A method of protecting solar cells from ion-induced degradation

Abstract

A bifacial solar cell comprising: a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell, wherein the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side. A process for depositing a substantially ion impermeable protective metal coating on a metal contact on a first side of a bifacial solar cell, comprising: electrically connecting a metal contact of a second side of the bifacial solar cell to a negatively charged electrode at least partially immersed in a plating solution via an electrical bias source; immersing at least a portion of the first side in the plating solution; and applying a bias and / or exposing at least a portion of the first side to light.

Description

"A METHOD OF PROTECTING SOLAR CELLS FROM ION-INDUCED DEGRADATION"CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority from Australian Provisional Patent Application No 2024903924 filed on 28 November 2024, the contents of which are incorporated herein by reference in their entirety.TECHNICAL FIELD

[0002] This disclosure generally relates to photovoltaic devices which may display improved stability. In particular, the disclosure relates to a bifacial solar cell comprising a protective metal coating. In addition, the present disclosure relates to methods of forming a protective metal coating on photovoltaic devices.BACKGROUND

[0003] According to the International Technology Roadmap for Photovoltaic (ITRPV) 2024, n-type Si is predicted to dominate the mono-Si solar cell market from 2024. Tunneling oxide passivated contact (TOPCon) cells and Si heterojunction (SHJ) cells are expected to be the dominant solar cell architectures. In particular, TOPCon solar cells will account for up to 53% of the solar cell market share within the next 10 years.

[0004] Manufacturers mainly focus on increasing the initial efficiency of solar cell and the efficiency of large-area TOPCon solar cell has been reported at up to 25.25%. Less attention has been given to long-term stability. For economic and sustainability reasons, longer warranties and better stability are very valuable, as long as the devices can still work at a certain power output level

[0005] The front side metallization of TOPCon solar cells is reported to be susceptible to corrosion. In addition, TOPCon solar cells can suffer severely from ion-induced degradation, including from sodium and chloride ions, most notably the front side. Sodium can be released from the soda-lime glass in the presence of moisture. In addition, sodium can also be introduced into solar cells when these are exposed to seawater, dust, rainwater, and soil. The introduced sodium can degrade the power output, fill factor and open-circuit voltage.

[0006] Therefore, it is desirable to provide alternative device architectures which incorporate features which can prevent and / or inhibit the introduction of unwanted ions into the cells. It is also desirable to provide alternative methods for producing alternative photovoltaic devices incorporating these features, which can prevent and / or inhibit the introduction of unwanted ions into the cells.

[0007] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.SUMMARY

[0008] The present disclosure relates to a bifacial solar cell comprising a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell. The protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

[0009] In a first aspect, disclosed herein is a bifacial solar cell comprising: a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell, wherein the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

[0010] In a second aspect, provided herein is a process for depositing a substantially ion impermeable protective metal coating on a metal contact of a first side of a bifacial solar cell, the process comprising: establishing electrical communication between a metal contact of a second side of the bifacial solar cell and a negatively charged electrode at least partially immersed in a plating solution comprising an ion of the protective metal; establishing electrical communication between the metal contact of the second side of the bifacial solar cell and an electrical bias source;immersing at least a portion of the first side of the bifacial solar cell in the plating solution; and applying a bias from the metal contact of the second side of the bifacial solar cell and / or exposing at least a portion of the first side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the protective metal ion from the plating solution on at least a portion of the front side metal contact of the bifacial solar cell to form the protective metal coating.

[0011] In a third aspect, disclosed herein is a protective metal coating produced by a process as described herein, for example according to the second aspect.

[0012] In a fourth aspect, disclosed herein is a bifacial solar cell comprising a protective metal coating produced by a process as described herein, for example according to the second aspect.

[0013] The inventors of the present application have surprisingly discovered that, according to various aspects and / or embodiments of the present disclosure, the inclusion of a protective metal coating on the front and / or back side metal contacts can provide a protective effect against performance degradation, in particular against ion induced degradation. In addition, the inventors have advantageously discovered, according to various aspects and / or embodiments of the present disclosure, that the inclusion of the protective metal coating on the front and / or back side metal contacts can reduce the amount of metal used, for example silver, used in the front and / or back side metal contacts thereby reducing resource requires and / or the cost associated with the manufacture of bifacial solar cells. Advantageously, according to various aspects and / or embodiments of the present disclosure, bifacial solar cells with improved longterm stability are provided, particularly if said cells are to be installed in regions of high humidity and / or with exposure, for example, to seawater, dust, and / or rainwater which may introduce ions, for example sodium, which can degrade the cells.BRIEF DESCRIPTION OF DRAWINGS

[0014] Preferred embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

[0015] Figure 1 : Experimental design.

[0016] Figure 2: Schematic of TOPCon solar cells with Cu plated on the front grid.

[0017] Figure 3: Top-view SEM images of the front metal contact of the as-received sample.

[0018] Figure 4: Top-view SEM images of the front metal contact of the Cu-plated sample.

[0019] Figure 5: Top-view EDS images of the front metal contact after the plating process, with EDS mapping of elements Si, Ag, and Cu.

[0020] Figure 6: Cross-sectional SEM images of the as-received sample and corresponding EDS mappings for Ag.

[0021] Figure 7: Cross-sectional SEM images of (the Cu- plated sample and corresponding EDS mappings for Ag and Cu.

[0022] Figure 8: Relative variations of Rs, FF, Voc, Jsc and PCE for groups shown in Figure 1 during DH testing.

[0023] Figure 9: Rsimages of as received and plated cells with exposure to NaCl solution before and after 2 and 4 hours of DH testing.

[0024] Figure 10: PL images of as received and plated cells exposed to NaCl before and after 6 hours of DH testing.DESCRIPTION OF EMBODIMENTS

[0025] The present disclosure describes the following various non-limiting embodiments, which relate to the present disclosure.Definitions

[0026] In the following description, reference is made, where needed, to any accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be used, and structural changes may be made without departing from the scope of the present disclosure.

[0027] With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended tolimit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0028] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0029] Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.

[0030] Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, processes, and compositions, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

[0031] The term “and / or”, e.g., “X and / or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.

[0032] Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g., a “first” item) and / or a higher-numbered item (e.g., a “third” item).

[0033] As used herein, the phrase “at least one of’, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In otherwords, “at least one of’ means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.

[0034] As used herein, the term “about”, unless stated to the contrary, typically refers to a range of up to + / - 10% of the designated value, and includes smaller ranges therein, for example + / - 5% or + / - 1% of the designated value.

[0035] It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination.

[0036] Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 4.5, 4.75, and 5, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.

[0037] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0038] Throughout this specification, the term "consisting essentially of' is intended to exclude elements which would materially affect the properties of the claimed composition, method or process.

[0039] The terms "comprising", "comprise" and "comprises" herein are intended to be optionally substitutable with the terms "consisting essentially of, "consist essentially of, "consists essentially of, "consisting of, "consist of and "consists of, respectively, in every instance.

