A metal electrode for a solar cell, a solar cell, and a photovoltaic module

Abstract

The utility model relates to the technical field of solar energy, disclose a kind of metal electrode for solar cell, solar cell and photovoltaic module.The metal electrode includes: be located in the metal seed layer (it is at least one layer in silver seed layer, nickel seed layer, zirconium seed layer, titanium seed layer, chromium seed layer, nickel silicon alloy seed layer, copper alloy seed layer) of silicon matrix surface grid line area, be located in the base metal grid line (it is copper grid line and / or aluminum grid line) of metal seed layer surface, and be located in the copper phosphate protective layer (it is copper phosphate layer and / or organic copper phosphate compound layer) of base metal grid line surface.The metal electrode is cooperated by metal seed layer, base metal grid line (such as copper grid line) and copper phosphate protective layer, can reduce contact resistance and ensure interface bonding force, can also save cost, can also improve the corrosion resistance of base metal grid line, the stability and reliability of the metal electrode long-term use outdoors are improved, and battery efficiency decay is slowed down.

Description

Technical Field

[0001] This utility model relates to the field of solar energy technology, specifically to a metal electrode for solar cells, a solar cell, and a photovoltaic module. Background Technology

[0002] Currently, a feasible approach is the base metal substitution method, such as using inexpensive base metals like copper and aluminum instead of silver to make the metal grid lines of solar cells. For example, silver paste (used to make silver grid lines, with a price of 8,000-9,000 yuan / kg) is about 150 times the price of copper (which costs around 60 yuan / kg).

[0003] However, although copper electrodes are cheaper, their conductivity is slightly worse than that of silver electrodes (silver electrodes have a conductivity of 62.1 × 10⁻⁶). 6 The conductivity is approximately S / m, while the conductivity of the copper electrode is 59.6 × 10⁻⁶. 6 The contact resistance of copper electrodes is around S / m, and the bonding performance of copper electrodes on the silicon surface is poor. Therefore, when using copper as an electrode to contact the silicon of a crystalline silicon solar cell, the contact resistance will increase, leading to current loss, and may even cause delamination or peeling, resulting in a decrease in cell efficiency.

[0004] Currently, a feasible approach is partial substitution, such as using silver-clad copper or silver wire-plated copper to fabricate the metal electrodes. For example, as shown in publication CN119593028A, silver wire-plated copper involves using screen printing to create a low-profile silver wire on the battery surface as a contact layer with the silicon surface. The high conductivity and low resistance of silver reduce contact resistance and loss. Copper is then electroplated onto the silver wire surface, using copper as the current-carrying material. While this method minimizes silver consumption while ensuring sufficient contact, copper is more reactive than silver, resulting in poorer corrosion resistance. In outdoor photovoltaic modules, they face industrial pollution (sulfur dioxide, nitrogen oxides, etc. emitted from industrial areas), salt spray in coastal areas, EVA film hydrolysis, water vapor permeation, and high temperature and humidity. Compared to silver grid lines, copper grid lines are significantly more susceptible to corrosion. Therefore, the existing technology, such as silver wire copper plating, does not provide a good protection method and cannot ensure that the copper grid line can remain stable during the 30-year outdoor use cycle of photovoltaic modules, resulting in the degradation of battery efficiency. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a metal electrode for solar cells, a solar cell, and a photovoltaic module.

[0006] Based on this, the present invention discloses a metal electrode for solar cells, comprising a metal seed layer in a grid region disposed on the surface of a silicon substrate, base metal grid lines disposed on the surface of the metal seed layer, and a copper phosphate protective layer disposed on the surface of the base metal grid lines.

[0007] The metal seed layer is at least one of the following: silver seed layer, nickel seed layer, zirconium seed layer, titanium seed layer, chromium seed layer, nickel-silicon alloy seed layer, and copper alloy seed layer.

[0008] The base metal grid lines are copper grid lines and / or aluminum grid lines;

[0009] The copper phosphate protective layer is a copper phosphate layer and / or an organocopper phosphate composite layer.

[0010] Preferably, the metal seed layer is a silver seed layer with a thickness of 0.8-1.2 μm.

[0011] Preferably, the base metal grid line is a copper grid line with a height of 8-15 μm.

[0012] Preferably, the copper phosphate protective layer is a copper phosphate layer with a thickness of 8-12 nm.

[0013] Preferably, the copper phosphate protective layer is an organocopper phosphate composite layer with a thickness of 8-12 nm.

[0014] More preferably, the organophosphate copper composite layer is a Cu3(PO4)2·copper phytate composite layer.

[0015] More preferably, a nickel transition layer is provided between the base metal gate line and the copper phosphate protective layer, and the thickness of the nickel transition layer is 8-15 nm.

[0016] More preferably, the silicon substrate includes: a silicon wafer and a passivation film disposed on the front and / or back sides of the silicon wafer; the gate area of ​​the passivation film has an open film region that locally exposes the silicon substrate, and the metal electrode contacts the silicon substrate through the open film region.

[0017] More preferably, the silicon substrate further includes a doped silicon layer disposed between the silicon wafer and the passivation film.

