Composite conductive structure and preparation method, and photovoltaic cell

Abstract

Disclosed in the present disclosure are a composite conductive structure and a preparation method, and a photovoltaic cell. The composite conductive structure comprises: a substrate; a first conductive layer, which is formed on the substrate, wherein the thickness of the first conductive layer ranges from 1 μm to 2 μm, and the material of the first conductive layer comprises a silver-based conductive material, a glass material and an inorganic additive; and a second conductive layer, which is formed on the first conductive layer, wherein a conductive material of the second conductive layer comprises a base metal conductive material. The preparation method is used for preparing the composite conductive structure, and the photovoltaic cell comprises the composite conductive structure. The composite conductive structure and the preparation method, and the photovoltaic cell in the embodiments of the present disclosure are used for ensuring the conversion efficiency of a cell, and also for reducing the silver consumption.

Description

A composite conductive structure, its preparation method, and a photovoltaic cell

[0001] This application claims priority to Chinese Patent Application No. 202411811236.3, filed on December 10, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of photovoltaic cell manufacturing technology, and in particular to a composite conductive structure, its preparation method, and a photovoltaic cell. Background Technology

[0003] TOPCon (Tunnel Oxide Passivated Contact) battery technology is becoming increasingly mature and is gaining popularity in the market. In related technologies, when forming the gate on the front side of a TOPCon battery using laser-assisted sintering, the thickness of the front gate is typically sintered to 5μm–9μm. This sufficient thickness ensures that the silver paste forms a continuous and dense conductive path after sintering.

[0004] However, when the thickness of the front gate is 5μm to 9μm, a large amount of paste is used, and the amount of silver used in the paste is large, which is not conducive to saving costs. Summary of the Invention

[0005] In view of this, the present disclosure provides a composite conductive structure, a preparation method thereof, and a photovoltaic cell to solve the problems existing in the related technologies.

[0006] A first aspect of this disclosure provides a composite conductive structure, comprising:

[0007] Substrate;

[0008] A first conductive layer is formed on the substrate, the thickness of the first conductive layer is 1μm to 2μm, and the material of the first conductive layer includes silver-based conductive material, glass material and inorganic additives;

[0009] And a second conductive layer formed on the first conductive layer, wherein the conductive material of the second conductive layer includes a base metal conductive material.

[0010] A second aspect of this disclosure provides a method for preparing a composite conductive structure, comprising:

[0011] Provide a substrate;

[0012] A first conductive layer is formed on the substrate using a first conductive paste, the thickness of the first conductive layer being 1μm to 2μm;

[0013] A second conductive layer is formed on the first conductive layer using a second conductive paste, wherein the conductive material of the second conductive layer includes a base metal conductive material.

[0014] A third aspect of this disclosure provides a photovoltaic cell, including the composite conductive structure of the first aspect of this disclosure.

[0015] In one or more technical solutions provided in this disclosure, a first conductive layer is formed on a substrate using a first conductive paste, and the thickness of the first conductive layer is 1 μm to 2 μm. Therefore, compared to sintering the grid line thickness on the front side of the battery to 5 μm to 9 μm using a conductive paste, the thickness of the first conductive layer in this disclosure is significantly reduced, meaning that the volume of the first conductive layer is reduced for the same area. Since the material of the first conductive layer includes silver-based conductive materials, glass materials, and inorganic additives, the silver content in the first conductive layer can be reduced when forming a thinner first conductive layer, thereby reducing production costs.

[0016] Based on this, to avoid the problem of high lateral resistance caused by the thinness of the first conductive layer, the embodiments of this disclosure form a second conductive layer on the first conductive layer. The conductive material of the second conductive layer includes a base metal conductive material. Therefore, the current in the first conductive layer can be transferred to the second conductive layer. The base metal conductive material in the second conductive layer has a large number of free electrons. These free electrons can move relatively smoothly in the lateral direction under the action of an electric field. Thus, the second conductive layer can be used to conduct the current laterally, so that the current no longer depends solely on the thin and potentially high-resistance first conductive layer during lateral conduction, thereby avoiding the problem of high lateral resistance caused by the thinness of the first conductive layer.

[0017] In addition, if the total thickness of the first conductive layer and the second conductive layer is 5μm to 9μm, the presence of base metal conductive material significantly reduces the proportion of silver in the entire conductive structure without changing the overall thickness of the gate line, thus saving costs. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this disclosure and form part of this disclosure, illustrate exemplary embodiments of the present disclosure and are used to explain the disclosure, but do not constitute an undue limitation of the disclosure. In the drawings:

[0019] Figure 1 is a schematic diagram of the composite conductive structure according to an embodiment of the present disclosure;

[0020] Figure 2 is a flowchart of the preparation method of the composite conductive structure provided in the embodiments of this disclosure;

[0021] Figure 3 is a scanning electron microscope cross-sectional view of the first conductive layer according to an embodiment of the present disclosure;

[0022] Figure 4 is a viscosity diagram of the first conductive paste under steady-state shear in an embodiment of this disclosure;

[0023] Figure 5 is a dynamic strain amplitude scan of the first conductive paste according to an embodiment of this disclosure;

[0024] Figure 6A is a scanning electron microscope image of a first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure.

