Conductive paste, crystalline silicon solar cell and preparation method of crystalline silicon solar cell

Abstract

The invention discloses conductive paste, a crystalline silicon solar cell and a preparation method of the crystalline silicon solar cell, and belongs to the technical field of photovoltaic cells. The conductive paste comprises glass powder which accounts for 1.5 wt%-6 wt% of total solids in the conductive paste; an organic carrier accounting for 9 wt% to 15 wt% of total solids in the conductive paste; a first conductive metal, which accounts for 70 wt% to 88 wt% of total solids in the conductive paste; a second conductive metal which accounts for 1 wt% to 10 wt% of the total solid content in the conductive paste; wherein the specific surface area of the second conductive metal is larger than 0.5 m < 2 > / g and smaller than 1.8 m < 2 > / g, and the second conductive metal is selected from nickel or nickel alloy. The nickel or the nickel alloy with the specific surface area is adopted to replace part of silver, the influence on the density of a sintered silver structure and the conductivity of a silver / nickel electrode can be reduced, the photoelectric conversion efficiency of the solar cell can be maintained by adding the nickel powder, and the preparation cost of the solar cell can be reduced by reducing the use amount of the silver.

Description

Technical Field

[0001] The present application belongs to the technical field of solar photovoltaic cells, and specifically relates to conductive paste, crystalline silicon solar cells and preparation methods thereof. Background Art

[0002] The back of TOPCon crystalline silicon solar cells is the N-side (N-poly side), and silver powder is usually used as the main conductive phase of the metallized conductive paste. However, the cost of silver accounts for a large proportion of the cost of amorphous silicon wafers in solar cells, so it is necessary to reduce the amount of silver used while maintaining a good solar cell photoelectric conversion efficiency. Using base metal powder to replace silver powder can reduce the silver content in the paste, thereby reducing the cost of the conductive paste, but the sintering or oxidation of the base metal powder will cause the conductivity of the electrode to be greatly reduced, which will lead to a loss in the photoelectric conversion efficiency of the cell. Summary of the invention

[0003] Purpose of the invention: The embodiments of the present application provide a conductive paste, a crystalline silicon solar cell and a method for preparing the same. By adding nickel powder with a specific specific surface area to the conductive paste to replace silver powder, the amount of silver used can be significantly reduced while maintaining the photoelectric conversion efficiency of the solar cell.

[0004] Technical solution: A conductive paste of the present application includes:

[0005] Glass powder, accounting for 1.5wt% to 6wt% of the total solids in the conductive paste;

[0006] An organic vehicle, which accounts for 9 wt % to 15 wt % of the total solids in the conductive paste;

[0007] A first conductive metal, which accounts for 70 wt % to 88 wt % of the total solids in the conductive paste;

[0008] A second conductive metal, which accounts for 1 wt % to 10 wt % of the total solids in the conductive paste;

[0009] Wherein, the specific surface area of ​​the second conductive metal is greater than 0.5 m 2 / g and less than 1.8m 2 / g, the second conductive metal is selected from nickel or nickel alloy.

[0010] In some embodiments, the specific surface area of ​​the second conductive metal is greater than or equal to 0.7 m 2 / g and less than or equal to 1.5m 2 / g.

[0011] In some embodiments, the second conductive metal is spherical or spherical in shape.

[0012] In some embodiments, the second conductive metal is nickel metal particles, and the surface of the second conductive metal is a smooth surface or a rough surface.

[0013] In some embodiments, the second conductive metal is a cluster structure formed by a plurality of nickel metal particles, and the surface of the second conductive metal is a rough surface.

[0014] In some embodiments, the D of the second conductive metal v 50 is 1~10μm, D v 50 is the particle size corresponding to when the cumulative volume percentage of the second conductive metal reaches 50%.

[0015] In some embodiments, the first conductive metal is selected from at least one of silver powder, silver alloy powder, silver oxide, and silver salt.

[0016] In some embodiments, based on the molar percentage of the glass frit powder, the glass powder includes 20 mol% to 40 mol% of PbO, 20 mol% to 45 mol% of TeO2, 5 mol% to 15 mol% of Bi2O3, 5 mol% to 15 mol% of Li2O, 2 mol% to 12 mol% of SiO2 and 3 mol% to 15 mol% of transition metal oxides, wherein the transition metal oxides are selected from a mixture of one or more of Ag2O, CuO, ZnO and WO3.

[0017] In some embodiments, the present application further provides a crystalline silicon solar cell, comprising:

[0018] a substrate having a first side receiving illumination and a second side facing away from illumination;

[0019] a first conductive electrode, the first conductive electrode being disposed on the second surface, the first conductive electrode penetrating the second surface and forming an electrical connection with the n+ polysilicon;

[0020] Wherein, the first conductive electrode is obtained by sintering the conductive slurry.

[0021] In some embodiments, the substrate comprises:

[0022] substrate;

[0023] A tunneling layer, located on one side of the substrate;

[0024] n + a polysilicon layer, located on a side of the tunneling layer away from the substrate;

[0025] The first passivation layer is located on the n + The polysilicon layer is away from one side of the tunnel layer, and the first passivation layer is away from the n+ The surface of the polysilicon layer is the second surface;

[0026] Wherein, a portion of the first conductive electrode penetrates the first passivation layer and is connected to the n + The polysilicon layer forms the electrical connections.

