A copper paste metallization interconnect electrode, a preparation method thereof and a photovoltaic system

Abstract

The application provides a copper paste metallization interconnection electrode and a preparation method thereof and a photovoltaic system, and belongs to the technical field of photovoltaic technology. The method comprises the following steps: sequentially arranging a copper paste and a tin paste on a target welding area on the surface of a cell; solidifying under the protection of an inert gas to obtain a first IMC layer; performing welding treatment to obtain a second IMC layer on the surface of the first IMC layer, and the copper paste metallization interconnection electrode is obtained; wherein the first IMC layer comprises Cu6Sn5; and the second IMC layer comprises Cu6Sn5 and Cu3Sn. The preparation method provided by the application has a relatively simple implementation process, low process control scheme implementation difficulty and low cost. The investment cost can be greatly reduced, similar process effects can be achieved, and industrial production can be met.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a copper paste metallized interconnect electrode, its preparation method, and a photovoltaic system. Background Technology

[0002] Traditional solar cell solder joints use a silver or copper paste with a tin plating layer. The tin layer on the interconnect strips can be formed into a silver-tin alloy or a copper-tin alloy at high temperatures. While copper paste is cheaper, it has poor oxidation resistance, requiring additional tin plating for protection and increasing process complexity. Furthermore, the CTE (Coefficient of Thermal Expansion) of silver, copper, and tin differs significantly from that of the solar cell substrate (such as silicon wafers), which can easily generate stress under long-term thermal cycling, leading to solder joint cracks or delamination. Silver-tin or copper-tin alloys are also prone to forming brittle phases (such as Ag3Sn and Cu6Sn5) at high temperatures, reducing solder joint toughness and increasing the risk of fracture.

[0003] Current technology typically involves depositing a 1-2µm tin layer on the surface of copper paste via electroplating. Electroplating requires specialized equipment, resulting in high investment costs; furthermore, the wastewater from electroplating is difficult to treat and pollutes the environment. Additionally, alloy formation requires high temperatures (200-300℃), which may damage the passivation layer on the cell surface, reducing photoelectric conversion efficiency. Controlling the thickness and uniformity of the tin plating layer is difficult, easily leading to localized poor soldering or short circuits. This results in potential differences between different metals (such as the potential difference between silver and tin), which can easily lead to electrochemical corrosion in humid environments, accelerating solder joint failure. Furthermore, pure tin or tin alloys may grow tin whiskers under stress, increasing the risk of short circuits. Summary of the Invention

[0004] The purpose of this application is to provide an electrode with copper paste metallized interconnect, a method for preparing the same, and a photovoltaic system to solve the above-mentioned problems.

[0005] To achieve the above objectives, this application adopts the following technical solution: This application provides a method for fabricating electrodes with copper paste metallized interconnects, comprising: Copper paste and solder paste are sequentially applied to the target welding area on the surface of the battery cell; the mixture is then cured under the protection of an inert gas to obtain the first IMC layer. A welding process is performed to obtain a second IMC layer on the surface of the first IMC layer, thus obtaining the copper paste metallized interconnect electrode; The first IMC layer includes Cu6Sn5; the second IMC layer includes Cu6Sn5 and Cu3Sn.

[0006] Preferably, the solder paste is a tin-bismuth mixture.

[0007] Preferably, the solder paste has a particle size of 25-45 μm.

[0008] Preferably, the viscosity of the solder paste is 180–250 Pa·s.

[0009] Preferably, the thickness of the solder paste is not less than 5 μm.

[0010] Preferably, the inert gas includes nitrogen.

[0011] Preferably, the curing temperature is 140-160℃ and the time is 30-60min.

[0012] Preferably, the thickness of the first IMC layer is 0.1-1 μm.

[0013] Preferably, the welding process is performed at a temperature of 280-320°C for 2-3 seconds.

[0014] Preferably, the thickness of the second IMC layer is 1-3 μm.

[0015] This application also provides a copper paste metallized interconnect electrode, which is prepared according to the preparation method of the copper paste metallized interconnect electrode.

[0016] This application also provides a photovoltaic system including the copper paste metallized interconnected electrodes.

[0017] Compared with the prior art, the beneficial effects of this application include: The preparation method provided in this application is relatively simple to implement, with low difficulty in process control and low cost. It can significantly reduce investment costs while achieving similar process effects to meet industrial production requirements. By utilizing staged reaction temperatures and controlling time, two metal alloys are achieved, satisfying the metallization interconnection scheme for solar cells. Furthermore, a layer of solder paste is applied to the solar cell solder joints. First, a shallow Cu6Sn5 IMC layer (achieving a seed layer effect) is formed between tin and copper through low-temperature curing. Then, high-temperature soldering is used to further and rapidly grow the copper-tin alloy layer, resulting in a thicker alloy layer, which is beneficial for improving the alloy's strength and conductivity.

