Double-sided PERC solar cell and method for producing same

Abstract

The present disclosure generally relates to a burn-through aluminum paste composition and fired compositions thereof for selectively burn-through a passivation layer. In particular, the burn-through aluminum paste compositions of the present disclosure include an aluminum component and a glass component, where the glass component includes at least two glass frits. The present disclosure also relates to a method for preparing a burn-through aluminum paste composition and its use in the manufacture of a double sided PERC solar cell.

Description

Technical Field

[0001] The present disclosure generally relates to a burn-through aluminum paste composition for selectively burning through a passivation layer and a fired composition thereof. Specifically, the burn-through aluminum paste composition of the present disclosure comprises an aluminum component and a glass component, wherein the glass component comprises at least two glass frits. The present disclosure also relates to a method for preparing the burn-through aluminum paste composition and its use in the manufacture of bifacial PERC solar cells. Background Art

[0002] Solar cell cells are typically manufactured to include a semiconductor substrate / body (usually silicon), a passivating dielectric layer on or above the silicon, and a metallization structure. When light is absorbed in the semiconductor substrate, charges are excited and move to the semiconductor surface, where they can be extracted at the metallization structure for use in external circuits. The dielectric passivation layer reduces the recombination of charges at the semiconductor surface, thereby improving device efficiency.

[0003] To efficiently extract charge from the solar cell, the metallization structure penetrates the dielectric passivation layer to contact the semiconductor below the dielectric passivation layer or to contact the conductive layer below the dielectric passivation layer. In the case of contact with the semiconductor material, the conductive layer can contact the conductive area of ​​the semiconductor material, such as the emitter or P-type bulk for screen-printed passivated rear emitter contact (PERC) solar cells.

[0004] Two different techniques can be used to create post-local contacts. One approach involves partially opening the passivation layer, followed by full-area screen printing or other patterning techniques of aluminum paste, and subsequent thermal alloying to form the contacts. Another approach involves full-area screen printing of aluminum paste on the passivation layer, followed by laser firing through the dielectric layer to form local contacts at the laser openings. The laser step and the use of full-area printed aluminum increase costs. Using full-area printed aluminum can also cause the wafer to bow during firing, driven by the well-known differential thermal expansion between silicon and the metallization layer, the extent of which is controlled by the composition and relative thickness of the printed material and the silicon substrate. Excessive bowing beyond a threshold can pose challenges to cell handling, module assembly, and lifetime performance, as cracks or cell fracture may occur. Therefore, to reduce failures, the bow threshold is specified to be below a certain value. This means that solar cells need to be formed from silicon wafers with a thickness exceeding a certain value to reduce the effects of differential thermal expansion, maintain flatness, and therefore prevent fracture during cell handling during production. Furthermore, silicon is a relatively brittle material and prone to cracking and even breaking, however, below a critical thickness and size, silicon wafers become flexible without crack propagation. Conversely, at the same metallization print thickness, thin and flexible cells are more easily bent, which avoids cell handling during production and module assembly. The thickness of silicon used by industry standards reduces the effects of bending, however, this in turn limits the industry to producing flat and rigid modules, which incurs additional costs during both production and installation. The cost of silicon is the largest component in the bill of materials, and reducing costs by reducing the thickness of silicon is an obvious incentive to reduce overall energy costs. Full rear aluminum printing is opaque and blocks light from the rear side, so the standard PERC process is not compatible with bifaciality.

[0005] Therefore, there is a need to provide new and alternative fire-through paste compositions for bifacial PERC solar cells that avoid the use of lasers, especially those containing aluminum-glass composites that can promote aluminum metallization on the back side of the silicon substrate to form an Al-Si alloy and a localized back surface field. Summary of the Invention

[0006] In one aspect, a fire-through aluminum paste composition for selectively firing through a passivation layer is provided. The paste composition comprises an aluminum component, a glass component, and a patterning medium. The glass component comprises at least a first glass frit (A) and a second glass frit (B). The first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature (i.e., within the glass transition temperature range), and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy). The volume of the low-viscosity liquid and the concentration of the first glass frit (A) are controlled. In this case, A and / or B can be crystalline, crystallizable, or vitreous glass, or a crystalline system.

[0007] In another aspect, a method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer is provided, the method comprising: (i) providing an aluminum component and a glass component, and (ii) dispersing the aluminum component and the glass component in a patterning medium to form the fire-through aluminum paste composition, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

[0008] In another aspect, a fired back contact paste is provided that adheres to a passivation layer of a bifacial PERC solar cell unit comprising a silicon substrate, wherein the passivation layer is fired through to contact the silicon and allow aluminum to approach the silicon to form an Al-Si alloy, whereupon cooling enables formation of a p+ layer by doping Al atoms at the silicon sites, wherein prior to firing, the fired back contact paste is a fire-through paste composition comprising: an aluminum component, a glass component, and a patterning medium; wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature (i.e., a glass transition temperature range), and the second glass frit (B) does not contain silicon nitride (SiN x) or hydrogenated silicon nitride (SiN x :H y ) and controlling the volume of the low viscosity liquid and the concentration of the first glass frit (A). The firing profile for forming the p+ layer must be designed to be compatible with the formation of the n+ contact, either on opposite sides of a double-sided design or on the same side (in the case of an interdigitated rear contact cell), otherwise the composition design of the n+ contact may require significant changes to conventional firing processes in the art.

[0009] In another aspect, a bifacial PERC solar cell unit is provided, the cell unit comprising a silicon substrate and a back contact thereon, the back contact comprising a passivation layer, the passivation layer being at least partially coated with a fired back contact paste at the back side of the silicon substrate, wherein the back contact paste is a fire-through aluminum paste composition for selectively firing through the passivation layer, wherein before firing, the fire-through aluminum paste composition comprises an aluminum component, a glass component, and a patterning medium; wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

[0010] On the other hand, a method for preparing a bifacial PERC solar cell unit is provided, the method comprising: providing a silicon substrate and a rear passivation layer thereon, applying a fire-through aluminum paste composition to at least partially coat the passivation layer, and selectively fire-through the passivation layer, the paste composition comprising an aluminum component, a glass component, and a patterning medium, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y) and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A), heating the paste composition to a predetermined temperature to burn through at least a portion of the passivation layer to contact the silicon and enable aluminum to approach the silicon to promote contact metallization, doping aluminum in the silicon, and formation of a back surface field. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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:

[0012] Figure 1 is a cross-sectional view of a first embodiment of a battery cell.

[0013] Figure 2 is a cross-sectional view of a second embodiment of a battery cell.

[0014] Figure 3 is an orthogonal view of a third embodiment of a battery cell.

[0015] Figure 4 is an orthogonal view of a fourth embodiment of a battery cell.

[0016] Figure 5 is an optical image (Olympus OLS3000 laser microscope) of an example printed battery cell after firing, showing the formation of the Al-Si alloy.

[0017] Figure 6 is a graph comparing Voc as a function of relative frit content in fired compacts with varying AlOx thickness in the passivation stack.

[0018] Figure 7 The effect of relative frit content on PERC cell efficiency with different AlOx thicknesses in the passivation layer. DETAILED DESCRIPTION

[0019] The present disclosure describes various non-limiting examples below relating to research conducted to identify alternative and improved fire-through aluminum paste compositions and fired compositions thereof, and any methods of making and using the same. The present disclosure also relates to bifacial PERC solar cell units and methods of producing the same.

[0020] General Definitions and Terminology

[0021] In the following description, reference is made to the accompanying drawings, which form a part of the description and which show several embodiments by way of illustration. It should be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure.

[0022] With respect to the definitions provided herein, unless otherwise stated or implied from the context, the defined terms and phrases include the provided meanings. In addition, unless otherwise expressly stated or apparent from the context, the following terms and phrases do not exclude the meanings of the terms or phrases as acquired by one skilled in the relevant art. These definitions are provided to aid in describing particular embodiments and are not intended to limit the claimed invention, as the scope of the invention is limited only by the claims. In addition, unless the context requires otherwise, singular terms shall include the plural, and plural terms shall include the singular.

[0023] All publications discussed and / or referenced herein are incorporated herein in their entirety.

[0024] Throughout this disclosure, unless otherwise specifically stated or the context requires otherwise, references to individual steps, compositions of matter, groups of steps, or groups of compositions of matter should be considered to encompass one and multiple (i.e., one or more) of these 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 single as well as two or more; reference to "a" includes single as well as two or more; reference to "the" includes single as well as two or more, etc.

[0025] Those skilled in the art will appreciate that the disclosure herein may be subject to changes and modifications other than those specifically described. It is to be understood that the present disclosure includes all such changes and modifications. The present disclosure also includes all examples, steps, features, methods, compositions, coatings, processes, and coated substrates referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of the steps or features.

[0026] The term "and / or," such as "X and / or Y," should be understood to mean "X and Y" or "X or Y," and should be considered to provide explicit support for both meanings or either meaning.

[0027] 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. Furthermore, reference to a "second" item does not require or preclude the presence of lower-numbered items (e.g., a "first" item) and / or higher-numbered items (e.g., a "third" item).

[0028] As used herein, when used with a list of items, the phrase “at least one of…” means that different combinations of one or more of the listed items may be used, and only one of the items in the list may be required. The item may be a specific object, thing, or category. In other words, “at least one of…” means that any combination of items or numbers of items in the list may be used, but not all 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, but not limited to, 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.

[0029] It will be appreciated that certain features described herein in the context of separate embodiments for clarity may also be provided in combination in a single embodiment. Conversely, various features described in the context of a single embodiment for brevity may also be provided individually or in any subcombination.

[0030] Throughout this specification, various aspects and components of the present invention may be presented in a range format. The range format is included for convenience and should not be construed as an inflexible limitation on the scope of the invention. Therefore, unless otherwise stated, the description of a range should be considered to have explicitly disclosed all possible subranges and individual values ​​within the range. For example, unless an integer is required or the context implies an integer, a description of a range such as from 1 to 5 should be considered to have specifically disclosed subranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 5, 3 to 5, etc.; as well as individual and partial numbers within the stated range, for example, 1, 2, 3, 4, 5, 5.5, and 6. This applies regardless of the breadth of the disclosed range. When specific values ​​are required, these values ​​will be indicated in the specification.

[0031] Throughout this specification, the word "comprising" 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.

[0032] Throughout this specification, the term "consisting essentially of is intended to exclude elements that would materially affect the properties of the claimed composition.

[0033] The terms "comprising," "comprise," and "comprises" herein are in each case intended to be optionally replaced with the terms "consisting essentially of," "consist essentially of," "consists essentially of," "consisting of," "consists of," and "consists of," respectively.

