TW201705239A - Methods for forming metal electrodes on silicon surfaces of opposite polarity - Google Patents

Abstract

A method is provided for concurrently forming a first metal electrode on an n-type region of a silicon substrate and a second metal electrode on a p-type region of the silicon substrate. The method comprises providing a silicon substrate comprising an n-type region and a p-type region, wherein the n-type region is exposed at a first substrate surface in a first area and wherein the p-type region is exposed at a second substrate surface in a second area; depositing an initial Ni layer on the substrate simultaneously in the first area and in the second area by performing a Ni immersion plating process; and depositing a further metal layer on the initial Ni layer in the first area and in the second area by performing an electroless metal plating process or by performing an immersion metal plating process.

Description

Method for forming a metal electrode on a reverse polarity surface of tantalum

This invention relates to the field of semiconductor processing. More specifically, the present invention relates to a plating-based method for forming metal electrodes on n-type regions and p-type regions of a germanium substrate in parallel or even simultaneously. Furthermore, the present invention relates to a method for manufacturing a photovoltaic cell, such as a double-sided photovoltaic cell, wherein the metal electrode is formed on the n-type germanium region and the p-type germanium region in parallel by plating or even simultaneously, and thus Get a photovoltaic battery.

Two important objectives of the photovoltaic industry are to improve photovoltaic cell and module efficiency and reduce battery and module manufacturing costs. One of the possible ways to improve the efficiency of photovoltaic cells and modules is to use double-sided photovoltaic cells. One possible way to reduce the cost of battery and module fabrication is to use less expensive metallized materials as an alternative to traditional metallization methods based on silver (Ag) paste.

One of the known alternatives to Ag-based metallization for forming metal electrodes for tantalum photovoltaic cells is based on Ni/Cu metallization. In this method, a thin nickel (Ni) layer is used to provide a low contact resistance to the low doped germanium region as a diffusion barrier of the main conductor (copper (Cu)) and as a crystal for forming the Cu layer. Layer. The Cu layer is used to provide a good electrical conductivity and, therefore, a low resistance of one of the metal electrodes. A typical process flow includes: providing a dielectric layer (eg, an anti-reflective coating) over the entire surface of the crucible; locally removing the dielectric layer to expose the underlying portion where the metal contact is to be provided矽 surface; and by metal The plating provides a metal contact at the exposed crucible region. Common methods for depositing this Ni/Cu stack are photoinduced plating, electroplating, and field induced plating. One of the disadvantages of such methods is that they require electrical contact with the substrate and they require an external current or voltage source and/or controlled illumination. To deposit the Ni layer, "electroless plating" can be used. For example, in electroless plating, an autocatalytic electroless plating technique can be used to deposit a nickel or nickel alloy layer, for example, by using a chemical reaction in an aqueous solution without applying an external power. However, one of the disadvantages of an electroless plating process is its poor thickness uniformity due to the tendency of non-uniform nucleation and Ni preferential plating on the most conductive regions. Also for depositing a Cu layer on top of the Ni seed layer, electroless plating can be used. However, electroless Cu plating is extremely slow (eg, ten times slower than plating) and requires more bath renewals, resulting in increased waste generation.

It is described in "Metallization improvement on fabrication of interdigitated backside and double sided buried contact solar cells" by Jiun-Hua Guo et al., Solar Energy Materials & Solar Cells 86 (2005), pp. 485-498. Impregnation of palladium chloride activates a process in which a nickel layer is nucleated on both the phosphorus and boron diffusion contact regions. However, this method requires an additional step for surface activation. In addition, the use of palladium leads to an increase in manufacturing costs. With this method, it is also difficult to avoid spurious plating or ghost plating.

It is an object of embodiments of the present invention to provide a good and efficient method for forming metal electrodes on an n-type region and a p-type region of a germanium substrate in parallel.

The above object is achieved by a method according to the invention.

An advantage of an embodiment of the present invention is to provide a metal electrode (such as to form a good one) on a n-type region and a p-type region of a germanium substrate in parallel (for example, simultaneously) by performing a plating process. Method of thickness uniformity of metal electrodes).

An advantage of an embodiment of the present invention is to provide a metal electrode for forming a metal electrode on an n-type region and a p-type region of a germanium substrate in parallel (for example, simultaneously) by performing a plating process. The method wherein the metal electrode is free of copper (Cu).

An advantage of an embodiment of the present invention is to provide a method for forming a metal electrode on an n-type region and a p-type region of a germanium substrate in parallel (for example, simultaneously) by performing a plating process, wherein Known methods for forming metal electrodes can reduce costs.

An advantage of an embodiment of the present invention is to provide a method for forming a metal electrode on an n-type region and a p-type region of a germanium substrate in parallel (for example, simultaneously) by performing a plating process without the need for the plating process. An electrical contact or a physical contact is provided to the substrate during the process and/or a method of providing controlled illumination during the plating process is not required.

In a first aspect, embodiments of the present invention are directed to a method for forming a first metal electrode on one of n-type regions of a germanium substrate in parallel (eg, simultaneously) and p-type one of the germanium substrates A method of forming a second metal electrode on a region. The method includes providing a substrate including a substrate including an n-type region and a p-type region, wherein the n-type region is exposed to a first region at a substrate surface, and wherein the p-type region Exposure to a second region at the surface of a substrate. The method further includes: simultaneously depositing an initial nickel (Ni) layer on the first region and the second region on the surface of the substrate by performing a nickel (Ni) immersion plating process; and by performing a A further metal layer is deposited on the initial nickel (Ni) layer in the first region and the second region by an electroless metal plating process or by performing an immersion metal plating process or a combination of the two.

In a method according to an embodiment of the present invention, the step of depositing the further metal layer may include simultaneously depositing the further metal layer on the initial nickel (Ni) layer in the first region and the second region.

In one method in accordance with an embodiment of the present invention, depositing the further metal layer can include depositing a further layer of nickel by performing an electroless nickel plating process.

In a method according to an embodiment of the present invention, the step of depositing the further metal layer may comprise a sequence of one of the following steps: depositing a further metal layer on the initial nickel layer in the first region; Perform a nickel immersion plating process and a further nickel Depositing a layer in the second region; and depositing the further metal layer on the further nickel layer in the first region and the second region.

In a method according to an embodiment of the present invention, the step of depositing the further metal layer may comprise the sequence of: depositing a first nickel layer into the first region by performing an electroless nickel plating process Depositing a second further nickel layer in the second region by performing a nickel immersion plating process; and performing a third electroless nickel plating process to perform a third further nickel A layer is deposited on the first further nickel layer in the first region and on the second further nickel layer in the second region. Moreover, in this method, the step of depositing the initial nickel layer can have a program step duration in the range of 15 seconds to 60 seconds (e.g., 40 seconds to 50 seconds, such as 30 seconds).

In a method according to an embodiment of the present invention, the initial Ni layer may have, for example, a thickness in a range between 4 nm and 2 μm, but embodiments of the invention are not limited thereto.

In a method according to an embodiment of the present invention, depositing the further metal layer on the initial Ni layer may include, for example, depositing a further Ni layer by performing an electroless Ni plating process or performing an electroless Ag plating An Ag layer is deposited by a coating process or an immersion Ag plating process.

In a method according to an embodiment of the invention, the first region and the second region may be positioned at the same substrate side, such as at the same substrate surface. In one method according to an embodiment of the invention, the first region and the second region can be positioned at opposite sides (eg, opposite surfaces) of the substrate.

