Seed layer slurry for TOPCon battery and preparation method and application thereof

Abstract

The invention relates to seed layer slurry for a TOPCon battery and a preparation method of the seed layer slurry, and belongs to the technical field of photovoltaic cells, the slurry comprises conductive powder, glass powder, organic resin, a thixotropic agent, other auxiliaries and a solvent, the conductive powder is mainly composed of silver-coated nickel powder and silver powder, the total silver content of the slurry is 5%-65%, and the total silver content of the slurry is 5%-65%. The core-shell structure of the silver-coated nickel powder is designed through a theoretical formula, the silver coating compactness is ensured, and the combination of the powder particle size and the silver content is preferably selected. Slurry preparation comprises the steps of organic carrier preparation, premixing, grinding dispersion, viscosity adjustment and the like, the slurry is suitable for a seed layer in a TOPCon battery overprinting process, the silver consumption can be remarkably reduced, the cost is reduced, meanwhile, the electrical performance and stability of a battery are kept, and the good industrial application prospect is achieved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell technology, specifically to a method for preparing a seed layer slurry for use in the TOPCon (tunneling oxide passivated contact) cell overlay process (seed layer + conductive layer). Background Technology

[0002] With the continued growth of global demand for clean energy, solar cells, as a crucial component of renewable energy, are rapidly evolving towards higher efficiency and lower costs. Crystalline silicon (c-Si) solar cells have dominated the photovoltaic market for decades due to their mature manufacturing processes and lower costs. However, with continuous technological advancements, new high-efficiency solar cell technologies are gradually emerging, among which tunneling oxide passivated contact (TOPCon) cells have attracted significant attention as a mainstream technology following PERC. TOPCon cells significantly reduce recombination losses at the metal-silicon interface by introducing an ultrathin silicon oxide (SiOx) and heavily doped polycrystalline silicon (poly-Si) layer onto a silicon substrate. Thanks to its excellent surface passivation effect and carrier selectivity, it improves the overall efficiency of the cell. The application of this technology provides a new direction for the development of high-efficiency solar cells.

[0003] However, despite the significant performance advantages of TOPCon cells, the cost of the metallization process remains a significant challenge. With the continuous rise in silver prices, the cost of metallization using pure silver paste has gradually increased, becoming a bottleneck limiting its large-scale application. This is especially true after the introduction of LECO technology, which uses pure silver paste on both the front and back sides, resulting in persistently high costs. Therefore, reducing the cost of metallization has become a key challenge in the current development of solar cell technology.

[0004] Among numerous cost-reduction solutions, the method of using high-temperature sintered silver paste as a seed layer and overlaying it with base metals such as silver-clad copper and pure copper has become an effective way to improve efficiency and reduce costs by combining the advantages and disadvantages of high-temperature and low-temperature silver pastes. However, since the seed layer needs to be etched on the silicon nitride layer to achieve the conductivity of the nano-silver, the seed layer paste is usually pure silver paste.

[0005] Currently, patent 202411165529.9 discloses a scheme using a seed layer plus a silver-copper electrode, which has been successfully applied to TOPCon batteries. The silver-copper electrode features: a silver contact layer, disposed on a substrate, composed of silver microcrystalline particles; and a silver-coated copper layer, disposed on the silver contact layer and in contact with the substrate, composed of silver-coated copper particles and silver particles; wherein the copper component has a mass content greater than 30%. Specifically, the silver contact layer is pure silver, with the silver microcrystalline particles having a diameter of 5nm to 30nm; the silver-coated copper particles having a diameter of 1μm to 10μm; and the silver particles having a diameter of 30nm to 100nm. However, in practical applications, when pure silver is used as a seed layer to form contact with the battery cell, it is difficult to reduce the silver content to below 70%, and the processing cost of nano-silver powder is high, making it difficult to significantly reduce the overall cost. Patent 202411610057.3 also proposes a scheme of overprinting non-silver paste using a metal seed layer. The metal seed layer includes, but is not limited to, a silver seed layer, a nickel seed layer, a silver-coated copper seed layer, and a silver-coated nickel seed layer; the non-silver paste includes one or more of silver-coated copper paste, silver-coated aluminum paste, silver-coated nickel paste, and pure copper paste. However, this patent does not clearly describe the specific characteristics of the silver powder, nano-silver powder, silver-coated copper paste, silver-coated aluminum paste, and silver-coated nickel paste involved in the metallization process.

