A method for texturing a crystalline silicon wafer

Abstract

The application discloses a texturing method of a crystalline silicon wafer. The hole digging process comprises the following steps: placing a silver-deposited silicon wafer in a hole digging treatment solution, soaking for 30s-50s, and then starting ultrasonic intermittent hole digging treatment to obtain a hole-digged silicon wafer; wherein the hole digging treatment solution comprises 10%-20% hydrofluoric acid, 20%-30% hydrogen peroxide, 0.5%-2% soluble silicate, and the rest is deionized water. The texturing method of the crystalline silicon wafer provided by the application can make the bubbles attached to the surface of the silicon wafer timely separate by adopting specific intermittent ultrasonic treatment and adding a specific content of silicate into the hole digging solution, so that more uniform holes are formed on the surface of the silicon wafer, the silicon wafer has moderate reflectivity, and the conversion efficiency of the battery can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cell manufacturing, and particularly relates to a texturing method of a crystalline silicon wafer. BACKGROUND

[0002] Texturing is a process of removing the damage layer on the surface of a silicon wafer by chemical or physical methods and forming an anti-reflective textured surface structure, and the texturing process of a silicon wafer can reduce the reflection of incident sunlight on the light-receiving surface of a cell and is one of effective means for improving the photoelectric conversion efficiency of a solar cell. At present, black silicon technology is widely used in the preparation of crystalline silicon solar cells, and the black silicon texturing technology can form a nanoscale textured surface on the surface of a silicon wafer and effectively reduce the reflection of incident sunlight on the surface of a silicon wafer, improve light trapping, and greatly improve the optical properties of a solar cell, so that the light absorption capacity of a solar cell is enhanced, the quantum efficiency is effectively improved, and the photoelectric conversion efficiency is significantly improved.

[0003] The preparation method of black silicon mainly includes dry and wet methods. The dry black silicon technology, i.e., reactive ion etching (RIE), can significantly reduce the reflectivity and improve the surface optical properties, but the RIE technology still has problems of low safety, complicated process, high upgrade cost, etc. in the production and application process. The wet black silicon technology based on metal catalytic corrosion technology is widely used due to its excellent performance and low cost. The process of wet black silicon texturing generally includes: silicon wafer pretreatment, silver deposition, hole digging, silver removal, hole expansion, and cleaning. The hole digging step, as one of the key steps, uses a mixed solution of hydrofluoric acid and hydrogen peroxide to accelerate the reaction of Ag deposited on the surface of a silicon wafer with silicon. As the reaction proceeds, the silicon under the silver particles is continuously corroded, and the silver particles continue to move downward, and finally form certain pits on the surface of a silicon wafer. During the above reaction process, certain gas is generated, which first attaches to the surface and edge of a silicon wafer. If the cleanliness of the surface of a silicon wafer is not enough, it will be difficult for the bubbles to detach from the surface of a silicon wafer, especially when a silicon wafer is vertically placed in the solution, the bubbles are more likely to accumulate on the upper edge of a silicon wafer during the reaction. If the bubbles are not detached in time, it will affect the hole digging process in the bubble attachment area, and finally lead to the formation of a poor surface in the bubble attachment area.

[0004] At present, the main solution to the bubble attachment during the hole digging process is to increase the amount of hydrogen peroxide to promote the detachment of bubbles from the surface and edge of a silicon wafer by using the easy decomposition of hydrogen peroxide. However, if the hydrogen peroxide is not added in time or the amount of hydrogen peroxide is insufficient, the problem that the bubbles cannot be detached from the surface of a silicon wafer in time still exists. If the amount of hydrogen peroxide is too much, it will also affect the chemical reaction during the hole digging process, leading to the formation of a poor textured surface. Therefore, it is necessary to develop a new texturing process to improve the controllability of the process and the quality of the prepared textured surface. SUMMARY

[0005] In view of the problems that the dosage of hydrogen peroxide is too large in the hole digging process in the prior art, and the quality of the suede is difficult to control and needs to be further improved, the application provides a suede making method for a crystalline silicon wafer.

[0006] To solve the above technical problems, the technical scheme provided by the application is:

[0007] A suede making method for a crystalline silicon wafer, comprising the following steps of silicon wafer pretreatment, silver deposition, hole digging, silver removal, hole expansion and cleaning.

