Photovoltaic cell alkali polishing method capable of improving liquid carrying phenomenon

Abstract

The invention relates to a photovoltaic cell alkaline polishing method capable of improving a liquid carrying phenomenon, which comprises a step of carrying out alkaline polishing on a silicon wafer, and in the alkaline polishing step, the alkaline polishing temperature is 55-60 DEG C, and the alkaline polishing time is 150-200s. The alkaline polishing temperature and time are adjusted, so that the corrosion amount of the silicon wafer is reduced, the thickness of the silicon wafer is ensured, the risk that the bending degree is too large due to the fact that the silicon wafer is too thin is reduced, and the silicon wafer is prevented from being attached and carrying liquid; meanwhile, the reaction intensity of the tank body is reduced, the integrity of the silicon wafer in the basket is improved, and the tooth staggering risk is reduced, so that the liquid carrying phenomenon is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic cells, and in particular to an alkali polishing method for photovoltaic cells capable of improving the phenomenon of liquid carrying. Background Art

[0002] In the preparation process of TOPCon cells, the TOPCon alkaline polishing process mainly polishes the pyramid velvet structure on the back side. Polishing the pyramid velvet structure on the back side can effectively reduce the surface recombination rate of carriers, increase the minority carrier lifetime, and increase the internal reflection of light, thereby improving the cell conversion efficiency. The back polishing process prepares for the subsequent preparation of the tunneling layer of the cell. Its polishing effect affects the uniformity of the poly tunneling layer, and then affects the uniformity and passivation effect of the tunneling layer. Therefore, the alkaline polishing process plays an important role in the production of cells.

[0003] At present, cost reduction has become the top priority in the industry. The development of thin silicon wafers and the continuous reduction of chemical consumption have become the mainstream direction. With the introduction of thin wafers, the thickness of silicon wafers has gradually become thinner, and the thickness of silicon wafers has gradually decreased from 180μm to the current 120μm. The processing difficulty of downstream solar cells has become increasingly greater, and the process fragmentation rate has become increasingly higher. The production line needs to cooperate with the continuous development and matching of the process to solve the efficiency fluctuations and yield effects caused by thin wafers. After the wet process section is corroded by two stages of texturing and alkaline polishing, the overall thickness of the silicon wafer is between 110-115μm. If the silicon wafer is too thin, it will cause problems such as fragmentation and patch liquid in production.

[0004] During the production process of the alkali polishing line, the following situations are likely to cause liquid contamination: 1. The original silicon wafer is getting thinner and thinner. The greater the curvature of the wafer, the easier it is to deform. During the production process, it is easy to bend and fit. At the same time, the alkaline solution is viscous, which makes the fit tight and difficult to separate. In the subsequent tank reaction, there is a risk of liquid contamination and fragments; 2. The silicon wafer reacts violently with alkali and silicon in the alkali polishing tank, releasing a large amount of hydrogen bubbles, causing the silicon wafer to protrude from the teeth of the flower basket. When the robot arm is used to lift / put it into the basket, it is easy to cause the silicon wafer to misalign the teeth at the bottom of the flower basket, resulting in the middle of the silicon wafer being mounted and the bottom misaligned. Liquid contamination; 3. The surface dehydration of the silicon wafer is biased. This is because in the PE-Poly route, In the alkali polishing process, the HF in the acid tank will destroy the silicon oxide film structure on the back of the battery, causing the exposed silicon substrate on the back to be naturally oxidized by oxygen in the air, and the thickness uniformity of the naturally grown silicon oxide will deviate, which will affect the passivation effect and cause serious efficiency loss. Therefore, in the conventional PE-Poly route, the alkali polishing acid tank only uses hydrochloric acid to neutralize the alkaline residue in the previous process and remove metal impurities on the surface of the silicon wafer without using hydrofluoric acid. The acid tank does not use hydrofluoric acid, which will aggravate the poor dehydration effect on the surface of the silicon wafer (because hydrofluoric acid can remove the silicon oxide layer on the surface, form Si-H passivation bonds with the silicon dangling bonds on the silicon surface, and increase the hydrophobicity of the silicon wafer) and aggravate the generation of liquid. The above three situations are the main reasons for liquid on the production line. However, the phenomenon of liquid on the alkali polishing is easy to cause electroluminescence (EL) and appearance yield problems, such as: EL basket print (liquid contaminates the basket teeth, causing problems such as residual liquid at the position of the basket teeth), EL dirt (after the liquid-carrying wafer is unloaded from the silicon wafer, the intermediate liquid is not cleaned and remains on the surface, and the EL imaging is locally dark and dirty), which urgently needs to be improved and solved. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a photovoltaic cell alkaline polishing method that can improve the liquid carrying phenomenon, so as to solve the problem of liquid carrying during alkali polishing.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a photovoltaic cell alkali polishing method capable of improving the liquid carrying phenomenon, which comprises the step of alkali polishing a silicon wafer, wherein the alkali polishing temperature is 55-60° C. and the alkali polishing time is 150-200 s.

