A cleaning method for grid line electrodes of crystalline silicon solar cell wafers

Abstract

The present invention belongs to the technical field of crystalline silicon solar cells, and particularly relates to a cleaning method for grid line electrodes of crystalline silicon solar cell wafers. The present invention develops a cleaning method for grid line electrodes of crystalline silicon solar cell wafers. By using an alkaline solution and a mixed acid solution to clean and remove the grid lines on the screen-printed and sintered cell wafers, each process can be carried out at room temperature, which can better control the reaction rate and cleaning degree, with a short process time and low energy consumption. Through the implementation of this technical route, the grid line electrodes on the surface of the cell wafers can be effectively removed. After the cleaning process, the surface of the cell wafers has a high cleanliness, no residue, and the overall cleaning process does not damage the silicon wafers, and has good conformal properties for the etching marks formed on the surface of the emitter due to the high-temperature sintering of the paste.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline silicon solar cells, and particularly relates to a cleaning method for grid line electrodes of crystalline silicon solar cell wafers. Background Art

[0002] A large number of waste products and greenhouse gases generated during the utilization of traditional fossil energy have exacerbated the pollution of the natural environment and led to the increasingly deteriorating ecology of the earth. Since the 21st century, people have generally recognized the key position of various new clean and renewable energies in the future energy structure. Among them, photovoltaic power generation has been widely recognized due to its advantages such as pollution-free and not restricted by the usage area. Among various solar cells, crystalline silicon solar cells occupy a dominant position in the photovoltaic field due to their rich raw material reserves and mature processes. At the same time, further improving efficiency and reducing costs has also become the focus of research in the field of crystalline silicon solar cells. Screen printing metallization is currently the most widely used electrode preparation process in the mass production of crystalline silicon solar cells and has an important impact on the energy output of the cell wafers. At present, the photoelectric conversion efficiency of crystalline silicon solar cells gradually shows a bottleneck, and the recombination loss caused by metallization accounts for a large proportion. In order to optimize the paste formula and sintering process and further improve the cell efficiency, it is necessary to accurately calculate the recombination current density at the metal-semiconductor contact interface. One method is to remove the grid line electrodes on the surface of the finished cell wafers and then test and calculate through the QSSPC (quasi-steady-state photoconductance) technology. Screen printing requires extremely high precision, and it is inevitable to produce defective wafers due to mechanical factors or human factors during the operation. To save materials and reduce production costs, defective products after the metallization process are often reworked, and the grid lines are removed by chemical corrosion and other means for reprinting.

[0003] Patent CN111641387A proposes a method for testing the metal contact recombination value and a solar cell. At least two grid line patterns with different metal ratios are printed on a sample to be tested. After rapid sintering, the grid line patterns with different metal ratios are cleaned, and the total dark saturation current density values corresponding to the grid line patterns with different metal ratios are tested. The data of different metal ratios and the data of the total dark saturation current density values corresponding to the grid line patterns with different metal ratios are collected, and a scatter plot is drawn to obtain the slope and intercept of the linear function; according to the slope and intercept of the linear function and the surface recombination model, the metal contact recombination value is calculated. The method used to clean the metal grid line patterns on the sample to be tested in this technology is the solution corrosion method, and the corrosion solution is one or any mixture of hydrochloric acid, nitric acid, and hydrofluoric acid. The corrosion time is 4 - 24h. The overall time of the metal grid line cleaning process in this technology is too long, which is not conducive to carrying out continuous test experiments.

[0004] Patent CN102629644B proposes a rework process for finished crystalline silicon solar cell wafers. The finished cell wafers to be reworked are screened and classified, and silicon under the grid line electrodes is etched away using a NaOH solution with a mass percentage content of 20 - 40%, thereby stripping the front and back electrodes of the finished cell wafers, restoring the defective cell wafers to the original silicon wafers, and then manufacturing the original silicon wafers into qualified cell wafers according to the conventional process. The grid line cleaning process of this technology damages the textured surface of defective wafers, and it is necessary to re-texture and re-form a junction during subsequent rework, complicating the rework process, which restricts its industrial promotion.

