Micro-texturing method, silicon wafer, and photovoltaic cell

Abstract

Disclosed in the present disclosure are a micro-texturing method, a silicon wafer, and a cell. The micro-texturing method comprises: at least sequentially performing alkali polishing, first alkali washing, a micro-texturing process, and second alkali washing on a surface to be machined of a workpiece, so that said surface forms a micro-textured surface, wherein a solution used in the first alkali washing and the second alkali washing includes a 0.3%-0.5% of alkali solution, and a solution used in the micro-texturing process includes a 1%-1.5% alkali solution. The micro-texturing method provided by the present disclosure can mitigate the gas flow marks generated when texturing is performed by using a PECVD route, thereby improving the yield of workpieces.

Description

Microtexturing methods, silicon wafers, photovoltaic cells

[0001] This disclosure claims priority to Chinese Patent Application No. 202510182431.2, filed on February 18, 2025, entitled “Microtexturing Method, Silicon Wafer, Photovoltaic Cell”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of photovoltaic cell manufacturing technology, and more specifically, to a microtexturing method, silicon wafers, and cells. Background Technology

[0003] In the production of photovoltaic cells, most manufacturers use the PECVD (Plasma Enhanced Chemical Vapor Deposition) route, which has advantages such as high yield, fast film formation speed, high doping efficiency, and low cost, to expand production. However, the problem of easily exploding films generated by the PECVD route needs to be solved by performing a micro-texturing process after alkaline polishing on the back of the cell. However, the existing micro-texturing process is prone to producing irregular airflow marks in actual production. As the number of production batches increases, the airflow marks will gradually worsen. In severe cases, it will directly affect the appearance after coating, leading to a degradation of the appearance of the cell and even affecting the efficiency of the cell. Summary of the Invention

[0004] One object of this disclosure is to provide a new technical solution for a microtexturing method, silicon wafers, and photovoltaic cells.

[0005] According to a first aspect of this disclosure, a microtexturing method is provided for use in photovoltaic cell production, comprising:

[0006] The workpiece surface to be processed is subjected to at least the following steps: alkaline polishing, first alkaline washing, micro-texturing, and second alkaline washing, so that the surface to be processed is formed with a micro-textured surface.

[0007] The solutions used in the first and second alkaline washes include 0.3% to 0.5% alkaline solutions, and the solutions used in the micro-texturing process include 1% to 1.5% alkaline solutions.

[0008] Optionally, the alkaline solution is a KOH solution or a NaOH solution.

[0009] Optionally, the process time for the first alkaline wash and the second alkaline wash is 90s to 120s, and the reaction time for the micro-texturing process is 80s to 120s.

[0010] Optionally, the process temperatures for the first alkaline wash and the second alkaline wash are 60℃~65℃, and the process temperature for the micro-texturing process is 68℃~70℃.

[0011] Optionally, the solution used for the first and second alkaline washes may further include 1% to 3% H2O2.

[0012] Optionally, the solution used in the microtexturing process may further include 0.2 to 0.4% of additives, wherein the additives are one or more of surfactants, nucleating agents, dispersants, catalysts, and defoamers.

[0013] Optionally, the workpiece is assembled using a basket assembly method, exposing the surface to be processed. The method further includes:

[0014] The equipment containing the solutions for the first alkaline wash, the micro-texturing process, and the second alkaline wash is circulated and replenished, and the solution is bubbled before the flower basket is immersed in the solution, and the bubbling is stopped when the flower basket is immersed in the solution.

[0015] Optionally, it also includes:

[0016] Before alkaline polishing, the workpiece is pre-cleaned and given a first water rinse.

[0017] A second water wash is performed after alkaline polishing and before the first alkaline wash.

[0018] A third water wash is performed after the first alkaline wash and before the micro-texturing process;

[0019] A fourth water wash is performed after the micro-texturing process and before the second alkaline wash.

