Composite cleaning solution, solar cell and preparation method of solar cell

Abstract

The invention relates to the technical field of photovoltaics, in particular to a composite cleaning solution, a solar cell and a preparation method of the solar cell. The preparation method comprises the following steps: coating, printing and developing a copper seed layer of a yellow diaphragm; a grid line is formed on the copper seed layer through electroplating; injecting light; cleaning: removing copper particles on the surface of the grid line by using a composite cleaning solution; performing tin melting, and forming a tin protection layer on the surface of the grid line; wherein the composite cleaning solution comprises the following raw materials: a surfactant and a complexing agent. The composite cleaning solution can be used for cleaning a battery piece before a tin melting process for preparing a solar battery so as to remove copper particles on the surface of a grid line, so that the condition of replacement of the copper particles and tin particles in a tin melting solution can be reduced in the tin melting process, the service life of the tin melting solution can be prolonged, and the production efficiency of the solar battery is improved. And tin mud in the tin melting liquid can be reduced, so that the problem that holes are formed in a tin layer formed on the surface of the grid line is solved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and more specifically, to composite cleaning solutions, solar cells, and methods for their preparation. Background Technology

[0002] The related technologies provide a method for fabricating solar cells that uses copper interconnect technology to prepare copper grid lines, replacing the grid lines prepared by screen printing.

[0003] The technology for copper interconnects involves: depositing a seed layer of copper on a transparent conductive layer (TCO) via PVD sputtering for conductivity (i.e., as a seed layer for electroplating), then coating it with photosensitive emulsion, followed by pattern transfer, and finally electroplating to form copper grid lines. This can be followed by processes such as stripping, photoinjection, and tin plating.

[0004] The tinning process involves forming a tin protective layer on the surface of the copper grid lines to protect them from oxidation by air.

[0005] However, after the high-temperature process of light injection, the surface of the copper grid lines will form multiple layers of oxides (including Cu2O and CuO) under strong oxidation conditions. Before the tinning process, acid pickling is also required. During the acid pickling process, the oxides formed by light injection can easily form copper particles that remain on the grid line surface. During tinning, these particles will replace the tin particles in the tinning solution and float in the tinning solution, reducing the lifespan of the tinning solution. At the same time, after the copper particles replace the tin particles, they can easily exist in the tinning solution as tin sludge, causing the formed tin layer to have holes. This not only has an adverse effect on the appearance of the solar cell, but also reduces the performance of the solar cell. Summary of the Invention

[0006] The purpose of this invention is to provide a composite cleaning solution, a solar cell, and a method for preparing the same. The composite cleaning solution provided by this invention can be used to clean the solar cell before the tinning process in the preparation of the solar cell, so as to remove copper particles on the grid surface. This reduces the replacement of copper particles with tin particles in the tinning solution during the tinning process, thereby extending the service life of the tinning solution. Furthermore, by reducing the amount of tin sludge in the tinning solution, it can improve the problem of voids in the tin layer formed on the grid surface. This not only improves the appearance of the prepared solar cell but also enhances its performance.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a composite cleaning solution for cleaning solar cells after the light injection process in the fabrication of solar cells; The raw materials for composite cleaning solutions include surfactants and complexing agents.

[0008] In an optional embodiment, the composite cleaning solution comprises, by mass percentage: 0.01-0.5% surfactant, 0.01-0.05% complexing agent, balance water.

[0009] In an optional embodiment, the surfactant includes ammonium dodecyl sulfate.

[0010] In an optional embodiment, the complexing agent includes ethylenediaminetetraacetic acid (EDTA).

[0011] In an optional embodiment, the pH of the composite cleaning solution is 5.5 to 7.0.

[0012] In an optional implementation, the pH of the composite cleaning solution is adjusted with sulfuric acid.

[0013] Secondly, the present invention provides a method for preparing a solar cell, comprising: Coating, printing, and developing are performed on the copper seed layer of the yellow film. Electroplating is performed on the copper seed layer to form gate lines; Light injection; Cleaning, which includes removing copper particles from the surface of the gate line using a composite cleaning solution of any of the foregoing embodiments; Tinning is used to form a tin protective layer on the surface of the gate lines.

