Solar conductive silver paste and preparation method and application thereof

Abstract

The invention discloses solar conductive silver paste and a preparation method and application thereof, and the preparation raw materials of the solar conductive silver paste comprise the following components in parts by weight: 65-92 parts of silver powder, 2-30 parts of silicide powder, 1-5 parts of glass powder and 4-15 parts of an organic carrier. By selecting the silicide powder and controlling the mass ratio of the silicide to the silver powder to be within the range, on one hand, the silver-silicon contact quality of a solar cell is improved, and the solar conductive silver paste capable of improving the photoelectric conversion efficiency is developed.

Description

Technical Field

[0001] This invention relates to the fields of solar conductive pastes and solar cells, and more specifically, to a solar conductive silver paste, its preparation method, and its application. Background Technology

[0002] In the renewable energy sector, solar cells, as a key technology for converting solar energy into electricity, have always had performance improvement and cost control as core issues for industrial development. Conductive silver paste, as a crucial functional material in solar cell manufacturing, directly affects the photoelectric conversion efficiency and long-term reliability of the cell. However, existing conductive silver paste technology faces several technical bottlenecks: First, traditional conductive silver pastes contain as much as 65-92 wt% silver powder, resulting in high production costs. The global photovoltaic industry consumes over 3,000 tons of silver annually, facing severe constraints on precious metal resources. Second, conventional hot sintering processes struggle to achieve low contact resistance (<1 mΩ·cm). 2 The present invention addresses the inherent contradiction between good surface passivation (minority carrier lifetime > 1ms) and the protection of the passivation layer. Furthermore, the electrode linewidth / height ratio > 1 prepared with traditional silver paste leads to increased shading loss, and non-uniform alloying exists at the silver-silicon contact interface, resulting in cell efficiency generally falling 1-1.5 percentage points below the theoretical limit. In addition, existing silver pastes are difficult to adapt to the requirements of the novel LECO (Laser Enhanced Contact Optimization) process. During laser sintering, the thermal expansion coefficients of silver paste and silicon are mismatched (7-8ppm / ℃ vs 2.6ppm / ℃), and insufficient laser energy absorption (<40%) leads to uneven local sintering. Finally, in passivated contact cell structures such as TOPCon and HJT, traditional silver pastes have insufficient penetration into the TCO / polycrystalline silicon layer, easily causing warping and microcracks under the trend of silicon wafer thinning. These technical problems severely restrict the development of the photovoltaic industry towards high efficiency and low cost, urgently requiring the development of conductive pastes that can significantly reduce silver usage, adapt to advanced LECO processes, and simultaneously improve photoelectric conversion efficiency. Summary of the Invention

[0003] The present invention aims to solve the aforementioned technical problems existing in the prior art. To this end, the present invention proposes a solar conductive silver paste, its preparation method, and its application, which effectively improves the silver-silicon contact quality to enhance the photoelectric conversion efficiency of solar cells and reduces the amount of silver powder used in the paste, thereby significantly reducing metallization costs.

[0004] The present invention also proposes a method for preparing solar conductive silver paste.

[0005] The present invention also proposes a solar cell, wherein the raw materials for preparing the solar cell include the aforementioned solar conductive silver paste.

[0006] According to one aspect of the present invention, a solar conductive silver paste is provided, wherein the raw materials for preparing the solar conductive silver paste, by weight, comprise the following components: 65-92 parts of silver powder, 2-30 parts of silicide powder, 1-5 parts of glass powder, and 4-15 parts of organic carrier.

[0007] The silicide includes at least one of nickel silicide and cobalt silicide.

[0008] The solar conductive silver paste solution provided by this invention introduces silicides as a partial substitute for silver powder. First, the introduction of silicides reduces the amount of silver powder used to less than 1 / 3 of the traditional formula, significantly reducing dependence on precious metals. Second, the excellent lattice matching between silicides and silicon substrates effectively reduces contact resistance and improves minority carrier lifetime through interface passivation, thereby improving battery efficiency.

[0009] In some embodiments of the present invention, the silicide comprises silicide powder having a median particle size range of 0.5-3 μm.

[0010] At the aforementioned silicide particle size, the silicide is uniformly dispersed between silver particles during sintering, forming a continuous epitaxial silicide interlayer at the silver-silicon interface. Due to its compatibility with the silicon substrate, it effectively reduces the interface state density and carrier recombination, thereby improving the open-circuit voltage (Voc) and fill factor (FF).