[0018] This utility model also discloses a solar cell, which includes: a silicon substrate, and metal electrodes disposed on the front and / or back sides of the silicon substrate;

[0019] The silicon substrate includes: a silicon wafer and a passivation film disposed on the front and / or back sides of the silicon wafer;

[0020] The metal electrode is the same as the metal electrode for solar cells described above in this utility model.

[0021] This utility model also discloses a photovoltaic module, which includes a solar cell as described above.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] This invention utilizes the high stability of copper phosphate in humid or weakly acidic environments to prepare a copper phosphate protective layer on the surface of base metal grid lines, thereby improving the corrosion resistance of base metal grid lines such as copper grid lines. Therefore, the metal electrode of this invention, through the synergy of a metal seed layer (especially a silver seed layer), base metal grid lines (especially copper grid lines), and a copper phosphate protective layer, can reduce contact resistance and ensure interfacial adhesion to prevent detachment, while significantly reducing silver consumption and saving costs. It also enhances the corrosion resistance of base metal grid lines such as copper grid lines, improving their stability and increasing the reliability of non-silver metal electrodes for long-term outdoor use. This effectively slows down the degradation of battery photoelectric conversion efficiency (i.e., battery efficiency degradation) after metal electrode corrosion. Furthermore, the preparation of the metal electrode of this invention does not require additional investment in new equipment; it can be directly implemented on existing equipment (electroplating equipment), saving equipment investment costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the cross-sectional structure of a solar cell according to the present invention.

[0025] Reference numerals: 1. Silicon substrate; 10. Silicon wafer; 11. p+ emitter; 12. Alumina film; 13. Front silicon nitride film; 14. Silicon oxide tunneling layer; 15. n+ polycrystalline silicon layer; 16. Back silicon nitride film; 2. Metal electrode; 20. Metal seed layer; 21. Base metal gate line; 22. Nickel transition layer; 23. Copper phosphate protective layer. Detailed Implementation

[0026] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This utility model discloses a metal electrode 2 for a solar cell, see [link]. Figure 1 It includes a metal seed layer 20 on the surface of the silicon substrate 1, a base metal gate line 21 on the surface of the metal seed layer 20, and a copper phosphate protective layer 23 on the surface of the base metal gate line 21.

[0028] The metal seed layer 20 can be at least one of the following: silver seed layer, nickel seed layer, zirconium seed layer, titanium seed layer, chromium seed layer, nickel-silicon alloy seed layer, and copper alloy seed layer. The metal seed layer 20 has two main purposes: first, to enhance adhesion or bonding force, so that the metal grid lines can better adhere to the battery surface and prevent them from falling off; and second, to reduce contact resistance.

[0029] In this invention, to reduce contact resistance, the metal seed layer 20 is preferably a silver seed layer with the best conductivity. The thickness of the metal seed layer 20 is 0.8-1.2 μm (e.g., 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm or 1.2 μm).

[0030] Wherein, the base metal grid line 21 is a copper grid line and / or an aluminum grid line. The base metal grid line 21 is preferably a copper grid line with a height of 8-15 μm (e.g., 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm).

[0031] The copper phosphate protective layer 23 is a copper phosphate layer and / or an organocopper phosphate composite layer. For example, the copper phosphate protective layer 23 is a copper phosphate layer; the thickness of the copper phosphate layer is 8-12 nm (e.g., 8 nm, 9 nm, 10 nm, 11 nm or 12 nm).

[0032] The main acid generated during the use of photovoltaic modules comes from acetic acid produced by the hydrolysis of EVA film. Secondary acids come from the hydrolysis of sulfides and nitrogen oxides in the air. Therefore, copper phosphate can serve as an excellent protective layer for base metal grid lines 21, mainly based on the following:

[0033] 1. Copper phosphate is extremely stable in humid or weakly acidic environments and hardly reacts. Copper phosphate can dissolve in strong acids, but it is extremely resistant to weak acids, such as dilute acetic acid.

[0034] 2. Phosphate has high chemical inertness. Copper phosphate can effectively prevent the copper grid wires from reacting with sulfides in the air (such as H2S and SO2) to form Cu2S, which has poor conductivity, and can also effectively prevent the corrosion of copper grid wires by low concentrations of nitrogen oxides in the air (such as NO and NO2). Although other copper compounds (such as Cu2S, Cu2O, CuI, CuCl, CuBr, etc.) have slightly better conductivity than copper phosphate, copper phosphate can prevent the copper grid wires from transforming into other copper compounds because these other copper compounds have their own harmful effects. For example, Cu2S has poor stability and will decompose at high temperatures and humidity, and it will absorb light, affecting the light absorption rate of the solar cell. As another example, Cu2O, as an alkaline oxide, is easily corroded by acetic acid, which will lead to the corrosion of the copper grid wires. Furthermore, CuI (copper halides, including CuI, CuCl, CuBr, etc.) is extremely easy to decompose under light conditions and is unstable. Even with various technical means, its existence time under light conditions is only a few days, which will lead to the corrosion of the copper grid wires. Furthermore, the copper phosphate protective layer is extremely thin (only 8-12 nm thick), so it does not affect the conductivity of the copper grid lines, which serve as the conductive substrate of the metal electrode 2. Therefore, compared to other copper compounds (such as Cu2S, Cu2O, CuI, CuCl, CuBr, etc.), the copper phosphate protective layer 23 is preferred.