[0040] Herein “weight %” may be abbreviated to as “wt%” or “wt.%”. The weight % may be w / w or w / v, unless specifically indicated or clear from context.

[0041] Herein, unless specifically defined a “device” may refer to a “photovoltaic precursor device” or a “photovoltaic device”.Bifacial solar cell

[0042] Disclosed herein is a bifacial solar cell comprising a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell.

[0043] In one embodiment, the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

[0044] Also disclosed herein is a bifacial solar cell comprising: a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell, wherein the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

[0045] In some embodiments, the bifacial solar cell further comprises a second protective metal coating on at least a portion of a metal contact of a second side of a bifacial solar cell. In some embodiments, the second protective metal coating forms a substantially ion impermeable coating on the metal contact of the second side of a bifacial solar cell. In some embodiments, the second protective metal coating covers substantially all of the second side metal contact.Solar cells

[0046] In some embodiments, the bifacial solar cell is selected from a tunnelling oxide passivated contact solar cell (TOPCon), passivated emitter and rear cell solar cell (PERC), silicon heterojunction solar cell (SHJ), back-contact solar cell, and tandem solar cell. In some embodiments, the bifacial solar cell is a tunnelling oxide passivated contact solar cell.First side and second side

[0047] In some embodiments, the first side of the bifacial solar cell is the front side of the bifacial solar cell. In some embodiments, the second side of the bifacial solar cell is the back side of the bifacial solar cell.

[0048] In some embodiments, the first side of the bifacial solar cell is the back side of the bifacial solar cell. In some embodiments, the second side of the bifacial solar cell is the front side of the bifacial solar cell.Protective metal coating

[0049] In one or more embodiments, the protective metal coating forms a substantially ion impermeable coating, for example on the metal contact of the first side of a bifacial solar cell. In some embodiments, the substantially ion impermeable coating is a relatively dense (compared to the metal contact of the first side of a bifacial solar cell) and continuous barrier layer on the metal contact of the first side of a bifacial solar cell. The inventors present disclosures have surprisingly discovered that in various embodiments of the bifacial solar cell described herein, the protective coating may reduce ion migration into the solar cell, protect the bifacial solar cell against corrosion, protect the bifacial solar cell from degradation and / or maintaining integrity under environmental and operational stresses.

[0050] The term substantially ion-impermeable will be understood to refer to a protective coating that forms a barrier and can reduce the migration of ions into various parts of the bifacial solar cell, including, but not limited to the metal contact of the first side, and / or one or more underlying layers. The ion concentration can be measured by the EDS analysis on the cross- sectional SEM images of the metal contact. In some embodiments, the term substantially ion- impermeable is quantifiable in terms of the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is about, or greater than about: 10, 20, 30, 40, 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99, 99.5, 99.9. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is less than about: 99.9, 99.5, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 80, 70, 60, 50, 40, 30, 20, or 10. The reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell may be in a range provided by any two of these upper and / or lower values. In some embodiments, the reduction in penetrated ion concentration into the metalcontact relative to an uncoated control bifacial solar cell (in %) is between about 10 to about 99.9, between about 50 to about 99.5. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is greater than about 80. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is greater than about90.

[0051] In some embodiments, the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof. In some embodiments, the protective metal coating comprises copper. In some embodiments, the protective metal coating essentially consists of copper. In some embodiments, the protective metal coating comprises silver. In some embodiments, the protective metal coating essentially consists of silver. In some embodiments, the protective metal coating comprises tin. In some embodiments, the protective metal coating essentially consists of tin. In some embodiments, the protective metal coating comprises nickel. In some embodiments, the protective metal coating essentially consists of nickel.

[0052] In some embodiments the protective metal coating comprises a single metal. In some embodiments, the protective metal coating essentially consists of a single metal. In some embodiments the protective metal coating comprises a plurality of metals, e.g. 2 or 3 metals. In some embodiments, the protective metal coating essentially consists of a plurality of metals, e.g. 2 or 3 metals. The plurality of metals may be a mixture or an alloy.

[0053] In some embodiments, the protective metal coating covers substantially all, or all, of one or more a surface, article and / or layers, for example on a bifacial solar cell, such as on the first side metal contact. In some embodiment the protective metal coating is contiguous or substantially contiguous over one or more of a surface, article and / or layers, for example on a bifacial solar cell, such as on the first side metal contact. In some embodiments, the protective metal coating covers at (in %) about, or greater than about: 10, 20, 30, 40, 50, 60, 70, 80, 90,91, 92, 93, 94, 95, 96, 97, 98, or 99, 99.5, 99.9, of one or more of a of a surface, article and / or layers, for example on a bifacial solar cell, such as on the first side metal contact. In some embodiments, the protective metal coating covers (in %) less than about: 99.9, 99.5, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 80, 70, 60, 50, 40, 30, 20, or 10, of one or more of a of a surface, article and / or layers, for example on a bifacial solar cell, such as on the first side metal contact.

[0054] In some embodiments, the protective metal coating, for example on the first side metal contact, has an average thickness (in pm) of about, or greater than about: 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 400, or 500. In some embodiments, the protective metal coating, for example on the first side metal contact, has an average thickness (in pm) of less than about: 500, 400, 300, 250, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, or 0.001. The average thickness of the protective metal coating, for example on the first side metal contact, may be in a range provided by any two of these upper and / or lower values. In some embodiments, the protective metal coating, for example on the first side metal contact, has an average thickness (in pm) of between about 0.001 to about 500, between about 0.001 to about 100, between about 0.001 to about 50, between about 0.01 to about 20, between about 0.05 to about 10, between about 0.1 to about 2.

[0055] In some embodiments, the protective metal coating, for example on the first side metal contact, has an average thickness (in pm) of less than about 10, or less than about 2.Metal contact of the first side

[0056] The metal contact on the first side of the solar cell may be formed by any suitable method know in the art. In some embodiments, the metal contact of the first side is a screen- printed metal contact. In some embodiments, the metal contact of the first side is a plated metal contact.

[0057] In some embodiments, the metal contact of the first side has an average width (in pm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 400, or 500. In some embodiments, the metal contact of the first side has an average width (in pm) of less than about: 500, 400, 300, 250, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the first side has an average width (in pm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the first side has an average width (in pm) of between about 1 to about 500, between about 1 to about 100, between about 5 to about 40.

[0058] In some embodiments, the metal contact of the first side has an average height (in gm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200. In some embodiments, the metal contact of the first side has an average height (in gm) of less than about: 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the first side has an average height (in gm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the first side has an average height (in pm) of between about 1 to about 200, between about 1 to about 50, between about 5 to about 20.