In a method according to an embodiment of the present invention, wherein depositing the further metal layer on the initial Ni layer comprises depositing a further Ni layer, a solderable cap layer may be provided on the further Ni layer. The solderable cap layer may, for example, be, for example, a thin silver (Ag) layer having a thickness in a range between 150 nm and 350 nm, although embodiments of the invention are not limited thereto. The thin Ag layer can be deposited on top of the further Ni layer, for example by performing an Ag dip coating process.

One of the advantages of providing such a thin Ag layer on the Ni layer is that it substantially increases the conductivity of the first metal electrode and the second metal electrode. As an alternative to a thin Ag layer, the solderable cap layer can be, for example, a thin Sn layer or an organic cap layer.

A method according to an embodiment of the present invention may further include, after the initial Ni layer has been deposited or after the further metal layer has been deposited, for example, at a temperature in the range of 250 ° C to 400 ° C An annealing or sintering step is performed whereby the metal-helium contact resistance is reduced.

In a method according to an embodiment of the present invention, the providing the substrate may include: providing a substrate including an n-type region and a p-type region; providing a dielectric layer on at least one surface of the germanium substrate; The dielectric layer is removed from the first region and the second region of the substrate, thereby exposing one surface of the germanium substrate in the first region and the second region.

It is advantageous to use in parallel to (eg, simultaneously) a substrate in accordance with an embodiment of the present invention in a manufacturing process of a photovoltaic cell, such as, for example, a double-sided photovoltaic cell or a back-contact photovoltaic cell. A method of forming a first metal electrode on one of the n-type regions and forming a second metal electrode on one of the p-type regions of the germanium substrate. For example, embodiments of the present invention may also be directed to a method of fabricating a photovoltaic cell, such as, for example, a double-sided photovoltaic cell or a back-contact photovoltaic cell, wherein the method of fabrication includes the first in accordance with the present invention The embodiment of the invention in parallel forms a first metal electrode on one of the n-type regions of the germanium substrate and a second metal electrode on one of the p-type regions of the germanium substrate. For example, the manufacturing method may include: providing one of the photovoltaic cells of the photovoltaic cell to be fabricated; and applying the first metal electrode and the second metal respectively on one of the n-type region and the p-type region of the germanium substrate This step of the electrode.

An advantage of one of the methods according to an embodiment of the present invention is that it allows parallelism on surfaces of opposite polarities (e.g., simultaneously on one of the p-doped regions of a germanium substrate and on one of the n-doped regions) A metal electrode having a good thickness uniformity is formed. For example, using other plating methods known in the art (such as light induced plating or field temptation) Guide plating), it is not possible to deposit a metal directly on the n-type germanium region and the p-type germanium region in parallel or simultaneously. For example, photoinduced plating can only be used to metallize n-type regions and not for metallization of p-type regions, while field-induced plating can only be used to metallize p-type regions and not for metallization of n-type regions.

An advantage of one of the methods according to an embodiment of the present invention is that one of the first region and the second region having a good thickness uniformity can be obtained by using an immersion plating process for forming the initial Ni layer. Full coverage. The step of thickening the initial Ni layer by depositing a further metal layer by electroless plating or immersion plating is substantially independent of the polarity of the surface of the germanium substrate underlying the initial Ni layer.

A method in accordance with an embodiment of the present invention can be advantageously used to provide metal electrodes (e.g., metal fingers) to a busbarless photovoltaic cell. These bus-free photovoltaic cells can be further contacted and/or interconnected by soldering a plurality of electrical leads to the metal electrodes after completion of the battery manufacturing process. These electrical wires replace the bus bars of a conventional photovoltaic cell and are provided for collecting a current from the metal electrode of the cell. The plurality of electrical leads are provided after battery processing (e.g., during a module manufacturing process), such as, for example, 10 to 50 metal wires.

For example, embodiments of the present invention may also be directed to a method of fabricating a bus barless photovoltaic cell, wherein the method of fabrication includes paralleling one of the n-type substrates in accordance with an embodiment of the first aspect of the present invention. Forming a first metal electrode on the region and forming a second metal electrode (such as) on one of the p-type regions of the germanium substrate to form a metal finger of the bus barless photovoltaic cell.

One advantage of such a bus bar photovoltaic cell is that the conductivity of the metal electrode can be lower compared to a "standard" or conventional photovoltaic cell that typically has three to five bus bars. Therefore, a metal having a conductivity lower than that of Ag or Cu such as Ni can be used to form an electrode of a busbar-free battery without significantly increasing the risk of the resistance of the metallization pattern. An additional advantage is that Ni is one of the materials that is less expensive than Ag or Cu. In a preferred embodiment, for example by dipping Ag plating is applied to provide a thin Ag layer on top of the Ni layer to enable the metal wire to be soldered to the metal electrode and further improve the conductivity of the metal electrode. The thickness of this Ag layer can be, for example, in the range between 150 nm and 350 nm, such as about 250 nm.

Alternatively, for such a bus bar photovoltaic cell, one of the metals having a good conductivity, such as Ag, may be used to form the electrode, for example to form the further metal layer on an initial Ni layer, as compared to conventional One of the thicknesses required for the "standard" photovoltaic cells of three to five bus bars, the busbarless photovoltaic cells have a reduced thickness. One of the advantages of this reduced thickness is that it results in a cost reduction.

An advantage of one of the methods according to one embodiment of the invention is that the metal electrode can be free of Cu. It is known that in a photovoltaic cell having a Ni/Cu electrode, there is a risk that Cu penetrates into the underlying layer from the Ni layer, which may result in degradation of the device and a decrease in battery efficiency. One of the advantages of the Cu-free metal electrode is to avoid the risk of degradation of the battery due to the diffusion of Cu into the underlying crucible, resulting in improved long-term reliability of one of the photovoltaic cells. The use of a Cu-free electrode can also result in a cost reduction.

One advantage of one of the methods in accordance with an embodiment of the present invention is that a metal electrode can be provided without the need to provide an electrical contact or a physical contact to the substrate during the plating process and without providing controlled illumination during the plating process.

One advantage of one of the methods in accordance with an embodiment of the present invention is that the metal electrode can be provided without false plating (e.g., where a metal is not deposited at an undesirable location on the surface of the crucible).

A method according to an embodiment of the present invention may be advantageously used to provide a metal electrode to a double-sided photovoltaic cell or a back-contact photovoltaic cell, but embodiments of the invention are not limited thereto.

One of the advantages of one of the methods according to an embodiment of the present invention is that the photovoltaic cell shielding or shielding loss can be reduced compared to a "standard" photovoltaic cell, since the conventional bus bar can be substantially narrower than the confluence Replace the conductive line of the strip. This reduction in shadow loss results in electricity One of the pool efficiencies increases.

One advantage of one of the methods in accordance with an embodiment of the present invention is that it allows a large number of wafers to be processed in batches with relatively inexpensive tools having one of the small footprints.

Certain objects and advantages of various aspects of the invention have been described above. Of course, it is to be understood that not all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that a <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; Or the invention is practiced. In addition, it should be understood that the present invention is not intended to limit the scope of the invention. The present invention (with respect to both operational organization and methods), as well as features and advantages thereof, may be best understood by referring to the following detailed description when read in the claims.

Particular aspects and preferred aspects of the invention are set forth in the accompanying independent technical solutions and the accompanying claims. The features from the subsidiary technical solutions may be combined with the features of the independent technical solutions and the features of other subsidiary technical solutions, and not only as explicitly stated in the technical solutions.

These and other aspects of the invention will be apparent from and elucidated with reference to the <RTIgt;

1‧‧‧First area

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11‧‧‧n type area

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20‧‧‧Substrate

21‧‧‧ substrate surface

22‧‧‧Substrate surface

31‧‧‧First metal electrode

32‧‧‧Second metal electrode

33‧‧‧Initial Nickel Ni Layer

34‧‧‧ Further metal layer/further Ni layer

100‧‧‧ method

101‧‧‧Steps

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200‧‧‧ procedure

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1 is a schematic illustration of the procedural steps of an exemplary method for forming metal electrodes on one surface of one of the n-type regions and one of the p-type regions of a germanium substrate in parallel, in accordance with an embodiment of the present invention.