[0020] After the second alkaline wash, the process proceeds in sequence with the fifth water wash, acid wash, sixth water wash, slow lifting process, and drying process.

[0021] According to a second aspect of this disclosure, a silicon wafer is provided, comprising: the microtextured surface formed by the microtexturing method described in the first aspect.

[0022] According to a third aspect of this disclosure, a photovoltaic cell is provided, comprising: the silicon wafer described in the second aspect.

[0023] According to one embodiment of this disclosure, the microtexturing method provides a microtextured surface formed on the workpiece surface after at least alkaline polishing, a first alkaline wash, a microtexturing process, and a second alkaline wash, thus solving the problem of film bursting in PECVD. Furthermore, by controlling the solution concentration in each process, the phenomenon of airflow marks easily appearing on the microtextured surface is optimized, improving the quality of the workpiece. When applied to photovoltaic cells, this method can improve cell yield and efficiency.

[0024] Other features and advantages of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0026] Figure 1 shows the airflow imprints produced by the PECVD route in the prior art.

[0027] Figure 2 shows a micro-textured surface produced by the micro-texturing method provided in this disclosure.

[0028] Attached image labels or descriptions: 1. Airflow mark; 2. Pyramid structure. Detailed Implementation

[0029] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present disclosure.

[0030] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use.

[0031] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0032] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0033] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0034] In the production of photovoltaic cells, TOPCon (Tunnel Oxide Passivating Contacts) cells are gradually replacing PERC (Passivated Emitter and Rear Cell) cells. The mainstream expansion route for TOPCon cells mainly includes the PECVD route.

[0035] PECVD coating requires high-temperature annealing after deposition, with annealing temperatures ranging from 600℃ to 850℃. During high-temperature annealing, the polycrystalline silicon layer becomes rich in hydrogen atoms, reaching a concentration of 10. 20 ~10 22 cm -3 High-temperature annealing can cause "hydrogen atom leakage," which accumulates at the interface between the polycrystalline silicon layer and SiO2, a phenomenon known as film bursting. Film bursting can lead to uneven film layers, increased lateral transport channels, and even film detachment, severely impacting battery efficiency.

[0036] The phenomenon of film bursting is directly related to the surface roughness of the silicon wafer. The greater the roughness, the stronger the surface adhesion, and the lower the probability of film bursting. Therefore, in the actual production of PECVD, the back of the cell is alkaline polished and then microtextured to solve the film bursting problem of PECVD. However, due to the irregular airflow marks on the back surface during the actual production process (see Figure 1), and the airflow marks gradually worsen with the increase of production batches, in severe cases, it will directly affect the appearance after coating, causing a degradation in the appearance of the cell and even affecting the cell efficiency.

[0037] As shown in Figure 2, according to a first aspect of this disclosure, a microtexturing method is provided for use in photovoltaic cell production, comprising: performing at least one alkaline polishing, a first alkaline washing, a microtexturing process, and a second alkaline washing on the surface to be processed of a workpiece, thereby forming a microtextured surface on the surface to be processed; wherein the solutions used in the first alkaline washing and the second alkaline washing comprise 0.3% to 0.5% alkaline solution, and the solution used in the microtexturing process comprises 1% to 1.5% alkaline solution.

[0038] Specifically, in this embodiment, a silicon wafer is used as the workpiece, and the surface to be processed is the back side of the silicon wafer. The silicon wafer is processed to form a micro-textured surface, that is, a micro-textured surface with tiny pyramidal structure is grown on the polished surface of the back side of the silicon wafer (as shown in Figure 2). In other words, by micro-texturing the back side of the silicon wafer, its surface roughness is increased, the surface adhesion of the back side of the silicon wafer is improved, the probability of film bursting is reduced, and the efficiency and yield of the battery manufactured in the subsequent process are guaranteed.