[0018] The battery cell provided in this application has good alloy strength and conductivity. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0020] Figure 1 This is a schematic diagram of the first IMC layer during the low-temperature curing stage; Figure 2This is a schematic diagram of the IMC layer during the high-temperature curing stage; Figure 3 Microscopic view of the cross-section after welding; Figure 4 for Figure 3 The energy spectrum at point A in the middle; Figure 5 for Figure 3 Energy spectrum at point B; Figure 6 for Figure 3 The energy spectrum at point C. Detailed Implementation

[0021] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0022] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0023] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0024] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0025] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0026] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0027] To better explain the technical solution of this application, the overall technical solution of this application will be described before the specific embodiments.

[0028] In a first aspect, this application provides a method for preparing an electrode with copper paste metallized interconnect, comprising: Copper paste and solder paste are sequentially applied to the target welding area on the surface of the battery cell; the mixture is then cured under the protection of an inert gas to obtain the first IMC layer. A welding process is performed to obtain a second IMC layer on the surface of the first IMC layer, thus obtaining the copper paste metallized interconnect electrode; The first IMC layer includes Cu6Sn5; the second IMC layer includes Cu6Sn5 and Cu3Sn.

[0029] This application employs a method of printing the back electrode with pure copper paste and printing low-temperature solder paste on the electrode. In the first stage, a low-temperature curing process is used to form Cu6Sn5 (η phase) between the solder paste and copper. In the second stage, a high-temperature soldering process is used to form Cu6Sn5 (η phase) and Cu3Sn (ε phase) between the solder paste and copper. This method ensures that the tin layer of the interconnect strip achieves good ohmic contact and mechanical properties through the tin-copper layer on the surface of the copper paste during the packaging process.

[0030] In the low-temperature curing stage, the layer diagram of the first IMC layer is as follows: Figure 1 As shown; a schematic diagram of the IMC layer during the high-temperature welding stage is shown below. Figure 2 As shown.

[0031] In an optional embodiment, the solder paste is a tin-bismuth mixture.

[0032] Conventional solder paste is a tin-lead mixture, in which Sn participates in the reaction, while Pb serves to lower the alloy's melting point but does not participate in the reaction. The solder paste used in this application is a tin-bismuth mixture, eliminating Pb and increasing Bi, where Bi serves to lower the alloy's melting point. Increasing the proportion of Sn increases its participation in the alloy's reaction.

[0033] In one optional embodiment, the solder paste has a particle size of 25-45 μm.

[0034] Optionally, the particle size of the solder paste can be 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, or any value between 25 and 45μm.

[0035] In one optional embodiment, the viscosity of the solder paste is 180–250 Pa·s.

[0036] Optionally, the viscosity of the solder paste can be 180 Pa·s, 185 Pa·s, 190 Pa·s, 195 Pa·s, 200 Pa·s, 205 Pa·s, 210 Pa·s, 215 Pa·s, 220 Pa·s, 225 Pa·s, 230 Pa·s, 235 Pa·s, 240 Pa·s, 245 Pa·s, 250 Pa·s, or any value between 180 and 250 Pa·s.

[0037] Understandably, during the solder paste preparation process, Sn and Bi elements are first cured at 210-220℃ for 100-200s, completely melting to form alloy particles. After mixing with 8-11 wt% flux and 8%-10% organic solvent, the final viscosity is 180-250 Pa·s. The flux includes reducing agents and rosin resin; the organic solvent includes synthetic resin surfactants, organic acid activators, corrosion inhibitors, cosolvents, and film-forming agents.

[0038] In one optional embodiment, the thickness of the solder paste is not less than 5 μm.

[0039] Optionally, the thickness of the solder paste can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value not less than 5μm.

[0040] In one alternative implementation, the inert gas includes nitrogen.

[0041] In one optional embodiment, the curing temperature is 140-160°C and the time is 30-60 minutes.

[0042] Optionally, the curing temperature can be 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃, 150℃, 151℃, 152℃, 153℃, 154℃, 155℃, 156℃, 157℃, 158℃, 159℃, or 160℃, or any value between 140℃ and 160℃. The curing time can be 30min, 35min, 40min, 45min, 50min, 55min, or 60min, or any value between 30min and 60min.

[0043] In an optional implementation, the thickness of the first IMC layer is 0.1-1 μm.

[0044] Optionally, the thickness of the first IMC layer can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, or any value between 0.1 and 1μm.