[0014] In an optional embodiment, a specific method for removing copper particles from the grid surface using a composite cleaning solution includes immersing the battery cell in the composite cleaning solution and performing ultrasonic stirring.

[0015] In an optional embodiment, the cleaning process further includes acid washing before removing copper particles from the gate surface using a composite cleaning solution.

[0016] Thirdly, the present invention provides a solar cell prepared by the solar cell preparation method of any of the foregoing embodiments.

[0017] The present invention has the following beneficial effects: The composite cleaning solution provided in this invention can clean solar cells after the light injection process, followed by the tinning process. The composite cleaning solution includes a surfactant and a complexing agent. The complexing agent can form stable complexes with metal ions (copper ions) adhering to the grid surface of the solar cell, and these complexes are soluble in the composite cleaning solution. Therefore, the complexing agent ensures that metal ions (copper ions) do not redeposit on the grid surface, effectively removing metal ions (copper ions). The surfactant significantly reduces the surface tension of water, making it easier for the composite cleaning solution to wet the metal surface, especially ensuring that the composite cleaning solution can effectively penetrate hard-to-reach corners and crevices. This, in turn, ensures that the complexing agent can effectively complex more metal ions (copper ions), further ensuring the effective removal of metal ions (copper ions).

[0018] The solar cell fabrication method provided in this invention involves cleaning the solar cell with the aforementioned composite cleaning solution after light injection and before tinning to reliably remove copper particles from the grid surface. This reduces the number of copper ions entering the tinning solution during tinning, minimizing the displacement of copper particles with tin particles in the tinning solution, thereby extending the service life of the tinning solution. Furthermore, reducing tin sludge in the tinning solution improves the problem of voids in the tin layer formed on the grid surface, thus improving both the appearance and performance of the solar cell.

[0019] The solar cell provided in this embodiment of the invention is prepared by the aforementioned method. The tin layer formed on the grid surface of the solar cell is less prone to pores, which not only improves the appearance of the solar cell but also enhances its performance. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The related technologies provide methods for fabricating solar cells, including: 1. Cleaning and texturing: Acid and alkali solutions are used to etch the surface of the original silicon wafer to form a pyramidal textured surface, improving surface utilization.

[0022] 2. PECVD, vapor deposition of an amorphous silicon layer onto a textured surface to prepare the substrate for forming a PN junction.

[0023] 3. PVD / RPD: After the PN junction is formed, a transparent conductive film (TCO) is formed on its surface.

[0024] 4. PVD-Cu: Due to the poor conductivity of TCO, a high-conductivity copper seed layer is pretreated on the surface of TCO to improve the poor adhesion between electroplated copper and TCO.

[0025] 5. Coating: Apply a layer of negative photosensitive adhesive (as an electroplating mask) to the front and back of the yellow film (the semi-finished battery cell after copper seed layer deposition).

[0026] 6. Printing exposure: Use a light source with a wavelength greater than 400nm to expose the non-grid line parts to induce a cross-linking reaction in the mask, causing it to denature and become less susceptible to corrosion by weak alkaline solutions.

[0027] 7. Development: Use Na2CO3 solution (concentration of 10g / L) to rinse the mask for 40s at a temperature of 30℃ to clean the unexposed reaction parts of the mask and form pre-plated grooves.

[0028] 8. Edge binding: Use edge binding adhesive to cover the sides of the yellow film to prevent copper plating from causing a circuit between the front and back sides.

[0029] 9. Electroplating, utilizing the principle of a galvanic cell, causes the Cu in the electroplating solution to... 2+ The electrons migrate to the surface of the PVD copper seed layer with the electric field, capture electrons, and deposit to fill the pre-plated grooves formed after development.

