Methods to improve graphite boat dot printing for solar cells

Abstract

This invention discloses a method for improving the spot markings on graphite boats used in solar cells. The method includes: (1) cleaning the graphite boat to be cleaned to remove silicon nitride from the graphite boat; (2) washing the cleaned graphite boat with water; (3) performing a first gas purging on the washed graphite boat; (4) drying the graphite boat after the first gas purging; (5) performing a second gas purging on the dried graphite boat; and (6) saturating the graphite boat after the second gas purging. This invention solves the problem of spot markings still existing in the field after cleaning and drying graphite boats, greatly reducing the spot marking phenomenon. Furthermore, the method of this invention is simple, highly compatible with existing processes, and easy to operate.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to an improved method for printing dots on graphite boats used in solar cells. Background Technology

[0002] The main processes for producing crystalline silicon solar cells include: texturing, diffusion, laser doping, high-temperature oxidation, wet etching, high-temperature annealing, deposition of anti-reflective coatings, screen printing, and sintering. In the anti-reflective coating deposition process, silicon nitride is deposited on the surface of the graphite boat. After repeated use, the deposited silicon nitride becomes thicker and unevenly distributed, leading to greater variability in the silicon nitride film deposited on the solar cell surface. Therefore, the graphite boat needs to be cleaned regularly.

[0003] Although the routine cleaning of graphite boats already includes multiple processes, contamination can still occur again after drying, resulting in frequent spot marks. Spot marks on graphite boats are a defect that is difficult to improve. Summary of the Invention

[0004] This invention aims to at least partially address one of the technical problems in related technologies. Therefore, the objective of this invention is to propose a method for improving the method of preventing dot-jamming on graphite boats used in solar cells. This invention solves the pain point in the art of dot-jamming that still exists on graphite boats after cleaning and drying, significantly reducing the dot-jamming phenomenon. Furthermore, the method of this invention is simple, highly compatible with existing processes, and easy to operate.

[0005] To achieve the above objectives, the present invention proposes an improved method for dot printing on graphite boat cards used in solar cells. According to an embodiment of the present invention, the method includes:

[0006] (1) The graphite boat to be cleaned is cleaned in order to remove silicon nitride from the graphite boat;

[0007] (2) The cleaned graphite boat is then washed with water;

[0008] (3) Perform a first gas purging on the graphite boat after water washing;

[0009] (4) Dry the graphite boat after the first gas purging;

[0010] (5) Perform a second gas purging on the dried graphite boat;

[0011] (6) The graphite boat after the second gas purging is saturated.

[0012] The present invention provides an improved method for removing ink residue from graphite boats used in solar cells. Based on the existing graphite boat cleaning and drying process, a second gas purging process is added between the drying and saturated plating processes. Specifically, this second gas purging process is performed after the graphite boat is dried and before it is placed on the plating line. A gas at a certain pressure is used to purge away residual complexes (NH4)2SiF6 from the cleaning solution and / or secondary contaminants caused during the oven drying process. This reduces the degree of contamination on the graphite boat surface and solves the long-standing problem of ink residue remaining after cleaning and drying, significantly reducing ink residue. Specifically, the method of the present invention reduces the ink residue percentage to below 0.05%, while the ink residue percentage in existing technologies is as high as 0.37%. Furthermore, the method of the present invention is simple, highly compatible with existing processes, and easy to operate.

[0013] In addition, the method according to the above embodiments of the present invention may also have the following additional technical features:

[0014] In some embodiments of the present invention, in step (5), the second gas purging is performed on the jamming point of the dried graphite boat.

[0015] In some embodiments of the present invention, the air pressure at the purge port of the second gas purging is 0.7-0.9 MPa, and the distance between the purge port of the second gas purging and the jamming point does not exceed 1.5 cm.

[0016] In some embodiments of the present invention, the purging time for each of the checkpoints is not less than 0.5 s; and / or, the second gas purging is performed using a purging gun.

[0017] In some embodiments of the present invention, the gas used for the second gas purging is nitrogen or an inert gas.

[0018] In some embodiments of the present invention, the locking point includes a connected protrusion and a recess, the recess being connected to the surface of the graphite boat; in step (5), the recess of the locking point after drying is subjected to a second gas purging.