[0025] Figure 6B is a scanning electron microscope image of another first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure;

[0026] Figure 7 is an EL emission characteristic diagram of the first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure.

[0027] Reference numerals: 110 - substrate, 120 - first conductive layer, 130 - second conductive layer. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this disclosure clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this disclosure and are not intended to limit it.

[0029] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means two or more, unless otherwise expressly and specifically defined. "Several" means one or more, unless otherwise expressly and specifically defined.

[0031] In the description of this disclosure, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0032] In the description of this disclosure, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0033] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this disclosure should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0034] In this invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0035] TOPCon cell technology, a highly anticipated innovation in the photovoltaic field in recent years, is playing an increasingly important role in the context of energy transition. TOPCon cells achieve high photoelectric conversion efficiency thanks to their unique tunneling oxide passivated contact structure. In the cell manufacturing process, laser-assisted sintering technology is widely used to form the gate on the front side of the cell. By precisely controlling the sintering process, the thickness of the front gate is sintered to 5μm–9μm. This thickness range ensures that the silver paste forms a continuous and dense conductive path after sintering, thereby effectively transferring current and improving cell performance.

[0036] However, current technology faces some challenges in processing the back-side gate. When the front-side gate thickness is also 5μm to 9μm, a larger amount of paste is required, with silver being used in significant quantities. In the current market environment, silver, as a precious metal, has a relatively high and volatile price. The large-scale use of silver paste not only increases production costs but also makes the battery price less competitive in the market, hindering the sustainable development and large-scale application of the photovoltaic industry.

[0037] To address the aforementioned issues, this disclosure provides a composite conductive structure, its fabrication method, and a photovoltaic cell, thereby reducing the amount of silver used in the front-side grid lines of the photovoltaic cell and lowering costs. The photovoltaic cell includes this composite conductive structure.

[0038] Figure 1 is a schematic diagram of the composite conductive structure provided in an exemplary embodiment of the present disclosure. As shown in Figure 1, the composite conductive structure of the present disclosure includes a substrate 110 and a first conductive layer 120 formed on the substrate 110, the thickness of the first conductive layer 120 being 1 μm to 2 μm.

[0039] Compared to sintering the grid line thickness on the front of the battery to 5μm to 9μm using conductive paste, the thickness of the first conductive layer 120 in this embodiment is significantly reduced, which means that the volume of the first conductive layer 120 is reduced for the same area. Since the material of the first conductive layer 120 includes silver-based conductive material, glass material and inorganic additives, the silver content in the first conductive layer 120 can be reduced when forming a thinner first conductive layer 120, thereby reducing production costs.

[0040] It is understood that the aforementioned substrate may include an N-type silicon substrate. On the front side of the N-type silicon substrate, a very thin tunneling oxide layer (usually silicon dioxide) and a doped polycrystalline silicon layer can be formed. These two layers constitute the passivation contact structure of the TOPCon cell, and the front gate line is usually formed by printing conductive paste (such as silver paste) on this passivation contact structure.

[0041] In one example, the material of the first conductive layer includes a silver-based conductive material, a glass material, and inorganic additives. It should be understood that the glass material in this embodiment can be in powder form. The silver-based conductive material, as a conductive component, provides good conductivity. During the sintering stage, the glass material plays a primary role, melting at a lower temperature and acting as a flux. The molten glass material can encapsulate the silver-based conductive material, lowering its sintering temperature and promoting the formation of continuous conductive pathways between the silver-based conductive materials. The glass material acts as a bond and filler between the silver-based conductive materials and on the battery surface, filling the gaps between them and enhancing the density of the gate. The inorganic additives can undergo physical adsorption or chemical bonding with the glass material and the silver-based conductive material. For example, the inorganic additives can form cross-linked structures with certain components in the glass material, enhancing the strength of the glass phase. Simultaneously, for the silver-based conductive material, the inorganic additives can form a protective film on its surface, improving its oxidation resistance and corrosion resistance. This mutual cooperation enables the formed gate structure to remain stable during long-term use, and it can effectively transmit current even under harsh environmental conditions such as high temperature, high humidity, and ultraviolet radiation.

[0042] For silver-based conductive materials, it can be any one or two of silver powder, Ag-M alloy powder, and Ag-Cu-N alloy powder, wherein M includes one or more of Al, Au, Ba, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Ho, In, Ir, La, Lu, Mg, Mn, Mo, Nd, Ni, Pb, Pd, Pm, Pr, Pt, Re, Rh, Ru, Sb, Sc, Si, Sm, Sn, Sr, Tb, Te, Ti, Tm, Y, Yb, Zn, and Zr; wherein N includes one or more of P, Zn, Ni, Pb, and Sn.

[0043] For example, as shown in FIG1, the composite conductive structure of this embodiment further includes a second conductive layer 130 formed on the first conductive layer 120, wherein the conductive material of the second conductive layer 130 includes a base metal conductive material.

