Silver-aluminum paste and preparation method thereof, electrode and solar cell

Abstract

The invention relates to silver-aluminum paste and a preparation method thereof, an electrode and a solar cell, the silver-aluminum paste at least comprises conductive silver powder, aluminum-silicon alloy powder, glass powder and an organic carrier, the silver-aluminum paste further comprises or does not contain aluminum boride powder, and the silver-aluminum paste further comprises or does not contain aluminum powder. The photoelectric conversion efficiency of the solar cell can be improved.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a silver-aluminum paste, its preparation method, electrodes, and solar cells. Background Technology

[0002] Currently, P-type PERC (passivated emitter and back cell) solar cells dominate the market, but N-type crystalline silicon cells are gradually gaining market share due to their high minority carrier lifetime and reduced light-induced degradation. During solar cell fabrication, electrodes need to be introduced by screen printing on the front and back of the cell. For the boron-diffused p+ emitter of N-type cells, silver-aluminum paste screen printing is commonly used to form the metallized contact. Traditional silver-aluminum paste uses silver and aluminum powders as conductive metal powders, providing better electrical contact compared to traditional silver paste and aluminum paste. However, the metallization of the boron-diffused p+ emitter in N-type cells using traditional silver-aluminum paste presents a challenge in balancing metal composite and electrical contact, and the photoelectric conversion efficiency of the cell needs further improvement. Summary of the Invention

[0003] This application provides a silver-aluminum paste and its preparation method, an electrode, and a solar cell, which reduces the contact barrier between the silver-aluminum paste and p+Si, improves electrical contact, thereby increasing the open-circuit voltage of the solar cell, reducing contact resistance, increasing the fill factor, and ultimately improving the photoelectric conversion efficiency.

[0004] In a first aspect, this application provides a silver-aluminum paste, which comprises at least conductive silver powder, aluminum-silicon alloy powder, glass powder and an organic carrier, and may or may not contain aluminum boride powder, and may or may not contain aluminum powder.

[0005] In some embodiments, the aluminum-silicon alloy powder contains aluminum and silicon, and the weight percentage of silicon in the aluminum-silicon alloy powder is 20wt% to 40wt%.

[0006] In some embodiments, the weight percentage of silicon in the aluminum-silicon alloy powder is 20wt% to 32wt%.

[0007] In some embodiments, the average particle size of the aluminum-silicon alloy powder is 0.1 μm to 5 μm.

[0008] In some embodiments, the silver-aluminum paste comprises the following components by weight percentage, based on the total weight of the silver-aluminum paste: 60wt%~90wt% conductive silver powder, 0.1wt%~20wt% aluminum-silicon alloy powder, 0~20wt% aluminum boride powder, 0~20wt% aluminum powder, 1wt%~20wt% glass powder, and 1wt%~30wt% organic carrier.

[0009] In some embodiments, the mass ratio of the aluminum-silicon alloy powder to the aluminum boride powder is 1:100 to 100:1.

[0010] In some embodiments, the aluminum boride powder comprises boron and aluminum.

[0011] In some embodiments, the average particle size of the aluminum boride powder is 0.1 μm to 5 μm.

[0012] In some embodiments, the aluminum boride powder includes AlB2, AlB4, and AlB. 12 At least one of them.

[0013] In some embodiments, the aluminum boride powder is AlB2.

[0014] In some embodiments, the average particle size of the aluminum powder is 0.1 μm to 5 μm.

[0015] In some embodiments, the average particle size of the conductive silver powder is 0.1 μm to 5 μm.

[0016] In some embodiments, the average particle size of the glass powder is 0.1 μm to 5 μm.

[0017] In some embodiments, based on the total weight of the glass powder, the glass powder comprises the following components in weight percentages: Bi₂O₃ 0~50wt%, PbO 0~50wt%, B₂O₃ 5wt%~20wt%, SiO₂ 3wt%~20wt%, Al₂O₃ 3wt%~10wt%, TeO₂ 3wt%~10wt%, SnO₂ 2wt%~4wt%, Li₂O 2wt%~4wt%, ZnO 1wt%~2wt%, and BaO 0.5wt%~2wt%.

[0018] In some embodiments, the organic carrier comprises an organic solvent, an organic binder, a surfactant, a thixotropic agent, and a diluent.