[0035] 3. The crystal structure of copper phosphate can lock in base metal ions (such as copper ions), reducing the risk of migration and producing an effect similar to field passivation.

[0036] 4. Copper phosphate has weak absorption in the visible light range and will not cause light loss like Cu2S. Even if a small amount of copper phosphate protective layer 23 is attached outside the copper grid area when it is prepared on the copper grid line, the absorption of sunlight by the copper phosphate protective layer 23 is very small, which helps to improve the light absorption and light utilization of the solar cell.

[0037] 5. Copper phosphate is an environmentally friendly and non-toxic material that is easy to prepare.

[0038] Therefore, this invention utilizes the characteristic of copper phosphate's extremely high stability in humid or weakly acidic environments to prepare a copper phosphate protective layer 23 on the surface of the base metal grid line 21, thereby improving the corrosion resistance of the base metal grid line 21, such as the copper grid line. Thus, the metal electrode 2 of this invention, through the synergistic effect of the aforementioned metal seed layer 20 (especially the silver seed layer), the base metal grid line 21 (especially the copper grid line), and the copper phosphate protective layer 23, can reduce contact resistance, significantly reduce silver consumption and lower costs, and also improve the corrosion resistance of the base metal grid line 21, such as the copper grid line. This enhances the stability of the base metal grid line 21 and improves the reliability of the non-silver metal electrode 2, thereby effectively slowing down the degradation of the battery's photoelectric conversion efficiency after the metal electrode 2 is corroded.

[0039] Furthermore, under high temperature and high humidity (85℃ / 85% humidity), the copper phosphate layer may slowly hydrolyze to form copper hydroxyphosphate Cu2(OH)PO4, thus losing its corrosion resistance. Therefore, the copper phosphate protective layer 23 is preferably an 8-12 nm thick organocopper phosphate composite layer (such as a Cu3(PO4)2·copper phytate composite layer) to improve its corrosion resistance, adhesion, and functionality. The mechanism of action of the organocopper phosphate composite layer is as follows: the hydrophobicity and chelating ability of organophosphates can compensate for the instability of copper phosphate under strong humid and hot environments and reduce the peeling of protective layers such as the copper phosphate layer.

[0040] Taking the Cu3(PO4)2·copper phytate complex layer as an example, the multiple phosphate groups (-PO4) of phytic acid in the complex... 3- Cu on the surface of Cu3(PO4)2 2+ Or PO4 3- Vacancy bonding forms a core-shell structure (Cu3(PO4)2·copper phytate complex). At this time, the hydrophobic carbon chains of phytic acid are arranged outward, giving the complex hydrophobicity (contact angle >90°), thereby reducing water vapor accumulation and ultimately further reducing corrosion and preventing the protective layer from peeling off.

[0041] Furthermore, the copper phosphate protective layer 23 (especially the copper phosphate layer) and the base metal gate line 21 (such as the copper gate line) have different coefficients of thermal expansion (the coefficient of thermal expansion of the copper gate line is 17 ppm / ℃; while the coefficient of thermal expansion of the copper phosphate layer is even lower, in the range of 4-10 ppm / ℃), which may cause cracking or peeling of the copper phosphate layer on the surface of the copper gate line. Therefore, this invention preferably provides a nickel transition layer 22 between the base metal gate line 21 and the copper phosphate protective layer 23 to enhance the interfacial adhesion. The thickness of the nickel transition layer 22 is 8-15 nm (such as 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm or 15 nm).

[0042] The nickel transition layer 22 can improve the mechanical adhesion of the copper phosphate protective layer 23 to the surface of the base metal grid line 21, such as the copper grid line. This is mainly because the difference in the coefficients of thermal expansion between the copper grid line and the copper phosphate layer is large. Temperature changes can cause significant mechanical stress between the copper grid line and the copper phosphate layer, potentially leading to the detachment of the copper phosphate layer. The coefficient of thermal expansion of the copper grid line is 17 ppm / ℃; while the coefficient of thermal expansion of the copper phosphate layer is even lower, in the range of 4-10 ppm / ℃; the coefficient of thermal expansion of C70600 copper alloy (90% Cu, 10% Ni) is 16.2 ppm / ℃, the coefficient of thermal expansion of CuNi34 alloy (57% Cu, 34% Ni) is 13.5 ppm / ℃, and the coefficient of thermal expansion of the nickel transition layer 22 is 13.4 ppm / ℃. The nickel transition layer 22 has a coefficient of thermal expansion between the copper grid lines and the copper phosphate layer, thus serving as a transition layer. Furthermore, the nickel transition layer 22 can form chemical bonds with both the copper grid lines and the copper phosphate layer, achieving chemical bonding. In addition, the high surface roughness of the nickel transition layer 22 increases its contact area with the copper grid lines and the copper phosphate layer, enhancing its mechanical anchoring. Therefore, adding a nickel transition layer 22 can reduce the mechanical stress generated during temperature changes and improve the adhesion between the base metal grid lines 21 (e.g., copper grid lines) and the copper phosphate protective layer 23.