2 is a schematic diagram showing the procedural steps of an exemplary manufacturing process for fabricating a double-sided photovoltaic cell in accordance with an embodiment of the present invention, wherein a front side of the cell and the battery are provided using a metallization process based on plating Metal electrode at the back side.

3 shows the measured thickness of the Ni layer provided on the initial Ni layer by electroless plating, which varies according to the thickness of the initial immersion plating Ni layer on one of the p-type germanium region and the n-type germanium region. A first example for illustrating features and aspects of a method in accordance with an embodiment of the present invention.

4 shows one of the measured thicknesses of the Ni layer provided on the initial Ni layer by electroless plating, which varies according to the thickness of the initial immersion plating Ni layer on one of the p-type germanium region and the n-type germanium region. Examples for illustrating features and aspects of a method in accordance with an embodiment of the present invention.

Figure 5 shows the results of solder tab adhesion measurements of metal electrodes provided on an n-type region by a method in accordance with one embodiment of the present invention, varying from the concentration of NH ₄ F in the immersion Ni plating bath.

Figure 6 shows the results of solder tab adhesion measurements of metal electrodes provided on a p-type region by a method according to one embodiment of the present invention, varying from the concentration of NH ₄ F in the immersion Ni plating bath.

Figure 7 shows schematically a p-type region having one of the n-type regions exposed in a first region at a first substrate surface and one of the second regions exposed at a second substrate surface (the first region And an example of a cross-section of a substrate of the second region positioned at an opposite side of the substrate to illustrate features and properties of embodiments of the present invention.

Figure 8 is a schematic illustration of one p-type region having one of the first regions in a first region exposed to a first substrate surface and one of the second regions exposed to one of the second substrate surfaces (the first An example of a cross section of a substrate of the region and the second region positioned at the same side of the substrate to illustrate features and properties of embodiments of the present invention.

Figure 9 is a schematic illustration of the structure of Figure 7 after forming a first metal electrode and a second metal electrode by a method in accordance with an embodiment of the present invention.

Figure 10 is a schematic illustration of the structure of Figure 8 after forming a first metal electrode and a second metal electrode by a method in accordance with an embodiment of the present invention.

11 illustrates another exemplary method in accordance with an embodiment of the present invention.

Any reference signs in the patent application should not be construed as limiting the invention. category.

In the different figures, the same reference symbols refer to the same or similar elements.

The drawings are merely illustrative and not limiting. In the drawings, the size of some elements may be exaggerated and not to scale.

The invention will be described with reference to a particular embodiment and with reference to certain drawings, but the invention is not limited thereto The drawings are only schematic and are non-limiting. In the drawings, the size of some elements may be exaggerated and not drawn to scale. The dimensions and relative dimensions do not correspond to the actual degree of reduction of the practice of the invention.

In addition, the terms first, second, and the like are used in the context of the description and the scope of the claims, and are not intended to be used to describe a sequence in time, space, order, or in any other manner. It is understood that the terms so used are interchangeable under the appropriate circumstances and the embodiments of the invention described herein are capable of operation in other sequences than those described or illustrated herein.

Moreover, the terms top, bottom, over, under, and the like in the description and claims are for the purpose of description and are not necessarily used to describe the relative position. It is understood that the terms so used are interchangeable under the appropriate circumstances and the embodiments of the invention described herein are capable of operation in other aspects than those described or illustrated herein.

It should be noted that the term "comprising", used in the context of the claims, is not to be construed as limited. Thus, the term "comprise" or "an" Group. Therefore, the scope of expressing "a device including components A and B" should not be limited to devices consisting only of components A and B. This means that with respect to the invention, the relevant components of the device are only A and B.

Reference throughout the specification to "an embodiment" or "an embodiment" means a knot A particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment of the invention. The appearances of the phrase "in an embodiment" or "in an embodiment" are not necessarily all referring to the same embodiment, but may refer to the same embodiment. In addition, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Similarly, in the description of the exemplary embodiments of the present invention, in order to simplify the present invention and to assist in understanding one or more of the various aspects of the present invention, various features of the present invention are sometimes combined in a single In the examples, figures or description. However, this method of the invention should not be construed as reflecting the following intent: the invention requires more features than those explicitly recited in each claim. Rather, as the following claims reflect, the invention is characterized by a less than a single feature of the single disclosed embodiments. Therefore, the scope of the patent application following the embodiments is explicitly incorporated into this embodiment, each of which is independently a separate embodiment of the invention.

In addition, although some of the embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are intended to fall within the scope of the invention and form different embodiments. The technician will understand. For example, in the scope of the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth in the description However, it is understood that the embodiments of the invention may be practiced without the specific details. In other instances, well-known methods, structures, and techniques are not shown in detail to avoid obscuring the understanding of the description.

In the context of the embodiments provided below, a front surface or front side of a photovoltaic cell or a photovoltaic module is adapted to be oriented toward a source and thus for receiving a surface or side of illumination. In the case of a double-sided photovoltaic cell or module, the two surfaces are adapted to receive illumination. In this case, the front or front side is adapted to receive the surface or side of the largest portion of the light or illumination. a photovoltaic cell or a photovoltaic module The back surface, the back surface, the back side or the back side is a surface or side opposite the front surface or the front side.

In the context of the embodiments provided below, a bus bar is used to collect a current from a plurality of metal contacts or metal electrodes provided on one surface of a photovoltaic cell (eg, one under illumination) Conductive strip of current). A bus bar is provided for direct electrical connection to an external electrical conductor. A bus bar typically collects current from thinner or narrower metal contacts (also known as metal fingers) on the battery. These thinner or narrower metal contacts collect a current from the battery and deliver the current to the bus bar; these are typically not provided for direct electrical connection to an external electrical conductor.

In the context of the embodiments provided below, a busbarless photovoltaic cell does not have a photovoltaic cell. A busbarless photovoltaic cell typically includes a plurality of metal contacts or metal electrodes on one surface of the cell, but after the cell is fabricated, the cell does not include a conductive element for collecting current from the plurality of metal contacts. . After the battery processing is completed, for example, during module fabrication, a conductive element, such as, for example, a conductive wire, is soldered to the plurality of metal contacts. The conductive elements are provided for collecting a current from the plurality of metal electrodes and the like can replace the conventional bus bars.

The present invention provides a surface and a p-type region (or a plurality of p-type regions) for one of n-type regions (or a plurality of n-type regions) on a substrate having a good uniformity in parallel (for example, simultaneously) A method of forming a metal electrode on one of the surfaces. In a particularly advantageous embodiment of the invention, the metal electrodes may be free of copper (Cu). Moreover, the method can be based on a plating procedure in which no electrical or physical contact is required to the germanium substrate during plating, and wherein no controlled illumination is required during plating. This method is compatible with high volume batch processing.

In a first aspect, embodiments of the present invention provide a first region in a surface of one of an n-type germanium region (or a plurality of n-type germanium regions) in parallel (for example, such as simultaneously) ( Or a plurality of first regions forming a first metal electrode (or a plurality of first metal electrodes) and a second region (or a plurality of regions) on a surface of one of the p-type germanium regions (or the plurality of p-type germanium regions) A method of forming a second metal electrode (or a plurality of second metal electrodes) in the second region).