[0039] Furthermore, the processing of the workpiece's surface requires a series of steps: alkaline polishing, a first alkaline wash, micro-texturing, and a second alkaline wash. The alkaline polishing process involves etching the back surface of the silicon wafer using an alkaline solution and additives to create a polished surface structure. Since the additives used in the alkaline polishing solution differ from those used in the micro-texturing process, a first alkaline wash is performed before micro-texturing. This wash uses an alkaline solution of a specific concentration to remove residual dirt and additives from the back surface of the silicon wafer after polishing, facilitating the subsequent micro-texturing process. The micro-texturing process involves passing an alkaline solution over the back surface of the silicon wafer to create tiny pyramidal structures, forming a micro-textured surface. The second alkaline wash similarly involves passing an alkaline solution of a specific concentration over the back surface of the silicon wafer to remove any remaining impurities and additives from the micro-texturing process.

[0040] In practical applications, uneven growth of the microtextured surface can lead to airflow marks. In the above embodiments, this disclosure uses solutions containing 0.3% to 0.5% alkali, such as 0.4% KOH solution, for the first and second alkaline washes. This lowers the alkali concentration in the solution, reducing the degree of reaction between the alkali solution and the back surface of the silicon wafer, thus avoiding a decrease in the overall uniformity of the surface to be processed. Simultaneously, by using a solution containing 1% to 1.5% alkali, such as 1.25% KOH solution, to texturize the back surface of the silicon wafer in the microtexturing process, a suitable pyramid structure can be grown on the surface to be processed, resulting in a more uniform distribution of the microtextured surface. This improves the linearity of airflow marks and prevents a decrease in the overall uniformity of the back surface of the silicon wafer.

[0041] In the above embodiments, various additives, such as surfactants, nucleating agents, dispersants, catalysts, and defoamers, can be added to the solutions for the first alkaline wash, microtexturing, and second alkaline wash to ensure that the reaction time and temperature of each process are maintained within a suitable range. For example, the reaction time for the first and second alkaline washes can be designed to be 90s–150s, and the reaction temperature can be designed to be 60℃–70℃, while the microtexturing reaction time can be designed to be 80s–125s, and the reaction temperature can be designed to be 65℃–70℃, to ensure the uniformity of the microtextured surface. The alkaline polishing, first alkaline wash, microtexturing, and second alkaline wash can all be performed in a solution bath. The silicon wafer can also be washed with water before and after each process to further remove solutions and impurities from each process.

[0042] Optionally, the alkaline solution is a KOH solution or a NaOH solution.

[0043] Specifically, in practical applications, KOH solution or NaOH solution can be used for the first alkaline wash, the microtexturing process, and the second alkaline wash. These solutions are low in cost and serve as anisotropic etching solutions for silicon to clean and etch the surface of the silicon wafer to be processed, enabling the growth of microtextured surfaces and improving the yield and efficiency of the battery.

[0044] Optionally, the process time for the first alkaline wash and the second alkaline wash is 90s to 120s, and the reaction time for the micro-texturing process is 80s to 120s.

[0045] Specifically, in this embodiment, by controlling the process time of the first and second alkaline washes within 90s to 120s, such as 100s or 110s, the reaction time between the silicon wafer surface to be processed and the alkaline solution during the first and second alkaline washes is reduced. Furthermore, by controlling the reaction time of the microtexturing process within 80s to 120s, such as 90s, 100s or 110s, the uniformity of the microtextured surface in the microtexturing process is further improved, thereby achieving the goal of further improving the airflow printing.

[0046] Optionally, the process temperatures for the first alkaline wash and the second alkaline wash are 60℃~65℃, and the process temperature for the micro-texturing process is 68℃~70℃.

[0047] Specifically, in this embodiment, by controlling the process temperature of the first and second alkaline washes within 60°C to 65°C, such as 62°C and 64°C, the degree of reaction between the silicon wafer surface to be processed and the alkaline solution during the first and second alkaline washes is reduced. Furthermore, by controlling the reaction temperature of the microtexturing process within 68°C to 70°C, such as 69°C, the uniformity of the microtextured surface in the microtexturing process is further improved, thereby achieving the goal of further improving the airflow printing.

