Back contact photovoltaic cell and method of making same

Abstract

The application provides a back contact photovoltaic cell and a preparation method thereof. The back contact photovoltaic cell comprises a cell piece, a plurality of main grid lines arranged on the back surface of the cell piece and extending in a first direction, and a plurality of auxiliary grid lines perpendicular to the main grid lines. The cell piece comprises a silicon substrate, a poly-Si layer and a passivation layer arranged in sequence from bottom to top. Each auxiliary grid line comprises a plurality of silver seed layers arranged at intervals and a silver-copper composite layer connecting all the silver seed layers. The silver seed layer penetrates the passivation layer from top to bottom and is in contact with the poly-Si layer. The silver-copper composite layer partially or completely covers the silver seed layer and is in contact with the passivation layer. The layered auxiliary grid line structure with segmented pure silver seed layer and silver-copper composite layer is adopted to replace the traditional full-silver auxiliary grid line, which can significantly reduce the amount of pure silver, compress the material cost of the auxiliary grid line by 35%-45%, and relieve the pain point of high silver paste consumable cost of the back contact photovoltaic cell.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell manufacturing technology, and in particular to a back-contact photovoltaic cell and its preparation method. Background Technology

[0002] Back-contact solar cells (such as IBC and TBC) integrate both positive and negative electrodes on the back of the cell, eliminating the shading loss caused by the front-side grid lines, and are one of the core technologies for high-efficiency photovoltaic cells. However, existing back-contact solar cell electrodes have the following shortcomings: First, in the traditional pure silver sub-grid line manufacturing process, the amount of silver paste used is large, accounting for a high proportion of the material cost. The silver paste used for the sub-grid lines is a key factor restricting mass production costs. If silver-copper paste is used directly to replace silver paste, although the cost can be reduced, the contact recombination between silver-copper materials and silicon is severe, resulting in a significant decrease in open-circuit voltage (Voc). If only the length of the pure silver grid lines is shortened, additional carrier lateral transport resistance will be introduced, causing a significant decrease in the fill factor (FF), making it difficult to balance performance and cost. In addition, existing composite grid line solutions often have problems such as high interlayer contact resistance, sintering shrinkage mismatch, and local current concentration, which can easily lead to a decrease in cell yield and fluctuations in electrical performance.

[0003] Therefore, it is necessary to design a back-contact photovoltaic cell and its fabrication method to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a back-contact photovoltaic cell that balances battery performance and manufacturing cost.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a back-contact photovoltaic cell, comprising a cell, a plurality of main grid lines extending along a first direction disposed on the back of the cell, and a plurality of sub-grid lines perpendicular to the main grid lines. The cell comprises a silicon substrate, a poly-Si layer, and a passivation layer arranged sequentially from bottom to top. Each sub-grid line comprises a plurality of spaced silver seed layers and a silver-copper composite layer connecting all the silver seed layers. The silver seed layers penetrate the passivation layer vertically and are in contact with the poly-Si layer. The silver-copper composite layer partially or completely covers the silver seed layers and is in contact with the passivation layer.

[0006] As a further improvement of the present invention, the length direction of the silver seed layer is perpendicular to the length direction of the silver-copper composite layer, or the length direction of the silver seed layer is parallel to the length direction of the silver-copper composite layer.

[0007] As a further improvement of the present invention, the number of silver seed layers for each sub-gate line is 5-15.

[0008] As a further improvement of the present invention, the width of the silver seed layer is 15-25μm, the thickness is 3-5μm, and the total length of the silver seed layer is 2 / 5-3 / 5 of the length of the silver-copper composite layer.

[0009] As a further improvement of the present invention, the width of the silver-copper composite layer is 40-50μm and the thickness is 8-12μm.

[0010] As a further improvement of the present invention, the width of the silver seed layer gradually narrows from the middle to both ends to 6-8 μm.

[0011] As a further improved technical solution of the present invention, the silver seed layer is made by printing and sintering silver paste, wherein the silver paste comprises the following components in weight percentage: silver powder 84.0%-92.0%, dodecyl alcohol ester 3.5%-6.0%, butyl carbitol acetate 3.5%-6.0%, glass powder 1.0%-4.0%, ethyl cellulose 0.1%-2.0%, and the peak sintering temperature of the silver paste is 700-800℃.