[0043] The silicon substrate 1 includes a silicon wafer 10 and passivation films disposed on the front and / or back sides of the silicon wafer 10; the passivation film is preferably an aluminum oxide film 12 and / or a silicon nitride film; the gate area of ​​the passivation film has an open film region that locally exposes the silicon substrate 1, and the metal electrode 2 contacts the silicon substrate 1 through the open film region. The passivation film is preferably an aluminum oxide film 12 and / or a silicon nitride film.

[0044] Furthermore, the silicon substrate 1 also includes a doped silicon layer disposed between the silicon wafer 10 and the passivation film.

[0045] Taking TOPCon batteries as an example, such as Figure 1As shown, the silicon substrate 1 includes: a silicon wafer 10, a front-side doped silicon layer (such as a p+ emitter 11 on the front side of the silicon wafer 10) and a front-side passivation film (such as an aluminum oxide film 12 and a front-side silicon nitride film 13 on the front side of the p+ emitter 11) sequentially disposed on the front side of the silicon wafer 10, and a back-side doped silicon layer (such as a silicon oxide tunneling layer 14 and an n+ polysilicon layer 15 on the back side of the silicon wafer 10) and a back-side passivation film (such as a back-side silicon nitride film 16 on the back side of the n+ polysilicon layer 15) sequentially disposed on the back side of the silicon wafer 10. Furthermore, since the TOPCon cell has metal electrodes 2 on both the front and back sides, the grid line area of ​​the front passivation film has a front open film area that locally exposes the p+ emitter 11, so that the front metal electrode 2 contacts the p+ emitter 11 through the front open film area; the grid line area of ​​the back passivation film has a back open film area that locally exposes the n+ polycrystalline silicon layer 15, so that the back metal electrode 2 contacts the n+ polycrystalline silicon layer 15 through the back open film area.

[0046] Of course, the metal electrode 2 for solar cells of this invention can be used not only in TOPCon cells, but also in other types of solar cells in the photovoltaic industry.

[0047] The present invention discloses a method for preparing a metal electrode 2 for a solar cell, comprising the following preparation steps:

[0048] Step S1: Prepare silicon substrate 1.

[0049] Step S2: Fabricating a metal electrode 2 on the surface of the silicon substrate 1, specifically including:

[0050] Step S21: Open the passivation film of the predetermined gate line region on the surface of the silicon substrate 1 to form an open film region of the locally exposed silicon surface (such as the p+ emitter 11 surface and the n+ polysilicon layer 15 surface).

[0051] Step S22: Sequentially prepare a metal seed layer 20, a base metal gate line 21, and a copper phosphate protective layer 23 on the silicon surface of the open film region to obtain the metal electrode 2.

[0052] Specifically, the metal seed layer 20 can be prepared by direct sputtering or electroplating. After electroplating to prepare the metal seed layer 20, the silicon substrate 1 is cleaned with water (preferably deionized water) (optimally ultrasonic cleaning) before the base metal gate line 21 is prepared.

[0053] The following example uses a silver seed layer for electroplating. The electroplating solution can be formulated as follows: the mass ratio of silver nitrate, EDTA (ethylenediaminetetraacetic acid), glucose, and deionized water is 1.5-3:20:10:1000. The electroplating temperature is 60-70℃, the electroplating time is 3-8 minutes, and the pH of the electroplating solution is 10-10.5 (adjusted with an alkaline solution such as KOH).

[0054] Specifically, the base metal gate line 21 is prepared by methods including but not limited to electroplating. After electroplating to prepare the base metal gate line 21, the silicon substrate 1 is cleaned sequentially with ethanol, dilute hydrochloric acid and water (preferably deionized water) (optimally ultrasonic cleaning) to remove grease, oxide layer and electroplating solution residues from the surface of the silicon substrate 1.

[0055] The following example uses electroplated copper grid lines, which consists of two steps: the first step is pre-plating with neutral copper, and the second step is standard acid copper electroplating.

[0056] The first step is pre-plating with neutral copper. The electroplating solution formula is as follows: copper citrate, sodium citrate, boric acid, sodium sulfate, antioxidant, and deionized water in a mass ratio of 18-25:90-120:20:10:0.1:1000. The pH is controlled at 6.8-7.2 (adjusted with KOH or H3PO4), the electroplating temperature is 25-30℃, and the DC pulse current density is 1.0-1.5A / dm³. 2 The electroplating time is 2-3 minutes.

[0057] The second step is standard acid copper electroplating, with the following plating solution formula: copper sulfate, sulfuric acid, potassium chloride, sodium citrate, antioxidant, and deionized water in a mass ratio of 180-250:30:0.05:10:0.1:1000; the plating temperature is 25-30℃; the current mode is pulsed reverse current, and the forward current density is 5-15 A / dm³. 2 The reverse current density is 20-40 A / dm². 2 The forward current accounts for 90% and the reverse current accounts for 10%; the electroplating time is 10-12 minutes. After the base metal grid line 21 of the copper grid line is prepared, the silicon substrate 1 is ultrasonically cleaned sequentially with ethanol, dilute hydrochloric acid (HCl volume percentage content is 5-10%) and deionized water to remove grease, oxide layer and electroplating solution residues on the surface of the silicon substrate 1.