[0011] At the same time, the above-mentioned particle size can promote solid-state reaction with silicon (forming low-resistance ohmic contact) through sufficient surface active sites, and can avoid over-reaction of too small particle size or insufficient reaction of too large particle size to achieve a reduction in contact resistance (Rc).

[0012] In some embodiments of the present invention, the median particle size of the silicide powder is 1-2 μm.

[0013] In some embodiments of the present invention, the median particle size of the silver powder is 1-2 μm.

[0014] In some embodiments of the present invention, the glass powder includes at least one of the following: PbO, SiO2, B2O3, Al2O3, TeO2, Bi2O3, ZnO, Li2O, Na2O, K2O, CuO, WO3, TiO2, Tl2O3, SrO, BaO, CaO, MgO, NiO, SnO2, Ag2O, MoO3, Sb2O3, Co3O4, CeO2, Fe2O3, and SeO2.

[0015] In some embodiments of the present invention, the nickel silicide includes: Ni3Si, Ni2Si, Ni 31 Si 12 Ni5Si2, Ni74 Si 26 At least one of Ni3Si2, NiSi and NiSi2.

[0016] In some embodiments of the present invention, the nickel silicide includes NiSi2.

[0017] In some embodiments of the present invention, the cobalt silicide includes at least one of Co2Si, CoSi, Co2Si3, and CoSi2.

[0018] In some embodiments of the present invention, the cobalt silicide includes CoSi2.

[0019] In some embodiments of the present invention, the silicide includes NiSi2 and CoSi2.

[0020] The combination of NiSi2 and CoSi2 significantly improves the photoelectric performance of solar cells through multiple synergistic mechanisms: both silicides have a face-centered cubic structure that is highly matched to silicon, and under ultra-high temperature conditions, they can be epitaxially grown to form a low-defect-density interface layer, effectively reducing the interface state density and suppressing carrier recombination, thus increasing the open-circuit voltage (Voc). The work function of NiSi2 and CoSi2 forms an optimized bandgap match with the P-type emitter, synergistically reducing the contact barrier and enhancing carrier collection efficiency, resulting in an increase in short-circuit current (Isc). At the same time, the particle size matching of the two silicides forms a dense composite structure with silver powder, improving the grid conductivity and optimizing the interface composition distribution through the solid solution effect. Through the synergistic effect of lattice matching, bandgap modulation, and process adaptation, the above combination achieves a comprehensive improvement in photoelectric performance while reducing the amount of silver used.

[0021] In some embodiments of the present invention, the raw materials for preparing the solar conductive silver paste, by weight, include the following components: 79-81 parts of silver powder, 7-9 parts of silicide powder, 1-2 parts of glass powder, and 10-11 parts of organic carrier.

[0022] In some embodiments of the present invention, the organic carrier comprises: 1-2 parts of ethyl cellulose, 1-2 parts of polyvinyl butyral, 1-1 parts of cellulose acetate, 5-6 parts of polyamide wax, 50-55 parts of butyl carbitol acetate, 20-25 parts of butyl carbitol, and 20-25 parts of dodecyl alcohol ester.

[0023] According to two aspects of the present invention, a method for preparing solar conductive silver paste is provided, comprising: mixing and grinding the raw materials for preparing the solar conductive silver paste.

[0024] In some embodiments of the present invention, the raw materials for preparing the solar cell include the aforementioned solar conductive silver paste.

[0025] According to three aspects of the present invention, a solar cell is proposed, the solar cell comprising one of a BSF solar cell, a PERC solar cell, a TOPCon solar cell, and a BC solar cell.

[0026] In some embodiments of the present invention, the method for fabricating the solar cell includes laser-assisted enhanced sintering.

[0027] This invention addresses the characteristics of laser-assisted enhanced sintering processes by selecting the type of silicide powder, the range of its median particle size, and the range of its relative mass ratio with silver powder. This approach improves the contact quality of the metallized region in the aforementioned types of solar cells, especially TOPCon and BC cells, thereby reducing carrier recombination losses. Furthermore, it reduces the proportion of silver powder used in the metallization process of solar cells, thus improving photoelectric conversion efficiency and reducing metallization costs. Detailed Implementation

[0028] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0029] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0030] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0031] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0032] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0033] Example 1

[0034] This embodiment provides a solar conductive silver paste. The raw materials for preparing the solar conductive silver paste in this embodiment are shown in Tables 1 and 2. The glass powder is composed of 78 wt% PbO, 15 wt% B2O3, 6.5 wt% SiO2 and 0.5 wt% Al2O3.