[0027] In some embodiments, the substrate comprises an n-type doped semiconductor substrate; and / or

[0028] The tunneling layer comprises an ultra-thin silicon dioxide layer; and / or

[0029] The + The polysilicon layer includes a phosphorus-doped polysilicon layer.

[0030] In some embodiments, the solar cell is a solar cell having a tunnel oxide layer passivation contact structure.

[0031] In some embodiments, the present application also provides a method for preparing a crystalline silicon solar cell, comprising providing a substrate, the substrate having a first surface for receiving light and a second surface facing away from the light;

[0032] Applying the conductive paste to at least a portion of the second surface;

[0033] Sintering the semiconductor substrate coated with the conductive paste, so that the conductive paste penetrates the second-side passivation layer during the sintering process to form a first conductive electrode electrically connected to the n+ polysilicon of the substrate;

[0034] After sintering, the substrate is laser scanned, and a reverse voltage is applied to the substrate to form an induced current in the first conductive electrode to obtain the crystalline silicon solar cell.

[0035] In some embodiments, the laser scanning time is 1 ms to 1000 ms.

[0036] Beneficial effect: Compared with the prior art, the conductive paste of the present application comprises: glass powder, accounting for 1.5wt% to 6wt% of the total solids in the conductive paste; organic carrier, accounting for 9wt% to 15wt% of the total solids in the conductive paste; a first conductive metal, accounting for 70wt% to 88wt% of the total solids in the conductive paste; a second conductive metal, accounting for 1wt% to 10wt% of the total solids in the conductive paste; wherein the specific surface area of ​​the second conductive metal is greater than 0.5m 2 / g and less than 1.8m 2 / g, the second conductive metal is selected from nickel or nickel alloy. In the conductive paste of the present application, by using a specific surface area greater than 0.5m 2 / g and less than 1.8m 2 / g range of nickel or nickel alloy to replace part of the silver conductive metal can reduce the impact on the sintered silver structure density and the conductivity of the silver / nickel electrode. The addition of part of the nickel powder can maintain the photoelectric conversion efficiency of the solar cell, and the reduction in the amount of silver can further reduce the preparation cost of the solar cell.

[0037] It can be understood that the crystalline silicon solar cell and the preparation method thereof provided in the embodiments of the present application may include all the technical features and beneficial effects of the above-mentioned conductive paste, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 A cross-sectional view of a crystalline silicon solar cell provided in an embodiment of the present application;

[0040] Figure 2 This is the SEM image of the silver conductive paste doped with nickel powder after sintering;

[0041] Figure 3 To illustrate the effect of nickel powder with different specific surface areas on bulk resistivity;

[0042] Reference numerals: 10 - substrate, 20 - first conductive electrode, 30 - second conductive electrode, 100 - first surface, 200 - second surface, 101 - substrate, 102 - tunneling layer, 103 - n + Polysilicon layer, 104 - first passivation layer, 105 - p-type doping layer, 106 - second passivation layer 106 . DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0044] In the description of the present application, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, "plurality" means two or more than two, and at least one means one, two or more than two, unless otherwise clearly and specifically defined.

[0045] The applicant has found that the N-side (N-poly side or the second side mentioned above) metallized conductive paste of a typical TOPCon solar cell uses silver powder as the main conductive phase. Silver is a stable precious metal that can be sintered into a dense structure with high conductivity after a high-temperature sintering process. However, the cost of silver accounts for a large proportion of the cost of amorphous silicon wafers in solar cells. Therefore, it is necessary to reduce the amount of silver used while maintaining a good photoelectric conversion efficiency of solar cells. Replacing silver powder with base metal powder can reduce the silver content in the paste, thereby reducing the cost of the conductive paste. However, base metals are easily oxidized during high-temperature rapid sintering in an oxygen-containing environment (such as air), so they need to be sintered in an oxygen-free environment. However, for crystalline silicon solar cells, such as TOPCon solar cells, the high-temperature sintering environment commonly used is oxygen-containing, and the temperature to which the conductive paste is subjected during the sintering process usually reaches 700-780C. In this oxygen-containing and high-temperature environment, base metal powders such as copper powder and nickel powder will oxidize, resulting in a significant reduction in the conductivity of the electrode, which in turn leads to a loss in the photoelectric conversion efficiency of the cell. Therefore, it is unclear how to replace silver powder with nickel powder in TOPCon metallization paste to achieve efficiency and cost-effectiveness.

