solar cell

Abstract

A solar cell comprising a semiconductor region, a dielectric layer, and at least one finger located above the semiconductor region, characterized in that the finger comprises contact segments and connecting segments arranged alternately, a lower surface of the contact segment passing through the dielectric layer and being in contact with the semiconductor region, the connecting segment being located above the dielectric layer and having a side surface in contact with the adjacent contact segment, the ratio between the length of the contact segment and the length of the connecting segment being equal to or greater than 1:1.5, the lower surface of the contact segment being provided with a plurality of grooves, and the plurality of grooves being filled by the dielectric layer.

Description

Technical FieldThe present application relates mainly to the field of photovoltaic technology, in particular to a solar cell.Prior ArtMetal grid lines have the function for the collection of current carriers. The contact of the metallic grid lines with a semiconductor region could lead to the bonding and in turn to reduced efficiency of solar cells. By reducing the bond, the efficiency of solar cells can be improved. How to reduce the bond is one of the important research directions in the present field.Disclosure of the InventionA technical problem to be solved in the present application is to provide a solar cell by which the composite can be reduced.In order to solve the above technical problem, the present application provides a solar cell including a semiconductor region, a dielectric layer, and fingers located above the semiconductor region. The finger comprises contact segments and connection segments arranged alternately, wherein a lower surface of the contact segment passes through the dielectric layer and is in contact with the semiconductor region, wherein the connection segment is located above the dielectric layer and is in contact with a side surface of the adjacent contact segment, and wherein the ratio between the length of the contact segment and the length of the connection segment is equal to or greater than 1:1.5.In an embodiment of the present application, it is provided that the contact segment comprises an upper layer and a lower layer stacked on top of each other, wherein the material for the lower layer comprises silver and the material for the upper layer is the same as that for the connection segment, wherein an upper surface of the contact segment is flush with an upper surface of the connection segment, and wherein the porosity of the upper layer is smaller than the porosity of the lower layer.In an embodiment of the present application, it is provided that an interface between the upper layer and the lower layer is higher than the dielectric layer.In an exemplary embodiment of the present application, it is provided that the porosity of the connection segment is smaller than the porosity of the contact segment, and that the upper surface of the contact segment is higher than the upper surface of the connection segment.In an embodiment of the present application, it is provided that the connecting segment comprises a first portion, a main portion and a second portion which are connected to one another in sequence, wherein the first portion and the second portion partially cover the side surface and at least partially cover the upper surface of the contact segment, and wherein an upper surface of the main portion is lower than the upper surface of the contact segment.In one exemplary embodiment of the present application, it is provided that the width of the contact segment is greater than the width of the connecting segment.In an exemplary embodiment of the present application, it is provided that the width of the side surface of the contact segment is greater than the width of the connecting segment in contact with the same.In an embodiment of the present application, it is provided that the lower surface of the contact segment is provided with a plurality of grooves, and the plurality of grooves are filled by the dielectric layer.In one exemplary embodiment of the present application, it is provided that the connecting segment has a rectangular cross section.In one exemplary embodiment of the present application, it is provided that the material for the contact segment comprises silver and that the material for the connecting segment comprises base metal.Compared to the prior art, the present application has the following advantages:(1) The finger comprises contact segments and connecting segments which are arranged alternately, wherein the contact segment is in contact with the semiconductor region and the connecting segment is not in contact with the semiconductor region, whereby a contact area between the finger and the semiconductor region and thus the bond can be reduced.(2) The upper low porosity layer can prevent moisture from corrodeting the interface between the contact segment and the semiconductor region, thereby improving the reliability of the solar cell against moisture and heat.