[0044] In this embodiment of the present disclosure, a second conductive layer 130 is formed on the first conductive layer 120, which can transmit the current of the first conductive layer 120 to the second conductive layer 130. The base metal conductive material of the second conductive layer 130 has a large number of free electrons. These free electrons can move relatively smoothly in the lateral direction under the action of an electric field. Thus, the second conductive layer 130 can be used to conduct the current laterally, so that the current does not rely solely on the thin and potentially high-resistance first conductive layer 120 during lateral conduction. This avoids the problem of high lateral resistance caused by the thin thickness of the first conductive layer 120.

[0045] Based on this, if the total thickness of the first conductive layer 120 and the second conductive layer 130 is 5μm to 9μm, then without changing the overall thickness of the gate line, the presence of the base metal conductive material significantly reduces the proportion of silver in the entire conductive structure, thus saving costs.

[0046] For example, the aforementioned base metal conductive materials include at least one of copper-based conductive materials, aluminum-based conductive materials, nickel-based conductive materials, and zinc-based conductive materials. Copper-based conductive materials include at least one of copper and copper alloys, aluminum-based conductive materials include at least one of aluminum and aluminum alloys, nickel-based conductive materials include at least one of nickel and nickel alloys, and zinc-based conductive materials include at least one of zinc and zinc alloys.

[0047] In one feasible embodiment, the mass ratio of silver-based conductive material, glass material, and inorganic additives in the first conductive layer 120 of this disclosure is (70-85):(3-10):(0.1-2). In this mass ratio, the silver-based conductive material dominates, ensuring good conductivity, forming a superior conductive path, and reducing energy loss during current transmission. The glass material can effectively melt at the sintering temperature, lowering the sintering temperature of the silver-based conductive material and effectively fluxing it, resulting in more complete sintering. Furthermore, it prevents excessive glass phase from covering the silver-based conductive material after sintering, thus avoiding negatively impacting conductivity. Simultaneously, this ratio of inorganic additives ensures that the silver-based conductive material sinters in a suitable chemical environment, preventing oxidation, agglomeration, and other problems. If the proportion of inorganic additives is too high, it may introduce excessive impurities, interfering with the sintering process. If the proportion is too low, the sintering process cannot be effectively regulated, affecting the quality of the gate.

[0048] In one possible implementation, in the first conductive layer 120 of this disclosure, the particle size parameters D50 of the silver-based conductive material, the glass material, and the inorganic additives are all less than or equal to 1.5 μm, and D100 are all less than 3 μm.

[0049] In practical applications, since the thickness of the first conductive layer 120 is 1μm to 2μm, setting the particle size parameters D50 of the silver-based conductive material, glass material, and inorganic additives to less than or equal to 1.5μm, and D100 to less than 3μm, ensures that the material particles do not occupy a large volume due to excessive particle size. Therefore, smaller particle sizes can improve the uniformity of glass distribution and contact effect, while avoiding the potential for unevenness in the first conductive layer 120 caused by large particles, which could be detrimental to lateral charge transport. Moreover, the limitations on D50 and D100 parameters allow the silver-based conductive material, glass material, and inorganic additives to fill better during deposition or coating, ensuring the density of the first conductive layer. For example, in screen printing or other coating processes, materials with suitable particle sizes can be more uniformly distributed on the substrate, forming a conductive layer with stable quality. This uniform conductive layer can more effectively collect and transport current, reducing local current overload or underload, thereby improving the photoelectric conversion efficiency of the battery.

[0050] In one possible implementation, the first conductive layer 120 of this embodiment includes a first glass material, a second glass material, and a third glass material. The glass transition temperature of the first glass material is less than or equal to 400°C, the glass transition temperature of the second glass material is greater than 400°C, and the glass transition temperature of the third glass material is 400°C to 450°C.

[0051] In practical applications, by selecting three glass materials with different glass transition temperatures, the particle contact and fusion of the silver-based conductive material can be optimized, and they are melted sequentially. This melting sequence at different temperatures creates a temperature gradient, which helps to gradually optimize the structure of the first conductive layer throughout the sintering process. Specifically, the first glass material acts as a binder in the initial stage, the second glass material acts as a filler in the middle and later stages, and the third glass material acts as a transition and synergistic agent. Together, they enable the silver-based conductive material to form a more continuous and uniform conductive path, thereby reducing the resistance of the conductive layer and improving the photoelectric conversion efficiency of the battery.

[0052] For example: First, in the initial stage of the sintering process, as the temperature gradually rises and reaches the transition temperature of the first glass material, the first glass material softens and melts. This helps to promote the particle fusion of the silver-based conductive material at a lower temperature stage, laying the foundation for the subsequent formation of a continuous conductive path. Simultaneously, the first glass material acts as an initial binder, initially fixing the silver-based conductive material and inorganic additives together, preventing material displacement during subsequent heating. Second, when the temperature rises above the transition temperature of the second glass material, the second glass material begins to melt and further mixes with the already initially fused silver-based conductive material and the first glass material. The second glass material can fill any gaps that may exist between the first glass material and the silver-based conductive material, further enhancing the density of the conductive layer. The third glass material, located in the intermediate temperature range, plays a transitional and balancing role in the sintering process. It functions in the temperature range where the first glass material has begun to soften but the second glass material has not yet melted, regulating the viscosity and flowability of the entire glass system. Within this temperature range, the third glass material can work in tandem with the first glass material to better encapsulate the silver-based conductive material, while simultaneously preparing for the subsequent melting and filling of the second glass material, making the formation process of the conductive layer more stable and continuous.