[0046] For TOPCon metallization, the conductive silver paste needs to be properly sintered to form a continuous and dense structure to provide good conductivity. However, due to the high cost of silver, low-silver conductive paste is a new research direction. Replacing silver powder with base metal powder, such as nickel powder, can reduce the silver content in the paste, but after high-temperature sintering, a thin surface shell of nickel oxide will form on the surface of the nickel powder in the paste, such as Figure 2 As shown in (a). Since nickel oxide NiO is not conductive, the nickel powder added after sintering not only does not participate in the conductive function of the electrode, but will reduce the conductivity of the electrode. In addition, due to the obstruction of the thin NiO shell on the surface, nickel powder cannot form sintering or alloying with nickel powder or silver powder. Therefore, after sintering, the nickel powder will remain in the electrode in the form of discrete particles, such as Figure 2As shown in (b). In summary, adding nickel powder to the silver paste will cause the silver structure after sintering to be not dense enough and the conductivity of the electrode to deteriorate. The deterioration of the conductivity of the electrode will lead to higher series resistance, resulting in a loss of fill factor (FF) and photoelectric conversion efficiency (Eff). Therefore, in order to use nickel powder instead of silver powder to reduce the metallization cost of solar cells, it is necessary to select suitable nickel powder to minimize its impact on the sintering structure of silver powder, thereby avoiding a significant reduction in the conductivity of the nickel / silver electrode after sintering. The nickel powder is dispersed throughout the electrode by screen printing a conductive silver paste containing nickel powder. After high-temperature sintering, the nickel powder cannot form an alloy with silver due to the NiO shell on the surface of the nickel powder. The residual nickel powder can be imagined as a "void" in the silver electrode, similar to Figure 2 As shown in (c) in the figure. Therefore, nickel powder needs to reduce the void ratio of sintered silver as much as possible to ensure good conductivity. One of the more direct approaches is to add only a very small amount of nickel powder, but this method can only reduce the amount of metallized silver and the cost to a very limited extent.

[0047] Based on this, it is necessary to provide a conductive paste, a crystalline silicon solar cell and a preparation method thereof, which is a metallization paste for a solar cell structure containing N-poly polycrystalline silicon tunneling oxide passivation contact. By adding nickel powder with a specific specific surface area to the conductive paste to replace silver powder, the photoelectric conversion efficiency of the solar cell can be maintained while the amount of silver can be significantly reduced.

[0048] A conductive paste of the present application includes: glass powder, an organic carrier, a first conductive metal and a second conductive metal; the glass powder accounts for 1.5wt% to 6wt% of the total solids in the conductive paste; the organic carrier accounts for 9wt% to 15wt% of the total solids in the conductive paste; the first conductive metal accounts for 70wt% to 88wt% of the total solids in the conductive paste; the second conductive metal accounts for 1wt% to 10wt% of the total solids in the conductive paste; wherein the specific surface area of ​​the second conductive metal is greater than 0.5m 2 / g and less than 1.8m 2 / g, the second conductive metal is selected from nickel or nickel alloy.

[0049] It is understandable that the specific surface area (specific surface area or SSA) of the second conductive metal plays a key role in the conductivity of the sintered silver-nickel electrode. The specific surface area SSA is specifically expressed as the total surface area of ​​particles per unit mass. Taking nickel powder as an example, for the same amount of nickel powder, a lower SSA means that the total volume occupied by the nickel powder in a dispersion will also be smaller. Therefore, when low-SSA nickel powder is dispersed in a conductive silver paste, it will reduce its effect on the density of the sintered silver structure and on the conductivity of the silver / nickel electrode. Among them, when the specific surface area is greater than 0.5m 2 / g and less than 1.8m 2Nickel powder in the range of 1-10wt% can maintain the volume resistivity of the solar cell within the appropriate range of the all-silver electrode, which can maintain the photoelectric conversion efficiency of the solar cell while significantly reducing the amount of silver used.

[0050] In some embodiments, glass powder, the first conductive metal, and the second conductive metal are used as solid components in the conductive paste; the organic carrier is used as a dispersed phase in the conductive paste and a material that provides printing performance, including one or more components that can impart functional properties such as polymers, surfactants, thickeners, thixotropic agents, and adhesives, etc. The sum of the weight percentages of the components in the conductive paste is 100%.

[0051] In some embodiments, the specific surface area of ​​the second conductive metal is greater than or equal to 0.7 m 2 / g and less than or equal to 1.5m 2 / g. For example, the specific surface area of ​​the second conductive metal can be 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or any value or a range between any two values. By controlling the specific surface area of ​​the second conductive metal, the formation of nickel oxide can be reduced. The surface area of ​​nickel powder with a lower specific surface area is relatively small, and the surface area exposed to the air is also less, thereby reducing the possibility of oxidation reaction.

[0052] In some embodiments, the shape of the second conductive metal is spherical or quasi-spherical. Quasi-spherical can be understood as a shape similar to a sphere. The spherical or quasi-spherical shape can generally ensure that the second conductive metal has a reasonable specific surface area. The surface area of ​​spherical particles is smaller, which means that at the same addition amount, the total volume occupied by the spherical particles is less, reducing its impact on the compactness and conductivity of the electrode, so that a higher addition amount of the second metal can be achieved to reduce the amount of silver. In addition, the spherical or quasi-spherical shape is conducive to contact and bonding between particles to ensure that the conductive metal forms a more continuous and dense structure during the sintering process, which can provide a better electron conduction path, thereby improving the conductivity of the electrode.

[0053] In some embodiments, the second conductive metal is nickel metal particles, and the surface of the second conductive metal is a smooth surface or a rough surface. It is understood that when the second conductive metal is nickel metal particles, each particle is an independent entity, and the nickel powder of this monomer structure usually has a more suitable particle size and specific surface area to ensure that it can replace silver powder. In addition, the smooth surface can reduce the effect of the second conductive metal on the density of the sintered silver structure, and the rough surface can control the specific surface area to a certain extent, thereby further reducing the effect on the conductivity of the electrode.

[0054] In some embodiments, the second conductive metal is a cluster structure formed by a plurality of nickel metal particles, and the surface of the second conductive metal is a rough surface. It is understandable that the cluster structure makes the second conductive metal a multi-body structure, in which there is a certain binding force between each nickel metal particle, and the surface of the second conductive metal after bonding has a certain roughness, which can play a role in controlling the specific surface area, thereby reducing the impact on the conductivity of the electrode.