[0008] The present invention adjusts the alkali polishing temperature and time to reduce the corrosion amount of the silicon wafer, ensure the thickness of the silicon wafer, reduce the risk of excessive bending caused by the silicon wafer being too thin, and avoid the silicon wafer being fitted and carrying liquid; at the same time, the intensity of the reaction of the tank body is reduced, the integrity of the silicon wafer inside the flower basket is improved, the risk of misalignment is reduced, and thus the liquid carrying phenomenon is reduced.

[0009] As a further improvement of the above scheme of the present invention, after the alkali polishing step, the weight loss of the silicon wafer is 0.13-0.15g.

[0010] As a further improvement of the above solution of the present invention, after the alkali polishing step, the tower base size of the silicon wafer is 5-7 μm.

[0011] As a further improvement of the above scheme of the present invention, the photovoltaic cell alkali polishing method further includes a slow pulling step after the alkali polishing step: in the slow pulling step, the slow pulling temperature is 50-60°C.

[0012] As a further improvement of the above solution of the present invention, the slow pulling time is 15-30s.

[0013] As a further improvement of the above-mentioned solution of the present invention, the photovoltaic cell alkali polishing method further includes a loading step, a pre-cleaning step, and a water washing step which are sequentially arranged before the alkali polishing step.

[0014] As a further improvement of the above scheme of the present invention, the pre-cleaning liquid used in the pre-cleaning is a mixture of sodium hydroxide solution and hydrogen peroxide in a volume ratio of (1-3): (8-12), the pre-cleaning temperature is 40-50°C, and the time is 80-120s;

[0015] And / or, the temperature of the first water washing is 20-30°C and the time is 110-130s.

[0016] As a further improvement of the above scheme of the present invention, the photovoltaic cell alkaline polishing method also includes a secondary water washing step, an alkaline washing step, a tertiary water washing step, an acid washing step, and a fourth water washing step, which are sequentially arranged between the alkaline polishing step and the slow pulling step.

[0017] As a further improvement of the above scheme of the present invention, the temperature of the second water washing, the third water washing and the fourth water washing are all 20-30°C, and the time is 110-130s;

[0018] And / or, the alkali solution used in the alkali washing is a mixture of sodium hydroxide solution and hydrogen peroxide in a volume ratio of (2-6):(10-25), the temperature of the alkali washing is 40-60° C., and the time is 90-120 s;

[0019] And / or, the acid solution used for pickling is a hydrochloric acid solution, the temperature of the pickling is 20-30° C., and the time is 90-110 s.

[0020] As a further improvement of the above-mentioned solution of the present invention, the photovoltaic cell alkaline polishing method further includes a drying step arranged after the slow pulling step, and the drying temperature is 95-98° C. and the drying time is 660-720 seconds.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The photovoltaic cell alkaline polishing method proposed in the present invention reduces the corrosion amount of silicon wafers by adjusting the alkali polishing temperature and time, ensures the thickness of silicon wafers, reduces the risk of excessive bending caused by too thin silicon wafers, and avoids silicon wafers being fitted and carrying liquid; at the same time, the reaction temperature is lowered to reduce the intensity of the reaction, improve the integrity of the silicon wafers inside the flower basket, reduce the risk of misalignment, and thus reduce the liquid carrying phenomenon.

[0023] After alkaline polishing, the weight reduction of the silicon wafer of the present invention is 0.13-0.15g. As the basic material of the battery, the thickness of the silicon wafer directly affects the absorption depth of sunlight. Too thin silicon wafers may not be able to fully absorb the long-wave part of the spectrum, resulting in this part of energy not being utilized, thereby reducing the overall photoelectric conversion efficiency of the battery. With the trend of thinning, the low weight reduction of the present invention also brings efficiency gains.

