Silver-aluminum paste for N-TOPCon solar cells, preparation method, and application thereof

Abstract

The present invention provides a silver-aluminum paste for N-TOPCon solar cells, a preparation method thereof, and an application thereof, and relates to the technical field of solar cell metallization. Specifically, the silver-aluminum paste comprises silver powder, aluminum powder, a first additive, a second additive, and a solvent, wherein the aluminum powder is a tin oxide-coated powdered material; the preparation method is simple, efficient, and easy to reproduce. The present invention uses aluminum powder with a special structure to replace traditional aluminum powder or high-oxygen aluminum powder. In the process of forming a nano-tin oxide covering layer on the surface of the aluminum powder, the thickness of the surface aluminum oxide film layer will not increase. At the same time, it can promote the mutual dissolution of aluminum and silver, slow down the penetration of aluminum in the p+ silicon layer, reduce contact resistance and slow down the aluminum-silicon eutectic, and improve the electrical performance of solar cells. It has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a silver-aluminum paste for N-TOPCon solar cells, a preparation method thereof, and applications thereof. Background Art

[0002] The photovoltaic industry is a key driver of energy transformation. Cost reduction and efficiency improvement are fundamental to achieving grid parity for photovoltaic power generation in my country, and the research and development of photovoltaic cells is a crucial component of the industry. As market demands for crystalline silicon solar cell efficiency continue to rise, N-type silicon solar cells, with their advantages such as longer carrier diffusion lengths and minority carrier lifetimes, are gradually replacing the market share of traditional P-type silicon solar cells. N-type solar cells are primarily categorized by their process technology into interdigitated back contact (IBC) solar cells, heterojunction (HIT) solar cells, fully passivated emitter rear localized diffusion (PREL) solar cells, fully back field diffused emitter passivated (PERT) solar cells, and tunneling oxide passivated contact (TOPCon) solar cells. Among them, heterojunction and tunnel oxide passivated contact solar cells are both representative processes in N-type silicon solar cells, and the technology is currently developing rapidly; and tunnel oxide passivated contact (TOPCon, Tunnel Oxide Passivated Contact) has lower costs than heterojunction and better inheritance than traditional P-type PERC process, and is growing rapidly in the market.

[0003] Like solar cells produced using the PERC process, metallization technology is key to reducing costs and increasing efficiency for tunneling oxide passivation contact solar cells. The metallization process not only affects the photovoltaic conversion efficiency of the cell, but also its service life. The metallization raw material slurry plays a crucial role in the metallization process. For the front emitter of an N-type TOPCon solar cell, the contact resistance between the boron-diffused p+ region and silver is very large, requiring a small amount of aluminum to improve the contact. However, during the sintering process, aluminum powder is more active than silver powder, and it is easy for the aluminum-silicon eutectic to form an aluminum wedge effect and aluminum-silicon voids, resulting in a sharp drop in open-circuit voltage and affecting the cell's electrical performance.

[0004] The traditional approach to addressing this problem involves using high-oxygen aluminum powder (Al-Al2O3), creating a thick aluminum oxide film on the surface to suppress the aluminum-silicon eutectic. However, the compactness of the surface aluminum oxide inevitably affects the contact resistance after sintering, necessitating a compromise in oxygen content, but this ultimately fails to resolve this conflict. Therefore, a new silver-aluminum paste is needed to address the impact of aluminum on electrical properties.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first object of the present invention is to provide a silver-aluminum paste for N-TOPCon solar cells. In order to achieve the above object of the present invention, the following technical solutions are adopted:

[0007] A silver-aluminum paste for N-TOPCon solar cells, the silver-aluminum paste comprising the following components: silver powder, aluminum powder, a first additive, a second additive, and a solvent;

[0008] Wherein, the aluminum powder is a tin oxide coated powder material.