[0005] Patent CN102208488B proposes a method for treating screen-printed defective wafers. First, the printed defective wafers are placed in an ultrasonic bath containing an alcohol solution to remove the paste, and then the defective wafers after removing the paste are successively soaked in an HCl solution with a concentration of 6 - 7% for 6 - 12 h, soaked in water for 0.5 - 1 h, and finally placed in an ultrasonic bath containing a pure alcohol solution for further cleaning and drying. In the industrial screen printing metallization process, the rapid sintering process will cause complex silicides to form at the metal-semiconductor interface, and this technology is insufficient for reworking defective wafers after sintering.

[0006] Therefore, it is very necessary to find a cleaning process that can quickly remove the grid line electrodes completely and cause no damage to the surface morphology of the silicon wafer. Summary of the Invention

[0007] In the screen printing metallization process, in order to rework defective cell wafers or characterize the recombination current density under the metal, it is often necessary to clean and remove the grid line electrodes after printing and sintering. To achieve this purpose, some technical solutions use a mixed etching solution including a combination of nitric acid / hydrofluoric acid, which also damages the silicon wafer while removing the grid line electrodes; some technical solutions have incomplete cleaning, resulting in a large number of recombination centers on the silicon wafer surface, affecting the rework or measurement and characterization of the cell wafers.

[0008] The present invention aims at the shortcomings of these existing technologies and develops a grid line electrode cleaning method with a short process time, good cleaning effect, and no damage to the surface morphology of the silicon wafer, which is applied to optimize the paste formula and sintering process, improve the cell efficiency, and is applied to the rework of defective wafers to save materials and reduce production costs.

[0009] To solve the above existing technical problems, the present application provides the following technical solutions:

[0010] The present invention provides a method for cleaning grid line electrodes of crystalline silicon solar cell wafers, comprising the following steps:

[0011] S1: Add the cell after screen printing and sintering into the mixed solution for corrosion for 5 - 15 minutes, then wash with water to obtain the once - corroded cell; the mixed solution includes ammonia water, hydrogen peroxide and water.

[0012] S2: Add the once - corroded cell into hydrofluoric acid for corrosion for 5 - 25 minutes, then wash with water to obtain the twice - corroded cell.

[0013] S3: Add the twice - corroded cell into the mixed solution again for corrosion for 1 - 10 minutes, then wash with water to obtain the thrice - corroded cell.

[0014] S4: Add the thrice - corroded cell into mixed acid solution A for corrosion for 5 - 15 minutes, then wash with water to obtain the four - times - corroded cell; the mixed acid solution A includes hydrochloric acid and nitric acid.

[0015] S5: Wash the four - times - corroded cell with mixed acid solution B for 5 - 15 minutes, then wash with water for 1 - 10 minutes, and dry, thus completing the cleaning of the grid electrodes of the crystalline silicon solar cell. The mixed acid solution B includes hydrofluoric acid and hydrochloric acid.

[0016] Preferably, in the mixed solution, the concentrations of ammonia water and hydrogen peroxide are both 1 - 10 wt%.

[0017] Specifically, in the mixed solution, the concentration of ammonia water is 4 wt%.

[0018] Specifically, in the mixed solution, the concentration of hydrogen peroxide is 4.3 wt%.

[0019] Specifically, in step S1, the corrosion time is 10 minutes, and the main part of the grid electrode is removed through the silver - ammonia complex reaction.

[0020] Preferably, in step S2, the concentration of hydrofluoric acid is 0.5 - 10 wt%.

[0021] Preferably, in step S2, the concentration of hydrofluoric acid is 2 - 3 wt%.

[0022] Specifically, in step S2, the corrosion time is 15 minutes, and the glass layer and silicon nitride at the metal - semiconductor contact interface are removed.

[0023] Specifically, in step S3, the corrosion time is 5 minutes, and the silver and its compounds originally covered by the glass layer on the emitter are removed.

