A method for manufacturing a photovoltaic module and a photovoltaic module

Abstract

This invention discloses a photovoltaic module manufacturing method and a photovoltaic module, comprising the following steps: Step 1, preparing multiple back-contact photovoltaic cells; Step 2, connecting adjacent back-contact photovoltaic cells using metal connecting strips, the metal connecting strips having a width of 2 mm to 8 mm and a thickness of 0.01 mm to 0.1 mm; Step 3, forming a reliable connection between the metal connecting strips and the back electrodes of the back-contact photovoltaic cells using a welding process; Step 4, using the metal connecting strips as a light-reflecting layer to increase the reflectivity of the back side of the back-contact photovoltaic cells to long-wavelength spectra, and the surface of the metal connecting strips being polished or coated with a reflective enhancement layer. This application utilizes a photovoltaic module manufacturing method that uses wide metal strip connections to increase back-side light reflectivity, thereby improving module power. The aim is to improve the back-side reflectivity to long-wavelength spectra by optimizing the cell connection structure, achieving light energy recovery and utilization, and thus improving module conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic cell technology, and in particular relates to back contact cells such as MWT, IBC, PBC, HPBC, and HBC, as well as their preparation methods. Background Technology

[0002] In the field of photovoltaic technology, back-contact (BC) photovoltaic cells have become a research hotspot and development direction in recent years due to their aesthetically pleasing appearance and potential for higher conversion efficiency. Currently, in the encapsulation process of BC photovoltaic modules, the electrical connection between cells almost entirely relies on traditional solder ribbons. The core function of these solder ribbons is to complete the current conduction between adjacent cells, ensuring the electrical performance of the module.

[0003] However, the conventional solder ribbons used in existing technologies have significant drawbacks: to reduce shading of the cell surface (although the BC cell electrodes are on the back, the conventional solder ribbon design still follows a narrow approach), the width of each solder ribbon is typically less than 2.0 mm. While this narrow solder ribbon can meet basic electrical connection requirements, it suffers from serious deficiencies in optical performance—the solar spectrum contains multiple wavelengths of light, such as... Figure 3 The light reflection path shown in the diagram indicates that longer wavelength light (such as red light and near-infrared light, with wavelengths typically ranging from 800nm ​​to 1200nm) penetrates deeper into the silicon material. Some of these longer wavelengths directly penetrate the BC photovoltaic cell and cannot be captured and utilized by the cell's light absorption layer, resulting in a direct waste of light energy.

[0004] Especially in BC (Browser-Based Photovoltaic) cell structures, all electrodes are located on the back of the cell. Traditional narrow solder strips have a small surface area and extremely weak reflection capability for long-wavelength light penetrating the cell, making it impossible to reflect this light back into the cell for reuse. As the photovoltaic industry continues to demand higher conversion efficiency, how to recycle and utilize these long-wavelength spectra that would otherwise be lost during transmission to improve the light energy utilization rate of BC photovoltaic modules has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the problem that existing BC photovoltaic modules using narrow solder strips cannot effectively utilize long-wavelength light penetrating the cells, resulting in wasted light energy and limited module conversion efficiency, this invention provides a photovoltaic module manufacturing method that uses wide metal strips to increase backside light reflectivity, thereby improving module power. The aim is to improve the backside reflectivity to long-wavelength spectra by optimizing the cell connection structure, thereby achieving light energy recovery and utilization, and ultimately improving module conversion efficiency.

[0006] The technical solution adopted in this invention is: a method for manufacturing photovoltaic modules, comprising the following steps:

[0007] Step 1: Prepare multiple back-contact photovoltaic cells;

[0008] Step 2: A metal connecting strip is used to make a back-side electrical connection between adjacent back-contact photovoltaic cells. The width of the metal connecting strip is 2 mm to 8 mm and the thickness is 0.01 mm to 0.1 mm.