[0059] In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from, but not limited to: aluminium, gold, silver, titanium, copper, nickel, chromium, caesium, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from, but not limited to: aluminium, silver, nickel, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from silver, nickel, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises silver. In some embodiments, the metal contact of the first side of the bifacial solar cell consists essentially of silver. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises or consists essentially of silver.Second protective metal coating

[0060] The second protective metal coating forms a substantially ion impermeable coating, for example on the metal contact of the second side of a bifacial solar cell. In some embodiments, the substantially ion impermeable second protective metal coating is a relatively dense (compared to the metal contact of the second side of a bifacial solar cell) and continuous barrier layer on the metal contact of the second side of a bifacial solar cell. The inventors present disclosures have surprisingly discovered that in various embodiments of the bifacial solar cell described herein, the second protective metal coating may reduce ion migration into the solar cell, protect the bifacial solar cell against corrosion, protect the bifacial solar cell from degradation and / or maintaining integrity under environmental and operational stresses.

[0061] The term substantially ion-impermeable will be understood to refer to a second protective metal coating that forms a barrier and can reduce the migration of ions into various parts of the bifacial solar cell, including, but not limited to the metal contact of the second side, and / or underlying layers. The ion concentration can be measured by the EDS analysis on thecross-sectional SEM images of the metal contact. In some embodiments, the term substantially ion-impermeable is quantifiable in terms of the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is about, or greater than about: 10, 20, 30, 40, 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99, 99.5, 99.9. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is less than about: 99.9, 99.5, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 80, 70, 60, 50, 40, 30, 20, or 10. The reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell may be in a range provided by any two of these upper and / or lower values. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is between about 10 to about 99.9, between about 50 to about 99.5. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is greater than about 80. In some embodiments, the reduction in penetrated ion concentration into the metal contact relative to an uncoated control bifacial solar cell (in %) is greater than about 90.

[0062] In some embodiments, the second protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof. In some embodiments, the second protective metal coating comprises copper. In some embodiments, the second protective metal coating essentially consists of copper. In some embodiments, the second protective metal coating comprises silver. In some embodiments, the second protective metal coating essentially consists of silver. In some embodiments, the second protective metal coating comprises tin. In some embodiments, the second protective metal coating essentially consists of tin. In some embodiments, the second protective metal coating comprises nickel. In some embodiments, the second protective metal coating essentially consists of nickel.

[0063] In some embodiments the second protective metal coating comprises a single metal. In some embodiments, the second protective metal coating essentially consists of a single metal. In some embodiments the second protective metal coating comprises a plurality of metals, e.g. 2 or 3 metals. In some embodiments, the second protective metal coating essentially consists of a plurality of metals, e.g. 2 or 3 metals. The plurality of metals may be a mixture or an alloy.

[0064] In some embodiments, the second protective metal coating covers substantially all, or all, of one or more a surface, article and / or layers, for example on a bifacial solar cell, such as on the second side metal contact. In some embodiment the second protective metal coating is contiguous or substantially contiguous over one or more of a surface, article and / or layers, for example on a bifacial solar cell, such as on the second side metal contact. In some embodiments, the second protective metal coating covers at (in %) about, or greater than about: 10, 20, 30, 40, 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99, 99.5, 99.9, of one or more of a of a surface, article and / or layers, for example on a bifacial solar cell, such as on the second side metal contact. In some embodiments, the second protective metal coating covers (in %) less than about: 99.9, 99.5, 99, 98, 97, 96, 95, 94, 93, 92, 91, 90, 80, 70, 60, 50, 40, 30, 20, or 10, of one or more of a of a surface, article and / or layers, for example on a bifacial solar cell, such as on the second side metal contact.

[0065] In some embodiments, the second protective metal coating, for example on the second side metal contact, has an average thickness (in pm) of about, or greater than about: 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 400, or 500. In some embodiments, the second protective metal coating, for example on the second side metal contact, has an average thickness (in pm) of less than about: 500, 400, 300, 250, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.009, 0.008, 0.007, 0.006, 0.005, 0.004, 0.003, 0.002, or 0.001. The average thickness of the second protective metal coating, for example on the second side metal contact, may be in a range provided by any two of these upper and / or lower values. In some embodiments, the second protective metal coating, for example on the second side metal contact, has an average thickness (in pm) of between about 0.001 to about 500, between about 0.001 to about 100, between about 0.001 to about 50, between about 0.01 to about 20, between about 0.05 to about 10, between about 0.1 to about 2.

[0066] In some embodiments, the second protective metal coating, for example on the second side metal contact, has an average thickness (in pm) of less than about 10, or less than about 2.Metal contact of the second side

[0067] The metal contact on the second side of the solar cell may be formed by any suitable method know in the art. In some embodiments, the metal contact of the second side is a screen- printed metal contact.

[0068] In some embodiments, the metal contact of the second side has an average width (in pm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 400, or 500. In some embodiments, the metal contact of the second side has an average width (in pm) of less than about: 500, 400, 300, 250, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the second side has an average width (in pm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the second side has an average width (in pm) of between about 1 to about 500, between about 1 to about 100, between about 5 to about 40.

[0069] In some embodiments, the metal contact of the second side has an average height (in pm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200. In some embodiments, the metal contact of the second side has an average height (in pm) of less than about: 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the second side has an average height (in pm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the second side has an average height (in pm) of between about 1 to about 200, between about 1 to about 50, between about 5 to about 20.

[0070] In some embodiments, the metal contact of the second side of the bifacial solar cell comprises a metal selected from, but not limited to: aluminium, gold, silver, titanium, copper, nickel, chromium, caesium, and combinations thereof. In some embodiments, the metal contact of the second side of the bifacial solar cell comprises a metal selected from, but not limited to: aluminium, silver, nickel, and combinations thereof. In some embodiments, the metal contact of the second side of the bifacial solar cell comprises a metal selected from, but not limited to: silver, nickel, and combinations thereof. In some embodiments, the metal contact of the second side of the bifacial solar cell comprises silver. In some embodiments, the metal contact of the second side of the bifacial solar cell consists essentially of silver. In some embodiments, the metal contact of the second side of the bifacial solar cell comprises or consists essentially of silver.Performance metrics

[0071] In some embodiments, the power conversion efficiency (PCE) loss of the bifacial solar cell post exposure to sodium relative to an unexposed control (in %) is less than about: 50, 45, 40, 35, 30, 25, or 20.

[0072] In some embodiments, the open-circuit voltage (Foe) loss of the bifacial solar cell post exposure to sodium relative to an unexposed control (in %) is less than about: 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, or 1.

[0073] In some embodiments, the maximum current that flows through a solar cell when the voltage across it is zero (Jsc loss of the bifacial solar cell post exposure to sodium relative to an unexposed control (in %) is less than about: 20, 15, 10, 9, 8, 7, 6, or 5.

[0074] In some embodiments, the fill factor (FF) loss of the bifacial solar cell post exposure to sodium relative to an unexposed control (in %) is less than about: 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, or 15.

[0075] In some embodiments, the series (Rs) increase of the bifacial solar cell post exposure to sodium relative to an unexposed control (in %) is less than about: 1500, 1400, 1300, 1200, 1100, 1000, 900, 800, 700, 600, or 500.