[0024] Preferably, in the mixed acid solution A, the concentration of hydrochloric acid is 10 - 50 wt%.

[0025] Preferably, in the mixed acid solution A, the concentration of nitric acid is 5 - 35 wt%.

[0026] Specifically, in the mixed acid solution A, the concentration of hydrochloric acid is 28 wt%.

[0027] Specifically, in the mixed acid solution A, the concentration of nitric acid is 17 wt%.

[0028] Specifically, in step S4, the corrosion time is 10 min to remove aluminum, lead, tellurium and their compounds in the grid electrode.

[0029] Preferably, in the mixed acid solution B, the concentration of hydrofluoric acid is 0.5 - 10 wt%.

[0030] Preferably, in the mixed acid solution B, the concentration of hydrochloric acid is 0.5 - 10 wt%.

[0031] Specifically, in the mixed acid solution B, the concentration of hydrofluoric acid is 2.5 wt%.

[0032] Specifically, in the mixed acid solution B, the concentration of hydrochloric acid is 2 wt%.

[0033] Preferably, in step S5, the method of cleaning with the mixed acid solution B is ultrasonic cleaning, with an ultrasonic power of 110 - 130 W and a frequency of 35 - 45 kHz, to thoroughly remove the residual impurities on the emitter surface.

[0034] Specifically, the ultrasonic cleaning time is 10 min.

[0035] Preferably, in step S5, the method of cleaning with water is ultrasonic cleaning, with an ultrasonic power of 110 - 130 W and a frequency of 35 - 45 kHz.

[0036] Specifically, the ultrasonic cleaning time is 3 min.

[0037] The present invention provides a cleaning method for the grid electrode of a crystalline silicon solar cell wafer, that is, using an alkali solution and a mixed acid solution to chemically corrode the wafer after screen printing and sintering to achieve the cleaning and removal of the grid electrode. This process not only has a good cleaning effect but also does not damage the morphology of the silicon wafer, and can be applied to the rework of defective wafers and the measurement and calculation of the recombination current density at the metal-semiconductor contact interface.

[0038] The technical solution of the present invention has the following advantages compared with the prior art:

[0039] 1. The present invention develops a cleaning method for the grid electrode of a crystalline silicon solar cell wafer. By using an alkali solution and a mixed acid solution to clean and remove the grid of the wafer after screen printing and sintering, each process can be carried out at room temperature, which can better control the reaction rate and cleaning degree, with a short process time and low energy consumption.

[0040] 2. By implementing this technical route, the grid electrodes on the surface of the battery cells can be effectively removed. After the cleaning process, the surface of the battery cells has a high cleanliness, no residue, and the overall cleaning process causes no damage to the silicon wafers. It has good conformal properties for the etching marks formed on the emitter surface due to the high-temperature sintering of the paste. Description of the Drawings

[0041] Figure 1 SEM (scanning electron microscope) scan of the surface of the battery cell before cleaning the grid electrodes Figure I (1K).

[0042] Figure 2 SEM scan of the surface of the battery cell after cleaning the grid electrodes Figure II (1K).

[0043] Figure 3 SEM scan image (30K) of the surface of the battery cell after cleaning the grid electrodes. Detailed Embodiment

[0044] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments given are not intended to limit the present invention.

[0045] Embodiment 1

[0046] (1) The battery cells after screen printing and sintering are corroded in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature to remove the main part of the grid electrodes through the silver ammonia complex reaction. The mass concentration of ammonia water is 4%, the mass concentration of hydrogen peroxide is 4.3%, and the corrosion time is 10 min;

[0047] (2) After the battery cells obtained in step (1) are washed with deionized water and spun dry, they are soaked in a hydrofluoric acid solution at room temperature (25 ± 5 °C) to remove the glass layer and silicon nitride at the metal-semiconductor contact interface. The mass concentration of hydrofluoric acid is 2.5%, and the corrosion time is 15 min;