[0055] In some embodiments, the D of the second conductive metal v 50 is 1~10μm, D v 50 is the particle size corresponding to when the cumulative volume percentage of the second conductive metal reaches 50%. When the particle size meets the above range, the specific surface area of ​​the second conductive metal can be guaranteed to be within the particle range, so that the volume resistivity of the prepared solar cell can be maintained within a reasonable range.

[0056] In some embodiments, the D of the second conductive metal v 50 is any value among 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, or a range between any two values.

[0057] In some embodiments, the first conductive metal is selected from at least one of silver powder, silver alloy powder, silver oxide, and silver salt.

[0058] In some embodiments, the first conductive metal as a conductive source of the conductive paste can be metal powder commonly used in electrodes formed on circuit substrates such as semiconductor substrates without particular limitation. Exemplary first conductive metals include but are not limited to silver and its alloys and mixtures.

[0059] In some embodiments, the first conductive metal accounts for 70wt% to 88wt% of the total solids in the conductive paste; in other embodiments, the first conductive metal accounts for 72wt% to 86wt% of the total solids in the conductive paste, and can also be 74wt% to 84wt%; and can further be 76wt% to 82wt%. It is understood that the adjustment of the proportion of the first conductive metal in the conductive paste needs to ensure that the sum of the weight percentages of the components in the conductive paste is 100%. The first conductive metal is used to play a conductive role after forming a solar cell.

[0060] In some embodiments, the first conductive metal may be selected from metal powders, or may be a mixture of two or more such metals or alloys directly combined; the metal is provided by a metal oxide or salt, which decomposes to form a metal when exposed to firing heat. When the metal powder is silver powder, it should be understood to refer to elemental silver metal, silver alloys, silver oxides or silver salts, and mixtures thereof, and may further include silver powders derived from silver oxide (Ag2O or AgO) or silver salts such as AgCl, AgNO3, AgOOCCH3 (silver acetate), AgOOCF3 (silver trifluoroacetate), Ag3PO4 (silver orthophosphate), or mixtures thereof.

[0061] In some embodiments, the first conductive metal may be provided as finely dispersed particles having a morphology such as powder form, flake form, spherical form, rod form, granular form, nodular form, layered or coated form, other irregular forms, or mixtures thereof.

[0062] In some embodiments, the median particle size of the first conductive metal is in the range of 0.5 μm to 3.5 μm. v 50 refers to the 50% volume distribution size. The main function of silver powder is to form a high-density silver body after sintering to improve good conductivity. Spherical silver powder with a median particle size of 0.5μm to 3.5μm can also inhibit agglomeration and ensure uniform dispersion of silver powder.

[0063] In some embodiments, glass powder refers to a composition containing one or more types of anions and cations. Glass powder has the ability to flow when heated, and the glass powder can be crystalline or partially or completely glassy or amorphous. In some embodiments, glass refers to a particulate solid form.

[0064] In some embodiments, the glass powder of this embodiment can be understood as a composition having a glass component, and the mass percentage of the glass powder in the conductive paste composition is 1.5wt% to 6wt%; in some other embodiments, the mass percentage of the glass frit in the conductive paste composition is 2.0wt% to 5.5wt%, and can also be 2.5wt% to 5wt%; can further be 3.0wt% to 4.5wt%; can further be 3.5wt% to 4.0wt%. It can be understood that the adjustment of the proportion of the glass powder in the conductive paste composition needs to ensure that the sum of the weight percentages of the components in the conductive paste composition is 100%. The components of the glass powder directly affect its solubility, fluidity and etching properties, so the components of the glass powder need to be well balanced to achieve excellent composite properties.

[0065] In some embodiments, based on the molar percentage of the glass frit powder, the glass frit includes 20 mol% to 40 mol% of PbO, 20 mol% to 45 mol% of TeO2, 5 mol% to 15 mol% of Bi2O3, 5 mol% to 15 mol% of Li2O, 2 mol% to 12 mol% of SiO2, and 3 mol% to 15 mol% of transition metal oxides, wherein the transition metal oxides are selected from Ag2O, CuO, ZnO, and WO3. In the following description, unless otherwise specified, the "mol%" of the content of each component of the glass frit represents the molar percentage converted to oxide.

[0066] In some embodiments, in the glass powder, PbO contained is the main component controlling the corrosivity of the glass, which enables etching of the passivation layer. PbO is also an intermediate glass former that can be incorporated into the glass network, and the residual PbO will exist outside the glass skeleton as a glass modifier.

[0067] In some embodiments, TeO2 contained in the glass powder serves as a glass former and can increase the fluidity of the glass during molding.

[0068] In some embodiments, the preparation method of glass powder can be produced by the method conventionally used in the field of glass manufacturing. For example, the oxides corresponding to the composition ratio of the glass powder described in the embodiment are batched, mixed, added to a crucible (e.g., platinum or ceramic crucible) and heated to a peak temperature (e.g., 800°C to 1400°C) and kept for a period of time to melt the oxides therein together. The molten material can then be quenched in any suitable manner, including but not limited to passing it between counter-rotating stainless steel rollers to form a sheet 0.25 to 0.50 mm thick, by pouring it on a thick stainless steel plate, or by pouring it into water. The resulting glass material is then subjected to a commonly used grinding technique to form a powder with a particle size of 0.5 μm to 2 μm. Commonly used grinding techniques include airflow milling, ball milling, sand milling, or planetary milling.

