Diffusion method for preparing solar cell, solar cell and photovoltaic module

Abstract

The invention discloses a diffusion method for preparing a solar cell, the solar cell and a photovoltaic module, and the diffusion method for preparing the solar cell comprises the following steps: placing a carrier boat carrying a silicon wafer in a diffusion furnace which is provided with a gas inlet for gas to enter, the distance D between the first end, close to the air inlet, of the carrier boat and the air inlet is larger than 10 cm, the distance between the first end and the air inlet is smaller than the distance between the first end and a furnace door of the diffusion furnace, and the size of the silicon wafer is larger than 158 mm * 158 mm; performing deposition treatment, preparing an oxide layer and a film layer containing doping elements on the surface of the silicon wafer, and doping dichloroethylene into oxidizing gas used for preparing the oxide layer; and carrying out propelling treatment to form a diffusion layer on one side, close to the oxide layer, of the silicon wafer, and the diffusion layer comprises doping elements. According to the invention, the problem of smudginess of the central area of the solar cell in EL detection can be effectively improved, and the energy conversion efficiency and the product yield of the solar cell are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, and in particular to a diffusion method for preparing a solar cell, a solar cell and a photovoltaic module. BACKGROUND

[0002] With the continuous development of the photovoltaic industry, the increase of the size of silicon wafers has obvious advantages in reducing the loss of silicon materials and improving the energy conversion efficiency of solar cells, and is widely used. However, when large-size silicon wafers are used as raw materials, the sheet resistance non-uniformity of the prepared solar cells is significantly increased, and the center area contamination phenomenon in the electroluminescence (EL) detection is intensified, thereby causing the yield of the product to decrease. SUMMARY

[0003] In order to improve the center area contamination problem of the solar cell in the EL detection, the embodiments of the present application disclose a diffusion method for preparing a solar cell, a solar cell and a photovoltaic module.

[0004] In a first aspect, the embodiments of the present application provide a diffusion method for preparing a solar cell.

[0005] The diffusion method for preparing a solar cell comprises the following steps:

[0006] Placing a boat carrying a silicon wafer in a diffusion furnace, wherein the diffusion furnace has a gas inlet, the distance D between the first end of the boat close to the gas inlet and the gas inlet is greater than 10 cm, and the distance from the first end to the gas inlet is less than the distance from the first end to the door of the diffusion furnace, and the size of the silicon wafer is greater than 158mm×158mm;

[0007] Deposition treatment, preparing an oxide layer and a film layer containing a doping element on the surface of the silicon wafer, wherein the oxide gas used to prepare the oxide layer is doped with dichloroethylene;

[0008] Pushing treatment, forming a diffusion layer on the side of the silicon wafer close to the oxide layer, and the diffusion layer comprises the doping element.

[0009] As an optional implementation, in the embodiments of the present application, in the deposition treatment step, oxygen and dichloroethylene are first passed at a temperature of 800-830℃ to form the oxide layer on the surface of the silicon wafer, and then the film layer containing the doping element is prepared.

[0010] As an optional implementation, in the embodiments of the present application, in the step of preparing the oxide layer, the oxygen is first passed at a temperature of 800-830℃ before the oxygen and the dichloroethylene are passed;

[0011] After the oxygen and the dichloroethylene are introduced, the oxygen is introduced at a temperature of 800°C to 830°C.

[0012] As an optional embodiment, in the embodiment of the present application, the amount of the oxygen introduced before the oxygen and the dichloroethylene are introduced is 800sccm to 1000sccm;

[0013] In the introduction of the oxygen and the dichloroethylene, the ratio of the flow rate of the dichloroethylene to the flow rate of the oxygen is 30sccm to 50sccm: 1050sccm to 1200sccm;

[0014] After the oxygen and the dichloroethylene are introduced, the amount of the oxygen introduced is 800sccm to 1000sccm.

[0015] As an optional embodiment, in the embodiment of the present application, the oxidation time before the oxygen and the dichloroethylene are introduced is 1min to 2min;

[0016] In the introduction of the oxygen and the dichloroethylene, the oxidation time is 4min to 6min, and the dichloroethylene is carried into the diffusion furnace by nitrogen;

[0017] After the oxygen and the dichloroethylene are introduced, the oxidation time is 1min to 2min.

[0018] As an optional embodiment, in the embodiment of the present application, the thickness of the oxide layer is 40nm to 50nm.

[0019] As an optional embodiment, in the embodiment of the present application, in the film layer containing the doping element, the doping element is an N-type doping element or a P-type doping element;

[0020] and / or,

[0021] The sheet resistance of the silicon wafer has an in-situ non-uniformity of less than 6.03%;

[0022] and / or, the size of the silicon wafer is (182.2nm to 183.75nm) x (182.2nm to 183.75nm).