[0008] The silicon wafer after silver deposition is placed in a hole digging treatment liquid, and after soaking for 30s-50s, intermittent ultrasonic hole digging treatment is performed by starting the ultrasonic wave, to obtain a silicon wafer with holes dug.

[0009] The hole digging treatment liquid comprises the following components in mass percentage: 10%-20% of hydrofluoric acid, 20%-30% of hydrogen peroxide, 0.5%-2% of soluble silicate, and the rest is deionized water.

[0010] Compared with the prior art, the suede making method for a crystalline silicon wafer provided by the application combines the ultrasonic treatment process, so that the bubbles generated in the hole digging treatment reaction process can be timely separated from the surface of the silicon wafer, and the intermittent ultrasonic wave is used in combination with the addition of a specific content of soluble silicate into the hole digging treatment liquid, so that the reaction of the silicate and the hydrofluoric acid generates silicic acid, the reaction of the hydrofluoric acid and the silicon is inhibited, the reaction speed of the hydrofluoric acid and the silicon is reduced, the influence of the ultrasonic treatment on the hole digging process reaction of the silicon wafer is avoided, the corrosion rate of the silicon wafer is more easily controlled, and thus it is beneficial to form more uniform holes on the surface of the silicon wafer, so that the silicon wafer has a suitable reflectivity, which is beneficial to the passivation of the suede in the subsequent battery preparation, and thus it is beneficial to significantly improve the conversion efficiency of the battery, and the process is simple and controllable, and can effectively improve the qualification rate of the silicon wafer suede making process, and has high popularization and application value.

[0011] Preferably, the specific steps of the intermittent ultrasonic wave are as follows: ultrasonic wave is performed every 5s-10s, and the ultrasonic time is 3s-5s each time.

[0012] Preferably, the ultrasonic power is 20KHz-50KHz.

[0013] Preferably, the ultrasonic process can reduce the influence on the hole digging process reaction as much as possible, avoid the increase of the corrosion depth caused by the ultrasonic wave, make the reflectivity of the silicon wafer lower, although a good light trapping surface is obtained, but the subsequent passivation of the suede cannot be good, and thus large carrier recombination is formed on the surface of the silicon wafer, and finally the problem of low battery conversion efficiency occurs; at the same time, the ultrasonic treatment is also insufficient, so that the bubbles attached to the surface of the silicon wafer cannot be fully separated, and the problem of the product qualification rate of the suede making process cannot be effectively improved occurs.

[0014] Preferably, the temperature of the hole digging treatment is 30-40℃, and the time of the hole digging treatment is 150-300s.

[0015] Preferably, the soluble silicate is at least one of potassium silicate or sodium silicate.

[0016] Further preferably, the soluble silicate is potassium silicate.

[0017] Preferably, after the texturing process of 400 wafers is completed, 200-600mL of hydrofluoric acid, 50-150mL of hydrogen peroxide, and 20-50g of soluble silicate are added to the hole digging treatment solution.

[0018] Preferably, the pretreatment solution of the wafer pretreatment process comprises the following components with the mass percentage: 5-20% of potassium hydroxide, 0.5-1% of the first additive, and the rest is deionized water.

[0019] Illustratively, the first additive is the additive A of Nanjing Nexin New Material Co., Ltd.

[0020] Preferably, the silver deposition solution of the silver deposition process comprises the following components with the mass percentage: 1-3% of hydrofluoric acid, 0.1-1% of the second additive, and the rest is deionized water.

[0021] Illustratively, the second additive is the additive B of Nanjing Nexin New Material Co., Ltd.

[0022] Preferably, the treatment solution of the silver removal process comprises the following components with the mass percentage: 2-10% of hydrogen peroxide, 20-40% of ammonia, and the rest is deionized water.

[0023] Preferably, the hole expanding solution of the hole expanding process comprises the following components with the mass percentage: 2-10% of hydrofluoric acid, 20-40% of nitric acid, and the rest is deionized water.

[0024] Preferably, the cleaning solution of the cleaning process comprises the following components with the mass percentage: 5-15% of potassium hydroxide, 1-10% of hydrogen peroxide, 1-5% of ammonia, and the rest is deionized water.