[0053] For example, the mass ratio of the first glass material, the second glass material and the third glass material is (10-50):(20-50):(0-80), preferably (10-20):(30-40):(30-60).

[0054] In an optional embodiment, the first conductive layer 120 of this disclosure comprises SiO2, B2O3, Al2O3, PbO, ZnO, Bi2O3, alkali metal oxides, and alkaline earth metal oxides, all of which are first, second, and third glass materials. In the first glass material, the ratio of the sum of the molar numbers of cations in PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the first glass material is greater than 40%. In the second glass material, the ratio of the sum of the molar numbers of cations in PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the second glass material is less than or equal to 20%. In the third glass material, the ratio of the sum of the molar numbers of cations in PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the third glass material is less than or equal to 40%.

[0055] This disclosure specifies the molar number of cations (PbO, ZnO, Bi₂O₃, alkali metal oxides, and alkaline earth metal oxides) in the first, second, and third glass materials. PbO, ZnO, Bi₂O₃, alkali metal oxides, and alkaline earth metal oxides typically lower the glass transition temperature, while glass forgings such as SiO₂, B₂O₃, and Al₂O₃ raise the glass transition temperature. Therefore, by specifying the molar number of cations, the transition temperatures of the first, third, and second types of glasses increase sequentially.

[0056] Based on this, by limiting the molar number of cations in the three glass materials, the glass materials can play an optimal role at different stages of the sintering process, thereby optimizing the particle arrangement and connection of the silver-based conductive material. The first glass material mainly provides a passivation layer, such as SiNx and Al2O3 layers, for etching the silicon wafer surface. The second glass material has weaker corrosivity and can further supplement the etching effect of the first glass. The third glass mainly restricts corrosion and provides better sintering between silver powder particles.

[0057] In one example, in the first conductive layer 120 of this disclosure, the inorganic additives include at least one of alumina, silicon powder, silicon oxide, titanium oxide, boron oxide, silicon boride, and silicon nitride.

[0058] Figure 2 shows a flowchart of the preparation method of the composite conductive structure provided in the embodiments of this disclosure. As shown in Figure 2, this disclosure also provides a preparation method of the composite conductive structure, including:

[0059] Step 201: Provide a substrate.

[0060] Step 202: Form a first conductive layer on the substrate using a first conductive paste. The thickness of the first conductive layer is 1 μm to 2 μm.

[0061] For example, the first conductive paste can be printed onto the substrate using screen printing or other printing methods such as laser transfer. The deposition thickness of the first conductive paste is less than or equal to 4 μm, and the thickness after sintering is less than or equal to 2 μm. The sintering process of the first conductive paste on the substrate can include laser-assisted sintering or other feasible sintering processes. Therefore, ohmic contact can be achieved by combining the first paste layer with laser-assisted sintering to ultimately etch the dielectric layer on the substrate.

[0062] Compared to sintering the grid line thickness on the front of the battery to 5μm to 9μm using conductive paste, the thickness of the first conductive layer in this embodiment is significantly reduced, which means that the volume of the first conductive layer is reduced for the same area. Since the material of the first conductive layer includes silver-based conductive material, glass material and inorganic additives, the silver content in the first conductive layer can be reduced when forming a thinner first conductive layer, thereby reducing production costs.

[0063] Figure 3 shows a scanning electron microscope cross-sectional view of the first conductive layer according to an embodiment of the present disclosure. As shown in Figure 3, the thickness of the first conductive layer is 1 μm to 2 μm.

[0064] Step 203: Form a second conductive layer on the first conductive layer using a second conductive paste. The conductive material of the second conductive layer includes a base metal conductive material.

[0065] In this embodiment, a second conductive layer is formed on the first conductive layer, which can transmit the current from the first conductive layer to the second conductive layer. The base metal conductive material of the second conductive layer has a large number of free electrons. These free electrons can move smoothly in the lateral direction under the action of an electric field, so that the second conductive layer can be used to conduct the current laterally. This means that the current does not rely solely on the thin and potentially high-resistance first conductive layer during lateral conduction, thus avoiding the problem of high lateral resistance caused by the thinness of the first conductive layer.

[0066] For example, the second conductive paste can be printed onto the first conductive layer using screen printing or other printing methods such as laser transfer. The sintering process of the second conductive paste onto the first conductive layer can include laser-assisted sintering, low-temperature paste curing to achieve densification, or high-temperature sintering paste can be densified by sintering under a protective atmosphere, which can be nitrogen or a nitrogen-hydrogen mixture.

[0067] In one example, the second conductive paste may include a base metal material, a glass material, and an organic carrier. The base metal material may include at least one of copper-based conductive materials, aluminum-based conductive materials, nickel-based conductive materials, zinc-based conductive materials, and silver-clad copper materials. Copper-based conductive materials include at least one of copper and copper alloys; aluminum-based conductive materials include at least one of aluminum and aluminum alloys; nickel-based conductive materials include at least one of nickel and nickel alloys; and zinc-based conductive materials include at least one of zinc and zinc alloys.