[0034] As used herein, the term "about" encompasses a tolerance of 10% of any value or values ​​associated with the term.

[0035] Herein, the term "weight %" may be abbreviated as "wt %."

[0036] Throughout this specification, the term "AlOx" is intended to include non-stoichiometric Al2O3 (oxygen deficient).

[0037] Burn-through aluminum paste composition

[0038] Conventional PERC aluminum pastes are designed for architectures where the dielectric is opened to access the silicon surface, for example typically by laser etching or by chemical etching, so that when the aluminum is fired, Al-Si alloying occurs at this silicon surface but does not burn through the dielectric around the opening. In contrast, the present disclosure provides an aluminum paste that can directly burn through the rear dielectric passivation layer, thus eliminating the need for a laser opening. It has been found that contact can be preferred at the thin edges of the printed and fired aluminum-glass composite (paste) because when the print thickness is above a critical value, the reaction chemistry switches from a beneficial oxidation reaction of SiNx to a reduction reaction, which inhibits or slows the etch rate of the passivation layer, thereby avoiding etching through. Therefore, increasing the fractal length of the print boundary can improve Voc. It has been surprisingly found that the aluminum paste compositions described herein provide one or more advantages, including lower cost, thinner wafers, larger format wafers, bifaciality, and the potential for flexible solar cell units / modules, which can be realized in emerging markets such as building integrated PV and solar electric vehicles.

[0039] The present disclosure relates to an aluminum paste that can be directly burned through the rear dielectric passivation layer of a PERC cell without the use of a laser. Aluminum can be printed in localized areas, with the resulting contacts interconnected using multiple busbar interconnects. The resulting solar cell advantageously exhibits PERC performance, can be bifacial, and exhibits little to no bowing. Consequently, the solar cell can be made from thin silicon wafers (e.g., as thin as 90 microns). In one embodiment, the thickness of the silicon wafer can be less than about 90 microns. It will be appreciated that since wafer bowing is no longer a limiting factor, large-area wafers (e.g., up to 210 mm) are also possible. Because the laser processing step is eliminated, the amount of aluminum required for full-area printing is only a fraction, and the silicon wafer can be thinner, allowing more wafers to be produced from a single ingot, potentially leading to lower costs for the solar cell described herein. Furthermore, since losses from brittle fracture of thicker wafers are reduced, production costs are reduced, thereby increasing yield. The solar cell can also be made flexible, shaped, and packaged with flexible module materials to form flexible or curved modules, which are very useful in emerging markets such as building integration and solar electric vehicles with curved surfaces. Implicitly, the module will be lighter, as a significant amount of the weight is associated with using thicker glass and a stronger frame to stabilize the module, otherwise the cells in the module would again risk brittle fracture under stress. The technology also makes it easier to retrofit traditional screen printing lines to achieve PERC performance, as no changes to the firing equipment are required and a low-tech printing process without lasers is used.

[0040] It will be understood that the local contact is a contact between silicon and aluminum, the purpose of which is to dope the silicon with aluminum to form an enhanced p+ semiconductor and to form an ohmic contact between the doped region and the aluminum metal contact. Typically, the p+ semiconductor is formed by forming an Al-Si alloy above the liquidus and cooling the melt using an appropriate high-temperature firing process, or by using a high-energy source such as a laser. Advantageously, the present disclosure relies on the use of a firing process, as will be described in detail below.

[0041] Regarding the composition of the surface layer (i.e., the passivation layer), contact can only be achieved in a localized format when the surface structure uses a silicon nitride layer (or a predominantly Si3N4 stoichiometry, in which hydrogen is either contained in the crystal lattice or chemically incorporated in the form of hydrides, imides, or amides in solid-state solution, referred to as SiNx:Hy or simply SiNx), which can be a single layer or part of a multilayer of other metals or metal oxides in the thickness ranges described herein. Typically, SiNx is referred to as the capping layer of the passivation stack. The multilayer oxide design is optimized for surface passivation and increased open-circuit voltage and is therefore referred to as a passivation stack.

[0042] Multilayer stacks are deployed to improve passivation and increase open circuit voltage by reducing minority carrier recombination at the rear surface. Typically, these passivation stacks are composed of SiNx-AlOx-SiOx or SiNx-AlOx or other combinations known in the literature. AlOx can be formed by atomic layer deposition (ALD) or chemical vapor deposition (CVD). In some embodiments, silicon nitride can be stoichiometric or can include hydrogen in the composition (as imines or amides) or incorporated into the crystal lattice. It will be understood that the thickness and coherence of the silicon nitride layer across the semiconductor surface are nominally consistent. In some embodiments, the silicon surface can be planar or textured. It will be understood that the thickness of the silicon nitride layer is defined by the reaction stoichiometry.

[0043] In some embodiments of the present disclosure, a burn-through aluminum paste composition for selectively burning through a passivation layer is provided. The paste composition may include an aluminum component, a glass component, and a patterning medium. In other embodiments, the paste composition may include or consist of an aluminum component, a glass component, a patterning medium, optional silver particles or other silver source, and optional additives.

[0044] In some embodiments, the aluminum component may be present in an amount of about 40 wt.% to about 85 wt.% based on the total weight of the paste composition, the glass component may be present in an amount of about 0.1 wt.% to about 20 wt.% based on the total weight of the paste composition, and the patterning medium may be present in an amount of about 5 wt.% to about 50 wt.% based on the total weight of the paste composition. In some embodiments, the paste composition may further include silver particles, wherein when the aluminum content is less than about 80 wt.%, the silver particles may be present in an amount of less than about 0.5 wt.% based on the total weight of the paste composition.

[0045] In some embodiments, the viscosity of the paste composition can be in the range of about 5 Pa.s to about 200 Pa.s. In some embodiments, the viscosity of the paste composition (in Pa.s) can be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200. In some embodiments, the viscosity of the paste composition (in Pa.s) can be less than about 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 95, 90, 85, 80, 70, 60, 50, 40, 30, 20, 10, or 5. Any two or more combinations of these higher viscosity values ​​and / or lower viscosity values ​​are also possible. All viscosity values ​​stated herein can all be under a given shear rate. In an embodiment, the shear rate can be the shear rate used in any generally recognized standard test method in the art.

[0046] In some embodiments, the shear rate of the paste composition set to monitor the design target viscosity is typically about 4 seconds to 1 .

[0047] In some embodiments, the thickness (in μm) of the deposited layer of the paste composition may be in the range of about 1 to about 40. In some embodiments, the thickness (in μm) of the deposited layer of the paste composition may be at least about 1, 5, 10, 15, 20, 25, 30, 35, or 40. In some embodiments, the thickness (in μm) of the deposited layer of the paste composition may be less than about 40, 30, 20, 10, 5, or 1. Combinations of any two or more of these higher and / or lower values ​​are also possible. It will be understood that, according to at least some embodiments or examples as described herein, one or more advantages of the present disclosure lie in the physical thickness of the paste composition, and subsequently the thickness of the fired paste composition. For example, at appropriate temperatures, the paste composition and / or the thin porous layer of the fired paste composition will have interconnected porosity, which will promote the flow of oxygen to the SiNx surface and the escape of nitrogen reaction products, thereby maintaining the etching reaction, as shown in Equation 1 below. At thicknesses greater than a threshold, the porosity of the interconnects may be compromised, or oxidation of the aluminum metal at temperatures where it preferentially consumes available oxygen may switch the reaction mode to that shown in Equation 2 below. Thus, once deposited, the reaction mode in thin regions or at the edges of the paste composition will differ from the reaction mode in thick regions. Using the chemical reactions described in Equations 1 and 2, the extent of penetration into the SiNx (passivation) layer (or stack) can be controlled. When the reaction conditions described in Equation 2 are achieved, the passivation function of the stack is maintained while controlling the SiNx thickness.

[0048] Aluminum component

[0049] In some embodiments, the primary metal component of the burn-through paste is aluminum. Aluminum is used because it forms a low-contact resistance p+ / p surface on n-type silicon and provides a back surface field (BSF) to enhance solar cell performance. In some embodiments, the aluminum component may comprise aluminum particles that, depending on their manufacturing method, essentially have a nanometer-thick layer of oxide, nitride, carbide, or a mixture.

[0050] In some embodiments, the aluminum particles can be in any form, for example, in the form of flakes, fibers, agglomerates, colloids, nodules, particles, powders, spheres, amorphous, crushed materials, and the like, and combinations thereof. For example, the aluminum particles are spherical, flaky, colloidal, amorphous, or a combination thereof. The aluminum particles can have any desired shape, including but not limited to cubic, rod-shaped, polyhedral, spherical or hemispherical, nodular, circular or semicircular, angular, irregular, and the like. In one embodiment, the aspect ratio (i.e., the ratio of length to width, where length and width are measured perpendicular to each other and length refers to the longest linear dimension) of the aluminum particles can be 1.0 to 10.0, 1.0 to 5.0, or 1.0 to 2.0. In one embodiment, the aluminum particles can have an aspect ratio of about 1.0 to 2.0, such as about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0. For example, the morphology can be uniform spheres or nodules.

[0051] The average aluminum particle size average can be in the range of about 1 μm to about 20 μm. For example, the average aluminum particle size average can be in the range of about 4 μm to about 8 μm. In some embodiments, the particle size (in μm) of the aluminum particles can be at least 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 particle size (in μm) of the aluminum particles can be less than about 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. Combinations of any two or more of these higher and / or lower particle sizes are also possible. The particle size is taken as the longest cross-sectional diameter across the aluminum particle. For non-spherical aluminum particles, the particle size is taken as the distance corresponding to the longest cross-sectional dimension across the particle.

[0052] Particle size can be measured by any standard method, such as laser diffraction, electron microscopy (e.g., TEM or SEM), X-ray diffraction (e.g., Scherrer equation), or dynamic light scattering. In one embodiment, particle size can be measured using laser diffraction according to industry standard ISO 13320:2020.

[0053] In some embodiments, the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof. For example, as a p+ contact, the metal contains Al or Al-Si or an Al-B alloy, or a combination thereof.

[0054] Glass components

[0055] The present disclosure requires dispersing a glass component in a patterning medium along with an aluminum component. In some embodiments, the glass component may include at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy), and the volume of the low-viscosity liquid and the concentration of the first glass frit (A) are controlled.