(3) The porosity of the connecting segment is less than the porosity of the contact segment, and the upper surface of the contact segment is higher than the upper surface of the connecting segment. As a result, the line resistance of the contact segment can be reduced, so that the line resistance of the contact segment corresponds to the line resistance of the connection segment.(4) By forming the connecting segment with base metal, the cost of silver can be reduced, thus reducing the cost of fingers.Brief Description of the FiguresFor a better understanding of the present application, the drawings are recorded which form a part of the present application. The drawings show the embodiments of the present application, and together with the description explain the principle of the present application. In the figures: FIG. 1 shows a schematic plan view of a solar cell according to an exemplary embodiment of the present application; FIG. 2 shows a schematic sectional illustration of the solar cell along the line A-A in FIG. 1 ; FIG. 3 shows a schematic plan view of a finger according to an exemplary embodiment of the present application; FIG. 4 shows a schematic sectional illustration of the solar cell according to an exemplary embodiment of the present application; FIG. 5 shows a schematic sectional illustration of the solar cell according to a further exemplary embodiment of the present application; FIG. 6 shows a schematic flow diagram of a method for producing a solar cell according to an exemplary embodiment of the present application; FIG. 7 shows a scanning electron microscope image of a cross section of a contact segment according to an exemplary embodiment of the present application; FIG. 8 is a scanning electron microscope image of a cross section of a connection segment according to an embodiment of the present application; and FIG. 9 shows the dependence of the electrical parameters of the solar cell on different relationships between the length of the contact segment and the length of the connection segment.List of reference numbers: semiconductor region 110, dielectric layer 120, fingers 130, contact segment 131, upper layer 131 a, lower layer 131 b, lower surface 131 c, first side surface 131 d, second side surface 131 e, connection segment 132, first portion 132 a, main portion 132 b, second portion 132 c.DETAILED EMBODIMENTSIn order to explain the technical solutions of the exemplary embodiments of the present application in more detail, the drawings required for the description of the exemplary embodiments are briefly summarized below. Of course, the following drawings merely represent some examples or embodiments of the present application, and after these drawings, those skilled in the art, without inventive activity, may apply the present application to other similar scenarios as well. Unless otherwise indicated or otherwise understood by context, the same reference numerals in the figures represent the same structures or operations.As shown in the present application and the claims, the terms "a / an / an" and / or "the / the" need not necessarily refer to the singular form, but may also include the plural form unless clearly stated otherwise in the context. In general, the terms "comprise" and "contain" only include the clearly indicated steps and elements which do not represent an exclusive list, so that the method or the device can also have a further step or a further element.Unless otherwise specified, the relative arrangement, numerical indication, and values of the components and steps explained in the exemplary embodiments are not intended to limit the scope of the application. Moreover, it should be understood that in the figures, the individual parts are not shown to scale in order to facilitate the description. The technologies, methods, and devices known to those of ordinary skill in the art would not be discussed in detail, but they are to be considered a part of the specification where appropriate. In all examples illustrated and discussed herein, a specific value is to be construed as exemplary, not limiting. Therefore, in another example of the exemplary embodiment, another value may be given. It should be noted that in the figures, the similar numerals and characters mean the similar items, and that an item need not be discussed further if it is already defined in a previous figure.It is to be understood that, within the scope of the description of the present application, the direction or positioning denoted by the positional terms "front", "rear", "top", "bottom", "left", "right", and "lateral", "longitudinal", "perpendicular", "horizontal", and "top", "bottom", etc. is in each case generally used with reference to the direction or positioning shown in the respective illustration in order merely to describe the present application and to simplify the description. Unless otherwise stated, these positional terms are used to indicate neither implicit nor explicit positioning and configuration and operation of the device or element in question in a predetermined position, and therefore do not represent a restriction of the application here. The directional terms "inner", "outer" mean the inner side and outer side with respect to the profile of a part itself.Herein, to facilitate description, the terms relative spatial relationship, such as "over," "above," "on top," "on top," etc., may be used to describe the spatial positional relationship of one agent or feature to another agent or feature in the figure. It is understood that these terms relative spatial relationship are intended to include other positions in use or operation besides the position shown in the figure. For example, if the means in the figure is arranged in the reverse direction, a means previously described as "above another means or component" or "above another means or component" is now positioned as "below another means or component" or "below another means or component". Thus, the exemplary term "above" may include the two positions of "above" and "below.". The means may of course also be positioned in other ways, such as rotated 90 degrees or in yet another position, and the spatial description used herein is to be constructed thereafter.It should also be noted that the use of the words "first", "second", etc. is only for differentiation between the respective parts, and these words do not have any particular meaning unless otherwise indicated. Therefore, they should not be construed as limiting the scope of the present application. Although the terms used in the present application are selected from well-known terms, some terms are selected in the description of the present application based on the judgment of the applicant or the applicant, and the concrete meaning is to be taken from corresponding parts of the present description. Furthermore, the present application is to be understood not only with reference to the concrete terms used, but with the aid of the meaning of individual terms.In the application, a flowchart is used to describe the operations performed by the system according to the embodiment of the application. It is to be understood that the previous or subsequent operations need not necessarily be performed exactly in order. In contrast, the steps may be performed in a reverse order or simultaneously. Moreover, another operation may also be added to this process or one operation or plural operations may be removed therefrom.A solar cell and a method for production according to the present application are described below with reference to exemplary embodiments.FIG. 1 shows a schematic plan view of a solar cell according to an embodiment, and FIG. 2 shows a schematic sectional illustration of the solar cell along the line A-A in FIG. 1. see FIGS. 1 and 2. the solar cell comprises a semiconductor region 110, a dielectric layer 120 and fingers 130 which are located above the semiconductor region 110, wherein current carriers are transmitted to the outside via the semiconductor region 110. To better understand the semiconductor region 110 of the present application, an example is given here that for a solar cell having a passivated tunnel oxide passivated contact (Engl.: tunnel oxide passivated contact) structure, the semiconductor region 110 may be a passivated tunnel oxide contact structure. The dielectric layer 120 is insulated, and the dielectric layer 120 may be one or more of an aluminum oxide (Al 2 O 3)- film, a silicon nitride (SiN x)- film, and a silicon oxynitride (SiO x N y) - film.The finger 130 includes contact segments 131 and connection segments 132 arranged alternately in its extension direction. The contact segment 131 is in contact with the semiconductor region 110 and the connection segment 132 is not in contact with the semiconductor region 110, whereby a contact area between the finger and the semiconductor region 110 and thus the bond can be reduced. In FIG. 2, a lower surface 131 cof the contact segment 131 passes through the dielectric layer 120 and is in contact with a surface of the semiconductor region 110. In some other embodiments, the bottom surface 131 cmay be dipped into the semiconductor region 110 to a certain depth.In FIG. 2, the contact segment 131 includes an upper layer 131 aand a lower layer 131 bstacked on each other. The upper layer 131 aand the lower layer 131 bare described below in detail, and will not be extended here.The connection segment 132 is located above the dielectric layer 120, and the left and right side surfaces of the connection segment 132 are each in contact with an adjacent contact segment 131 (see FIG. 2 ). The connection segment 132 is electrically connected to the contact segment 131. The connection segment 132 is directly in contact with a surface of the dielectric layer 120 facing away from the semiconductor region 110, while another film layer may also be arranged between the connection segment 132 and the dielectric layer 120.In one exemplary embodiment, it is provided that the material for the contact segment 131 comprises silver and that the material for the connecting segment 132 comprises base metal. The "base metal" has the opposite meaning to a "base metal". The base metal includes metals such as copper, aluminum, and the like, which are less expensive than the base metal. For example, the connecting segment 132 is made of a material such as aluminum. The connecting segment 132 may contain silver, while the connecting segment 132 may not contain silver. In the case of the connecting segment 132 without silver, the outlay for silver