Micro texturing method, silicon wafer and photovoltaic cell

Abstract

The invention discloses a micro texturing method, a silicon wafer and a battery. The micro-texturing method comprises the following steps: at least sequentially carrying out alkali polishing, first alkali washing, micro-texturing and second alkali washing on a to-be-processed surface of a workpiece, so that a micro-textured surface is formed on the to-be-processed surface; wherein a solution adopted for the first alkali washing and a solution adopted for the second alkali washing comprise 0.3%-0.5% of an alkali solution, and a solution adopted for the micro texturing procedure comprises 1%-1.5% of an alkali solution. According to the micro texturing method provided by the invention, airflow marks generated during texturing by adopting a PECVD (Plasma Enhanced Chemical Vapor Deposition) route can be improved, and the yield of workpieces is improved.

Description

Technical Field

[0001] The present application relates to the technical field of photovoltaic cell production, and more specifically, to a micro-texturing method, a silicon wafer and a battery. Background Art

[0002] In the process of photovoltaic cell production, most of them adopt the PECVD (Plasma Enhanced Chemical Vapor Deposition) route with advantages such as high yield, fast film formation speed, high doping efficiency, and low cost for production expansion. However, the problem of explosive films generated by the PECVD route needs to be solved by performing a micro-texturing process after alkali polishing on the back of the battery. The existing micro-texturing process is prone to generate irregular air flow marks in actual production, and as the number of production batches increases, the air flow marks will gradually worsen. Seriously, it will directly affect the appearance after coating, resulting in the appearance degradation of the battery wafers, and even affecting the efficiency of the battery wafers. Summary of the Invention

[0003] An object of the present application is to provide a new technical solution for a micro-texturing method, a silicon wafer and a photovoltaic cell.

[0004] According to the first aspect of the present application, there is provided a micro-texturing method applied to photovoltaic cell production, including:

[0005] At least successively performing alkali polishing, first alkali washing, micro-texturing process and second alkali washing on the surface to be processed of the workpiece, so as to form a micro-roughened surface on the surface to be processed;

[0006] Wherein, the solutions used in the first alkali washing and the second alkali washing include an alkali solution of 0.3% - 0.5%, and the solution used in the micro-texturing process includes an alkali solution of 1% - 1.5%.

[0007] Optionally, the alkali solution is a KOH solution or a NaOH solution.

[0008] Optionally, the process times of the first alkali washing and the second alkali washing are respectively 90s - 120s, and the reaction time of the micro-texturing process is 80s - 120s.

[0009] Optionally, the process temperatures of the first alkali washing and the second alkali washing are respectively 60°C - 65°C, and the process temperature of the micro-texturing process is 68°C - 70°C.

[0010] Optionally, the solutions used in the first alkali washing and the second alkali washing further include 1% - 3% of H 2 O 2 .

[0011] Optionally, the solution used in the micro-texturing process further includes 0.2 - 0.4% of an additive, which is one or more of a surfactant, a nucleating agent, a dispersant, a catalyst, and an antifoaming agent.

[0012] Optionally, the workpiece is assembled in a basket with the surface to be processed exposed, and the method further includes:

[0013] Circulating and replenishing the solution in the equipment containing the solution for the first alkali wash, the micro-texturing process, and the second alkali wash, and bubbling the solution before the basket is immersed in the solution, and stopping bubbling when the basket is immersed in the solution.

[0014] Optionally, it further includes:

[0015] Before alkali polishing the workpiece, pre-cleaning and the first water wash are performed on it;

[0016] The second water wash is performed after alkali polishing and before the first alkali wash;

[0017] The third water wash is performed after the first alkali wash and before the micro-texturing process;

[0018] The fourth water wash is performed after the micro-texturing process and before the second alkali wash;

[0019] After the second alkali wash, the fifth water wash, acid wash, sixth water wash, slow lift process, and drying process are performed in sequence.

[0020] According to the second aspect of the present application, a silicon wafer is provided, including: the micro-roughened surface formed by the micro-texturing method described in the first aspect.

[0021] According to the third aspect of the present application, a photovoltaic cell is provided, including: the silicon wafer described in the second aspect.

[0022] According to an embodiment of the present application, the micro-texturing method provided by the present application enables the workpiece to form a micro-roughened surface on its surface to be processed after at least undergoing alkali polishing, the first alkali wash, the micro-texturing process, and the second alkali wash, solving the problem of film bursting in PECVD. Further, by controlling the solution concentration in each process, the phenomenon of airflow marks prone to appear on the micro-roughened surface is optimized, improving the quality of the workpiece. When applied to a photovoltaic cell, it can improve the cell yield and efficiency.