[0056] According to at least some embodiments or examples as described herein, one or more advantages of the present disclosure is that the present invention is facilitated by the use of inorganic components that chemically react with silicon nitride to form nitrogen (which escapes), as described in more detail below. These elements can be selected from metal oxides (or halides) that act as oxidants for silicon nitride. In some embodiments, this inorganic component is a chemically active ingredient in the paste composition. For example, the inorganic component is a glass frit (A). In some embodiments, the glass frit (A) is selected from the group consisting of: Pb-based glass, Bi-based glass, Bi-Zn-based glass, Bi-Zn-B-based glass, Te-based glass, Bi-Te-based glass, V-based glass, and combinations thereof. In some embodiments, the glass frit (A) can be part of an inorganic oxide mixture that forms a discrete melt at a predetermined temperature, or a glass that softens within a certain temperature range to provide a low viscosity liquid medium. It will be understood that the melt or liquid system can wet the surface and interface, for example, where the silicon nitride is wetted, the temperature is above a threshold temperature, and in this way, the rate at which the reaction proceeds will be much higher than the rate of solid-state chemical reactions.

[0057] In some embodiments, glass frit (B) may be present in the glass composition. Glass frit (B) may be an oxide or silica glass containing elements known to be non-reactive with silicon nitride. The purpose of this glass frit (B) is to effectively control the amount of inorganic glass melted and the concentration of the active components.

[0058] In some embodiments, the glass frit (A) can react (i.e., chemically) with silicon nitride in air or in the presence of oxygen to etch the silicon nitride surface. The reaction pathway, stoichiometry, and reaction products can be determined by the oxygen partial pressure. In systems with moderate or high oxygen partial pressures, the reaction products will form glassy metal silicates and release nitrogen gas. For example, when PbO is used as a component in the glass composition, the chemical reaction is:

[0059] 3PbO+Si3N4+3O2→3PbSiO3+2N2 (Formula 1).

[0060] As the oxygen partial pressure decreases, the reaction and the reaction products will transition to a chemical reaction, and the molar consumption of the reactant PbO will double. In this example, the reaction ends after the reactants are consumed:

[0061] 6PbO+Si3N4→3SiO2+6Pb+2N2 (Formula 2).

[0062] In examples involving aluminum, above the melting point of aluminum (i.e., 680°C) or in the presence of an Al-Si liquidus, the aluminum liquid level will oxidize and consume the available oxygen, thereby further reducing the oxygen partial pressure and pushing the reaction mode toward the mode shown in Equation 2.

[0063] In some embodiments, the ratio of the aluminum component to the first glass frit (A) is preferably minimized. For example, for a 50:50 blend of glass frit A and glass frit B, the relative frit content of the aluminum component to the first glass frit (A) can be between about 0.25% and 5%.

[0064] In some embodiments, the glass frit (A) can be a mixture of oxides (or halides) or glasses consisting of a glass system that chemically reacts with silicon nitride (active) and another oxide or glass mixture that acts as a diluent and does not chemically react with silicon nitride (inactive). In some embodiments, the glass frit (B) can dissolve any other oxide. It will be understood that such a glass system can be used as a burn-through system and selectively removed using water-based chemistry in a subsequent contacting process. It will be understood that the glass frit (B) can dissolve aluminum oxide (AlOx) in the passivation stack.

[0065] In some embodiments, the total amount of the glass component present in the paste composition can be in an amount of about 0.05 wt % to about 25 wt %, based on the total weight of the paste composition. In some embodiments, the amount of the glass component (in wt %) can be at least about 0.05, 0.1, 0.2, 0.4, 0.8, 1, 2, 4, 8, 10, 15, 20, or 25. In some embodiments, the amount of the glass component (in wt %) can be less than about 25, 20, 15, 10, 8, 4, 2, 1, 0.8, 0.4, 0.2, 0.1, or 0.05. Combinations of any two or more of these higher and / or lower amounts are also possible. In some embodiments or examples, the solids content of the glass component present in the paste composition can be in the range of about 0.5 wt % to about 20 wt %. In some embodiments, the solids content of the glass component in the paste composition can be at least about 0.5 wt%, 0.8 wt%, 1 wt%, 2 wt%, 4 wt%, 8 wt%, 10 wt%, 15 wt%, or 20 wt%. In some embodiments, the solids content of the glass component in the paste composition can be less than about 20 wt%, 15 wt%, 10 wt%, 8 wt%, 4 wt%, 2 wt%, 1 wt%, 0.8 wt%, or 0.5 wt%. Combinations of any two or more of these higher and / or lower amounts are also possible. According to at least some embodiments or examples as described herein, one or more advantages of the present disclosure are to provide a minimum glass content in the system to reduce any degradation of the passivation stack while still being able to contact the silicon.

[0066] In some embodiments, the glass component D 50 The particle size may be from about 0.1 micrometers to about 20 micrometers. In some embodiments, the glass component has a D 50 The particle size (in micrometers) may be at least about 0.1, 0.2, 0.4, 0.8, 1, 2, 4, 8, 10, 15, or 20. In some embodiments, the glass component has a D 50 The particle size (in micrometers) can be less than about 20, 15, 10, 8, 4, 2, 1, 0.8, 0.4, 0.2, or 0.1. Combinations of any two or more of these higher and / or lower particle sizes are also possible. For screen printing paste compositions, the particle size of each component must be limited to promote particle penetration through the screen and prevent clogging of the screen mesh, with the upper limit determined by the area grid count and open area.

[0067] Patterning media

[0068] The paste herein can include a patterning medium, which is typically a solution of one or more resins dissolved in one or more solvents, and is often a solvent solution containing a resin, a thixotropic or shear-thinning modifier, and a surfactant (dispersant and stabilizer) at the same time. Glass frits A and B as described herein can be combined with patterning media to form a printable paste composition. Patterning media can be selected based on end-use applications. In one embodiment, the patterning media fully suspends the particles and easily burns off when the paste is fired on a silicon substrate. The patterning media is typically organic. Examples of solvents for preparing patterning media include alkyl ester alcohols, terpineols, dialkyl glycol ethers, pine oil, vegetable oils, mineral oils, low molecular weight petroleum fractions, etc. In another embodiment, surfactants and / or other film-forming modifiers may also be included.

[0069] The amount and type of patterning medium utilized depends primarily on the final desired formulation viscosity, rheology, fineness of grind of the paste, substrate wetting, and desired wet print thickness. In one embodiment, the paste includes from about 1 wt.% to about 50 wt.% of the patterning medium. In another embodiment, the paste includes from about 1 wt.% to about 10 wt.% of the patterning medium.

[0070] The patterning medium typically comprises (a) up to 80 wt.% of an organic solvent; (b) up to about 15 wt.% of a resin; (c) up to about 4 wt.% of a thixotropic agent; and (d) up to about 1.5 wt.% of a wetting agent. It is also contemplated that more than one solvent, resin, thixotropic agent, and / or wetting agent may be used. Ethyl cellulose is a commonly used resin. However, resins such as hydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins, polymethacrylates of lower alcohols, and monobutyl ether of ethylene glycol monoacetate may also be used. Solvents having a boiling point (1 atm) of about 130°C to about 350°C are suitable. Widely used solvents include terpenes such as α- or β-terpineol or higher boiling alcohols such as (diethylene glycol monoethyl ether), or a mixture thereof with other solvents, such as butyl (Diethylene glycol monobutyl ether); dibutyl (Diethylene glycol dibutyl ether), butyl Acetate (diethylene glycol monobutyl ether acetate), hexanediol, (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) and other alcohol esters, kerosene.

[0071] Various combinations of these and other solvents can be formulated to obtain the desired viscosity and volatility requirements for each application. Other dispersants, surfactants, and rheology modifiers, which are commonly used in thick film paste formulations, may be included. Commercial examples of such products include those sold under the following trademarks: (Eastman Chemical Company, Kingsport, TN); and (Dow Chemical Co., Midland, MI); (Union Carbide Division of Dow Chemical, Midland, Michigan), (Elementis Company, Hightstown NJ) and (Transene Co. Inc., Danvers, MA); Akzo Nobel TDO (tallow propylene diamine dioleate) and BYKChemie GmbH 110 or 111. Disperbyk 110 is a copolymer solution containing acidic groups with an acid number of 53 g KOH / g, a density of 1.03 at 20°C, and a flash point of 42°C. Disperbyk 111 is a copolymer containing acidic groups with an acid number of 19 mg KOH / g, a density of 1.16, and a flash point exceeding 100°C. Patterning media comprising oleic acid, DisperBYK 111, and Duomeen TDO are preferred.

[0072] Commonly used organic thixotropic agents are hydrogenated castor oil and its derivatives. A thixotropic agent is not always necessary, as any solvent in the suspension, combined with its inherent shear-thinning properties, can be used alone. Additionally, wetting agents such as fatty acid esters, for example, N-tallow-1,3-diaminopropane dioleate; N-tallow trimethylene diamine diacetate; N-coco trimethylene diamine, beta diamine; N-oleyl trimethylene diamine; N-tallow trimethylene diamine; N-tallow trimethylene diamine dioleate, and combinations thereof, can be used.

[0073] Silver particles

[0074] In some embodiments, the paste composition may further include silver particles or other silver sources. According to at least some embodiments or examples as described herein, one or more advantages of the present disclosure is that adding silver to the paste composition can increase the contact resistance between Al and p+ silicon.

[0075] In one embodiment, the silver particles can be in any form, for example, in the form of flakes, fibers, agglomerates, microparticles, powders, spheres, crushed materials, and the like, and combinations thereof. The silver particles can have any desired shape, including but not limited to cubic, rod-shaped, polyhedral, spherical or hemispherical, circular or hemispherical, angular, irregular, and the like. In one embodiment, the silver particles can have an aspect ratio (i.e., the ratio of length to width, where length and width are measured perpendicular to each other and length refers to the longest linear dimension) of 1.0 to 10.0, 1.0 to 5.0, or 1.0 to 2.0. In one embodiment, the silver particles can have an aspect ratio of about 1.0 to 2.0, for example, about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0. In another embodiment, the silver can be in an organometallic form, such as silver neodecanoate or the like.

[0076] In some embodiments, the average silver particle size average can be in the range of about 0.03 μm to about 5 μm. In some embodiments, the average silver particle size average (in μm) is at least about 0.03, 0.05, 0.1, 0.3, 0.5, 0.7, 1, 1.5, 2, 2.5, 3, 3.5, 4, or 5. In some embodiments, the silver particles have a particle size (in μm) of less than about 5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.7, 0.5, 0.3, 0.1, 0.05, or 0.03. Combinations of any two or more of these higher and / or lower particle sizes are also possible. Particle size is taken as the longest cross-sectional diameter across the silver particle. For non-spherical silver particles, particle size is taken as the distance corresponding to the longest cross-sectional dimension across the particle. The size of the silver particles can be measured by electron microscopy (e.g., TEM or SEM) or X-ray diffraction (e.g., Scherrer analysis of one or more diffraction peaks) or laser particle size analyzer.