[0019] A second aspect of this application provides a method for preparing a silver-aluminum paste, comprising the following steps:

[0020] The raw materials of the silver-aluminum paste are mixed to obtain the silver-aluminum paste; the raw materials include at least conductive silver powder, aluminum-silicon alloy powder, glass powder and organic carrier, and the raw materials may or may not contain aluminum boride powder, and the raw materials may or may not contain aluminum powder.

[0021] A third aspect of this application provides an electrode made from at least one of the silver-aluminum paste described in the first aspect of this application and the silver-aluminum paste prepared by the preparation method described in the second aspect of this application.

[0022] In some embodiments, the electrode includes a solar cell p+ electrode.

[0023] A fourth aspect of this application provides a solar cell including the electrodes described in the third aspect of this application.

[0024] Compared with traditional technologies, the above-mentioned silver-aluminum paste has at least the following advantages:

[0025] Compared to traditional silver-aluminum pastes based on silver and aluminum powders, the aluminum-silicon alloy powder in the aforementioned silver-aluminum paste can provide aluminum during high-temperature sintering, enabling the formation of silver-aluminum contact points with silicon-containing solar cells, thereby reducing the contact resistance of the solar cells. Furthermore, the aluminum-silicon alloy powder has a higher melting point than aluminum powder and contains a certain amount of silicon, which can significantly limit the reactivity of aluminum in alloying with silicon at high temperatures, greatly reducing the penetration of silver-aluminum spikes into the emitter. Therefore, the aforementioned silver-aluminum paste can lower the contact barrier with p+Si, improve electrical contact, thereby increasing the open-circuit voltage of the solar cell, reducing contact resistance, increasing the fill factor, and ultimately improving the photoelectric conversion efficiency. Attached Figure Description

[0026] Figure 1 SEM image (scanning electron microscope image) of the battery cell after chemical cleaning and electrode removal, provided for Comparative Example 1.

[0027] Figure 2 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 1.

[0028] Figure 3 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 2.

[0029] Figure 4 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 3.

[0030] Figure 5 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 4.

[0031] Figure 6 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 5.

[0032] Figure 7 This is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Example 6.

[0033] Figure 8 The contact potential diagram of the electrode and p-Si of the battery cell provided for Comparative Example 1.

[0034] Figure 9 The contact potential diagram between the electrode and p-Si of the battery cell provided in Example 3. Detailed Implementation

[0035] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0036] In this application, terms such as "first aspect," "second aspect," and "third aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," and "third" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0037] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0038] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0039] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0040] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in this application and in its specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items. The term "multiple" in this application means at least two, such as two, three, etc., unless otherwise expressly specified.

[0041] One embodiment of this application provides a silver-aluminum paste, which includes at least conductive silver powder, aluminum-silicon alloy powder, glass powder and an organic carrier. The silver-aluminum paste may or may not contain aluminum boride powder, and may or may not contain aluminum powder.

[0042] The aforementioned silver-aluminum paste uses aluminum-silicon alloy powder to replace part or all of the aluminum powder. The addition of aluminum boride powder enhances the heavy doping of boron and aluminum elements into the emitter. Compared to traditional silver-aluminum pastes based on silver and aluminum powder, the aluminum-silicon alloy powder in this paste provides aluminum during high-temperature sintering, enabling the formation of silver-aluminum contact points with silicon-containing solar cells, thereby reducing the contact resistance of the solar cell. Furthermore, the aluminum-silicon alloy powder has a higher melting point than aluminum powder and contains a certain amount of silicon, which significantly limits the reactivity of aluminum alloying with silicon during high-temperature processes, greatly reducing the penetration of silver-aluminum spikes into the emitter. Therefore, this silver-aluminum paste can lower the contact barrier with p+Si, improve electrical contact, thereby increasing the open-circuit voltage of the solar cell, reducing contact resistance, increasing the fill factor, and ultimately improving the photoelectric conversion efficiency.

[0043] In some embodiments, the silver-aluminum paste comprises conductive silver powder, aluminum-silicon alloy powder, glass powder, and an organic carrier.

[0044] In other embodiments, the silver-aluminum paste comprises conductive silver powder, aluminum-silicon alloy powder, glass powder, an organic carrier, and aluminum boride powder. The combined use of aluminum-silicon alloy powder and aluminum boride powder in the silver-aluminum paste can adjust the silver-aluminum spikes, reduce the penetration of the silver-aluminum spikes into the emitter, and lower the contact barrier between the silver-aluminum paste and p+Si, which is beneficial to further improve the photoelectric conversion efficiency of the solar cell.

