Polishing and etching method of crystalline silicon solar cell

Abstract

The invention provides a polishing and etching method for a crystalline silicon solar cell. The polishing and etching method comprises the following steps: S1, polishing the back surface of a silicon wafer by using a mixed solution of KOH and an alkali polishing additive; s2, using a mixed solution of KOH and H2O2 to carry out a first round of post-cleaning on the silicon wafer; s3, performing a first round of hydrophobic pickling on the surface of the silicon wafer by using an HF solution; s4, using a mixed solution of KOH and H2O2 to carry out a second round of post-cleaning on the silicon wafer; s5, performing a second round of hydrophobic pickling on the surface of the silicon wafer by using an HF solution; and S6, drying the silicon wafer. According to the polishing and etching method of the crystalline silicon solar cell, the production efficiency is improved, the cost is reduced, and the environmental protection property is enhanced by optimizing the whole process steps.

Description

Technical Field

[0001] The invention relates to the field of solar cell manufacturing, and in particular to a polishing and etching method for a crystalline silicon solar cell. Background Art

[0002] Polishing and etching is a key technical step in the production process of crystalline silicon solar cells to improve cell efficiency and quality. Specific methods include traditional acid etching, alkaline etching and polishing. These methods achieve back polishing by removing the damaged layer and contaminants on the surface of the silicon wafer, reducing the electron recombination rate and improving the photoelectric conversion efficiency of the cell. Among them, the traditional acid etching process uses a HF / HNO3 mixed solution to polish the silicon wafer. This method can achieve a certain flatness and polishing effect. However, the drug consumption of this method increases, and the cost also increases by 2-3 times. In addition, although acid etching can achieve back polishing, the high concentration of nitrogen and fluorine-containing element emissions has placed a great burden on wastewater treatment, which has increased the environmental protection pressure on photovoltaic cell manufacturing companies.

[0003] Alkali etching polishing uses inorganic alkali to polish the back and edge of the diffused silicon wafer in the etching process. Compared with the traditional acid polishing process, this method can not only achieve better polishing performance, but also significantly reduce the process cost. However, the current alkaline polishing process still uses a high amount of chemicals in the pre-cleaning and alkaline polishing stages.

[0004] Therefore, it is necessary to design a polishing and etching method for crystalline silicon solar cells to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a polishing and etching method for a crystalline silicon solar cell with high production efficiency, reduced cost and high environmental protection.

[0006] To achieve the above object, the present invention adopts the following technical solution: a polishing and etching method for a crystalline silicon solar cell, comprising the following steps:

[0007] S1, using a mixed solution of KOH and an alkali polishing additive to polish the back side of the silicon wafer;

[0008] S2, using a mixed solution of KOH and H2O2 to perform a first round of post-cleaning on the silicon wafer;

[0009] S3, using HF solution to perform a first round of hydrophobic acid washing on the surface of the silicon wafer;

[0010] S4, using a mixed solution of KOH and H2O2 to perform a second round of post-cleaning on the silicon wafer;

[0011] S5, using HF solution to perform a second round of hydrophobic acid washing on the surface of the silicon wafer;

[0012] S6, drying the silicon wafer.

[0013] As a further improved technical solution of the present invention, in step S1, in the mixed solution of KOH and alkali polishing additive, the concentration of alkali polishing additive is 0.5-1wt%, the concentration of KOH is 3-6wt%, the polishing temperature is 55-60°C, and the polishing time is 180-250s.

[0014] As a further improved technical solution of the present invention, in step S2, in the mixed solution of KOH and H202, the concentration of KOH is 0.03-0.1wt%, the concentration of H202 is 1-3wt%, the cleaning temperature is 30-45°C, and the cleaning time is 40-80s.

[0015] As a further improved technical solution of the present invention, in step S3, the concentration of the HF solution is 3-6wt%, the pickling temperature is 15-20°C, and the pickling time is 70-100s.

[0016] As a further improved technical solution of the present invention, in step S4, in the mixed solution of KOH and H202, the concentration of KOH is 0.03-0.5wt% and the concentration of H202 is 1-2wt%, the cleaning temperature is controlled at 20-30°C, and the cleaning time is 60-100s.

[0017] As a further improved technical solution of the present invention, in step S5, the concentration of the HF solution is 2-4wt%, the pickling temperature is 15-20°C, and the pickling time is 50-80s.

[0018] As a further improved technical solution of the present invention, in step S6, the drying temperature is 90-98°C, and the drying time is 400-600s.