for the production of the fingers can be reduced. In the connection segment 132 including silver, it is preferable that the content of silver for the connection segment 132 is smaller than the content of silver for the contact segment 131, so that the cost of silver can be reduced to reduce the cost of fingers.Referring to FIG. 1, the ratio between the length of the contact segment 131 and the length of the connection segment 132 is equal to or greater than 1:1.5. The ratio between the length of the contact segment 131 and the length of the connection segment 132 may be 1:1.5, 1.1:1.5, 1.2:1.5, 1.3:1.5, 1.4:1.5, 1.5:1.5 (i.e., 1:1), or 1.6:1.5. When the ratio between the length of the contact segment 131 and the length of the connection segment 132 is equal to or greater than 1:1.5, good conversion efficiency (Eta) can be obtained. See FIG. 9, FIG. 9 shows the dependence of the electrical parameters of the solar cell on different relationships between the length of the contact segment and the length of the connection segment. Specifically, in Serial Nos. 1 to 3, the ratios of the lengths are equal to or greater than 1:1.5, while in Serial Nos. 4 and 5, the ratios of the lengths are less than 1:1.5. It is found that all the conversion efficiencies at serial numbers 1 to 3 are greater than the conversion efficiencies at serial numbers 4 and 5, with the conversion efficiency at serial number 2 being the highest.Referring to FIG. 2, in an embodiment in FIG. 2, the contact segment 131 includes an upper layer 131 aand a lower layer 131 bstacked on each other. The lower layer 131 bis in contact with the semiconductor region 110. An upper surface (i.e., an upper surface of the upper layer 131 a) of the contact segment 131 is flush with an upper surface of the connection segment 132. The material for the lower layer 131 bincludes silver, and the material for the upper layer 131 ais the same as that for the connection segment 132.Further, referring to FIG. 2, the porosity of the upper layer 131 ais smaller than the porosity of the lower layer 131 b, so that the reliability of the solar cell against moisture and heat can be improved. In particular, moisture may enter the fingers along a pore, so that an interface between the contact segment 131 and the semiconductor region 110 is corroded. The upper layer 131 aat the top of the contact segment 131 covers the lower layer 131 bat the bottom thereof, and the porosity of the upper layer 131 ais smaller than the porosity of the lower layer 131 b. Thereby, the upper low porosity layer 131 acan prevent moisture from corrodeting the interface between the contact segment 131 and the semiconductor region 110, thereby improving the reliability of the solar cell against moisture and heat.The contact segment 131 and the connection segment 132 in FIG. 2 may be formed by a following method. A paste for forming the lower layer 131 bis printed, and the paste is thermally treated to form the lower layer 131 b. Subsequently, a paste for covering the lower layer 131 band the dielectric layer is printed in a predetermined area, and the paste is thermally treated to form the connection segment 132 and the upper layer 131 a. Here, the "predetermined area" is an area where the connection segment 132 is located. The paste covering the lower layer 131 bbecomes the upper layer 131 aafter the thermal treatment. When printing the paste to form the joint segment 132 and the upper layer 131 a, the paste may fill the pore in the surface of the lower layer 131 b, so that the upper layer of the lower layer 131 bbecomes denser, thereby preventing the penetration of the moisture into the lower layer 131 b.See FIG. 1, in one exemplary embodiment, it is provided that the contact segment 131 and the connecting segment 132 are rectangular, as seen in the plan view, and the width of the contact segment 131 is greater than the width of the connecting segment 132. The greater width of the contact segment 131 may increase a process window for printing the paste to form the connection segment 132. That is, the contact of the paste with the contact segment 131 can be ensured when printing the paste to form the connection segment 132. Referring to FIG. 2, the interface between the upper layer 131 aand the lower layer 131 bis higher than the dielectric layer 120, so that after printing the paste for forming the connection segment 132, the paste also covers an exposed side surface of the lower layer 131 bin addition to the upper surface of the lower layer 131 b. Thereby, the connecting segment 132 after the thermal treatment can simultaneously cover three surfaces of the contact segment 131, so that the stability of the connection between the contact segment 131 and the connecting segment 132 can be increased.See FIG. 3 : In one exemplary embodiment, it is provided that the width of a first side surface 131 dof the contact segment 131 is greater than the width of the connection segment 132 in contact with the same, and that the width of a second side surface 131 eof the contact segment 131 is greater than the width of the connection segment 132 in contact with the same. The first side surface 131 dand the second side surface 131 eare opposed to each other