[0076] In some embodiments, the bifacial solar cell exhibits at least one of the following performance metrics post exposure to sodium relative to an unexposed control:PCE loss of less than about 50%, or less than about 20%;Voc loss of less than about 2%, or less than about 1%;Jsc loss of less than about 20%, or less than about 5%;FF loss of less than about 25%, or less than about 15%; andRsincrease of less than about 1000%, or less than about 700%.Process

[0077] Also disclosed herein is a process for depositing a substantially ion impermeable protective metal coating on a metal contact of a first side of a bifacial solar cell, the process comprising: establishing electrical communication between a metal contact of a second side of the bifacial solar cell and a negatively charged electrode at least partially immersed in a plating solution comprising an ion of the protective metal;establishing electrical communication between the metal contact of the second side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the first side of the bifacial solar cell in the plating solution; and applying a bias from the metal contact of the second side of the bifacial solar cell and / or exposing at least a portion of the first side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the protective metal ion from the plating solution on at least a portion of the front side metal contact of the bifacial solar cell to form the protective metal coating.

[0078] In some embodiments, the applying the bias from the second side metal contact and the exposing the first side of the bifacial solar cell to the light source occur simultaneously.

[0079] In some embodiments, the depositing of the ion impermeable protective metal coating on a metal contact of the first side of the bifacial solar cell is self-aligning. Self-aligning refers to deposition of the protective metal on the metal contact without requiring a masking or additional alignment step to be performed to prevent deposition on regions of the first side of the bifacial solar cell other than the metal contact.Solar cell

[0080] In some embodiments, the bifacial solar cell is selected from a tunnelling oxide passivated contact solar cell (TOPCon), passivated emitter and rear cell solar cell (PERC), Silicon heterojunction solar cell (SHJ), back-contact solar cell, and tandem solar cell. In some embodiments, the bifacial solar cell is a tunnelling oxide passivated contact solar cell.First side and second side

[0081] In some embodiments, the first side of the bifacial solar cell is the front side of the bifacial solar cell. In some embodiments, the second side of the bifacial solar cell is the back side of the bifacial solar cell.

[0082] In some embodiments, the first side of the bifacial solar cell is the back side of the bifacial solar cell. In some embodiments, the second side of the bifacial solar cell is the front side of the bifacial solar cell.Metal contact of the first side

[0083] The metal contact on the first side of the solar cell may be formed by any suitable method know in the art. In some embodiments, the metal contact of the first side is a screen- printed metal contact.

[0084] In some embodiments, the metal contact of the first side has an average width (in pm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 400, or 500. In some embodiments, the metal contact of the first side has an average width (in pm) of less than about: 500, 400, 300, 250, 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the first side has an average width (in pm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the first side has an average width (in pm) of between about 1 to about 500, between about 1 to about 100, between about 5 to about 40.

[0085] In some embodiments, the metal contact of the first side has an average height (in pm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200. In some embodiments, the metal contact of the first side has an average height (in pm) of less than about: 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The metal contact of the first side has an average height (in pm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the metal contact of the first side has an average height (in pm) of between about 1 to about 200, between about 1 to about 50, between about 5 to about 20.

[0086] In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from aluminium, gold, silver, titanium, copper, nickel, chromium, caesium, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from aluminium, silver, nickel, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises a metal selected from silver, nickel, and combinations thereof. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises silver. In some embodiments, the metal contact of the first side of the bifacial solar cell consists essentially of silver. In some embodiments, the metal contact of the first side of the bifacial solar cell comprises or consists essentially of silver.Light

[0087] In some embodiments, the amount of light (W / m2) that the first side of the bifacial solar cell is exposed to is about or greater than about: 200, 300, 400, 500, 600, or 700. In some embodiments, the amount of light (W / m2) that the first side of the bifacial solar cell is exposed to is less than about: 700, 600, 500, 400, 300, or 200. The amount of light (W / m2) that the first side of the bifacial solar cell is exposed may be in a range provided by any two of these upper and / or lower values. In some embodiments, the amount of light (W / m2) that the first side of the bifacial solar cell is exposed to is between about 200 to about 700, or between about 400 to about 700.

[0088] In some embodiments, the wavelength (nm) of the light that the first side of the bifacial solar cell is exposed to is about or greater than about: 350, 380, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, or 1100. In some embodiments, the wavelength (nm) of the light that the first side of the bifacial solar cell is exposed to is less than about: 1100, 1050, 1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 380, 350. The wavelength (nm) of the light that the first side of the bifacial solar cell is exposed to may be in a range provided by any two of these upper and / or lower values. In some embodiments, the wavelength (nm) of the light that the first side of the bifacial solar cell is exposed to is between about 380 to about 1100, or about 380 to about 700.

[0089] In some embodiments, the period of time (mins) that the bifacial solar cell is exposed to the light source for is about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, the period of time (mins) that the bifacial solar cell is exposed to the light source for is less than about: 0, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. The period of time (mins) that the bifacial solar cell is exposed to the light source may be in a range provided by any two of these upper and / or lower values. In some embodiments, the period of time (mins) that the bifacial solar cell is exposed to the light source for is between about 1 to about 20, between about 3 to about 10, or about 5.Current

[0090] In some embodiments, the current (mA) applied by the bias is about or greater than about: 50, 75, 100, 125, 150, 175, 200, 225, or 250. In some embodiments, the current (mA) applied by the bias is less than about: 250, 225, 200, 175, 150, 125, 100, 75, or 50. The current (mA) applied by the bias may be in a range provided by any two of these upper and / or lowervalues. In some embodiments, the current (mA) applied by the bias is between about 100 to about 200, or about 150.

[0091] In some embodiments, the period of time (mins) that the bias is applied to the solar cell for is about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. In some embodiments, the period of time (mins) that the bias is applied to the solar cell for is less than about: 0, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. The period of time (mins) that the bias is applied to the solar cell may be in a range provided by any two of these upper and / or lower values. In some embodiments, the period of time (mins) that the bias is applied to the solar cell for is between about 1 to about 20, between about 3 to about 10, or about 5.Swing

[0092] In some embodiments, the process further comprises moving the bifacial solar cell in the plating solution in one or more directions in the plane of the first side of the bifacial solar cell. Moving the bifacial solar cell in the plating solution in one or more directions in the plane of the first side of the bifacial solar cell is an optional process on to reduce the shadow effect.

[0093] In some embodiments, the moving the bifacial solar cell comprises swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell.

[0094] In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) of less than about: 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) is between about 1 to about 100, between about 5 to about 100, or between about 10 to about 30.

[0095] In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing rate (in mm / s) of about, or greater than about: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performedat a swing rate (in mm / s) of less than about: 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1. The swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing rate (in mm / s) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing rate (in mm / s) of between about 1 to about 100, or between about 5 to about 20.Protective metal and metal ion

[0096] In some embodiments, the plating solution comprises an ion of the protective metal. In some embodiments, the protective metal is selected from copper, silver, tin, nickel, and combinations thereof. In some embodiments, the protective metal is copper.

[0097] In some embodiments, the ion of the protective metal in the plating solution is obtained from a metal salt. In some embodiments, the anion of the metal salt is selected from a chloride, sulfate, nitrate, phosphate, carbonate, cyanide, borate, acetate, fluoroborate, sulfonate, and combinations thereof. In some embodiments, the anion is a sulfate.