[0069] In some embodiments, the organic vehicle accounts for 9 wt % to 15 wt % of the total solids in the conductive paste. In some other embodiments, the organic vehicle may account for 10 wt % to 14 wt %, or further may account for 11 wt % to 13 wt %.

[0070] In some embodiments, relative to the solids composed of the first conductive metal, the second conductive metal, and the glass powder, the organic vehicle is used as a liquid phase in the conductive paste to disperse the above solids to form a paste with a certain viscosity. The viscosity and rheology of the paste can not only make the above first conductive metal, the second conductive metal, and the glass powder dispersed therein for a long time and stably, but also make the conductive paste composition dispersed on the printing screen, and apply the desired pattern to the surface of the substrate by screen printing.

[0071] In some embodiments, the organic carrier may include a polymer and an organic solvent. The polymer may include cellulose, resin, esters, etc. Cellulose includes cellulose resins such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, propyl cellulose, nitrocellulose, or mixtures thereof. Resins include wood rosin, phenolic resins, acrylic resins, or mixtures thereof. Esters include polymethacrylates of lower alcohols, etc. The organic solvent may include terpineol, diethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, propylene glycol diacetate, alpha terpene, beta terpene, dibutyl phthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol, etc.

[0072] In some embodiments, the organic vehicle has a consistency and rheology that makes it suitable for printing methods, including but not limited to screen printing. The organic vehicle may also include other additives such as non-ionic surfactants, thixotropic agents, dispersants, rheological agents, etc. to adapt the organic medium to different needs.

[0073] In some embodiments, the preparation method of the conductive paste may include: preparing the paste components described in the embodiments, stirring and dispersing, and then grinding with a three-roll mill to a fineness of less than 10 μm, and then further filtering. The amount of glass frit and nickel powder added in some embodiments may be different. In these cases, silver powder is used to replace the amount, and the amount of other components such as the organic carrier remains unchanged. The adjustment of the ratio of glass frit, the first conductive metal, the second conductive metal, and the organic carrier needs to ensure that the sum of the mass percentages of each component in the conductive paste is 100%.

[0074] See also Figure 1 , a crystalline silicon solar cell is provided, comprising: a substrate 10, the substrate 10 having a first surface 100 for receiving light and a second surface 200 facing away from light; a first conductive electrode 20, the first conductive electrode 20 is arranged on the second surface 200, the first conductive electrode 20 penetrates the second surface 200 and is electrically connected to the substrate 10; wherein the first conductive electrode 20 is obtained by sintering the above-mentioned conductive paste. The solar cell is a solar cell (Tunnel Oxide Passivated Contacts) containing a tunnel oxide passivated contact structure, which uses the above-mentioned conductive paste during preparation. Among them, a solar cell containing a tunnel oxide passivated contact structure is called a TOPCon solar cell (Tunnel Oxide Passivated Contact Solar Cell). This solar cell uses a tunnel oxide layer as a charge transfer channel and a surface passivation layer to improve the efficiency and performance of the cell. The TOPCon solar cell structure has lower electron reflection and surface recombination, and has higher photoelectric conversion efficiency and lower electron defects.

[0075] It is understood that the first conductive electrode 20 can form an electrical connection with the substrate 10 with lower carrier recombination.

[0076] In some embodiments, see further Figure 1 The substrate 10 includes: a substrate 101; a tunneling layer 102, located on one side of the substrate 101; + The polysilicon layer 103 is located on the side of the tunnel layer 102 away from the substrate 101; the first passivation layer 104 is located on the n + The polysilicon layer 103 is away from one side of the tunneling layer 102, and the first passivation layer 104 is away from the n + The surface of the polysilicon layer 103 is the second surface 200; wherein a portion of the first conductive electrode 20 penetrates the first passivation layer 104 and is connected to the n + The polysilicon layer 103 forms an electrical connection.

[0077] In some embodiments, see further Figure 1, the substrate 10 further includes a p-type doping layer 105 and a second passivation layer 106; the p-type doping layer 105 is located on the side of the substrate 101 away from the tunneling layer 102, the second passivation layer 106 is located on the side of the p-type doping layer 105 away from the substrate 101, and the side of the second passivation layer 106 away from the p-type doping layer 105 is the first surface 100. The p-type doping layer 102 can be a p-type semiconductor, and the substrate 101 can be an n-type doped semiconductor substrate. In addition, in the TOPCon cell, the p-type doping layer 102 is also called a p-type emitter.

[0078] In some embodiments, see further Figure 1 The solar cell further includes: a second conductive electrode 30 , which penetrates the second passivation layer 106 and forms an electrical connection with the p-type doping layer 105 .

[0079] In some embodiments, see Figure 1 The first surface 100 is the front side of the solar cell, also called the light-exposed side, and is the working side of the solar cell; the second surface 200 is the back side of the solar cell, which usually does not directly receive light. The conductive paste of this embodiment is used to form a conductive electrode on the back side.

[0080] In some embodiments, the tunneling layer 102 and the n-type substrate 104 are formed by a tunneling oxide layer passivation contact method. + Polysilicon layer 103 .