[0009] Preferably, the silver-aluminum paste is prepared by comprising the following components in parts by mass: 75-100 parts of silver powder, 0.5-5 parts of aluminum powder, 0.2-8 parts of a first additive, 0.5-8 parts of a second additive, and 1-7 parts of a solvent;

[0010] More preferably, the silver-aluminum paste is prepared by comprising the following components by mass: 87-90 parts of silver powder, 1-3 parts of aluminum powder, 1-4 parts of a first additive, 2.5-5.5 parts of a second additive, and 3-5 parts of a solvent;

[0011] As an optional embodiment, the mass fractions of the components include but are not limited to the following values: silver powder 75, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100; aluminum powder 0.5, 1, 2, 3, 4, 5; first additive 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8; second additive 0.5, 1, 2, 3, 4, 5, 6, 7, 8; solvent 1, 2, 3, 4, 5, 6, 7;

[0012] Further preferably, the silver-aluminum paste is prepared from the following components by mass percentage: 87% to 90% silver powder, 1% to 3% aluminum powder, 1% to 4% first additive, 2.5% to 5.5% second additive, and 3% to 5% solvent; wherein the total of the mass percentages is maintained as 100%;

[0013] As an optional embodiment, the raw materials for preparing the silver-aluminum paste only contain the above components, and the mass percentages of the components include but are not limited to the following values: silver powder 87%, 88%, 89%, 90%; aluminum powder 1%, 1.5%, 2%, 2.5%, 3%; first additive 1%, 2%, 3%, 4%; second additive 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%; solvent 3%, 3.5%, 4%, 4.5%, 5%;

[0014] In the present invention, by rationally proportioning the weight ranges of the components, the slurry or solar cell is made to have sintering performance, conductive performance and printing performance.

[0015] Preferably, the particle size of the aluminum powder is 3 μm to 10 μm;

[0016] As an optional embodiment, the particle size of the aluminum powder includes but is not limited to the following parameters or any value within the range of the following parameters: 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm.

[0017] Preferably, the particle size of the tin oxide is 20 nm to 100 nm;

[0018] As an optional embodiment, the particle size of the tin oxide includes but is not limited to the following parameters or any value within the range of the following parameters: 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm;

[0019] Preferably, in the aluminum powder, the molar ratio of aluminum to tin is 1:1 to 1:3;

[0020] As an optional embodiment, the molar ratio of aluminum to tin includes but is not limited to the following parameters or any value within the range of the following parameters: 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3;

[0021] In the present invention, a specific tin oxide-coated aluminum powder is used to replace traditional high-oxygen aluminum powder. Nano-sized tin oxide is evenly distributed on the surface of the aluminum precursor as a covering layer, thereby reducing the rate of aluminum oxidation to form an aluminum oxide film during the subsequent high-temperature metallization process. At the same time, even if partial aluminum oxidation occurs, the tin oxide coating layer will also play a role in limiting the thickness of the aluminum oxide film, thereby preventing the formation of aluminum wedge effect or aluminum-silicon voids in the aluminum-silicon eutectic, thereby avoiding the loss of electrical performance caused by aluminum doping.

[0022] In addition, compared with conventional aluminum powder, the aluminum powder coated with the tin oxide layer has better mutual solubility with silver powder, and the micron-level particle size slows down the penetration of aluminum into the p+ silicon layer, which can also reduce contact resistance and avoid aluminum-silicon eutectic, significantly improving electrical properties such as Voc.

[0023] Preferably, the silver powder adopts micron-graded, nano-graded or a mixture of the two; specifically, the particle size of the silver powder is 2 μm to 8 μm, and / or the particle size of the silver powder is 10 nm to 100 nm;

[0024] As a preferred embodiment, the particle size of the silver powder includes but is not limited to the following parameters or any value within the range formed by the following parameters: 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm; or, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm.

