of all leaky composite contact structures 40 to the area of ​​the front side 13 or back side 14 of the silicon wafer 10 (i.e., the light-receiving area of ​​the solar cell 100). The "area of ​​the solar cell 100" refers to the orthographic projection area of ​​the solar cell 100 in the thickness direction, i.e., the area of ​​the light-receiving and back-light-receiving surfaces of the solar cell 100.

[0067] 7 and 8 , in some embodiments, the solar cell 100 may also be a bifacial solar cell, such as a PERC solar cell, a Topcon solar cell, or the like.

[0068] As shown in Figure 8, in such a case, the silicon wafer 10 has a first surface 11 and a second surface 12 relative to each other, the first doped layer 20 is stacked on the first surface 11, and the second doped layer 30 is stacked on the second surface 12. The second doped layer 30 forms a composite contact with the first doped layer 20 at a preset position 101 at the edge of the silicon wafer 10, thereby forming a leakage composite contact structure 40.

[0069] Specifically, as shown in FIG8 , in a bifacial solar cell, the first doping layer 20 and the second doping layer 30 are stacked on two opposite surfaces of the silicon wafer 10 , respectively. The first doping layer 20 and the second doping layer 30 can form a composite contact at a preset position 101 at the edge of the silicon wafer 10 , thereby forming a leakage composite contact structure 40 .

[0070] As shown in FIG8 , in such an embodiment, the first doped layer 20 may be stacked on the first surface 11 while, at a preset position 101 at the edge of the silicon wafer 10 , the first doped layer 20 extends along the edge of the silicon wafer 10 toward the second surface 12 , thereby forming a composite contact with the second doped layer 30 at the edge of the second surface 12 , thereby forming a leakage composite contact structure 40 .

[0071] Of course, it is understood that in some embodiments, the second doped layer 30 may be stacked on the second surface 12, and at a predetermined position 101 at the edge of the silicon wafer 10, the second doped layer 30 may extend along the edge of the silicon wafer 10 toward the first surface 11, thereby forming a composite contact with the first doped layer 20 at the edge of the first surface 11. Furthermore, in other embodiments, the first doped layer 20 and the second doped layer 30 may extend relative to each other at the predetermined position 101 at the edge of the silicon wafer 10, thereby forming a composite contact on the side surface of the silicon wafer 10 (i.e., the plane connecting the first surface 11 and the second surface 12). This is not limited to the specific embodiment, as long as the two layers can form a composite contact in a portion of the edge of the silicon wafer 10.

[0072] Similarly, as shown in FIG9 , in a bifacial solar cell, the first doped layer 20 and the second doped layer 30 may form a composite contact by direct contact between the two or by providing a fourth dielectric layer 90 therebetween. The material and properties of the fourth dielectric layer 90 may be the same as those of the first dielectric layer 60 described above, and are not further described here.

[0073] It should be noted that the bifacial solar cells shown in Figures 8 and 9 are bifacial Topcon solar cells. In such cells, a fifth dielectric layer 110 is provided between the first doped layer 20 and the first surface 11, and a sixth dielectric layer 120 is provided between the second doped layer 30 and the second surface 12. Both the fifth dielectric layer 110 and the sixth dielectric layer 120 can be tunneling layers, such as silicon oxide tunneling layers or other film layers having passivation and tunneling functions. The specific type can be selected according to actual conditions and is not specifically limited here.

[0074] Similarly, as shown in FIG7 , it is not difficult to understand that, in a bifacial solar cell, the length L of the leakage composite contact structure 40 refers to the length of the orthographic projection of the leakage composite contact structure 40 on the edge of the silicon wafer 10, that is, the length of the leakage composite contact structure 40 in the longitudinal direction or the transverse direction in FIG7 . When the leakage composite contact structure 40 is located at the left and right edges of the silicon wafer 10, its length L is the length in the longitudinal direction. When the leakage composite contact structure 40 is located at the upper and lower edges of the silicon wafer, its length L is the length in the transverse direction, that is, the length of the surface where the first doped layer 20 and the second doped layer 30 are in composite contact in the longitudinal direction or the transverse direction.