[0023] and / or,

[0024] The thickness of the silicon wafer is 120nm to 135nm;

[0025] and / or,

[0026] Before the step of placing the boat carrying the silicon wafer in the diffusion furnace, the silicon wafer is subjected to a texturing treatment.

[0027] In a second aspect, the embodiments of the present application provide a solar cell.

[0028] A solar cell is prepared by using the silicon wafer processed by the diffusion method according to the first aspect.

[0029] In a third aspect, the embodiments of the present application provide a photovoltaic module.

[0030] A photovoltaic module comprises the solar cell according to the second aspect.

[0031] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0032] The diffusion method for preparing a solar cell provided by the embodiments of the present application is used for a silicon wafer with a size greater than 158mm*158mm. The boat is placed at a specific position in the diffusion furnace, so that the distance between the first end of the boat and the air inlet is greater than 10cm and less than the distance between the first end and the furnace door, thereby optimizing the air flow field in the diffusion furnace. This adjustment not only makes the air flow more uniform, but also keeps the silicon wafer away from the turbulent flow area of the air inlet, reducing the influence of turbulent flow on the central area of the large-size silicon wafer. In this way, during the deposition process, the oxidation layer with better uniformity can be formed by adding dichloroethylene into the oxidation gas for oxidation treatment, and the introduction of impurities is reduced, and then during the advancing process, the doping elements obtain better diffusion effect on the side of the silicon wafer close to the oxidation layer, effectively improving the within-wafer sheet resistance uniformity of the silicon wafer. Through the above setting, the phenomenon that the sheet resistance of the large-size silicon wafer is low around and high in the middle is effectively inhibited, the within-wafer sheet resistance uniformity is improved, and thus the EL central area is effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0034] Figure 1 is an EL test result schematic diagram of a solar cell prepared before the boat position is adjusted;

[0035] Figure 2 is a structural schematic diagram of a boat carrying a silicon wafer placed in a diffusion furnace according to the embodiments of the present application;

[0036] Figure 3 is an EL test result schematic diagram of a solar cell disclosed by the embodiments of the present application;

[0037] Figure 4 is a sheet resistance test site schematic diagram of a surface of a single silicon wafer disclosed by the present application.

[0038] Icon: 1, solar cell; 11, silicon wafer; 2, boat; 3, diffusion furnace; 31, air inlet; 32, furnace door. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0040] In the present application, the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", and the like are based on the orientations or positional relationships shown in the drawings. These terms are mainly used for better describing the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0041] In addition, the above-mentioned partial terms can be used to represent other meanings in addition to the orientation or positional relationship, for example, the term "upper" can also be used to represent a certain dependent relationship or connection relationship in some cases. Those of ordinary skill in the art can understand the specific meanings of these terms in the present application according to the specific circumstances.

[0042] In addition, the terms "mount", "set", "provided with", "connect", "connected" should be understood broadly. For example, it can be fixedly connected, detachably connected, or integrally constructed; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication between two devices, elements or components. Those of ordinary skill in the art can understand the specific meanings of the above-mentioned terms in the present application according to the specific circumstances.

[0043] In addition, the terms "first", "second", and the like are mainly used to distinguish different devices, elements or components (the specific types and structures can be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, the meaning of "multiple" is two or more.

[0044] With the continuous progress of technology and the higher pursuit of market for solar cell energy conversion efficiency and production efficiency, the size of silicon wafer gradually increases, such as from 158mmx158mm to 183mmx183mm, or even larger size of silicon wafer begins to be widely used in the production of solar cells. The application of large size silicon wafer has important significance in many aspects: on the one hand, large size silicon wafer can effectively reduce the loss of silicon material and improve the utilization rate of silicon material, thereby reducing the production cost to a certain extent; on the other hand, large size silicon wafer can increase the light receiving area of solar cell, which helps to improve the energy conversion efficiency of solar cell, and thus improves the overall performance and market competitiveness of solar cell.

[0045] However, it is not easy to use large size silicon wafer, which faces many technical challenges and difficulties in practical application. Under the existing process equipment conditions in the cell workshop, the original production equipment and technical parameters are mainly designed for small size silicon wafer. When large size silicon wafer is introduced, due to the compatibility and adaptability of the equipment, the heating area and the area affected by the airflow of large size silicon wafer in the diffusion furnace increase significantly, which makes the center area of the silicon wafer more susceptible to turbulent flow, thereby increasing the non-uniformity of sheet resistance, causing EL center area contamination as shown in the figure. Figure 1 This phenomenon not only reduces the photoelectric conversion efficiency of solar cell 1, but also seriously affects the yield and quality stability of the product, which brings many troubles to the large-scale production of solar cell 1.