[0024] The photovoltaic cell alkaline polishing method proposed in the present invention also optimizes the slow pulling step. The slow pulling temperature is increased from room temperature of 20-30°C to 50-60°C hot water slow pulling, which helps to reduce the surface tension of the silicon wafer and can effectively pull most of the water film adsorbed on the surface of the silicon wafer off the silicon wafer, thereby achieving pre-dehydration; secondly, increasing the slow pulling temperature can make the surface of the silicon wafer fully contact with hot water. The hot water has a high dissolution rate and high saturation, which is beneficial to the cleaning of silicates and acid and alkali residues, thereby reducing the adhesion between silicon wafers and reducing the risk of patch liquid.

[0025] The present invention improves the silicon wafer corrosion depth and reaction intensity by optimizing the reaction temperature and time of the alkali blasting tank, and secondly, by increasing the slow pulling temperature, changes the surface tension of the silicon wafer, solves the problems of silicon wafer surface dehydration and residual liquid on the silicon wafer surface, and finally improves the problem of liquid carrying when alkali blasting is discharged. DETAILED DESCRIPTION

[0026] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] Example 1

[0029] This embodiment provides a photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon, which comprises the following steps:

[0030] 1. Loading: Place the silicon wafer after PSG treatment on the loading table through the robotic arm;

[0031] 2. Pre-cleaning: Soak the silicon in a pre-cleaning solution, which is a mixture of a sodium hydroxide solution with a mass concentration of 46% and a hydrogen peroxide solution with a mass concentration of 35%. The volume ratio of the sodium hydroxide solution to the hydrogen peroxide solution is 2:10. The temperature of the pre-cleaning solution is 44°C and the pre-cleaning time is 100s.

[0032] 3. Primary water washing: Soak the pre-cleaned silicon wafer in pure water for 120 seconds;

[0033] 4. Alkali polishing: The silicon wafer that has been washed once is immersed in an alkali solution for back polishing. The alkali solution contains a sodium hydroxide solution with a mass concentration of 46% and an additive. The volume ratio of the sodium hydroxide solution to the additive is 9:1.6. The alkali solution temperature is 58°C and the alkali polishing time is 200s. After alkali polishing, the weight loss of the silicon wafer is 0.13-0.15g, and the tower base size is 5-7μm.

[0034] 5. Secondary water washing: Soak the alkaline polished silicon wafer in pure water for 120 seconds;

[0035] 6. Alkali washing: Soak the silicon wafers that have completed the secondary water washing in an alkali solution, which is a mixture of a sodium hydroxide solution with a mass concentration of 46% and a hydrogen peroxide solution with a mass concentration of 35%. The volume ratio of the sodium hydroxide solution to the hydrogen peroxide solution is 4:20, the alkali solution temperature is 50°C, and the alkali washing time is 100s;

[0036] 7. Three-time water washing: Soak the silicon wafer after alkaline washing in pure water for 120 seconds;

[0037] 8. Pickling: Soak the silicon wafers that have completed three water washings in a 37% HCL solution for pickling at a temperature of 25°C and a pickling time of 100 seconds.

[0038] 9. Four times water washing: Soak the acid-washed silicon wafer in pure water for 120 seconds;

[0039] 10. Slow pulling: Soak the silicon wafer that has been washed four times in pure water and slowly pull it out of the water for pre-dehydration. The pulling temperature is 55°C and the slow pulling time is 25s.

[0040] 11. Drying: Place the pre-dehydrated silicon wafers in a drying tank for drying at a temperature of 95°C for 700 seconds.

[0041] Steps 1-11 are the entire alkali polishing process. In this embodiment, each batch of 400 sheets is subjected to alkali polishing.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that in this embodiment, the temperature of the alkali polishing step in step 4 is 55° C., and the alkali polishing time is 180 s; the temperature of the slow pulling step in step 10 is 50° C.

[0044] Example 3

[0045] The difference between this embodiment and embodiment 1 is that in this embodiment, the temperature of the alkali polishing step in step 4 is 60°C, and the alkali polishing time is 150s; the temperature of the slow pulling step in step 10 is 60°C.