[0075] The "unit length of the leakage composite contact structure 40" refers to the length of the leakage composite contact structure per unit area, that is, the ratio of the total length of all leakage composite contact structures 40 to the area of ​​the first surface 11 or the second surface 12 of the silicon wafer 10 (i.e., the light-receiving area of ​​the solar cell 100). It will be understood that the first surface 11 and the second surface 12 mentioned here are actually equivalent to the front surface 13 and the back surface 14 mentioned above.

[0076] In summary, in the solar cell 100, the battery assembly 200, and the photovoltaic system 1000 in the embodiments of the present disclosure, the first doped layer 20 and the second doped layer 30 in the solar cell 100 are in composite contact at a preset position 101 to form a leakage composite contact structure 40. When the reverse voltage applied across the solar cell 100 is 17 V or less than 17 V, the leakage current per unit length of the leakage composite contact structure 40 is greater than Impp / S / N, where Impp is the maximum power point current of the solar cell 100, S is the area of ​​the solar cell 100, and N is the length per unit area of ​​the leakage composite contact structure 40 in the solar cell 100, and N is less than or equal to 4.32 cm / cm 2 .

[0077] Thus, by introducing a leakage composite contact structure 40 formed by two doped layers of different polarities at a predetermined position 101 and rationally designing the leakage current per unit length of the leakage composite contact structure 40, the leakage capability of the solar cell 100 can be improved, allowing the leakage composite contact structure 40 to exhibit high reverse leakage characteristics. Thus, with the improvement in leakage capability, at the module end, when a solar cell 100 is shaded, when the leakage current of the solar cell 100 reaches the maximum power point (Impp), the voltage across the shaded solar cell 100 will decrease (the voltage will be less than the sum of the voltages of other unshaded solar cells connected in series with the solar cell), reducing the heat generation power of the solar cell 100, thereby achieving the purpose of controlling the risk of hot spots. At the same time, the technical solution of the present disclosure, by intentionally introducing a leakage composite contact structure 40 at a preset position 101, provides protection against hot spots caused by defects in the silicon wafer 10 itself (i.e., it can reduce the heat generated by the defects), thereby reducing or even eliminating the need for defect management. This reduces the risk of hot spots caused by defects while improving the manufacturing capacity of the solar cell 100. Furthermore, in the present disclosure, by rationally designing the length of the leakage composite contact structure 40 per unit area, it is possible to avoid excessive efficiency losses, thereby ensuring the conversion efficiency of the solar cell 100.

[0078] That is to say, by adopting the technical solution disclosed in the present invention, through the reasonable design of the leakage current per unit length of the leakage composite contact structure 40 and the length of the leakage composite contact structure 40 per unit area, the relationship between conversion efficiency and control of hot spot risk can be balanced. It can reduce the hot spot risk while ensuring that the conversion efficiency of the solar cell 100 is not excessively lost. At the same time, it can also reduce or even eliminate the defect control requirements of the solar cell 100, thereby improving the manufacturing capacity of the solar cell 100.

[0079] Furthermore, in the present disclosure, by introducing the leaky composite contact structure 40 at the predetermined position 101, it functions as a bypass diode in the battery string. Therefore, in some embodiments, the bypass diode can be omitted in the battery assembly 200 to reduce costs. Of course, in some embodiments, a bypass diode can also be provided in the battery assembly 200, and this is not limited to the specific embodiment.

[0080] It should be noted that in the embodiments of the present disclosure, "preset position 101" refers to the location where the first doped layer 20 and the second doped layer 30 contact to form a composite contact. For example, in a back-contact solar cell, the preset position 101 refers to a portion or the entire region of the spacer 50, preferably a portion thereof. A single spacer 50 may have one or more preset positions 101. In a bifacial solar cell, the preset position 101 refers to a portion or the entire region of the edge of the silicon wafer 10, preferably a portion thereof. Each edge of the silicon wafer 10 may have one or more preset positions 101, without limitation herein.

[0081] It is understandable that, in the solar cell 100 , there may be a plurality of preset positions 101 , which may be evenly distributed or unevenly distributed, and there is no specific limitation here.

[0082] The following describes the specific background of the present disclosure and the specific principles of the technical solutions of the present disclosure.