[0019] As a further improved technical solution of the present invention, the alkali polishing additive includes the following components in weight fractions: 70%-75% water, 3%-8% protective agent, 3%-8% defoaming agent, 4%-10% surfactant, and 1%-3% penetrant.

[0020] As a further improved technical solution of the present invention, before step S1, it also includes: washing the silicon wafer with pure water.

[0021] As a further improved technical solution of the present invention, the water washing temperature is 30-45°C and the cleaning time is 5-20s.

[0022] It can be seen from the above technical scheme that the polishing and etching method of the crystalline silicon solar cell of the present invention improves production efficiency, reduces costs, and enhances environmental protection by optimizing the overall process steps. First, by replacing the KOH and H2O2 mixed solution in the pre-cleaning step before alkali polishing with water, the use of KOH and H2O2 is reduced while ensuring the cleanliness and wetness of the silicon wafer, directly reducing the consumption and cost of chemicals, thereby reducing the production cost of the single-chip battery. Secondly, the use and discharge of harmful chemicals are reduced, further reducing the impact on the environment. In addition, by adding a round of post-cleaning and pickling, the surface additive residues are quickly cleaned at high temperature in the first post-cleaning, and the second post-cleaning is carried out at a low concentration and slow cleaning at a lower temperature to deeply clean the surface of the silicon wafer, and the corresponding different pickling concentrations are synchronously guaranteed to ensure hydrophobicity and neutralization, so as to improve the cleaning effect of the silicon wafer, not only improve the metal ion complexing ability, thereby bringing about the opening voltage gain, improving the conversion efficiency of the cell, and compressing the consumption of chemicals. This method can be easily integrated into the existing crystalline silicon solar cell production line, does not require large-scale equipment update or transformation, and provides a flexible technology upgrade path for enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the silicon wafer processed by the method in Comparative Example 1.

[0024] Figure 2 This is a scanning electron microscope image of a silicon wafer processed by the polishing and etching method of the crystalline silicon solar cell in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] A polishing and etching method for a crystalline silicon solar cell comprises the following steps:

[0028] 1. Use pure water to wash the silicon wafer at a temperature of 30°C and a cleaning time of 10 seconds;

[0029] 2. Use a mixed solution of KOH and an alkali polishing additive to polish the back side of the silicon wafer. In the mixed solution of KOH and an alkali polishing additive, the concentration of the alkali polishing additive is 1 wt %, the concentration of KOH is 4 wt %, the polishing temperature is 58° C., and the polishing time is 210 s.

[0030] 3. Use a mixed solution of KOH and H202 to perform the first round of post-cleaning on the silicon wafer. In the mixed solution of KOH and H202, the concentration of KOH is 0.05wt%, the concentration of H202 is 2wt%, the cleaning temperature is 35°C, and the cleaning time is 40s;

[0031] 4. Use HF solution to perform the first round of hydrophobic pickling on the surface of the silicon wafer, the HF solution concentration is 3wt%, the pickling temperature is 20°C, and the pickling time is 70s;

[0032] 5. Use a mixed solution of KOH and H202 to perform a second round of post-cleaning on the silicon wafer. In the mixed solution of KOH and H202, the concentration of KOH is 0.03wt% and the concentration of H202 is 1wt%. The cleaning temperature is controlled at 25°C and the cleaning time is 60s.

[0033] 6. Use HF solution to perform a second round of hydrophobic pickling on the surface of the silicon wafer, the HF solution concentration is 2wt%, the pickling temperature is 20°C, and the pickling time is 50s;

[0034] 7. Dry the silicon wafer at a temperature of 95°C and a drying time of 550 seconds.

[0035] The specific steps of Example 2 and Example 3 are consistent with those of Example 1, and the difference lies in the processing parameters of each step. For detailed parameters, please refer to Table 1, which will not be repeated here.

[0036] Comparative Example 1

[0037] A polishing and etching method for a crystalline silicon solar cell comprises the following steps:

[0038] 1. Use a mixed solution of KOH and H202 to clean the silicon wafer at a cleaning temperature of 35°C and a cleaning time of 10s; in the mixed solution of KOH and H202, the concentration of KOH is 0.1wt% and the concentration of H202 is 2wt%

[0039] 2. Use a mixed solution of KOH and an alkali polishing additive to polish the back side of the silicon wafer. In the mixed solution of KOH and an alkali polishing additive, the concentration of the alkali polishing additive is 1 wt %, the concentration of KOH is 4 wt %, the polishing temperature is 58° C., and the polishing time is 210 s.