[0058] Specifically, the preparation methods of copper phosphate layers include, but are not limited to, electroplating. The following uses the electroplating of copper phosphate layers as an example to illustrate the electroplating process: First, a phosphate electrolyte is prepared, with the following basic formula: including 0.2-0.4 mol / L K3PO4 and 0.1-0.2 mol / L H3PO4 (pH 3-5, adjusted with H3PO4 or KOH); then an oxidizing agent (such as H2O2, accounting for 0.05-0.1% of the total volume of the phosphate electrolyte) is added to accelerate copper dissolution and film formation; then a corrosion inhibitor (such as benzotriazole, accounting for 0.01-0.02% of the total volume of the phosphate electrolyte) is added to control the reaction rate and improve the uniformity of the film.

[0059] It should be noted that oxidants in electroplating solutions or electrolytes primarily maintain the reduction potential of metal ions, promote metal deposition, and affect the uniformity of the coating. In practice, other oxidants can also be selected, such as persulfates (e.g., ammonium persulfate). The core function of corrosion inhibitors is to protect the silicon substrate 1 and the metal layer from corrosion by the electroplating solution or electrolyte, while ensuring the accurate morphology of base metal grid lines 21, such as copper grid lines. Other corrosion inhibitors can also be selected, including silicates (e.g., Na₂SiO₃), azole compounds (e.g., mercaptobenzothiazole), or amines (e.g., hexadecaneamine).

[0060] After preparing the phosphate electrolyte, a constant voltage of +0.5V to +1.5V is applied, and electroplating is performed at room temperature for 60-90 seconds. The following reaction is achieved through electroplating:

[0061] 3Cu + 2PO4 3- →Cu3(PO4)2+6e - A copper phosphate layer can then be electroplated onto the surface of the base metal grid line 21, such as the copper grid line. After the reaction is complete, the surface is rinsed with water (preferably deionized water) and then dried with hot nitrogen gas to complete the preparation of the metal electrode 2, thus obtaining the solar cell.

[0062] Specifically, if both the base metal grid line 21 and the metal seed layer 20 are non-copper materials, then when preparing the copper phosphate layer on the surface of the base metal grid line 21, copper salts such as copper pyrophosphate need to be added to the electroplating solution as a copper source. The electroplating solution formula is as follows (taking copper pyrophosphate as the copper source): the mass ratio of copper pyrophosphate, potassium pyrophosphate, dipotassium hydrogen phosphate, potassium citrate, and deionized water is 60-100:240-400:50:20:1000; the pH of the electroplating solution is 8.5-8.8 (adjusted with H3PO4 or KOH); the electroplating temperature is 50-55℃; and the cathode current density is 1-5 A / dm³. 2 The electroplating time is 90-100 seconds. Mechanical stirring must be carried out during the electroplating process to prevent precipitation and local changes in copper ion concentration.

[0063] Specifically, the preparation methods for the organocopper phosphate composite layer include, but are not limited to, electroplating, solution co-precipitation, hydrothermal methods, or physical mixing. The thickness of the organocopper phosphate composite layer is 8-12 nm (e.g., 8 nm, 9 nm, 10 nm, 11 nm, or 12 nm). The organocopper phosphate composite layer includes, but is not limited to, the copper phytate composite layer: Cu3(PO4)2·copper phytate composite layer. The following uses the electroplating of the Cu3(PO4)2·copper phytate composite layer as an example to illustrate its electroplating process in detail:

[0064] In the above phosphate electrolyte, the following organic phase is additionally added: phytic acid (C6H3O3) from this organic phase. 18 O24 P6) and Cu 2+ Prepare the electroplating solution by mixing at a molar ratio of 1:5-8. Adjust the pH of the electroplating solution to 4.5-5.5 using KOH to avoid excessive acidity and phytic acid precipitation. Adjust the constant voltage to +0.5V to +1.0V and increase the electroplating time to 3 minutes (150-200 seconds) at room temperature (to avoid phytic acid precipitation due to excessive acidity of the solution, the acidity of the electroplating solution is reduced, so the time needs to be slightly increased). This allows the phosphate groups of copper phytate to bond with the surface of Cu3(PO4)2 through coordination bonds or hydrogen bonds, thereby electroplating a Cu3(PO4)2·copper phytate composite layer on the surface of base metal grid lines 21, such as copper grid lines.

[0065] Furthermore, in step S22, before preparing the copper phosphate protective layer 23, a nickel transition layer 22 is prepared on the surface of the base metal gate line 21. The preparation method of the nickel transition layer 22 includes, but is not limited to, electroplating, as detailed in the prior art, and will not be elaborated here.

[0066] In practice, the preparation process of the front metal electrode 2 and / or the back metal electrode 2 is the same as the above steps S21-22, so it will not be described in detail here.

[0067] The present invention provides a solar cell comprising: a silicon substrate 1, and metal electrodes 2 disposed on the front and / or back sides of the silicon substrate 1 (i.e., the metal electrodes 2 include a front metal electrode 2 and / or a back metal electrode 2); the metal electrodes 2 are the metal electrodes 2 for solar cells described above in the present invention.

[0068] The present invention provides a photovoltaic module, which includes a solar cell as described above.