[0030] 10. Etching back: Dissolve the mask adhesive and edge-sealing adhesive with strong alkaline solution, and use strong oxidizing acid to etch the PVD-copper seed layer until the ITO layer is exposed.

[0031] 11. Light injection: using infrared light to repair Si-H bonds, internal defects in saturated heterojunction cells, and release internal stress in silicon wafers and coatings through high-temperature annealing.

[0032] 12. Tinning: A chemical solution replaces the elemental Cu on the surface of the copper grid lines, forming a tin protective layer on the surface of the copper grid lines to protect them from oxidation by air.

[0033] The inventors discovered that after the high-temperature process of light injection, the surface of the copper grid lines forms multiple layers of oxides (including Cu2O and CuO) under strong oxidation conditions. Furthermore, acid pickling is required before the tinning process. During acid pickling, due to the thickness or complex structure of the oxide layers (e.g., Cu2O and CuO), they do not completely dissolve, and some oxides peel off and remain as copper particles, adhering to and remaining on the grid line surface. During tinning, the copper particles remaining on the grid line surface replace tin particles in the tinning solution, detaching from the grid line surface and floating in the tinning solution, reducing the lifespan of the tinning solution. They also adhere to the machine or settle at the bottom of the tinning tank as the tinning solution flows. Additionally, the replacement of copper and tin particles in the tinning solution can easily lead to the formation of tin sludge, causing porosity in the tin layer. This not only negatively impacts the appearance of the solar cell but also reduces its performance.

[0034] To address the aforementioned issues, this disclosure provides a composite cleaning solution for cleaning solar cells after photoinjection and before tinning, in order to remove copper particles from the grid surface.

[0035] The method for preparing the solar cell disclosed herein includes: Coating, printing, and developing are performed on the copper seed layer of the yellow film to form pre-plated grooves; Electroplating is performed on the copper seed layer within the pre-plated groove to form grid lines; Light injection; Cleaning, which includes removing copper particles from the surface of the gate lines using a composite cleaning solution; Tinning is used to form a tin protective layer on the surface of the gate lines.

[0036] The raw materials for the composite cleaning solution include surfactants and complexing agents.

[0037] The complexing agent can form stable complexes with the metal ions (copper ions) attached to the grid surface of the battery cell, and these complexes are soluble in the composite cleaning solution. Therefore, the complexing agent can ensure that the metal ions (copper ions) do not redeposit on the grid surface, thus achieving the purpose of effectively removing the metal ions (copper ions). The surfactant can significantly reduce the surface tension of water, making it easier for the composite cleaning solution to wet the metal surface, especially ensuring that the composite cleaning solution can effectively penetrate some hard-to-reach corners and crevices, and thus ensuring that the complexing agent can effectively complex more metal ions (copper ions) to further ensure the effective removal of metal ions (copper ions). At the same time, the complexing agent and the anionic groups of the surfactant form complexes through hydrogen bonding or electrostatic interaction, which can enhance the peeling ability of particles.

[0038] After removing copper particles from the grid surface using a composite cleaning solution, the presence of tin sludge in the tinning solution is reduced, and the problem of voids in the tin layer on the grid surface can be further improved. This not only improves the appearance of the fabricated solar cell, but also enhances its performance.

[0039] Optionally, the composite cleaning solution, by mass percentage, includes: 0.01-0.5% surfactant (e.g., 0.01%, 0.05%, 0.07%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc., without specific limitation), if the amount of surfactant is too low, it is difficult to effectively reduce the surface tension of the composite cleaning solution; 0.01-0.05% complexing agent (e.g., 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc., without specific limitation), if the amount of complexing agent is too low, it is difficult to form an effective complex with free copper ions; the balance is water.

[0040] Of course, in other embodiments, the percentage of surfactant by mass can be further increased, for example, to 0.01-0.6%.

[0041] In other embodiments, the mass percentage of the complexing agent may be further increased, for example, to 0.01-0.07%.