[0045] In one optional embodiment, the welding process is performed at a temperature of 280-320°C for 2-3 seconds.

[0046] Optionally, the welding temperature can be 280℃, 285℃, 290℃, 295℃, 300℃, 305℃, 310℃, 315℃, 320℃, or any value between 280℃ and 320℃; the welding time can be 2s, 2.1s, 2.2s, 2.3s, 2.4s, 2.5s, 2.6s, 2.7s, 2.8s, 2.9s, 3s, or any value between 2 and 3s.

[0047] In an optional embodiment, the thickness of the second IMC layer is 1-3 μm.

[0048] Optionally, the thickness of the second IMC layer can be 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3μm, or any value between 1 and 3μm.

[0049] Understandably, during the curing stage of this application, the temperature of 140-160℃ is relatively low, resulting in a lower diffusion rate for Cu and Sn. Therefore, the thickness of the grown IMC layer is typically 0.1-1µm. During the soldering stage, the temperature is higher, and the IMC layer is thicker, ranging from 1-5µm. This method ensures that the tin layer of the interconnects achieves good ohmic contact and mechanical properties through the tin-copper layer connecting the copper paste surface during the encapsulation process.

[0050] Secondly, this application also provides a copper paste metallized interconnect electrode, which is prepared according to the preparation method of the copper paste metallized interconnect electrode.

[0051] Thirdly, this application also provides a photovoltaic system including the electrodes with copper paste metallized interconnects.

[0052] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0053] Example 1 This application provides a method for fabricating electrodes with copper paste metallized interconnects, the specific steps of which are as follows: Copper paste and solder paste are applied to the target welding area on the surface of the battery cell, with a solder paste thickness of not less than 5 μm. The solder paste is a tin-bismuth mixture Sn90 Bi10 (90% tin, 10% bismuth), with a particle size of 30 μm and a viscosity of 180 Pa·s (25℃, 10 rpm).

[0054] After the solder paste is printed, the battery cell is sent into a low-temperature curing oven. The oven is first evacuated and then filled with nitrogen as a protective gas. The temperature is 150°C and the curing is carried out for 30 minutes to form the first IMC layer of solder paste and copper. The first IMC layer includes Cu6Sn5 and has a thickness of 0.2μm.

[0055] Solder strips are laid on the solar cell and a clamping fixture is placed. High-temperature welding is then performed for 2.0 seconds at 280°C using contact welding or infrared welding, linking the interconnect strips to the solar cell through a high-temperature metallization process. During the welding process, solder paste and copper form a second IMC layer, which consists of Cu6Sn5 and Cu3Sn, with a thickness of 1 μm. After welding, copper paste metallized interconnect electrodes are obtained.

[0056] Microscopic images of the cross-section after welding are shown below. Figure 3 As shown; Figure 3 The energy spectrum of point A is as follows Figure 4 As shown; Figure 3 The energy spectrum at point B is as follows Figure 5 As shown; Figure 3 The energy spectrum at point C is as follows Figure 6 As shown.

[0057] Example 2 This application provides a method for fabricating electrodes with copper paste metallized interconnects, the specific steps of which are as follows: Copper paste and solder paste are applied to the target welding area on the surface of the solar cell, with the solder paste thickness not less than 5 μm. The solder paste is a tin-bismuth mixture Sn90 Bi10 with a particle size of 30 μm and a viscosity of 200 Pa·s.

[0058] After the solder paste is printed, the battery cell is sent into a low-temperature curing oven. The oven is first evacuated and then filled with nitrogen as a protective gas. The temperature is 150°C and the curing is carried out for 45 minutes to form the first IMC layer of solder paste and copper. The first IMC layer includes Cu6Sn5 and has a thickness of 0.3μm.

[0059] Solder strips are laid on the solar cell and a clamping fixture is placed. High-temperature soldering is then performed for 2.5 seconds at 300°C using either contact soldering or infrared soldering, linking the interconnect strips to the solar cell through a high-temperature metallization process. During the soldering process, solder paste and copper form a second IMC layer, which consists of Cu6Sn5 and Cu3Sn, with a thickness of 3μm. After soldering, electrodes with copper paste metallized interconnects are obtained.

[0060] Example 3 This application provides a method for fabricating electrodes with copper paste metallized interconnects, the specific steps of which are as follows: Copper paste and solder paste are applied to the target welding area on the surface of the solar cell, with the solder paste thickness not less than 5 μm. The solder paste is a tin-bismuth mixture Sn90 Bi10 with a particle size of 30 μm and a viscosity of 200 Pa·s.