[0046] The inventors have conducted a large number of experimental researches and technical verifications, and deeply analyzed the problems of large size silicon wafer in the diffusion process. Through careful observation and analysis, the inventors found that when the size of the silicon wafer is greater than 158mmx158mm, the airflow field distribution in the diffusion furnace is significantly different from that of small size silicon wafer. This difference is the key to the non-uniform diffusion of large size silicon wafer and the EL center area contamination. Specifically, when the large size silicon wafer is close to the air inlet in the diffusion furnace, the center area will be subjected to more intense turbulent flow, which makes the distribution of doping gas on the surface of the silicon wafer uneven, thereby affecting the diffusion effect of doping elements and increasing the non-uniformity of sheet resistance. At the same time, due to the large surface area of large size silicon wafer, it has higher requirements for the uniformity of gas flow and temperature field during diffusion, while the existing diffusion furnace equipment and process parameters often fail to meet these requirements when dealing with large size silicon wafer, thereby further aggravating the severity of the problem.

[0047] To this end, the inventors propose a solution: by adjusting the position of the boat in the diffusion furnace, the distance between the first end of the boat and the gas inlet is greater than 10 cm, and less than the distance from the first end to the furnace door, so as to optimize the distribution of the gas flow field in the diffusion furnace. This adjustment not only makes the gas flow more uniform, reduces the influence of turbulence on the central area of large-size silicon wafers, but also significantly improves the uniformity of the silicon wafer surface oxide layer and the doped element-containing film layer, thereby improving the diffusion effect of the doped element in the silicon wafer, effectively solving the problem of non-uniform sheet resistance and EL center area contamination of large-size silicon wafers during diffusion.

[0048] The technical solutions of the present application will be further described below in conjunction with the embodiments and drawings.

[0049] In a first aspect, the embodiments of the present application provide a diffusion method for preparing a solar cell.

[0050] A diffusion method for preparing a solar cell, comprising the following steps:

[0051] Referring to Figure 2 The boat 2 carrying the silicon wafer 11 is placed in the diffusion furnace 3, wherein the diffusion furnace 3 has a gas inlet 31 for gas to enter, the distance D between the first end of the boat 2 close to the gas inlet 31 and the gas inlet 31 is greater than 10 cm, and the distance from the first end to the furnace door 32 of the diffusion furnace 3 is less than the distance from the first end to the gas inlet 31, and the size of the silicon wafer 11 is greater than 158mm×158mm;

[0052] Deposition treatment, depositing an oxide layer and a doped element-containing film layer on the surface of the silicon wafer 11, wherein dichloroethylene is added to the oxidation gas for oxidation treatment of the oxide layer;

[0053] Pushing treatment, forming a diffusion layer on the side of the silicon wafer 11 close to the oxide layer, the diffusion layer comprising a doped element.

[0054] In the diffusion method for preparing solar cells, for the silicon wafer 11 with a size greater than 158mmx158mm, the boat 2 is placed in a specific position in the diffusion furnace 3, so that the distance between the first end of the boat 2 and the gas inlet 31 is greater than 10cm and less than the distance between the first end of the boat 2 and the furnace door 32, so as to optimize the air flow field in the diffusion furnace 3. This adjustment not only makes the air flow more uniform, but also keeps the silicon wafer 11 away from the turbulent flow area of the gas inlet 31, reducing the influence of turbulent flow on the central area of the large-size silicon wafer 11. In this way, during the deposition process, combined with the oxidation treatment by adding dichloroethylene in the oxidation gas, a more uniform oxidation layer can be formed, while reducing the introduction of impurities, and then during the advancing process, the doping elements on the side of the silicon wafer 11 close to the oxidation layer have a better diffusion effect, effectively improving the within-wafer sheet resistance uniformity of the silicon wafer 11. Through the above setting, the phenomenon of low sheet resistance around and high sheet resistance in the middle of the large-size silicon wafer 11 is effectively suppressed, the within-wafer sheet resistance uniformity is improved, and as shown in the EL test results, the EL central area contamination is effectively reduced. Figure 3

[0055] It should be noted that the boat is a component used to carry the silicon wafer 11 to be processed during the diffusion process. The commonly used boat 2 can be a quartz boat.

