JP2015528645A - A method for improving the adhesion of plated metal layers to silicon. - Google Patents

Abstract

A method for making a solar cell is described, the method comprising a plated metal contact having a contact pattern that includes a plurality of fingers and at least one first securing element at a free end of each of the plurality of fingers. Forming a step. Furthermore, it is a related solar cell.

Description

  The present disclosure is technically related to a method of improving the adhesion of plated metal layers, such as plated Cu contacts, to silicon. This method can be advantageously used to improve the adhesion of plated metal contacts in silicon solar cells.

  New concepts and manufacturing processes are developed for silicon solar cells, taking into account those concepts and process improvements in the manufacturing environment. An example of such development for industrial products is the use of a plating process for the formation of metal contacts as an alternative to the screen printing process.

  For example, a typical process flow using plating such as frontside metallization of a silicon solar cell consists of forming a dielectric layer, such as an antireflective coating, over the entire surface, followed by an antireflective coating. And partially exposing the underlying silicon surface at locations where metal contacts need to be formed. The step of partially removing the antireflection coating may be performed, for example, by laser ablation. After partial removal of the antireflective coating, a front metal contact is formed in the exposed silicon region by metal plating to form the front metal contact.

  Due to their excellent contact properties, Ni layers or nickel silicide layers are used, for example, to form good contacts.

  The nickel silicide layer is formed by forming a thin nickel layer (eg, by electroless plating) on the silicon surface in the opening formed in the antireflective coating, followed by silicidation. An annealing process or a sintering process is performed, and as a result, a nickel-silicon alloy (nickel silicide) is formed. In a process for making a silicon solar cell, on a nickel silicide layer, at least one additional metal layer (eg, a Cu layer) is electroplated using a nickel silicide layer as a seed layer to provide a low resistance front metal. Form a pattern.

  In an alternative process for manufacturing silicon solar cells, a Ni layer is first formed in the openings formed in the antireflective coating, for example by photoinduced plating, and then the Ni layer is formed by, for example, electrolytic plating. A Cu layer is formed on top. Thereafter, a sintering process is performed to change the Ni layer into a nickel silicide layer at least partially.

  In such a process using plated metal contacts, the challenge is to achieve a good bond between the different metal layers and between the metal layer and the underlying silicon substrate. Weak adhesion between the metal layers or between the metal layer and the silicon substrate results in delamination of the metal layer, leading to an unacceptable decrease in solar cell efficiency. The risk of delamination of the metal layer is generally higher with narrow metal shapes. For example, in a typical solar cell front metal grid that includes a plurality of narrow lines (fingers) connected to at least one wider line (busbar), the metal stripping problem is narrower than for a wider busbar. Higher than finger.

  The individual solar cells are typically electrically connected into the module by means of Cu ribbons soldered to the cell bus bars. If the bond between the metal stack (including the busbar and soldered ribbon) and the silicon substrate is weak, the metal contacts will degrade and the module efficiency will also drop to failure levels.

  Certain embodiments of the invention provide a plated metal contact that substantially reduces the risk of stripping of the plated metal contact and / or improves the adhesion of the metal ribbon soldered to the bus bar as compared to current methods. The present invention relates to a method for manufacturing a solar cell.

  In one aspect of the invention, the method includes a plurality of fingers and at least one first pinning element or anchoring element at each free end of the plurality of fingers. Providing a plated metal contact having a pattern. It is an advantage of the process of providing a first securing element at the free end of the finger to substantially reduce the risk of finger peeling.

  In one aspect of the invention, the method preferably comprises at least one bus bar, a plurality of fingers connected to the at least one bus bar, and at least one end of the finger physically connected to the bus bar. Providing a plated metal contact having a contact pattern including at least one second securing element or anchoring element at the end of each finger that physically connects to one bus bar. It is an advantage of the process of forming such a second fastening element that it improves the adhesion of the ribbon soldered to at least one bus bar.

  In one aspect of the invention, the method includes at least one bus bar, a plurality of fingers connected to the at least one bus bar, at least one first securing element at each free end of the plurality of fingers, and at least one Providing a plated metal contact having a contact pattern including at least one second securing element at the end of the finger physically connected to one bus bar.