[0019] In some embodiments of the present invention, the cleaning solution in step (1) is a mixture of HF and HCl, wherein the mass concentration of HF is 10%-20%, the mass concentration of HCl is 2%-4%, and the cleaning time is 300-400 min.

[0020] In some embodiments of the present invention, in step (2), the water washing time is 60-120 min; and / or, in step (3), the first gas purging is carried out in a purging tank, the air pressure at the purging port of the purging tank is 0.4-0.7 MPa, and the first gas purging time is 20-40 min.

[0021] In some embodiments of the present invention, in step (4), the drying temperature is 160-200°C and the drying time is 8-12 hours.

[0022] In some embodiments of the present invention, in step (5), the temperature for saturation treatment is 450-470°C.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0025] Figure 1 This is a flowchart illustrating an improved method for dot printing on a graphite boat for solar cells according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of the structure of a unit graphite boat according to an embodiment of the present invention;

[0027] Figure 3 for Figure 2 A cross-sectional view along the AA direction.

[0028] Attached image captions:

[0029] 100-Graphite boat, 110-Card point, 111-Protrusion, 112-Concave part, 200-Battery piece. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] In one aspect of the invention, a method for improving graphite boat dot printing for solar cells (e.g., PERC monocrystalline cells) is proposed. According to embodiments of the invention, refer to the appendix... Figure 1The method includes: S100: cleaning the graphite boat to be cleaned to remove silicon nitride from the graphite boat; S200: washing the cleaned graphite boat with water; S300: performing a first gas purging on the washed graphite boat; S400: drying the graphite boat after the first gas purging; S500: performing a second gas purging on the dried graphite boat; S600: performing a saturation treatment on the graphite boat after the second gas purging. Therefore, this invention adds a second gas purging treatment between the drying treatment and the saturation plating treatment of the graphite boat. A certain pressure of gas is used to purge away the residual complex (NH4)2SiF6 crystallization in the cleaning solution and / or the secondary contamination caused during the oven drying process, thereby reducing the degree of contamination on the surface of the graphite boat. This solves the pain point in the art of graphite boats still having spot marks after cleaning and drying, greatly reducing the phenomenon of spot marks. Specifically, the method of the present invention reduces the percentage of card-point printing to below 0.05%, while the percentage of card-point printing in the prior art is as high as 0.37%. Furthermore, the method of the present invention is simple, highly compatible with existing processes, and easy to operate.

[0032] The principle behind the improved graphite boat dot printing method for solar cells proposed in this invention, which enables the aforementioned beneficial effects, will be explained in detail below:

[0033] In existing technology, the cleaning process for off-line graphite boats includes: 1) placing the off-line graphite boat in a chemical cleaning tank to remove the film layer on the graphite boat; the chemical cleaning tank includes an acid washing tank, etc.; 2) rinsing in a water tank to remove the cleaning solution from step 1); 3) entering a purging tank, generally using onboard nitrogen to purge from top to bottom, generally removing water stains from the surface of the graphite boat; 4) placing the washed graphite boat in an oven to dry; 5) saturating the dried graphite boat. The inventors discovered that although conventional cleaning of graphite boats already includes multiple processes, contamination at the cleaning points still occurs again after drying, leading to frequent contamination. Through extensive and in-depth analysis and research, the inventors found that the main reason for the continued contamination at the cleaning points after drying is:

[0034] (a) During the cleaning of the graphite boat in the chemical cleaning tank, a water-soluble complex (NH4)2SiF6 is generated (the solubility of (NH4)2SiF6 at 17°C is 186 g / 100 g water). In the prior art, the graphite boat is in a wetted state after purging, and the moisture is not completely removed. The small amount of water remaining on the surface of the graphite boat contains dissolved (NH4)2SiF6 complex. When the graphite boat is dried in the oven, as the moisture evaporates, the complex (NH4)2SiF6 crystals precipitate on the graphite boat surface, resulting in poor boat plating effect in the subsequent saturation treatment process and poor uniformity of silicon nitride on the graphite boat surface.

[0035] During the cleaning of the graphite boat in the chemical cleaning tank, the following chemical reactions occur: Si3N4+HF→SiF4+NH3↑, SiF4+HF→H2SiF6 (a strong diprotic acid with a strong tendency to ionize), NH3+H2SiF6→(NH4)2SiF6 (a complex)↓.