[0098] In some embodiments, the metal salt is copper sulfate.

[0099] In some embodiments, the concentration of the metal ion in the casting solution (mol / L) is maintained at about, or greater than about: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2. In some embodiments, the concentration of the metal ion in the casting solution (mol / L) is maintained at less than about: 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1. The concentration of the metal ion in the casting solution (mol / L) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the concentration of the metal ion in the casting solution (mol / L) is maintained at between about 0.1 to about 2, is between about 0.3 to about 1.

[0100] In some embodiments, the ion impermeable protective metal coating comprises copper. In some embodiments, the ion impermeable protective metal coating consists essentially of copper.

[0101] In some embodiments, the positive electrode comprises the same metal as the protective metal. In some embodiments, the positive electrode comprises a metal selected from copper, silver, tin, nickel, and combinations thereof. In some embodiments, the positiveelectrode comprises copper. In some embodiments, the positive electrode consists essentially of copper.Arrangement

[0102] In some embodiments, the process further comprises preventing contact between the metal contact of the second side of the bifacial solar cell and the plating solution during deposition of the protective metal coating on the first side of the bifacial solar cell. In some embodiments, the process further comprises contacting the metal contact of the second side of the bifacial solar cell with the negative electrode to prevent contact between the rear side metal contact and the plating solution during deposition of the protective metal coating on the first side of the bifacial solar cell.

[0103] In some embodiments, the positive electrode and the at least a portion of the first side of the bifacial solar cell are arranged in the plating solution such that a surface of the positive electrode and a surface of the first side of the bifacial solar cell are substantially parallel to each other.

[0104] In some embodiments, a surface of the positive electrode and the surface of first side of the bifacial solar cell are separated by an average distance (in mm) of about or greater than about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or 200. In some embodiments, a surface of the positive electrode and the surface of first side of the bifacial solar cell are separated by an average distance (in mm) of less than about: 200, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50, 40, 30, 20, or 10. The surface of the positive electrode and the surface of first side of the bifacial solar cell are separated by an average distance (in mm) may be in a range provided by any two of these upper and / or lower values. In some embodiments, the surface of the positive electrode and the surface of first side of the bifacial solar cell are separated by an average distance (in mm) of between about 10 to about 200, or between about 50 to about 100.Second side coating

[0105] In some embodiments, the process further comprising depositing a substantially ion impermeable second protective metal coating on a metal contact of a second side of a bifacial solar cell.

[0106] In some embodiments, the process the process comprises:establishing electrical communication between a metal contact of the first side of the bifacial solar cell and a second negatively charged electrode at least partially immersed in a second plating solution comprising an ion of the second protective metal; establishing electrical communication between the metal contact of the first side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the second side of the bifacial solar cell in the second plating solution; and applying a bias from the metal contact of the first side of the bifacial solar cell and / or exposing at least a portion of the second side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the second protective metal ion from the second plating solution on at least a portion of the second side metal contact of the bifacial solar cell to form the second protective metal coating.

[0107] In some embodiments, the second protective metal is the same as the protective metal.Additional process steps

[0108] In some embodiments, the process further comprises washing the front side of the bifacial solar cell prior to immersing at least a portion of the front side of the bifacial solar cell in a plating solution. In some embodiments, the washing is performed using deionized water. In some embodiments, the process further comprises drying the front side of the bifacial solar cell after washing and prior to immersing in the plating solution. In some embodiments, the drying is performed with nitrogen.

[0109] In some embodiments, the process further comprises washing the front side of the bifacial solar cell after the protective coating is formed. In some embodiments, the washing is performed using deionized water. In some embodiments, the process further comprises drying the front side of the bifacial solar cell after washing after the protective coating is formed. In some embodiments, the drying is performed with nitrogen.Product by process

[0110] Also disclosed herein is a bifacial solar cell obtained from a process as described herein.EXAMPLE EMBODIMENTS