[0083] In the field of solar cell technology, past experience has generally used a low leakage solution + bypass diode approach to control hot spots. Bypass diodes are used to limit the voltage across the battery to a certain range, and then the battery leakage current is reduced by optimizing defects in the silicon wafer, thereby controlling the heating power of the leakage point caused by the defects. However, this method is difficult to control the leakage of the battery cell and is difficult to achieve.

[0084] Specifically, with the current packaging materials and technologies for crystalline silicon modules, when the temperature of the hot spot is greater than 160°C, the packaging material begins to decompose and carbonize, resulting in appearance failure and fire risk.

[0085] As can be seen from Figure 10, Figure 10 shows the relationship between the hot spot temperature and the heating power it carries, with the horizontal axis being the heating power and the vertical axis being the hot spot temperature. The black curve represents a situation where the spacing between leakage points is large, and the blue curve represents a situation where the spacing between leakage points is small. In the prior art, in order to meet the hot spot requirements, the hot spots are usually caused by defective points, which are often caused by single-point leakage. The hot spot efficiency is large, and the spacing between leakage points is large, which can be referred to the black curve. As can be seen from Figure 10, in order to meet the hot spot requirements to avoid decomposition and carbonization of the packaging material and affect the fire, the minimum requirement for the heating power of a single point is: the heating power must be at least less than 8.85W.

[0086] Further, please refer to Figure 11, which shows the equivalent circuit diagram of a battery assembly using a low leakage solution in the prior art. Under the most advanced production capacity of high-efficiency batteries such as IBC, TOPCon, and HJT, the open circuit voltage is usually between 0.73-0.755V, with 0.74V as a representative, and the short-circuit current density is between 38-43mA / cm 2 , take 42mA / cm 2 As a representative, the Vmpp and Jmpp of the battery at the component end are respectively 0.634V and 39.5mA / cm2. The battery size is 18.2cm*9.1cm, and the format is 72. The short-circuit current and Impp current (maximum power point current) are: 6.95A and 6.54A.

[0087] As shown in Figure 11, when a single cell (the shaded area in the lower left corner of Figure 11) is blocked, the voltage across the cell rises to its highest value because the blocked cell is a low reverse leakage solution. Specifically, in this case, in Figure 11, I1 = Isc = 6.95A. Since the cells are all low leakage solutions, the current passing through them rises to a maximum value of Isc, where Isc is the short-circuit current.

[0088] When there is a defect between the P / N junctions and leakage is introduced, then:

[0089] I3=I4=I5=I6=6.54A, I7=6.54A*2-6.95A-3A=3.13A, I8=I9=0A;

[0090] Assuming the bypass diode has a startup voltage of approximately 1V, V4-V3 is approximately -1V; the reverse bias voltage across the obscured cell is:

[0091] V6-V5=-1V-(0.74V*(24-1)=-18V;

[0092] Among them, V3-V2=V2-V1=15.2V;

[0093] If the reverse bias voltage is 18V, the leakage current at this leakage point is 3A. When the defect introduces leakage, the heat generation power P = 18V * 3A = 54W, which is much greater than 8.85W. This shows that traditional low leakage solutions have a significant risk of hot spot failure and fire.

[0094] From this, we can see that in traditional low-leakage solutions, the hot spot heating power P = the carried reverse bias voltage * the leakage current under the carried reverse bias voltage; where the carried reverse bias voltage = the battery open-circuit voltage * (the number of batteries controlled by a single bypass diode - 1) + the startup voltage of the bypass diode.

[0095] In the traditional technical solution, for a 72-panel component, the number of cells controlled by a single bypass diode is 24 pcs. It can be seen that for different formats and types of components, taking the starting voltage of the bypass diode as 1V as an example, it can be seen through experimental calculations that when there are defects in the silicon wafer and leakage points are introduced, in order to meet the hot spot temperature of <160°C, it is necessary to ensure that the leakage current under the reverse voltage carried by the battery is <8.85W / (battery open circuit voltage*(number of cells controlled by a single bypass diode-1)+1V), thereby obtaining the following Table 1, which shows the electrical performance parameters of PERC, Topcon, HJT and BC components and the size of the leakage current that needs to be controlled. The carrying voltage in the table is the reverse bias voltage at both ends of the battery cell when it is blocked.