[0006] Silver, as an important industrial material, is widely used in the metallization layer of solar cells. Its excellent conductivity and stability significantly improve the electrical performance and long-term stability of the cells. However, the price of silver is highly volatile, influenced by market demand, supply chain fluctuations, and global economic and financial markets. This makes the cost of silver an increasingly significant challenge for the photovoltaic industry. Furthermore, the environmental burden of silver mining and refining further exacerbates the demand for sustainable alternative materials. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and propose an innovative technology that uses silver-coated nickel powder to replace pure silver powder, aiming to reduce the amount of silver used while maintaining the excellent performance of the seed layer.

[0008] This invention can effectively reduce the amount of silver used, reduce the impact of silver price fluctuations on metallization costs, and ensure the battery's performance in terms of electrical properties and long-term stability.

[0009] On the other hand, regarding the overprinting process of TOPCon batteries, the purpose of this invention is to provide a seed layer paste to replace pure silver seed layer paste, so as to further reduce the dependence on silver.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a seed layer slurry for TOPCon batteries, prepared from the following raw materials by weight percentage:

[0012] Conductive powder 65-85%,

[0013] Glass powder 2-6%,

[0014] Organic resin 0.1-16%,

[0015] Thixotropic agent 0-4%,

[0016] Other adjuvants 0-1%,

[0017] Solvent balance.

[0018] The conductive powder mainly consists of silver-coated nickel powder and silver powder. The silver content of the slurry is the sum of the silver content in the silver-coated nickel powder and the mass of the silver powder, divided by the total weight of the slurry.

[0019] Based on the published patent 202510149201.6, this invention continues the characterization methods for silver-coated nickel powder in the patent content, such as the resistivity and antioxidant resistivity of the powder, and the characterization of the density of silver coating by liquid phase titration; especially the detection method for characterizing the density of silver-coated nickel by liquid phase titration.

[0020] This invention addresses the three most important parameters of silver-coated nickel powder: the diameter of the nickel powder (…). ), thickness of the silver casing ( ) and silver content of silver-coated nickel powder The inherent correlation between them is presented through theoretical simulation calculations.

[0021] Formula 1 is as follows:

[0022]

[0023] in:

[0024] The effective diameter of the nickel core (usually the volume equivalent diameter, in μm).

[0025] Shape correction factor

[0026] : Coating uniformity correction coefficient, with 1 for perfect uniform coating;

[0027] The density of nickel is taken as 8.91 g / cm³. 3

[0028] The density of silver is taken as 10.49 g / cm³. 3

[0029] The mass fraction of silver in the composite particles (e.g., 10% corresponds to 10% silver content on the surface of the silver-coated nickel powder).

[0030] Silver shell thickness (unit: μm)

[0031] The silver-coated nickel powder used in this invention has the following core characteristics: it must be used to ensure that the nickel content in the liquid phase titration is ≤0.01mol / L.

[0032] Furthermore, the silver-coated nickel powder used is mainly divided into three categories, all of which are self-synthesized:

[0033] The characteristics of silver-coated nickel powder A are: D50 is 1-2μm; silver content is 10%-40%, with a minimum of 10%; and the thickness of the silver shell can be predicted to be between 20-163nm using formula 1.

[0034] The characteristics of silver-coated nickel powder are: D50 is 2-4μm; silver content is 5%-40%; and the silver shell thickness can be predicted to be between 30-322nm using formula 1.

[0035] The D50 of silver-coated nickel powder is 4-6μm; the silver content is 5%-40%, and the thickness of the silver shell can be tested as 29-484nm using Formula 1.

[0036] Furthermore, the silver-coated nickel powder used in this invention is composed of one or more combinations of the above-mentioned powders of types A, B, and C.