  The method according to embodiments of the present invention can be advantageously used to form a metallization pattern on the front side of a solar cell. The manufacturing method includes forming a dielectric layer, such as an anti-reflective coating, over the entire surface of the silicon substrate, and partially removing the anti-reflective coating, whereby the metal contact is formed according to the contact pattern of the present disclosure. A step of exposing a lower silicon surface at a position where it needs to be formed, and a step of forming a front side metal contact in an exposed silicon region by metal plating for forming a front side metal contact. good.

  Certain embodiments of the invention provide a plated metal contact that substantially reduces the risk of stripping of the plated metal contact and / or improves the adhesion of the metal ribbon soldered to the bus bar as compared to current methods. The present invention relates to a method for manufacturing a solar cell.

  In one aspect of the invention, a solar cell has a plated metal contact having a contact pattern that includes a plurality of fingers and at least one first securing element or anchoring element at each end of the plurality of fingers. .

  In one aspect of the invention, the solar cell includes at least one second of at least one bus bar, a plurality of fingers connected to the at least one bus bar, and an end of the finger physically connected to the at least one bus bar. A plated metal contact having a contact pattern including a fixed element or a fixed element.

  In one aspect of the invention, the solar cell includes at least one bus bar, a plurality of fingers connected to the at least one bus bar, at least one first securing element at each free end of the plurality of fingers, and at least one A plated metal contact having a contact pattern including at least one second securing element at the end of the finger physically connected to one bus bar.

  The first anchoring element is an element or shape that leads to a partial increase in contact area between the finger and the underlying silicon at the free end of the finger. The first securing element is provided by partially increasing the width of the finger at the free end of the finger, or it is linear, square, rectangular, polygonal, circular, or elliptical, or other suitable It may be an element having a shape and formed at the free end of the finger.

  The second anchoring element may be any element or shape that leads to a partial increase in contact area between the finger and the underlying silicon at the end of the finger connecting to the bus bar. The second securing element is provided by partially increasing the width of the finger at the free end of the finger connected to the busbar, or it is linear, square, rectangular, polygonal, circular, or oval, or It may be an element formed at the free end of a finger having another suitable shape and connected to the bus bar.

  Certain objectives and advantages of various inventive aspects have been described above. Of course, it will be understood that not all such objectives or advantages need be achieved with respect to any particular embodiment of the present disclosure. Thus, for example, in a manner that achieves or optimizes one advantage or group of advantages taught herein, the disclosure may be embodied without the need to achieve other objectives or advantages taught or suggested herein. Those skilled in the art will understand that the Further, it is understood that this summary is merely an example and is not intended to limit the scope of the present disclosure. The present disclosure will be best understood by reference to the following detailed description of both the organization and method of operation, together with its features and advantages, when read in conjunction with the accompanying drawings.

An example of a typical front side metallization pattern of a solar cell is shown. 2 shows an example of front side metallization according to one aspect of the invention. The example of the 1st fixing element concerning the form of invention of this indication is shown. 2 shows an example of front side metallization according to one aspect of the invention. The example of the 2nd fixing element concerning the form of invention of this indication is shown. FIG. 3 shows details of FIG. 2 with an enlarged specific finger line.

  In the different drawings, the same reference signs refer to the same or analogous elements.

  In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure and how they are implemented in specific embodiments. However, it will be understood that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, and techniques have not been shown in detail in order not to obscure an understanding of this disclosure. While the invention will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto. The drawings included and described herein are schematic and are not limiting the scope of the disclosure. Also, in the drawings, the size of some of the elements is exaggerated and therefore not drawn on scale for illustrative purposes.

  In addition, the first, second, third, etc. terms in the disclosure are used to distinguish between similar elements and need to be listed in order, temporally, spatially, in order or otherwise. There is no. It is understood that the terms so used are interchangeable under appropriate circumstances, and that the embodiments of the present disclosure described herein can be operated in a different order than the order described or illustrated herein. Should.

  In addition, terms such as “up”, “down”, “up”, and “down” in the disclosure are used for the purpose of disclosure and do not indicate relative positions. It is to be understood that the terminology so used is interchangeable under appropriate circumstances, and that the embodiments of the present disclosure described herein can be operated at different locations than those disclosed or illustrated herein. is there.