[0077] In some embodiments, the total amount of silver (in % w / w, based on the total weight of the paste composition) is at least 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, or 0.5. In some embodiments, the total amount of silver (in % w / w, based on the total weight of the paste composition) is less than about 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, 0.09, 0.08, 0.06, 0.05, 0.04, 0.03, 0.02, or 0.01. Combinations of any two or more of these higher and / or lower amounts are also possible. In some embodiments, the total amount of silver (in % w / w, based on the total weight of the paste composition) is less than about 0.5, preferably less than about 0.2.

[0078] Optional additives

[0079] In some embodiments, the paste may include optional additives.

[0080] In some embodiments or examples, the paste may contain a functional organometallic compound that enhances local oxidation of SiNx.

[0081] Other functional or inorganic additives may also be added to the paste at levels of about 0.1 wt.% to about 30 wt.%, preferably about 0.1 wt.% to about 10 wt.%, alternatively about 2 wt.% to about 25 wt.%, and more preferably about 5 wt.% to about 20 wt.%, based on the weight of the paste before firing. Other additives, such as finely divided silicon, silicon dioxide, silicon, or combinations thereof, may also be added to control the reactivity of aluminum with silicon.

[0082] (a) Glass, (b) a crystallizing additive and glass, or (c) a mixture of one or more crystallizing additives can be used to adjust the glass component to a desired composition range. The goal is to improve the electrical performance of the solar cell by increasing the removal rate of SiNx, AlOx, and SiO2 (if present). For example, second-phase crystalline ceramic materials such as Bi2O3, V2O5, WO3, TeO, TeO2, and their reaction products and combinations can be added to the glass component to adjust contact characteristics.

[0083] Fired paste composition

[0084] The present disclosure also provides a fired back contact paste that adheres to the passivation layer of a bifacial PERC solar cell unit comprising a silicon substrate. In some embodiments, the passivation layer can be fired through to make contact with the silicon and bring aluminum into proximity with the silicon to form an Al-Si alloy as a path to the p+ doped silicon layer. It will be understood that prior to firing, the fired back contact paste is a burn-through paste composition, as described herein, and can include an aluminum component, a glass component, and a patterning medium. In some embodiments, the paste composition, as described herein, can include or consist of an aluminum component, a glass component, a patterning medium, optional silver particles or other silver sources, and optional additives. The aluminum component, the glass component, the patterning medium, the optional silver particles or other silver sources, and the optional additives can be selected from any one or more of the embodiments or examples as described herein.

[0085] In some embodiments, Al-Si alloy formation can be localized at the edges of the print, while the passivation layer function is maintained beneath the pattern, thereby maximizing the open circuit voltage. In some embodiments, the localized region can be controlled by the thickness and / or porosity of the fired back contact paste layer. In one embodiment, at least a portion of the fired back contact paste layer thickness can be less than approximately 10 μm to form a localized back surface field. In another embodiment, at least a portion of the fired back contact paste layer thickness can be greater than approximately 10 μm to provide a region that does not penetrate the passivation layer to reach the silicon substrate.

[0086] In some embodiments, the surface area density of the fired back contact paste layer can be 0.8 mg / cm 2 Up to 5.5 mg / cm 2 , where the area density at the edge is an important determinant of functionality, which is driven by the oxygen partial pressure threshold of the reaction mechanism.

[0087] A method for preparing a burn-through aluminum paste composition

[0088] The present disclosure also relates to a method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer. The method comprises: (i) providing an aluminum component and a glass component, and (ii) dispersing the aluminum component and the glass component in a patterning medium to form the fire-through aluminum paste composition, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

[0089] In some embodiments, the method may further comprise dispersing silver particles or an organometallic silver compound (forming silver particles during pyrolysis) in the patterning medium. In some embodiments, the silver may be in an organometallic form, such as silver neodecanoate or the like. In other embodiments, the silver may be in the form of silver particles as described herein. In some embodiments, the method may further comprise dispersing one or more additives in the printing medium. In some embodiments, the paste composition may comprise or consist of the following in the patterning medium: an aluminum component, a glass component, optional silver particles or other silver source, and optional additives. The aluminum component, the glass component, the patterning medium, the optional silver particles or other silver source, and the optional additives may be selected from any one or more of the embodiments or examples as described herein.

[0090] The average aluminum particle size average can be in the range of about 1 μm to about 20 μm. For example, the average aluminum particle size average can be in the range of about 4 μm to about 8 μm. In some embodiments, the particle size (in μm) of the aluminum particles can be at least 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 particle size (in μm) of the aluminum particles can be less than about 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1. Combinations of any two or more of these higher and / or lower particle sizes are also possible. The particle size is taken as the longest cross-sectional diameter across the aluminum particle. For non-spherical aluminum particles, the particle size is taken as the distance corresponding to the longest cross-sectional dimension across the particle.

[0091] Particle size can be measured by any standard method, such as laser diffraction, electron microscopy (e.g., TEM or SEM), X-ray diffraction (e.g., Scherrer's formula), or dynamic light scattering. In one embodiment, particle size can be measured using laser diffraction according to industry standard ISO 13320:2020.

[0092] In some embodiments, the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof. For example, as a p+ contact, the metal contains Al or Al-Si or an Al-B alloy, or a combination thereof.

[0093] In some embodiments, the amount of the aluminum component dispersed in the patterning medium can be in an amount of about 40 wt % to about 85 wt % based on the total weight of the paste composition. In some embodiments, the amount of the aluminum component dispersed in the patterning medium can be at least about 40, 45, 50, 55, 60, 65, 70, 75, 80, or 85 (in wt.%) based on the total weight of the paste composition. In some embodiments, the amount of the aluminum component dispersed in the patterning medium can be less than about 85, 80, 75, 70, 65, 60, 55, 50, 45, or 40 (in wt.%) based on the total weight of the paste composition. Combinations of any two or more of these higher and / or lower amounts are also possible.

[0094] In some embodiments, the amount of the glass component dispersed in the patterning medium can be in an amount of about 0.1 wt.% to about 20 wt.%, based on the total weight of the paste composition. In some embodiments, the amount of the glass component dispersed in the patterning medium can be at least about 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 wt.%, based on the total weight of the paste composition. In some embodiments, the amount of the glass component dispersed in the patterning medium can be less than about 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, or 0.1 wt.%, based on the total weight of the paste composition. Combinations of any two or more of these higher and / or lower amounts are also possible.

[0095] In some embodiments, when the aluminum content is provided in an amount less than about 80 wt. %, the amount of silver particles dispersed in the patterning medium may be in an amount less than about 0.5 wt. % based on the total weight of the paste composition.

[0096] In some embodiments, the amount of patterning medium can be provided in an amount of about 5 wt.% to about 50 wt.% based on the total weight of the paste composition. In some embodiments, the patterning medium can be provided in an amount of at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 (in wt.%) based on the total weight of the paste composition. In some embodiments, the patterning medium can be provided in an amount of less than about 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 (in wt.%) based on the total weight of the paste composition. Combinations of any two or more of these higher and / or lower amounts are also possible.

[0097] The glass component comprising glass frit (A) and glass frit (B) can be formed in situ using an optional organometallic compound that generates chemically active elements upon pyrolysis. The organometallic compound can be deployed in the patterning medium as an optional insoluble or soluble component.

[0098] The glass component can be combined and mixed with the aluminum component as a formulation that includes a patterning medium having a rheology suitable for patterning using techniques known in the art (e.g., screen printing, pen writing, inkjet printing, extrusion processes, etc.). The patterning medium is designed to be compatible with drying and firing processes. The patterning medium is designed to maintain the dispersed properties of the suspended solids.

[0099] In some embodiments, the viscosity of the paste composition can be in the range of about 5 Pa.s to about 200 Pa.s. In some embodiments, the viscosity (Pa.s) of the paste composition can be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200. In some embodiments, the viscosity (Pa.s) of the paste composition can be less than about 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 95, 90, 85, 80, 70, 60, 50, 40, 30, 20, 10, or 5. Any two or more combinations of these higher viscosity values ​​and / or lower viscosity values ​​are also possible. All viscosity values ​​stated herein can all be under a given shear rate. In an embodiment, the shear rate can be the shear rate used in any generally recognized standard test method in the art.

[0100] In some embodiments, the shear rate of the paste composition set to monitor the design target viscosity is typically about 4 seconds to 1 .

[0101] Bifacial PERC solar cell

[0102] The present disclosure also relates to a bifacial PERC solar cell unit comprising a silicon substrate and a back contact thereon. In some embodiments, the silicon substrate may be crystalline silicon having a monocrystalline or polycrystalline morphology. In some embodiments, the back contact may comprise a passivation layer that is at least partially coated with a fired back contact paste at the back side of the silicon substrate. The back contact paste is a burn-through aluminum paste composition as described herein for selectively burning through the passivation layer, wherein prior to firing, the burn-through aluminum paste composition comprises an aluminum component, a glass component, and a patterning medium. The paste composition may further comprise silver particles or other silver sources and / or optional additives. In some embodiments, the paste composition may comprise or consist of: an aluminum content, a glass component, a patterning medium, optional silver particles or other silver sources, and optional additives. The aluminum component, the glass component, the patterning medium, the optional silver particles or other silver sources, and the optional additives may be selected from any one or more of the embodiments or examples as described herein.

[0103] In some embodiments, the solar cell may be p-type or n-type. Preferably, the solar cell may be p-type. In some embodiments, the passivation layer may comprise SiN deposited on a silicon substrate. x 、SiN x H y 、AlOx / SiN x 、AlOx / SiN x H y 、SiO2 / AlOx / SiN x or SiO2 / AlOx / SiN x H y .

[0104] In some embodiments, the thickness of the silicon substrate can be less than about 150 μm. For example, the thickness of the silicon substrate can be less than about 125 μm. In one example, the thickness of the silicon substrate can be about 90 μm. It will be understood that the thickness and curvature of the silicon substrate are implicitly associated with the lateral dimensions. As mentioned above, excessive curvature means that the solar cell needs to be formed from a silicon substrate that exceeds a certain threshold thickness related to the lateral dimensions (e.g., 160 μm) to reduce the thermal expansion curvature difference effect and maintain flatness, and thus prevent cracking during cell handling, cell interconnection, placement, and panel assembly during the production process. Metallization coverage and thickness are the main factors that determine curvature.