[0036] (b) During the drying process in the oven, various abnormalities such as abnormal acid exhaust, metal corrosion, and substandard oven hygiene can also cause secondary pollution on the surface of the graphite boat (including pollution such as acid and metal ion pollution), which will form composite centers on the surface of the battery cells, resulting in blackening and spot marks.

[0037] The contamination in (a) and (b) is particularly prominent at the graphite boat jamming points and is difficult to detect with the naked eye, leading to a large-scale outbreak of jamming marks when new boats are put into use. During the saturated plating process, the complexes and other contaminants at the jamming points are covered by the silicon nitride film layer formed by the saturated plating boat, resulting in poor uniformity of the silicon nitride film layer on the surface of the jamming points, inconsistent process deposition rates, and large current fluctuations, which in turn leads to color differences and scorching at the jamming points. In addition, during the saturated plating process, the decomposition temperature of (NH4)2SiF6 complex is around 450℃, and the process temperature of saturated plating boat is around 450-470℃. Therefore, the (NH4)2SiF6 complex covered by the silicon nitride film layer may decompose during the saturated plating process, generating gas and causing pores in the silicon nitride film layer, resulting in poor uniformity of the silicon nitride film layer on the surface of the jamming points.

[0038] To address the aforementioned technical problems, based on the reasons for persistent contamination after cleaning and drying as analyzed above, the inventors added a second gas purging process between the drying and saturated plating stages of the graphite boat. This second purging, performed after drying and before plating, uses pressurized gas to remove residual (NH4)2SiF6 complex crystals from the cleaning solution and / or secondary contamination caused during oven drying. This reduces the degree of contamination on the graphite boat surface, solving the long-standing problem of persistent contamination marks after cleaning and drying, significantly reducing the incidence of these marks. Specifically, the method of this invention reduces the proportion of contamination marks to below 0.05%, while the proportion in existing technologies is as high as 0.37%. Furthermore, the method of this invention is simple, highly compatible with existing processes, and easy to operate.

[0039] Specifically, see the attached document. Figure 1 The above method includes the following steps:

[0040] S100: Clean the graphite boat to be cleaned.

[0041] In this step, the graphite boat to be cleaned is cleaned to remove the silicon nitride film on it. Specifically, the graphite boat is placed in a chemical cleaning tank for cleaning to remove the silicon nitride film layer on it. The chemical cleaning tank includes an acid washing tank, etc.

[0042] As some specific examples, the cleaning solution in step S100 is a mixture of HF and HCl, wherein the mass concentration of HF is 10%-20% (e.g., 10 / 12 / 14 / 16 / 18 / 20%), the mass concentration of HCl is 2%-4% (e.g., 2 / 3 / 4%), and the cleaning time is 300-400 min (e.g., 300 / 320 / 340 / 360 / 380 / 400 min), thereby further ensuring that the silicon nitride layer on the graphite boat is completely removed.

[0043] During the cleaning of the graphite boat in the chemical cleaning tank, the following chemical reactions occur: Si3N4 + HF → SiF4 + NH3↑, SiF4 + HF → H2SiF6 (a strong diprotic acid with a strong tendency to ionize), NH3 + H2SiF6 → (NH4)2SiF6 (complex)↓. This (NH4)2SiF6 complex is a water-soluble complex, dissolving in water. The solubility of (NH4)2SiF6 at 17℃ is 186 g / 100 g water.

[0044] S200: Rinse the cleaned graphite boat with water.

[0045] In this step, the cleaned graphite boat is washed with water to remove the reaction liquid remaining in the graphite boat in step S100.

[0046] As specific examples, the washing time is 60-120 minutes (e.g., 60 / 80 / 100 / 120 minutes) to further ensure that the acidic solution remaining in the graphite boat in step S100 is washed away. However, even after washing for 60-120 minutes, the water remaining on the surface of the graphite boat may still contain dissolved (NH4)2SiF6 complexes. This is because: firstly, (NH4)2SiF6 complexes have extremely high solubility in water; the solubility of (NH4)2SiF6 at 17°C is approximately 186 g / 100 g water; secondly, the unique porous structure of the graphite boat surface has a water-retaining function, preventing the (NH4)2SiF6 solution on the surface of the graphite boat from being completely washed away. Therefore, a small amount of (NH4)2SiF6 solution hidden in the porous structure on the surface of the graphite boat precipitates and crystallizes after drying, leading to the subsequent difficulties.