[0096] Table 1

[0097] As shown in Table 1 above, taking Topcon solar cells as an example, in a 72-panel module, the leakage current needs to be reduced to 0.52A at a reverse bias of -17.8V to effectively curb the risk of hot spot failure. Even for a 54-panel module, the leakage current needs to be reduced to 0.66A at a reverse bias of -13.4V. This is a difficult problem to overcome for the current photovoltaic industry's manufacturing capabilities. Any defect introduced during the cell production process will cause the leakage current to exceed the control value.

[0098] At present, in order to ensure the yield rate so that the manufactured products are cost-competitive, a -12V bias is usually used to control the leakage current, where the leakage current is controlled to <1A or <0.5A. However, even if the leakage current is controlled to a certain extent during the production process, it still has a high risk of hot spots, because the reverse leakage current is not linearly related to the reverse bias voltage. When the reverse bias voltage is 18V, the leakage current is more than 4 times that of 12V. In other words, if the reverse bias voltage at both ends of the blocked cell at the component end is 18V, the leakage current will reach 2A. At this time, the heat generation power is ~36W, which is more than 4 times the control requirement of 160℃. However, if the bias voltage at the component end is directly used to control the leakage current of the cell, the quality requirements of the cell are very high, resulting in a low yield response and poor manufacturing capabilities.

[0099] It can be seen from this that in the existing technology, it is difficult to adopt a low leakage solution and control the leakage current. Its yield is low, which is a difficult problem to overcome for the current manufacturing capabilities of the photovoltaic industry.

[0100] Based on this, the inventors of the present disclosure have discovered through research that, in a solar cell 100, if the solar cell 100 has a high reverse leakage characteristic (improved leakage capability), then when the solar cell 100 is shaded, only a relatively small reverse voltage is required to achieve a relatively large reverse leakage current. Specifically, for the solar cell 100, when the battery is shaded, as the reverse leakage capability of the battery increases, the reverse leakage current increases, the voltage across the battery remains unchanged, and the heat generation power increases. When the reverse leakage current increases to the maximum current value (Impp), the heat generation power also increases to the power limit.

[0101] However, as the reverse leakage capacity of the battery increases, the reverse leakage current remains unchanged at the maximum current value, but the voltage across the battery decreases compared to batteries with lower leakage capacity, which reduces the heat generation power compared to batteries with worse reverse leakage capacity. That is, as the reverse leakage capacity of the battery becomes stronger, the reverse leakage current increases, and the heat generation power reaches a maximum value. When the leakage capacity is further improved, the heat generation power will decrease, thereby curbing the hot spot effect. In other words, by improving the leakage capacity of the solar cell to give it a high reverse leakage characteristic, when the cell is blocked, only a small reverse voltage is required to make the reverse leakage current of the cell reach the maximum value (i.e., the Impp point of the solar cell 100). From another perspective, as the leakage capacity increases, when the reverse leakage current reaches the maximum value, the voltage across the blocked battery will become smaller, so that the heat generation power will be reduced instead.

[0102] Moreover, as the leakage capacity of the battery increases, the heat generation power has an extreme value. When the reverse leakage current increases to the maximum current value, the heat generation power will decrease as the leakage capacity increases. When the leakage current reaches the maximum power point current of the solar cell 100, the voltage across the blocked battery is not related to the number of batteries in series, but is limited by the reverse current-voltage characteristics of the battery itself. That is, when the battery cell is blocked, the voltage across it is not determined by the number of batteries in series, but by the reverse current-voltage characteristics of the battery cell itself. When the leakage capacity increases, the reverse voltage across it will become smaller. In this way,

[0103] Based on this, the inventors of the present disclosure have discovered that by introducing a specific leakage composite contact structure 40 on the solar cell 100, the solar cell 100 can have a high reverse leakage characteristic, and can achieve the purpose of controlling the risk of hot spots and protecting defects. Specifically, by introducing the leakage composite contact mechanism 40, the reverse bias of the solar cell 100 can be reduced, thereby reducing the heating power of the hot spots caused by the defects, and thereby reducing the requirements for leakage current control during the production process. At the same time, considering that the introduction of the leakage composite contact structure 40 will affect the efficiency of the cell, the desired efficiency loss is not greater than 0.5%.