[0056] In the present application, in order to solve the problems of sheet resistance non-uniformity and EL central area contamination of large-size silicon wafers 11 during the diffusion process, the position of the boat 2 in the diffusion furnace 3 is specifically set. The specific requirement is that the distance D between the first end of the boat 2 close to the gas inlet 31 and the gas inlet 31 is greater than 10cm, and the distance D is less than the distance between the first end of the boat 2 and the furnace door 32 of the diffusion furnace 3. This setting means that during the diffusion process, the boat 2 carrying the silicon wafer 11 needs to be appropriately moved inward to the deep part of the furnace. After such adjustment, the silicon wafer 11 will be away from the turbulent flow area of the gas inlet 31, the air flow field in the diffusion furnace 3 is optimized, the air flow is more uniform, thereby reducing the influence of turbulent flow on the central area of the large-size silicon wafer 11. Further, this helps to improve the uniformity of the oxidation layer and the doping element-containing film layer on the surface of the silicon wafer 11, improve the diffusion effect of the doping elements in the silicon wafer 11, and thus effectively improve the problems of sheet resistance non-uniformity and EL central area contamination of large-size silicon wafers 11 during the diffusion process.

[0057] ​The deposition of the oxide layer is a key step for diffusion. The main role of the oxide layer is to provide a stable chemical environment and physical barrier for the subsequent diffusion of the doping elements, therefore, improving the quality of the oxide layer plays an important role in improving the sheet resistance uniformity and reducing the EL center area contamination. Specifically, during the deposition process, the oxidation gas containing dichloroethylene is first introduced into the surface of the silicon wafer 11 to better reduce the introduction of impurities and improve the deposition quality of the oxide layer (such as introducing oxygen and dichloroethylene to form a silicon oxide layer). The oxide layer blocks impurities and contaminants from entering the interior of the silicon wafer 11, creating conditions for the uniform diffusion of the doping elements. In the subsequent push process, the doping elements in the film layer containing the doping elements pass through the oxide layer by heat treatment to form a diffusion layer on the side of the silicon wafer 11 close to the oxide layer. The presence of the oxide layer helps to control the diffusion rate and distribution of the doping elements, improve the quality and uniformity of the diffusion layer, and further improve the electrical performance and reliability of the solar cell.

[0058] In some embodiments, the distance D between the first end and the gas inlet 31 is between 20 cm and 25 cm.

[0059] By setting the distance between the first end and the gas inlet 31 to be between 20 cm and 25 cm, the gas flow field in the diffusion furnace 3 can be optimized, the gas flow distribution is more uniform, the influence of turbulence on the center area of the silicon wafer 11 is effectively reduced, the diffusion uniformity of the silicon wafer 11 is further improved, and the EL center area contamination is reduced. At the same time, since the distance between the first end and the gas inlet 31 is less than 25 cm, not only the advantage of reducing the influence of turbulence is maintained, but also the space utilization in the diffusion furnace 3 is improved.

[0060] In some embodiments, the oxygen and dichloroethylene are first introduced at a temperature of 800°C to 830°C to form an oxide layer on the surface of the silicon wafer 11, and then a film layer containing the doping elements is prepared.

[0061] When the introduced oxidation gas is oxygen and dichloroethylene, the oxide layer formed on the surface of the silicon wafer 11 is a silicon oxide layer. In this process, dichloroethylene reacts with oxygen to generate CO2, H2O and Cl atom radicals. Among them, the Cl atom radicals react with the silicon atoms on the surface of the silicon wafer 11 to generate chlorosilicates (such as NaSiCl x, x is a variable, indicating that the number of chlorine atoms will change according to the reaction conditions and the progress of the reaction), the chlorosilicate is converted into sodium chloride and SiO2 in the presence of oxygen (such as O2), thereby increasing the thickness of the silicon oxide layer and improving the quality of the silicon oxide layer, creating favorable conditions for the uniform diffusion of the doping elements. At the same time, the Cl atom radicals, by combining with sodium ions, passivate the activity of the sodium ions, thereby reducing the adverse effects of sodium ion contamination on diffusion, and react with trace metal ions on the wall of the diffusion furnace 3 to form chlorometal salts, fixing the metal ions on the wall and avoiding ionization contamination of the battery in subsequent doping processes. After a certain amount of these chlorometal salts are formed, they will be carried out of the diffusion furnace 3 by the gas flow from the tail gas pipe. In addition, the H2O water vapor formed by the above reaction can also react with silicon atoms to form silicon oxide and hydrogen, further improving the thickness and quality of the silicon oxide layer, thereby better improving the uniformity of the diffusion of the doping elements, and ultimately improving the electrical performance and reliability of the solar cell.

[0062] In some embodiments, in the step of preparing the silicon oxide layer, oxygen is introduced at a temperature of 800-830°C before the introduction of oxygen and dichloroethylene;

[0063] After the introduction of oxygen and dichloroethylene, oxygen is introduced at a temperature of 800-830°C.

[0064] Before the introduction of oxygen and dichloroethylene, oxygen is introduced at a temperature of 800-830°C, which can perform a preliminary oxidation treatment on the surface of the silicon wafer 11 to form silicon oxide, and the chlorine atoms produced by the subsequent dichloroethylene reaction are more likely to act on the interface between the silicon oxide and the silicon wafer 11, promoting further oxidation of the surface of the silicon wafer 11 and more quickly increasing the thickness of the silicon oxide layer.