[0048] In the above embodiments, by controlling the concentration of the alkaline solution, the process temperature, and the process time in each process, the degree of reaction between the first and second alkaline washes and the silicon wafer is reduced, the corrosion of the silicon wafer by the alkaline solution is reduced, and additives and impurities are effectively removed, ensuring the uniformity of the micro-textured surface formed on the surface to be processed and guaranteeing the efficiency of the solar cells made from the silicon wafer. Specifically, the alkaline solution concentration, process temperature, and process time for micro-texturing are all reduced compared to the parameters of the texturing process on the front side of the silicon wafer (the process time for the front-side texturing process is typically 420s–480s, the process temperature is typically 80℃–82℃, and the alkaline solution concentration is 1%–1.5%), so that the roughness of the formed micro-textured surface can avoid the problem of film bursting.

[0049] Optionally, the solution used for the first and second alkaline washes may further include 1% to 3% H2O2.

[0050] Specifically, in practical applications, by adding 1% to 3% H2O2, such as 2% H2O2, to the first and second alkaline washing solutions, the strong oxidizing properties of hydrogen peroxide can be used to clean the dirt remaining on the surface of the silicon wafer after polishing or microtexturing.

[0051] Optionally, the solution used in the microtexturing process may further include 0.2 to 0.4% of additives, wherein the additives are one or more of surfactants, nucleating agents, dispersants, catalysts, and defoamers.

[0052] Specifically, in this embodiment, by adding 0.2 to 0.4% of additives in the micro-texturing process, the reaction rate and texturing effect in the micro-texturing process are controlled, thereby further ensuring the uniformity of the generated micro-textured surface.

[0053] Optionally, the workpiece is assembled using a basket and the surface to be processed is exposed. The method further includes: circulating and replenishing the equipment containing the solutions for the first alkaline wash, the micro-texturing process, and the second alkaline wash; bubbling the solution before the basket is immersed in the solution; and stopping the bubbling when the basket is immersed in the solution.

[0054] Specifically, a photovoltaic flower basket is a specialized tool used in the photovoltaic industry to carry, protect, and transport silicon wafers, solar cells, or other photovoltaic modules. It is usually made of high-strength, corrosion-resistant materials, such as stainless steel, aluminum alloy, and plastics (such as PVDF and PP). Its main function is to ensure that the silicon wafers or solar cells are not damaged during processing, cleaning, and transportation, and to maintain their cleanliness and integrity.

[0055] In this embodiment, using a basket to support the silicon wafer for alkaline polishing, first alkaline washing, microtexturing, and second alkaline washing of the surface to be processed facilitates the operation of each process and protects the silicon wafer from damage. In one embodiment, the alkaline polishing, first alkaline washing, microtexturing, and second alkaline washing processes are all performed in a solution tank, and the solution in each tank is circulated and replenished, for example, by using a circulating pump that operates continuously in the tank to achieve circulation and replenishment, ensuring the concentration and uniformity of the solution.

[0056] Furthermore, before the flower basket is immersed in each tank, that is, before the first alkaline wash, the micro-texturing process, and the second alkaline wash, the corresponding solution tank can be continuously bubbled to improve the uniformity of the solution. When the flower basket is immersed in the tanks of the first and second alkaline washes, the bubbling operation in the corresponding process tank is stopped to avoid unnecessary texturing effect during the first and second alkaline washes. This ensures both the uniformity of the solution and the independence of each process.

[0057] Optionally, the process may also include: pre-cleaning and a first water wash before alkaline polishing of the workpiece; a second water wash after alkaline polishing and before the first alkaline wash; a third water wash after the first alkaline wash and before the micro-texturing process; a fourth water wash after the micro-texturing process and before the second alkaline wash; and a fifth water wash, acid wash, a sixth water wash, a slow lifting process, and a drying process in sequence after the second alkaline wash.