[0023] Through the following detailed description of the exemplary embodiments of the present application with reference to the accompanying drawings, other features and advantages of the present application will become clear. Description of the Drawings

[0024] The drawings incorporated in the specification and constituting a part of the specification illustrate the embodiments of the present application, and together with the description are used to explain the principles of the present application.

[0025] Figure 1 are the airflow imprint traces generated by the PECVD process in the prior art.

[0026] Figure 2 is the micro-roughened surface made by the micro-texturing method provided in this application.

[0027] Reference numerals or descriptions:

[0028] 1. Airflow imprint; 2. Pyramid structure. Detailed implementation manners

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

[0030] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present application or its application or use.

[0031] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification.

[0032] In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0033] It should be noted that: similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

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

[0035] PECVD requires high-temperature annealing after coating, and the annealing temperature is between 600 °C and 850 °C. During the high-temperature annealing process, the polysilicon layer is rich in H atoms, and the concentration reaches 10 20 ~10 22 cm -3 . "H atom exudation" will occur during high-temperature annealing and accumulate in the polysilicon layer and SiO 2At the interface, there is the phenomenon of film bursting. Film bursting may lead to uneven film layers, increased lateral transmission channels, and even film layer peeling off, seriously affecting the battery efficiency.

[0036] The film bursting phenomenon is directly related to the surface roughness of the silicon wafer. The greater the roughness, the greater the surface adhesion force, and the lower the film bursting probability. Therefore, in the actual production of the PECVD process, after the back surface of the battery is alkali polished, micro-texturing is performed to solve the film bursting problem of PECVD. However, due to the irregular air flow marks on the back surface appearance during the actual production process of micro-texturing (see Figure 1 ), and as the number of production batches increases, the air flow marks gradually become more serious. In severe cases, it will directly affect the appearance after coating, causing the appearance degradation of the battery chips, and even affecting the efficiency of the battery chips.

[0037] As Figure 2 shown, according to the first aspect of the present application, a micro-texturing method is provided, which is applied to the production of photovoltaic cells and includes: performing at least alkali polishing, first alkali washing, micro-texturing process, and second alkali washing on the surface to be processed of the workpiece in sequence, so as to form a micro-velvet surface on the surface to be processed; wherein, the solutions used in the first alkali washing and the second alkali washing include 0.3% - 0.5% alkali solution, and the solution used in the micro-texturing process includes 1% - 1.5% alkali solution.

[0038] Specifically, in this embodiment, a silicon wafer is used as the workpiece, and the surface to be processed is the back surface of the silicon wafer. By performing process processing on the surface to be processed of the silicon wafer to form a micro-velvet surface, that is, a micro-velvet surface with tiny pyramid structures grows on the basis of the polished surface of the back surface of the silicon wafer (as Figure 2 shown). That is, by micro-texturing the back surface of the silicon wafer, its surface roughness is increased, the surface adhesion force of the back surface of the silicon wafer is improved, the film bursting probability is reduced, and the efficiency and yield of the subsequent manufactured battery are ensured.

[0039] Furthermore, when processing the surface to be processed of the workpiece, it is necessary to go through alkali polishing, first alkali washing, micro-texturing, and second alkali washing in sequence. Among them, the alkali polishing process refers to first using an alkali solution and an additive to etch the back surface of the silicon wafer to form a polished surface structure. In addition, based on the different types of solution additives in the alkali polishing and the solution in the micro-texturing process, therefore, a first alkali washing is performed before the micro-texturing process, and a specific concentration of alkali solution is used to clean and remove the stains and additives remaining on the back surface of the silicon wafer after polishing, so as to facilitate the subsequent micro-texturing process. The micro-texturing process is to generate tiny pyramid structures on the back surface of the silicon wafer through an alkali solution to form a micro-velvet surface. The second alkali washing is also to clean the residual impurities and additives, etc. on the back surface of the silicon wafer through an alkali solution containing a specific concentration.

[0040] In practical applications, if the growth of the micro-textured surface is uneven, it will lead to the phenomenon of air flow marks. In the above embodiments, the present application sets the solutions for the first alkali wash and the second alkali wash to include 0.3% - 0.5% alkali solution, such as 0.4% KOH solution, so that the alkali concentration in the solution is relatively low, reducing the degree of reaction between the alkali solution and the back surface of the silicon wafer, and avoiding the problem of the overall uniformity of the surface to be processed decreasing. At the same time, by using a solution containing 1% - 1.5% alkali solution to texture the back surface of the silicon wafer in the micro-texturing process, such as 1.25% KOH solution, a suitable pyramid structure can grow on the surface to be processed, thereby making the distribution of the micro-textured surface more uniform, and thus improving the linearity of the air flow marks and ensuring that the overall uniformity of the back surface of the silicon wafer is not decreased.