[0065] After the introduction of oxygen and dichloroethylene, oxygen is introduced at a temperature of 800°C, which ensures the complete reaction of dichloroethylene, improves the utilization rate of dichloroethylene, and further improves the quality of the silicon oxide layer.

[0066] In some embodiments, before the introduction of oxygen and dichloroethylene, the amount of oxygen introduced is 800-1000sccm;

[0067] In the introduction of oxygen and dichloroethylene, the ratio of the gas flow rates of dichloroethylene and oxygen is 30-50sccm: 1050-1200sccm;

[0068] After the introduction of oxygen and dichloroethylene, the amount of oxygen introduced is 800-1000sccm.

[0069] In the process of preparing the oxidation layer, by limiting the gas flow of oxygen, dichloroethylene and other gases that are sequentially introduced, the oxygen and dichloroethylene gas can better act on the surface of the silicon wafer 11, ensuring sufficient mixing and reaction of dichloroethylene and oxygen, thereby more effectively improving the quality of the silicon oxide layer and enhancing the masking ability of impurities on the surface of the silicon wafer 11, reducing the dirt in the central area of the solar cell.

[0070] In some embodiments, the oxidation time is 1-2 minutes before the introduction of oxygen and dichloroethylene;

[0071] In the introduction of oxygen and dichloroethylene, the oxidation time is 4-5 minutes, and dichloroethylene is carried into the diffusion furnace 3 by nitrogen;

[0072] After the introduction of oxygen and dichloroethylene, the oxidation time is 1-2 minutes.

[0073] By limiting the oxidation time of each stage, 800 sccm of oxygen is introduced first for 1 minute to form a relatively thin initial silicon oxide layer, providing a basis for subsequent oxidation reactions. Then 800 sccm of oxygen and dichloroethylene are introduced for 4 minutes, and the chlorine atoms formed by the reaction of dichloroethylene and oxygen act on the interface between the silicon oxide layer and the silicon. Finally, 800 sccm of oxygen is introduced for 1 minute to further improve the quality of the silicon oxide layer.

[0074] In some embodiments, the thickness of the silicon oxide layer is 35 nm.

[0075] By limiting the thickness of the silicon oxide layer, it is ensured that the doping elements can pass through while effectively blocking impurities, thereby improving the performance and reliability of the solar cell.

[0076] In some embodiments, the doping elements in the film layer containing doping elements are N-type doping elements or P-type doping elements. In the film layer containing doping elements, the N-type doping elements can be phosphorus (P), arsenic (As), etc., and the P-type doping elements can be boron (B), etc. By selecting the appropriate type of doping element, the electrical performance of the solar cell can be better controlled, thereby preparing a solar cell that meets the needs of different application scenarios. When preparing an N-type solar cell, selecting phosphorus as a doping element can effectively increase the electron concentration of the solar cell and enhance the photoelectric conversion efficiency of the solar cell. When preparing a P-type solar cell, selecting boron as a doping element can help improve the hole concentration of the solar cell and optimize the electrical performance of the solar cell.

[0077] Exemplarily, when phosphorus is selected as the doping element, the diffusion coefficient of phosphorus in the silicon wafer 11 is larger than that in the oxide layer, and thus the phosphorus can diffuse through the oxide layer at a relatively low temperature to form a uniform and stable diffusion layer on the side of the silicon wafer 11 close to the oxide layer. In combination with the regulation of the position of the boat 2 in the diffusion furnace 3 and the optimization of the air flow field in the diffusion furnace 3, the diffusion of the phosphorus is more uniform, the non-uniformity of the sheet resistance in the central region of the large-size silicon wafer 11 is reduced, the EL center region contamination problem is reduced, and the overall performance and reliability of the solar cell are improved.

[0078] In some embodiments, the sheet resistance in the solar cell has a non-uniformity of less than 6.03%.

[0079] In the above solar cell, the non-uniformity of the sheet resistance is low, which means that the current distribution in the solar cell is more uniform, the local hot spots and power loss are reduced, and thus the photoelectric conversion efficiency and reliability of the solar cell are improved.

[0080] In some embodiments, the size of the silicon wafer 11 is (182.2 nm-183.75 nm) x (182.2 nm-183.75 nm).

[0081] Limiting the size of the silicon wafer 11 to the above range can meet the application requirements of large-size silicon wafers 11 in the current photovoltaic industry and improve the energy conversion efficiency and production efficiency of the solar cell.

[0082] In some embodiments, the thickness of the silicon wafer 11 is 120 nm-125 nm.