[0047] S300: Perform the first gas purging on the water-washed graphite boat.

[0048] In this step, the washed graphite boat undergoes a first gas purging to remove residual aqueous solution from its surface. As specific examples, this first gas purging is performed in a purging tank with an air pressure of 0.4-0.7 MPa (e.g., 0.4 / 0.5 / 0.6 / 0.7 MPa) at the purging port, and the purging time is 20-40 minutes (e.g., 20 / 25 / 30 / 35 / 40 minutes). However, the graphite boat surface remains wet after the first gas purging, with moisture not completely removed, especially from the porous structure of the graphite boat surface. Therefore, the small amount of water remaining on the graphite boat surface contains dissolved (NH4)2SiF6 complexes.

[0049] S400: Drying the graphite boat after the first gas purging.

[0050] In this step, the graphite boat after the first gas purging is dried to completely remove residual moisture from its surface. As specific examples, the drying temperature is 160-200°C (e.g., 160 / 170 / 180 / 190 / 200°C), and the drying time is 8-12 hours (e.g., 8 / 9 / 10 / 11 / 12 hours), thereby further ensuring the complete removal of residual moisture from the graphite boat's surface.

[0051] However, when the graphite boat enters the drying oven, as the moisture evaporates, the residual complex (NH4)2SiF6 crystals on the surface of the graphite boat precipitate out. If the graphite boat is not subjected to a second gas purging after drying, it will lead to poor boat plating effect and poor uniformity of silicon nitride on the surface of the graphite boat in the subsequent saturation treatment process. The present invention solves the above problems by performing a second gas purging after drying.

[0052] Meanwhile, during the drying process in the oven, various abnormalities such as abnormal acid exhaust, metal corrosion, and substandard oven hygiene can cause secondary contamination on the surface of the graphite boat (such as contamination from acid or metal ions). If the graphite boat is not purged with gas a second time after drying, composite centers will form on the surface of the solar cells, resulting in blackening and markings.

[0053] Furthermore, the aforementioned contamination is particularly prominent at the jamming points of the graphite boat and is difficult to detect with the naked eye. If the graphite boat is not subjected to a second gas purging after drying, it will lead to a large-scale outbreak of jamming marks when new boats are put into operation. This invention solves the above problem by performing a second gas purging at the jamming points after drying.

[0054] S500: Perform a second gas purging on the dried graphite boat.

[0055] In this step, the dried graphite boat undergoes a second gas purging. This second purging process, performed after the graphite boat is dried but before it is loaded onto the plating line, uses gas at a certain pressure to remove residual (NH4)2SiF6 complex crystals from the cleaning solution and / or secondary contamination caused during the oven drying process. This reduces the degree of contamination on the graphite boat surface and solves the long-standing problem of ink splatter marks remaining on the graphite boat after cleaning and drying, significantly reducing the incidence of ink splatter marks. Specifically, the method of this invention reduces the ink splatter mark percentage to below 0.05%, while the ink splatter mark percentage in existing technologies is as high as 0.43%.

[0056] As mentioned earlier, the crystallization of the (NH4)2SiF6 complex remaining in the cleaning solution and / or the secondary contamination caused during the oven drying process are particularly prominent at the sticking points of the graphite boat, and are difficult to detect with the naked eye. If the graphite boat is not purged with a second gas after drying, it will lead to a large-scale outbreak of sticking points when new boats are put into use. In order to solve the problem of severe (NH4)2SiF6 complex crystallization and / or secondary contamination at the sticking points of the graphite boat, as a preferred solution of the present invention, the second gas purging is performed on the sticking points of the dried graphite boat to accurately remove the (NH4)2SiF6 complex crystallization and / or secondary contamination at the sticking points of the graphite boat.

[0057] As specific examples, the air pressure at the purging port of the second gas purging is 0.7-0.9 MPa (e.g., 0.7 / 0.8 / 0.9 MPa), and the distance between the purging port of the second gas purging and the jamming point does not exceed 1.5 cm (e.g., 1.5 / 1.3 / 1.1 / 1 / 0.8 / 0.6 / 0.4 / 0.2 cm). This further ensures that the complex (NH4)2SiF6 crystals and / or secondary contaminants at the jamming point of the graphite boat are thoroughly cleaned. Specifically, a purging gun can be used for the second gas purging. Preferably, the purging gun is continuously shaken during purging to enhance the purging effect.