[0041] In the above embodiments, various additives can also be added to the solutions for the first alkali wash, micro-texturing, and second alkali wash, such as surfactants, nucleating agents, dispersants, catalysts, defoamers, etc., so that the reaction time, reaction temperature, etc. of each process can be maintained within a suitable range. For example, the reaction time for the first alkali wash and the second alkali wash can be designed to be 90s - 150s, the reaction temperature can be designed to be 60°C - 70°C, and the reaction time for micro-texturing can be designed to be 80s - 125s, the reaction temperature can be designed to be 65°C - 70°C, to ensure the uniformity of the micro-textured surface. Among them, alkali polishing, the first alkali wash, the micro-texturing process, and the second alkali wash can all be carried out in a solution tank, and the silicon wafer can be washed with water before and after each process to further remove the solutions and impurities of each process.

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

[0043] Specifically, in practical applications, the first alkali wash, the micro-texturing process, and the second alkali wash can all use a KOH solution or an NaOH solution, which has a relatively low cost and, as an anisotropic etching solution for silicon, is used to clean and etch the surface to be processed of the silicon wafer, so that a micro-textured surface can grow on it, improving the yield and efficiency of the battery.

[0044] Optionally, the process times for the first alkali wash and the second alkali wash are 90s - 120s respectively, and the reaction time for the micro-texturing process is 80s - 120s.

[0045] Specifically, in this embodiment, by controlling the process times for the first alkali wash and the second alkali wash within 90s - 120s, such as 100s, 110s, etc., to reduce the reaction time between the surface to be processed of the silicon wafer and the alkali solution during the first alkali wash and the second alkali wash, and by controlling the reaction time for the micro-texturing process within 80s - 120s, such as 90s, 100s, 110s, etc., to further improve the uniformity of the micro-textured surface in the micro-texturing process, the purpose of further improving the air flow marks is achieved.

[0046] Optionally, the process temperatures of the first alkali washing and the second alkali washing are 60°C to 65°C respectively, and the process temperature of the micro-texturing step is 68°C to 70°C.

[0047] Specifically, in this embodiment, the process temperatures of the first alkaline washing and the second alkaline washing are controlled within the range of 60°C to 65°C, for example, 62°C, 64°C, etc., so as to reduce the degree of reaction between the surface to be processed of the silicon wafer and the alkaline solution during the first alkaline washing and the second alkaline washing, and the reaction temperature of the micro-texturing process is controlled within the range of 68°C to 70°C, for example, 69°C, etc., so as to further improve the uniformity of the micro-texturing surface in the micro-texturing process, thereby achieving the purpose 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 reaction degree between the first and second alkaline washes and the silicon wafer is reduced, the degree of corrosion of the alkaline solution on the silicon wafer is reduced, and the additives and impurities can be removed well, thereby ensuring the uniformity of the micro-velvet surface formed on the surface to be processed and the efficiency of the battery cell made of the silicon wafer. Among them, the alkaline solution concentration, process temperature and process time of micro-velvet are reduced compared to the parameters of the texturing process on the front side of the silicon wafer (the process time of the front texturing process is usually 420s to 480s, the process temperature is usually 80℃ to 82℃, and the alkaline solution concentration is 1% to 1.5%), so that the roughness of the formed micro-velvet surface can avoid the problem of film explosion.

[0049] Optionally, the solution used in the first alkali wash and the second alkali wash further comprises 1% to 3% H 2 O 2 .

[0050] Specifically, in practical applications, by adding 1% to 3% H 2 O 2 , for example, H 2 O 2 %, using the strong oxidizing property of hydrogen peroxide, it is possible to clean the dirt remaining on the surface of the silicon wafer after polishing or micro-texturing.

[0051] Optionally, the solution used in the micro-texturing process further comprises 0.2-0.4% of an additive, wherein the additive is one or more of a surfactant, a nucleating agent, a dispersant, a catalyst, and a defoaming agent.

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

[0053] Optionally, a flower basket is used to assemble the workpiece, and the surface to be processed is exposed. The method also includes: circulating the liquid in the equipment containing the solution of the first alkaline washing, the micro-texturing process and the second alkaline washing, and bubbling the solution before the flower basket is immersed in the solution, and stopping the bubbling when the flower basket is immersed in the solution.