in the extending direction of the finger. As shown in FIG. 3, the width of the first side surface 131 dand the width of the second side surface 131 emay be increased by thickening both ends of the contact segment 131. The greater widths of the side surfaces of the contact segment 131 promote not only an increased effect for the collection of current carriers by the fingers, but also the ensuring of the contact of the connection segment 132 with the contact segment 131.In one exemplary embodiment, it is provided that the connecting segment has a rectangular cross section. With the same height and width, the rectangular cross section can reduce the transmission resistance of the finger as compared to a cross section in the form of a curved surface or the like.Referring to FIG. 4, in an embodiment in FIG. 4, it is provided that the porosity of the connection segment 132 is smaller than the porosity of the contact segment 131, and that the upper surface of the contact segment 131 is higher than the upper surface of the connection segment 132. The present application has found that constituents of the paste would be adjusted to form the contact segment 131 such that the paste of the contact segment 131 may burn through the dielectric layer 120. The adaptation of the constituents results in the porosity of the contact segment 131 being greater than the porosity of the connection segment 132 and thus the conduction resistance of the contact segment 131 being greater than the conduction resistance of the connection segment 132. In order to solve the problem that the line resistances do not match each other, it is provided in an embodiment in FIG. 4 that the upper surface of the contact segment 131 is higher than the upper surface of the connection segment 132. Thereby, the line resistance of the contact segment 131 can be reduced so that the line resistance of the contact segment 131 matches the line resistance of the connection segment 132.Referring still to FIG. 4, in an embodiment, the bottom surface 131 cof the contact segment 131 is provided with a plurality of grooves (not shown), the plurality of grooves being filled by the dielectric layer 120. In expanded terms, the paste does not partially burn through the dielectric layer 120 upon thermal treatment of the paste to form the contact segment 131. Grooves are formed at non-burned-through locations. Between the grooves and the semiconductor region 110, there is a non-blown dielectric layer 120 (i.e., the dielectric layer 120 fills the grooves). The grooves in the lower surface 131c promote the reduction of the bond. The number of grooves can be increased by reducing the amount of lead oxide, tellurium oxide, or the like in the paste.Referring to FIG. 5, in one embodiment, the connecting segment 132 includes a first portion 132 a, a main portion 132 b, and a second portion 132 cconnected to each other in sequence. The first portion 132 aand the second portion 132 care disposed opposite to each other at both ends of the main portion 132 bin the extending direction of the finger, and are both located above the main portion 132 b. The first portion 132 aand the second portion 132 cpartially cover the side surface and part of the upper surface of the contact segment 131, and an upper surface of the main portion 132 bis lower than the upper surface of the contact segment 131. In FIG. 5, the first portion 132 aand the second portion 132 cpartially cover the upper surface of the contact segment 131. In some other embodiments, the first portion 132 aand the second portion 132 cmay collectively completely cover the top surface of the contact segment 131. By the first portion 132 aand the second portion 132 c, the contact area between the connection segment 132 and the contact segment 131 can be increased, so that the stability of connection between the two is increased.In a further aspect of the present application, a method for producing a solar cell is furthermore provided. Referring to FIGS. 1 and 2, the solar cell includes a semiconductor region 110 and a dielectric layer 120 above the semiconductor region 110. A plurality of fingers 130 are spaced apart above the semiconductor region 110. The fingers 130 are electrically connected to the semiconductor region 110. The finger 130 includes contact segments 131 and connection segments 132 arranged alternately in its extension direction. The ratio between the length of the contact segment 131 and the length of the connection segment 132 is equal to or greater than 1:1.5. the left and right side surfaces of the connection segment 132 are each in contact with an adjacent contact segment 131 (see FIG. 2 ).Referring to FIG. 6, a method of manufacturing a finger includes the following steps:Step S 210: printing a first paste on a dielectric layer;Step S220: printing a second paste on the dielectric layer;Step S 230: Thermally treat the first paste and the second paste, wherein the first paste burns through the dielectric layer but the second paste does not burn through the dielectric layer to form a contact segment and a connection segment.Steps S 210 to S 230 will be described in detail below.In step S 210, a first paste is printed on the dielectric layer, wherein the