[0068] In one example, a first conductive paste can be printed onto the substrate surface using high-temperature sintering to form a first conductive layer, followed by laser-assisted sintering of the first conductive layer to achieve good ohmic contact. Alternatively, a first conductive paste can be printed onto the substrate surface using high-temperature sintering to form a first conductive layer, followed by printing a second conductive paste onto the first conductive layer to form a second conductive layer, and then laser-assisted sintering can be performed to achieve good ohmic contact.

[0069] For example, when the base metal material is silver-clad copper, a laser-assisted sintering process can be used to sinter the first conductive paste, and a second conductive layer can be formed on the first conductive layer using a low-temperature curing method. When the base metal material is a copper-based, aluminum-based, nickel-based, or zinc-based conductive material, the first conductive paste is first printed on the substrate surface using high-temperature sintering to form a first conductive layer, and then a second conductive paste is printed on the first conductive layer, and a laser-assisted sintering process is used to sinter the second conductive paste. It should be understood that the use of laser sintering after the formation of either the first or second conductive layer is for the purpose of achieving good ohmic contact.

[0070] In one example, before forming a first conductive layer on the substrate using a first conductive paste, the preparation method further includes: mixing a silver-based conductive material, a glass material, an inorganic additive, and an organic carrier to obtain a first conductive paste.

[0071] For example, silver-based conductive materials, glass materials and inorganic additives are premixed and then added to an organic carrier and stirred for 2 to 4 hours. The stirred raw materials are then rolled 6 to 10 times on a three-roll mill to further disperse and homogenize them. When the scraper fineness is less than 5 μm, it is filtered with a 400-mesh filter cloth to obtain the first conductive slurry.

[0072] In an alternative embodiment, Figure 4 shows the viscosity diagram of the first conductive paste under steady-state shear according to an embodiment of the present disclosure. Figure 5 shows the dynamic strain amplitude scan of the first conductive paste according to an embodiment of the present disclosure. As shown in Figures 4 and 5, the rheological characteristics of the first conductive paste according to an embodiment of the present disclosure are as follows: under the test of an Antombard rheometer, the shear viscosity at a shear rate of 1 / second for 30 seconds is 50 Pa·s to 500 Pa·s. Under the oscillating shear condition after testing at a constant shear rate of 1 / second, with an amplitude scan at a frequency of 6.28 radians per second, when the shear strain is 0.1%, the storage modulus value is less than or equal to 10000 Pa and greater than 100 Pa, and the intersection point of the storage modulus and loss modulus curves appears in the range of strain from 10% to 100%.

[0073] In one example, Figure 6A shows a scanning electron microscope (SEM) image of a first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure, and Figure 6B shows a scanning electron microscope (SEM) image of another first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure. As shown in Figures 6A and 6B, after laser sintering of the above-mentioned first conductive paste and etching with hydrofluoric acid, the diagonal length of the opening in the SEM image is 300–800 nm, preferably 300–420 nm. It should be understood that the diagonal length of the opening can be understood as the length of the diagonal when the opening shape is polygonal (usually approximately rectangular or rhomboid). An opening diagonal length of 300–800 nm avoids both excessively small openings that would obstruct current flow and excessively large openings that would increase the passivation layer damage area and affect the open-circuit voltage, thereby ensuring the effectiveness of the conductive path to a certain extent and helping to maintain or improve the overall conductivity.

[0074] The above-mentioned hydrofluoric acid corrosion conditions include: immersing the silicon wafer in a 5% hydrofluoric acid aqueous solution for 30 seconds at room temperature, maintaining magnetic stirring during the immersion process, rotating at 600 rpm to maintain a uniform concentration of the hydrofluoric acid aqueous solution, removing it and placing it in pure water for ultrasonication for 10 minutes, and then placing it on a lint-free cloth to absorb the moisture.

[0075] For example, Figure 7 shows an EL emission characteristic image of the first conductive paste after laser-assisted sintering according to an embodiment of the present disclosure. As shown in Figure 7, before the formation of the second conductive paste, an inspection is performed by electroluminescence (EL), and the image shows a uniform distribution of broken grids, with more than 10 broken grids.

[0076] For example, the above-mentioned organic carrier includes a resin, a solvent, a surface dispersant, and a thixotropic agent. The resin may include one or more of ethyl cellulose, cellulose acetate butyrate, rosin resin, acrylic resin, and polyvinyl butyral. The organic solvent may include one or more of terpineol, butyl carbitol, butyl carbitol acetate, diethylene glycol butyl ether acetate, diethylene glycol dibutyl ether, tripropylene glycol monomethyl ether, diisooctyl adipate, diethylene glycol butyl ether, oleic acid, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, Thixatrol Max, triethylene glycol butyl ether, oleic acid ester, and oleic acid ester hexadecyl. The surface dispersant may include one or more of TDO, ED120, BYK111, and KYC913. For thixotropic agents, they may include one or more of alcohol ester 12, terpineol, diethylene glycol butyl ether acetate and diethylene glycol monobutyl ether.