[0104] On this basis, the inventors of the present disclosure have conducted detailed research and verification and found that in the solar cell 100, the length of the leakage composite contact structure 40 per unit area has an effect on the efficiency of 0.1158%. In the 18.2*18.2 solar cell 100, the effect of the leakage composite contact structure 40 on the efficiency of 3.5*10 is increased by 1 cm for every 1 cm increase in the length of the leakage composite contact structure 40. -4 %.

[0105] Therefore, in order to control the efficiency loss to no more than 0.5%, the inventors of the present disclosure have found that the length N per unit area of ​​the leakage composite contact structure 40 needs to be set to be less than or equal to 4.32 cm / cm 2 . Based on this, the inventors of the present disclosure have found through research and verification that in order to make the solar cell 100 have high reverse leakage characteristics when the efficiency impact is no more than 0.5%, thereby effectively controlling hot spots and reducing the control of leakage current to improve manufacturing capabilities, it is at least necessary to ensure that the solar cell 100 can meet the condition that the leakage current per unit length of the leakage composite contact structure 40 is greater than Impp / S / N when a reverse voltage of 17V or less than 17V is applied to the solar cell 100, wherein Impp is the maximum power point current of the solar cell 100, S is the area of ​​the solar cell 100, N is the length of the leakage composite contact structure 40 per unit area in the solar cell 100, and N is less than or equal to 4.32cm / cm 2 , and then the technical solution of the present disclosure is obtained, that is, this is to avoid excessive efficiency loss, control hot spot risks and improve manufacturing capabilities.

[0106] Furthermore, in some embodiments, in order to make the efficiency loss of the solar cell 100 no greater than 0.4%, the value N may be less than or equal to 3.45 cm / cm 2 In this way, the efficiency loss can be further reduced while the solar cell 100 can have a high reverse leakage characteristic.

[0107] Preferably, in some embodiments, in order to make the efficiency loss of the solar cell 100 no more than 0.3%, the above value N may be preferably less than or equal to 2.59 cm / cm 2 In this way, the efficiency loss can be further reduced while the solar cell 100 can have a high reverse leakage characteristic.

[0108] In some embodiments, when the reverse voltage applied across the solar cell 100 is 9V, the leakage current per unit length of the leakage composite contact structure 40 also satisfies the condition of being greater than Impp / S / N. When the reverse voltage applied across the solar cell 100 is 6V, the leakage current per unit length of the leakage composite contact structure 40 also satisfies the condition of being greater than Impp / S / N.

[0109] In some embodiments, in the battery assembly 200 , the battery assembly 200 includes a plurality of battery strings, each of which includes a plurality of solar cells 100 connected in series, and a bypass diode is connected in parallel at both ends of the battery string;

[0110] The reverse bias voltage across the blocked solar cell 100 <D*Voc*(M-1)+L:

[0111] Wherein, the reverse bias voltage is the voltage across the shaded solar cell 100 when the solar cell 100 is shaded and the leakage current of the shaded solar cell 100 reaches the maximum power point current; Voc is the open circuit voltage of the solar cell 100, M is the number of solar cells 100 in the battery string connected in parallel with the bypass diode, D is a constant less than 1, and L is the startup voltage of the bypass diode.

[0112] In this way, a bypass diode is provided in the battery assembly 200 and when the solar cell 100 is blocked, the reverse bias voltage of the solar cell 100 when operating at the maximum power point current meets the above conditions, which is smaller than the reverse bias voltage in the traditional solution and the heat generation power is smaller, thereby achieving the purpose of controlling the risk of hot spots.

[0113] Specifically, in such an embodiment, V Impp The size of V is determined by the leakage capability of the solar cell 100, which has a high reverse leakage characteristic. The stronger the reverse leakage capability, the higher the V ImppThe smaller the voltage, the stronger the reverse leakage capability. When the leakage current of the blocked cell reaches the maximum power point current, the smaller the reverse bias voltage across the cell. In other words, compared to conventional solutions, when the cell is blocked, the reverse voltage across the cell is lower than that of the conventional solution. This reduces the heat generation power and the risk of hot spots caused by defects. It also reduces the requirements for leakage current control during the production process.