[0025] Preferably, the first additive includes elemental B and B2O3; in the present invention, the first additive is an inorganic binder, and boron glass powder can be optionally used;

[0026] More preferably, the first additive further comprises at least one of PbO, V2O5, and Bi2O3;

[0027] More preferably, the first additive further comprises at least one of ZnO, TeO2, WO3, Sb2O3, BaO, CaO, AgO, Tl2O3, and SiO2;

[0028] Preferably, the particle size of the first additive is 1 μm to 3 μm;

[0029] As an optional embodiment, the particle size of the first additive includes but is not limited to the following parameters or any value within the range of the following parameters: 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm;

[0030] In the present invention, by doping other metal oxides into the first additive, the conductive paste begins to melt at a relatively low temperature (about 200°C to 300°C). The first additive quickly forms a colloid with the silver powder and the glass phase during the melting process, forming a wettability coating on the silver powder, reducing the melting temperature and contact potential energy, and achieving rapid metallization under low temperature conditions.

[0031] Preferably, the second additive includes an adhesive; more preferably, the second additive also includes at least one of a thixotropic agent, a dispersant, and a wetting agent; the second additive may be only an adhesive, or a combination of the adhesive and the wetting agent, or a combination of the adhesive, the thixotropic agent, and the wetting agent, or a combination of the adhesive, the thixotropic agent, the dispersant, and the wetting agent, etc.;

[0032] More preferably, the adhesive comprises at least one of ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, phenoxy resin, PVB resin, and acrylic resin. In the present invention, the adhesive not only guides the silver-aluminum paste to adhere to the silicon layer, but also assists in dissolving the silver powder and aluminum powder, and reduces the sintering temperature.

[0033] More preferably, the thixotropic agent includes at least one of fumed silica, polyamide wax, and polyamide-modified hydrogenated castor oil; the thixotropic agent can better improve the fluidity of the adhesive, form a liquid phase during the sintering process, promote the coating of the phase body and efficient heat conduction, and further accelerate the rapid realization of metallization;

[0034] More preferably, the dispersant includes one of acrylic acid-based dispersants; the dispersant can prevent the powders from agglomerating; the smaller the powder, the easier it is to melt; otherwise, the powder is likely to agglomerate, which reduces the melting speed;

[0035] More preferably, the wetting agent includes dimethyl silicone oil; the wetting agent forms contact with each powder and plays a role of surface transition, accelerating the dispersion of the powder by the solvent component, and the wetting agent can also accelerate heat transfer.

[0036] Preferably, the solvent includes at least one of alcohol ester dodecanedioate, ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol dibutyl ether, dimethyl adipate, glycerol triacetate and dimethyl phthalate.

[0037] The second object of the present invention is to provide a method for preparing the silver-aluminum paste for N-TOPCon solar cells, comprising the following steps:

[0038] The silver powder, aluminum powder, the first additive, the second additive and the solvent are fully mixed and homogenized and dispersed until the fineness of the mixture is less than 10 μm to obtain the silver-aluminum paste;

[0039] Preferably, the method for preparing the aluminum powder comprises the following steps: synthesizing a micron-sized aluminum powder precursor by a vapor phase method, adding the aluminum powder precursor to a dispersion containing tin ions, impregnating and filtering, and drying the filtered solid to obtain the aluminum powder. However, it should be noted that the present invention only provides a feasible method for preparing tin oxide-coated aluminum powder as described above, and does not mean that tin oxide-coated aluminum powder can only be prepared by the above method.

[0040] More preferably, the gas phase method includes one of physical vapor deposition (PVD), chemical vapor deposition (CVD), and vacuum evaporation on silicon (VEROS);

[0041] More preferably, the dispersion containing tin ions comprises a solution of any soluble tin salt, further preferably a tin chloride solution;

[0042] Preferably, the mixing comprises the following steps: pre-mixing the first additive, the second additive and the solvent, and then adding the silver powder and the aluminum powder and mixing them thoroughly.

[0043] Preferably, the mixing is performed by a sizing machine; the dispersion is performed by a three-roller machine, and when the scraper fineness of the three-roller machine is less than 10 μm, the operation is stopped and the silver-aluminum paste is obtained.

[0044] The third object of the present invention is to provide a use of the silver-aluminum paste for N-TOPCon solar cells in solar cells.