FIG. 1 schematically illustrates the steps of a method 100 in accordance with an embodiment of the present invention. The method includes providing 101 a substrate comprising a substrate. The germanium substrate has an n-type region exposed in a first region at a surface of the first substrate and a p-type region in a second region exposed at a surface of the second substrate.

An example of a substrate 20 that can be used in embodiments of the present invention is schematically illustrated in Figures 7 and 8. 7 shows an example of a cross section of a substrate 20 including a substrate 10 having an n-type region 11 exposed in a first region 1 at a substrate surface 21, the ruthenium substrate 10 further A p-type region 12 is disclosed that is exposed to one of the second regions 2 at a substrate surface 22. In the example shown in FIG. 7, the first region 1 and the second region 2 are positioned at opposite sides or opposite surfaces 21 and 22 of the ruthenium substrate 10. 8 shows an example of a cross section of a substrate 20 including a substrate 10 having an n-type region 11 exposed in a first region 1 at a substrate surface 21, the ruthenium substrate 10 further A p-type region 12 of one of the second regions 2 exposed at a substrate surface 21 is included. In the example shown in FIG. 8, the first region 1 and the second region 2 are positioned on the same side or the same surface 21 of one of the ruthenium substrates 10.

In a region where the n-type region 11 and the p-type region 12 are not exposed, a layer 13 such as a dielectric layer may be present on the substrate surfaces 21, 22. Figures 7 and 8 show a single n-type region and a single p-type region. However, embodiments of the invention are not limited thereto. In an embodiment of the invention, the germanium substrate may comprise a plurality of p-type regions and/or a plurality of n-type regions on which metal electrodes are formed simultaneously or in parallel.

9 and 10 show that a first metal electrode 31 can be formed in the first region 1 and a second metal electrode 32 can be formed in the second region 2, as provided by one of the embodiments of the present invention. The respective structures correspond to the exemplary structures of the exemplary substrates illustrated in FIGS. 7 and 8. In the illustrated example, according to an embodiment of the present invention, the first metal electrode 31 and the second metal electrode 32 include one of an initial Ni layer 33 and a top portion of the initial Ni layer 33 formed by Ni immersion plating. One of the further metal layers 34 is stacked.

In the method illustrated in FIG. 1, an initial nickel (Ni) layer 33 is simultaneously deposited 102 on the substrate by an immersion plating process (also referred to as a galvanic displacement plating process). The first region 1 and the second region 2 on the surface or surface(s) of the substrate. Then, the initial Ni layer 33 is thickened by depositing 103 a further metal layer 34 on the initial Ni layer 33. In particular, in one method in accordance with an embodiment of the present invention, the step of depositing the further metal layer may include simultaneously depositing the further metal layer on the initial Ni layer in the first region and the second region.

However, in another method in accordance with an embodiment of the present invention, the step of depositing the further metal layer may be performed in a plurality of steps, wherein at least one of the first steps is directed to depositing the further metal layer primarily in the first On the initial Ni layer in a region, and at least a second such step is directed to depositing the further metal layer primarily on the initial Ni layer in the second region. For example, the step of depositing the further metal layer can include depositing the further metal layer on the initial nickel layer in the first region, for example, without depositing any further metal in the second region, for example No significant or substantial mass of the further metal is deposited in the second region. Thereafter, a further nickel layer can be deposited in the second region, for example, by performing a nickel immersion plating process (eg, by repeating a nickel plating procedure similar to or the same as applied to depositing the initial nickel layer). And subsequently depositing the further metal layer on the initial nickel layer and/or the further nickel layer in the first region and in the second region.

Depositing further metal layer 34 (eg, a further Ni layer or a silver (Ag) layer) can be accomplished by performing an electroless metal plating process (eg, an electroless Ni plating process or an electroless Ag plating process) .

In other embodiments, depositing 103 further metal layer 34 (eg, an Ag layer) can be accomplished by performing an immersion metal plating process (eg, an immersion Ag plating process).

In other embodiments, depositing a further metal layer 34 (eg, a nickel layer or a silver layer) may be performed by performing at least one electroless metal plating process and at least one immersion plating process. to make.

In embodiments in which the further metal layer 34 is a further Ni layer, the further Ni layer 34 may be covered with an additional layer (such as a thin dip-plated Ag or Sn layer or an organic cap layer), for example to improve solderability. Sex. One of the advantages of covering the further Ni layer 34 with, for example, a thin immersion-plated Ag layer having a thickness in a range between 150 nm and 350 nm is that it results in increased conductivity of one of the first metal electrode and the second metal electrode. . In the embodiment in which the further metal layer 34 is an Ag layer, it is not necessary to provide an additional layer to improve solderability or to improve the conductivity of the first metal electrode and the second metal electrode.

A method in accordance with an embodiment of the present invention can be advantageously used to provide a metal electrode to a busbarless photovoltaic cell wherein a plurality of electrically conductive wires are connected (e.g., soldered) to the metal electrode after fabrication of the cell.

Accordingly, embodiments of the present invention may be directed to a method of fabricating a busbarless photovoltaic cell, wherein the method of fabricating includes forming a first on an n-type region of a germanium substrate in accordance with an embodiment of the present invention. A metal electrode and a second metal electrode (for example, such as) formed on one of the p-type regions of the germanium substrate to form a metal finger of the bus barless photovoltaic cell.

Using this method, the desired conductivity of a metal electrode (e.g., metal fingers) can be lower than that of a conventional photovoltaic cell typically having three to five bus bars. Therefore, a metal having a conductivity lower than that of Ag or Cu, such as Ni, can be used to form the metal electrode without increasing the risk of one of the series resistances of the battery without risking a decrease in the fill factor of the battery.

In one method in accordance with an embodiment of the present invention, an initial Ni layer 33 may first be deposited 102 by a dip Ni plating or a Galvani displacement plating, see for example step 102 in FIG. For example, the initial Ni layer 33 can be a thin and uniform initial Ni layer. This non-contact plating method allows simultaneous plating on the exposed n-type tantalum surface and the p-type tantalum surface. The plating procedure can be performed until all of the exposed defects are plated, i.e., until all of the exposed tantalum surface is covered with a Ni layer. This program can be self-limiting. Therefore, by plating, for example, it is enough to completely cover two One of the surface polarities is sufficient time (for example, such as 2 minutes to 10 minutes) to deposit a uniform initial Ni layer on both the n-type surface and the p-type surface, wherein the layer completely covers the exposed surface.

However, in one method of the invention, partially covering the exposed surface by the initial Ni layer may be sufficient to allow for subsequent good metal plating and a good metal layer thickness uniformity. For example, the thickness of the initial Ni layer in at least one of the first region and the second region may generally be in a range between 5 nm and 2 μm, but embodiments of the invention are not limited thereto. Next, the initial layer 33 is thickened by depositing a further metal layer 34 on the initial Ni layer 33 by means of a metal plating process (for example, an electroless plating process or an immersion plating process), for example, see FIG. 103 of 1.

For example, a further Ni layer may be deposited on the initial Ni layer by electroless Ni plating until a thickness in a range between, for example, 0.2 μm and 8 μm is obtained, but the invention is not limited thereto. The electroless plating rate can typically be about 0.2 microns per minute. The initial Ni layer 33 has a function as a seed layer for electroless Ni plating. The electroless plating rate is substantially independent of the polarity (n-type or p-type) underlying the initial Ni layer. Therefore, a good thickness uniformity can be obtained.