[0058] Specifically, multiple cleaning operations, including water washing and acid washing, are required before and after each process. Acid washing removes residual alkali and metal ions from the micro-textured surface of the silicon wafer, while water washing removes desorbed impurities and alkaline or acidic solutions from the wafer surface. Additionally, the slow-lifting process dehydrates the silicon wafer by utilizing the surface tension of water to slowly pull it away from the water surface, resulting in a relatively dry wafer. After dehydration, further drying is performed to improve the output power and conversion efficiency of the solar cells.

[0059] To make the effects of the microtexturing method provided in this disclosure clearer, Comparative Example 1 and two embodiments are provided below for detailed description:

[0060] Comparative Example 1:

[0061] After the TOPCon process reaches the boron diffusion process and completes the BSG (borosilicate glass) removal step, the alkaline polishing and microtexturing process begins, passing through the following process tanks in sequence: pre-cleaning - water wash 1 - alkaline polishing - water wash 2 - alkaline wash 1 - water wash 3 - microtexturing - water wash 4 - alkaline wash 2 - water wash 5 - acid washing - water wash 6 - slow lifting - drying tank.

[0062] Among them, alkaline washing tank 1 and alkaline washing tank 2 correspond to the first alkaline washing and the second alkaline washing, respectively. The reaction temperature is set to 65℃, the process time is set to 150s, the solution ratio is 0.8% KOH and 4% H2O2, and the self-replenishing solution volume is continuously replenished by circulation and bubbling.

[0063] The micro-texturing tank corresponds to the micro-texturing process, with a reaction temperature of 70℃, a process time of 120s, a solution ratio of 2% KOH and 0.5% additives, a continuous circulation method for the solution, and a bubbling method for the solution where bubbling continues until the basket enters the tank, and bubbling stops when the basket enters.

[0064] Example 1:

[0065] This embodiment 1 provides a micro-texturing method, which differs from Comparative Example 1 in the process formulations of the alkaline washing tank 1, alkaline washing tank 2, and micro-texturing tank, specifically as follows:

[0066] The reaction temperature in alkaline washing tanks 1 and 2 was set at 62℃, the process time was 100s, and the solution ratio was 0.4% KOH and 2.5% H2O2. The solution was continuously replenished through circulation, with continuous bubbling. The reaction temperature in the micro-texturing tank was 70℃, the process time was 120s, the solution ratio was 1.5% KOH and 0.4% additives, the solution was continuously circulated, and the bubbling method was no bubbling when there was a basket, and no bubbling when there was a basket.

[0067] Example 2

[0068] This embodiment 2 provides a micro-texturing method, which differs from Comparative Example 1 in the process formulation of alkaline washing tanks 1 and 2 and the micro-texturing tank, specifically as follows:

[0069] The reaction temperature in alkaline washing tanks 1 and 2 is set at 62℃, the process time is 90s, and the solution ratio is 0.3% KOH and 1.5% H2O2. The solution is continuously circulated, with no bubbling in the basket and no bubbling in the basket. The reaction temperature in the micro-texturing tank is 70℃, the process time is 120s, the solution ratio is 1.2% KOH and 0.3% additives, and the solution is continuously circulated, with no bubbling in the basket and no bubbling in the basket.

[0070] Observation and comparison show that: the airflow mark distribution ratio of Comparative Example 1 is 5%, and the airflow mark phenomenon is relatively serious (see Figure 1); the airflow mark distribution ratio of Example 1 has been improved to 3%, and the airflow mark phenomenon is relatively mild; while the airflow mark distribution ratio of Example 2 has been reduced to 0.2%, and there is no obvious airflow mark when viewed visually.