[0045] The silver-aluminum paste of the present invention is compounded with the various hierarchical structures of the N-TOPCon solar cell and then metallized. The sintered silver-aluminum paste constitutes the emitter (electrode) of the solar cell. For a bifacial cell structure, the silver-aluminum paste of the present invention can be used on both the front and back surfaces to improve the photoelectric conversion efficiency, or it can be used only on the front or back surface to achieve the effect of reducing costs. When used on both the front and back surfaces, the pastes used on the front and back surfaces can be different, such as using a paste with a high silver powder ratio on the front and a paste with a low silver powder ratio on the back.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] In the present invention, a special tin oxide-coated aluminum material is used to replace traditional aluminum powder or high-oxygen content aluminum powder, thereby solving the technical problems in the prior art that aluminum powder is prone to produce aluminum-silicon eutectic, or that the dense oxide film on the surface of high-oxygen content aluminum powder will increase the contact resistance after metallization; the present invention also provides a preparation method of tin oxide-coated aluminum powder, which is simple and easy to implement and can be easily mass-produced. DETAILED DESCRIPTION

[0048] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0049] Example 1

[0050] (1) Preparation of aluminum powder: Grind and mix electronic grade pure boron, PbO, and SiO2 in a mass ratio of 1:1:1, so that the particle size of the monomer phase is less than 100 nm and the powder particle size is about 3 μm to 5 μm.

[0051] (2) Preparation of silver-aluminum paste: The components calculated by mass percentage are as follows: silver powder 80%, aluminum powder 1%, first additive (Te-Bi-B-Pb-Zn glass powder system) 3%, hydroxyethyl cellulose resin 5%, fumed silica 3%, solvent (ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate) 8%;

[0052] Hydroxyethyl cellulose resin, fumed silica, and the first additive were added to a homogenizer for premixing, and stirring was started for 15 minutes at a frequency of 120 r / min. The aluminum powder and silver powder prepared in step (1) were then added and stirred for 15 minutes at a frequency of 120 r / min. The materials were then transferred to a three-roll mill for dispersion until the scraper fineness reached 10 μm, and the three-roll mill was stopped to obtain a silver-aluminum slurry.

[0053] (3) Preparation of N-TOPCon solar cells:

[0054] After cleaning and texturing the n-type silicon wafer, boron is diffused to form a pn junction, achieving a p+ emitter level. An oxide layer is deposited on the back of the cell as a passivation layer, and a thin film approximately 80nm to 100nm thick is formed on the front via PECVD to achieve surface passivation. A conductive paste is printed via ion implantation, and after implantation, the cell is rapidly sintered within a continuously varying temperature range (480°C to 550°C).

[0055] Example 2

[0056] It is basically the same as Example 1, except that:

[0057] In step (1): electronically pure PbO, V2O and SiO2 are ground and mixed in a mass fraction of 2:1:2;

[0058] In step (2), the following components are weighed in percentage by mass: 80% silver powder, 1% aluminum powder, 3% first additive (Te-Bi-B-Pb-Zn glass powder system), 5% hydroxyethyl cellulose resin, 3% fumed silica, 1% solvent (ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate), 0.005% polyamide-modified hydrogenated castor oil, 3% acrylic resin, and 4% dimethyl silicone oil.

[0059] Example 3

[0060] It is basically the same as Example 1, except that:

[0061] Acrylic acid-phenoxy resin is used to replace the hydroxyethyl cellulose resin system, the first additive is replaced by a Te-Bi-B-Pb-Zn glass powder system, and the fumed silica is replaced by polyamide wax.

[0062] Comparative Example 1

[0063] The same as Example 1, the only difference is that the aluminum powder is replaced with conventional analytical pure aluminum powder.

[0064] Comparative Example 2

[0065] It is basically the same as Example 1, except that the aluminum powder is replaced with high oxygen content aluminum powder (Al-Al2O3).

[0066] Comparative Example 3

[0067] The method is basically the same as Example 2, except that the aluminum powder is replaced with conventional analytical pure aluminum powder, and fumed silica, acrylic resin, dimethyl silicone oil and polyamide-modified hydrogenated castor oil are not added.