[0077] In an alternative embodiment, the aforementioned organic carrier may contain, by weight percentage, 1%–6% ethyl cellulose, 1%–40% polyvinyl butyral, 10%–70% diethylene glycol butyl ether acetate, 10%–60% tripropylene glycol monomethyl ether, 5%–50% diethylene glycol dibutyl ether, 0%–15% triethylene glycol diisooctanoate, 3%–15% diisooctanoate adipate, 0%–30% diethylene glycol butyl ether, 0%–30% terpineol, 0%–10% oleic acid, 0%–20% 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, 0%–20% 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and 1%–10% Thixatrol. Max, 0%–10% hydrogenated castor oil, 0%–10% TDO, 0%–10% ED120, 0%–10% BYK111 and 0%–10% KYC913.

[0078] As can be seen from the above, in this embodiment, a first conductive layer is formed on a substrate using a first conductive paste, and the thickness of the first conductive layer is 1 μm to 2 μm. Therefore, compared to sintering the grid line thickness on the front side of the battery to 5 μm to 9 μm using a conductive paste, the thickness of the first conductive layer in this embodiment is significantly reduced, meaning that the volume of the first conductive layer is reduced for the same area. Furthermore, since the material of the first conductive layer includes silver-based conductive materials, glass materials, and inorganic additives, the silver content in the first conductive layer can be reduced when forming a thinner first conductive layer, thereby reducing production costs.

[0079] Based on this, to avoid the problem of high lateral resistance caused by the thinness of the first conductive layer, the embodiments of this disclosure form a second conductive layer on the first conductive layer. The conductive material of the second conductive layer includes a base metal conductive material. Therefore, the current in the first conductive layer can be transferred to the second conductive layer. The base metal conductive material in the second conductive layer has a large number of free electrons. These free electrons can move relatively smoothly in the lateral direction under the action of an electric field. Thus, the second conductive layer can be used to conduct the current laterally, so that the current no longer depends solely on the thin and potentially high-resistance first conductive layer during lateral conduction, thereby avoiding the problem of high lateral resistance caused by the thinness of the first conductive layer.

[0080] To verify the effectiveness of the composite conductive structure provided in the embodiments of this disclosure, the embodiments of this disclosure are demonstrated by comparing the embodiments with comparative examples.

[0081] Example 1

[0082] The method for preparing the composite conductive structure provided in Embodiment 1 of the present invention includes the following steps:

[0083] The first step is to provide a substrate with a tunneling oxide layer and a doped polysilicon layer on the front side.

[0084] The second step is to prepare the organic carrier: Weigh out 10% butyl carbitol, 33% butyl carbitol acetate, 70% diethylene glycol dibutyl ether, 10% tripropylene glycol monomethyl ether, and 10% tetrazol (by weight percentage) and mix them thoroughly to obtain a mixed solvent. Then weigh out 5% polyvinyl butyral and add it to the mixed solvent, followed by 5% polyamide wax thixotropic agent. Heat the mixture to 80°C while stirring until the resin is completely dissolved. Continue stirring for 60 minutes, then cool to room temperature to obtain the organic carrier.

[0085] The third step is to prepare the first conductive paste: 79.6% silver powder, 4.5% glass material, 1.2% inorganic additives and 14.7% organic carrier are premixed, then added to the organic carrier and stirred for 2 hours. The stirred raw materials are then rolled 6 times on a three-roll mill to further disperse and homogenize them. When the scraper fineness is less than 5μm, it is filtered with a 400-mesh filter cloth to obtain the first conductive paste.

[0086] The glass material comprises 50% first glass material and 50% second glass material. The first glass material consists of 40.9% PbO, 9.1% ZnO, 13.6% Bi₂O₃, 27.3% B₂O₃, and 9.1% SiO₂. The second glass material consists of 9.7% PbO, 4.9% BaO, 2.9% Bi₂O₃, 4.9% ZnO, 29.1% SiO₂, and 48.5% B₂O₃. The third glass material consists of 30% PbO, 5% ZnO, 5% Bi₂O₃, 5% TiO₂, 5% Al₂O₃, 20% B₂O₃, and 20% SiO₂.

[0087] The fourth step involves printing a 3.5μm to 4μm first conductive paste on the substrate, which is then sintered to form a 2μm first conductive layer.

[0088] Example 2

[0089] The method for preparing the composite conductive structure provided in Embodiment 2 of the present invention includes the following steps:

[0090] The first step is to provide a substrate with a tunneling oxide layer and a doped polysilicon layer on the front side.

[0091] The second step is to prepare the organic carrier: Weigh out 10% butyl carbitol, 33% butyl carbitol acetate, 70% diethylene glycol dibutyl ether, 10% tripropylene glycol monomethyl ether, and 10% tetrazol (by weight percentage) and mix them thoroughly to obtain a mixed solvent. Then weigh out 5% polyvinyl butyral and add it to the mixed solvent, followed by 5% polyamide wax thixotropic agent. Heat the mixture to 80°C while stirring until the resin is completely dissolved. Continue stirring for 60 minutes, then cool to room temperature to obtain the organic carrier.