[0009] Step 3: The metal connecting strip is reliably connected to the back electrode of the back contact photovoltaic cell through a welding process, which is either low-temperature welding or high-temperature welding.

[0010] Step 4: Use the metal connecting strip as a light reflective layer to increase the reflectivity of the back of the back contact photovoltaic cell to long wavelength spectrum, and the surface of the metal connecting strip is polished or coated with a reflective enhancement layer.

[0011] Furthermore, the width of the metal connecting strip is 3 mm to 6 mm.

[0012] Furthermore, the metal connecting strip is a pure copper strip or a copper-aluminum composite strip.

[0013] Furthermore, when using the aforementioned low-temperature welding, the welding temperature is controlled between 150℃ and 190℃.

[0014] Furthermore, when using the aforementioned high-temperature welding, the welding temperature is controlled between 250℃ and 350℃.

[0015] Furthermore, the reflection enhancement layer is a silver plating layer or an aluminum plating layer, with a plating thickness of 0.5 micrometers to 5 micrometers.

[0016] Furthermore, the thickness of the metal connecting strip is 0.02 mm to 0.05 mm.

[0017] Furthermore, in step 2, the gap between adjacent back-contact photovoltaic cells is 0.5 mm to 2 mm, and the length of the metal connecting strip covers the gap and extends to the back electrode area of ​​the adjacent back-contact photovoltaic cells at both ends, with an extension length of 1 mm to 3 mm.

[0018] This application also provides a photovoltaic module, which is prepared using the above method.

[0019] Compared with the prior art, the present invention has the following significant advantages:

[0020] 1. Significantly improved light energy utilization: Through metal connecting strips with a width of 2-8mm (compared to traditional <2mm narrow solder strips, the reflective area is increased by 1-4 times), the reflectivity of long wavelength spectrum of 800nm-1200nm is increased to more than 70%, effectively recovering the light energy originally lost through transmission and reducing light energy waste.

[0021] 2. Significantly improved module conversion efficiency: Experimental data shows that the photovoltaic modules prepared using the method of this invention can improve the conversion efficiency by 0.2%-0.8%. Among them, the modules using 4mm wide pure copper connecting strips (polished surface) can improve the efficiency by up to 0.3%; the modules using 6mm wide copper-aluminum composite connecting strips (silver plated) can improve the efficiency by up to 0.5%, which is far higher than the optimization space of existing technologies.

[0022] 3. Strong process compatibility: This invention does not require changing the core production process of existing BC photovoltaic modules. It only requires replacing the traditional narrow welding strip with a wide metal connecting strip and adapting to the corresponding welding parameters (both low temperature and high temperature welding are possible). It does not require major modifications to the production line, reduces the equipment investment cost for enterprises, and facilitates rapid mass production and promotion.

[0023] 4. Controllable cost and high reliability: Although the material usage of wide metal connectors is slightly higher than that of traditional narrow welding strips, the power generation benefits brought by the efficiency improvement (calculated based on a 25-year module life cycle) far outweigh the increase in material costs. At the same time, the wide metal connectors have a larger cross-sectional area, better conductivity (contact resistance reduced by 20%-30%), and higher mechanical strength (tensile and bending resistance improved by 15%-25%), which helps to extend the service life of the modules and improve long-term reliability.

[0024] 5. Wide range of applications: This invention is applicable to various back-contact photovoltaic cells such as N-type BC cells, P-type BC cells, and intrinsic BC cells, and can be adapted to photovoltaic modules of different sizes (166mm, 182mm, 210mm, etc.) and different formats (57 cells, 60 cells, 72 cells, etc.), with strong versatility. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A comparative schematic diagram of traditional narrow solder strip and wide metal strip connection structures;

[0027] Figure 2 This is a schematic diagram of the wide metal strip connection structure in an embodiment of this application;

[0028] Figure 3 This is a schematic diagram of the light reflection path. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The photovoltaic module manufacturing method provided in this application is a method for increasing the back light reflectivity and thus improving the module power by using wide metal strips for connection, and includes the following steps:

[0031] Preparation of back-contact photovoltaic cells: Prepare multiple back-contact photovoltaic cells. The back-contact photovoltaic cells can be N-type BC cells, P-type BC cells, or intrinsic BC cells. The size and thickness of the cells are determined according to the specifications of the target photovoltaic module (such as conventional 166mm×166mm, 182mm×182mm, or 210mm×210mm sizes). It is also necessary to ensure that the position and shape of the back electrodes (positive and negative electrodes) of the cells meet the design requirements and are free from defects such as damage and oxidation.

[0032] Metal connecting strip selection and pretreatment: Metal connecting strips with a width of 2 mm to 8 mm and a thickness of 0.01 mm to 0.1 mm are selected, preferably with a width of 3 mm to 6 mm (balancing reflective area and material cost) and a thickness of 0.02 mm to 0.05 mm (ensuring conductivity and flexibility). The metal connecting strip can be made of pure copper (excellent conductivity and high reflectivity) or copper-aluminum composite strip (lower cost and good reflective performance). To further improve reflectivity, the surface of the metal connecting strip is pretreated—using mechanical polishing to achieve a surface roughness Ra ≤ 0.8 μm, or depositing a reflective enhancement layer (such as a silver plating or aluminum plating, with a plating thickness of 0.5 μm to 5 μm) on its surface, ensuring that the reflectivity of the metal connecting strip for the 800 nm-1200 nm long-wavelength spectrum is ≥ 70%.

[0033] Figure 2As shown, the metal connecting strip is welded to the solar cell: The pre-treated metal connecting strip is placed at the back gap of adjacent back-contact photovoltaic cells, so that both ends of the metal connecting strip cover the back electrode area of ​​the adjacent cells (extending length 1 mm to 3 mm), and the gap between adjacent cells is controlled at 0.5 mm to 2 mm (to avoid damage to the cell edge contact). Then, a welding process is used to connect the metal connecting strip to the back electrode of the solar cell: If low-temperature welding is used, the welding temperature is controlled at 150℃-190℃ (suitable for BC cells with poor temperature resistance of electrode materials), and low-temperature solder paste (such as Sn-Bi solder paste) is used for connection; if high-temperature welding is used, the welding temperature is controlled at 250℃-350℃ (suitable for BC cells with better temperature resistance), and high-temperature solder strip or laser welding is used to ensure that the contact resistance at the weld is ≤5mΩ, and there are no incomplete solder joints or detachment.

[0034] Module encapsulation and performance optimization: Multiple back-contact photovoltaic cells with welded metal connectors are arranged according to module layouts (e.g., 57-cell, 60-cell, or 72-cell layouts). Glass, EVA film, cell array, EVA film, and backsheet are then sequentially laid. The modules are then fed into a laminator for lamination (lamination temperature 130℃-150℃, lamination time 15-25 minutes). Finally, the frame and junction box are installed to complete the photovoltaic module fabrication. In this process, the metal connectors not only act as conductors for current conduction between adjacent cells but also as light-reflecting layers, reflecting long-wavelength light penetrating the cells back to the cell's light-absorbing layer for reabsorption and utilization, thereby improving the module's light energy utilization and power output.

[0035] This application also provides a photovoltaic module, which is prepared by the above method and has the following structure. Figure 1 As shown.

[0036] Example 1: Fabrication of photovoltaic modules based on N-type BC cells

[0037] Cell preparation: 57 N-type BC cells with a size of 182mm×182mm were selected. The back electrode of the cell was printed with silver paste. The positive and negative electrodes were located on the two sides of the back of the cell, respectively. The electrode width was 2mm and the thickness was 10μm.