[0069] The following embodiments use TOPCon batteries as an example. Figure 1 As shown, a metal electrode 2, a solar cell having the metal electrode 2, and a method for preparing the present invention will be specifically described below:

[0070] Example 1

[0071] This embodiment describes a method for fabricating a solar cell, see [link to relevant documentation]. Figure 1 It includes the following preparation steps:

[0072] Step 1: The silicon wafer 10 is processed as follows: texturing, front diffusion to prepare p+ emitter 11, cleaning and back polishing, back passivation contact structure (including silicon oxide tunneling layer 14 and n+ polysilicon layer 15) is prepared on the back side, and passivation film is deposited (for example, the front passivation film is aluminum oxide film 12 and front silicon nitride film 13 sequentially disposed on the front side of p+ emitter 11, and the back passivation film is back silicon nitride film 16 disposed on the back side of n+ polysilicon layer 15) to obtain silicon substrate 1.

[0073] The above-mentioned processing procedures in step 1 all refer to the existing TOPCon battery preparation technology, so they will not be described in detail here.

[0074] Step 2: Prepare the front metal electrode 2 that contacts the p+ emitter 11, and prepare the back metal electrode 2 that contacts the n+ polycrystalline silicon layer 15. The specific preparation steps for the front metal electrode 2 and the back metal electrode 2 include:

[0075] Step 21: Use a laser to open the front passivation film of the predetermined gate line area on the front side of the silicon substrate 1 to form a front open film area that locally exposes the p+ emitter 11; and use a laser to open the back passivation film of the predetermined gate line area on the back side of the silicon substrate 1 to form a back open film area that locally exposes the n+ polysilicon layer 15.

[0076] Step 22: Prepare a front silver seed layer on the p+ emitter 11 surface of the front open film area by electroplating, and prepare a back silver seed layer on the n+ polysilicon layer 15 surface of the back open film area by electroplating; the thickness of the front silver seed layer and the back silver seed layer is 1 μm; clean the silicon substrate 1 with deionized water.

[0077] In step 22, taking the preparation of the front silver seed layer by electroplating as an example, the electroplating solution formula is as follows: the mass ratio of silver nitrate, EDTA (ethylenediaminetetraacetic acid), glucose and deionized water is 2:20:10:1000, the electroplating temperature is 60℃, the electroplating time is 5min, and the pH of the electroplating solution is 10.5 (adjusted with KOH).

[0078] The preparation process of the silver seed layer on the back side is the same as the electroplating method of the silver seed layer on the front side, so it will not be described in detail.

[0079] Step 23: Then, replace the electroplating solution and electroplat the front copper grid lines and the back copper grid lines on the front silver seed layer surface and the back silver seed layer surface, respectively; the height of the front copper grid lines and the back copper grid lines is 10μm.

[0080] Step 23, taking the electroplating preparation of the front copper grid lines as an example, consists of two steps: the first step is pre-plating with neutral copper, and the second step is standard acid copper electroplating.

[0081] The first step is pre-plating with neutral copper. The electroplating solution formula is as follows: copper citrate, sodium citrate, boric acid, sodium sulfate, antioxidant, and deionized water in a mass ratio of 20:100:20:10:0.1:1000. The pH is controlled at 7.0 (adjusted with KOH or H3PO4), the electroplating temperature is 25℃, and the DC pulse current density is 1.0 A / dm³. 2 The electroplating time is 150 seconds.

[0082] The second step is standard acid copper electroplating, with the following plating solution formula: copper sulfate, sulfuric acid, potassium chloride, sodium citrate, antioxidant, and deionized water in a mass ratio of 200:30:0.05:10:0.1:1000; the plating temperature is 25℃; the current mode is pulsed reverse current, and the forward current density is 10A / dm³. 2 The reverse current density is 20 A / dm. 2 The forward current accounts for 90% and the reverse current accounts for 10%; the electroplating time is 10 minutes. After the front and back copper grid lines are prepared, the silicon substrate 1 is ultrasonically cleaned sequentially with ethanol, dilute hydrochloric acid (HCl volume percentage is 5%), and deionized water to remove grease, oxide layer, and electroplating solution residues from the surface of the silicon substrate 1.

[0083] The preparation process of the copper grid lines on the back side is the same as the electroplating method of the copper grid lines on the front side, so it will not be described in detail.

[0084] It should be noted that there are multiple methods for preparing the silver seed layer in step 22 and the copper grid lines in step 23, and the electroplating solutions and processes used for electroplating the silver seed layer and copper grid lines are also varied; in this embodiment, steps 22-23 above only provide an example of one electroplating process for preparing the silver seed layer and copper grid lines. Of course, other existing processes for preparing the silver seed layer and copper grid lines are also feasible.

[0085] Step 24: Then, the following process is used to electroplate a front copper phosphate layer and a back copper phosphate layer on the front copper grid line surface and the back copper grid line surface, respectively; the thickness of the front copper phosphate layer and the back copper phosphate layer is 10 nm.