[0012] As a further improvement of the present invention, the viscosity of the silver paste is 280-350 Pa·s.

[0013] As a further improved technical solution of the present invention, the silver-copper composite layer is made by printing and low-temperature curing of silver-copper composite paste. The silver-copper composite paste includes the following components in weight percentage: copper powder 50.0%-80.0%, silver powder 10.0%-45.0%, epoxy resin 1.0%-10.0%, butyl carbitol acetate 0.3%-5.0%, and hexadecyl alcohol ester 0.3%-5.0%. The peak curing temperature of the silver-copper composite paste is 180-240℃.

[0014] The present invention also aims to provide a method for preparing back-contact photovoltaic cells that balances battery performance and process cost.

[0015] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a back-contact photovoltaic cell as described in any of the above claims, comprising the following steps: S1. Prepare the battery cell to be printed. The position of the preset silver seed layer on the battery cell is pre-exposed by laser drilling to expose the poly-Si layer of the battery cell at a fixed point. S2. Print a silver seed layer at the laser-drilled opening position of the battery cell and dry it; S3. Print the main grid lines on the solar cells and dry them; S4. Place the printed battery cells at 700-800℃ for sintering for 5-15 seconds. S5. Print a silver-copper composite layer on the battery cell and cure it at 180-240℃ for 5-10 seconds.

[0016] As can be seen from the above technical solutions, the back-contact photovoltaic cell and its preparation method of the present invention have the following advantages: 1. This invention adopts a segmented pure silver seed layer combined with a silver-copper composite layer layered sub-grid structure to replace the traditional all-silver sub-grid; it can significantly reduce the amount of pure silver used, compress the sub-grid material cost by 35%~45%, and alleviate the pain point of high cost of silver paste consumables for back contact photovoltaic cells.

[0017] 2. The silver seed layer is sintered with high-temperature silver paste, penetrating the passivation layer and directly bonded to the poly-Si layer, ensuring stable ohmic contact between the silicon substrate and the metal electrode; the outer silver-copper composite layer is cured with low-temperature paste, completely or partially covering the silver seed layer and bonding it to the passivation layer, which not only connects the segmented silver seed layer to achieve current collection and conduction, but also relies on the excellent conductivity of the silver-copper composite layer to compensate for the conductivity loss caused by the reduction of pure silver, ensuring reliable electrode contact and guaranteeing the basic electrical performance of the battery.

[0018] 3. The composite grid structure can slightly increase the open-circuit voltage Voc and short-circuit current Isc of the battery, while suppressing the decay of the fill factor FF. Ultimately, the photovoltaic conversion efficiency is basically the same as that of traditional all-silver grid cells. Under the premise of significantly reducing the consumption of precious metal silver and reducing manufacturing costs, the battery performance is not sacrificed, and the production cost and power generation efficiency are balanced. Attached Figure Description

[0019] Figure 1 This is a cross-sectional schematic diagram of the sub-grid lines and the battery cell in Embodiment 1 of the present invention.

[0020] Figure 2 This is a diagram showing the positional relationship between the silver seed layer and the silver-copper composite layer in Example 1.

[0021] Figure 3 This is a diagram showing the positional relationship between the silver seed layer and the silver-copper composite layer in Example 2.

[0022] Figure 4 This is a diagram showing the positional relationship between the sub-busbars and the solar cells in a comparative example. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1

[0025] Fabrication of back-contact photovoltaic cells: S1. Prepare 50 182mm×182mm solar cells to be printed (BC substrate blue film). The positions of the preset silver seed layer on the solar cell are pre-drilled by laser to expose the poly-Si layer of the solar cell at the specified points. S2. Use silver paste to print a silver seed layer at the laser-drilled opening position of the battery cell and dry it. The silver paste includes the following components by weight percentage: silver powder 88%, 12-ethyl alcohol ester 5.0%, butyl carbitol acetate 4.5%, glass powder 1.5%, ethyl cellulose 1.0%, and the viscosity of the silver paste is 305 Pa·s. S3. Print the main grid lines on the back of the battery cell and dry them. The main grid line material is the existing high-temperature silver paste for grid lines (silver content ≥92%), and the main grid line size is the commonly used size for existing back contact batteries. S4. Place the printed battery cells in a tubular sintering furnace and sinter them at a peak temperature of 785°C for 10 seconds. S5. Print a silver-copper composite layer on the battery cell using a silver-copper composite paste. The silver-copper composite paste comprises the following components by weight percentage: 68% copper powder, 20% silver powder, 4.2% epoxy resin, 3.9% butyl carbitol acetate, and 3.9% hexadecyl alcohol ester. The peak curing temperature of the silver-copper composite paste is 220℃, and the curing time is 10s.