[0025] The present application provides a method for etching a silicon wafer, which comprises the following steps: pretreating the silicon wafer, silver deposition, hole digging, silver removal, hole expanding and cleaning. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0027] In order to better illustrate the present application, the following examples are further illustrated.

[0028] Example 1

[0029] A method for etching a silicon wafer, which comprises the following steps: pretreating the silicon wafer, silver deposition, hole digging, silver removal, hole expanding and cleaning, wherein the hole digging process comprises the following steps:

[0030] After the silicon wafer after silver deposition is placed in a hole digging treatment solution and soaked for 40s, intermittent ultrasonic hole digging treatment is performed, and the ultrasonic treatment is performed every 5s-10s, and the ultrasonic time is 3s-5s each time, the hole digging treatment temperature is 35℃, and the hole digging treatment time is 250s, thereby obtaining a hole-digging silicon wafer.

[0031] The hole digging treatment solution comprises the following components in mass percentage: hydrofluoric acid 15%, hydrogen peroxide 25%, potassium silicate 1%, and the balance is deionized water.

[0032] After every 400 pieces of silicon wafer are processed, 250mL of hydrofluoric acid, 100mL of hydrogen peroxide and 25g of soluble silicate are added to the hole digging treatment solution.

[0033] Example 2

[0034] A method for etching a silicon wafer, which comprises the following steps: pretreating the silicon wafer, silver deposition, hole digging, silver removal, hole expanding and cleaning, wherein the hole digging process comprises the following steps:

[0035] The silicon wafer after silver immersion is placed in the hole-digging solution and soaked for 30 seconds. Then, the ultrasonic waves are turned on to perform intermittent ultrasonic hole-digging. The ultrasonic waves are performed once every 5-10 seconds, and each ultrasonic wave lasts for 3-5 seconds. The hole-digging temperature is 30℃ and the hole-digging time is 300 seconds to obtain the hole-digging silicon wafer.

[0036] The hole-drilling treatment fluid comprises the following components by mass percentage: 10% hydrofluoric acid, 20% hydrogen peroxide, 0.5% potassium silicate, and the balance being deionized water.

[0037] Example 3

[0038] A texturing method for a crystalline silicon wafer includes silicon wafer pretreatment, silver deposition, hole drilling, silver removal, hole enlargement, and cleaning processes. The hole drilling process includes the following steps:

[0039] The silicon wafer after silver immersion is placed in the hole-digging solution and soaked for 50 seconds. Then, the ultrasonic waves are turned on to perform intermittent ultrasonic hole-digging. The ultrasonic waves are performed once every 5-10 seconds, and each ultrasonic wave lasts for 3-5 seconds. The hole-digging temperature is 40℃ and the hole-digging time is 150 seconds to obtain the hole-digging silicon wafer.

[0040] The hole-drilling treatment fluid comprises the following components by mass percentage: 20% hydrofluoric acid, 30% hydrogen peroxide, 2% potassium silicate, and the remainder is deionized water.

[0041] In the texturing process of the crystalline silicon wafers in Examples 1-3 above:

[0042] The pretreatment solution for the silicon wafer pretreatment process comprises the following components by mass percentage: 10% potassium hydroxide, 0.6% additive A, and the remainder is deionized water; the silicon wafer pretreatment time is 400s.

[0043] The silver immersion solution for the silver immersion process comprises the following components by mass percentage: 2% hydrofluoric acid, 0.5% additive B, and the balance being deionized water; the silver immersion process takes 150 seconds.

[0044] The treatment solution for the silver removal process comprises the following components by mass percentage: 5% hydrogen peroxide, 30% ammonia, and the remainder is deionized water; the silver removal process takes 150 seconds.

[0045] The reaming solution for the reaming process comprises the following components by mass percentage: 6% hydrofluoric acid, 30% nitric acid, and the balance being deionized water; the reaming process takes 200 seconds.

[0046] The cleaning solution for the cleaning process comprises the following components by mass percentage: 10% potassium hydroxide, 5% hydrogen peroxide, 3% ammonia, and the remainder is deionized water; the cleaning process takes 150 seconds.