[0058] In embodiments of the present invention, reference is made to the appendix. Figure 2 and 3 Each graphite boat 100 is provided with multiple locking points 110, which are used to fix the battery cell 200 on the graphite boat 100. The purging time of each locking point is not less than 0.5s, thereby further ensuring that the complex (NH4)2SiF6 crystals and / or secondary contaminants at the locking points of the graphite boat are purged clean.

[0059] In embodiments of the present invention, the type of gas used for the second gas purging is not particularly limited; for example, nitrogen or inert gases (helium, neon, argon, etc.) can be used, with nitrogen being preferred.

[0060] Further, see attached document. Figure 3The jamming point 110 includes a connected protrusion 111 and a recess 112. The recess 112 is connected to the surface of the graphite boat 100. The recess 112 is not easy to be rinsed, so it is easier for complex (NH4)2SiF6 crystals and / or secondary contamination to remain in the recess 112. In order to solve this problem, as a preferred embodiment of the present invention, the recess 112 of the dried jamming point 110 is subjected to a second gas purging in order to accurately remove the complex (NH4)2SiF6 crystals and / or secondary contamination in the recess of the jamming point.

[0061] S600: Saturation treatment of the graphite boat after the second gas purging.

[0062] The graphite boats used in tubular PECVD have a porous structure. To deposit a uniform passivation film, a silicon nitride film layer needs to be pre-deposited on the surface of the boat before it is put into use online, in order to eliminate the influence of the porous graphite boat structure on the coating uniformity. As some specific examples, saturation is carried out for 2.5-3 hours under the reaction of silane and ammonia, and the saturation treatment temperature is 450-470℃.

[0063] The inventors discovered that if the graphite boat is not purged a second time before saturation treatment, the silicon nitride film from the saturation treatment process will deposit on the surface of the graphite boat, which has complex (NH4)2SiF6 crystals and / or secondary contamination, resulting in poor boat plating performance and poor uniformity of silicon nitride on the graphite boat surface. This invention solves these problems by performing a second gas purging before saturation treatment.

[0064] In particular, if the graphite boat is not purged a second time before saturation treatment, during the saturation plating process, the complexes and other contaminants at the stuck points will be covered by the silicon nitride film formed by the saturation plating boat, resulting in poor uniformity of the silicon nitride film at the stuck points, inconsistent deposition rates, and large current fluctuations, leading to color differences and scorching at the stuck points. Furthermore, during the saturation plating process, the decomposition temperature of the (NH4)2SiF6 complex is around 450°C, while the saturation plating process temperature is around 450-470°C. Therefore, the (NH4)2SiF6 complex covered by the silicon nitride film may decompose during the saturation plating process, generating gas and causing pores in the silicon nitride film, resulting in poor uniformity of the silicon nitride film at the stuck points. This invention solves these problems by performing a second gas purging at the stuck points before saturation treatment.

[0065] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0066] Example 1

[0067] This embodiment provides a method for improving the dot markings on the graphite boat of PERC monocrystalline solar cells, the method being as follows:

[0068] 1) Place the graphite boat that is not in production into a chemical cleaning tank for cleaning to remove the film layer on the graphite boat. The cleaning solution is a mixture of HF and HCl, wherein the mass concentration of HF is 15% and the mass concentration of HCl is 3%, and the cleaning time is 350 min.

[0069] 2) The graphite boat is rinsed in a water tank to remove the cleaning solution from step 1), and the rinsing time is 90 minutes.

[0070] 3) Enter the purging tank, and generally use onboard nitrogen to purge from top to bottom for 30 minutes;

[0071] 4) Place the washed graphite boat in a 180℃ oven and dry for 10 hours;

[0072] 5) Use a nitrogen gun at an angle to purge the recessed area of ​​the dried graphite boat with gas for a second time. The distance between the nozzle of the gas gun and the point should be 1 cm. The nitrogen valve should be opened to the maximum and the air pressure should be 0.8 MPa. Purge each point for 1 second.

[0073] 6) The dried graphite boat was saturated for 3 hours under the reaction of silane and ammonia. The saturation temperature was 460℃.