As mentioned above, in one method of the invention, partial coverage of the exposed surface by the initial Ni layer may be sufficient to allow for subsequent good metal plating and a good metal layer thickness uniformity. For example, in one method according to an embodiment of the present invention, when the initial Ni layer is at least one of the first region and the second region, it is sufficient to allow subsequent good metal plating in the further metal layer of the deposition 103 (for example) In the case of a coverage, uniformity, and/or thickness, such as sufficient to obtain a good metal layer thickness uniformity after deposition of a further metal layer, the deposition 102 of the initial Ni layer may be terminated (eg, terminated). For example, when the initial Ni layer reaches this coverage, uniformity, and/or thickness on at least one of the first region and the second region but exceeds this coverage, uniformity, and/or thickness level to attribution Before the thickness of one of the initial Ni layers is further increased to obtain an unfavorable increase in contact resistance, The deposition 102 of the initial Ni layer can be terminated.

Thus, those skilled in the art can perform a deposition 102 of one of the initial Ni layers such that the initial Ni layer is not too thick (as would undesirably increase the contact resistance) and is not too thin (as would be insufficient to fully perform deposition 103 under further metal layers) One of the first steps of the initial Ni layer, for example, is insufficient for further metal layer deposition therein. In one embodiment of an electroless Ni plating process, no electroless Ni plating or only poor electroless Ni plating will occur. Tuning the deposition of the initial Ni layer 102 to obtain sufficient thickness in view of further metal layer deposition and in view of a possible unfavorable contact resistance is not within the capabilities of those skilled in the art, such as by initial Ni A simple experimental optimization of the duration of one of the depositions 102 of the layer is achieved.

Furthermore, when the initial Ni layer is only on the first region (eg, on the first region) has been sufficient to allow subsequent good metal plating but in view of the implied contact resistance is not excessive (and not necessarily sufficient to allow good on the second region) The step of depositing 102 the initial Ni layer may be terminated (eg, terminated) upon coverage, uniformity, and/or thickness of one of the metal platings. For example, the rate at which the initial Ni layer deposition 102 is in the first region 1 (where the n-type region 11 is exposed) may be higher than the rate at which the initial Ni layer deposition 102 is in the second region 2 (where the p-type region 12 is exposed), such that An adequate but not excessive initial layer thickness is achieved on the first region 1 before a specific selection of a sufficient but not excessive initial layer thickness is reached on the second region 2.

For example, the step of depositing 102 the initial Ni layer may be performed in the range of 10 seconds to 1.5 minutes, preferably in the range of 15 seconds to 45 seconds (such as about 30 seconds), for example, up to 30 seconds. One of the program steps lasts. Although the initial nickel layer 33 is simultaneously deposited 102 in the first region 1 and the second region 2 on the surface of the substrate, the first region 1 may be mainly plated during this step, that is, the exposed n-type region. For example, during this deposition 102, only a relatively small amount of nickel may be deposited on the second region 2 (ie, the exposed p-type region).

Next, a further metal layer 34 can be deposited 401 on the initial Ni layer 33 in the first region 1, as depicted in FIG. For example, the deposition 401 of a further metal layer on the initial Ni layer in the first region 1 may comprise an electroless or immersion plating process, such as an electroless Ni Plating step. For example, an electroless Ni plating can be applied for one of the program step durations in the range of 1 minute to 3 minutes (for example, 2 minutes). After depositing a further metal layer 401 on the initial Ni layer in the first region (eg, a first electroless Ni plating process (eg, one of the first electroless Ni plating processes of about 2 minutes), the first region may Fully covered with nickel, for example, the exposed n-type region may be completely covered by the initial Ni layer forming a good seed layer on the n-type material, but the second region may only be partially covered with nickel, or attributable to The initial Ni layer forms an under-plated layer on the p-type material without being covered by nickel to any substantial extent.

Next, a further Ni layer can be deposited 402 in the second region 2 by immersion plating (e.g., by applying the same or similar procedure for depositing one of the initial Ni layers). For example, the step of depositing 402 further Ni layers may be performed in the range of 45 seconds to 3 minutes, preferably in the range of 60 seconds to 120 seconds (such as about 90 seconds), for example, 90 seconds. One of the program steps lasts. Although a further nickel layer is deposited 402 in the second region 2 on the surface of the substrate in this step, no further Ni is deposited 402 in the first region 1. For example, a substantial or significant amount of nickel may not be deposited 402 in the first region 1 because after the further metal layer is deposited 401 on the initial Ni layer in the first region, no or negligible amount will be Keep exposed to the first area.

Next, the further metal can be, for example, by the same or similar to a process step (eg, an electroless Ni plating process step) on depositing a further metal layer on the initial Ni layer in the first region (eg, an electroless Ni plating process step) A layer is deposited 403 on the further Ni layer in the second region. This deposition 403 of the further metal layer on the further Ni layer in the second region may, for example, have one of the program step durations in the range of 4 minutes to 15 minutes (e.g., in the range of 5 minutes to 12 minutes). Those skilled in the art will appreciate that even if a further metal layer is deposited 403 on a further Ni layer in the second region, this does not preclude the deposition of more metal in the first region by the same procedure steps, and thus will further The metal layer is further grown in the first region. Those skilled in the art will appreciate that even if a further metal layer is deposited 403 on a further Ni layer in the second region, this does not preclude further gold by the same procedure steps. The genus layer is deposited on the initial Ni layer in the second region.

An advantage of this method in accordance with an embodiment of the present invention is to decouple the amount of nickel deposited by each of: an initial plating step of depositing an initial Ni layer on the n-type material in the first region; and A further Ni layer deposits 402 a subsequent plating step on the p-type material in the second region. Due to this decoupling, an additional degree of freedom for one of the optimization procedures is obtained, for example the program duration of each step can be used as a separate optimization parameter. Therefore, the specific constraints caused by design considerations can be more easily met by conventional optimization, such as imposed on an upper limit of the contact resistance.

In an embodiment of the invention, another metal (such as, for example, silver (Ag)) may be provided on the initial Ni layer 33 instead of electroless Ni to thicken the initial Ni layer. The Ag layer can be provided, for example, by electroless plating or by immersion plating. The advantage of providing an Ag layer as one of the further metal layers 34 is compared to a procedure in which a further Ni layer is provided which results in a lower resistance of one of the metal electrodes. The use of Ag can have a higher cost disadvantage than Ni. However, when the method is used to provide a metal electrode without a bus bar photovoltaic cell, the Ag layer thickness and (and therefore) Ag can be reduced compared to a "typical" photovoltaic cell having, for example, three to five bus bars. The amount of material (and (and therefore the cost)).

In an embodiment of the invention (eg, wherein the further metal layer 34 is a Ni layer, for example, provided on the initial Ni layer in both the first region and the second region or in multiples in a single program step Provided in the first region and the second region (as described above), the method may further comprise depositing a layer of copper (Cu) on the further metal layer after the electroless Ni plating process has been performed, for example Deposited on a further Ni layer. Depositing the copper layer can be accomplished, for example, by an electroless copper plating process. This can result in a further increase in the thickness of the metal electrode and an increase in one of its electrical conductivity. Such embodiments may be advantageously used to provide a metal electrode comprising a bus bar, such as for a battery having a limited number of bus bars (for example, three to five bus bars), although embodiments of the invention do not Limited to this.

In an embodiment of the invention, for example, in the manufacture of a bus without a bus bar photovoltaic cell In the vein, the first metal electrode and/or the second metal electrode may be composed of a plurality of continuous parallel metal wires or metal fingers extending from one edge of the substrate or the battery to the opposite edge of the substrate or the battery. However, embodiments of the invention are not limited thereto. In an embodiment of the invention, the first metal electrode and/or the second metal electrode may, for example, also consist of an interrupt line. In an embodiment of the invention, the first metal electrode and/or the second metal electrode may have a configuration different from that of a finger configuration, that is, different from a group consisting of a plurality of substantially parallel metal lines state. For example, the first metal electrode and/or the second metal electrode may be composed of a plurality of metal features extending in different non-parallel directions.