[0045] In other embodiments, the silver-aluminum paste comprises conductive silver powder, aluminum-silicon alloy powder, glass powder, organic carrier, aluminum boride powder, and aluminum powder.

[0046] In some embodiments, the aluminum-silicon alloy powder contains aluminum and silicon, with the silicon content ranging from 20 wt% to 40 wt% by weight. This design allows for control of the melting point of the aluminum-silicon alloy powder within a reasonable range, limiting the formation of silver-aluminum spikes and thus further improving the photoelectric conversion efficiency of the solar cell. It is understood that the weight percentage of silicon in the aluminum-silicon alloy powder includes, but is not limited to, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, and 40 wt%. Further, the weight percentage of silicon in the aluminum-silicon alloy powder is 20 wt% to 32 wt%.

[0047] In some embodiments, the average particle size of the aluminum-silicon alloy powder is 0.1 μm to 5 μm. This design is beneficial for improving the adhesion between particles after sintering the silver-aluminum paste, thereby further improving the photoelectric conversion efficiency of the solar cell. It is understood that the average particle size of the aluminum-silicon alloy powder includes, but is not limited to: 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0048] In some embodiments, based on the total weight of the silver-aluminum paste, the silver-aluminum paste comprises the following components in weight percentages: 60wt%~90wt% conductive silver powder, 0.1wt%~20wt% aluminum-silicon alloy powder, 0~20wt% aluminum boride powder, 0~20wt% aluminum powder, 1wt%~20wt% glass powder, and 1wt%~30wt% organic carrier. This can further improve the photoelectric conversion efficiency of the solar cell.

[0049] In the above embodiments, the weight percentage of conductive silver powder in the silver-aluminum paste includes, but is not limited to: 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, and 90wt%; the weight percentage of aluminum-silicon alloy powder includes, but is not limited to: 0.1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 15wt%, and 20wt%; the silver-aluminum paste may contain aluminum boride powder, and the weight percentage of aluminum boride powder includes, but is not limited to: 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, and 20wt%. The silver-aluminum paste may contain aluminum powder, and the weight percentage of aluminum powder includes, but is not limited to: 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%; the weight percentage of glass powder includes, but is not limited to: 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%; and the weight percentage of organic carrier includes, but is not limited to: 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%.

[0050] In some embodiments, based on the total weight of the silver-aluminum paste, the silver-aluminum paste comprises the following components in weight percentages: 60wt%~90wt% conductive silver powder, 0.1wt%~20wt% aluminum-silicon alloy powder, 0.1wt%~20wt% aluminum boride powder, 0.1wt%~20wt% aluminum powder, 1wt%~20wt% glass powder, and 1wt%~30wt% organic carrier.

[0051] In some embodiments, the mass ratio of aluminum-silicon alloy powder to aluminum boride powder is 1:100 to 100:1. A mass ratio of aluminum-silicon alloy powder to aluminum boride powder within this range can further improve the photoelectric conversion efficiency of the solar cell. It is understood that the mass ratio of aluminum-silicon alloy powder to aluminum boride powder includes, but is not limited to, 1:100, 1:50, 1:1, 50:1, and 100:1.

[0052] In some embodiments, the aluminum boride powder contains boron and aluminum.

[0053] In some embodiments, the average particle size of the aluminum boride powder is 0.1 μm to 5 μm. It is understood that the average particle size of the aluminum boride powder includes, but is not limited to, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0054] In some embodiments, the aluminum boride powder includes AlB2, AlB4, and AlB 12 At least one of the following. Optionally, the aluminum boride powder is AlB2.

[0055] In some embodiments, the average particle size of the aluminum powder is 0.1 μm to 5 μm. It is understood that the average particle size of the aluminum powder includes, but is not limited to: 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0056] In some embodiments, the average particle size of the conductive silver powder is 0.1 μm to 5 μm. It is understood that the average particle size of the conductive silver powder includes, but is not limited to, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0057] In some embodiments, the average particle size of the glass powder is 0.1 μm to 5 μm. It is understood that the average particle size of the glass powder includes, but is not limited to: 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0058] In some embodiments, the glass powder comprises the following components in weight percentages based on the total weight of the glass powder: Bi₂O₃ 0~50wt%, PbO 0~50wt%, B₂O₃ 5wt%~20wt%, SiO₂ 3wt%~20wt%, Al₂O₃ 3wt%~10wt%, TeO₂ 3wt%~10wt%, SnO₂ 2wt%~4wt%, Li₂O 2wt%~4wt%, ZnO 1wt%~2wt%, and BaO 0.5wt%~2wt%.