[0074] Example 2

[0075] This embodiment provides a method for improving the dot marking on the graphite boat of PERC monocrystalline cells. The only difference between this embodiment and Embodiment 1 is that:

[0076] 5) Use a nitrogen gun at an angle to purge the recessed area of ​​the dried graphite boat with gas for a second time. The distance between the nozzle and the point should be 1.5 cm, the air pressure should be 0.9 MPa, and each point should be purged for 0.5 seconds.

[0077] All other contents are the same as in Example 1.

[0078] Example 3

[0079] This embodiment provides a method for improving the dot marking on the graphite boat of PERC monocrystalline cells. The only difference between this embodiment and Embodiment 1 is that:

[0080] 5) Use a nitrogen gun at an angle to purge the recessed area of ​​the dried graphite boat with gas for a second time. The distance between the nozzle and the point should be 0.7 cm, the air pressure should be 0.75 MPa, and each point should be purged for 4 seconds.

[0081] All other contents are the same as in Example 1.

[0082] Example 4

[0083] This embodiment provides a method for improving the dot marking on the graphite boat of PERC monocrystalline cells. The only difference between this embodiment and Embodiment 1 is that:

[0084] 5) Use a nitrogen gun at an angle to purge the recessed area of ​​the dried graphite boat with gas for a second time. The distance between the nozzle and the point should be 0.8 cm, the air pressure should be 0.85 MPa, and each point should be purged for 3 seconds.

[0085] All other contents are the same as in Example 1.

[0086] Example 5

[0087] This embodiment provides a method for improving the dot marking on the graphite boat of PERC monocrystalline cells. The only difference between this embodiment and Embodiment 1 is that:

[0088] 5) Use a nitrogen gun at an angle to purge the recessed area of ​​the dried graphite boat with gas for a second time. The distance between the nozzle and the point should be 1.3 cm, the air pressure should be 0.7 MPa, and each point should be purged for 2 seconds.

[0089] All other contents are the same as in Example 1.

[0090] Comparative Example 1

[0091] The only difference between this comparative example and Example 1 is that step 5 is not included; all other contents are the same as in Example 1.

[0092] The printing percentage of the graphite boats treated in Examples 1-5 and Comparative Example 1 was verified, and the results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, compared with Comparative Example 1, the proportion of card mark printing in Examples 1-5 is significantly reduced, all below 0.05%, while the proportion of card mark printing in Comparative Example 1 is as high as 0.37%.

[0096] In the description of this specification, references to the terms "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for improving the dot printing of graphite boat cards for solar cells, characterized in that, include: (1) The graphite boat to be cleaned is cleaned in order to remove silicon nitride from the graphite boat; (2) The cleaned graphite boat is then washed with water; (3) Perform a first gas purging on the graphite boat after water washing; (4) Dry the graphite boat after the first gas purging; (5) Perform a second gas purging on the dried graphite boat; (6) The graphite boat after the second gas purging is subjected to saturation treatment; The cleaning solution in step (1) is a mixture of HF and HCl, wherein the mass concentration of HF is 10%-20% and the mass concentration of HCl is 2%-4%, and the cleaning time is 300-400 min.

2. The method according to claim 1, characterized in that, In step (5), the second gas purging is performed on the jamming point of the dried graphite boat.

3. The method according to claim 2, characterized in that, The air pressure at the purge port of the second gas purging is 0.7-0.9 MPa, and the distance between the purge port of the second gas purging and the jamming point does not exceed 1.5 cm.

4. The method according to claim 3, characterized in that, The purging time for each of the aforementioned checkpoints shall not be less than 0.5 seconds; And / or, the second gas purging is performed using a purge gun.

5. The method according to claim 4, characterized in that, The second gas purging uses nitrogen or an inert gas.

6. The method according to claim 2, characterized in that, The locking point includes a connected protrusion and a recess, the recess being connected to the surface of the graphite boat; In step (5), a second gas purging is performed on the recess of the dried card point.

7. The method according to any one of claims 1-6, characterized in that, In step (2), the washing time is 60-120 min; And / or, in step (3), the first gas purging is carried out in a purging tank, the air pressure at the purging port of the purging tank is 0.4-0.7MPa, and the time of the first gas purging is 20-40min.

8. The method according to any one of claims 1-6, characterized in that, In step (4), the drying temperature is 160-200℃ and the drying time is 8-12h.

9. The method according to any one of claims 1-6, characterized in that, In step (6), the temperature for saturation treatment is 450-470℃.

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