[0105] In some embodiments, SiN x or SiN x H y The thickness of the coating may be in the range of about 30 nm to about 200 nm. x or SiNx H y The thickness of the coating (in nm) may be at least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200. In some embodiments, SiN x or SiN x H y The coating may have a thickness (in nm) of less than about 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30. Combinations of any two or more of these higher and / or lower thickness values ​​are also possible. For example, SiN x or SiN x H y The thickness of the coating may range between about 50 nm and about 100 nm.

[0106] In some embodiments, the thickness of AlOx can be in a range between about 2 nm and about 20 nm. In some embodiments, the thickness of AlOx (in nm) can be at least about 2, 5, 7, 10, 12, 15, 18, or 20. In some embodiments, the thickness of AlOx (in nm) can be less than about 20, 18, 15, 12, 10, 7, 5, or 2. Combinations of any two or more of these higher and / or lower thickness values ​​are also possible. For example, the thickness of AlOx can be in a range between 7 nm and about 12 nm.

[0107] It will be appreciated that laser ablation or chemical etching may be used, but is preferably not applied at the back side of the battery cell, to form the localized openings.

[0108] The preparation and patterning process can be designed to provide or access the resistor network after processing. In some embodiments, the paste composition can be patterned to form dots or lines on the passivation layer. For example, the pattern can be lines, lines showing meanders, dots, circles, and other patterns that maximize edge length (fractal length).

[0109] The pattern mask (e.g., a silk screen) that can be used to pattern the contact paste composition can be designed to be compatible with the goals of the electronic device. For example, for a bifacial PERC solar cell, lines, dots, or other patterns can be used to form p+ ohmic contacts that interconnect the solar cell array to extract current from the cell. The patterning process is designed to control the print (i.e., the paste composition) and the cross-sectional thickness after printing and firing. As mentioned above, the thickness of the fired print will affect the oxygen partial pressure, and therefore the reaction path, and whether the SiNx layer is burned through to contact the silicon, thereby allowing Al to approach Si, thereby promoting the formation of an Al-Si alloy, i.e., a precursor to the Al-doped silicon lattice.

[0110] The conductor pattern can be designed to benefit from the advantages of the present disclosure, in which the formation of the Al-Si contact can be preferably formed locally at the edge of the print, while below the pattern, the passivation stack function is maintained and the open circuit voltage is maximized. The local area can be controlled by the thickness of the printed layer, the porosity of the layer and / or the volume of the liquid containing the oxidizing species (cations), which should be below the limit determined by the firing paste composition. As discussed, in the case of interconnects, porosity can be important as a channel for oxygen. Conversely, the passivation (i.e., the formation of the Al-Si alloy) below the metallization can be retained by increasing the thickness, reducing the free volume porosity and / or increasing the liquid volume fraction in the system, such as changing the reaction between the silicon nitride so that nitrogen no longer escapes in the chemical reaction, i.e., the reduction reaction. In some embodiments, after firing, the paste composition promotes the aluminum metallization on the back side of the silicon substrate to form an Al-Si alloy at the edge of the fired back contact paste, wherein the fired thickness of the edge of the fired back contact paste is less than about 10 μm to form a local back surface field.

[0111] In some embodiments, at least a portion of the paste composition can be patterned on the passivation layer to achieve a fired thickness of less than about 10 μm. In some embodiments, at least a portion of the paste composition can be patterned on the passivation layer to achieve a fired thickness of greater than about 10 μm.

[0112] To maximize the open circuit voltage, the metallization design can be designed to maximize the fractal length of the edge and minimize the area where the printed thickness exceeds the SiNx threshold thickness to prevent burn-through in the anaerobic reaction pathway (as shown in Equation 2 above).

[0113] The patterned article can be fired in a furnace with a gas flow. The furnace can be capable of controlling the oxygen content by mixing the gas flow with nitrogen or other inert gases such as argon.

[0114] In some embodiments, the surface area density of the fired back contact paste layer can be 0.8 mg / cm 2 Up to 5.5 mg / cm 2 , where the area density at the edge is an important determinant of functionality, which is driven by the oxygen partial pressure threshold of the reaction mechanism.

[0115] Figure 1 A cross-sectional view of a bifacial PERC solar cell is shown, comprising a silicon wafer substrate 100, a p-side aluminum oxide passivation layer 200 for creating a pn junction, a p-side silicon nitride capping layer 300, and an n-side silicon nitride passivation layer 400. The silicon wafer substrate 100 may have a thickness of less than approximately 150 nm, preferably less than approximately 90 nm. The aluminum oxide passivation layer 200 may have a thickness of approximately 2 nm to approximately 20 nm, preferably approximately 7 nm to approximately 12 nm. The silicon nitride capping layer 300 may have a thickness of approximately 30 nm to approximately 200 nm, preferably approximately 50 nm to approximately 100 nm.

[0116] Figure 2 A cross-sectional view of a bifacial PERC solar cell is shown, comprising a silicon wafer substrate 100, a p-side aluminum oxide passivation layer 200, a p-side silicon nitride capping layer 300, and an n-side silicon nitride passivation layer 400. A printed p-side aluminum contact line 500 may extend above the p-side silicon nitride capping layer 300. The Al / Si alloy contact to silicon 600 penetrates the p-side silicon nitride capping layer 300 and the p-side aluminum oxide passivation layer 200, allowing aluminum access to the silicon, thereby facilitating contact metallization and back surface field formation. A busbar or conductive line 700 lies above the aluminum contact fingers 500.

[0117] Figure 3 The schematic diagram shows an orthogonal view of a bifacial PERC solar cell with a silicon wafer substrate 100, a p-side aluminum oxide passivation layer 200, a p-side silicon nitride capping layer 300, and an n-side silicon nitride passivation layer 400. A printed p-side aluminum contact line 500 extends above the p-side silicon nitride capping layer 300. The Al / Si alloy contact to silicon 600 penetrates the p-side silicon nitride capping layer 300 and the p-side aluminum oxide passivation layer 200, allowing aluminum access to the silicon, thereby facilitating contact metallization and back surface field formation. Busbars or conductive lines 700 are positioned above and extend perpendicular to the aluminum contact fingers 500.

[0118] Figure 4The schematic diagram shows an orthogonal view of a bifacial PERC solar cell with a silicon wafer substrate 100, a p-side aluminum oxide passivation layer 200, and a p-side silicon nitride capping layer 300. A printed p-side aluminum contact 800 is located above the p-side silicon nitride capping layer 300. The Al / Si alloy contact to silicon 600 penetrates the p-side silicon nitride capping layer 300 and the p-side aluminum oxide passivation layer 200, allowing aluminum access to the silicon, thereby facilitating contact metallization and back surface field formation. A busbar or conductive line 700 is located above and in contact with the printed p-side aluminum contact pad 800.

[0119] A method for preparing a double-sided PERC solar cell unit

[0120] The present disclosure also relates to a method for preparing a bifacial PERC solar cell unit. The method comprises the following steps: providing a silicon substrate and a rear passivation layer thereon, applying a burn-through aluminum paste composition as described herein to at least partially coat the passivation layer, and selectively burning through the passivation layer, wherein the paste composition comprises an aluminum component, a glass component, and a patterning medium, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A), heating the paste composition to a predetermined temperature to burn through at least a portion of the passivation layer to contact silicon and enable aluminum to approach silicon to promote contact metallization and the formation of a back surface field. The paste composition may further contain silver particles or other silver sources and / or optional additives. In some embodiments, the paste composition may contain or consist of an aluminum component, a glass component, a patterning medium, optional silver particles or other silver sources, and optional additives. The aluminum component, the glass component, the patterning medium, the optional silver particles or other silver sources, and the optional additives may be selected from any one or more of the embodiments or examples described herein.

[0121] In some embodiments, the fired thickness of the edge of the fired paste composition may be less than about 10 μm to form a local back surface field. The paste composition may be applied to the passivation layer using screen printing, pen writing, inkjet printing or extrusion technology. In some embodiments, the paste composition may be applied to the passivation layer in the form of dots or lines. The dot diameter or line width may be in the range of about 20 μm to about 500 μm. In some embodiments, the dot diameter or line width (in μm) may be at least 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480 or 500. In some embodiments, the dot diameter or line width (in μm) may be less than about 500, 450, 400, 350, 300, 250, 200, 150, 100, 50, or 20. Combinations of any two or more of these higher and / or lower values ​​are also possible.

[0122] In some embodiments, the passivation layer is not locally pre-opened using laser ablation or chemical etching.

[0123] In some embodiments, the heating step may be a two-step process, ie, (i) drying the paste composition, and then (ii) firing the paste composition at a temperature above the Al-Si eutectic or the melting point of Al.

[0124] In some embodiments, the heating step can be a one-step process, ie, (i) firing the wet paste composition at a temperature above the Al-Si eutectic or the melting point of Al.

[0125] In some embodiments, the predetermined temperature for heating step (i) may be in the range of about 250°C to about 350°C. In some embodiments, the predetermined temperature for heating step (ii) may be in the range of about 500°C to about 1000°C. For step (i), the temperature may be at least about 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C. The temperature for step (i) may be lower than about 350°C, 340°C, 330°C, 320°C, 310°C, 300°C, 290°C, 280°C, 270°C, 260°C, or 250°C. Combinations of any two or more of these higher and / or lower temperatures are also possible. For step (ii), the temperature can be at least about 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C. The temperature of step (ii) can be less than about 1000°C, 950°C, 900°C, 850°C, 800°C, 750°C, 700°C, 650°C, 600°C, 550°C, or 500°C. Combinations of any two or more of these higher firing temperatures and / or lower firing temperatures are also possible. It will be understood that the heating step is carried out in an O2 environment, or in other words, in the presence of O2.

[0126] In some embodiments, the passivation layer may include SiN deposited on a silicon substrate. x 、SiN x H y 、AlOx / SiN x 、AlOx / SiN x H y 、SiO2 / AlOx / SiN x or SiO2 / AlOx / SiN x H y .

[0127] In some embodiments, the thickness of the silicon substrate can be less than about 150 μm. For example, the thickness of the silicon substrate can be less than about 125 μm. In one example, the thickness of the silicon substrate can be about 90 μm.

[0128] In some embodiments, SiN x or SiN x H yThe thickness of the coating ranges from about 30 nm to about 200 nm. In some embodiments, the thickness (in nm) of the SiNx or SiNxHy coating may be at least 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or 200. In some embodiments, the thickness (in nm) of the SiNx or SiNxHy coating may be less than about 200, 190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, or 30. Combinations of any two or more of these higher and / or lower values ​​are also possible. x or SiN x H y The thickness of the coating may range between about 50 nm and about 100 nm.