[0059] In some embodiments, the organic carrier includes an organic solvent, an organic binder, a surfactant, a thixotropic agent, and a diluent.

[0060] In some embodiments, the organic solvent includes one or more of terpineol, butyl carbitol, dodecyl alcohol ester, and diethyl phthalate.

[0061] In some embodiments, the organic binder includes ethyl cellulose.

[0062] In some embodiments, the surfactant includes sodium dodecylbenzenesulfonate.

[0063] In some embodiments, the thixotropic agent includes, but is not limited to, polyamide wax.

[0064] In some embodiments, the diluent includes, but is not limited to, hydrogenated castor oil.

[0065] Another embodiment of this application provides a method for preparing a silver-aluminum paste, comprising the following steps:

[0066] The raw materials for silver-aluminum paste are mixed to obtain silver-aluminum paste; the raw materials include at least conductive silver powder, aluminum-silicon alloy powder, glass powder and organic carrier, and may or may not contain aluminum boride powder, and may or may not contain aluminum powder.

[0067] The silver-aluminum paste prepared by the above method can provide aluminum during high-temperature sintering, enabling the formation of silver-aluminum contact points with silicon-containing solar cells, thereby reducing the contact resistance of the solar cells. Furthermore, the aluminum-silicon alloy powder has a higher melting point than aluminum powder and contains a certain amount of silicon, which can significantly limit the reactivity of aluminum in alloying with silicon during high-temperature processes, greatly reducing the penetration of silver-aluminum spikes into the emitter. Therefore, the above-mentioned silver-aluminum paste can lower its contact barrier with p+Si, improve electrical contact, thereby increasing the open-circuit voltage of the solar cell, reducing contact resistance, increasing the fill factor, and ultimately improving the photoelectric conversion efficiency. The above preparation method also has the advantages of simple operation and ease of large-scale production.

[0068] By adjusting the process parameters of the above preparation method, the silver-aluminum paste in one embodiment of this application can be obtained.

[0069] This application also provides an electrode made using at least one of the silver-aluminum pastes described above and the silver-aluminum pastes prepared by the methods described above.

[0070] In some implementations, the electrode includes a solar cell p+ electrode.

[0071] This application also provides a solar cell including the electrodes described above.

[0072] To further illustrate this application, the technical solution of this application is described in detail below with reference to specific embodiments. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0073] Example 1

[0074] The silver-aluminum paste for solar cells in this embodiment includes the following components (raw materials) by weight percentage: 85wt% conductive silver powder and aluminum-silicon alloy powder mixture, 5wt% glass powder, and 10wt% organic carrier; the conductive silver powder and aluminum-silicon alloy powder mixture is composed of conductive silver powder and aluminum-silicon alloy powder, and the mass ratio of conductive silver powder to aluminum-silicon alloy powder is 39:1.

[0075] The average particle size of conductive silver powder is 1μm~3μm, the average particle size of aluminum-silicon alloy powder is 1μm~3μm, and the average particle size of glass powder is 0.1μm~5μm.

[0076] The weight percentage of silicon in the aluminum-silicon alloy powder is 20 wt%.

[0077] The glass powder contains the following components (raw materials) in weight percentage: PbO 30wt%, Bi2O3 30wt%, B2O3 20wt%, Al2O3 6wt%, SiO2 4wt%, TeO2 4wt%, SnO2 2wt%, Li2O 2wt%, BaO 1wt%, ZnO 1wt%. The glass powder is obtained by mixing the above components evenly, melting and quenching them in a crucible at high temperature, and then grinding the resulting glass frit to 2μm.

[0078] The organic carrier comprises the following components (raw materials) in weight percentages: terpineol 25wt%, butyl carbitol 25wt%, dodecyl alcohol 20wt%, diethyl phthalate 15wt%, ethyl cellulose 8wt%, polyamide wax 2.5wt%, hydrogenated castor oil 2.5wt%, and sodium dodecylbenzene sulfonate 2wt%.