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

[0055] In this embodiment, the alkali polishing, first alkali cleaning, micro-texturing and second alkali cleaning of the surface to be processed are carried out by carrying the silicon wafer on the basket, which can facilitate the operation of each process and protect the silicon wafer from damage. In one embodiment, the alkali polishing, first alkali cleaning, micro-texturing and second alkali cleaning processes are all carried out in a solution tank, and the solution in each solution tank is circulated and replenished, for example, a circulating pump is used to work in the tank body to achieve circulated replenishment and ensure the concentration and uniformity of the solution.

[0056] Furthermore, before the flower basket is immersed in each tank body, that is, before the first alkaline washing, micro-texturing process and the second alkaline washing, bubbling can be carried out in the corresponding solution tank to improve the uniformity of the solution. When the flower basket invades the tank bodies of the first alkaline washing and the second alkaline washing, the bubbling operation in the corresponding process tank is stopped to avoid unnecessary texturing effect during the first alkaline washing and the second alkaline washing, thereby ensuring the uniformity of the solution and the independence of each process.

[0057] Optionally, the method further includes: pre-cleaning and washing the workpiece with water before alkaline polishing; washing the workpiece with water for the second time after alkaline polishing and before the first alkaline washing; washing the workpiece with water for the third time after the first alkaline washing and before the micro-texturing process; washing the workpiece with water for the fourth time after the micro-texturing process and before the second alkaline washing; and washing the workpiece with water for the fifth time, acid washing, water washing for the sixth time, slow pulling process and drying process in sequence after the second alkaline washing.

[0058] Specifically, before and after each process, multiple water washing, acid washing and other cleaning operations are required. Among them, acid washing can remove the alkali and metal ions remaining on the micro-suede surface of the silicon wafer, and water washing can remove the impurities that have been desorbed and the alkali or acid on the surface of the silicon wafer. In addition, the slow pulling process dehydration uses the surface tension of water to allow the silicon wafer to be slowly pulled away from the water surface, peeling off water from the surface of the silicon wafer to obtain a relatively dry silicon wafer. After dehydration is completed, further drying is carried out to improve the output power and conversion efficiency of the battery cell.

[0059] To make the effects of the micro-texturing method provided in this application clearer, the following provides Comparative Example 1 and two Examples for detailed description:

[0060] Comparative Example 1:

[0061] After the TOPCon process reaches the boron diffusion process, after completing the step of removing BSG (borosilicate glass), the alkali polishing micro-texturing process is started, and it passes through the following process tanks in sequence: pre-cleaning - water washing 1 - alkali polishing - water washing 2 - alkali washing 1 - water washing 3 - micro-texturing - water washing 4 - alkali washing 2 - water washing 5 - acid washing - water washing 6 - slow lifting - drying tank.

[0062] Among them, the alkali washing 1 tank and the alkali washing 2 tank correspond to the first alkali washing and the second alkali washing respectively. Their reaction temperature is set at 65 °C, the process time is set at 150 s, and the solution ratio is 0.8% KOH and 4% H 2 O 2 , and the self-supplemented solution volume is continuously circulated and replenished, and bubbling is continuous.

[0063] The micro-texturing tank corresponds to the micro-texturing process. Its reaction temperature is 70 °C, the process time is 120 s, the solution ratio is 2% KOH and 0.5% additive. The solution circulation method is continuous circulation, and the bubbling method of the solution is continuous bubbling when the basket does not enter the tank and no bubbling when the basket enters.

[0064] Example 1:

[0065] This Example 1 provides a micro-texturing method. The difference from Comparative Example 1 lies in the process formulations of the alkali washing 1 tank, the alkali washing 2 tank and the micro-texturing tank. Specifically:

[0066] The reaction temperatures of the alkali washing 1 and 2 tanks are set at 62 °C, the process time is 100 s, and the solution ratio is 0.4% KOH and 2.5% H 2 O 2 , and the self-supplemented solution volume is continuously circulated and replenished, and bubbling is continuous. The reaction temperature of the micro-texturing tank is 70 °C, the process time is 120 s, the solution ratio is 1.5% KOH and 0.4% additive. The solution circulation method is continuous circulation, and the bubbling method is bubbling without a basket and no bubbling with a basket.