[0047] Additive A and Additive B are both produced by Nanjing Naxin New Materials Co., Ltd.

[0048] Comparative Example 1

[0049] This comparative example provides a method for texturing a crystalline silicon wafer, including silicon wafer pretreatment, silver immersion, hole drilling, silver removal, hole enlargement, and cleaning processes. The hole drilling process includes the following steps:

[0050] The silicon wafers after silver immersion are placed in a hole-removal treatment solution, the hole-removal temperature is controlled at 35℃, and the immersion time is 250s to obtain the hole-removed silicon wafers.

[0051] The hole-drilling treatment fluid comprises the following components by mass percentage: 15% hydrofluoric acid, 30% hydrogen peroxide, 0.7% additive C, 0.3% additive D, and the balance being deionized water.

[0052] Additives C and D are both produced by Nanjing Naxin New Materials Co., Ltd.

[0053] The remaining pretreatment, silvering, silver removal, hole enlargement and cleaning processes are exactly the same as those in Examples 1-3.

[0054] After texturing 400 silicon wafers, add 250 mL of hydrofluoric acid, 400 mL of hydrogen peroxide, 50 mL of additive C, and 20 mL of additive D to the hole-removing treatment solution.

[0055] Comparative Example 2

[0056] This comparative example provides a method for texturing a crystalline silicon wafer, including silicon wafer pretreatment, silver immersion, hole drilling, silver removal, hole enlargement, and cleaning processes. The hole drilling process includes the following steps:

[0057] The silicon wafers after silver immersion are placed in a hole-removal treatment solution, the hole-removal temperature is controlled at 35℃, and the immersion time is 250s to obtain the hole-removed silicon wafers.

[0058] The hole-drilling treatment fluid comprises the following components by mass percentage: 15% hydrofluoric acid, 30% hydrogen peroxide, 1% potassium silicate, and the remainder is deionized water.

[0059] The remaining pretreatment, silvering, silver removal, hole enlargement and cleaning processes are exactly the same as those in Examples 1-3.

[0060] Comparative Example 3

[0061] This comparative example provides a method for texturing a crystalline silicon wafer, including silicon wafer pretreatment, silver immersion, hole drilling, silver removal, hole enlargement, and cleaning processes. The hole drilling process includes the following steps:

[0062] The silicon wafer after silver immersion was placed in the hole-digging solution and immersed for 40 seconds. Then, continuous ultrasonic hole-digging was performed. The hole-digging temperature was 35℃ and the hole-digging time was 250 seconds to obtain the hole-digging silicon wafer.

[0063] The hole-drilling treatment fluid comprises the following components by mass percentage: 15% hydrofluoric acid, 30% hydrogen peroxide, 1% potassium silicate, and the remainder is deionized water.

[0064] The remaining pretreatment, silvering, silver removal, hole enlargement and cleaning processes are exactly the same as those in Examples 1-3.

[0065] Comparative Example 4

[0066] This comparative example provides a method for texturing a crystalline silicon wafer, including silicon wafer pretreatment, silver immersion, hole drilling, silver removal, hole enlargement, and cleaning processes. The hole drilling process includes the following steps:

[0067] The silicon wafer after silver immersion is placed in the hole-digging solution and soaked for 40 seconds. Then, the ultrasonic waves are turned on to perform intermittent ultrasonic hole-digging. The ultrasonic waves are performed once every 5-10 seconds, and each ultrasonic wave lasts for 3-5 seconds. The hole-digging temperature is 35℃ and the hole-digging time is 250 seconds to obtain the hole-digging silicon wafer.

[0068] The hole-drilling treatment fluid comprises the following components by mass percentage: 15% hydrofluoric acid, 30% hydrogen peroxide, 0.7% additive C, 0.3% additive D, and the balance being deionized water.

[0069] Additives C and D are both produced by Nanjing Naxin New Materials Co., Ltd.

[0070] The remaining pretreatment, silvering, silver removal, hole enlargement and cleaning processes are exactly the same as those in Examples 1-3.

[0071] The reflectivity of the silicon wafer surface obtained by the process of Example 1 and Comparative Examples 1-4 was tested. The test standard was to use a D8 tester to select the integral of each reflectivity within the wavelength range of 350nm-1050nm. The results are shown in Table 1.