[0071] This indicates that the microtexturing method provided in this disclosure optimizes the process formulation of alkaline washing tanks 1 and 2 and the microtexturing tank. Without requiring modifications to other machine hardware, it can improve the appearance of airflow marks during microtexturing, reduce defective products in the workshop, and increase the yield of the battery workshop. The proportion of airflow marks typically refers to the percentage of products with noticeable airflow marks out of every 100 cells.

[0072] According to a second aspect of this disclosure, a silicon wafer is provided, comprising: the microtextured surface formed by the microtexturing method described in the first aspect.

[0073] Specifically, in this embodiment, the provided silicon wafer has a microtextured surface formed by the microtexturing method provided in the first aspect. The structure of the microtextured surface can be referred to in Figure 2, which shows the microtextured surface and the pyramid structure 2 as observed under a microscope at 100x magnification. The surface of the silicon wafer provided in this embodiment improves the airflow imprint formed in conventional microtexturing technology, thereby improving the appearance and yield of the silicon wafer.

[0074] According to a third aspect of this disclosure, a photovoltaic cell is provided, comprising: the silicon wafer described in the second aspect.

[0075] Specifically, the photovoltaic cell in this embodiment is made using a silicon wafer with improved back microtextured airflow pattern provided in the second aspect, which improves the yield and efficiency of the cell.

[0076] The above embodiments mainly describe the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. For the sake of brevity, they will not be elaborated here.

[0077] While specific embodiments of this disclosure have been described in detail by way of example, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A micro-texturing method, applied to photovoltaic cell production, characterized in that, include: The workpiece surface to be processed is subjected to at least the following steps: alkaline polishing, first alkaline washing, micro-texturing, and second alkaline washing, so that the surface to be processed is formed with a micro-textured surface. The solutions used in the first and second alkaline washes include 0.3% to 0.5% alkaline solutions, and the solutions used in the micro-texturing process include 1% to 1.5% alkaline solutions.

2. The micro-texturing method according to claim 1, characterized in that, The alkaline solution is a KOH solution or a NaOH solution.

3. The micro-texturing method according to claim 1 or 2, characterized in that, The process times for the first and second alkaline washes are 90s to 120s, respectively, and the reaction time for the micro-texturing process is 80s to 120s.

4. The microtexturing method according to any one of claims 1-3, characterized in that, The process temperatures for the first and second alkaline washes are 60°C to 65°C, and the process temperature for the micro-texturing process is 68°C to 70°C.

5. The microtexturing method according to any one of claims 1-4, characterized in that, The solutions used in the first and second alkaline washes also include 1% to 3% H2O2.

6. The microtexturing method according to any one of claims 1-5, characterized in that, The solution used in the micro-texturing process also includes 0.2-0.4% of additives, which are one or more of surfactants, nucleating agents, dispersants, catalysts, and defoamers.

7. The micro-texturing method according to any one of claims 1-6, characterized in that, The method further includes assembling the workpiece using a basket assembly method, exposing the surface to be processed. The equipment containing the solutions for the first alkaline wash, the micro-texturing process, and the second alkaline wash is circulated and replenished, and the solution is bubbled before the flower basket is immersed in the solution, and the bubbling is stopped when the flower basket is immersed in the solution.

8. The micro-texturing method according to any one of claims 1-7, characterized in that, Also includes: Before alkaline polishing, the workpiece is pre-cleaned and given a first water rinse. A second water wash is performed after alkaline polishing and before the first alkaline wash. A third water wash is performed after the first alkaline wash and before the micro-texturing process; A fourth water wash is performed after the micro-texturing process and before the second alkaline wash. After the second alkaline wash, the process proceeds in sequence with the fifth water wash, acid wash, sixth water wash, slow lifting process, and drying process.

9. A silicon wafer, characterized in that, include: The micro-textured surface is produced by the micro-texturing method according to any one of claims 1-8.

10. A photovoltaic cell, characterized in that, include: The silicon wafer as described in claim 9.

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