[0079] The method for preparing the silver-aluminum paste for solar cells described in this embodiment includes the following steps:

[0080] (1) Preparation of organic carriers

[0081] Weigh out the raw materials of the organic carrier according to the proportion, mix them, heat to 80℃, stir for 1.5 hours, mix evenly, and obtain the organic carrier;

[0082] (2) Preparation of silver-aluminum paste

[0083] Weigh out conductive silver powder, aluminum boride powder, and glass powder in proportion, add them to an organic carrier, stir and mix evenly, and then feed them into a three-roll mill for grinding and dispersion to obtain silver-aluminum paste for solar cells.

[0084] Example 2

[0085] This embodiment is basically the same as Embodiment 1, except that the weight percentage of silicon in the aluminum-silicon alloy powder in the silver-aluminum paste is 30wt%.

[0086] Example 3

[0087] This embodiment is basically the same as Embodiment 1, except that the silver-aluminum paste includes the following components (raw materials) in weight percentage: 85wt% of a mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, 5wt% of glass powder, and 10wt% of organic carrier; the mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is composed of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, and the mass ratio of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is 78.5:1:1.5, the aluminum boride powder is AlB2, and the average particle size of the aluminum boride powder is 0.1μm~5μm.

[0088] Example 4

[0089] This embodiment is basically the same as Embodiment 2, except that the silver-aluminum paste includes the following components (raw materials) in weight percentage: 85wt% of a mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, 5wt% of glass powder, and 10wt% of organic carrier; the mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is composed of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, and the mass ratio of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is 68:1:1.5, the aluminum boride powder is AlB2, and the average particle size of the aluminum boride powder is 0.1μm~5μm.

[0090] Example 5

[0091] This embodiment is basically the same as Embodiment 1, except that the silver-aluminum paste includes the following components (raw materials) in weight percentage: 85wt% of a mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, 5wt% of glass powder, and 10wt% of organic carrier; the mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is composed of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, and the mass ratio of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is 78.5:1:2, the aluminum boride powder is AlB4, and the average particle size of the aluminum boride powder is 0.1μm~5μm.

[0092] Example 6

[0093] This embodiment is basically the same as Embodiment 2, except that the silver-aluminum paste includes the following components (raw materials) in weight percentage: 85wt% of a mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, 5wt% of glass powder, and 10wt% of organic carrier; the mixture of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is composed of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder, and the mass ratio of conductive silver powder, aluminum-silicon alloy powder and aluminum boride powder is 78.5:1:2, the aluminum boride powder is AlB4, and the average particle size of the aluminum boride powder is 0.1μm~5μm.

[0094] Example 7

[0095] This embodiment is basically the same as Embodiment 1, except that the weight percentage of silicon in the aluminum-silicon alloy powder in the silver-aluminum paste is 32wt%.

[0096] Example 8

[0097] This embodiment is basically the same as Embodiment 1, except that the weight percentage of silicon in the aluminum-silicon alloy powder in the silver-aluminum paste is 40wt%.

[0098] Comparative Example 1

[0099] This comparative example is basically the same as Example 1, except that the silver-aluminum paste contains the following components (raw materials) by weight percentage: 85wt% conductive silver powder and aluminum powder mixture, 5wt% glass powder, and 10wt% organic carrier; the conductive silver powder and aluminum powder mixture is composed of conductive silver powder and aluminum powder, and the silver-aluminum paste does not contain aluminum-silicon alloy powder; the aluminum content in the conductive silver powder and aluminum powder mixture is the same as the aluminum content in the conductive silver powder and aluminum-silicon alloy powder mixture in Example 1.

[0100] Comparative Example 2

[0101] This comparative example is basically the same as Example 1, except that the silver-aluminum paste contains the following components (raw materials) in weight percentage: 85wt% conductive silver powder and aluminum boride powder mixture, 5wt% glass powder, and 10wt% organic carrier; the conductive silver powder and aluminum boride powder mixture is composed of conductive silver powder and aluminum boride powder, with a mass ratio of conductive silver powder to aluminum boride powder of 26.5:1, the aluminum boride powder is AlB2, and the average particle size of the aluminum boride powder is 0.1μm~5μm.

[0102] Performance testing

[0103] The fabrication process of the N-type TopCon cell is as follows: cleaning and texturing, front boron diffusion, back etching, LPCVD (low-pressure chemical vapor deposition) for preparing the tunneling oxide layer and polycrystalline silicon layer, back phosphorus diffusion, plating around and cleaning removal, front and back passivation layer deposition, and front and back metallization. During the metallization process, screen printing was used to prepare the grid electrodes. The front metallization used silver-aluminum paste prepared in each embodiment or comparative example. The peak sintering temperature for the screen-printed grid lines was 850℃, and the sintering furnace belt speed was 225 inches / min. After the metallization process, a standard testing and sorting machine was used for efficiency testing and sorting. The relevant data are shown in Table 1.