[0037] Furthermore, the silver-coated nickel powder undergoes surface modification treatment, specifically through the following steps:

[0038] The surface-modified silver-coated nickel powder is obtained by mixing surface modifier of 0.05% to 0.5% by weight of silver-coated nickel powder with the powder using a dry modification method.

[0039] Furthermore, the surface modifier is selected from one or more of terpineol, fatty acids, dodecylbenzenesulfonic acid, and silane coupling agents KH550 and KH560.

[0040] Furthermore, the particle size of the glass powder is 0.5-5 μm.

[0041] Furthermore, the glass powder is obtained from a mixture of raw materials through melting, cooling, and ball milling; the raw materials consist of the following components by weight percentage:

[0042] Lead oxide (PbO) 35.3%-46.31%,

[0043] Silicon oxide (SiO2) 5.38%-13.2%,

[0044] Lithium oxide (Li₂O) 2.64%-4.16%,

[0045] Zinc oxide (ZnO) 1.85%-3.5%,

[0046] Sodium oxide (Na₂O) 1.22%-1.76%,

[0047] Magnesium oxide (MgO) 0.43%-2.61%,

[0048] Calcium oxide (CaO) 0.35%-1.57%,

[0049] Tellurium oxide (TeO2) 0-30.53%,

[0050] Barium oxide (BaO) 0-21.72%,

[0051] Boron oxide (B₂O₃) 0-19.55%,

[0052] Tungsten oxide (WO3) 0-9.65%,

[0053] Copper oxide (CuO) 0-0.53%

[0054] The specific preparation steps of the glass powder are as follows: weigh the raw materials according to the proportion and mix them to obtain a homogeneous mixture; place the mixture at 1250-1300℃ for 1.5 hours to melt, and then quench to obtain glass fragments. The obtained glass fragments are preliminarily ground and sieved to obtain coarse glass powder.

[0055] The obtained coarse glass powder needs further refinement. The refinement process is as follows: Place the glass fragments in a 20L vertical ball mill, add 15kg of zirconia balls with a diameter of 5-10mm, along with 2kg of deionized water and an appropriate amount of oleic acid. Ball mill at 250r / min for 8 hours to obtain a glass slurry. Finally, sieve and dry the slurry to obtain glass powder with a particle size range of 2-5μm.

[0056] The organic resin is one or more of PVB resin, rosin resin, acrylic resin, phenoxy resin and ethyl cellulose, or a mixture thereof.

[0057] The thixotropic agent is one or a mixture of polyamide wax, hydrogenated castor oil, fumed silica, and polyethylene glycol.

[0058] The other additives are one or more of palmitic acid, silane coupling agent, dimethyl silicone oil, oleic acid, and TDO dispersant, or a mixture thereof.

[0059] The solvent is selected from one or more of diethylene glycol butyl ether acetate, tripropylene glycol butyl ether, dibutyl phthalate, terpineol, tributyl citrate, butyl carbitol, triethylene glycol butyl ether, and diethylene glycol butyl ether.

[0060] Secondly, this invention also provides a method for preparing a seed layer slurry, comprising the following steps:

[0061] (1) Preparation of organic carrier: Dissolve ethyl cellulose in a selected solvent and stir at 60-80℃ until completely dissolved and a transparent solution is formed to obtain a uniform organic carrier, which is then cooled for later use.

[0062] (2) Premixing: The silver-coated nickel powder, silver powder, glass powder and some organic carrier are initially mixed in a planetary mixer to ensure uniform distribution of raw materials.

[0063] (3) Grinding and dispersing: Transfer the premix to a three-roll mill or sand mill for thorough grinding and dispersion until the fineness of the slurry meets the requirements and there are no visible agglomerated particles.

[0064] (4) Viscosity adjustment: Add the remaining organic carrier and optional additives, stir evenly, and adjust the viscosity and thixotropic index of the slurry until the required rheological properties are achieved to obtain the final slurry.

[0065] Furthermore, the silver content of the seed layer slurry is 5%-65%, preferably 10-30%.

[0066] Thirdly, this application provides a method for applying the seed layer paste: using a solar photovoltaic screen printing machine, with a suitable screen, the front side is printed according to the existing process; the seed layer paste prepared in this invention is printed on the back side of the battery cell, and after high-temperature sintering to form contact, a conductive layer (silver-coated copper paste containing 20% ​​silver) is printed, cured at low temperature, and the efficiency is tested.