[0081] In some embodiments, the substrate 101 includes an n-type doped semiconductor substrate; the tunneling layer 102 includes an ultra-thin silicon dioxide layer; + The polysilicon layer 103 includes a phosphorus-doped polysilicon layer.

[0082] In some embodiments, a method for preparing a crystalline silicon solar cell is provided, comprising:

[0083] 1) Provide a substrate 10, the substrate 10 has a first surface 100 for receiving light and a second surface 200 for facing away from light; the substrate 10 uses a commercially available semi-finished TOPCon solar cell or a blue film. The blue film is based on an n-type base silicon wafer with a TOPCon cell structure, that is, a tunnel oxide passivated back surface with an n-doped polysilicon layer, and the n-doped polysilicon is passivated by a dielectric layer. The front surface is based on a B diffused emitter, which is also passivated by a dielectric layer. The dielectric insulating layer usually includes SiN x 、SiN x O y , Al2O3 or a combination thereof;

[0084] 2) Apply the conductive paste provided in this embodiment to at least a portion of the second surface 200; specifically, apply the conductive paste in a patterned form to at least a portion of the surface of the second surface 200; the patterning method can be screen printing; it can be understood that the conductive paste involved in this embodiment is used as a fine grid for the back side (N side) of a solar cell containing a tunneling oxide layer passivation contact structure, and is processed by four screen printers corresponding to the back main grid (commercially available Solamet PVD2L), the back fine grid, the front main grid (commercially available Solamet PVD2L), and the front fine grid (commercially available Solamet PV3NL); the conductive paste of this embodiment is used for the back fine grid, and each printing is dried after each printing and then the next paste is printed;

[0085] 3) sintering the substrate 10 coated with the conductive paste, so that the conductive paste penetrates the second surface 200 during the sintering process to form a first conductive electrode 20 electrically connected to the substrate 10;

[0086] 4) After sintering, the substrate 10 provided with the conductive paste is laser scanned, and a reverse voltage is applied to form an induced current in the first conductive electrode 20 to obtain a crystalline silicon solar cell.

[0087] The serial numbers of the above steps are not to be construed as limiting the order of the steps.

[0088] In some embodiments, step 4) is a method of laser enhanced contact improvement optimization, which is a method of using laser to improve the electrical contact of the slurry during the manufacturing process of solar cells. The basic principle of laser enhanced contact improvement technology is to use a large number of carriers generated by laser, use bias to guide these carriers through the formed metallized contact points, and use the heat energy generated by the current to improve the contact effect and uniformity, which can improve the uniformity of electrical contact, reduce contact defects, and thus improve the efficiency and reliability of solar cells. In this technology, the amount of carrier injection can be controlled by parameters such as laser power and time to achieve better contact uniformity and improvement effect.

[0089] In some embodiments, the laser scanning time is 1 ms to 1000 ms. Using laser enhanced contact optimization technology to process the conductive structure can reduce contact resistance, which is more conducive to increasing open circuit voltage and improving efficiency.

[0090] In some embodiments, the reverse voltage should be less than the built-in breakdown voltage of the battery PN junction to avoid efficiency loss. The voltage corresponding to the critical breakdown of the PN junction is the breakdown voltage of the PN junction, which mainly depends on the doping concentration of the P and N regions.

[0091] In some embodiments, the reverse voltage is 5V to 25V. In some other embodiments, the reverse voltage is 10V to 20V.

[0092] The technical solution of the present application is further described below in conjunction with specific embodiments.

[0093] The contents of the components of the conductive pastes of Examples 1 to 12 and Comparative Examples 1 to 6 are shown in Table 1.

[0094] The specific surface area of ​​the second conductive metal used in Examples 1 to 6 is 0.7 m 2 / g nickel powder, spherical in shape, smooth in surface, D v 50 is 3.5 μm; the specific surface area of ​​the second conductive metal used in Examples 7 and 8 is 1.0 m 2 / g, spherical in shape, rough surface, D v 50 is 3 μm; the specific surface area of ​​the second conductive metal used in Examples 9 and 10 is 1.3 m 2 / g, spherical shape, D v 50 is 2 μm; the specific surface area of ​​the second conductive metal used in Example 11 and Example 12 is 1.5 m 2 / g,D v 50 is 1μm.

[0095] The specific surface area of ​​the second conductive metal used in Comparative Examples 1 and 2 is 1.8 m 2 / g of nickel powder; the specific surface area of ​​the second conductive metal used in Comparative Examples 3 and 4 is 3.6m 2 / g of nickel powder; the specific surface area of ​​the second conductive metal used in Comparative Example 5 is 0.7m 2 / g of nickel powder, but the added amount is 12wt%; Comparative Example 6 uses pure silver paste without adding any nickel powder.

[0096] It should be noted that all the examples and comparative examples use the same glass powder. When the amount of nickel powder added is greater than 3%, the content of the glass powder is adjusted accordingly to maintain the contact resistance. The organic carrier specifically includes: 1.5wt% ethyl cellulose, 1.5wt% polyvinyl alcohol butyral copolymer (PVB), 1.6wt% diethylene glycol butyl ether acetate, 0.3wt% silicone oil, 0.15wt% Duomeen TDO (non-ionic surfactant, which belongs to the amine oxide category), 0.15wt% Brij L4 (non-ionic surfactant, which belongs to the polyoxyethylene alcohol category), 0.4wt% Thixotrolplus (rheological agent), 2.8wt% ester alcohol (Ethoxylated Alcohol C12), 0.6wt% dibasic acid ester, and the rest is solvent. The specific configuration process of the conductive paste is: the above components are mixed, stirred and dispersed, and then grinded with a three-roll mill to a fineness of less than 10um, and then further filtered to obtain.