[0042] Optionally, the surfactant includes ammonium dodecyl sulfate. Ammonium dodecyl sulfate has hydrophilic groups (ammonium sulfate salt) and hydrophobic groups (dodecyl chain), which can significantly reduce the surface tension of water, making it easier for the composite cleaning solution to wet the grid lines, especially some hard-to-reach corners and gaps. That is, it can enable the liquid to quickly wet the copper surface and penetrate into the tiny gaps between the copper particles and the substrate, thus disrupting the physical adsorption between the particles and the substrate.

[0043] Optionally, the complexing agent includes ethylenediaminetetraacetic acid (EDTA). EDTA can form a stable complex with copper ions, reducing the redox potential of copper (Cu). 2+ / Cu), reducing chemical corrosion of the copper substrate during cleaning, maintaining surface smoothness, and these complexes are soluble in the composite cleaning solution, so they will not be redeposited on the gate lines.

[0044] Optionally, the pH of the composite cleaning solution is 5.5~7.0, such as 5.5, 6.0, 6.5, 7.0, etc., and no specific limitation is made here.

[0045] Optionally, the pH of the composite cleaning solution is adjusted with sulfuric acid; the concentration of sulfuric acid is not specifically limited, as long as it is sufficient to adjust the pH. Sulfuric acid can provide hydrogen ions, enhancing the composite cleaning solution's ability to micro-etch copper surface particles and creating a stable active atmosphere for the surfactant, thereby ensuring the effective removal of copper particles from the grid surface.

[0046] Optionally, a specific method for removing copper particles from the grid surface using a composite cleaning solution includes immersing the solar cell in the composite cleaning solution and then ultrasonically agitating it. This further ensures effective removal of copper particles and guarantees a high removal efficiency.

[0047] It should be noted that there are no restrictions on the frequency of ultrasonic stirring, as long as ultrasonic waves are used in conjunction with the soaking of the battery cells in the composite cleaning solution.

[0048] Optionally, the cleaning process may also include acid pickling before using a composite cleaning solution to remove copper particles from the gate surface.

[0049] It should be noted that the pickling method is similar to related technologies, and will not be described in detail here.

[0050] The present invention will be further described in detail below with reference to the embodiments.

[0051] Example 1 Coating, printing, and developing are performed on the copper seed layer of the yellow film. Electroplating is performed on the copper seed layer to form gate lines; Light injection; Cleaning: First, acid washing is performed, followed by the removal of copper particles from the grid surface using a composite cleaning solution. The composite cleaning solution, by mass percentage, comprises: 0.2% ammonium dodecyl sulfate, 0.01% ethylenediaminetetraacetic acid, with the balance being water, and a pH of 5.5. The cleaning method using the composite cleaning solution includes immersing the battery cells in the solution and then ultrasonically stirring.

[0052] Tinning is used to form a tin protective layer on the surface of the gate lines.

[0053] Example 2 Coating, printing, and developing are performed on the copper seed layer of the yellow film. Electroplating is performed on the copper seed layer to form gate lines; Light injection; Cleaning involves first acid washing, followed by the removal of copper particles from the grid surface using a composite cleaning solution. The composite cleaning solution, by mass percentage, comprises: 0.5% ammonium dodecyl sulfate, 0.05% ethylenediaminetetraacetic acid, with the balance being water, and a pH of 7.0. The cleaning method using the composite cleaning solution includes immersing the battery cells in the solution and then ultrasonically agitating them.

[0054] Tinning is used to form a tin protective layer on the surface of the gate lines.

[0055] Example 3 Coating, printing, and developing are performed on the copper seed layer of the yellow film. Electroplating is performed on the copper seed layer to form gate lines; Light injection; Cleaning involves first acid washing, followed by the removal of copper particles from the grid surface using a composite cleaning solution. The composite cleaning solution, by mass percentage, comprises: 0.01% ammonium dodecyl sulfate, 0.02% ethylenediaminetetraacetic acid, with the balance being water, and a pH of 6.5. The cleaning method using the composite cleaning solution includes immersing the battery cells in the solution and then ultrasonically agitating them.