[0111] The present disclosure may be defined by one or more example embodiments as described herein:1. A bifacial solar cell comprising: a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell, wherein the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.2. The bifacial solar cell of embodiment 1, wherein the protective metal coating on the first side metal contact has an average thickness (in pm) of less than about 10, or less than about2.3. The bifacial solar cell any one of the preceding embodiments, wherein the protective metal coating on the first side metal contact comprises or consists essentially of copper.4. The bifacial solar cell of any one of the preceding embodiments, wherein: the metal contact of the first side is a screen-printed metal contact; and / or the protective metal coating covers substantially all of the first side metal contact.5. The bifacial solar cell of any one of the preceding embodiments, wherein the metal contact of the first side has an average width (in pm) of between about 1 to about 100, or between about 5 to about 40.6. The bifacial solar cell of any one of the preceding embodiments, wherein the metal contact of the first side has an average height (in pm) of between about 1 to about 50, or between about 5 to about 20.7. The bifacial solar cell of any one of the preceding embodiments, wherein the metal contact of the first side of the bifacial solar cell comprises or consists essentially of silver.8. The bifacial solar cell of any one of the preceding embodiments, wherein the bifacial solar cell is a tunnelling oxide passivated contact solar cell.9. The bifacial solar cell of any one of the preceding embodiments, wherein the first side is the front side of the bifacial solar cell.10. The bifacial solar cell of any one of the preceding embodiments, further comprising a protective metal coating on at least a portion of a metal contact of a second side of a bifacial solar cell, optionally wherein the protective metal coating covers substantially all of the second side metal contact; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.11. The bifacial solar cell of any one of the preceding embodiments, wherein the bifacial solar cell exhibits at least one of the following performance metrics post exposure to sodium relative to an unexposed control:PCE loss of less than about 50%, or less than about 20%;Voc loss of less than about 2%, or less than about 1%;Jsc loss of less than about 20%, or less than about 5%;FF loss of less than about 25%, or less than about 15%; andRsincrease of less than about 1000%, or less than about 700%.12. A process for depositing a substantially ion impermeable protective metal coating on a metal contact of a first side of a bifacial solar cell, the process comprising: establishing electrical communication between a metal contact of a second side of the bifacial solar cell and a negatively charged electrode at least partially immersed in a plating solution comprising an ion of the protective metal; establishing electrical communication between the metal contact of the second side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the first side of the bifacial solar cell in the plating solution; and applying a bias from the metal contact of the second side of the bifacial solar cell and / or exposing at least a portion of the first side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the protective metal ion from the plating solution on at least a portion of the front side metal contact of the bifacial solar cell to form the protective metal coating.13. The process of embodiment 12, wherein the applying the bias from the second side metal contact and the exposing the first side of the bifacial solar cell to the light source occur simultaneously.14. The process of embodiment 12 or embodiment 13, wherein the depositing of the ion impermeable protective metal coating on a metal contact of the first side of the bifacial solar cell is self-aligning.15. The process of any one of embodiments 12 to 14, wherein the bifacial solar cell is a tunnelling oxide passivated contact solar cell.16. The process of any one of embodiments 12 to 15, wherein the metal contact of the first side of the bifacial solar cell is a screen-printed metal contact.17. The process of any one of embodiments 12 to 16, wherein the metal contact of the first side of the bifacial solar cell comprises silver.18. The process of any one of embodiments 12 to 17, wherein the metal contact of the first side of the bifacial solar cell consists essentially of silver.19. The process of any one of embodiments 12 to 18, wherein the process further comprises preventing contact between the metal contact of the second side of the bifacial solar cell and the plating solution.20. The process of any one of embodiments 12 to 19, wherein the process further comprises contacting the metal contact of the second side of the bifacial solar cell with the cathode to prevent contact between the rear side metal contact and the plating solution.21. The process of any one of embodiments 12 to 20, wherein the amount of light (W / m2) that the first side of the bifacial solar cell is exposed to is between about 400 to about 700.22. The process of any one of embodiments 12 to 21, wherein the wavelength (nm) of the light that the first side of the bifacial solar cell is between about 380 to about 1100, or about 380 to about 700.23. The process of any one of embodiments 12 to 22, wherein the period of time (mins) that the bifacial solar cell is exposed to the light source for is between about 1 to about 20, between about 3 to about 10, or about 5.24. The process of any one of embodiments 12 to 23, wherein the current (mA) applied by the bias is between about 100 to about 200, or about 150.25. The process of any one of embodiments 12 to 24, wherein the period of time (mins) that the bias is applied to the solar cell is between about 1 to about 20, between about 3 to about 10, or about 5.26. The process of any one of embodiments 12 to 25, wherein the process further comprises moving the bifacial solar cell in the plating solution in one or more directions in the plane of the first side of the bifacial solar cell.27. The process of embodiment 26, wherein the moving the bifacial solar cell comprises swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell.28. The process of embodiment 27, wherein the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) of between about 1 to about 100, between about 5 to about 100, or between about 10 to about 30.29. The process of embodiment 27 or embodiment 28, wherein the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing rate (in mm / s) of between about 1 to about 100, or between about 5 to about 20.30. The process of any one of embodiments 12 to 29, wherein the ion impermeable protective metal coating comprises or consists essentially of: copper, silver, tin, nickel, and combinations thereof.31. The process of any one of embodiments 12 to 30, wherein the ion impermeable protective metal coating comprises or consists essentially copper.32. The process of any one of embodiments 12 to 31, wherein the concentration of the metal ion in the casting solution (mol / L) is maintained at between about 0.1 to about 2, is between about 0.3 to about 1.33. The process any one of embodiments 12 to 32, wherein the positive electrode comprises the same metal as the protective metal.34. The process any one of embodiments 12 to 33, wherein the positive electrode comprises copper.35. The process of any one of embodiments 12 to 34, wherein the positive electrode and the at least a portion of the first side of the bifacial solar cell are arranged in the plating solution such that a surface of the positive electrode and the first side of the bifacial solar cell are substantially parallel to each other.36. The process of embodiment 35, wherein the surface of the positive electrode and the first side of the bifacial solar cell are separated by an average distance (in mm) of between about 10 to about 200, between about 50 to about 100, optionally 80.37. The process of any one of embodiments 12 to 36, wherein the process further comprises washing the front side of the bifacial solar cell prior to immersing at least a portion of the front side of the bifacial solar cell in a plating solution.38. The process of any one of embodiments 12 to 37, wherein the process further comprises washing the front side of the bifacial solar cell after the protective coating is formed.39. The process of embodiment 37 or embodiment 38, wherein the washing is performed using deionized water.40. The process of embodiment 37 or embodiment 39, wherein the process further comprises drying the front side of the bifacial solar cell after washing.41. The process of any one of embodiments 12 to 40, the process further comprising depositing a substantially ion impermeable second protective metal coating on a metal contact of a second side of a bifacial solar cell.42. The process of embodiment 41, wherein the process comprises: establishing electrical communication between a metal contact of the first side of the bifacial solar cell and a second negatively charged electrode at least partially immersed in a second plating solution comprising an ion of the second protective metal; establishing electrical communication between the metal contact of the first side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the second side of the bifacial solar cell in the second plating solution; and applying a bias from the metal contact of the first side of the bifacial solar cell and / or exposing at least a portion of the second side of the bifacial solar cell to a light source;wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the second protective metal ion from the second plating solution on at least a portion of the second side metal contact of the bifacial solar cell to form the second protective metal coating.43. The process of embodiment 41, wherein the second protective metal is the same as the protective metal.44. A bifacial solar cell obtained from the process of any one of embodiments 12 to 43.EXAMPLES

[0112] The design of an exemplary experiment is shown in Figure 1.Bifacial solar cell

[0113] Bifacial nine-busbar (9BB) 158 mm TOPCon solar cells were used in this work. The TOPCon cells featured a tunneling SiCh / phosphorus-doped poly silicon (n+ poly-Si) / SiNx:H stack and a screen-printed H-pattern silver grid on the rear. The front side featured a boron- doped emitter (p+ emitter), silicon dioxide (SiChyAhCh / SiNx H stack, and a screen-printed H- pattern silver grid as shown in Figure 2.Plating process

[0114] Plating was done on the screen-printed solar cells using a Conifer plating tool at the Solar Industrial Research Facility (SIRF), UNSW. Samples were cleaned with deionized water (DIW) before the plating. The rear side completely contacted the cathode electrode, and the front side was immersed in the plating solution (CuSCh at 0.3 mol / L.). Bias-assisted light- induced plating (LIP) with a 150 mA constant current during the process.

[0115] An approximately! pm (estimated from plating rate) copper layer was deposited on the front side metal contact of the TOPCon solar cells.

[0116] Top-view Scanning electron microscopy (SEM) images were taken by a FEI Nova NanoSEM 450 FE-SEM, while a ZEISS Cryogenic focused ion beam (Cryo-FIB)-SEM tool was used to cut through the finger contact of cells and take cross-sectional SEM images as well. The energy dispersive spectroscopy (EDS) data was measured by the Oxford Instruments Ultim® Max, and analysed with AZtec software.

[0117] The top-view SEM images on the front metal of bare and as-plated samples are shown in Figure 3 and Figure 4, respectively. As shown in Figure 3, the metal contact of the bare sample showed a highly porous structure. As shown in Figure 4, the Cu-plated contact does not show any pores.

[0118] In Figure 5, the top-view EDS results demonstrated that the plated-Cu well covered the metal surface. The Ag signal could hardly be detected after the plating process, except for some scattered Ag particles separated from the metal bulk.

[0119] Cryo-FIB was utilized to cut through the fingers and subsequently capture cross- sectional SEM and EDS results for detailed analysis. In Figure 6 and Figure 7, the images of the front metal of as received and plated samples are shown respectively. In Figure 6, the finger bulk showed structures with high porosity, which was consistent with what we observed on the metal surface. Importantly, the Cu signal of the plated sample shown in Figure 7 illustrated that the Cu layer completely covered the surface of the contact and even filled some voids in the metal bulk, as long as those voids were accessible for the plating solution during the plating process.