[0083] When the thickness of the silicon wafer 11 is 120 nm-125 nm, the thickness of the silicon wafer 11 is relatively thin, which can reduce the material cost, but the non-uniformity of the sheet resistance and the EL center region contamination problem are prone to occur during the diffusion process. However, the present application can effectively reduce these defects by adjusting the position of the boat 2 and optimizing the preparation process of the oxide layer. Therefore, the scheme of the present application is particularly suitable for improving the non-uniformity of the sheet resistance and the EL center region contamination problem of the large-size and thin silicon wafer 11.

[0084] In some embodiments, before the step of placing the boat 2 carrying the silicon wafer 11 in the diffusion furnace 3, the silicon wafer 11 is subjected to a texturing treatment.

[0085] Before the diffusion process, the surface of the silicon wafer 11 needs to be cleaned to remove impurities on the surface of the silicon wafer 11, reduce the influence of impurity diffusion, and improve the uniformity of the diffusion layer. The texturing process is generally arranged before the diffusion process. The texturing process not only forms a textured structure on the surface of the silicon wafer 11 to enhance light absorption, but also effectively cleans the surface of the silicon wafer 11. When the silicon wafer 11 is textured, the silicon wafer 11 is usually arranged in a flower basket. When the size of the silicon wafer 11 increases and the silicon wafer 11 is relatively thin (for example, the thickness of the silicon wafer 11 is between 120 nm and 125 nm), the adjacent two pieces in the flower basket placed in the texturing tank will be close to each other or even stick together under the attraction of the texturing liquid, resulting in that the oil stains and metal impurities in the center region of the silicon wafer 11 are not easy to be cleaned, the diffusion effect of the silicon wafer 11 after texturing is poor, and the EL center is dirty, which reduces the A-level rate of the product. Therefore, the subsequent process needs to be optimized for corresponding improvement. However, the present application adjusts the position of the boat 2 and optimizes the preparation process of the oxide layer, reduces the influence of the impurities remaining in the cleaning step of the texturing process on the sheet resistance uniformity of the diffusion layer, and improves the quality of the diffusion layer, thereby weakening the EL center dirty phenomenon.

[0086] After the diffusion process, cleaning can be performed to remove the oxide layer and the film layer containing the doping element, and further remove the impurities remaining on the surface of the silicon wafer 11.

[0087] In a second aspect, an embodiment of the present application provides a solar cell.

[0088] A solar cell is prepared by using a silicon wafer 11 treated by the diffusion method mentioned in the first aspect.

[0089] The silicon wafer 11 prepared by the diffusion method has more uniform sheet resistance distribution and lower EL center region dirt, thereby improving the photoelectric conversion efficiency and reliability of the solar cell and reducing the product failure rate.

[0090] In a third aspect, an embodiment of the present application provides a photovoltaic module.

[0091] A photovoltaic module includes a solar cell mentioned in the second aspect.

[0092] The technical solutions of the present application will be further described below in combination with more specific embodiments.

[0093] Embodiment one

[0094] An embodiment of the present application provides a preparation method of a PERC (emitter and back surface passivation cell) solar cell, including the following steps:

[0095] Setting the boat position: after the texturing process, the P-type silicon wafer is provided, and the boat carrying the P-type silicon wafer (the size is 183mmx183mm, and the average thickness is 125nm) is placed in the diffusion furnace. The first end of the boat close to the air inlet is 20cm away from the air inlet, and the first end is 20cm away from the furnace door of the diffusion furnace;

[0096] Deposition treatment, depositing a silicon oxide layer on the light-receiving surface of the silicon wafer, the steps are as follows:

[0097] Passing oxygen at a temperature of 800℃, the oxygen volume flow rate is 800sccm, and the oxidation time is 1min;

[0098] Carrying dichloroethylene vapor by nitrogen into the diffusion furnace tube at 800℃, the dichloroethylene flow rate is 30sccm, the oxygen volume flow rate is 1050sccm, and the oxidation time is 4min;

[0099] Passing oxygen again at a temperature of 800℃, the oxygen volume flow rate is 800sccm, and the oxidation time is 1min;

[0100] Depositing a phosphorus-containing film layer on the surface of the silicon oxide layer by chemical vapor deposition method, providing a doping source for subsequent push treatment;

[0101] Push treatment, making the phosphorus element in the phosphorus-containing film layer pass through the silicon oxide layer to form a phosphorus-containing diffusion layer on the side of the silicon wafer close to the silicon oxide layer;

[0102] Oxidation treatment, continuing to deposit a PSG (Phosphorus Silicate Glass) layer containing phosphorus, silicon and silicon dioxide on the surface of the phosphorus-containing film layer;