[0048] (3) After the battery cells obtained in step (2) are washed with deionized water and spun dry, they are again placed in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature for cleaning to remove the silver and its compounds originally covered by the glass layer on the emitter. The mass concentration of ammonia water is 4%, the mass concentration of hydrogen peroxide is 4.3%, and the corrosion time is 5 min;

[0049] (4) After the battery cells obtained in step (3) are washed with deionized water and spun dry, they are corroded in a mixed solution of hydrochloric acid and nitric acid at room temperature to remove aluminum, lead, tellurium, and their compounds in the grid electrodes. The mass concentration of hydrochloric acid is 28%, the mass concentration of nitric acid is 17%, and the corrosion time is 10 min;

[0050] (5) After cleaning the solar cell obtained in step (4) with deionized water and spin-drying it, perform ultrasonic cleaning in a mixed solution of hydrofluoric acid and hydrochloric acid at room temperature to thoroughly remove the residual impurities on the surface of the emitter. The mass concentration of hydrofluoric acid is 2.5%, the mass concentration of hydrochloric acid is 2%, the etching time is 10 min, the ultrasonic power is 120 W, and the frequency is 40 kHz.

[0051] (6) Perform ultrasonic cleaning of the solar cell obtained in step (5) with deionized water and spin-drying it. The cleaning time is 3 min, the ultrasonic power is 120 W, and the frequency is 40 kHz.

[0052] Example 2

[0053] (1) Corrode the screen-printed and sintered solar cell in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature to remove the main part of the grid electrode through the silver-ammonia complex reaction. The mass concentration of ammonia water is 1%, the mass concentration of hydrogen peroxide is 1%, and the etching time is 5 min;

[0054] (2) After cleaning the solar cell obtained in step (1) with deionized water and spin-drying it, soak it in a hydrofluoric acid solution at room temperature to remove the glass layer and silicon nitride at the metal-semiconductor contact interface. The mass concentration of hydrofluoric acid is 0.5%, and the etching time is 5 min;

[0055] (3) After cleaning the solar cell obtained in step (2) with deionized water and spin-drying it, place it again in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature for cleaning to remove the silver and its compounds on the emitter that were originally covered by the glass layer. The mass concentration of ammonia water is 1%, the mass concentration of hydrogen peroxide is 1%, and the etching time is 1 min;

[0056] (4) After cleaning the solar cell obtained in step (3) with deionized water and spin-drying it, corrode it in a mixed solution of hydrochloric acid and nitric acid at room temperature to remove aluminum, lead, tellurium, and their compounds in the grid electrode. The mass concentration of hydrochloric acid is 10%, the mass concentration of nitric acid is 5%, and the etching time is 5 min;

[0057] (5) After cleaning the solar cell obtained in step (4) with deionized water and spin-drying it, perform ultrasonic cleaning in a mixed solution of hydrofluoric acid and hydrochloric acid at room temperature to thoroughly remove the residual impurities on the surface of the emitter. The mass concentration of hydrofluoric acid is 0.5%, the mass concentration of hydrochloric acid is 0.5%, the etching time is 5 min, the ultrasonic power is 110 W, and the frequency is 35 kHz.

[0058] (6) Perform ultrasonic cleaning of the solar cell obtained in step (5) with deionized water and spin-drying it. The cleaning time is 1 min, the ultrasonic power is 110 W, and the frequency is 35 kHz.

[0059] Example 3

[0060] (1) The cell after screen printing and sintering is etched in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature, and the main part of the grid electrode is removed through the silver ammonia complex reaction. The mass concentration of ammonia water is 10%, the mass concentration of hydrogen peroxide is 10%, and the etching time is 15 min;

[0061] (2) After the cell obtained in step (1) is washed with deionized water and spun dry, it is soaked in a hydrofluoric acid solution at room temperature to remove the glass layer and silicon nitride at the metal-semiconductor contact interface. The mass concentration of hydrofluoric acid is 10%, and the etching time is 25 min;