[0129] In some embodiments, the thickness of AlOx can be in a range between about 2 nm and about 20 nm. In some embodiments, the thickness of AlOx (in nm) can be at least about 2, 5, 7, 10, 12, 15, 18, or 20. In some embodiments, the thickness of AlOx (in nm) can be less than about 20, 18, 15, 12, 10, 7, 5, or 2. Combinations of any two or more of these higher and / or lower values ​​are also possible. For example, the thickness of AlOx can be in a range between 7 nm and about 12 nm.

[0130] In some embodiments, the method may further comprise applying a multi-wire grid to the back side of the battery cell and optionally applying the multi-wire grid to the front surface of the silicon substrate to interconnect the battery cells. The interconnection can be achieved by a network capable of making contact with p+. For example, Smartwire technology can be used and provided by Meyer Burger AG. In some embodiments, the multi-wire grid can comprise from about 15 to about 50 wires. The wires can be Cu-based wires coated with a low melting point alloy. According to the stringing operation, it is intended to enable the Al burn-through contact area on the back side to be interconnected with the front metallization contact on the next battery cell.

[0131] In some embodiments, one or more battery cells may be arranged to be interconnected in series or in parallel. In some embodiments, the battery cells may be encased in a module with glass having a thickness of about 1 mm to about 4 mm.

[0132] Those skilled in the art will appreciate that various changes and / or modifications may be made to the above embodiments without departing from the broad general scope of the present disclosure. Therefore, the embodiments of the present invention should be considered in all aspects as illustrative and not restrictive.

[0133] The present disclosure can be described by the following examples:

[0134] A fire-through aluminum paste composition for selectively burning through a passivation layer, the paste composition comprising: an aluminum component, a glass component, and a patterning medium; wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

[0135] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the aluminum component comprises aluminum particles.

[0136] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the average aluminum particle size is from about 1 μm to about 20 μm.

[0137] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the average aluminum particle size is about 4 μm to about 8 μm.

[0138] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the aluminum particles are spherical, nodular, flaky, colloidal, amorphous, or a combination thereof.

[0139] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof.

[0140] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the first glass frit (A) is selected from the group consisting of: Pb-based glass, Bi-based glass, Bi-Zn-based glass, Bi-Zn-B-based glass, Te-based glass, Bi-Te-based glass, V-based glass, or combinations thereof.

[0141] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the glass component has a D50 particle size of about 0.1 micrometers to about 20 micrometers.

[0142] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the paste composition further comprises silver particles or other silver sources.

[0143] The fire-through aluminum paste composition according to any one or more embodiments described herein has an average silver particle size of about 0.03 μm to about 5 μm.

[0144] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the silver particles are present in an amount of less than about 0.5 wt. % based on the total weight of the paste composition.

[0145] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the silver particles are present in an amount of less than about 0.2 wt. % based on the total weight of the paste composition.

[0146] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein: the aluminum component is present in an amount of about 40 wt.% to about 85 wt.% based on the total weight of the paste composition, the glass component is present in an amount of about 0.05 wt.% to about 20 wt.% based on the total weight of the paste composition, and the patterning medium is present in an amount of about 5 wt.% to about 50 wt.% based on the total weight of the paste composition.

[0147] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the paste further comprises silver particles, wherein the silver particles are present in an amount of less than about 0.5 wt. % based on the total weight of the paste composition when the aluminum content is present in an amount of less than about 80 wt. %.

[0148] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the viscosity of the paste composition is in the range of about 5 Pa.s to about 200 Pa.s, suitable for use in a patterning process.

[0149] The fire-through aluminum paste composition according to any one or more embodiments described herein, wherein the shear rate of the paste composition set to monitor the design target viscosity is generally about 4 seconds to 1 .

[0150] The fire-through aluminum paste composition according to any one or more embodiments described herein further comprises one or more organic or inorganic additives.

[0151] A method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer, the method comprising: providing an aluminum component and a glass component, and dispersing the aluminum component and the glass component in a patterning medium to form the fire-through aluminum paste composition, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy), and the volume of the low-viscosity liquid and the concentration of the first glass frit (A) are controlled.

[0152] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein further comprises dispersing silver particles in the patterning medium.

[0153] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the aluminum component comprises aluminum particles, and the average aluminum particle size is about 1 μm to about 20 μm.

[0154] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the average aluminum particle size is about 4 μm to about 8 μm.

[0155] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof.

[0156] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the amount of the aluminum component dispersed in the patterning medium is in an amount of about 40 wt.% to about 85 wt.% based on the total weight of the paste composition.

[0157] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the patterning medium is provided in an amount of about 5 wt.% to about 50 wt.% based on the total weight of the paste composition.

[0158] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the amount of the glass component dispersed in the patterning medium is in an amount of about 0.05 wt.% to about 20 wt.% based on the total weight of the paste composition.

[0159] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the amount of silver particles dispersed in the patterning medium is less than about 0.5 wt. % when the aluminum content is provided in an amount less than about 80 wt. %, based on the total weight of the paste composition.

[0160] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein, wherein the viscosity of the paste composition is in a range from about 5 Pa·s to about 200 Pa·s.

[0161] The method for preparing a fire-through aluminum paste composition for selectively burning through a passivation layer according to any one or more embodiments described herein, wherein the shear rate of the paste composition is set to monitor the designed target viscosity and is typically about 4 seconds to 1 .

[0162] The method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer according to any one or more embodiments described herein further comprises one or more additives dispersed in a printing medium.

[0163] A fire-through aluminum paste composition for selectively firing through a passivation layer is prepared according to any one or more embodiments of the method for preparing a fire-through aluminum paste composition for selectively firing through a passivation layer described herein.

[0164] A fired back contact paste adheres to the passivation layer of a bifacial PERC solar cell unit comprising a silicon substrate, wherein the passivation layer is fired through to contact the silicon and enable aluminum to approach the silicon to form an Al-Si alloy, wherein before firing, the fired back contact paste is a fire-through paste composition comprising: an aluminum component, a glass component, and a patterning medium; wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy), and the volume of the low-viscosity liquid and the concentration of the first glass frit (A) are controlled.

[0165] The fired back contact paste according to any one or more embodiments described herein, wherein the Al-Si alloy formation is localized at the edge of the print, while the passivation layer function is maintained underneath the pattern, thereby maximizing the open circuit voltage.

[0166] The fired back contact paste according to any one or more embodiments described herein, wherein the localized region is controlled by the thickness and / or porosity of the fired back contact paste layer.

[0167] The fired back contact paste according to any one or more embodiments described herein, wherein at least a portion of the fired back contact paste layer has a thickness less than 10 μm to form a localized back surface field.

[0168] The fired back contact paste according to any one or more embodiments described herein, wherein at least a portion of the fired back contact paste layer has a thickness greater than 10 μm to provide an area that does not penetrate the passivation layer to reach the silicon substrate.

[0169] The fired back contact paste according to any one or more embodiments described herein, wherein the surface area density of the fired back contact paste layer may be 0.8 mg / cm 2 Up to 5.5 mg / cm 2 , where the area density at the edge is an important determinant of functionality, which is driven by the oxygen partial pressure threshold of the reaction mechanism.

[0170] A bifacial PERC solar cell unit comprises a silicon substrate and a back contact thereon, the back contact comprising a passivation layer, the passivation layer being at least partially coated with a fired back contact paste at the back side of the silicon substrate, wherein the back contact paste is a fire-through aluminum paste composition for selectively burning through the passivation layer, wherein before firing, the fire-through aluminum paste composition comprises an aluminum component, a glass component, and a patterning medium; wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy), and the volume of the low-viscosity liquid and the concentration of the first glass frit (A) are controlled.

[0171] The bifacial PERC solar cell according to any one or more embodiments described herein, wherein the solar cell is p-type.

[0172] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the paste composition further comprises silver particles or other silver sources.

[0173] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the passivation layer comprises SiNx, SiNxHy, AlOx / SiNx, AlOx / SiNxHy, SiO2 / AlOx / SiNx, or SiO2 / AlOx / SiNxHy deposited on the silicon substrate.

[0174] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the thickness of the silicon substrate is less than about 150 μm.

[0175] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the thickness of the silicon substrate is less than about 125 μm.

[0176] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the silicon substrate has a thickness of about 90 μm.

[0177] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the thickness of the SiNx or SiNxHy coating is in a range between about 30 nm and about 200 nm.

[0178] The bifacial PERC solar cell according to any one or more embodiments described herein, wherein the thickness of AlOx is in a range between about 2 nm and about 20 nm.

[0179] The bifacial PERC solar cell according to any one or more embodiments described herein, wherein laser ablation or chemical etching to form the local openings may not be applied to the back side of the cell.

[0180] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the silicon substrate is crystalline silicon.

[0181] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the paste composition is patterned to form dots or lines on the passivation layer.

[0182] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein at least a portion of the paste composition is patterned on the passivation layer to achieve a fired thickness of less than about 10 μm.

[0183] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein at least a portion of the paste composition is patterned on the passivation layer to achieve a fired thickness greater than about 10 μm.

[0184] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein after firing, the paste composition promotes aluminum metallization on the back side of the silicon substrate to form an Al-Si alloy at the edge of the fired back contact paste, wherein the fired thickness of the edge of the fired back contact paste is less than about 10 μm to form a localized back surface field.

[0185] The bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the surface area density of the fired back contact paste layer can be 0.8 mg / cm 2 Up to 5.5 mg / cm 2 , where the area density at the edge is an important determinant of functionality, which is driven by the oxygen partial pressure threshold of the reaction mechanism.

[0186] A method for preparing a bifacial PERC solar cell unit, the method comprising: providing a silicon substrate and a rear passivation layer thereon, applying a fire-through aluminum paste composition to at least partially coat the passivation layer to selectively fire through the passivation layer, the paste composition comprising an aluminum component, a glass component, and a patterning medium, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy) and forms a low-viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain an oxidizer for silicon nitride (SiNx) or hydrogenated silicon nitride (SiNx:Hy), and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A), heating the paste composition to a predetermined temperature to fire through at least a portion of the passivation layer to contact silicon and enable aluminum to approach silicon to promote contact metallization and formation of a back surface field.

[0187] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the fired thickness of the edge of the fired paste composition is less than about 10 μm to form a localized back surface field.

[0188] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the paste composition is applied to the passivation layer using screen printing, pen writing, inkjet printing, or extrusion.

[0189] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the paste composition is applied to the passivation layer in the form of dots or lines.