[0061] After the solder paste is printed, the battery cell is sent into a low-temperature curing oven. The oven is first evacuated and then filled with nitrogen as a protective gas. The temperature is 150°C and the curing is carried out for 60 minutes to form the first IMC layer of solder paste and copper. The first IMC layer includes Cu6Sn5 and has a thickness of 1μm.

[0062] Solder strips are laid on the solar cell and a clamping fixture is placed. High-temperature welding is then performed for 3 seconds at 320°C using either contact welding or infrared welding, linking the interconnect strips to the solar cell through a high-temperature metallization process. During the welding process, solder paste and copper form a second IMC layer, which consists of Cu6Sn5 and Cu3Sn, with a thickness of 4μm. After welding, copper paste metallized interconnect electrodes are obtained.

[0063] Comparative Example 1 This comparative example provides a method for preparing copper paste metallized interconnect electrodes. The specific steps are as follows: tin is electroplated onto the surface of silver paste or copper paste at the welding points of the battery cell. The surface is then heated to 260-320℃ by contact welding or infrared welding for a high-temperature effective welding time of 0.8-1.5 seconds, so that the interconnect strip and the battery cell are linked together through a high-temperature metallization process. The thickness of the alloy layer after welding is approximately 3-4 μm.

[0064] Comparative Example 2 Copper paste and solder paste are applied to the target welding area on the surface of the battery cell, with the solder paste thickness not less than 5 μm. The solder paste is a tin-bismuth mixture Sn90 Bi10 with a particle size of 30 μm and a viscosity of 200 Pa·s.

[0065] The printed solder paste on the battery cells is placed in a low-temperature curing oven. The oven is first evacuated and then filled with nitrogen as a protective gas. The temperature is 150°C, and the curing process lasts for 30 minutes to form the first IMC layer between the solder paste and copper. The first IMC layer consists of Cu6Sn5 and has a thickness of 0.1 μm. Electrodes with copper paste metallized interconnects are obtained.

[0066] Comparative Example 3 Copper paste and solder paste are applied to the target welding area on the surface of the battery cell, with the solder paste thickness not less than 5 μm. The solder paste is a tin-bismuth mixture Sn90 Bi10 with a particle size of 30 μm and a viscosity of 200 Pa·s.

[0067] Solder strips are laid on the solar cell and a clamping fixture is placed. High-temperature welding is then performed for 2 seconds at 300°C using contact welding or infrared welding, linking the interconnect strips to the solar cell through a high-temperature metallization process. During the welding process, solder paste and copper form a second IMC layer, which consists of Cu6Sn5 and Cu3Sn, with a thickness of 1μm. After welding, electrodes with copper paste metallized interconnects are obtained.

[0068] The performance of the metallized interconnect electrodes prepared in the examples and comparative examples is shown in Table 1.

[0069] Table 1. Electrode performance of the examples and comparative examples.

[0070] As shown in Table 1, the thickness of the IMC layer during the welding process determines the electrical and mechanical properties after welding. The effective IMC layer thickness after welding needs to be ≥3μm to ensure the effectiveness of the welding.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0072] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing an electrode for copper paste metallization interconnection, characterized in that, include: Copper paste and solder paste are sequentially applied to the target welding area on the surface of the battery cell; the mixture is then cured under the protection of an inert gas to obtain the first IMC layer. A welding process is performed to obtain a second IMC layer on the surface of the first IMC layer, thus obtaining the copper paste metallized interconnect electrode; The first IMC layer includes Cu6Sn5; the second IMC layer includes Cu6Sn5 and Cu3Sn.

2. The production method according to claim 1, characterized by, The solder paste is a mixture of tin and bismuth.

3. The production method according to claim 2, characterized by, At least one of the following conditions must be met: a. The particle size of the solder paste is 25-45 μm; b. The viscosity of the solder paste is 180–250 Pa·s.

4. The method of claim 1, wherein, The thickness of the solder paste is not less than 5 μm.

5. The preparation method according to claim 1, characterized in that, The curing process satisfies at least one of the following conditions: c. The inert gas includes nitrogen; d. The curing temperature is 140-160℃ and the time is 30-60min.

6. The preparation method according to claim 1, characterized in that, The thickness of the first IMC layer is 0.1-1 μm.

7. The preparation method according to claim 1, characterized in that, The welding process is performed at a temperature of 280-320℃ for 2-3 seconds.

8. The preparation method according to any one of claims 1-7, characterized in that, The thickness of the second IMC layer is 1-3 μm.

9. An electrode for copper paste metallization interconnection, characterized in that, It is prepared according to any one of claims 1-8.

10. A photovoltaic system, characterized in that, The electrodes include those with copper paste metallized interconnects as described in claim 9.

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