[0072] Table 1

[0073] Group Post-texturing reflectance Nonconforming rate Example 1 12-15％ 1％-2％ Comparative Example 1 12-15％ 5％-10％ Comparative Example 2 10-12％ 3％-8％ Comparative Example 3 5-8％ 1％-2％ Comparative Example 4 7-10％ 2％-3％

[0074] The silicon wafers obtained in Example 1 and Comparative Examples 1-4 were then fabricated into solar cells using conventional processes. The open-circuit voltage (Voc), short-circuit current (Isc), and fill factor (FF) of the solar cells were measured using a Halm meter, and the cell conversion efficiency (Eff) was calculated. The results are shown in Table 2. The illumination amplitude was 100 mW / cm². 2 , 25±2℃.

[0075] Table 2

[0076] Group Voc (V) Isc (A) FF (%) Eff (%) Example 1 0.6497 9.226 82.68 19.984 Comparative Example 1 0.6463 9.213 82.15 19.724 Comparative Example 2 0.6426 9.232 82.19 19.661 Comparative Example 3 0.6331 9.367 80.67 19.290 Comparative Example 4 0.6404 9.307 81.33 19.546

[0077] In summary, the present application provides a method for etching a silicon wafer, by using a specific intermittent ultrasound in combination with adding a specific content of silicate to the etching solution, so that the bubbles attached to the surface of the silicon wafer are detached in time, thereby forming more uniform holes on the surface of the silicon wafer, so that the silicon wafer has moderate reflectivity, thereby effectively improving the conversion efficiency of the battery. The method of using continuous ultrasound or other additives cannot achieve a technical effect basically comparable to the embodiment of the present application.

[0078] The silicon wafer obtained by the process of Example 2-3 can achieve a technical effect basically comparable to that of Example 1.

[0079] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for texturing a crystalline silicon wafer, comprising the steps of silicon wafer pretreatment, silver deposition, hole drilling, silver removal, hole enlargement, and cleaning, characterized in that, The drilling process includes the following steps: After the silicon wafers are immersed in silver, they are placed in the hole-digging solution and soaked for 30-50 seconds. Then, the ultrasonic waves are turned on to perform intermittent ultrasonic hole-digging to obtain the hole-digging silicon wafers. The hole-drilling treatment solution comprises the following components in mass percentage: 10%-20% hydrofluoric acid, 20%-30% hydrogen peroxide, 0.5%-2% soluble silicate, and the balance being deionized water. The specific steps of intermittent ultrasound are as follows: ultrasound is performed every 5-10 seconds, each ultrasound session lasts 3-5 seconds, and the ultrasound power is 20KHz-50KHz.

2. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, The drilling temperature is 30℃-40℃, and the drilling time is 150s-300s.

3. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, The soluble silicate is at least one of potassium silicate or sodium silicate.

4. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, After texturing 400 silicon wafers, add 200mL-600mL of hydrofluoric acid, 50mL-150mL of hydrogen peroxide, and 20-50g of soluble silicate to the hole-removing treatment solution.

5. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, The pretreatment solution in the silicon wafer pretreatment process comprises the following components by mass percentage: 5%-20% potassium hydroxide, 0.5%-1% first additive, and the balance being deionized water.

6. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, The silver immersion solution in the silver immersion process includes the following components by mass percentage: 1%-3% hydrofluoric acid, 0.1%-1% second additive, and the balance being deionized water.

7. The texturing method for crystalline silicon wafers as described in claim 1, characterized in that, The treatment solution for the silver removal process comprises the following components by mass percentage: 2%-10% hydrogen peroxide, 20%-40% ammonia, and the balance being deionized water.

8. The texturing method for a crystalline silicon wafer as described in claim 1, characterized in that, The reaming solution in the reaming process comprises the following components by mass percentage: 2%-10% hydrofluoric acid, 20%-40% nitric acid, and the balance being deionized water; and / or The cleaning solution used in the cleaning process comprises the following components by mass percentage: 5%-15% potassium hydroxide, 1%-10% hydrogen peroxide, 1%-5% ammonia, and the remainder is deionized water.