[0035] The method for preparing the solar conductive silver paste in this embodiment is as follows: accurately weigh a certain mass of silver powder, silicide powder, glass powder and organic carrier according to the formula, add them to the tank and stir slowly until they are evenly mixed, and then transfer the paste to a three-roll mill for grinding.

[0036] The organic carrier is specifically composed of the following components (in parts by weight): 2 parts ethyl cellulose, 2 parts polyvinyl butyral, 1 part cellulose acetate, 5 parts polyamide wax, 50 parts butyl carbitol acetate, 20 parts butyl carbitol, and 20 parts dodecyl alcohol ester.

[0037] Examples 2-10

[0038] The raw materials for preparing the solar conductive silver pastes in Examples 2-10 are shown in Tables 1 and 2. The glass powder is composed of 78 wt% PbO, 15 wt% B2O3, 6.5 wt% SiO2 and 0.5 wt% Al2O3.

[0039] The composition of the organic carrier is the same as that in Example 1.

[0040] The preparation methods of the solar conductive silver paste in Examples 2-10 are the same as those in Example 1.

[0041] Table 1. Types of silicides in the examples

[0042] serial number Silicide type D50(μm) #1 <![CDATA[NiSi2]]> 1.5 #2 <![CDATA[CoSi2]]> 1.6 #3 <![CDATA[NiSi2]]> 3.2 #4 <![CDATA[CoSi2]]> 3.4 #5 <![CDATA[Ni2Si]]> 1.5 #6 <![CDATA[Co2Si]]> 1.6

[0043] Table 2. Raw materials for preparing solar conductive silver paste in the examples

[0044]

[0045] Comparative Examples 1-7

[0046] The raw materials for preparing the solar conductive silver pastes of Comparative Examples 1 to 7 are shown in Table 3. The glass powder is composed of 78 wt% PbO, 15 wt% B2O3, 6.5 wt% SiO2 and 0.5 wt% Al2O3.

[0047] The preparation methods of the solar conductive silver pastes in Comparative Examples 1 to 7 are the same as those in Example 1.

[0048] Table 3. Raw materials for preparing solar conductive silver paste in the comparative example

[0049]

[0050] Test case

[0051] To further evaluate the performance of conductive silver paste for solar cells, and to investigate the effects of different silicides and their relative proportions of silver powder on the photoelectric conversion efficiency of crystalline silicon solar cells, the silver pastes prepared according to the formulations of Examples 1-10 were screen-printed onto the front side of TOPCon solar cells (the back side of the TOPCon solar cells was screen-printed using the same N-type Poly silver paste), transferred to a rapid sintering furnace for firing, and finally subjected to the LECO process. In the LECO process described in this application, the laser power was 40W, the wavelength was 1064nm, and the reverse bias voltage applied to both sides of the cell was 15V. The electrical performance parameters of Examples 1-10 are shown in Table 4, and the electrical performance parameters of Comparative Examples 1-7 are shown in Table 5. Table 4. Performance Test of Conductive Silver Paste for Solar Cells in Examples

[0052]

[0053]

[0054] Table 5. Performance Tests of Comparative Solar Conductive Silver Paste

[0055]

[0056] Data from Examples 1-10 and Comparative Example 1 show that adding NiSi2 and CoSi2 powders to solar conductive silver paste can improve open-circuit voltage and fill factor, and reduce contact resistance, thereby improving photoelectric conversion efficiency. Therefore, it can be concluded that NiSi2 and CoSi2 contribute to improving the quality of silver-silicon contacts formed using the LECO process.

[0057] Data from Examples 1-5 and Comparative Example 2 show that adding excessive NiSi2 leads to the deterioration of various electrical performance parameters, thereby reducing photoelectric conversion efficiency. Data from Examples 6-10 and Comparative Example 3 show that adding excessive CoSi2 leads to the deterioration of various electrical performance parameters, thereby reducing photoelectric conversion efficiency.

[0058] Adding excessive amounts of NiSi2 and CoSi2 to silver paste increases the gate resistance and reduces the content of silver nanocrystals at the silver-silicon interface, thereby lowering various electrical parameters and resulting in reduced photoelectric conversion efficiency. The reasonable mass ratio of silicide to silver powder in the paste developed in this invention is 1 / 30 to 1 / 3, with the highest photoelectric conversion efficiency ranging from 1 / 18 to 1 / 10.