[0067] Example 2

[0068] This Example 2 provides a micro-texturing method. The difference from Comparative Example 1 lies in the process formulations of the alkali washing 1 and 2 tanks and the micro-texturing tank. Specifically:

[0069] The reaction temperatures of the alkali washing 1 and 2 tanks are set at 62 °C, the process time is 90 s, and the solution ratio is 0.3% KOH and 1.5% H 2 O 2, the self-complementary solution volume is that the solution circulates continuously, there is no bubbling in the basket, and there is no bubbling when there is a basket. The reaction temperature of the micro-texturing tank is 70°C, the process time is 120 s, the ratio is 1.2% KOH and 0.3% additive, and the solution circulation method is continuous circulation, with no bubbling in the basket and no bubbling when there is a basket.

[0070] It can be known through observation and comparison that the distribution ratio of the appearance air flow marks in Comparative Example 1 is 5%, and the air flow mark phenomenon is relatively serious. Refer to Figure 1 ; the distribution ratio of the appearance air flow marks in Example 1 has been improved to 3%, and the air flow mark phenomenon is relatively slight, while the distribution ratio of the appearance air flow marks in Example 2 has been reduced to 0.2%, and there are no obvious appearance air flow marks during visual inspection.

[0071] This shows that the micro-texturing method provided in this application optimizes the process formulas of the alkali washing tanks 1 and 2 and the micro-texturing tank. Without the need to modify other hardware of the machine, it can improve the appearance air flow marks of the micro-texturing, reduce the output of defective products in the workshop, and improve the yield of the battery workshop. Among them, the ratio of air flow marks usually refers to the ratio that there are 5 products with obvious appearance air flow marks in every 100 products.

[0072] According to the second aspect of this application, a silicon wafer is provided, including: the micro-textured surface made by the micro-texturing method described in the first aspect.

[0073] Specifically, in this embodiment, the provided silicon wafer has a micro-textured surface made by the micro-texturing method provided in the first aspect. The structure of the micro-textured surface can be referred to Figure 2 , which shows the micro-textured surface and the picture of the pyramid structure 2 observed at 100 times under the microscope. The surface of the silicon wafer provided in this embodiment improves the air flow marks formed in the conventional micro-texturing technology and improves the appearance and yield of the silicon wafer.

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

[0075] Specifically, the photovoltaic cell in this embodiment is made of the silicon wafer provided in the second aspect that improves the air flow marks on the back micro-textured surface, improving the yield and efficiency of the cell.

[0076] The differences between the above embodiments are mainly described. As long as the different optimization features between the embodiments are not contradictory, they can be combined to form a better embodiment. Considering the simplicity of the writing, it will not be elaborated here.

[0077] Although some specific embodiments of the present application have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration purposes and not for limiting the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A micro-texturing method, applied to photovoltaic cell production, characterized in that: include: The surface to be processed of the workpiece is subjected to at least alkali polishing, a first alkali washing, a micro-texturing process and a second alkali washing in sequence, so that the surface to be processed forms a micro-texture surface; Wherein, the solutions used in the first alkali washing and the second alkali washing include 0.3% to 0.5% alkali solution, and the solution used in the micro-texturing process includes 1% to 1.5% alkali solution.

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, characterized in that: The process time of the first alkali washing and the second alkali washing is 90s to 120s respectively, and the reaction time of the micro-texturing process is 80s to 120s.

4. The micro-texturing method according to claim 1, characterized in that: The process temperatures of the first alkali washing and the second alkali washing are 60°C to 65°C respectively, and the process temperature of the micro-texturing process is 68°C to 70°C.

5. The micro-texturing method according to claim 1, characterized in that: The solutions used in the first alkali washing and the second alkali washing also include 1% to 3% H2O2.

6. The micro-texturing method according to claim 1, characterized in that: The solution used in the micro-texturing process also includes 0.2-0.4% of an additive, and the additive is one or more of a surfactant, a nucleating agent, a dispersant, a catalyst, and a defoaming agent.

7. The micro-texturing method according to claim 1, characterized in that: The workpieces are assembled using a basket, and the surface to be processed is exposed. The method further comprises: The equipment containing the solution of the first alkali washing, the micro-texturing process and the second alkali washing 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 claim 1, characterized in that: Also includes: Before alkaline polishing of the workpiece, it is pre-cleaned and washed with water for the first time; After alkali polishing and before the first alkali wash, a second water wash is performed; After the first alkali washing and before the micro-texturing process, the third water washing is carried out; The fourth water washing is carried out after the micro-texturing process and before the second alkali washing; After the second alkali washing, the fifth water washing, acid washing, the sixth water washing, slow pulling process and drying process are carried out in sequence.

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

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

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