  It should be noted that the term “comprising” should not be construed as limited to the means listed thereafter, and does not exclude other elements or steps. Thus, features, numbers, steps, or ingredients referred to are construed accordingly and exclude the presence or addition of one or more other features, numbers, steps, or ingredients, or combinations thereof. must not. Thus, the scope of the expression “a device including means A and B” should not be limited to devices including only components A and B.

  In the context of the present disclosure, the surface or front side of a solar cell is the surface or side that is placed towards the light and thereby adapted to receive illumination. In the case of a double-sided solar cell, it is applied so as to receive light on which both sides act. In such cases, the surface or front side is the surface or side that is applied to receive the greatest proportion of light or illumination. The back surface, back side, back surface, or back side of the solar cell is a surface or side that faces the surface. The front side of the substrate is the side of the substrate corresponding to the front side of the solar cell, and the back side or back side of the substrate corresponds to the back side of the solar cell.

  In the context of the present disclosure, the fingers are relatively narrow conductive lines, for example having a width of about 10 to 150 micrometers, which are generally distributed over the cell region and the underlying semiconductor Collect the (photogenerated) current from The fingers can carry photogenerated current to at least one bus bar. In a preferred embodiment, the finger lines are defined by parallel, sidewall longitudinal sidewalls. In certain embodiments, the sidewalls in the longitudinal direction of the sidewalls may form a tapered (tilted) structure. The tapered structure may be relatively narrow and have a relatively wide end. The relatively narrow end may go away from the bus bar, i.e. correspond to the free end of the finger line.

  A busbar is a metallized region that is essentially wider than a finger (eg, having a width in the range of about 1 mm to 3 mm), collects (photogenerated) current from the finger, and makes the cell a cell interconnect material (eg, an interconnect ribbon). Used to solder). In the context of this disclosure, the free end of a finger refers to the end of the finger (line) that is not directly physically connected to the bus bar. In other aspects, the free ends are viewed as the ends pointing away from the bus bars or as the ends away from the respective bus bars.

  In the context of this disclosure, finger lines and bus bars are generally formed simultaneously, for example by means of one metallization (plating) process. They are thus generally formed in one metallized layer and are referred to as different, non-overlapping parts of such a metallized layer.

Processes for forming interconnect ribbons on bus bars are known to those skilled in the art. Ribbons typically include a copper strip containing tin-lead solder that covers both sides of the ribbon. This process is, for example,
Applying flux to the bus bar and cleaning the surface;
Placing a ribbon on the bus bar;
For example, using a soldering iron and soldering the ribbon to the underlying metal pattern at a temperature of 325 ° C., for example. For example, the soldering step is performed by providing a set of soldered (eg, five) spots each along the bus bar, preferably about 1 cm long, for example, so that the spots have equal distances. be able to.

  The present disclosure further shows an example in which the contact on the front side of the silicon solar cell is formed by means of metal plating. However, the present disclosure is not limited to this. The method according to embodiments of the present disclosure can be used to form contacts on the back side of a silicon solar cell, such as a double-sided battery, or on the back side of a back contact cell, such as an interdigitated back contact cell Can be used to form contacts.

  For example, in a silicon solar cell manufacturing process in which a front contact is formed by metal plating such as Cu plating, it is a problem to achieve good adhesion between a patterned plated metal layer and a silicon substrate. Poor adhesion between the metal pattern and the silicon substrate results in peeling of the metal pattern, resulting in an unacceptable reduction in solar cell efficiency. A typical front contact pattern for solar cells includes a plurality of relatively narrow metal lines (fingers), each finger being electrically connected to at least one wider metal line, for example as shown in FIG. The Alternatively, the front contact pattern may be busbar-free and the narrow metal fingers may be electrically connected to the interconnect ribbon via a conductive adhesive. The risk of metal pattern stripping is generally higher for narrow metal fingers. This is related to the fact that the narrower metal fingers have a relatively smaller metal-silicon contact area. Narrower lines, such as thicker plating layers with increasing stress in metals such as Cu (in relation to chemistry and / or deposition rate), and longer metal lines increase the risk of delamination . Therefore, for example in solar cells, the problem of metal stripping will be higher at narrow fingers than at wider bus bars.