[0104] Figures 1-7 This is a SEM image observed using a field emission scanning electron microscope after the front electrode was removed by cleaning with HNO3. Figure 8 and Figure 9 The contact potential diagram of the electrode and p-Si shown is obtained by KPFM (Kelvin probe microscopy) characterization of the contact cross-section after polishing.

[0105] Figure 1 The following is a SEM image of the battery cell after chemical cleaning to remove the electrodes, as provided in Comparative Example 1. Figure 2 and Figure 3 SEM images of the battery cells after chemical cleaning and electrode removal provided in Examples 1 and 2 are shown, respectively. Compared to the silver-aluminum paste based on silver and aluminum powder in Comparative Example 1, Examples 1 and 2 use aluminum-silicon alloy powder instead of aluminum powder. Figures 1-3 It can be seen that the silver-aluminum paste in Comparative Example 1 produces a large number of silver-aluminum spikes during sintering, resulting in numerous corrosion pits on the silicon wafer surface after electrode removal. In contrast, under the same aluminum content, the corrosion pits produced in Examples 1 and 2 are significantly reduced. The silver-aluminum pastes in Examples 1 and 2, due to the higher melting point of the aluminum-silicon alloy powder and the presence of a certain amount of silicon, greatly limit the reactivity of aluminum in alloying with silicon at high temperatures, thus reducing the generation of silver-aluminum spikes. This weakens the damage to the p+ emitter caused by large-sized silver-aluminum spikes.

[0106] Figures 4-7 SEM images of the battery cells provided in Examples 3-6 after chemical cleaning and electrode removal are shown. See also... Figures 4-7 As can be seen, compared with Comparative Example 1, the corrosion pits generated in Examples 3-6 were significantly reduced under the same aluminum content. In Examples 3-6, the silver-aluminum paste used aluminum-silicon alloy powder instead of aluminum powder, and also added a certain amount of high-melting-point aluminum boride powder. This greatly limited the reactivity of aluminum in alloying with silicon during high-temperature processes, reduced the generation of silver-aluminum spikes, and thus weakened the damage of large-sized silver-aluminum spikes to the p+ emitter.

[0107] Figure 8 and Figure 9 The contact potential diagrams of the electrodes and p-Si of the solar cells provided in Comparative Example 1 and Example 3 are shown respectively. Since the p+ electrode collects hole carriers, a higher electrode potential than the p+Si potential is more conducive to hole collection. Therefore, the potential difference between the silver-aluminum paste and p+Si represents a contact barrier; a smaller contact barrier is more conducive to hole carrier transport. Figure 8 and Figure 9 As can be seen, the contact barrier between the silver-aluminum paste and p+Si in Comparative Example 1 is 141.6 mV, while the contact barrier between the silver-aluminum paste and p+Si in Example 3 is only 98.8 mV, showing a significant reduction in the contact barrier. This is because the introduction of aluminum boride powder promotes the heavy doping of boron and aluminum elements into the p+ emitter, resulting in a substantial decrease in the contact barrier between the metal electrode and silicon, thereby significantly improving the photoelectric conversion efficiency of the battery.

[0108] The efficiency of the solar cells prepared in Examples 1-8 and the solar cells prepared in Comparative Examples 1-2 were tested, and the results are shown in Table 1.

[0109] Table 1

[0110]

[0111] In Table 1, Eta is the battery efficiency, Uoc is the open-circuit voltage, Jsc is the short-circuit current density, FF is the fill factor, Rs is the series resistance, and Rsh is the parallel resistance.