[0086] In step 24, taking the electroplating preparation of the front copper phosphate layer as an example, the electroplating process is explained in detail:

[0087] First, a phosphate electrolyte is prepared with the following basic formula: 0.2 mol / L K₃PO₄ and 0.1 mol / L H₃PO₄ (pH 3.5, adjusted with H₃PO₄ or KOH). Then, an oxidant (such as H₂O₂, accounting for 0.05% of the total volume of the phosphate electrolyte) is added to accelerate copper dissolution and film formation. Next, a corrosion inhibitor (such as benzotriazole, accounting for 0.01% of the total volume of the phosphate electrolyte) is added to control the reaction rate and improve film uniformity. Using this phosphate electrolyte, a constant voltage of +1.0V is applied, and electroplating is performed at room temperature for 1 minute. The following reaction is achieved through electroplating:

[0088] 3Cu + 2PO4 3- →Cu3(PO4)2+6e - This allows for the electroplating of a copper phosphate layer onto the surface of the front copper grid lines.

[0089] The preparation process of the back copper phosphate layer is the same as the electroplating method of the front copper phosphate layer described above, and therefore will not be repeated here. After the reaction is complete, rinse thoroughly with deionized water and then dry with hot nitrogen gas; by following steps 21-24 above, the preparation of a metal electrode 2 of this embodiment can be completed, thus obtaining the solar cell of this embodiment (which is a TOPCon cell, the structure of which is described in [reference needed]). Figure 1 ).

[0090] See Figure 1 In this embodiment, a metal electrode 2 includes a silver seed layer that contacts a doped silicon layer (such as a p+ emitter 11 or an n+ polysilicon layer 15), a copper gate line that contacts the silver seed layer, and a copper phosphate layer that contacts the copper gate line.

[0091] See Figure 1 A solar cell according to this embodiment includes a silicon substrate 1, a front metal electrode 2 contacting the front side of the silicon substrate 1, and a back metal electrode 2 contacting the back side of the silicon substrate 1. The silicon substrate 1 includes: a silicon wafer 10, a p+ emitter 11 and a front passivation film (the front passivation film is an aluminum oxide film 12 and a silicon nitride film 13 sequentially disposed on the front side of the p+ emitter 11), and a silicon oxide tunneling layer 14, an n+ polycrystalline silicon layer 15 and a back passivation film (such as a back silicon nitride film 16 disposed on the back side of the n+ polycrystalline silicon layer 15) sequentially disposed on the back side of the silicon wafer 10. The back metal electrode 2 passes through the back passivation film and contacts the n+ polycrystalline silicon layer 15; while the front metal electrode 2 passes through the front passivation film and contacts the p+ emitter 11.

[0092] Example 2

[0093] The metal electrode 2, the solar cell having the metal electrode 2, and the method for preparing the solar cell in this embodiment are all based on Embodiment 1, except that:

[0094] In this embodiment, after step 23, see [link to previous section]. Figure 1 First, a 10 nm thick front nickel transition layer 22 is electroplated on the front copper grid line surface, and a 10 nm thick back nickel transition layer 22 is electroplated on the back copper grid line surface to enhance the interfacial bonding force. Then, according to step 24 of Example 1, a front copper phosphate layer and a back copper phosphate layer are electroplated on the front nickel transition layer 22 and the back nickel transition layer 22 respectively, and the thickness of the front copper phosphate layer and the back copper phosphate layer is also the same as step 24 of Example 1.

[0095] Example 3

[0096] The metal electrode, the solar cell having the metal electrode, and the method for preparing the same in this embodiment are all based on Example 1, except that:

[0097] In this embodiment, step 24 is modified to prepare a Cu3(PO4)2·copper phytate composite layer (which correspondingly includes a front Cu3(PO4)2·copper phytate composite layer and a back Cu3(PO4)2·copper phytate composite layer) on the surface of the copper grid lines (which includes a front copper grid line surface and a back copper grid line surface) instead of the copper phosphate layer (which includes a front copper phosphate layer and a back copper phosphate layer) in step 24 of embodiment 1, in order to improve its corrosion resistance, adhesion and functionality; and the thickness of the Cu3(PO4)2·copper phytate composite layer is the same as the thickness of the copper phosphate layer in step 24 of embodiment 1. Taking the electroplating preparation of the front Cu3(PO4)2·copper phytate composite layer as an example, the specific operation is as follows:

[0098] In the phosphate electrolyte of step 24 of Example 1, the following organic phase was additionally added: phytic acid (C6H4O) of this organic phase. 18 O 24 P6) and Cu 2+ The electroplating solution was prepared at a 1:6 molar ratio. The pH of the solution was adjusted to 5 using KOH to prevent excessive acidity and phytic acid precipitation. The constant voltage was adjusted to +1.0V, and the electroplating time was increased to 3 minutes at room temperature. This allowed the phosphate groups of copper phytate to bond with the Cu3(PO4)2 surface through coordination bonds or hydrogen bonds, thereby electroplating a front-side Cu3(PO4)2·copper phytate composite layer onto the front-side copper grid line surface.

[0099] The preparation process of the Cu3(PO4)2·copper phytate composite layer on the back side is the same as the electroplating method of the Cu3(PO4)2·copper phytate composite layer on the front side, so it will not be described in detail.

[0100] Comparative Example 1

[0101] The metal electrode, the solar cell having the metal electrode, and the method for preparing the same in this comparative example are all based on Example 2, except that:

[0102] This comparative example omits the electroplating process for preparing the front and back copper phosphate layers in step 24 of Example 2.