2 schematically illustrates the procedural steps of an example of a fabrication process 200 for a double-sided photovoltaic cell in which the front side of the cell is provided using a plating-based metallization method 100 in accordance with one embodiment of the present invention. And the metal electrode at the back side of the cell, as described above. For a double-sided battery, an n-type germanium wafer is generally used as, for example, a germanium substrate 10 having a resistivity in a range between 3 Ohm.cm and 5Ohm.cm. However, embodiments of the present invention are not limited thereto, and a wafer having another resistivity and/or a p-type wafer may be used as a single substrate. After sawing damage removal, the front and back surfaces of the substrate can be textured using known techniques, as shown by step 201 in FIG. For example, an emitter region can be formed at one surface of the substrate by diffusion of boron when using an n-type substrate or by diffusion of phosphorus when a p-type substrate is used. If desired, for example, a high/low junction may be provided at the opposite surface of the substrate by diffusion of phosphorus when using an n-type substrate or by diffusion of boron when a p-type substrate is used. However, embodiments of the invention are not limited thereto and other methods may be used to form doped regions, such as, for example, ion implantation, APCVD, or PECVD. The emitter region may be formed at a rear surface of the substrate and the high/low junction may be formed at the front surface, or vice versa, the emitter region may be formed at the front surface and the high/low junction may be formed at At the back surface.

Both the front and back surfaces may be passivated by providing 204 a dielectric layer (such as, for example, a PECVD SiN _x layer) or by providing a dielectric stack. The dielectric stack may, for example, comprise a SiO ₂ layer (eg, a thermally grown SiO ₂ layer) and a SiN _x layer deposited by PECVD (plasma enhanced chemical vapor deposition), although embodiments of the invention are not limited thereto. For example, AlO _x layer may be used instead of the SiO ₂ layer, for example, such as by ALD (atomic layer deposition), PEVCD, APCVD (atmospheric pressure chemical vapor deposition), sputtering, or printing of AlO _x layer deposition plating. For example, another dielectric layer or a stack of layers (eg, including a deposited SiO _x layer or SiO _x N _y layer deposited by PECVD) may be used instead of a SiN _x layer. An identical stack or a different stack can be used at the front and back surfaces. The dielectric stack can also be used as an anti-reflective coating. After providing the dielectric layer or the dielectric layer stack, the dielectric layer or the dielectric layer stack at the front side and the back side of the substrate may be patterned by, for example, laser ablation or by photolithography, but Embodiments of the invention are not limited thereto. Patterning of the dielectric layer or dielectric layer stack may include partial removal of dielectric layers or stacks, for example, in the first region 1 and the second region 2, ie, using a pattern corresponding to one of the desired metallization patterns An opening is formed in the layer or stack to expose the underlying raft. In an embodiment of the invention, the metallization pattern is preferably a bus bar free pattern.

In an embodiment of the invention, a selective doping process may be used in which the doping concentration at the location corresponding to the metallization pattern is higher than the doping concentration at other locations, such as above the previously provided emitter region and Doping concentration of high/low junction. Selective doping at the n-type side can, for example, include providing a dopant source (eg, a spin-on dopant or a spray dopant) followed by laser doping and annealing for damage removal and The dopant is driven in. The laser doping step causes the openings to be formed in the dielectric stack according to the metallization pattern and result in selective doping at one of the opening locations. The selective doping at the p-type side may, for example, comprise providing an AlO _x layer (which may be part of passivating the dielectric layer stack as described above) as a dopant source, followed by laser doping and annealing for Damage removal and dopant drive in. However, embodiments of the invention are not limited thereto and other selective doping methods may be used. An annealing step for damage removal and dopant drive can be performed after the plating step for providing the metal electrode. Advantageously, the annealing step and metal annealing (sintering step) can then be additionally combined to reduce the metal-helium contact resistance. However, embodiments of the invention are not limited thereto, and the annealing step for damage removal and dopant drive-in can also be completed prior to forming the metal electrode.

At step 206, as shown in FIG. 2, a plating-based metallization process, such as steps 102 and 103 shown in FIG. 1, of method 100 in accordance with one embodiment of the present invention is performed.

An example of an experiment in which a metal contact is provided on a double-sided photovoltaic cell using a method in accordance with an embodiment of the present invention is provided below. The examples are provided to illustrate the features and advantages of the embodiments of the present invention and to assist those skilled in the art to practice the invention. However, such examples are not to be construed as limiting the invention in any way. For these experiments, an n-type wafer having a resistivity of from 3 Ohm.cm to 5 Ohm.cm was used. After the sawing damage is removed, the front and back surfaces of the substrate are textured. At the front side, a 90 ohm/square p-type region (emitter region) is formed by boron diffusion. At the back side, a phosphorus diffusion is completed to produce a 120 ohm/square height/low junction. Both the front surface and the back surface are passivated by providing a dielectric stack consisting of a thermally grown SiO ₂ layer and a SiN _x layer deposited by PECVD. Forming an opening in the dielectric layer stack, that is, according to a photovoltaic cell contact pattern including three bus bars and a plurality of parallel fingers separated by 1.5 mm at both the front side and the rear side, the partial removal medium is partially removed The electrical layer is stacked. Partial removal of the dielectric layer stack is accomplished by ps UV laser ablation.

A plating-based metallization process in accordance with one of the embodiments of the present invention is then performed. Prior to plating, the samples were washed in an 8:1 H ₂ SO ₄ :H ₂ O ₂ solution at 80 ° C for 45 seconds to remove any organics from the surface to be plated. Thereafter, a rinse was performed, and the oxide was removed from the surface to be plated in a 2% HF solution for 90 seconds, and rinsed.

An initial Ni layer is deposited on the exposed ruthenium substrate surface by performing an immersion plating process. The impregnated Ni (i-Ni) bath contains DI water, NH ₄ F, and nickel sulfamate Ni(SO ₃ NH ₂ ) ₂ . The NH ₄ F concentration in the range between 5 mass% and 15 mass% was used. For Ni(SO ₃ NH ₂ ) ₂ , different concentrations in the range between 0.1 M and 0.3 M were used. The pH of the plating bath was adjusted to a different pH in the range between 7 and 9.5 by the addition of NH ₄ OH. Impregnated Ni plating with different durations in the range between 2.5 minutes and 15 minutes was performed at 80 °C. An i-Ni bath was provided in a glass beaker placed on a hot plate. The temperature of the plating solution was measured by a thermocouple and the temperature of the solution was controlled within +/- 2 °C. The solution was stirred by a stirrer at 200 rpm. No controlled external illumination is applied, ie, only laboratory background light is present.

The sample was then rinsed in deionized (DI) water and the initial Ni layer was thickened by performing an electroless Ni plating procedure to thereby deposit a further Ni layer. A commercially available plating solution was applied to an electroless Ni (E-Ni) plating bath at 82 °C. The pH of the E-Ni bath was 4.8, and the E-Ni plating time was in the range between 10 minutes and 15 minutes.

After rinsing in DI water, a thin Ag layer was provided on top of the further Ni layer by dipping Ag plating using a commercially available procedure. This procedure used two baths: first using a pre-cleaning bath (pre-i-Ag bath) at 38 ° C for 30 s; and then using a deposition bath (i-Ag bath) at 52 ° C for 60 s. After rinsing the sample in DI water and drying with N ₂ , sintering (annealing) in a belt furnace in a nitrogen atmosphere (O ₂ concentration <10 ppm) at a temperature between 250 ° C and 400 ° C Contact for 4 minutes.

The thickness of the deposited layer was measured by XRF (X-ray fluorescence).