first paste can be directly in contact with a surface of the dielectric layer facing away from the semiconductor region 110, and wherein the first paste can be printed by screen printing. The first paste may comprise silver particles, while the first paste may also comprise other materials. For example, the first paste may include any kind of tellurium oxide, zinc oxide, bismuth oxide, and boron oxide.In step S220, a second paste is printed on the dielectric layer, wherein the second paste may be directly in contact with a surface of the dielectric layer facing away from the semiconductor region 110, and wherein the second paste may be printed by screen printing. The second paste may comprise particles of base metal. For example, the second paste may comprise copper and / or aluminum particles. However, the second paste may also comprise other materials. For example, the second paste may include any kind of tellurium oxide, zinc oxide, bismuth oxide, and boron oxide. It is possible to first perform step S 210 and then perform step S 220. However, it is also possible to first perform step S 220 and then perform step S 210.In one exemplary embodiment, it is provided that both the first paste and the second paste comprise a first glass, wherein the proportion by weight of the first glass for the second paste is greater than the proportion by weight of the first glass for the first paste. The first glass is a glass having a glass transition temperature of less than 600° C., for example tellurium oxide, zinc oxide, bismuth oxide and boron oxide, respectively. By making the weight fraction of the first glass for the second paste larger than for the first paste, it is possible that the porosity of a product by thermal treatment of the second paste is smaller than the porosity of a product by thermal treatment of the first paste.The second paste may include any kind or kinds of copper particles, aluminum particles, silver particles, particles having a core-shell structure (e.g., silver-clad copper).In step S 230, the first paste and the second paste are thermally treated, wherein the first paste burns through the dielectric layer but the second paste does not burn through the dielectric layer to form a contact segment and a connection segment. It is possible to treat the first paste and the second paste simultaneously or thermally, respectively. In extended terms, the printing and the thermal treatment can be carried out in the following order for the steps:Step 1: Printing a first paste;Step 2: Thermal treatment of the first paste;Step 3: Printing a second paste;Step 4: Thermal treatment of the second paste.The printing and the thermal treatment can also be carried out in the following sequence for the steps:Step 1: Printing a first paste and a second paste, wherein it is possible to print first the first paste and then the second paste, or first the second paste and then the first paste, or also simultaneously the first paste and the second paste.Step 2: Simultaneous thermal treatment of the first paste and the second paste.In the present application, methods for thermal treatment are not limited. For example, the thermal treatment may be performed by heating means such as heating furnace, laser, heating fan, or the like.As shown in FIG. 2, the contact segments 131 and the connection segments 132 in FIG. 2 may be manufactured by methods of Example 1 and Example 2 as follows.Example 1In FIG. 2, the contact segment 131 includes an upper layer 131 aand a lower layer 131 bstacked on each other. First, a first paste for forming the lower layer 131 bis printed, and thereafter, a second paste for forming the upper layer 131 aand the joint segment 132 is printed, the second paste covering the side surfaces and the upper surface of the first paste. The first paste and the second paste are thermally treated. After the thermal treatment, the first paste forms the lower layer 131 b, and the second paste above the first paste forms the upper layer 131 aafter the thermal treatment. The second paste at other locations forms the connecting segments 132 after the thermal treatment.Example 2Example 2 differs from Example 1 above all in that in Example 2, a second paste is printed after the formation of the lower layer 131 b. In extension, a first paste for forming the lower layer 131 bis printed and sintered, and the first paste forms the lower layer 131 bafter sintering. Thereafter, the second paste covering an upper surface and exposed side surfaces of the lower layer 131 bis printed. The second paste is sintered. The second paste above the lower layer 131 bconstitutes the upper layer 131 aafter thermal treatment. The second paste at other locations forms the connecting segments 132 after the thermal treatment.As shown in FIG. 4, the contact segments 131 and the connection segments 132 in FIG. 4 may be manufactured by methods of Example 3 as follows.Example 3A first paste and a second paste are printed, wherein the first paste and the second paste do not overlap. That is, the first paste is only in contact with the second paste, the first paste does not cover the second paste, and the second paste does not cover the first paste either. After thermal treatment of the first