[0068] Table 1 Comparison of performance parameters of various solar cells

[0069] Eff(%) Voc(V) Isc(A) FF(%) Rs(Ω) Example 1 23.56 0.698 11.27 81.22 0.00195 Example 2 23.74 0.699 11.32 81.29 0.00187 Example 3 23.42 0.693 11.29 81.17 0.00214 Comparative Example 1 22.19 0.645 10.80 80.06 0.00297 Comparative Example 2 22.79 0.667 11.18 80.04 0.00297 Comparative Example 3 22.92 0.672 11.28 80.98 0.00255

[0070] Where Eff is the photoelectric conversion efficiency, Voc is the open circuit voltage, Isc is the short circuit voltage, FF is the fill factor, and Rs is the series resistance. The above parameters are all tested under standard test conditions (STC, 25℃. 1000W / m 2 The test was carried out under light intensity).

[0071] As can be seen from Table 1, the present invention uses a special tin oxide-coated aluminum powder to replace conventional aluminum powder or high-oxygen-content aluminum powder, which improves Voc, FF, and Rs, has better electrical performance and increases the efficiency of solar cells, has high industrial value and good application prospects.

[0072] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A silver-aluminum paste for N-TOPCon solar cells, characterized in that: The silver-aluminum paste is prepared by including the following components in parts by mass: 75-100 parts of silver powder, 0.5-5 parts of aluminum powder, 0.2-8 parts of a first additive, 0.5-8 parts of a second additive and 1-7 parts of a solvent; Wherein, the aluminum powder is a tin oxide coated powder material; the first additive includes elemental B and B2O3; The particle size of the aluminum powder is 3 μm to 10 μm; the particle size of the tin oxide is 20 nm to 100 nm; The preparation method of the aluminum powder comprises the following steps: synthesizing a micron-sized aluminum powder precursor by a vapor phase method, adding the aluminum powder precursor to a dispersion containing tin ions, impregnating and filtering, and drying the filtered solid to obtain the aluminum powder.

2. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The silver-aluminum paste is prepared by including the following components in parts by mass: 87-90 parts of silver powder, 1-3 parts of aluminum powder, 1-4 parts of the first additive, 2.5-5.5 parts of the second additive and 3-5 parts of the solvent.

3. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The particle size of the silver powder is 2 μm to 8 μm; And / or, the particle size of the silver powder is 10 nm to 100 nm.

4. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The first additive further includes at least one of PbO, V2O5, and Bi2O3.

5. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The first additive also includes at least one of ZnO, TeO2, WO3, Sb2O3, BaO, CaO, AgO, Tl2O3, and SiO2.

6. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The particle size of the first additive is 1 μm to 3 μm.

7. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The solvent includes at least one of alcohol ester dodecyl alcohol, ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol dibutyl ether, dimethyl adipate, triacetin and dimethyl phthalate.

8. The silver-aluminum paste for N-TOPCon solar cells according to claim 1, characterized in that: The second additive includes an adhesive; the second additive also includes at least one of a thixotropic agent, a dispersant, and a wetting agent.

9. The silver-aluminum paste for N-TOPCon solar cells according to claim 8, characterized in that: The adhesive comprises at least one of ethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, phenoxy resin, PVB resin and acrylic resin; The thixotropic agent includes at least one of fumed silica, polyamide wax and polyamide-modified hydrogenated castor oil; The dispersant includes one of acrylic dispersants; The wetting agent includes dimethicone.

10. The method for preparing silver-aluminum paste for N-TOPCon solar cells according to any one of claims 1 to 9, characterized in that: The steps include: The silver powder, aluminum powder, the first additive, the second additive and the solvent are fully mixed and homogenized and dispersed until the fineness of the mixture is less than 10 μm to obtain the silver-aluminum paste.

11. The method for preparing silver-aluminum paste for N-TOPCon solar cells according to claim 10, characterized in that: The mixing comprises the steps of: The first additive, the second additive, and the solvent are premixed, and then the silver powder and the aluminum powder are added and mixed thoroughly.

12. Use of the silver-aluminum paste for N-TOPCon solar cells according to any one of claims 1 to 9 in solar cells.