[0067] Compared with the prior art, the present invention has the following advantages:

[0068] The present invention utilizes an ultra-low silver seed layer slurry prepared with silver-coated nickel powder, which offers the following advantages in future topcon overprinting processes:

[0069] (1) Reduce costs: By using silver-plated nickel powder instead of pure silver powder, the amount of silver used is significantly reduced, production costs are reduced, and the uncertainty caused by silver price fluctuations is reduced.

[0070] (2) Maintain or improve performance: Silver-coated nickel powder can effectively maintain the conductivity and stability of the battery seed layer, ensuring that the battery performance is not affected, and even improving long-term stability.

[0071] (3) Enhance sustainability and reduce risks: Reduce the amount of silver used, reduce dependence on limited resources, promote the sustainable development of solar cell materials, and at the same time avoid the impact of silver price fluctuations on production costs and improve market competitiveness. Attached Figure Description

[0072] Figure 1 This is a scanning electron microscope (SEM) image of the cross-section of the slurry of the present invention, used to show its core-shell structure morphology.

[0073] Figure 2 This is a further enlarged image of a scanning electron microscope (SEM) photograph of the cross-section of the slurry of the present invention.

[0074] Figure 3 A bar chart comparing the conversion efficiency of TOPCon batteries prepared using the paste of this invention and a comparative pure silver paste.

[0075] Figure 4 This is a schematic diagram illustrating the application process of the low-silver seed layer slurry of the present invention in the TOPCon battery overprinting process. Detailed Implementation

[0076] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0077] Example 1: Synthesis and Characterization of Silver-Coated Nickel Powder A

[0078] Type A silver-coated nickel powder was synthesized using a chemical plating method. Spherical nickel powder with a D50 of 1.5 μm was pretreated and activated, then placed in a silver ammonia solution for reduction plating. By controlling the reaction time and silver salt concentration, powder with a target silver content of 15% was obtained.

[0079] Characterization results:

[0080] Particle size D50: 1.6 μm (laser particle size analyzer)

[0081] Silver content ( 14.8% (ICP-OES test)

[0082] Coating density: The nickel ion concentration measured by liquid titration was 0.005 mol / L, which meets the requirement of ≤0.01 mol / L.

[0083] Silver casing thickness estimation: Take =1.0 (spherical), =0.9 (titration results are good), substituting into Equation 1, we get ≈38nm. TEM observations show that the average silver shell thickness is approximately 35±5nm, which agrees well with the theoretical calculation.

[0084] Example 2: Formulation and preparation of low-silver seed layer slurry

[0085] Prepare the raw materials according to the following weight percentages:

[0086] Type A silver-coated nickel powder (prepared in Example 1): 70%

[0087] Glass powder (composition: PbO 40%, SiO2 10%, B2O3 20%, TeO2 15%, other oxides 15%, D50=3μm): 5%

[0088] Ethyl cellulose: 4%

[0089] Hydrogenated castor oil (thixotropic agent): 1%

[0090] Silane coupling agent KH560 (additive): 0.3%

[0091] Terpineol (solvent): Bring to 100%

[0092] Preparation steps:

[0093] (1) Dissolve ethyl cellulose in 60% terpineol, stir in a water bath at 75°C for 2 hours to obtain a transparent organic carrier, and then cool.

[0094] (2) Mix the silver-coated nickel powder, glass powder and 40% of the above organic carrier in a planetary mixer at 500 rpm for 30 minutes.

[0095] (3) Transfer the mixture to a three-roll mill, gradually reduce the gap between the rollers, and grind for 6 passes until the fineness detected by the scraper fineness gauge is ≤8μm.

[0096] (4) Add the remaining organic carrier, hydrogenated castor oil and KH560, and homogenize by stirring at 200 rpm for 1 hour in a planetary mixer. Then, degas the mixture under vacuum to obtain the final slurry S1.

[0097] Slurry S1 properties: viscosity (25℃) 35 Pa·s, thixotropic index 2.1, total silver content approximately 10.4% (70%*14.8%).