[0120] The one-sun current-voltage (I-V) parameters of cells were measured by an LOANA I-V tester from pv-tools. A BTi (LIS-R3) luminescence imaging system was used to capture the photoluminescence (PL) and series resistance ( f) images with a high open-circuit voltage lens. PL images were processed by LumiTools and Rsimages were analysed by Imaged. A pv-tools TLM-SCAN+tool was used to carry out the transfer length method (TLM) measurement on the cell contact resistivity analysis at intervals during the DH testing. A four-point probe station was used to measure the line resistance of solar cells.

[0121] Table 1 summarises the electrical performance of samples before and after the plating process. It is notable that the PCE of samples improved ~0.39%reiafter the plating process, with no significant changes observed in Voc. The high-density plated-Cu layer reduced the line resistance of fingers and busbars

[0049] , resulting in a notable Rsdecrease, which was probably the main reason for the relative -0.67% higher fill factor (FF). On the contrary, the additional Cu layer increases the size of the front metal contact thereby increasing shading leading to a -0.29% lower Jscas shown in Table 1. Moreover, the overall improved efficiency caused by lower metal resistance also showed the potential of reducing Ag usage and material cost, by replacing part of the screen-printed Ag on the top with plated-Cu.Table 1. Rs, FF, Voc, Jsc and PCE of the as received and plated solar cells.PCE (%) Voc(mV) Jsc (mA / cm2) FF (%) Rs (Olmrcm2)Before Plating 23.24 ± 0.01 706.4 ± 0.7 39.79 ± 0.03 82.68 ± 0.77 0.30 ± 0.02After Plating 23.33 ± 0.02 706.6 ± 0.7 39.67 ± 0.04 83.23 ± 0.05 0.23 ± 0.07Relative Variation 0.39% 0.02% -0.29% 0.67% -24.69%Accelerated damp-heat testing of TOPCon solar cells

[0122] The protective effects on the NaCl-induced degradation of as-plated cells were assessed by accelerated damp-heat testing, together with bare samples without plated-Cu.

[0123] Before the damp heat testing, all of the samples were cleaned with deionized water (DIW) followed by nitrogen (N2) drying before the test to ensure they were clear. Then, a 0.9% weight (medical grade) NaCl solution was sprayed uniformly on the front side of bare (Group Bare NaCl) and plated (Group Plated NaCl) cells. After that, all of the cells were put into the ASLi Environment chamber for an 85 °C and 85% relative humidity accelerated damp-heat (DH) testing. Moreover, plated and non-plated cell stripes without busbars were cut by FOB A M1000 scribing laser tool. Then we measured the contact resistivity of those samples as a function of time during the DH testing, with exposure to NaCl solution.I-V results during DH testing

[0124] Figure 5 shows the I-V parameters of cells from different groups, as shown in Figure 1, as a function of the damp heat testing time. The Control samples remain stable, indicating that the high-temperature and high-humidity damp-heat test by itself did not induce degradation of TOPCon solar cells. Additionally, no significant degradation was observed in the Group Plated samples after the DH testing. The results further confirmed that the plated-Cu was not detrimental to cells and also remained stable under conditions of 85% relative humidity and 85°C. However, losses can be observed in the bare cells exposed to NaCl (Bare_NaCl) during the DH testing. After 6 hours of DH testing, a significant rise in series resistance (Rs) was observed, nearly 50 times higher than the initial value. The relative -52.2% lower short-circuit current Jsc) indicates a reduced carrier collection ability after DH testing, and the -2.8%reidrop of open-circuit voltage (Foc) indicated some induced recombination. Overall, the 6 hours of DH testing led to over 80% relative degradation of PCE for the Bare NaCl sample.

[0125] In contrast to the Bare NaCl samples, the Plated NaCl samples only presented a relatively minor drop (-11.5%rei) in PCE after 6 hours of DH testing. There was just a -1.2%reiJsc drop for the Plated NaCl samples after the DH testing, and only a ~0.2%rei Vocdrop. The performance degradation was mainly caused by the relative -10.2% decrease in FF, which could be attributed to Rsincrease (around 5 times higher). However, the FF loss was still significantly lower compared to the Bare NaCl samples (~64.6%reiloss after 6 hours of DH testing). Although the Plated NaCl sample exhibited slight degradation, the Bare NaCl sample just showed an end-of-life efficiency of less than 5% without plated-Cu protection. Consequently, Cu-plating was found to be highly effective in alleviating the NaCl-induced degradation during the DH testing.Series resistance and photoluminescence images

[0126] Figure 9 and Figure 10, respectively, show the Rsand PL images of representative samples of Group Control, Plated, Bare NaCl and Plated NaCl, which were captured at designated intervals by removing the solar cells from the climate chamber during the DH experiments. For the Control and Plated samples, no noteworthy degradation could be observed from either Rs or PL images. However, notable Rsissues can be observed for the Bare NaCl sample after only 2 hours of DH testing which deteriorated further after 4 hours of DH testing. Meanwhile, the Plated NaCl sample also showed a slight Rsissue with fabric-like patterns in the Rs image after 4 hours DH testing, but compared with the Bare NaCl sample, the Plated NaCl sample was a lot more stable.

[0127] On the other hand, no significant changes were revealed in the PL images of both Bare NaCl and Plated NaCl samples, indicating that the DH testing did not significantly increase the recombination all over the TOPCon solar cells in this study. However, the locally magnified images revealed that the Bare NaCl sample exhibited a blurry signal along the metal contact region, suggesting that NaCl-induced recombination primarily occurred at the contact after the DH testing. In contrast, the PL image of the Plated NaCl sample demonstrated a lower recombination signal at the contact region.

[0128] In summary, TOPCon cells were sensitive to the contaminants on the front side under 85 °C and 85% relative humidity accelerated damp-heat (DH) test. Bias-assisted LIP plating of approximately -1 pm Cu on the front grid of TOPCon cells provided a protective effect against degradation during accelerated cell-level damp heat test. The plated cells' efficiency relatively increased by -0.39% after the plating process due to lower series resistance. Moreover, the DH testing results illustrated that, without the plated-Cu layer, a significant degradation could be observed with the presence of NaCl solution after 6 hours of DH testing, with a rapid Rs increaseand Voc drop, resulting in notable over 80%reiefficiency degradation. However, with exposure to the NaCl solution, the samples with plated-Cu as the protection layer performed much better. Only ~11.5%rei drop in PCE could be observed after 6 hours of DH testing, with a slight Rsincrease. The plated-cell just performed ~1.2%reidrop in Jscafter DH testing and Vocwas also quite stable. The plated-Cu layer can effectively alleviate NaCl-induced degradation and improve device stability.