[0103] Laser selective doping treatment, diffusing the phosphorus element in the PSG layer to the diffusion layer below the laser selective doping treatment area, so as to form a laser selective doping area with higher phosphorus element doping concentration at a specific position of the diffusion layer;

[0104] Cleaning treatment, removing the PSG layer, phosphorus-containing film layer and silicon oxide layer on the surface of the diffusion layer, and polishing the back surface of the P-type silicon wafer to remove the plating layer;

[0105] Depositing a second silicon nitride layer on the back surface of the silicon wafer, and sequentially depositing a silicon oxynitride layer and a first silicon nitride layer on the surface of the diffusion layer;

[0106] Preparation of first electrode and second electrode, the first electrode forms ohmic contact with the laser selective doping area through the silicon oxynitride layer and the first silicon nitride layer, and the second electrode forms ohmic contact with the silicon wafer through the second silicon nitride layer.

[0107] Example two

[0108] The embodiment of the present application provides a preparation method of a PERC solar cell, which is different from the embodiment one in that the distance between the first end of the boat near the air inlet and the air inlet is 15 cm, and the rest is consistent with the embodiment one.

[0109] Embodiment three

[0110] The embodiment of the present application provides a preparation method of a PERC solar cell, which is different from the embodiment one in that the distance between the first end of the boat near the air inlet and the air inlet is 25 cm, and the rest is consistent with the embodiment one.

[0111] Comparative example one

[0112] The comparative example of the present application provides a preparation method of a PERC solar cell, which is different from the embodiment one in that the distance between the first end of the boat near the air inlet and the air inlet is 10 cm, and the rest is consistent with the embodiment one.

[0113] Comparative example two

[0114] The comparative example of the present application provides a preparation method of a PERC solar cell, which is different from the embodiment one in that the step of introducing dichloroethylene is omitted in the step of depositing a silicon oxide layer, and the rest is consistent with the embodiment one.

[0115] Experiment one

[0116] Sheet resistance uniformity test of silicon wafer

[0117] Test object: select the first 10 silicon wafers near the air inlet in the cleaning process in the embodiment one and the comparative example one, and mark them as 1 to 10 in order of distance from the air inlet, wherein 1 is the closest to the air inlet and 10 is the farthest from the air inlet.

[0118] Test position: measure the sheet resistance at the following five positions of each silicon wafer (as shown in the mark): central area P1, upper left area P2, upper right area P3, lower right area P4 and lower left area P5. Figure 4

[0119] Test: using the standard sheet resistance test method and the sheet resistance tester, the sheet resistance of the above test positions in the first 10 silicon wafers is tested.

[0120] Data recording and calculation: record the sheet resistance value of each position, and calculate the in-wafer non-uniformity by the following formula:

[0121] In-wafer non-uniformity = (maximum sheet resistance value - minimum sheet resistance value) x 100% / average sheet resistance value;

[0122] The test results of the embodiment one are recorded in Table 1, and the test results of the comparative example one are recorded in Table 2. ​

[0123] Sheet resistance uniformity test results of Example 1

[0124]

[0125] Note: In Table 1, P1, P2, P3, P4, P5 are the sheet resistance values at different test positions on the surface of the silicon wafer.

[0126] Sheet resistance uniformity test results of Comparative Example 1

[0127]

[0128] Note: In Table 2, P1, P2, P3, P4, P5 are the sheet resistance values at different test positions on the surface of the silicon wafer. By comparing the experimental results in Table 1 and Table 2, it can be seen that the sheet resistance in-wafer non-uniformity of the first 10 silicon wafers from the furnace mouth in Example 1 is significantly reduced, while the sheet resistance in-wafer non-uniformity of the first 10 silicon wafers from the furnace mouth in Comparative Example 1 is relatively high. This result shows that by adjusting the position of the boat and increasing the distance between the gas inlet and the boat, the sheet resistance uniformity of the silicon wafers in front of the furnace mouth can be effectively improved, thereby significantly reducing the EL center area contamination problem, which is conducive to improving the quality of large-scale production of large-sized solar cells, thereby improving the photoelectric conversion efficiency and reliability of large-sized solar cell products.

[0129] Experiment 2

[0130] Solar cell performance test

[0131] The performance of the solar cell was tested using a Wavelabs solar simulator, with test conditions of AM1.5, 1000 W / m 2 , and a test environment temperature of 25°C. Before testing, a standard silicon cell was used to correct the solar intensity simulated by the light source. The performance test was the energy conversion efficiency, with units of %, open circuit voltage, with units of V, and fill factor, with units of %.

[0132] Table 3 shows the arithmetic mean values of the photoelectric performance parameters of the examples and comparative examples (each greater than or equal to 1000 solar cells) obtained by the same test process.