[0092] The third step is to prepare the first conductive paste: 79.6% silver powder, 4.5% glass material, 1.2% inorganic additives and 14.7% organic carrier are premixed, then added to the organic carrier and stirred for 2 hours. The stirred raw materials are then rolled 6 times on a three-roll mill to further disperse and homogenize them. When the scraper fineness is less than 5μm, it is filtered with a 400-mesh filter cloth to obtain the first conductive paste.

[0093] The glass materials comprise: 17% first glass material, 50% second glass material, and 33% third glass material. The first glass material consists of 40.9% PbO, 9.1% ZnO, 13.6% Bi₂O₃, 27.3% B₂O₃, and 9.1% SiO₂. The second glass material consists of 9.7% PbO, 4.9% BaO, 2.9% Bi₂O₃, 4.9% ZnO, 29.1% SiO₂, and 48.5% B₂O₃. The third glass material consists of 30% PbO, 5% ZnO, 5% Bi₂O₃, 5% TiO₂, 5% Al₂O₃, 20% B₂O₃, and 20% SiO₂.

[0094] The fourth step involves printing a 3.5μm to 4μm first conductive paste on the substrate, which is then sintered to form a 2μm first conductive layer.

[0095] Example 3

[0096] The method for preparing the composite conductive structure provided in Embodiment 3 of the present invention includes the following steps:

[0097] The first step is to provide a substrate with a tunneling oxide layer and a doped polysilicon layer on the front side.

[0098] The second step is to prepare the organic carrier: Weigh out 10% butyl carbitol, 33% butyl carbitol acetate, 70% diethylene glycol dibutyl ether, 10% tripropylene glycol monomethyl ether, and 10% tetrazol (by weight percentage) and mix them thoroughly to obtain a mixed solvent. Then weigh out 5% polyvinyl butyral and add it to the mixed solvent, followed by 5% polyamide wax thixotropic agent. Heat the mixture to 80°C while stirring until the resin is completely dissolved. Continue stirring for 60 minutes, then cool to room temperature to obtain the organic carrier.

[0099] The third step is to prepare the first conductive paste: 79.6% silver powder, 4.5% glass material, 1.2% inorganic additives and 14.7% organic carrier are premixed, then added to the organic carrier and stirred for 2 hours. The stirred raw materials are then rolled 6 times on a three-roll mill to further disperse and homogenize them. When the scraper fineness is less than 5μm, it is filtered with a 400-mesh filter cloth to obtain the first conductive paste.

[0100] The glass materials comprise: 33% of a first glass material, 33% of a second glass material, and 34% of a third glass material. Alternatively, the glass materials can be 50% of a first glass material and 50% of a second glass material. The first glass material comprises 40.9% PbO, 9.1% ZnO, 13.6% Bi₂O₃, 27.3% B₂O₃, and 9.1% SiO₂. The second glass material comprises 9.7% PbO, 4.9% BaO, 2.9% Bi₂O₃, 4.9% ZnO, 29.1% SiO₂, and 48.5% B₂O₃. The third glass material comprises 30% PbO, 5% ZnO, 5% Bi₂O₃, 5% TiO₂, 5% Al₂O₃, 20% B₂O₃, and 20% SiO₂.

[0101] The fourth step involves printing a 3.5μm to 4μm first conductive paste on the substrate, which is then sintered to form a 2μm first conductive layer.

[0102] Comparative Example 1

[0103] Comparative Example 1 of the present invention provides a conductive structure having a substrate and a conductive layer formed on the substrate. The thickness of the conductive layer is 2 μm. The conductive layer is prepared by the same method as the first conductive layer in Embodiment 1 of the present disclosure and does not contain the first glass material in the first conductive paste.

[0104] Comparative Example 2

[0105] Comparative Example 2 of the present invention provides a conductive structure having a substrate and a conductive layer formed on the substrate. The thickness of the conductive layer is 2 μm. The conductive layer is prepared by the same method as the first conductive layer in Embodiment 1 of the present invention, except that it does not contain the second glass material in the first conductive layer.

[0106] Comparative Example 3

[0107] Comparative Example 3 of the present invention provides a conductive structure having a substrate and a conductive layer formed on the substrate. The thickness of the conductive layer is 6 μm, and the preparation method of the conductive layer is consistent with that of the first conductive layer in Embodiment 1 of the present disclosure.

[0108] Comparative Example 4

[0109] Comparative Example 4 of the present invention provides a conductive structure, which is consistent with the preparation method of the composite conductive structure in Embodiment 1 of the present disclosure. However, the glass material of the first conductive layer is a single glass powder, which includes: 40.9% PbO, 9.1% ZnO, 13.6% Bi2O3, and 36.4% SiO2.

[0110] The conductive structures prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested in this disclosure. The test results are shown in the table below:

[0111] As can be seen from the table above, the composite conductive structures prepared in Examples 1 to 3 of this invention, by using silver powder and glass as a thinner first conductive layer and a base metal conductive material as a second conductive layer formed on the first conductive layer, have a significantly lower silver content compared to the 6μm conductive layer used in Comparative Example 3, thus saving costs. Furthermore, the data in the table above shows that the composite conductive structure of this invention, while reducing the silver content, improves contact performance and open-circuit voltage. It is expected that after adding the second conductive layer, the lateral resistance will be reduced to a level comparable to that of Comparative Example 3.