[0038] Metal connecting strip pretreatment: Pure copper strips are selected as metal connecting strips, with a width of 4mm and a thickness of 0.035mm; the surface of the copper strip is treated by mechanical polishing process to make the surface roughness Ra=0.5μm. After testing, its reflectivity for long wavelength spectrum of 800nm-1200nm is 75%.

[0039] Welding connection: Place the copper strip at the back gap of adjacent N-type BC solar cells, with the gap between adjacent solar cells controlled at 1mm. Extend both ends of the copper strip to the back electrode area of ​​the adjacent solar cells, with an extension length of 2mm. Use a low-temperature welding process with a welding temperature of 180℃ and Sn-Bi low-temperature solder paste (melting point 138℃). Weld the copper strip to the back electrode of the solar cell using a string soldering machine. After welding, test the contact resistance. The average value is 3mΩ, and there are no signs of poor soldering or desoldering.

[0040] Module encapsulation: The glass is laid out in the following order: glass → EVA film → 57 N-type BC solar cell array in series → EVA film → backsheet. The cells are then fed into a laminator at a lamination temperature of 140℃ for 20 minutes. After lamination, the aluminum alloy frame and junction box are installed to obtain a 57-cell N-type BC photovoltaic module.

[0041] The performance of the components prepared using the above method was tested, as shown in the table below:

[0042]

[0043] The electrical performance of the prepared modules was tested under standard test conditions. The results showed that the short-circuit current (Isc) was 12.87A, the open-circuit voltage (Voc) was 41.43V, the fill factor (FF) was 79.45%, and the maximum output power (Pmpp) was 423.63W. The conversion efficiency was 0.3% higher than that of the same type of module using a 1.5mm wide traditional solder strip (Pmpp=420.91W).

[0044] Example 2: Fabrication of photovoltaic modules based on P-type BC cells

[0045] Cell preparation: Select 60 P-type BC cells with a size of 210mm×210mm. The back electrode of the cell is printed with aluminum paste. The positive and negative electrodes are alternately distributed on the back of the cell. The electrode width is 2.5mm and the thickness is 12μm.

[0046] Metal connecting strip pretreatment: Copper-aluminum composite strips are selected as metal connecting strips, with a width of 6mm and a total thickness of 0.06mm (of which the copper layer is 2μm thick and the aluminum layer is 56μm thick); a silver layer (reflection enhancement layer) is plated on the surface of the copper-aluminum composite strip, with a plating thickness of 2μm. After testing, its reflectivity for the long wavelength spectrum of 800nm-1200nm is 85%.

[0047] Welding connection: The copper-aluminum composite strip is placed at the back gap of adjacent P-type BC solar cells, with the gap between adjacent solar cells controlled at 1.5mm. Both ends of the composite strip extend to the back electrode area of ​​the adjacent solar cells, with an extension length of 2.5mm. A high-temperature welding process is adopted, with a welding temperature of 300℃. The composite strip is welded to the back electrode of the solar cell using laser welding equipment. After welding, the contact resistance is tested, with an average value of 2mΩ. There are no cases of incomplete welding or detachment.

[0048] Module encapsulation: The modules are laid out in the following order: glass → EVA film → 60 P-type BC solar cells in series → EVA film → backsheet. They are then fed into a laminator at a lamination temperature of 145℃ for 22 minutes. After lamination, the aluminum alloy frame and junction box are installed to obtain a 60-cell P-type BC photovoltaic module.

[0049] Performance tests were conducted on the modules prepared using the above method: electrical performance tests were performed on the modules under standard test conditions (STC), and the results showed that the conversion efficiency was improved by 0.5% compared with the same type of module using a traditional solder strip with a width of 1.8mm.

[0050] Example 3: Fabrication of photovoltaic modules based on intrinsic BC cells

[0051] Cell preparation: 72 intrinsic BC cells with a size of 166mm×166mm were selected. The back electrode of the cell was printed with copper paste. The positive and negative electrodes were symmetrically distributed on the back of the cell. The electrode width was 1.8mm and the thickness was 8μm.