  In one form of the invention, the present disclosure reduces the risk of delamination of patterned metal contacts compared to existing methods and / or improves the adhesion of metal ribbons soldered to busbars compared to existing methods. A method for producing a solar cell having a plated metal contact is provided.

  The present disclosure is further described for specific examples in which the plated metal layer is part of a metallization pattern on the front side of a silicon solar cell. However, the present disclosure is not so limited and the method can be used for other applications, such as, for example, a plated metal layer that is part of the backside metallization of a double sided solar cell or a back contact solar cell. .

  FIG. 1 shows an example of a metallization pattern on the front side of a solar cell. In the example shown, the metallization pattern includes two bus bars 100 and a plurality of fingers 101, 102, 103. However, the present disclosure is not limited to this, and other suitable metallization patterns known to those skilled in the art can be used. In the example shown in FIG. 1, each finger 101, 102, 103 is connected to at least one bus bar 100 at the finger end 12. The fingers 101, 103 have a free end 11 and an opposite end 12 connected to the bus bar 100. The finger 102 has both ends 12 connected to the bus bar 100.

  A method according to one embodiment may include providing a first anchoring element or anchoring element at the free end 11 of the finger of the metallization pattern of the solar cell. It has been surprisingly found that providing such a first anchoring element at the free end of the finger substantially reduces the risk of delamination. The method may include the step of forming a second anchoring element or anchoring element physically connected to the bus bar 100 at the finger end 12. It has been surprisingly found that forming such a second fastening element can improve the adhesion of the ribbon soldered to the bus bar.

  In one aspect of the invention, the present disclosure has a pattern having a plated metal contact that includes a plurality of metal fingers, the metal pattern further including, for example, a fixed line or a fixed line at a free end of the plurality of metal fingers. A solar cell comprising such a first anchoring element or anchoring element is provided.

  In one aspect of the invention, the present disclosure has a plated metal contact pattern including a plurality of fingers and at least one bus bar, the metal contact pattern further comprising a second physically connected to the bus bar at the finger ends. A solar cell comprising a fixing element or an anchoring element is provided.

  In a method of making a silicon solar cell with a plated front contact, generally an anti-reflective coating is first formed on the surface and then partially by means of laser cutting where a metal contact needs to be formed. Removed. The width of the laser aperture is generally in the range of about 5 to 50 micrometers, for example on the order of about 10 micrometers at the location where the contact fingers are formed. Next, metal contacts having a plating metal layer thickness in the range of about 5 micrometers to 35 micrometers, for example about 10 micrometers, are formed in the opening by means of metal plating. For example, using a 10 micrometer laser aperture and a 10 micrometer metal film thickness, only about 10 micrometers connect to silicon, with a typical width of about 30 micrometers (due to lateral overlap) Plating line (finger). The remaining part is plated on the anti-reflective coating, but here the adhesion is very poor, i.e. much worse than the possible adhesion of the finger lines to the silicon substrate.

  One approach used to improve finger adhesion is to form wider laser lines, which leads to increased shading loss. Instead, the plating thickness can be reduced, but has the disadvantage of reduced finger conductivity.

  In the method according to the present disclosure, finger adhesion is improved without limiting the increase in shadow loss only and reducing finger conductivity.

  In the method of the present disclosure, a first securing element or anchoring element is formed at the free end of each of the plurality of fingers. It has been surprisingly found that this is sufficient to substantially improve finger adhesion and substantially reduce peeling.

  In one form, the first securing element can partially increase the width of the fingers 101, 103 at the finger end 11. For example, partially increasing the finger width FW includes increasing the finger width from about 2 to 5 times, such as about 3 times, and the increased width is referred to as PW. However, the present disclosure is not limited to this. The width of the finger, when measured from the edge of the finger end, increases beyond a length PL in the range of about 5% to 50% of the finger length FL, eg about 10% to 30% of the finger length. However, the present disclosure is not limited to this. An example of a front side metallization pattern having a first fixing element 21 formed by partially increasing the finger width at the free end 11 is schematically shown in FIGS. FIG. 6 shows the details of FIG.