[0190] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the dot diameter or line width is in a range from about 20 μm to about 500 μm.

[0191] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the passivation layer is locally pre-opened without using laser ablation or chemical etching.

[0192] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the aluminum component further comprises silver particles or other silver sources.

[0193] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the heating step is a two-step process, namely (i) drying the paste composition, and then (ii) firing the paste composition.

[0194] In the method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, the predetermined temperature of the heating step (i) is in the range of about 250°C to about 350°C.

[0195] In the method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, the predetermined temperature of the heating step (ii) is in the range of about 500°C to about 1000°C.

[0196] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the passivation layer comprises SiNx, SiNxHy, AlOx / SiNx, AlOx / SiNxHy, SiO2 / AlOx / SiNx or SiO2 / AlOx / SiNxHy deposited on the silicon substrate.

[0197] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the thickness of the silicon substrate is less than about 150 μm.

[0198] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the thickness of the silicon substrate is less than about 125 μm.

[0199] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the thickness of the silicon substrate is about 90 μm.

[0200] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the thickness of the SiNx or SiNxHy coating is in a range between about 30 nm and about 200 nm.

[0201] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the thickness of AlOx is in a range between about 2 nm and about 20 nm.

[0202] The method for preparing bifacial PERC solar cell units according to any one or more embodiments described herein further comprises applying a multiwire grid to the back side of the cell unit and optionally applying the multiwire grid to the front surface of the silicon substrate to interconnect the cell units.

[0203] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the multi-wire grid comprises about 15 to about 50 wires.

[0204] The method for preparing a bifacial PERC solar cell unit according to any one or more embodiments described herein, wherein the wire is a Cu-based wire coated with a low melting point alloy.

[0205] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein one or more cells are arranged to be interconnected in series or in parallel.

[0206] The method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the cell is encapsulated in a module with glass, wherein the glass has a thickness of about 1 mm to about 4 mm.

[0207] A method for preparing a bifacial PERC solar cell according to any one or more embodiments described herein, wherein the cell is wrapped in a module comprising a transparent substance that provides sealing protection for the cell, wherein the transparent substance has a thickness of about 1 mm to about 4 mm.

[0208] Examples

[0209] The present disclosure is further described by the following examples. It should be understood that the following description is only for the purpose of describing specific examples and is not intended to limit the above description.

[0210] Example 1: Wafer Preparation

[0211] 156mm with a thickness of 160μm was prepared 2 A single crystal p-type silicon wafer was prepared. Saw marks were removed using processes known in the art. Both sides were textured using an alkaline bath to produce a typical etched single crystal surface with 7 μm pyramids. The wafer was cleaned using conventional methods known in the art.

[0212] In a conventional back-to-back diffusion process using POCl3, an n-type diffusion is produced on one side. The sheet resistance of the emitter is designed to be approximately 100 ohm.cm.

[0213] A conventional silicon nitride (SiNx:Hy) anti-reflective passivation layer was applied by PECVD to form a 60nm layer on the emitter. The rear surface was etched for 2 minutes with HNA acid (an acid of known composition in the art). In addition, a 2nm thick SiOx layer could also be formed to increase Voc. In these examples, this SiOx layer was not deployed. The stack passivation was constructed as a PECVD AlOx layer and a 60nm thick SiNx:Hy capping layer. The thickness of the AlOx layer was varied to 0nm, 7nm, 12nm and 20nm to determine its effect on electrical and chemical properties.

[0214] Example 2: Paste preparation

[0215] Pastes with varying amounts of aluminum powder and frit content were prepared by cross-blending two proprietary pastes. The first paste, ToyoAl TB-08E3-FTNoGF (herein referred to as A-0), consisted of 80 wt% Al powder dispersed in an organic vehicle. The second paste, ToyoAl TB-08E3-FTGFup (herein referred to as A-20), consisted of a blend of two proprietary glass frits and Al powder. The first proprietary glass, glass frit (A), was based on bismuth borosilicate, where bismuth is an oxidizer for silicon nitride. The second proprietary glass, glass frit (B), was based on an alkali borosilicate / alkaline earth glass, where neither component was known to oxidize silicon nitride. The blend ratio of the two glass frits was proprietary to ToyoAl. The Al content in TB-08E3-FTGFup was 65 wt% Al powder and 20 wt% glass frit. The two compositions are designed to be cross-blended and screen-printable using the same organic patterning vehicle to facilitate printing experimentation without the need for additional additives.

[0216] Blended mixtures of A-0 and A-20 were prepared according to Table 1 to provide compositions having a range of frit concentrations for aluminum content.

[0217] Table 1: Paste blends

[0218]

[0219] The pastes are stored separately until needed for printing.

[0220] Example 3: Printing and drying

[0221] For traceability purposes, blank (non-metallized) processed battery cells prepared according to Example 1 were laser etched with identification numbers prior to processing.

[0222] A commercial silver paste from Hereaus GmbH was printed using a standard front-side n-type pattern designed for contacting a 100 Ohm.sq emitter resistor. The printing width was designed using a 35 μm screen, and the lines were spaced 1000 μm apart. A Baccini screen printer was used, with the printing parameters suitable for the paste and screen being selected as known to those skilled in the art. No busbars were applied, but the Smartwire method was used instead. The average Ag consumption per cell was 45 mg. The silver prints were dried in a Baccini rotary disc dryer at 200°C for 20 minutes.

[0223] Each of the aluminum pastes described in Table 1 was printed on Ag-printed cells. Each composition was printed on a cell, where each SiOx-AlOx-SiNx passivation stack was represented by its different AlOx thickness (all other stack parameters were constant). The screen used to print the aluminum paste had 100 μm wide parallel lines (155 lines per cell). For these cells, the aluminum consumption per cell was approximately 250 mg.

[0224] Example 4: Firing

[0225] The printed cells were fired in a furnace manufactured by Centrotherm GmbH, which is a standard design for firing solar cells. The furnace has six firing zones (see Table 2). For each cell, the furnace was set to have the same profile and belt speed for producing a conventional full BSF cell (full area aluminum printed on one side, where the conventional design front grid is configured without busbars for emitter contact printing). In order to optimize the firing profile and belt speed, the settings of zones 5 and 6 were changed to 820°C, 840°C and 890°C using contact resistance as a probe, while changing the belt speed (2500 mm / min, 5400 mm / min and 7000 mm / min). This experiment was carried out using a textured cell with a 60nm SiNx layer. For this, the belt speed was set to 5400 mm / min.

[0226] Table 2: Furnace Zone Settings

[0227] Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 540℃ 570℃ 570℃ 610℃ 840℃ 840℃

[0228] When firing the cells, the n-type emitter (Ag metallization) faced downwards. Before adding the wafers to the furnace, 10 dummy wafers were positioned in front of and behind the example printed cells to ensure thermal balance of the furnace.

[0229] Figure 5is an optical image (Olympus OLS3000 laser microscope) of an example printed battery cell after firing, showing localized formation of Al-Si alloy at the edges of the print, while underneath the pattern the passivation layer function is maintained, maximizing the open circuit voltage.

[0230] The electrical characteristics of the cells were evaluated using conventional solar measurement equipment manufactured by Halm GmbH. The cells were held in a setup designed by Meyer-Burger SA to simulate measurements using a 12-wire Smartwire interconnect system. Because this was a measurement test setup, the wires were not soldered in place. The Meyer-Burger system was used to simulate a multi-wire interconnect configuration. Contact resistance was evaluated using a tool manufactured by GPSolar GmbH.

[0231] Example 5: Performance of PERC Cells

[0232] The effect of glass content on the electrical performance of the passivation stack is compared with using only SiNx as the capping layer.

[0233] The results of the effect of frit content on AlOx passivation thickness are as follows: Figure 6 As shown in Figure 3, when there is no AlOx in the stack, Voc is independent of the relative frit content in the fired film. When an AlOx layer is present in the stack, a decrease in Voc and a passivation effect are observed with increasing glass frit content. This effect appears to be due to either dissolution of the AlOx by the glass frit or the creation of more contact and removal of the passivation layer beneath the metallization.

[0234] It has been surprisingly found that in fired glass-metal compacts, good burn-through is achieved at very low glass frit contents, a trend that suggests even higher Voc values ​​at lower frit contents. Print thickness is also a decisive variable.

[0235] Figure 7 The effect of AlOx thickness on cell efficiency is shown. Increasing the relative frit content degrades the performance of the AlOx-SiNx passivation stack. In contrast, the SiNx layer shows no effect of glass concentration on electrical performance. It has been unexpectedly discovered that low and very low frit contents enhance the optimal efficiency of the passivation stack.

[0236] Advantageously, no measurable bowing was detected in the battery cells prepared and described herein.

[0237] It has been discovered that the composition of the aluminum paste as described herein can be designed to enable further reduction in the thickness of the AlOx component of the passivation stack to advantageously maximize the electrical performance of the PERC solar cell, for example by increasing the open circuit voltage.

Claims

1. A fire-through aluminum paste composition for selectively burning through a passivation layer, the paste composition comprising: Aluminum component, glass components, and patterning media; The glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A). 2 . The paste composition according to claim 1 , wherein the aluminum component comprises aluminum particles. 3 . The paste composition according to claim 2 , wherein the average aluminum particle size is from about 1 μm to about 20 μm.

4. The paste composition according to claim 2 or claim 3, wherein the average aluminum particle size is from about 4 μm to about 8 μm.

5. The composition of any one of claims 2 to 4, wherein the aluminum particles are spherical, nodular, flaky, colloidal, amorphous, or a combination thereof.

6. The paste composition according to any one of the preceding claims, wherein the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof.

7. The paste composition according to any one of the preceding claims, wherein the first glass frit (A) is selected from the group consisting of Pb-based glass, Bi-based glass, Bi-Zn-based glass, Bi-Zn-B-based glass, Te-based glass, Bi-Te-based glass, V-based glass, or combinations thereof.

8. The paste composition according to any one of the preceding claims, wherein the glass component has a D 50 The particle size is from about 0.1 microns to about 20 microns.

9. The paste composition according to any one of the preceding claims, wherein the paste composition further comprises silver particles or other silver sources.

10. The paste composition of claim 10, wherein the average silver particle size is from about 0.03 μm to about 5 μm.

11. The paste composition of claim 9 or claim 10, wherein the silver particles are present in an amount of less than about 0.5 wt. % based on the total weight of the paste composition.

12. The paste composition according to any one of claims 9 to 11, wherein the silver particles are present in an amount of less than about 0.2 wt. % based on the total weight of the paste composition.