[0062] (3) After the cell obtained in step (2) is washed with deionized water and spun dry, it is again placed in a mixed solution of ammonia water, hydrogen peroxide, and deionized water at room temperature for cleaning to remove the silver and its compounds originally covered by the glass layer on the emitter. The mass concentration of ammonia water is 10%, the mass concentration of hydrogen peroxide is 10%, and the etching time is 10 min;

[0063] (4) After the cell obtained in step (3) is washed with deionized water and spun dry, it is etched in a mixed solution of hydrochloric acid and nitric acid at room temperature to remove aluminum, lead, tellurium, and their compounds in the grid electrode. The mass concentration of hydrochloric acid is 50%, the mass concentration of nitric acid is 35%, and the etching time is 15 min;

[0064] (5) After the cell obtained in step (4) is washed with deionized water and spun dry, it is ultrasonically cleaned in a mixed solution of hydrofluoric acid and hydrochloric acid at room temperature to thoroughly remove the residual impurities on the emitter surface. The mass concentration of hydrofluoric acid is 10%, the mass concentration of hydrochloric acid is 10%, the etching time is 15 min, the ultrasonic power is 130 W, and the frequency is 45 kHz.

[0065] (6) The cell obtained in step (5) is ultrasonically cleaned with deionized water and spun dry. The cleaning time is 10 min, the ultrasonic power is 130 W, and the frequency is 45 kHz.

[0066] Effect Evaluation 1

[0067] Comparison Figure 1 With Figure 2 It can be seen that this scheme has a good cleaning effect on the grid electrode of the cell. By observing Figure 3 It can be seen that the surface morphology of the emitter has not changed after cleaning, that is, the method of the present invention has no damage to the silicon wafer and has good shape retention for the etching marks formed on the emitter surface due to high-temperature sintering of the paste.

[0068] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A cleaning method for the grid line electrodes of a crystalline silicon solar cell, characterized in that, it comprises the following steps: S1: Add the cell after screen printing and sintering into a mixed solution for etching for 5 - 15 min, then wash with water to obtain a once-etched cell; the mixed solution includes ammonia water, hydrogen peroxide and water; S2: Add the once-etched cell into hydrofluoric acid for etching for 5 - 25 min, then wash with water to obtain a twice-etched cell; S3: Add the twice-etched cell into the mixed solution again for etching for 1 - 10 min, then wash with water to obtain a thrice-etched cell; S4: Add the thrice-etched cell into mixed acid solution A for etching for 5 - 15 min, then wash with water to obtain a four-times-etched cell; the mixed acid solution A includes hydrochloric acid and nitric acid; S5: Wash the four-times-etched cell with mixed acid solution B for 5 - 15 min and then wash with water for 1 - 10 min, and dry, thus completing the cleaning of the grid line electrodes of the crystalline silicon solar cell; the mixed acid solution B includes hydrofluoric acid and hydrochloric acid; in step S5, the method of washing with mixed acid solution B is ultrasonic cleaning, the ultrasonic power is 110 - 130 W, and the frequency is 35 - 45 kHz; the method of washing with water is ultrasonic cleaning, the ultrasonic power is 110 - 130 W, and the frequency is 35 - 45 kHz.

2. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in the mixed solution, the concentrations of ammonia water and hydrogen peroxide are both 1 - 10wt%.

3. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in step S2, the concentration of hydrofluoric acid is 0.5 - 10wt%.

4. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in step S2, the concentration of hydrofluoric acid is 2 - 3wt%.

5. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in the mixed acid solution A, the concentration of hydrochloric acid is 10 - 50wt%.

6. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in the mixed acid solution A, the concentration of nitric acid is 5 - 35wt%.

7. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in the mixed acid solution B, the concentration of hydrofluoric acid is 0.5 - 10wt%.

8. The cleaning method for the grid line electrodes of a crystalline silicon solar cell according to claim 1, characterized in that, in the mixed acid solution B, the concentration of hydrochloric acid is 0.5 - 10wt%.

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