  In order to show improved results when using a finger having a first anchoring element according to the form of the present disclosure, compared to a common advanced technology finger with a fixed width and no anchoring element A tape peel test was performed. These Scotch tape peel tests were performed on cells containing 18 finger lines on either side of the central bus bar. Scotch tape is provided parallel to the fingers so as to extend from end to end of each cell of the bus bar (so as not to cover any part of the bus bar itself), thereby covering each 18 finger. Subsequently, the scotch tape was removed (peeled). Next, the number of finger lines peeled from the substrate by the process was counted. The process was repeated on the left and right sides of the bus bar. This is repeated for two solar cells including a state-of-the-art finger line and two solar cells including a finger line according to an embodiment of the invention in which a fixing element is formed only at the free end of the finger line. It was. Furthermore, it carried out similarly with four solar cells. Table 1 shows the results. It will be apparent to those skilled in the art that the adhesion of the plated metal finger lines to the underlying silicon substrate has been clearly improved. This is also supported quantitatively by the large difference in the average number of peeled finger lines between the state of the art and embodiments of the present invention.

表１：比較結果

Table 1: Comparison results

  FIG. 6 further shows that the finger lines are preferably defined by parallel longitudinal sidewalls. In the first part of the finger 101, called part I, the finger width PW is larger and is defined by a set of parallel sidewalls 211. In a second part, directly adjacent to and physically connected to the busbar or ribbon, referred to as part II, the fingers with FW are relatively small and are surrounded by a set of parallel sidewalls 1011. The transition part is a step type as shown. Alternatively, the transition portion may be more gradual. The transition portion may then include a transition structure corresponding to the transition region, for example, where the finger width gradually changes from the width FW to the width PL.

  Furthermore, one or both of the first part I and the second part II of the finger line may have a tapered structure. For example, the second portion II is tapered, and the narrower side of each tapered structure may point away from the bus bar or far from the bus bar.

  In other forms, the first securing element may include an element having a linear, square, rectangular, polygonal, circular, or elliptical shape, or other suitable shape, which element is at the free finger end 11. It is formed. An example is shown schematically in FIG. 3 and shows a finger end having a different first securing element 21. The first fastening element 21 is a fastening line, and the longitudinal direction of the fastening line may be parallel to the longitudinal direction of the fingers (corresponding to a partial increase in finger width as shown in FIG. 2), or The longitudinal direction of the fixing line may be substantially perpendicular to the longitudinal direction of the fingers or may be at a suitable angle with respect to the longitudinal direction of the fingers. Forming the first anchoring element according to the present disclosure is advantageous in that it substantially improves finger adhesion while not significantly increasing shadow losses or reducing finger conductivity.

  More generally, any element or shape that leads to a partial increase in contact area between the finger at the free end 11 of the finger and the underlying silicon may be used as the first securing element 21. good.

  In the method according to the present disclosure, the second fixing element or the fixing element may be formed to be physically connected to at least one bus bar at the finger end. Such a second fastening element on the bus bar side improves the adhesion of the ribbon soldered to the bus bar. This improvement may be related to the ribbon solder process, where the solder flow to the fixation element results in increased solder contact area and thereby better adhesion.

  In one form, the second securing element may be formed by physically connecting to the bus bar and partially increasing the width of the fingers 101, 102, 103 at the finger ends 12. For example, partially increasing the finger width includes increasing the finger width from about 2 to 5 times, such as about 3 times. However, the present disclosure is not limited to this. The width of the fingers may increase beyond a length in the range of about 5% to 50%, for example between about 10% and 30%, but the invention is not so limited. An example of a front side metallization pattern having a second fastening element 22 formed by partially increasing the finger width at the finger end 12 is schematically shown in FIG.

  In other embodiments, the second securing element includes an element having a linear, square, rectangular, polygonal, circular, or elliptical shape, or other suitable shape, which element is adjacent to the finger end of the bus bar 100. It may be formed in the portion 12. An example is shown schematically in FIG. 5 and shows a finger end 12 connected to the bus bar 100 having a different second securing element 22. The second fastening element 22 is a fastening line, the longitudinal direction of the fastening line may be parallel to the longitudinal direction of the fingers (corresponding to a partial increase in finger width, as shown in FIG. 4) or fixed. The longitudinal direction of the line may be substantially perpendicular to the longitudinal direction of the fingers or at a suitable angle with respect to the longitudinal direction of the fingers. Forming the second anchoring element according to the present disclosure has the advantage of substantially improving finger adhesion while not significantly increasing shadow losses or reducing finger conductivity.