[0052] Metal connecting strip pretreatment: Pure copper strips are selected as metal connecting strips, with a width of 3mm and a thickness of 0.02mm; an aluminum layer (reflection enhancement layer) is plated on the surface of the copper strip, with a coating thickness of 1μm. After testing, its reflectivity for long wavelength spectrum of 800nm-1200nm is 78%.

[0053] Welding connection: The copper strip is placed at the back gap of the adjacent intrinsic BC solar cells, with the gap between the adjacent cells controlled at 0.8mm. Both ends of the copper strip extend to the back electrode area of ​​the adjacent solar cells, with an extension length of 1.5mm. A low-temperature welding process is adopted, with a welding temperature of 160℃ and Sn-In low-temperature solder paste (melting point 117℃) is selected. The copper strip is welded to the back electrode of the solar cell using a string soldering machine. After welding, the contact resistance is tested, with an average value of 4mΩ. There are no signs of poor soldering or desoldering.

[0054] The performance of the modules prepared using the above method was tested: the modules were laid in the following order: glass → EVA film → 72 intrinsic BC solar cell array in series → EVA film → backsheet, and fed into a laminator. The lamination temperature was 135℃ and the lamination time was 18min. After lamination, the aluminum alloy frame and junction box were installed to obtain the 72-cell intrinsic BC photovoltaic module.

[0055] Performance testing: Electrical performance tests were conducted on the modules under standard test conditions (STC). The results showed that the conversion efficiency was improved by 0.25% compared to the same type of module (Pmpp=450.05W) using a traditional solder strip with a width of 1.2mm.

[0056] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. In particular, for the device embodiments, the above descriptions are merely preferred embodiments of the present invention. Since they are fundamentally similar to the method embodiments, the descriptions are relatively simple, and relevant parts can be referred to the descriptions of the method embodiments. The above descriptions are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention, without departing from the principle of the present invention, should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for manufacturing a photovoltaic module, characterized in that, Includes the following steps: Step 1: Prepare multiple back-contact photovoltaic cells; Step 2: A metal connecting strip is used to make a back-side electrical connection between adjacent back-contact photovoltaic cells. The width of the metal connecting strip is 2 mm to 8 mm and the thickness is 0.01 mm to 0.1 mm. Step 3: The metal connecting strip is reliably connected to the back electrode of the back contact photovoltaic cell through a welding process, which is either low-temperature welding or high-temperature welding. Step 4: Use the metal connecting strip as a light reflective layer to increase the reflectivity of the back of the back contact photovoltaic cell to long wavelength spectrum, and the surface of the metal connecting strip is polished or coated with a reflective enhancement layer.

2. The method of claim 1, wherein, The width of the metal connecting strip is 3 mm to 6 mm.

3. The method according to claim 1 or 2, characterized in that, The metal connecting strip is a pure copper strip or a copper-aluminum composite strip.

4. The method according to claim 1, characterized in that, When using the aforementioned low-temperature welding, the welding temperature is controlled between 150℃ and 190℃.

5. The method according to claim 1, characterized in that, When using the high-temperature welding method, the welding temperature is controlled between 250℃ and 350℃.

6. The method according to claim 1, characterized in that, The reflection enhancement layer is a silver plating layer or an aluminum plating layer, with a plating thickness of 0.5 micrometers to 5 micrometers.

7. The method according to claim 1, characterized in that, The thickness of the metal connecting strip is 0.02 mm to 0.05 mm.

8. The method according to claim 1, characterized in that, In step 2, the gap between adjacent back-contact photovoltaic cells is 0.5 mm to 2 mm, and the length of the metal connecting strip covers the gap and extends to the back electrode area of ​​the adjacent back-contact photovoltaic cells at both ends, with an extension length of 1 mm to 3 mm.

9. A photovoltaic module, characterized in that, The photovoltaic module is prepared using any one of the methods described in claims 1 to 8.

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