[0133] Table 3 performance test results

[0134]

[0135] The comparison of experimental data in Table 3 shows that the synergistic effect of the boat position and the ethylene dichloride oxidation treatment is crucial for improving the performance of the solar cell. Specifically:

[0136] Comparative Example 1 and Comparative Example 1 show that optimizing the position of the boat in the diffusion furnace can significantly improve the energy conversion efficiency, which confirms that the position of the boat plays a key role in improving the quality of the oxide layer;

[0137] Comparative Example 1 and Comparative Example 2 show that introducing dichloroethylene for oxidation treatment can also effectively improve the energy conversion efficiency, which shows the optimization effect of the process on the quality of the oxide layer;

[0138] The comparison of the three experiments shows that the synergistic effect of boat position control and dichloroethylene treatment can further reduce the contamination on the surface of the silicon wafer, and the effect is better than the simple superposition of a single process. This shows that adjusting the position of the boat not only directly optimizes the oxidation process, but also enhances the reaction efficiency of dichloroethylene.

[0139] In addition, it is found through Examples 2 and 3 that when the boat is controlled within a specific range from the air inlet, the quality of the solar cell can be stably improved, which proves that the process parameters have the advantage of repeatability.

[0140] The diffusion method for preparing a solar cell, the solar cell and the photovoltaic module disclosed in the embodiments of the present application are described in detail above, and specific examples are applied to explain the principles and implementation modes of the present application. The above examples are only used to help understand the diffusion method for preparing a solar cell, the solar cell and the photovoltaic module of the present application and its core idea; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the content of the specification should not be understood as a limitation of the present application.

Claims

1. A diffusion method for preparing a solar cell, characterized by, The method comprises the following steps: placing a boat carrying a silicon wafer in a diffusion furnace, wherein the diffusion furnace has a gas inlet, the boat is located at a distance D of more than 10 cm from the first end of the gas inlet, and the distance from the first end to the gas inlet is less than the distance from the first end to the furnace door of the diffusion furnace, and the size of the silicon wafer is greater than 158 mm x 158 mm; a deposition process for preparing an oxide layer and a doped element-containing film layer on the surface of the silicon wafer, wherein dichloroethylene is doped in the oxidizing gas used for preparing the oxide layer; a pushing process for forming a diffusion layer on the side of the silicon wafer close to the oxide layer, and the diffusion layer comprises the doped element.

2. The diffusion method according to claim 1, characterized by, The distance D from the first end to the gas inlet is between 20 cm and 25 cm.

3. The diffusion method according to claim 1, wherein, In the deposition process, oxygen and dichloroethylene are first introduced at a temperature of 800-830 ℃ to form the oxide layer on the surface of the silicon wafer, and then the doped element-containing film layer is prepared.

4. The diffusion method according to claim 3, characterized by, In the step of preparing the oxide layer, the oxygen is first introduced at a temperature of 800-830 ℃ before the oxygen and dichloroethylene are introduced. After the oxygen and dichloroethylene are introduced, the oxygen is again introduced at a temperature of 800-830 ℃.

5. The diffusion method according to claim 4, characterized in that, Before the oxygen and dichloroethylene are introduced, the flow rate of the oxygen introduced is 800-1000 sccm. In the introduction of the oxygen and dichloroethylene, the ratio of the flow rate of the dichloroethylene to the flow rate of the oxygen is 30-50 sccm: 1050-1200 sccm. After the oxygen and dichloroethylene are introduced, the flow rate of the oxygen introduced is 800-1000 sccm.

6. The diffusion method according to claim 5, wherein Before the oxygen and dichloroethylene are introduced, the oxidation time is 1-2 min. In the introduction of the oxygen and dichloroethylene, the oxidation time is 4-6 min, and the dichloroethylene is carried into the diffusion furnace by nitrogen. After the oxygen and dichloroethylene are introduced, the oxidation time is 1-2 min.

7. The diffusion method according to any one of claims 1 to 6, characterized by, The thickness of the oxide layer is 40-50 nm.

8. The diffusion method according to any one of claims 1 to 6, characterized by, In the doped element-containing film layer, the doped element is an N-type doped element or a P-type doped element. and / or, The sheet resistance inhomogeneity of the silicon wafer is less than 6.03%. and / or, The size of the silicon wafer is (182.2-183.75) x (182.2-183.75) nm. and / or, The thickness of the silicon wafer is 120-135 nm. and / or, Before the step of placing the boat carrying the silicon wafer in the diffusion furnace, the silicon wafer is subjected to a texturing process.

9. A solar cell, characterized by The silicon wafer is prepared by the diffusion method according to any one of claims 1-8.

10. A photovoltaic module, characterized by, The solar cell comprises the solar cell according to claim 9.

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