[0056] Tinning is used to form a tin protective layer on the surface of the gate lines.

[0057] Example 4 The difference between Example 4 and Example 1 is that the mass percentage of the complexing agent ethylenediaminetetraacetic acid in the composite cleaning solution is 0.07%; other processes are the same as in Example 1.

[0058] Example 5 The difference between Example 5 and Example 1 is that the mass percentage of the surfactant ammonium dodecyl sulfate in the composite cleaning solution is 0.6%; other processes are the same as in Example 1.

[0059] Example 6 The difference between Example 6 and Example 1 is that the mass percentage of the surfactant ammonium dodecyl sulfate in the composite cleaning solution is 0.6%, and the mass percentage of the complexing agent ethylenediaminetetraacetic acid is 0.07%; other processes are the same as in Example 1.

[0060] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the composite cleaning solution contains only the complexing agent ethylenediaminetetraacetic acid; other processes are the same as in Example 1.

[0061] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the mass percentage of the complexing agent ethylenediaminetetraacetic acid in the composite cleaning solution is 0.005%; other processes are the same as in Example 1.

[0062] The content of tin sludge in the tin-melting solution used in the tin-melting steps of Examples 1-3 and Comparative Examples 1-5 was tested, and the performance of the batteries prepared in Examples 1-3 and Comparative Examples 1-5 was also tested; the results are shown in Table 1.

[0063] Table 1

[0064] According to Table 1, comparing the various embodiments and comparative examples 1 and 2, it can be seen that if the composite cleaning solution contains only a complexing agent without adding a surfactant, or if the content of the complexing agent is too low, the amount of tin sludge in the tin-melting solution will increase significantly, and the performance of the battery will be significantly reduced, the open circuit voltage will be reduced, and Rs will increase significantly.

[0065] In summary, the composite cleaning solution provided by this invention can be used to clean the solar cells before the tinning process in the fabrication of solar cells, thereby removing copper particles from the grid surface. This reduces the displacement of copper particles with tin particles in the tinning solution during the tinning process, thus extending the service life of the tinning solution. Furthermore, by reducing tin sludge in the tinning solution, it improves the problem of voids in the tin layer formed on the grid surface, improving not only the appearance of the fabricated solar cells but also their performance.

[0066] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cleaning solution, characterized by comprising: A cleaning solution for cleaning a solar cell after a photo-injection process in the preparation of the solar cell; The raw materials of the composite cleaning solution include a surfactant and a complexing agent.

2. The composite cleaning solution according to claim 1, wherein The composite cleaning solution includes 0.01-0.5% of the surfactant, 0.01-0.05% of the complexing agent, and the rest is water in terms of mass percentage.

3. The composite cleaning solution of claim 1, wherein The surfactant includes ammonium lauryl sulfate.

4. The composite cleaning solution of claim 1, wherein The complexing agent includes ethylenediaminetetraacetic acid.

5. The composite cleaning solution according to any one of claims 1 to 4, wherein The pH of the composite cleaning solution is 5.5-7.

0.

6. The composite cleaning solution of claim 5, wherein, The pH of the composite cleaning solution is adjusted by sulfuric acid.

7. A method for producing a solar cell, characterized by, The method includes: coating, printing, and developing on a copper seed layer of a yellow film sheet; forming a grid line on the copper seed layer by electroplating; photo-injection; cleaning, which includes removing copper particles on the surface of the grid line by using the composite cleaning solution according to any one of claims 1-6; tin plating to form a tin protective layer on the surface of the grid line.

8. The method of producing a solar cell according to claim 7, wherein The specific method of removing the copper particles on the surface of the grid line by using the composite cleaning solution includes immersing the solar cell sheet in the composite cleaning solution and performing ultrasonic stirring.

9. The method of producing a solar cell according to claim 7, wherein The cleaning further includes pickling before removing the copper particles on the surface of the grid line by using the composite cleaning solution.

10. A solar cell, characterized by, The solar cell is prepared by the method for preparing a solar cell according to any one of claims 7-9.

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