[0114] Of course, in some embodiments, in the battery assembly 200, the reverse bias voltage across the shielded solar cell 100 is <D*Voc*(P-1);

[0115] Wherein, the reverse bias voltage is the voltage across the shaded solar cell 100 when the solar cell 100 is shaded and the leakage current of the shaded solar cell 100 reaches the maximum power point current; Voc is the open circuit voltage of the solar cell 100; P is the number of solar cells 100 connected in series with the shaded solar cell 100; and D is a constant less than 1.

[0116] That is, in this embodiment, regardless of whether a bypass diode is connected in parallel to the battery string, the reverse bias voltage across the obscured solar cell 100 satisfies this condition. Thus, the heat generated by the obscured solar cell 100 is reduced, thereby achieving the purpose of controlling the risk of hot spots.

[0117] Furthermore, in the above embodiment, the value range of the constant D is preferably 0.1-0.5. Thus, the reverse bias voltage across the shielded solar cell 100 is significantly reduced compared to the voltage in conventional solutions, significantly reducing heat generation. In other words, by improving the leakage resistance of the solar cell 100, the shielded solar cell 100 can achieve its maximum power point current at a lower reverse bias voltage.

[0118] In some embodiments, in the battery assembly 200 , when the solar cell 100 is shielded, the heat generation power of a single leakage composite contact structure 40 is less than 8.85W.

[0119] In this way, when the solar cell 100 is shielded, the heating power of each leakage composite contact structure 40 is less than 8.85 W, which can avoid the risk of fire caused by excessive heating power causing decomposition and carbonization of the component packaging material.

[0120] In such an embodiment, the heat generation power of a single leakage composite contact structure 40 may preferably be less than 6.23W.

[0121] Specifically, as shown in Figure 10, experiments have shown that in a solar cell 100, when the distance between the leakage points is large, the heating power needs to be controlled to be less than 8.85W, and when the distance between the leakage points is small, the heating power needs to be controlled to be less than 6.23W. Therefore, by setting the heating power of each leakage composite contact structure 40 to at least less than 8.85W, and preferably less than 6.23W, the decomposition and carbonization of the component packaging material can be avoided, reducing the risk of fire.

[0122] In some embodiments, in the battery assembly 200 , the number S of the leakage composite contact structures 40 satisfies the following conditions:

[0123] S>(Impp*V Impp ) / 8.85W;

[0124] Where, Impp is the maximum power point current of the solar cell 100, V Impp is the reverse bias voltage across the shaded solar cell 100 when the solar cell 100 is shaded and the leakage current of the shaded solar cell 100 reaches the maximum power point current, and S is a positive integer.

[0125] In this way, in order to ensure that the heat generated by each leakage composite contact structure 40 does not exceed 8.85W, the number of leakage composite contact structures 40 on the solar cell 100 can be set to be relatively large. In this way, when the maximum power point current and the reverse bias voltage across the cell are constant, by providing a sufficient number of leakage composite contact structures 40, the heat generated can be distributed, thereby avoiding excessive heat generation at a single point that causes decomposition and carbonization of the packaging material.

[0126] Specifically, Table 2 below shows the minimum required relationship between the number of leakage composite contact structures 40 and the total heating power;

[0127] Table 2

[0128] From Table 2 above, it can be seen that in order to achieve the anti-hot spot effect of the contact, the minimum number of the point-distributed leakage composite contact structures 40 on the battery cell should meet the requirement of being greater than (Impp*(V@Impp) / 8.85W).

[0129] In some embodiments, S may preferably be greater than (Impp*V Impp ) / 6.23W. In this way, even if the spacing between adjacent leakage composite structures is small, decomposition and carbonization of the packaging material can be avoided.

[0130] Of course, in one possible embodiment, the solar cell 100 can also be designed so that when the solar cell 100 is shielded, the total heat generated by all the leakage composite contact structures 40 is less than 8.85 W. In this way, regardless of the number of leakage composite contact structures 40, the total heat generated by all leakage composite contact structures 40 will not exceed 8.85 W, thereby achieving maximum protection against hot spot fire risks.