[0098] Example 3: Battery Application and Performance Testing

[0099] Application: Standard N-type TOPCon solar cells (size 182mm*182mm).

[0100] Application process:

[0101] Backside seed layer printing: The slurry S1 prepared in Example 2 was printed using a 350-mesh screen.

[0102] Sintering: carried out in a six-zone sintering furnace with a peak temperature of 800℃.

[0103] Backside conductive layer overprinting: Commercially available 20% silver content silver-coated copper paste is overprinted on the sintered seed layer.

[0104] Curing: Cur in an oven at 200℃ for 20 minutes.

[0105] Performance comparison:

[0106] Comparative Example D1: The seed layer used commercially available pure silver seed layer paste (silver content 82%), and all other steps were exactly the same.

[0107] Test results (average of 10 batteries each):

[0108]

[0109] Test results show that the core performance indicators (conversion efficiency and fill factor) of the battery prepared using the low-silver-content (10.4%) seed layer paste S1 of this invention are basically the same as those of the battery prepared using high-silver-content pure silver paste.

[0110] Example 4: Comparison of pastes with different silver contents

[0111] By changing the composition of the conductive powder, pastes with different total silver contents were prepared:

[0112] Slurry S2: Uses Class B silver-coated nickel powder (D50=3μm, =10%)80%, the remaining components are the same as in Example 2. The total silver content is calculated to be 8.0%.

[0113] Slurry S3: A blend of type A silver-coated nickel powder and micron-sized silver powder (60% silver-coated nickel powder, 10% silver powder), the rest is the same as in Example 2. The total silver content is calculated to be approximately 18.9%.

[0114] The battery was prepared and tested using the same process as in Example 3, and the results are as follows:

[0115]

[0116] Data shows that even with a silver content as low as 8%, the battery efficiency loss is minimal (<0.2%), and the contact resistance remains within an acceptable range. A silver content in the 10-20% range yields performance closest to that of pure silver.

[0117] Comparative Example 1 (non-dense coating)

[0118] A silver-coated nickel powder with a silver content of 10% but uneven coating was synthesized (nickel ion concentration determined by liquid phase titration to be 0.05 mol / L). A slurry with the same formulation was prepared using this powder and applied to a battery, but the average efficiency was only 24.65%, with large batch-to-batch variations. This indicates that simply controlling the silver content is insufficient; the structural compactness requirement implied in Equation 1 must also be met (through...). (and the titration method is reflected).

[0119] In summary, this invention, through theoretically guided powder design, successfully developed a low-silver-content, high-performance TOPCon battery seed layer slurry, achieving a balance between cost reduction and efficiency, and possessing significant industrial application value.

[0120] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A seed layer slurry for TOPCon batteries, characterized in that: It is made from the following raw materials by weight percentage: Conductive powder 65-85%; Glass powder 2-6%; Organic resin 0.1-16%; Thixotropic agent 0-4%; Other adjuvants: 0-1%; Solvent balance; The conductive powder mainly consists of silver-coated nickel powder and silver powder. The silver content of the slurry is the sum of the silver content in the silver-coated nickel powder and the mass of the silver powder, divided by the total weight of the slurry. The three most important parameters of the silver-coated nickel powder are the diameter of the nickel powder ( ), thickness of the silver casing ( ) and silver content of silver-coated nickel powder The inherent correlation is given by theoretical simulation calculation, as shown in Formula 1 below: (Equation 1) in: : The actual average thickness of the silver casing, in μm; : The effective diameter of the nickel core (usually the volume equivalent diameter, in μm); Shape correction factor; : Coating uniformity correction coefficient, with 1 for perfect uniform coating; The density of nickel is taken as 8.91 g / cm³. 3 ; The density of silver is taken as 10.49 g / cm³. 3 ; : The mass fraction of silver in the composite particles (for example, 10% corresponds to 10% silver content on the surface of the silver-coated nickel powder). : Thickness of silver casing (unit: μm); The glass powder has a particle size of 2-5 μm; The core characteristic of the silver-coated nickel powder is that it must be prepared under the condition that the nickel content in the liquid phase titration is ≤0.01mol / L.

2. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The D50 and silver content of the silver-coated nickel powder Satisfy at least one of the following combinations: D50 is 1-2μm. It is 12%-18%; D50 is 2-4μm. It is 8%-12%; D50 is 4-6μm. It is 4%-6%.

3. The seed layer slurry for TOPCon batteries according to claim 1 or 2, characterized in that: The silver-coated nickel powder undergoes surface modification treatment, specifically the following steps: The surface-modified nickel powder is obtained by mixing surface modifier of 0.05% to 0.5% by weight of silver-coated nickel powder with the powder using a dry modification method.

4. The seed layer slurry for TOPCon batteries according to claim 3, characterized in that: The surface modifier is selected from one or more of terpineol, fatty acids, dodecylbenzenesulfonic acid, and silane coupling agents KH550 and KH560.

5. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The glass powder is obtained by melting, cooling and ball milling a mixture of raw materials; the raw materials consist of the following components by weight percentage: composition: Lead oxide (PbO) 35.3%-46.31%; Silicon oxide (SiO2) 5.38%-13.2%; Lithium oxide (Li₂O) 2.64%-4.16%; Zinc oxide (ZnO) 1.85%-3.5%; Sodium oxide (Na₂O) 1.22%-1.76%; Magnesium oxide (MgO) 0.43%-2.61%; Calcium oxide (CaO) 0.35%-1.57%; Tellurium oxide (TeO2) 0-30.53%; Barium oxide (BaO) 0-21.72%; Boron oxide (B2O3) 0-19.55%; Tungsten oxide (WO3) 0-9.65%; Copper oxide (CuO) 0-0.53%; The specific preparation steps of the glass powder are as follows: weigh the raw materials according to the proportion and mix them to obtain a uniform mixture; place the mixture at 1250-1300℃ for 1.5 hours to melt, and then quench to obtain glass fragments; perform preliminary grinding and sieving on the obtained glass fragments to obtain coarse glass powder. The obtained coarse glass powder needs to be further refined. The refining process is as follows: place the glass fragments in a 20L vertical ball mill, add 15kg of zirconia balls with a diameter of 5~10mm, add 2kg of deionized water and an appropriate amount of oleic acid, and ball mill at a speed of 250r / min for 8 hours to obtain a glass slurry. Finally, sieve and dry the slurry to obtain glass powder with a particle size range of 2~5μm.

6. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The organic resin is one or more of PVB resin, rosin resin, acrylic resin, phenoxy resin and ethyl cellulose, or a mixture thereof.

7. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The thixotropic agent is one or a mixture of polyamide wax, hydrogenated castor oil, fumed silica, and polyethylene glycol.

8. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The other additives are one or more of palmitic acid, silane coupling agent, dimethyl silicone oil, oleic acid, and TDO dispersant, or a mixture thereof.

9. The seed layer slurry for TOPCon batteries according to claim 1, characterized in that: The solvent is selected from one or more of diethylene glycol butyl ether acetate, tripropylene glycol butyl ether, dibutyl phthalate, terpineol, tributyl citrate, butyl carbitol, triethylene glycol butyl ether, and diethylene glycol butyl ether.

10. A method for preparing a seed layer slurry for TOPCon batteries, characterized in that: Includes the following steps: (1) Preparation of organic carrier: Ethyl cellulose is dissolved in a selected solvent and stirred at 60-80℃ until it is completely dissolved and forms a transparent solution to obtain a uniform organic carrier, which is then cooled for later use. (2) Premixing: The silver-coated nickel powder, silver powder, glass powder and some organic carrier are premixed in a planetary mixer to ensure uniform distribution of raw materials; (3) Grinding and dispersing: Transfer the premix to a three-roll mill or sand mill for thorough grinding and dispersion until the fineness of the slurry meets the requirements and there are no visible agglomerated particles; (4) Viscosity adjustment: Add the remaining organic carrier and optional additives, stir evenly, and adjust the viscosity and thixotropic index of the slurry until the required rheological properties are achieved to obtain the final slurry; The silver content of the seed layer slurry is 5%-65%.

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