[0103] Performance testing

[0104] 1. The corrosion resistance tests of the metal electrodes (including the front metal electrode and the back metal electrode) of the solar cells of Example 2 and Comparative Example 1 are as follows:

[0105] A solution was prepared according to the weight ratio of potassium chloride: pure water: acetic acid = 125g: 199.4g: 0.6g. The solution and the solar cell were placed in a 10L sealed container and heated to 85℃ for 8 hours to conduct an acetic acid corrosion test.

[0106] Five of the corrosion-resistant copper-plated TOPCon solar cells of Example 2 (whose front and back metal electrodes are both silver seed layer + copper grid line + nickel transition layer + copper phosphate layer) and five of the conventional copper-plated TOPCon solar cells of Comparative Example 1 (whose front and back metal electrodes are both silver seed layer + copper grid line + nickel transition layer) were placed in the above-mentioned sealed container and subjected to acetic acid etching. The photoelectric conversion efficiency of the cells before and after etching was then tested, and the test results are shown in Table 1 below.

[0107] Among them, the data before corrosion is the battery photoelectric conversion efficiency before the metal electrode is corroded, the data after corrosion is the battery photoelectric conversion efficiency after the metal electrode is corroded, the attenuation data is the attenuation of the battery photoelectric conversion efficiency after the metal electrode is corroded, and the attenuation rate is the attenuation rate of the battery photoelectric conversion efficiency after the metal electrode is corroded.

[0108] Table 1

[0109]

[0110]

[0111] As can be seen from the test results in Table 1, the photoelectric conversion efficiency of the battery in Example 2 decreased by 24.39% after acetic acid corrosion, while that in Comparative Example 1 decreased by 25.79%. Compared to Comparative Example 1, the metal electrode in Example 2 showed improved corrosion resistance, resulting in a 1.40% reduction in the photoelectric conversion efficiency degradation rate after acetic acid corrosion.

[0112] 2. The corrosion resistance test results of the metal electrodes of Examples 2 and 3 are shown in Table 2 below:

[0113] Table 2

[0114]

[0115] When the metal electrode is paired with a copper phosphate layer (as in Example 2), the photoelectric conversion efficiency of the battery after acetic acid corrosion decreases by 24.39%. However, when the copper phosphate layer is replaced with a Cu3(PO4)2·copper phytate composite layer (as in Example 3), the photoelectric conversion efficiency of the battery after acetic acid corrosion of the metal electrode decreases by 23.86%. It is evident that when the metal electrode is paired with an organocopper phosphate composite layer such as the Cu3(PO4)2·copper phytate composite layer, its corrosion resistance is further improved, thereby further increasing the photoelectric conversion efficiency of the battery after acetic acid corrosion of the metal electrode by 0.53%.

[0116] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0117] The technical solution provided by this utility model has been described in detail above. Specific examples have been used to illustrate the principle and implementation of this utility model. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this utility model. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this utility model. Therefore, the content of this specification should not be construed as a limitation of this utility model.

Claims

1. A metal electrode for a solar cell, characterized in that, It includes a metal seed layer for a gate line region on the surface of a silicon substrate, a base metal gate line on the surface of the metal seed layer, and a copper phosphate protective layer on the surface of the base metal gate line. The metal seed layer is at least one of the following: silver seed layer, nickel seed layer, zirconium seed layer, titanium seed layer, chromium seed layer, nickel-silicon alloy seed layer, and copper alloy seed layer. The base metal grid lines are copper grid lines and / or aluminum grid lines; The copper phosphate protective layer is a copper phosphate layer and / or an organocopper phosphate composite layer.

2. The metal electrode for a solar cell according to claim 1, characterized in that, The metal seed layer is a silver seed layer with a thickness of 0.8-1.2 μm.

3. A metal electrode for a solar cell according to claim 1, characterized in that, The base metal grid line is a copper grid line with a height of 8-15 μm.

4. A metal electrode for a solar cell according to claim 1, characterized in that, The copper phosphate protective layer is a copper phosphate layer with a thickness of 8-12 nm.

5. A metal electrode for a solar cell according to claim 1, characterized in that, The copper phosphate protective layer is an organocopper phosphate composite layer with a thickness of 8-12 nm.

6. A metal electrode for a solar cell according to claim 5, characterized in that, The organophosphate copper complex layer is a Cu3(PO4)2·copper phytate complex layer.

7. A metal electrode for a solar cell according to any one of claims 1-6, characterized in that, A nickel transition layer with a thickness of 8-15 nm is also provided between the base metal gate line and the copper phosphate protective layer.

8. A metal electrode for a solar cell according to any one of claims 1-6, characterized in that, The silicon substrate includes: a silicon wafer and a passivation film disposed on the front and / or back sides of the silicon wafer; the gate area of ​​the passivation film has an open film region that locally exposes the silicon substrate, and the metal electrode contacts the silicon substrate through the open film region; A doped silicon layer is also provided between the silicon wafer and the passivation film.

9. A solar cell, characterized in that, It includes: A silicon substrate, and metal electrodes disposed on the front and / or back sides of the silicon substrate; The silicon substrate includes: a silicon wafer and a passivation film disposed on the front and / or back sides of the silicon wafer; The metal electrode is a metal electrode for a solar cell as described in any one of claims 1-8.

10. A photovoltaic module, characterized in that, It includes a solar cell as described in claim 9.

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