[0026] Please refer to Figure 1 and Figure 2 As shown, the battery prepared in this embodiment includes a battery cell 10, a plurality of main grid lines (not shown) extending along a first direction on the back of the battery cell 10, and a plurality of sub-grid lines 20 perpendicular to the main grid lines. The battery cell 10 includes a silicon substrate 11, a poly-Si layer 12, and a passivation layer 13 arranged sequentially from bottom to top. Each sub-grid line 20 includes a plurality of spaced silver seed layers 21 and a silver-copper composite layer 22 connecting all the silver seed layers 21. The silver seed layers 21 penetrate the passivation layer 13 vertically and are in contact with the poly-Si layer 12. The length direction of the silver seed layers 21 is parallel to the length direction of the silver-copper composite layer 22. The silver-copper composite layer 22 completely covers the silver seed layers 21 and is in contact with the passivation layer 13. The number of silver seed layers 21 for each sub-grid line is set to 8.

[0027] In this embodiment, the solar cells are divided into three groups (15 cells per group). The dimensions of the silver seed layer 21 and the silver-copper composite layer 22 of each group of solar cells are shown in Table 1. The width of the silver seed layer 21 gradually narrows from the middle to both ends to 6-8 μm, and the edge of the silver seed layer 21 forms a gentle slope to eliminate step differences.

[0028] Example 2

[0029] The back-contact photovoltaic cell structure and fabrication method in this embodiment are largely the same as those in Embodiment 1, with the following differences: Please refer to... Figure 3As shown, the sub-gate line 20' of the battery prepared in this embodiment includes a silver seed layer 21' and a silver-copper composite layer 22', with the length direction of the silver seed layer 21' perpendicular to the length direction of the silver-copper composite layer 22'. The number of silver seed layers 21' for each sub-gate line is set to 120, and the total length of the silver seed layers 21' is 1 / 2 the length of the silver-copper composite layer 22'.

[0030] Please refer to Table 1 for the dimensions of the silver seed layer 21' and the silver-copper composite layer 22' of the battery cell in this embodiment. The width of the silver seed layer 21 gradually narrows from the middle to both ends to 6-8 μm.

[0031] Table 1 shows the dimensional parameters of the silver seed layer and the silver-copper composite layer in the embodiments.

[0032] In the comparative example, back-contact photovoltaic cells were prepared using conventional methods: S1. Prepare 50 182mm×182mm solar cells to be printed (BC substrate blue film). The positions of the pre-set sub-grid lines on the solar cells are pre-drilled by laser to expose the poly-Si layer of the solar cells at specific points. S2. Print the main grid lines on the back of the battery cell and dry them. The main grid line material is the existing high-temperature silver paste for grid lines (silver content ≥92%), and the main grid line size is the commonly used size for existing back contact batteries. S3. Print pure silver sub-grid lines 20” on the back of the solar cell using silver paste. The silver paste used is the existing silver paste for sub-grid lines, and the sub-grid line size is 170mm×25μm. S4. Place the printed battery cells in a tubular sintering furnace and sinter at a peak temperature of 785°C for 10 seconds.

[0033] The battery samples prepared in the examples and comparative examples were subjected to electrical performance tests, and the test results are shown in Table 2. The electrical performance data for Examples 1, 2, and the comparative examples are the average values ​​of the measurements taken from 50 batteries in this example.

[0034] Table 2. Battery performance parameters for examples and comparative examples.

[0035] By comparison, we can see that: Example 1 is a preferred embodiment, where the slurry formulation, silver seed arrangement, and sintering process are within the optimal range. Only the fixed-point silver seed layer achieves ohmic contact with poly-Si, and the passivation layer reliably blocks copper atom diffusion. While reducing the amount of precious silver used and compressing electrode material costs, it comprehensively outperforms traditional all-silver grid lines in terms of series resistance, passivation level, and leakage current performance, with a slight improvement in photoelectric efficiency, making it suitable for high-power, premium-priced high-end BC battery product lines.