[0046] Example 4

[0047] The difference between this embodiment and embodiment 1 is that in this embodiment, the temperature of the alkali polishing step in step 4 is 56° C., and the alkali polishing time is 160 s; the temperature of the slow pulling step in step 10 is 58° C.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that in this comparative example, the temperature of the alkali polishing step in the fourth step is 68° C. and the time is 250 s; the temperature of the slow pulling step in the tenth step is 25° C.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that in this comparative example, the temperature of the alkali polishing step in the fourth step is 68°C, and the temperature of the slow pulling step in the tenth step is 25°C.

[0052] Comparative Example 3

[0053] The difference between this comparative example and Example 1 is that in this comparative example, the time of the alkali polishing step in the fourth step is 250 seconds, and the temperature of the slow pulling step in the tenth step is 25°C.

[0054] Comparative Example 4

[0055] The difference between this comparative example and Example 1 is that in this comparative example, the temperature of the fourth alkali polishing step is 68° C. and the time is 250 s.

[0056] Comparative Example 5

[0057] The difference between this comparative example and Example 1 is that in this comparative example, the time of the alkali polishing step in step 4 is 250s.

[0058] Comparative Example 6

[0059] The difference between this comparative example and Example 1 is that in this comparative example, the temperature of the alkali polishing step in step 4 is 68°C.

[0060] Comparative Example 7

[0061] The difference between this comparative example and Example 1 is that in this comparative example, the temperature of the slow pulling in step 10 is 25°C.

[0062] The above Example 1 and Comparative Examples 1-7 were experimented on the same production line, and the process line source and process were tracked under the same conditions for 12 hours, and the following liquid carrying data were obtained: Example 1 carried liquid 13 times; Example 2 carried liquid 9 times; Example 3 carried liquid 13 times; Example 4 carried liquid 7 times; Comparative Example 1 carried liquid 72 times; Comparative Example 2 carried liquid 55 times; Comparative Example 3 carried liquid 58 times; Comparative Example 4 carried liquid 49 times; Comparative Example 5 carried liquid 33 times; Comparative Example 6 carried liquid 38 times; Comparative Example 7 carried liquid 28 times. It can be seen from the above data that the present application effectively improves the liquid carrying problem of the overall alkali polishing process by adjusting the alkali polishing temperature, alkali polishing time and slow pulling temperature.

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon, comprising the step of alkaline polishing of a silicon wafer, characterized in that: In the alkali polishing step, the alkali polishing temperature is 55-60° C. and the alkali polishing time is 150-200 seconds.

2. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 1, characterized in that: After the alkaline polishing step, the weight loss of the silicon wafer is 0.13-0.15 g.

3. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 1, characterized in that: After the alkaline polishing step, the tower base size of the silicon wafer is 5-7 μm.

4. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 1, characterized in that: The photovoltaic cell alkali polishing method further comprises a slow pulling step after the alkali polishing step: in the slow pulling step, the slow pulling temperature is 50-60°C.

5. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 4, characterized in that: The slow pulling time is 15-30s.

6. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 1, characterized in that: The photovoltaic cell alkali polishing method further comprises a loading step, a pre-cleaning step, and a water washing step which are sequentially arranged before the alkali polishing step.

7. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 6, characterized in that: The pre-cleaning liquid used in the pre-cleaning is a mixture of sodium hydroxide solution and hydrogen peroxide in a volume ratio of (1-3): (8-12), the pre-cleaning temperature is 40-50° C., and the time is 80-120s; And / or, the temperature of the first water washing is 20-30°C and the time is 110-130s.

8. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 4, characterized in that: The photovoltaic cell alkali polishing method further includes a secondary water washing step, an alkali washing step, a tertiary water washing step, an acid washing step, and a quaternary water washing step which are sequentially arranged between the alkali polishing step and the slow pulling step.

9. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 8, characterized in that: The temperature of the second washing, the third washing and the fourth washing is 20-30°C and the time is 110-130s; And / or, the alkali solution used in the alkali washing is a mixture of sodium hydroxide solution and hydrogen peroxide in a volume ratio of (2-6):(10-25), the temperature of the alkali washing is 40-60° C., and the time is 90-120 s; And / or, the acid solution used for pickling is a hydrochloric acid solution with a mass concentration of 37%, the temperature of the pickling is 20-30° C., and the time is 90-110 s.

10. The photovoltaic cell alkaline polishing method capable of improving the liquid carrying phenomenon according to claim 4, characterized in that: The photovoltaic cell alkaline polishing method further comprises a drying step arranged after the slow pulling step, wherein the drying temperature is 95-98° C. and the drying time is 660-720 seconds.