The table below shows the measured thickness of the initial Ni layer 33 formed by immersion plating for different i-Ni plating baths and program conditions. The thickness is measured on both the n-type region and the p-type region. The results demonstrate simultaneous plating on both the n-type region and the p-type region for a wide range of procedural conditions. The program conditions affect the layer thickness and the ratio between the thickness on the n-type region and the thickness on the p-type region. The thickness of the i-Ni layer on the n-type region is greater than the thickness of the i-Ni layer on the p-type region.

The initial Ni layer provided on the p-type region and the n-type region is thickened by performing an electroless Ni (E-Ni) plating process as described above (as reported in the table above), thereby further The Ni layer 34 is deposited on the initial Ni layer 33. The E-Ni plating time is 10 minutes. Figure 3 shows the measured thickness d of a further Ni layer provided on top of the initial i-Ni layer (as reported in the table above), varying according to the initial i-Ni layer thickness d _i-Ni (in microns) _E-Ni (in microns). In FIG. 3, the solid circle 31 corresponds to the Ni layer formed on the n-type region and the solid triangle corresponds to the Ni layer on the p-type region. From these exemplary results, it can be seen that the thickness of the further Ni layer (i.e., the Ni layer provided by electroless plating on the initial Ni layer) can be substantially independent of the thickness of the underlying initial Ni layer, and it can be substantially independent of The polarity of the doped germanium region underlying the initial Ni layer (even for very thin initial Ni layers).

However, it is attributed to a faster deposition rate when the initial Ni layer i-Ni is formed on the n-type region compared to deposition on the p-type region (as confirmed by the information presented in the table above) For particularly short program durations of i-Ni deposition (eg, less than or equal to 5 minutes), between the thickness of the deposited i-Ni layer on the p-type region and the thickness of the deposited i-Ni layer on the n-type region Cause a big relative difference. Therefore, for these short program durations, further Ni layer E-Ni is not formed or well formed in the p-type region (as shown by data point 33 plotted in Figure 3), and for the same processing step, further Ni The layer E-Ni is sufficiently formed in the n-type region. However, as described above, a short program duration for forming the initial Ni layer i-Ni may preferably result in a particularly low contact resistance. As also described above, in one method in accordance with an embodiment of the present invention, the step of depositing a further metal layer can include easily combining the good contact resistance attributed to one of the particularly thin initial Ni layers, for example by the following steps. a plurality of sub-steps of well plating one of the further metal layers above the initial Ni layer: first forming a further metal layer on the initial Ni layer in the n-type region; and then initializing by a second immersion Ni plating step The Ni layer extends over the p-type region; and then a further metal layer is formed in the p-type region.

Another example relates to an experiment in which first, Ni plating is performed by using a plating solution having 10% by mass of NH ₄ F and 0.1 M of Ni(SO ₃ NH ₂ ) ₂ (having different pH values) for 10 minutes. An initial Ni layer was provided, and then an electroless Ni plating process was performed for 15 minutes, thereby depositing a further Ni layer on the initial Ni layer. 4 shows the measured thickness of a further Ni layer for a Ni layer formed on an n-type region (filled circle 31) and a p-type region (solid triangle 32), which varies according to the underlying initial Ni layer thickness d _i-Ni d _E-Ni . It can be seen that the thickness d _{E-Ni of the} further Ni layer is substantially independent of the thickness of the underlying initial Ni layer, and is substantially independent of the polarity of the doped germanium region underlying the initial Ni layer.

In another example, an experiment in which an initial Ni layer is deposited on an n-type region and a p-type region by immersion plating in the absence of light is performed. Prior to plating at 80 ℃, in a 8: washing the sample of 45 seconds a solution of H ₂ O ₂ to remove any organics from the surface to be coated: 1 H ₂ SO _4. Thereafter, rinsing was carried out, and the oxide was removed from the surface to be plated in a 2% HF solution for 90 seconds, and rinsed. The impregnated Ni (i-Ni) bath contained DI water, 7.5% by mass of NH ₄ F, and 0.1 M of nickel sulfamate Ni(SO ₃ NH ₂ ) ₂ . The pH of the plating bath was adjusted to a pH of 8.0 by the addition of NH ₄ OH. Immersion Ni plating was performed at 80 ° C for 10 minutes. An i-Ni bath was provided in a glass beaker placed on a hot plate. The temperature of the plating solution was measured by a thermocouple and the temperature of the solution was controlled within +/- 2 °C. The solution was stirred by a stirrer at 200 rpm. During immersion plating, the laboratory lamp was turned off and the glass beaker was covered with a black cloth.

The following table shows the measured thickness of Ni formed at different locations (both on the p-type region and the n-type region) by immersion plating in the absence of light. The results show that simultaneous plating is achieved on the polarity of the two substrates in the absence of light. The layer thickness on the n-type region is greater than the layer thickness on the p-type region.

In addition, the resistance between the bus bars (R _bb) is used to evaluate the conductive line. A 4-point probe type resistance measurement system is completed between the bus bars, and the measured resistance is considered to be proportional to the average line conductivity (Ohm/cm) of the fingers between the two bus bars.

Based on calculations and experimental data, it has been observed that sufficient line conductivity can be obtained in a reasonable program time when using a metallization procedure in accordance with an embodiment of the present invention. The calculation is performed to estimate the finger conductivity required to obtain a good fill factor for one of the photovoltaic cells including a bus barless finger pattern, wherein the fingers are soldered to thirty eight of the fingers Wires are connected and replace bus bars ("smart wire" technology). It is known that a current high fill factor standard n-PERT battery with three bus bars has a R _{bb of} about 25 m. Ohm. The desired finger conductivity of the Ni plated fingers from the I ² R ohm power loss in this n-PERT cell was obtained with fingers from 38 wires connected. For the conductivity of the fingers, it is calculated that the R _bb measured on the three-bar battery will be about 4 Ohms. Photovoltaic cells are fabricated as described above, having cells having a plurality of fingers provided in accordance with one of the embodiments of the present invention and having three bus bars for achieving wire conductivity measurements. The following sequence of procedures was used: H ₂ SO ₄ :H ₂ O ₂ cleaning for 45 s; oxide etching in 2% HF for 90 s; with 10% by mass of NH ₄ F, 0.1 M Ni(SO ₃ NH ₂ ) ₂ and 8.5 One of the pH values of a plating bath was immersed in Ni plating for 10 minutes; 15 minutes without electro-Ni plating; 30 s pre-i-Ag cleaning; 60 s i-Ag plating. The measured R _bb values for the four batteries are shown in the table below. Battery 1 was sintered; batteries 2, 3 and 4 were not sintered. On the battery 1, the thickness of the metal electrode was measured by X-ray fluorescence. On the n-type region, the Ni thickness is 2.9 μm, and on the p-type region, the Ni thickness is 2.3 μm. The Ni layer is covered by a 310 nm thick i-Ag layer on the n-type region and covered by a 294 nm thick i-Ag layer on the p-type region.

In the table presented above, #1 and #2 refer to two different measurements: a first measurement between a first bus bar and a second bus bar; and the second bus bar and A second measurement between the third bus bars. The results show that for all cells, R _bb values of significantly less than 4 Ohm (evaluated values, as described above) were obtained on both the n-type region and the p-type region. Therefore, it can be inferred that sufficient line conductivity can be achieved to integrate with smart wire connection technology using short processing times. In such experiments, the good conductivity of the fingers can be compared to the i-Ag layer (which is about 300 nm thick) on top of the Ni layer (in these examples, having a thickness of one of 2.3 microns to 2.9 microns). There is a close correlation.

No false plating was observed on either the p-type region or the n-type region based on the optical microscope image and based on the SEM image of the plated electrode.