[0131] Referring to FIG. 3 and FIG. 7 , in some embodiments, in the solar cell 100 , the distance between two adjacent leakage composite contact structures 40 is greater than or equal to 4 cm.

[0132] In this way, it is possible to avoid the leakage composite contact structures 40 being distributed too densely, which would result in poor heat dissipation and excessive concentration of heat generated when shielded, thereby causing temperature rise.

[0133] Specifically, it is not difficult to understand that in the solar cell 100 , the factors affecting the temperature at the final thermal equilibrium are: 1) heat generation power; 2) material heat capacity; 3) thermal conductivity; and 4) heat dissipation effect.

[0134] At present, the material combination of crystalline silicon solar cells is relatively fixed. Under certain material heat capacity, thermal conductivity, and heat dissipation conditions, the requirement of single-point heating power <8.85W has been obtained through experimental methods. However, if there are multiple heating points, their distribution has a significant impact on the heat dissipation effect. As can be seen from Figure 10, when the heating points are far away, the single-point heating power is required to be <8.85W. When the single heating points are relatively close, the power requirement is reduced to <6.23W. This is because the heating points that are too close reduce the temperature gradient around them, resulting in poor heat dissipation effect.

[0135] Based on this, the inventors of the present disclosure discovered through research that when the closest spacing between hot spots is 4 cm, the surrounding temperature gradient begins to significantly affect the heat dissipation effect, reducing the heat dissipation effect. Therefore, to ensure that the hot spot temperature is effectively controlled, the distance between hot spots needs to be controlled so that multiple heat dissipation points are spaced as evenly as possible on the silicon wafer 10. Based on this, the inventors of the present disclosure discovered that by controlling the spacing between two adjacent leakage composite contact structures 40 to be no less than 4 cm, better heat dissipation can be achieved, preventing excessive heat concentration and overheating.

[0136] It can be understood that “the distance between two adjacent leakage composite contact structures 40 is greater than or equal to 4 cm” means that within a 4 cm range around a leakage composite contact structure 40 , there are no other leakage composite contact structures 40 in any direction.

[0137] In some embodiments, when the solar cell 100 is shaded, within any 4 cm*4 cm square area in the solar cell 100, the leakage current I 漏 The following conditions are met:

[0138] I 漏 <8.85W / V Impp ;

[0139] Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures 40 within a 4cm*4cm square, V Impp It is the reverse bias voltage across the shaded solar cell 100 when the solar cell 100 is shaded and the leakage current of the shaded solar cell 100 reaches the maximum power point current.

[0140] In this way, by limiting the sum of the leakage currents of all leakage composite contact structures 40 within the 4×4 square range, on the one hand, it is possible to prevent excessive concentration of heat in a certain area, which may lead to a temperature increase; on the other hand, it is possible to limit the total heat generation within the 4×4 square range to at least less than 8.85 W, thereby preventing the temperature generated by the heat from exceeding 160°C, which may lead to decomposition and carbonization of the packaging material.

[0141] Furthermore, in some embodiments, in order to further reduce the temperature generated by the heat to less than 130°C and further reduce the risk of fire, when the solar cell 100 is blocked, in any 4cm*4cm square area of ​​the solar cell 100, the leakage current I 漏 The following conditions can be met: I 漏 <4.54W / V Impp .

[0142] Furthermore, in some embodiments, in order to further reduce the temperature generated by the heat to less than 110°C and further reduce the risk of fire, when the solar cell 100 is blocked, in any 4cm*4cm square area of ​​the solar cell 100, the leakage current I 漏 Meet the following conditions: I 漏 <2.26W / V Impp .

[0143] Throughout this specification, references to terms such as "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" indicate that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0144] In addition, the above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A solar cell comprising: silicon wafers; A first doping layer stacked on the silicon wafer; and a second doped layer stacked on the silicon wafer, the second doped layer having a polarity opposite to that of the first doped layer, the second doped layer being in composite contact with the first doped layer at a preset position to form a leakage composite contact structure, wherein when a reverse voltage applied across the solar cell is 17V or less than 17V, a leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N, where Impp is the maximum power point current of the solar cell, S is the area of ​​the solar cell, N is the length per unit area of ​​the leakage composite contact structure in the solar cell, and N is less than or equal to 4.32 cm / cm 2 .