[0097] Table 1

[0098]

[0099] The conductive pastes of different embodiments and comparative examples in Table 1 are used to prepare crystalline silicon solar cells. When preparing solar cells, the composition of the conductive paste can be adjusted accordingly to obtain the appropriate performance required. The preparation of the solar cell is as follows: first prepare the blue film of the TOPCon cell, and pass it through four screen printers corresponding to the back main grid, the back fine grid, the front main grid, and the front fine grid respectively; apply the conductive paste composition to the back fine grid; sinter the blue film and the conductive paste, so that the conductive paste composition etches the passivation layer during the sintering process to obtain a conductive structure formed on the N side of the blue film; perform laser enhanced contact optimization on the cell to prepare a solar cell. In the metallization process, screen printing uses a 4-pass printer. High-temperature sintering uses a commercially available Maxwell sintering furnace with 18 furnace temperatures; laser contact enhancement technology is a post-processing to enhance the contact of the sintered cell.

[0100] Volume resistivity evaluation method: Use screen printing (the pattern is 700μm wide × 17.5cm) to make a line pattern, and then sinter it at high temperature. After sintering, use a step meter to measure the actual line width (W) and line height (H), and use a Keithley multimeter to test the line resistance (R). Then use ρ = R * Area / Length to calculate the volume resistivity ρ, where Area is W * H, which represents the product of line width and line height, and Length is 700μm. Then use all-silver as BSL to calculate the relative resistance of different samples.

[0101] Solar cell performance evaluation: Use a commercially available IV tester to test the photoelectric conversion efficiency of the cell. Test items include efficiency (Eff), open circuit voltage (Voc), fill factor (FF), current (Isc) and series resistance (ΔRs). The contact resistance Rc test is to first use a laser to cut the cell into 1 cm wide strips perpendicular to the grid line direction, and then use the commercially available PV-ToolsTLM equipment to test.

[0102] The specific results of the above tests are shown in Tables 2 and 3.

[0103] Table 2

[0104]

[0105]

[0106] Figure 3 The effect of different specific surface area nickel powders used in different embodiments and comparative examples on the volume resistivity is shown in Table 2. Figure 3 It can be seen that as the specific surface area SSA of nickel powder increases, the effect of nickel powder on bulk resistance becomes more obvious. In addition, the higher the specific surface area SSA, the more significant the effect of nickel powder addition on resistance. At the same time, it can be seen that nickel powder with low specific surface area SSA can maintain good bulk resistance at a higher addition amount.

[0107] Table 3

[0108] Example ΔIsc(mA) ΔVoc(mV) ΔFF(%) ΔEff(%) ΔRs Rc(ohms) Example 1 1.7 0.1 0.13 0.05 -9.1E-05 0.77 Example 2 9.7 1.0 0.27 0.13 -3.3E-05 0.71 Example 3 16.8 0.8 0.21 0.12 6.9E-05 0.69 Example 4 16.0 0.6 0.25 0.13 1.8E-05 0.79 Example 5 8.3 0.1 0.11 0.05 -3.1E-05 0.75 Example 6 13.4 0.6 0.03 0.05 7.0E-05 0.85 Example 7 4.5 0.5 0.07 0.05 -9.6E-05 0.62 Example 8 7.0 0.8 -0.09 0.01 5.7E-05 1.10 Example 9 16.2 0.2 -0.04 0.03 1.8E-06 0.95 Example 10 26.7 0.7 -0.28 -0.01 2.2E-04 1.30 Embodiment 11 24.9 1.2 -0.22 0.02 1.7E-04 1.10 Example 12 19.6 0.7 -0.30 -0.03 2.8E-04 1.50 Comparative Example 1 16.5 0.5 -0.45 -0.09 3.2E-04 1.80 Comparative Example 2 22.9 -0.5 -0.90 -0.25 4.9E-04 3.60 Comparative Example 3 28.7 0.1 -0.76 -0.18 5.3E-04 2.00 Comparative Example 4 14.8 -3.2 -2.06 -0.71 9.9E-04 4.80 Comparative Example 5 0.9 0.3 -0.32 -0.09 1.1E-04 1.20 Comparative Example 6 \ \ \ \ \ 0.77

[0109] Table 3 shows the IV test data of TOPCon solar cells prepared in the examples and comparative examples corresponding to Table 2. The IV data is compared with the comparative example 6 (pure silver paste is BSL) as the benchmark, and then characterized by the difference between it and the comparative example 6. From Table 3, it can be seen that when the specific surface area SSA is greater than or equal to 0.7 m 2 / g and less than or equal to 1.5m 2 / g range of nickel powder can maintain a relatively small difference in series resistance ΔRs when partially replacing silver powder, and thus can achieve equal (within -0.03%) or better photoelectric conversion efficiency. It can be further seen from Data Table 3 that for nickel powder with low specific surface area, its effect on resistance is smaller, and excellent performance can be achieved when 10wt% of silver powder is replaced (Example 6). However, too high an addition amount will still lead to an increase in series resistance ΔRs due to the influence of electrode conductivity (Comparative Example 5).