The adhesion of the metal electrode was measured by solder tab adhesion, wherein a solder tab was soldered to the electrodes at 325 ° C and the solder tab was pulled at an angle of 45° to record the need to remove the tab The maximum force F _max . For the samples reported in Table 1, the results of the solder tab adhesion for the n-type region are depicted in Figure 5 and the solder tab adhesion results for the p-type region are depicted in Figure 6. FIG 5 and FIG 6 shows removal of the tab of the desired maximum force F _max (in Newton), for example, represents a welding adhesion, varies between the maximum [NH ₄ F] The ₄ F i-Ni bath concentration of NH Force F _max . These results indicate a correlation between NH ₄ F concentration and adhesion strength. 2.4 One of the maximum forces of Newton will be considered to correspond to one of the good adhesions suitable for bus bar and tab welding. In the completed experiment, this was obtained for a plating solution having 5% by mass of NH ₄ F but not for a plating solution having 10% by mass of NH ₄ F or 15% by mass of NH ₄ F. However, the adhesiveness required for successful integration of one of the smart wire technologies can be less than that required for conventional bus bar and tab welding.

In another example, an experiment in which one of the initial Ni layers is deposited primarily on the n-type region by a first immersion plating is performed. Prior to plating, the sample was washed to remove any organics from the surface to be plated, followed by DI water rinse, oxide removal from the surface to be plated in a 2% HF solution for 90 seconds, and DI water rinse. The impregnated Ni (i-Ni) bath contained DI water, 30% by mass of NH ₄ F, and 0.1 M of nickel sulfamate Ni(SO ₃ NH ₂ ) ₂ . The pH of the plating bath was adjusted to a pH of 8.5. This immersion Ni plating was performed at 60 ° C for 30 seconds while stirring with a solution provided by a magnetic stirrer at 200 rpm. This immersion Ni plating is performed in the dark as discussed above with respect to a prior example. Next, the sample was rinsed with DI water, and one of the procedure steps of electroless Ni plating for 2 minutes was performed at 82 ° C using a commercially available solution (Macdermid Ultraplanar, pH 4.8) for electroless Ni plating. In the next step, after the DI rinse sample again, under conditions similar to the previous immersion Ni plating step (for example, again at 60 ° C in the dark and at a 200 rpm stirring by a magnetic stirrer) B) Perform a further impregnation of Ni plating for 90 seconds. The impregnated Ni bath used in this immersion Ni plating step also has the same composition as in the previous immersion Ni plating step. After further DI rinsing of the sample, a further electroless Ni plating was performed at 82 ° C for 12 minutes (Macdermid Ultraplanar, pH 4.8).

As described above, by dividing the further metal layer in a plurality of steps (eg, in combination with a short step of depositing one of the initial Ni layers (such as in this example, a 30 second initial immersion plating step)), the thickness is not too thick. An initial Ni layer such as to substantially increase the contact resistance but sufficient to effect a good electroless Ni plating in the next step. Since the rate of Ni deposition on the n-type material in the Ni-plated immersion is higher than the rate at which Ni is deposited on the p-type material, the first step (specifically) of the immersion plating and the electroless Ni plating reaches the n-type material. One of the surfaces is well plated, and the following steps of immersion plating and electroless Ni plating complete the procedure for achieving a good plating on the p-type material, as discussed above.

In this example, the multi-step process of alternating immersion plating and electroless plating is further extended by the following step: using a commercially available solution after rinsing the sample again with DI (MacDermid Helios Silver IM 448) was subjected to a pre-i-Ag deposition step for 60 s; and a 90 s i-Ag deposition step (MacDermid Helios Silver IM 448).

The foregoing description details certain embodiments of the invention. However, it will be appreciated that the present invention may be practiced in many ways, no matter how detailed the text is. It should be noted that the use of a particular term in the description of certain features or aspects of the invention is to be construed as an implied that the term is re-restricted herein to be limited to any particular feature or feature of the invention. characteristic.

Although the above embodiments and the summary of the invention have focused on a method for forming a contact electrode, the invention is also directed to a device comprising a metal electrode obtained using a method according to any of the embodiments described above. For example, a photovoltaic battery.

While the above-described embodiments have shown, described and illustrated the novel features of the present invention as applied to the various embodiments, it will be understood by those skilled in the art Various forms, details and details are omitted, substituted and changed.

100‧‧‧ method

101‧‧‧Steps

102‧‧‧Steps

103‧‧‧Steps

Claims (10)

A method for forming a first metal electrode (31) on one of the n-type regions (11) of a substrate (10) in parallel and forming a first on a p-type region (12) of the germanium substrate (10) The method (100) of a two-metal electrode (32), the method comprising: providing (101) a substrate (20) comprising a substrate (10), the substrate (10) comprising an n-type region (11) and a a p-type region (12), wherein the n-type region (11) is exposed to one of the first regions (1) at one of the surfaces (21, 22) of the germanium substrate (10), and wherein the p-type region (12) Exposing to a second region (2) at one of the surfaces (21, 22) of the germanium substrate; simultaneously depositing (102) an initial nickel layer (33) by performing a nickel dip plating process And in the first region (1) and the second region (2) on the substrate surface (21, 22); and further by performing an electroless metal plating process or by performing an immersion metal plating process A metal layer (34) is deposited (103) on the initial Ni layer (33) in the first region (1) and the second region (2). The method (100) of claim 1, wherein depositing (103) the further metal layer (34) comprises: depositing a further nickel layer by performing an electroless nickel plating process. The method (100) of claim 1, wherein the depositing (103) of the further metal layer (34) comprises the sequence of: depositing (401) a further metal layer in the first region (1) Depositing a further nickel layer (402) in the second region (2) by performing a nickel immersion plating process; and depositing the further metal layer on the first region ( 1) and the further nickel layer in the second region (2). The method (100) of claim 3, wherein the depositing (103) of the further metal layer (34) comprises the sequence of: depositing a first further nickel layer by performing an electroless nickel plating process (401) ) on the initial nickel layer (33) in the first region (1); Depositing a second further nickel layer (402) in the second region (2) by performing a nickel immersion plating process; and depositing a third further nickel layer by performing an electroless nickel plating process And on the second further nickel layer in the first region (1) and on the second further nickel layer in the second region (2). The method (100) of claim 2 or claim 4, further comprising providing a solderable cap layer on the further nickel layer, wherein providing the solderable cap layer comprises: performing a silver immersion plating A silver layer is provided by the program; or a tin layer is provided by performing a tin plating process; or an organic cap layer is provided. The method (100) of claim 1, wherein depositing (103) the further metal layer (34) comprises depositing a silver layer by performing a electroless silver plating process or by performing a immersion silver plating process. The method (100) of any one of claims 1 to 4, wherein the providing (101) the substrate (20) comprises providing one of the n-type region (11) and the p-type region (12). a substrate (10); a dielectric layer (13) is provided on at least one surface (21, 22) of the germanium substrate (10); and the first region (1) and the second region (2) from the substrate The dielectric layer is removed. The method (100) of any one of claims 1 to 4 or 6, further comprising performing a sintering step at a temperature in a range between 250 ° C and 400 ° C. A method (200) for manufacturing a double-sided photovoltaic cell, the method comprising: in parallel with any one of claims 1 to 4 or 6 on an n-type region (11) of a substrate (10) A first metal electrode (31) is formed and a second metal electrode (32) is formed on one of the p-type regions (12) of the germanium substrate (10). A method for manufacturing a back contact photovoltaic cell, the method comprising: n-type one of the substrate (10) in parallel or simultaneously as claimed in any one of claims 1 to 4 or 6 A first metal electrode (31) is formed on the region (11) and a second metal electrode (32) is formed on one of the p-type regions (12) of the germanium substrate (10).