[0112] Based on this, the conductive structure of Comparative Example 1 does not contain the first glass material of this application, and the first conductive layer (silver paste) is also made to a thickness of 2μm. As can be seen from the data in the table above, compared with the composite conductive structures of Embodiments 1 to 3 of this disclosure, the contact resistance of Comparative Example 1 is significantly higher than that of the embodiments of this disclosure.

[0113] Furthermore, the conductive structure of Comparative Example 2 does not contain the second glass material of this application, and the first conductive layer (silver paste) is also made to a thickness of 2μm. As can be seen from the data in the table above, compared with the composite conductive structures of Embodiments 1 to 3 of this disclosure, the PL relative brightness of the embodiments of this disclosure is significantly higher than that of Comparative Example 2, and the corresponding open circuit voltage (VOC) is also higher.

[0114] The conductive structure of Comparative Example 4 uses a single glass powder. Even though its conductive structure is the same as that of the embodiments of this disclosure, the single glass powder cannot adjust the etching degree of the substrate, nor can it play a transition and synergistic role like the embodiments of this disclosure. The PL has a relatively low brightness, a poor corresponding Voc, and a high contact resistivity, and cannot maximize the photoelectric conversion efficiency of the battery.

[0115] As can be seen from the above, the glass materials in the first conductive layer of the composite conductive structure of this disclosure have a synergistic effect with each other. Therefore, a combination of various features is required to achieve the purpose of this disclosure.

[0116] The above description is merely a specific embodiment of the present invention. Obviously, various modifications and combinations can be made without departing from the spirit and scope of the present invention. Accordingly, this specification and accompanying drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the present invention. Clearly, those skilled in the art can make various alterations and modifications to the present invention without departing from its spirit and scope. Thus, if these modifications and variations of the present invention fall within the scope of the claims and their equivalents, the intent of the present invention includes these modifications and variations. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the claims.

[0117] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A composite conductive structure, characterized in that, include: Substrate; A first conductive layer is formed on the substrate, the thickness of the first conductive layer is 1μm to 2μm, and the material of the first conductive layer includes silver-based conductive material, glass material and inorganic additives; And a second conductive layer formed on the first conductive layer, wherein the conductive material of the second conductive layer includes a base metal conductive material.

2. The composite conductive structure according to claim 1, characterized in that, In the first conductive layer, the mass ratio of the silver-based conductive material, the glass material, and the inorganic additive is (70-85):(3-10):(0.1-2).

3. The composite conductive structure according to claim 2, characterized in that, In the first conductive layer, the particle size parameters D50 of the silver-based conductive material, the glass material, and the inorganic additive are all less than or equal to 1.5 μm, and D100 are all less than 3 μm.

4. The composite conductive structure according to claim 2, characterized in that, In the first conductive layer, the glass material includes a first glass material, a second glass material, and a third glass material. The glass transition temperature of the first glass material is less than or equal to 400°C, the glass transition temperature of the second glass material is greater than 400°C, and the glass transition temperature of the third glass material is 400°C to 450°C.

5. The composite conductive structure according to claim 4, characterized in that, The first glass material, the second glass material, and the third glass material all include SiO2, B2O3, Al2O3, PbO, ZnO, Bi2O3, alkali metal oxides, and alkaline earth metal oxides; In the first glass material, the ratio of the sum of the molar numbers of cations of PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the first glass material is greater than 40%; in the second glass material, the ratio of the sum of the molar numbers of cations of PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the second glass material is less than or equal to 20%; in the third glass material, the ratio of the sum of the molar numbers of cations of PbO, ZnO, Bi2O3, alkaline earth metal oxides, and alkali metal oxides to the total molar number of cations in the third glass material is less than or equal to 40%.

6. The composite conductive structure according to claim 2, characterized in that, The inorganic additives include at least one of alumina, silicon powder, silicon oxide, titanium oxide, boron oxide, silicon boride, and silicon nitride.

7. The composite conductive structure according to claim 1, characterized in that, The base metal conductive material includes at least one of copper-based conductive materials, aluminum-based conductive materials, nickel-based conductive materials, and zinc-based conductive materials.

8. A method for preparing a composite conductive structure according to claim 1, characterized in that, include: Provide a substrate; A first conductive layer is formed on the substrate using a first conductive paste, the thickness of the first conductive layer being 1μm to 2μm; A second conductive layer is formed on the first conductive layer using a second conductive paste, wherein the conductive material of the second conductive layer includes a base metal conductive material.

9. The method for preparing the composite conductive structure according to claim 8, characterized in that, Before forming the first conductive layer on the substrate using the first conductive paste, the method further includes: A first conductive paste is obtained by mixing silver-based conductive materials, glass materials, inorganic additives, and organic carriers.

10. A photovoltaic cell, characterized in that, The photovoltaic cell includes the composite conductive structure described in any one of claims 1 to 7.

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