[0129] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments and examples are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. Claims:

1. A bifacial solar cell comprising: a protective metal coating on at least a portion of a metal contact of a first side of a bifacial solar cell, wherein the protective metal coating comprises a metal selected from: copper, silver, tin, nickel, and combinations thereof; and wherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

2. The bifacial solar cell of claim 1, wherein: the protective metal coating on the first side metal contact has an average thickness (in pm) of less than about 10, or less than about 2; and / or the protective metal coating on the first side metal contact comprises or consists essentially of copper; and / or the metal contact of the first side is a screen-printed metal contact; and / or the protective metal coating covers substantially all of the first side metal contact; and / or the metal contact of the first side has an average width (in pm) of between about 1 to about 100, or between about 5 to about 40; and / or the metal contact of the first side has an average height (in pm) of between about 1 to about 50, or between about 5 to about 20; and / or the metal contact of the first side of the bifacial solar cell comprises or consists essentially of silver.

3. The bifacial solar cell of claim 1 or claim 2, wherein the bifacial solar cell is a tunnelling oxide passivated contact solar cell.

4. The bifacial solar cell of any one of claims 1 to 3, wherein the first side is the front side of the bifacial solar cell.

5. The bifacial solar cell of any one of claims 1 to 4, further comprising a protective metal coating on at least a portion of a metal contact of a second side of a bifacial solar cell, optionally wherein the protective metal coating covers substantially all of the second side metal contact; andwherein the protective metal coating forms a substantially ion impermeable coating on the metal contact of the first side of a bifacial solar cell.

6. The bifacial solar cell of any one of claims 1 to 5, wherein the bifacial solar cell exhibits at least one of the following performance metrics post exposure to sodium relative to an unexposed control:PCE loss of less than about 50%, or less than about 20%; and / orVoc loss of less than about 2%, or less than about 1%; and / orJsc loss of less than about 20%, or less than about 5%; and / orFF loss of less than about 25%, or less than about 15%; and / orRsincrease of less than about 1000%, or less than about 700%.

7. A process for depositing a substantially ion impermeable protective metal coating on a metal contact of a first side of a bifacial solar cell, the process comprising: establishing electrical communication between a metal contact of a second side of the bifacial solar cell and a negatively charged electrode at least partially immersed in a plating solution comprising an ion of the protective metal; establishing electrical communication between the metal contact of the second side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the first side of the bifacial solar cell in the plating solution; and applying a bias from the metal contact of the second side of the bifacial solar cell and / or exposing at least a portion of the first side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the protective metal ion from the plating solution on at least a portion of the front side metal contact of the bifacial solar cell to form the protective metal coating.

8. The process of claim 7, wherein the applying the bias from the second side metal contact and the exposing the first side of the bifacial solar cell to the light source occur simultaneously.

9. The process of claim 7 or claim 8, wherein the depositing of the ion impermeable protective metal coating on a metal contact of the first side of the bifacial solar cell is selfaligning.

10. The process of any one of claims 7 to 9, wherein the bifacial solar cell is a tunnelling oxide passivated contact solar cell.

11. The process of any one of claims 7 to 10, wherein: the metal contact of the first side of the bifacial solar cell is a screen-printed metal contact; and / or the metal contact of the first side of the bifacial solar cell comprises silver; and / or the metal contact of the first side of the bifacial solar cell consists essentially of silver.

12. The process of any one of claims 7 to 11, wherein the process further comprises: preventing contact between the metal contact of the second side of the bifacial solar cell and the plating solution; and / or contacting the metal contact of the second side of the bifacial solar cell with the cathode to prevent contact between the rear side metal contact and the plating solution.

13. The process of any one of claims 7 to 12, wherein: the amount of light (W / m2) that the first side of the bifacial solar cell is exposed to is between about 400 to about 700; and / or the wavelength (nm) of the light that the first side of the bifacial solar cell is between about 380 to about 1100, or about 380 to about 700; and / or the period of time (mins) that the bifacial solar cell is exposed to the light source for is between about 1 to about 20, between about 3 to about 10, or about 5; and / or the current (mA) applied by the bias is between about 100 to about 200, or about 150; and / or the period of time (mins) that the bias is applied to the solar cell is between about 1 to about 20, between about 3 to about 10, or about 5.

14. The process of any one of claims 7 to 13, wherein the process further comprises moving the bifacial solar cell in the plating solution in one or more directions in the plane of the first side of the bifacial solar cell and optionally the moving the bifacial solar cell comprises swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell.

15. The process of claim 14, wherein: the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing range (in mm) of between about 1 to about 100, between about 5 to about 100, or between about 10 to about 30; and / or the swinging the bifacial solar cell in the plane of the first side of the bifacial solar cell is performed at a swing rate (in mm / s) of between about 1 to about 100, or between about 5 to about 20.

16. The process of any one of claims 7 to 15, wherein: the ion impermeable protective metal coating comprises or consists essentially of: copper, silver, tin, nickel, and combinations thereof; and / or the ion impermeable protective metal coating comprises or consists essentially copper.

17. The process of any one of claims 7 to 16, wherein the concentration of the metal ion in the casting solution (mol / L) is maintained at between about 0.1 to about 2, or between about 0.3 to about 1.

18. The process any one of claims 7 to 17, wherein: the positive electrode comprises the same metal as the protective metal; and / or the positive electrode comprises copper; and / or the positive electrode and the at least a portion of the first side of the bifacial solar cell are arranged in the plating solution such that a surface of the positive electrode and the first side of the bifacial solar cell are substantially parallel to each other, optionally wherein the surface of the positive electrode and the first side of the bifacial solar cell are separated by an average distance (in mm) of between about 10 to about 200, between about 50 to about 100, or about 80.

19. The process of any one of claims 7 to 18, wherein: the process further comprises washing the front side of the bifacial solar cell prior to immersing at least a portion of the front side of the bifacial solar cell in a plating solution, optionally wherein the washing is performed using deionized water, and optionally wherein the process further comprises drying the front side of the bifacial solar cell after washing; and / orthe process further comprises washing the front side of the bifacial solar cell after the protective coating is formed, optionally wherein the washing is performed using deionized water, and optionally wherein the process further comprises drying the front side of the bifacial solar cell after washing.

20. The process of any one of claims 7 to 19, the process further comprising depositing a substantially ion impermeable second protective metal coating on a metal contact of a second side of a bifacial solar cell, optionally wherein the process comprises: establishing electrical communication between a metal contact of the first side of the bifacial solar cell and a second negatively charged electrode at least partially immersed in a second plating solution comprising an ion of the second protective metal; establishing electrical communication between the metal contact of the first side of the bifacial solar cell and an electrical bias source; immersing at least a portion of the second side of the bifacial solar cell in the second plating solution; and applying a bias from the metal contact of the first side of the bifacial solar cell and / or exposing at least a portion of the second side of the bifacial solar cell to a light source; wherein the amount of light from the light source and / or the applied bias are in an amount effective to achieve the deposition of an amount of the second protective metal ion from the second plating solution on at least a portion of the second side metal contact of the bifacial solar cell to form the second protective metal coating, and optionally wherein the second protective metal is the same as the protective metal.

21. A bifacial solar cell obtained from the process of any one of claims 7 to 20.

Images