13. A paste composition according to any one of the preceding claims, wherein: The aluminum component is present in an amount of about 40 wt.% to about 95 wt.%, based on the total weight of the paste composition, The glass component is present in an amount of about 0.1 wt. % to about 20 wt. % based on the total weight of the paste composition, and The patterning agent is present in an amount of about 5 wt. % to about 50 wt. %, based on the total weight of the paste composition.

14. The paste composition of claim 13, further comprising silver particles or other silver sources, wherein the silver particles or other silver sources are present in an amount of less than about 0.5 wt. % based on the total weight of the paste composition when the aluminum content is present in an amount of less than about 80 wt. %.

15. The paste composition according to any one of the preceding claims, wherein the viscosity of the paste composition is in the range of about 5 Pa.s to about 200 Pa.s.

16. The paste composition according to any one of the preceding claims, wherein the shear rate of the paste composition set to monitor the design target viscosity is typically about 4 seconds to 1 .

17. The paste composition according to any one of the preceding claims, further comprising one or more organic or inorganic additives.

18. A method for preparing a fire-through aluminum paste composition for selectively burning through a passivation layer, the method comprising: (i) providing an aluminum component and a glass component, and (ii) dispersing the aluminum component and the glass component in a patterning medium to form the fire-through aluminum paste composition, The glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

19. The method of claim 18, further comprising dispersing silver particles in the patterning medium.

20. The method of claim 18 or claim 19, wherein the aluminum component comprises aluminum particles and the average aluminum particle size average is from about 1 μm to about 20 μm.

21. The method of claim 20, wherein the average aluminum particle size averages from about 4 μm to about 8 μm.

22. The method of any one of claims 18 to 21, wherein the aluminum component comprises an Al-Si alloy, an Al-Si eutectic alloy, an Al-B alloy, or a combination thereof.

23. The method of any one of claims 18 to 22, wherein the amount of the aluminum component dispersed in the patterning medium is in an amount of about 40 wt.% to about 85 wt.% based on the total weight of the paste composition.

24. The method of any one of claims 18 to 23, wherein the patterning medium is provided in an amount of about 5 wt.% to about 50 wt.% based on the total weight of the paste composition.

25. The method of any one of claims 18 to 24, wherein the amount of the glass component dispersed in the patterning medium is in an amount of about 0.05 wt.% to about 20 wt.% based on the total weight of the paste composition.

26. The method of any one of claims 19 to 25, wherein the amount of silver particles dispersed in the patterning medium is an amount of less than about 0.5 wt. % based on the total weight of the paste composition when the aluminum content is provided in an amount less than about 80 wt. %.

27. The method according to any one of claims 18 to 26, wherein the viscosity of the paste composition is in the range of about 5 Pa.s to about 200 Pa.s.

28. The method according to any one of claims 18 to 22, wherein the shear rate of the paste composition set to monitor the design target viscosity is typically about 4 seconds to 1 .

29. The method of any one of claims 18 to 28, further comprising one or more additives dispersed in the print vehicle. 30 . A fire-through aluminum paste composition for selectively firing through a passivation layer, the fire-through aluminum paste composition being prepared by the method according to claim 18 .

31. A fired back contact paste adhered to a passivation layer of a bifacial PERC solar cell comprising a silicon substrate, wherein the passivation layer is fired through to contact the silicon and enable aluminum to access the silicon to form an Al-Si alloy, wherein prior to firing, the fired back contact paste is a fire-through paste composition comprising: Aluminum component, glass components, and patterning media; The glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

32. The fired back contact paste of claim 31 , wherein the Al-Si alloy formation is localized at the edge of the print, while under the pattern, the passivation layer function is maintained, thereby maximizing the open circuit voltage.

33. The fired back contact paste of claim 32, wherein the localized region is controlled by the thickness and / or porosity of the fired back contact paste layer.

34. The fired back contact paste of claim 33, wherein at least a portion of the fired back contact paste layer has a thickness less than 10 μm to form a localized back surface field.

35. The fired back contact paste of claim 33, wherein at least a portion of the fired back contact paste layer has a thickness greater than 10 μm to provide an area that does not penetrate the passivation layer to the silicon substrate.

36. The fired back contact paste of any one of claims 31 to 35, wherein the surface area density of the fired back contact paste layer is about 0.8 mg / cm 2 to about 5.5 mg / cm 2 .

37. A bifacial PERC solar cell comprising a silicon substrate and a back contact thereon, the back contact comprising a passivation layer at least partially coated with a fired back contact paste at the back side of the silicon substrate, wherein the back contact paste is a fire-through aluminum paste composition for selectively firing through the passivation layer, wherein prior to firing, the fire-through aluminum paste composition comprises: Aluminum component, glass components, and patterning media; The glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant and forms a low viscosity liquid at a predetermined temperature, and the second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of the oxidant, and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A).

38. The solar cell unit of claim 37, wherein the solar cell unit is p-type.

39. The solar cell unit of claim 37 or claim 38, wherein the paste composition further comprises silver particles or other silver source.

40. The solar cell unit of any one of claims 37 to 39, wherein the passivation layer comprises SiN deposited on the silicon substrate. x 、SiN x H y 、AlOx / SiN x 、AlOx / SiN x H y 、SiO2 / AlOx / SiN x or SiO2 / AlOx / SiN x H y .

41. The solar cell unit of any one of claims 37 to 40, wherein the silicon substrate has a thickness of less than about 150 μm.

42. The solar cell unit of any one of claims 37 to 41, wherein the silicon substrate has a thickness of less than about 125 μm.

43. The solar cell unit of any one of claims 37 to 42, wherein the silicon substrate has a thickness of about 90 μm.

44. The solar cell unit according to any one of claims 37 to 43, wherein SiN x or SiN x H y The thickness of the coating ranges between about 30 nm and about 200 nm.

45. The solar cell unit of any one of claims 37 to 44, wherein the thickness of AlOx is in a range between about 2 nm and about 20 nm.

46. ​​The solar cell unit according to any one of claims 37 to 45, wherein no laser ablation or chemical etching to form the local opening is applied to the back side of the cell.

47. The solar cell unit of any one of claims 37 to 46, wherein the silicon substrate is crystalline silicon.

48. The solar cell unit of any one of claims 33 to 46, wherein the paste composition is patterned to form dots or lines on the passivation layer.

49. The solar cell unit of any one of claims 37-48, wherein at least a portion of the paste composition is patterned on the passivation layer to achieve a fired thickness of less than about 10 μm.

50. The solar cell unit of any one of claims 37 to 48, wherein at least a portion of the paste composition is patterned on the passivation layer to achieve a fired thickness greater than about 10 μm.

51. The solar cell unit of any one of claims 37 to 49, wherein after firing, the paste composition promotes aluminum metallization on the back side of the silicon substrate to form an Al-Si alloy at the edge of the fired back contact paste, wherein the fired thickness of the edge of the fired back contact paste is less than about 10 μm to form a localized back surface field.

52. The solar cell unit of claim 48, wherein the fired back contact paste layer has a surface area density of about 0.8 mg / cm 2 to about 5.5 mg / cm 2 .

53. A method for preparing a bifacial PERC solar cell unit, the method comprising: providing a silicon substrate and a post-passivation layer thereon; A fire-through aluminum paste composition is applied to at least partially coat the passivation layer to selectively fire through the passivation layer, the paste composition comprising an aluminum component, a glass component, and a patterning medium, wherein the glass component comprises at least a first glass frit (A) and a second glass frit (B), wherein the first glass frit (A) is silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) of an oxidant and forms a low viscosity liquid at a predetermined temperature, and The second glass frit (B) does not contain silicon nitride (SiN x ) or hydrogenated silicon nitride (SiN x :H y ) and controlling the volume of the low-viscosity liquid and the concentration of the first glass frit (A), The paste composition is heated to a predetermined temperature to burn through at least a portion of the passivation layer to contact the silicon and allow aluminum to access the silicon to facilitate contact metallization and formation of a back surface field.

54. The method of claim 53, wherein the fired thickness of the edge of the fired paste composition is less than about 10 μm to form a localized back surface field.

55. A method according to claim 53 or claim 54, wherein the paste composition is applied to the passivation layer using a screen printing, pen writing, inkjet printing or extrusion process.

56. The method according to any one of claims 53 to 55, wherein the paste composition is applied to the passivation layer in the form of dots or lines.

57. The method of claim 54, wherein the dot diameter or line width is in the range of about 20 μm to about 500 μm.

58. The method of any one of claims 53 to 57, wherein the passivation layer is locally pre-opened without laser ablation or chemical etching.

59. The method of any one of claims 53 to 58, wherein the aluminum component further comprises silver particles or other silver source.

60. The method of any one of claims 53 to 59, wherein the heating step is a two-step process of (i) drying the paste composition, and then (ii) firing the paste composition.

61. The method of claim 60, wherein the predetermined temperature of heating step (i) is in the range of about 250°C to about 350°C.

62. The method of claim 60, wherein the predetermined temperature of heating step (ii) is in the range of about 500°C to about 1000°C.

63. The method of any one of claims 60 to 62, wherein the heating step is performed in an O2 environment.

64. The method of any one of claims 53 to 62, wherein the passivation layer comprises SiN deposited on the silicon substrate. x 、SiN x H y 、AlOx / SiN x 、AlOx / SiN x H y 、SiO2 / AlOx / SiN x or SiO2 / AlOx / SiN x H y .

65. The method of any one of claims 53 to 64, wherein the silicon substrate has a thickness of less than about 150 μm.

66. The method of any one of claims 53 to 65, wherein the silicon substrate has a thickness of less than about 125 μm.

67. The method of any one of claims 53 to 66, wherein the silicon substrate has a thickness of about 90 μm.

68. The method of any one of claims 63 to 67, wherein SiN x or SiN x H y The thickness of the coating ranges between about 30 nm and about 200 nm.

69. The method of any one of claims 63 to 68, wherein the thickness of AlOx is in a range between about 2 nm and about 20 nm.

70. The method of any one of claims 53 to 69, further comprising applying a multiwire grid to the backside of the battery cells, and optionally applying the multiwire grid to the front surface of the silicon substrate, to interconnect the battery cells.

71. The method of claim 70, wherein the multiwire grid comprises about 15 wires to about 50 wires.

72. The method of claim 71, wherein the wire is a Cu-based wire coated with a low melting point alloy.

73. The method of any one of claims 53 to 72, wherein one or more battery cells are arranged to be interconnected in series or in parallel.

74. The method of claim 73, wherein the battery cells are encased in a module with glass, wherein the glass is about 1 mm to about 4 mm thick.

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