2. The solar cell according to claim 1, wherein: N is less than or equal to 3.45 cm / cm 2 .

3. The solar cell according to claim 1, wherein: N is less than or equal to 2.59 cm / cm 2 .

4. The solar cell according to claim 1, wherein: When the reverse voltage applied across the solar cell is 9V, the leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N.

5. The solar cell according to claim 1, wherein: When the reverse voltage applied across the solar cell is 6V, the leakage current per unit length of the leakage composite contact structure is greater than Impp / S / N.

6. The solar cell according to claim 1, wherein: The solar cell is a double-sided solar cell, the silicon wafer has a first surface and a second surface opposite to each other, the first doped layer is stacked on the first surface, and the second doped layer is stacked on the second surface, and the second doped layer and the first doped layer form a composite contact at a preset position on the edge of the silicon wafer, thereby forming the leakage composite contact structure.

7. The solar cell according to claim 1, wherein: The solar cell is a back-contact solar cell, the silicon wafer has a relative front side and back side, a plurality of first doped layers and a plurality of second doped layers are stacked on the back side, the plurality of first doped layers and the plurality of second doped layers are alternately arranged in sequence, a spacer is provided between the first doped layers and the second doped layers, and at a preset position of the spacer, the first doped layers and the second doped layers are in composite contact to form the leakage composite contact structure.

8. A battery assembly comprising several solar cells according to any one of claims 1 to 7.

9. The battery assembly according to claim 8, wherein: The battery assembly includes a plurality of battery strings, each of which includes a plurality of solar cells connected in series, and a bypass diode is connected in parallel at both ends of the battery string; The reverse bias voltage across the blocked solar cell is less than D*Voc*(M-1)+L: The reverse bias voltage is the voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current; Voc is the open circuit voltage of the solar cell, M is the number of solar cells in the battery string connected in parallel with the bypass diode, D is a constant less than 1, and L is the startup voltage of the bypass diode.

10. The battery assembly according to claim 8, wherein: The battery assembly includes a plurality of battery strings, and the battery strings include a plurality of solar cells connected in series; The reverse bias voltage across the blocked solar cell is less than D*Voc*(P-1); The reverse bias voltage is the voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current; Voc is the open circuit voltage of the solar cell, P is the number of solar cells connected in series with the blocked solar cell, and D is a constant less than 1.

11. The battery assembly according to claim 9 or 10, wherein: The value range of D is 0.1-0.

5.

12. The battery assembly according to claim 8, wherein: When the solar cell is shielded, the heating power of a single leakage composite contact structure in the solar cell is less than 8.85W.

13. The battery assembly according to claim 8, wherein: The number S of the leakage composite contact structures in the solar cell satisfies the following condition: S>(Impp*V Impp ) / 8.85W; Wherein, Impp is the maximum power point current of the solar cell, V Impp is the reverse bias voltage across the shaded solar cell when the solar cell is shaded and the leakage current of the shaded solar cell reaches the maximum power point current, and S is a positive integer.

14. The battery assembly according to claim 8, wherein: When the solar cell is blocked, the leakage current I 漏 The following conditions are met: I 漏 <8.85W / V Impp ; Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within a 4cm*4cm square, V Impp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

15. The battery assembly according to claim 14, wherein: When the solar cell is blocked, the leakage current I 漏 The following conditions are met: I 漏 <4.54W / V Impp ; Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within the square range, V Impp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

16. The battery assembly according to claim 15, wherein: When the solar cell is blocked, within any 4cm*4cm square of the solar cell, the leakage current Ileak of the solar cell satisfies the following conditions: I 漏 <2.26W / V Impp ; Among them, I 漏 is the sum of the leakage currents of all the leakage composite contact structures within the square range, V Impp It is the reverse bias voltage across the blocked solar cell when the solar cell is blocked and the leakage current of the blocked solar cell reaches the maximum power point current.

17. The battery assembly according to claim 8, wherein: In the solar cell, the distance between two adjacent leakage composite contact structures is greater than or equal to 4 cm.

18. A photovoltaic system comprising the battery assembly according to any one of claims 8 to 17.

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