[0036] In Example 2, the interlayer contact area between the silver seed layer and the silver-copper composite layer is smaller, the contact resistance is slightly higher, and some electrical parameters are slightly lower than those in Example 1 and the comparative example, but the overall electrical performance meets the standards. Relying on the silver-copper composite grid structure, the silver paste consumption is further reduced, resulting in a significant cost advantage.

[0037] The comparative example represents a mature mass-production structure in the industry, with stable fill factor performance, but it has a large amount of silver paste consumption and high electrode material costs, making its overall cost competitiveness weaker than the two types of composite grid line solutions in the examples.

[0038] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. The understanding of this specification should be based on those skilled in the art. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still make modifications or equivalent substitutions to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A back-contact photovoltaic cell, comprising a cell, a plurality of main grid lines extending along a first direction disposed on the back side of the cell, and a plurality of sub-grid lines perpendicular to the main grid lines, characterized in that: The solar cell includes a silicon substrate, a poly-Si layer, and a passivation layer arranged sequentially from bottom to top. Each sub-gate line includes multiple spaced silver seed layers and a silver-copper composite layer connecting all the silver seed layers. The silver seed layers penetrate the passivation layer vertically and are in contact with the poly-Si layer. The silver-copper composite layer partially or completely covers the silver seed layers and is in contact with the passivation layer.

2. The back-contact photovoltaic cell as described in claim 1, characterized in that: The length direction of the silver seed layer is perpendicular to the length direction of the silver-copper composite layer, or the length direction of the silver seed layer is parallel to the length direction of the silver-copper composite layer.

3. The back-contact photovoltaic cell as described in claim 1, characterized in that: The number of silver seed layers for each subgate line is 5-15.

4. The back-contact photovoltaic cell as described in claim 1, characterized in that: The width of the silver seed layer is 15-25 μm, the thickness is 3-5 μm, and the total length of the silver seed layer is 2 / 5-3 / 5 of the length of the silver-copper composite layer.

5. The back-contact photovoltaic cell as described in claim 1, characterized in that: The width of the silver-copper composite layer is 40-50 μm and the thickness is 8-12 μm.

6. The back-contact photovoltaic cell as described in claim 1, characterized in that: The width of the silver seed layer gradually narrows from the middle to both ends to 6-8 μm.

7. The back-contact photovoltaic cell as described in claim 1, characterized in that: The silver seed layer is made by printing and sintering silver paste, which comprises the following components by weight percentage: silver powder 84.0%-92.0%, dodecyl alcohol ester 3.5%-6.0%, butyl carbitol acetate 3.5%-6.0%, glass powder 1.0%-4.0%, and ethyl cellulose 0.1%-2.0%. The peak sintering temperature of the silver paste is 700-800℃.

8. The back-contact photovoltaic cell as described in claim 7, characterized in that: The viscosity of the silver paste is 280-350 Pa·s.

9. The back-contact photovoltaic cell as described in claim 1, characterized in that: The silver-copper composite layer is made by printing and low-temperature curing of a silver-copper composite paste. The silver-copper composite paste comprises the following components by weight percentage: copper powder 50.0%-80.0%, silver powder 10.0%-45.0%, epoxy resin 1.0%-10.0%, butyl carbitol acetate 0.3%-5.0%, and hexadecyl alcohol ester 0.3%-5.0%. The peak curing temperature of the silver-copper composite paste is 180-240℃.

10. A method for preparing a back-contact photovoltaic cell as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Prepare the battery cell to be printed. The position of the preset silver seed layer on the battery cell is pre-exposed by laser drilling to expose the poly-Si layer of the battery cell at a fixed point. S2. Print a silver seed layer at the laser-drilled opening position of the battery cell and dry it; S3. Print the main grid lines on the solar cells and dry them; S4. Place the printed battery cells at 700-800℃ for sintering for 5-15 seconds. S5. Print a silver-copper composite layer on the battery cell and cure it at 180-240℃ for 5-10 seconds.

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