[0040] 3. Use a mixed solution of KOH and H202 to post-clean the silicon wafer. In the mixed solution of KOH and H202, the concentration of KOH is 0.1wt%, the concentration of H202 is 4wt%, the cleaning temperature is 35°C, and the cleaning time is 40s;

[0041] 4. Use HF solution to perform hydrophobic pickling on the surface of the silicon wafer, the HF solution concentration is 3wt%, the pickling temperature is 20°C, and the pickling time is 70s;

[0042] 5. Dry the silicon wafer at a temperature of 95°C and a drying time of 550 seconds.

[0043] The specific steps of Comparative Examples 2-4 are consistent with those of Comparative Example 1, except for the processing parameters of each step. For detailed parameters, please refer to Table 1, which will not be repeated here.

[0044] Table 1 Parameters of each step in each embodiment and comparative example

[0045]

[0046] The silicon wafers after treatment in each embodiment and comparative example were further tested, and the specific test items and results are shown in Table 2. Among them, the tower base size is a key parameter for measuring the size of the pyramid structure on the surface of the silicon wafer, which not only affects the photoelectric conversion efficiency of the battery cell, but also is related to the optimization and yield rate of the subsequent process. Figure 1 , Figure 2 It can be seen that the tower base and appearance of the embodiments are normal compared with the comparative examples. In addition, the reflectivity values ​​in Table 2 show that there is no difference between the embodiments and the comparative examples. The open circuit voltage of each embodiment is better than that of the comparative example, which is increased by about 5%.

[0047] Table 2 Test results of silicon wafers after treatment in various embodiments and comparative examples

[0048]

[0049]

[0050] The silicon wafers after treatment of each embodiment and the comparative example are further compared as shown in the following Table 3. As can be seen from Table 3, in the data comparison of each item of conversion efficiency (Eta), short circuit current (lsc), fill factor (FF), series resistance (RS), parallel resistance (Rsh) and reverse saturation current (IRev2), the embodiment shows advantages over the comparative example.

[0051] Table 3 Efficiency comparison data between the embodiments and comparative examples

[0052]

[0053] The above embodiments are only used to illustrate the present invention but not to limit the technical solutions described in the present invention. The understanding of this specification should be based on the technicians in the relevant technical field. Although this specification has described the present invention in detail with reference to the above embodiments, ordinary technicians in the field should understand that technicians in the relevant technical field can still modify or replace the present invention with equivalents, and 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 polishing and etching method for a crystalline silicon solar cell, characterized in that: The following steps are involved: S1, using a mixed solution of KOH and an alkali polishing additive to polish the back side of the silicon wafer; S2, using a mixed solution of KOH and H2O2 to perform a first round of post-cleaning on the silicon wafer; S3, using HF solution to perform a first round of hydrophobic acid washing on the surface of the silicon wafer; S4, using a mixed solution of KOH and H2O2 to perform a second round of post-cleaning on the silicon wafer; S5, using HF solution to perform a second round of hydrophobic acid washing on the surface of the silicon wafer; S6, drying the silicon wafer.

2. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S1, in the mixed solution of KOH and alkali polishing additive, the concentration of alkali polishing additive is 0.5-1wt%, the concentration of KOH is 3-6wt%, the polishing temperature is 55-60°C, and the polishing time is 180-250s.

3. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S2, in the mixed solution of KOH and H202, the concentration of KOH is 0.03-0.1wt%, the concentration of H202 is 1-3wt%, the cleaning temperature is 30-45°C, and the cleaning time is 40-80s.

4. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S3, the concentration of HF solution is 3-6wt%, the pickling temperature is 15-20°C, and the pickling time is 70-100s.

5. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S4, in the mixed solution of KOH and H202, the concentration of KOH is 0.03-0.5wt%, the concentration of H202 is 1-2wt%, the cleaning temperature is controlled at 20-30°C, and the cleaning time is 60-100s.

6. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S5, the concentration of the HF solution is 2-4 wt %, the pickling temperature is 15-20° C., and the pickling time is 50-80 s.

7. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: In step S6, the drying temperature is 90-98° C. and the drying time is 400-600 seconds.

8. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: The alkali polishing additive comprises the following components in weight fractions: 70%-75% of water, 3%-8% of a protective agent, 3%-8% of a defoaming agent, 4%-10% of a surfactant, and 1%-3% of a penetrant.

9. The polishing and etching method for a crystalline silicon solar cell according to claim 1, characterized in that: Before step S1, the method further includes: washing the silicon wafer with pure water.

10. The polishing and etching method for a crystalline silicon solar cell according to claim 9, characterized in that: The water washing temperature is 30-45℃ and the cleaning time is 5-20s.

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