paste and the second paste, the first paste forms the contact segments 131, and the second paste forms the connection segments 132. Example 3 does not limit the order for printing the first paste and the second paste. It is possible to treat the first paste and the second paste simultaneously or thermally, respectively.As shown in FIG. 5, the contact segments 131 and the connection segments 132 in FIG. 5 may be manufactured by methods of Example 4 and Example 5 as follows.Example 4A first paste and a second paste are printed in sequence. The second paste covers side surfaces and partially the upper surface of the first paste. The first paste forms the contact segments 131 after thermal treatment, and the second paste forms the connection segments 132 after thermal treatment. The connecting segment 132 has a first portion 132 aand a second portion 132 cthat partially cover the upper surface and partially cover the side surfaces of the contact segment 131.Example 5A first paste is printed and thermally treated, and the first paste forms the contact segments 131 after thermal treatment. After the formation of the contact segments 131, a second paste is printed. The second paste covers exposed side surfaces and partially covers the upper surface of the contact segment 131. The second paste is thermally treated and the second paste forms the connecting segments 132 after thermal treatment. The connecting segment 132 has a first portion 132 aand a second portion 132 cthat partially cover the upper surface and partially cover the side surfaces of the contact segment 131.In one exemplary embodiment, it is provided that the temperature for the thermal treatment of the first paste is higher than the temperature for the thermal treatment of the second paste. For example, the temperature for the thermal treatment of the first paste is higher than 600° C. and the temperature for the thermal treatment of the second paste is lower than 600° C. By the temperature for the thermal treatment of the second paste being lower, the second paste is prevented from burning through the dielectric layer. The thermal treatment of the first paste may include sintering. The thermal treatment of the second paste may include sintering, drying, or laser heating.In one exemplary embodiment, it is provided that the first paste and the second paste comprise silver particles, wherein the proportion of the silver particles of the second paste having a particle size of equal to and less than 1 μm is greater than the proportion of the silver particles of the first paste having a particle size of equal to and less than 1 μm. By making the silver particle content of the second paste larger with a particle size equal to or smaller than 1 μm, the porosity of a product after the thermal treatment of the second paste can be reduced. In a further exemplary embodiment, it is provided that the roughness of the silver particles of the second paste is greater than the roughness of the silver particles of the first paste, whereby the porosity of a product can be reduced after the thermal treatment of the second paste.FIG. 7 shows a scanning electron microscope image of a cross section of a contact segment 131 according to an embodiment, and FIG. 8 shows a scanning electron microscope image of a cross section of a connection segment 132 according to an embodiment. The contact segment 131 in FIG. 7 is formed of the first paste after the thermal treatment. The joint segment 132 in FIG. 8 is formed of the second paste after the thermal treatment. Comparing FIGS. 7 and 8, it can be seen that the product after the thermal treatment of the first paste has more pore (higher porosity) and the product after the thermal treatment of the second paste has less pore (lower porosity). In conjunction with FIGS. 2, 7, and 8, the lower layer 131 bis formed of the first paste after the thermal treatment, while the connecting segment 132 and the upper layer 131 aare formed of the second paste after the thermal treatment. The upper layer 131 aand the joint segment 132 wrap the upper surface and the side surfaces of the lower layer 131 b. Thereby, the upper layer 131 aand the lower porosity connection segment 132 can protect the lower layer 131 bfrom corrosion by moisture.The basic concepts have been described above. It should be understood that the above disclosure of the present application is only exemplary to those skilled in the art without limiting the present application. Although not clearly stated, a person skilled in the art can make various modifications, improvements and changes to the present application. These modifications, improvements, and changes are intended to be included in the present application, and are intended to be included within the spirit and scope of the exemplary embodiments of the present application.The present application also uses specific words to describe the embodiments of the present application. The terms "one embodiment," "a particular embodiment," and / or "some embodiments" mean a feature, structure, or characteristic associated with at least one embodiment of the present application. Therefore, it should be emphasized and noted that "particular embodiment" or "one embodiment" or "an alternative embodiment" mentioned in different paragraphs of the specification two or more times does not necessarily refer to the same embodiment. Moreover, some of the features, structures, or specifics of one or more exemplary embodiments of the present application may be combined with one another in a suitable manner.It should also be noted that in the above description of the embodiments of the present application, various features are sometimes classified into an embodiment, a figure, or a description thereof in order to simplify the description of the disclosure of the present application and facilitate understanding of one or more embodiments of the present application. This disclosure does not, however, mean that the features of the subject matter of the present application are more than those recited in the claims. In fact, the features of the exemplary embodiments are less than all features of one of the individual exemplary embodiments disclosed above.In some embodiments, numerals are used to describe the components and characteristics. It should be understood that the numerals for describing the embodiments are modified with "about", "about", or "substantially" in some cases. Unless otherwise indicated, the terms "about," "about," or "substantially" mean that these numbers may have a variation of ±20%. Accordingly, in some embodiments, the meaningful parameters used in the specification and claims are approximations that may change depending on the requirement of the individual embodiment. In some embodiments, the valid locations prescribed for the meaningful parameters are to be considered using a general round up and round down method. Although in some embodiments of the present application the value range and the parameters for determining their scope are approximate values, in a concrete embodiment the values can be set as accurately as possible.However, although the present application has been described with reference to the present specific embodiments, those skilled in the art should appreciate that the above-described embodiments are only for illustrating the present application, and various equivalent changes or substitutions may be made without departing from the spirit of the present application. Therefore, all changes to the above-described embodiments fall within the scope of the claims of the present application as long as they are made within the spirit of the present application.

Claims

A solar cell comprising a semiconductor region, a dielectric layer and at least one finger located above the semiconductor region, characterized in that the finger comprises contact segments and connection segments arranged alternately, wherein a lower surface of the contact segment passes through the dielectric layer and is in contact with the semiconductor region, wherein the connection segment is located above the dielectric layer and is in contact with the adjacent contact segment with a side surface, wherein the ratio between the length of the contact segment and the length of the connection segment is equal to or greater than 1:1.5, wherein the lower surface of the contact segment is provided with a plurality of grooves, and wherein the plurality of grooves are filled by the dielectric layer.The solar cell according to claim 1, characterized in that the contact segment comprises an upper layer and a lower layer stacked on each other, wherein the material for the lower layer comprises silver and the material for the upper layer is the same as that for the connection segment, wherein an upper surface of the contact segment is flush with an upper surface of the connection segment, and wherein the porosity of the upper layer is less than the porosity of the lower layer.The solar cell according to claim 2, characterized in that an interface between the upper layer and the lower layer is higher than the dielectric layer.The solar cell of claim 1, characterized in that the porosity of the connection segment is less than the porosity of the contact segment, and that the upper surface of the contact segment is higher than the upper surface of the connection segment.The solar cell of claim 1, characterized in that the connection segment comprises a first portion, a main portion and a second portion connected to each other in order, wherein the first portion and the second portion partially cover the side surface and at least partially cover the upper surface of the contact segment, and wherein an upper surface of the main portion is lower than the upper surface of the contact segment.Solar cell according to claim 1, characterised in that the width of the contact segment is greater than the width of the connecting segment.Solar cell according to claim 6, characterised in that the width of the side surface of the contact segment is greater than the width of the connecting segment in contact with the same.Solar cell according to claim 1, characterised in that the connecting segment has a rectangular cross-section.The solar cell of claim 1, characterized in that the material for the contact segment comprises silver, and that the material for the connection segment comprises base metal.

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