[0112] As shown in Table 1, the photoelectric conversion efficiency of the batteries obtained from the silver-aluminum pastes in Examples 1-8 is higher than that of Comparative Examples 1-2. This indicates that introducing aluminum-silicon alloy powder or a combination of aluminum-silicon alloy powder and aluminum boride powder into the silver-aluminum paste can effectively improve the photoelectric conversion efficiency of the batteries. Among them, Examples 3 and 4 show the most significant improvement. Compared with Comparative Example 1, the battery efficiency of Examples 3 and 4 is improved by more than 0.2%, mainly due to the improvement in open-circuit voltage Uoc, short-circuit current Jsc, and fill factor FF. The silver-aluminum pastes in Examples 1-2 and Examples 7-8 use aluminum-silicon alloy powder instead of aluminum powder, which limits the reaction activity of aluminum with silicon during high-temperature alloying, reduces the penetration emission of silver-aluminum spikes, and thus reduces contact recombination and shunt leakage, thereby significantly improving the open-circuit voltage, short-circuit current, and fill factor, ultimately improving the battery efficiency. In Examples 3-6, aluminum boride powder was introduced into the aluminum-silicon alloy powder, which not only reduced contact recombination and shunt leakage, but also significantly lowered the contact barrier between the silver-aluminum electrode and p+Si, improving electrical contact. This significantly increased the open-circuit voltage, short-circuit current and fill factor, reduced contact resistance, and ultimately improved the photoelectric conversion efficiency of the battery.

[0113] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A silver-aluminum paste, characterized in that, The silver-aluminum paste contains at least conductive silver powder, aluminum-silicon alloy powder, glass powder, and an organic carrier. The silver-aluminum paste may or may not contain aluminum boride powder, and may or may not contain aluminum powder.

2. The silver-aluminum paste according to claim 1, characterized in that, The aluminum-silicon alloy powder contains aluminum and silicon, and the weight percentage of silicon in the aluminum-silicon alloy powder is 20wt%~40wt%. Optionally, the weight percentage of silicon in the aluminum-silicon alloy powder is 20wt% to 32wt%. Optionally, the average particle size of the aluminum-silicon alloy powder is 0.1 μm to 5 μm.

3. The silver-aluminum paste according to claim 1, characterized in that, Based on the total weight of the silver-aluminum paste, the silver-aluminum paste comprises the following components by weight percentage: 60wt%~90wt% conductive silver powder, 0.1wt%~20wt% aluminum-silicon alloy powder, 0~20wt% aluminum boride powder, 0~20wt% aluminum powder, 1wt%~20wt% glass powder, and 1wt%~30wt% organic carrier; Optionally, the mass ratio of the aluminum-silicon alloy powder to the aluminum boride powder is 1:100 to 100:

1.

4. The silver-aluminum paste according to any one of claims 1 to 3, characterized in that, The aluminum boride powder contains boron and aluminum. Optionally, the average particle size of the aluminum boride powder is 0.1 μm to 5 μm.

5. The silver-aluminum paste according to claim 4, characterized in that, The aluminum boride powder includes AlB2, AlB4, and AlB. 12 At least one of them; Optionally, the aluminum boride powder is AlB2.

6. The silver-aluminum paste according to any one of claims 1 to 3, characterized in that, The silver-aluminum paste has at least one of the following characteristics (1) to (5): (1) The average particle size of the aluminum powder is 0.1 μm to 5 μm; (2) The average particle size of the conductive silver powder is 0.1 μm to 5 μm; (3) The average particle size of the glass powder is 0.1 μm to 5 μm; (4) Based on the total weight of the glass powder, the glass powder contains the following components in weight percentage: Bi2O3 0~50wt%, PbO 0~50wt%, B2O3 5wt%~20wt%, SiO2 3wt%~20wt%, Al2O3 3wt%~10wt%, TeO2 3wt%~10wt%, SnO2 2wt%~4wt%, Li2O 2wt%~4wt%, ZnO 1wt%~2wt%, and BaO 0.5wt%~2wt%; (5) The organic carrier includes organic solvent, organic binder, surfactant, thixotropic agent and diluent.

7. A method for preparing a silver-aluminum paste, characterized in that, Includes the following steps: The raw materials of the silver-aluminum paste are mixed to obtain the silver-aluminum paste; the raw materials include at least conductive silver powder, aluminum-silicon alloy powder, glass powder and organic carrier, and the raw materials may or may not contain aluminum boride powder, and the raw materials may or may not contain aluminum powder.

8. An electrode, characterized in that, The electrode is made of at least one of the silver-aluminum pastes according to any one of claims 1 to 6 and the silver-aluminum pastes prepared by the preparation method according to claim 7.

9. The electrode according to claim 8, characterized in that, The electrode includes the p+ electrode of a solar cell.

10. A solar cell, characterized in that, Includes the electrode as described in claim 8 or 9.

Images