[0110] In addition, it can be found from Table 3 that as the specific surface area SSA of nickel powder increases (e.g. 1.0 m 2 / g increased to 1.5m 2 / g), its effect on the series resistance ΔRs is more significant, and the amount that can be added is relatively small. 2 / g, 3wt% nickel powder addition has no obvious negative impact on electrical properties. However, it can be found from Comparative Examples 1 to Comparative Examples 4 that nickel powder with too large specific surface area SSA can cause significant efficiency loss at 1wt% addition.

[0111] In addition, the specific surface area SSA of nickel powder also has a significant effect on the contact resistance Rc. At the same amount of nickel powder added, the increase in the specific surface area of ​​nickel powder will also cause Rc to become worse, further affecting the final series resistance. Nickel powder with a small specific surface area can still maintain a relatively good contact resistance Rc (less than or equal to 1.5) at an addition amount of 12wt%.

[0112] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0113] The conductive paste, crystalline silicon solar cell and preparation method thereof provided in the embodiments of the present application are introduced in detail above, and the principles and implementation methods of the present application are explained by using specific examples. The description of the above embodiments is only used to help understand the technical solution and core idea of ​​the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A conductive paste, characterized in that: include: Glass powder, accounting for 1.5wt% to 6wt% of the total solids in the conductive paste; An organic vehicle, which accounts for 9 wt % to 15 wt % of the total solids in the conductive paste; A first conductive metal, which accounts for 70 wt % to 88 wt % of the total solids in the conductive paste; A second conductive metal, which accounts for 1 wt % to 10 wt % of the total solids in the conductive paste; Wherein, the specific surface area of ​​the second conductive metal is greater than 0.5 m 2 / g and less than 1.8m 2 / g, the second conductive metal is selected from nickel or nickel alloy.

2. The conductive paste according to claim 1, characterized in that: The specific surface area of ​​the second conductive metal is greater than or equal to 0.7 m 2 / g and less than or equal to 1.5m 2 / g.

3. The conductive paste according to claim 1, characterized in that: The second conductive metal is in a spherical or quasi-spherical shape.

4. The conductive paste according to claim 3, characterized in that: The second conductive metal is nickel metal particles, and the surface of the second conductive metal is a smooth surface or a rough surface.

5. The conductive paste according to claim 3, characterized in that: The second conductive metal is a cluster structure formed by a plurality of nickel metal particles, and the surface of the second conductive metal is a rough surface.

6. The conductive paste according to claim 3, characterized in that: The second conductive metal D v 50 is 1~10μm, D v 50 is the particle size corresponding to when the cumulative volume percentage of the second conductive metal reaches 50%.

7. The conductive paste according to claim 1, characterized in that: The first conductive metal is selected from at least one of silver powder, silver alloy powder, silver oxide and silver salt.

8. The conductive paste according to claim 1, characterized in that: Based on the molar percentage of the glass frit powder, the glass powder includes 20 mol% to 40 mol% of PbO, 20 mol% to 45 mol% of TeO2, 5 mol% to 15 mol% of Bi2O3, 5 mol% to 15 mol% of Li2O, 2 mol% to 12 mol% of SiO2 and 3 mol% to 15 mol% of transition metal oxides, wherein the transition metal oxides are selected from a mixture of one or more of Ag2O, CuO, ZnO and WO3.

9. A crystalline silicon solar cell, characterized in that: include: a substrate having a first side receiving illumination and a second side facing away from illumination; A first conductive electrode, the first conductive electrode is disposed on the second surface, the first conductive electrode penetrates the second surface and is electrically connected to the substrate; Wherein, the first conductive electrode is obtained by sintering the conductive paste described in any one of claims 1-8.

10. A crystalline silicon solar cell according to claim 9, characterized in that: The substrate comprises: substrate; A tunneling layer, located on one side of the substrate; n + A polysilicon layer, located on a side of the tunneling layer away from the substrate; The first passivation layer is located on the n + The polysilicon layer is away from one side of the tunnel layer, and the first passivation layer is away from the n + The surface of the polysilicon layer is the second surface; Wherein, a portion of the first conductive electrode penetrates the first passivation layer and is connected to the n + The polysilicon layer forms the electrical connections.

11. A crystalline silicon solar cell according to claim 10, characterized in that: The substrate comprises an n-type doped semiconductor substrate; and / or The tunneling layer comprises an ultra-thin silicon dioxide layer; and / or The + The polysilicon layer includes a phosphorus-doped polysilicon layer.

12. The crystalline silicon solar cell according to claim 9, characterized in that: The solar cell is a solar cell having a tunneling oxide layer passivation contact structure.

13. A method for preparing a crystalline silicon solar cell, characterized in that: include Providing a substrate having a first side receiving illumination and a second side facing away from illumination; Applying the conductive paste according to any one of claims 1 to 8 to at least a portion of the second surface; Sintering the substrate coated with the conductive paste, so that the conductive paste partially penetrates the second surface during the sintering process to form a first conductive electrode electrically connected to the substrate; After sintering, the substrate is laser scanned, and a reverse voltage is applied to the substrate to form an induced current in the first conductive electrode to obtain the crystalline silicon solar cell.

14. The method for preparing a solar cell according to claim 13, characterized in that: The laser scanning time is 1 ms to 1000 ms.

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