[0059] Data from Examples 1-5 and Comparative Example 4 show that adding excessively large-particle-size NiSi2 leads to the deterioration of various electrical performance parameters, thereby reducing photoelectric conversion efficiency. Data from Examples 6-10 and Comparative Example 5 show that adding excessively large-particle-size CoSi2 leads to the deterioration of various electrical performance parameters, thereby reducing photoelectric conversion efficiency. Adding excessively large-particle-size NiSi2 and CoSi2 powders to silver paste affects the density of the gate lines and leads to excessively fine paste, thereby increasing the gate breakage rate in screen printing. The particle size of the silicide powder in the paste developed in this invention should be similar to that of the silver powder, with a reasonable range of 0.5 to 3 μm for the median particle size, and the range with the highest photoelectric conversion efficiency being 1-2 μm.

[0060] Data from Examples 1-5 and Comparative Example 6 show that adding NiSi2 powder improves the photoelectric conversion efficiency of solar cells more effectively than adding Ni2Si powder. Data from Examples 6-10 and Comparative Example 7 show that adding CoSi2 powder improves the photoelectric conversion efficiency of solar cells more effectively than adding Co2Si powder.

[0061] NiSi2 and CoSi2 are the most thermodynamically stable silicides of Ni and Co, respectively. Compared to other silicide types, they share the same diamond lattice structure as silicon, resulting in a high degree of lattice matching, which is beneficial for reducing contact resistance and improving various parameters. Therefore, NiSi2 and CoSi2 should be the preferred silicide types in the slurry developed in this invention.

[0062] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: By selecting the above-mentioned types of silicide powders and controlling the median particle size of the silicide powders and the mass ratio of silicide to silver powder within the above-mentioned ranges, on the one hand, the silver-silicon contact quality of solar cells is improved, and a solar conductive silver paste with improved photoelectric conversion efficiency is developed. On the other hand, the amount of silver powder used in the solar conductive silver paste is reduced, greatly reducing the cost of the solar cell metallization process.

[0063] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A solar conductive silver paste, characterized in that, The raw materials for preparing the solar conductive silver paste, by weight, include the following components: 65-92 parts silver powder, 2-30 parts silicide powder, 1-5 parts glass powder, and 4-15 parts organic carrier. The silicide includes at least one of nickel silicide and cobalt silicide.

2. The solar conductive silver paste according to claim 1, characterized in that, The silicide comprises silicide powder, wherein the median particle size of the silicide powder is 0.5-3 μm.

3. The solar conductive silver paste according to claim 1, characterized in that, The median particle size of the silver powder is 1-2 μm.

4. The solar conductive silver paste according to claim 1, characterized in that, The glass powder includes at least one of the following: PbO, SiO2, B2O3, Al2O3, TeO2, Bi2O3, ZnO, Li2O, Na2O, K2O, CuO, WO3, TiO2, Tl2O3, SrO, BaO, CaO, MgO, NiO, SnO2, Ag2O, MoO3, Sb2O3, Co3O4, CeO2, Fe2O3, and SeO2.

5. The solar conductive silver paste according to claim 1, characterized in that, The nickel silicides include: Ni3Si, Ni2Si, Ni 31 Si 12 Ni5Si2, Ni 74 Si 26 At least one of Ni3Si2, NiSi and NiSi2.

6. The solar conductive silver paste according to claim 1, characterized in that, The cobalt silicides include at least one of Co2Si, CoSi, Co2Si3, and CoSi2.

7. The solar conductive silver paste according to claim 1, characterized in that, The raw materials for preparing the solar conductive silver paste, by weight, include the following components: 79-81 parts silver powder, 7-9 parts silicide powder, 1-2 parts glass powder, and 10-11 parts organic carrier.

8. A method for preparing solar conductive silver paste according to any one of claims 1 to 7, characterized in that, include: The raw materials for preparing the solar conductive silver paste are mixed and ground.

9. A solar cell, characterized in that, The raw materials for preparing the solar cell include any one of the solar conductive silver pastes according to claims 1-7.

10. The solar cell according to claim 9, characterized in that, The solar cells include one of BSF solar cells, PERC solar cells, TOPCon solar cells, and BC solar cells.

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