  More generally, at the end 12 of the finger physically connected to the bus bar 100, any element or shape that leads to a partial increase in contact area between the finger and the underlying silicon is the second fixed. It may be used as element 22.

  A wider fixed line deformation only in the vicinity of the bus bar will extend the wider line from the bus bar to about one-half of the length of the entire finger line. This has a metallization scheme that is used to maintain the same solar cell efficiency while having a higher specific contact resistance (such as for the lower surface doping level of silicon in the contact). The advantages of enabling and increasing the overall connection area to silicon and adjusting the optimal copper film thickness to lower the minimum resistance power loss, thereby reducing the required plating time Have.

  A method according to embodiments of the present disclosure may include forming a metallization pattern including a first securing element at a free end and a second securing element at an end of a finger connected to the bus bar.

  The foregoing description details certain specific examples of the disclosure. However, it will be appreciated that the present disclosure can be implemented in many ways, no matter how detailed the foregoing is set forth in the text. It should be noted that the use of a particular term when describing a given feature or form of the present disclosure includes the particular feature of any of the disclosed features or forms to which the term pertains here. It should not be taken to imply being redefined.

  Although the above detailed description shows, describes, and points out novel features of the present invention that have been applied in various forms, there are many omissions, substitutions, and changes in the form and detail of the described device or process. It will be understood that this can be done by those skilled in the art without departing from the spirit of the invention.

Claims (14)

  A method of manufacturing a solar cell, comprising: forming a plated metal contact having a contact pattern including a plurality of fingers and at least one first fixing element at a free end of each of the plurality of fingers.   Having a contact pattern including at least one bus bar, a plurality of fingers connected to the at least one bus bar, and at least one second securing element at a finger end physically connected to the at least one bus bar. The method according to claim 1, comprising the step of forming a plated metal contact.   3. The method according to claim 2, comprising forming a second securing element at each finger end physically connected to at least one bus bar.   The method according to claim 1, further comprising the step of soldering the ribbon to at least one contact pattern. And forming a dielectric layer on the entire surface of the silicon substrate;
Partially removing the dielectric layer, thereby exposing the underlying silicon surface in a portion where a metal contact needs to be formed according to the contact pattern of any of claims 1 to 4;
Forming a metal contact in a silicon region exposed by metal plating to form a front metal contact.   A solar cell comprising a plated metal contact having a contact pattern comprising a plurality of fingers and at least one first securing element or anchoring element at a free end of each of the plurality of fingers.   A contact including at least one bus bar, a plurality of fingers connected to the at least one bus bar, and at least one second securing or securing element at a finger end physically connected to the at least one bus bar The solar cell according to claim 6, comprising a plated metal contact having a pattern.   8. A solar cell according to claim 7, comprising a second fastening element at each finger end physically connected to at least one bus bar.   The method further comprises a substrate under the fingers, wherein the first securing element is shaped to partially increase the contact area between each finger and the substrate under the free end of the fingers. A solar cell according to any one of?   10. The solar cell according to claim 9, wherein the first securing element is embodied at the free finger end by a partial increase in finger width or comprises a partial increase in finger width.   Further, including a substrate under the fingers, the second securing element is shaped to partially increase the contact area between each finger and the substrate at the end of the finger connected to the bus bar. Item 10. A solar cell according to any one of Items 6 to 10.   The second securing element is embodied by a partial increase in the width of the finger at the end of the finger connected to the bus bar or comprises a partial increase in the width of the finger. Crab solar cell.   13. The finger width increases at a free finger end or finger end connected to a bus bar over a length ranging from 5% to 50% of the finger length. The solar cell described.   The solar cell according to any one of claims 6 to 13, wherein the first and / or second fixing element is linear, square, rectangular, polygonal, circular or elliptical.

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