A method for laser grooving a cell and a method for preparing a photovoltaic cell

Abstract

The embodiments of the present application provide a method for laser grooving of a cell and a method for preparing a photovoltaic cell, and relate to the field of photovoltaic cell products. The method for laser grooving of a cell is to use laser engraving to remove the passivation film in a part of the back of the silicon wafer to form a light spot. The power of the laser is 28-32W, the engraving speed is 40000-42000, and the light spots are arranged continuously to form multiple solid lines. The light spots in the same solid line are tangent in sequence, and the solid lines are arranged at intervals along the line type. Dotted lines are formed between adjacent solid lines on the same line type. The length of each solid line is 0.9-0.95mm, and the length of each dotted line is 0.75-0.85mm. The method for laser grooving of a cell and the method for preparing a photovoltaic cell can penetrate the back passivation film without causing obvious damage to the silicon wafer, so that the entire silicon wafer substrate is clearly exposed, and it is flat and smooth, without obvious traces of laser pulse corrosion, thereby improving product efficiency.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic cell products, and more specifically, to a method for laser grooving a cell sheet and a method for preparing a photovoltaic cell. Background Art

[0002] At present, conventional PERC cells (Passivated Emitter and Rear Cell) use a passivation dielectric film Al 2 O 3 The dangling bonds on the back surface of the cell are protected by SiN, forming a fixed electric field and a passivation effect, thereby reducing surface recombination and improving efficiency. At the same time, since the silicon wafer surface contains unsaturated dangling bonds formed by the interruption of the periodic arrangement of the atomic structure, space charges and surface potential barriers are generated on the surface and interface of the crystal structure, forming an unstable surface state, thereby affecting the normal transport of carriers. Therefore, PERC cells usually use a laser grooving process to make the aluminum back field form a local point contact with the silicon wafer, reducing the contact between the metal back electrode and the back surface, thereby increasing the open circuit voltage.

[0003] Since the laser slotting process is one of the key steps to improve the electrical performance of the battery cell, there have been a lot of studies on laser diffraction, depth, spacing, number of spots, etc. of the laser process. After analysis, the laser slotting process used by various manufacturers has the following problems: ① Abnormal laser spot, severe diffraction, large corrosion area, resulting in low battery efficiency; ② Unreasonable design of laser spot distribution, so that the aluminum back field cannot be effectively covered, the back recombination increases, resulting in low battery efficiency; ③ Poor spot overlap, increased surface recombination, resulting in increased series resistance, resulting in low battery efficiency.

[0004] Therefore, it is necessary to provide a laser grooving process to reduce the negative impact of the laser grooving on the passivation effect of the passivation layer during the processing and improve the quality and efficiency of the battery. Summary of the invention

[0005] The purpose of the embodiments of the present application is to provide a method for laser grooving of a cell and a method for preparing a photovoltaic cell, which can penetrate the back passivation film without causing obvious damage to the silicon wafer, so that the entire silicon wafer substrate is clearly exposed and is flat and smooth without obvious signs of laser pulse corrosion, thereby improving product efficiency.

[0006] In the first aspect, an embodiment of the present application provides a method for laser grooving of a battery cell, which uses laser engraving to remove part of the passivation film on the back of the silicon wafer to form a light spot. The laser power is 28-32W, and the engraving speed is 40000-42000mm / s. The light spots are arranged continuously to form multiple solid lines. The light spots in the same solid line are tangent to each other in sequence. The solid lines are arranged at intervals along the line type, and dotted lines are formed between adjacent solid lines on the same line type. The length of each solid line is 0.9-0.95mm, and the length of each dotted line is 0.75-0.85mm.

[0007] In the above technical scheme, the applicant found in the implementation process that: insufficient or excessive laser energy will lead to abnormal laser spot, severe diffraction, and large corrosion area; unreasonable engraving speed will lead to poor spot overlap, increased surface recombination, increased series resistance, and affected filling; unreasonable laser spot distribution will lead to a small number of spots, making it impossible for the back field aluminum paste to effectively cover, and increased back recombination. After a lot of exploration and experiments, the embodiment of the present application controls the laser power and engraving speed within a certain range during the laser drilling process, and the spot is distributed in a specific way, which can penetrate the back passivation film without causing obvious damage to the silicon wafer, so that the entire silicon wafer substrate is clearly exposed, and it is flat and smooth, without obvious laser pulse corrosion marks, that is, a spot with better roundness and no diffraction is obtained; and there is no residue of passivation film material at the groove, thereby improving product efficiency.

[0008] In a possible implementation, the laser power is set to 35 W, and the efficiency is set to 80%-90%.

[0009] In the above technical solution, by setting the power and efficiency of the laser, the actual output power of the laser is made almost constant, thereby avoiding the inconstancy of the actual output power caused by directly setting the output power of the laser; and the embodiment of the present application can adjust the actual energy of the laser on the silicon wafer by adjusting the actual output power of the laser within a certain range, thereby reducing the damage to the film layer, reducing surface recombination, and improving the conversion efficiency.

[0010] In a possible implementation, the virtual-to-real ratio is 48%-52%; and / or the number of light spots on each solid line is 25-28.

[0011] In the above technical solution, by adjusting the laser virtual-to-real ratio, the opening rate on the back side of the cell can be adjusted to facilitate better matching between the silicon wafer substrate and the aluminum paste; by increasing the number of laser spots on each solid line, the back field aluminum paste can be effectively covered to reduce back side recombination.

[0012] In a possible implementation, the opening rate of the same line type is 1.6%-1.75%; and / or the opening rate of the same silicon wafer is 0.14%-0.18%.

[0013] In the above technical solution, the opening rate can be increased to a certain extent through the specific arrangement of the light spots, thereby reducing the backside recombination of the battery cell.

[0014] In a possible implementation, all solid lines are arranged to form a plurality of mutually parallel line types, and the solid lines on adjacent line types are staggered.

[0015] In the above technical solution, the solid lines are arranged in a staggered manner, so that a greater number of light spots can be set under the same conditions.

[0016] In one possible implementation, the marking time during the laser engraving process is 0.68-0.7 ms / psc.

[0017] In the above technical solution, the idling speed can be reduced, the marking time can be reduced, and the time consumed in turning on and off the laser delay chip can be reduced.

[0018] In a possible implementation, the silicon wafer is a 166 mm single crystal silicon wafer; and / or the passivation film is an Al 2 O 3 The total thickness of the passivation film is 90-100 nm, and the refractive index is 2.08-2.09.

[0019] In the above technical solution, the laser grooving designed for PERC cells can achieve a "low damage, high production capacity, high efficiency" process, effectively improving the laser grooving effect on Al 2 O 3 The breakdown of the laser film and the SiN film causes obvious damage to the silicon wafer. The silicon wafer substrate in the entire groove is exposed, and it is flat and smooth without obvious signs of laser pulse corrosion. The groove is corroded cleanly without any SiN residue, thereby achieving the effect of increasing production, increasing efficiency and reducing costs.

[0020] In a second aspect, an embodiment of the present application provides a method for preparing a photovoltaic cell, which includes sequentially performing texturing, diffusion, SE (selective emitter) laser doping, thermal oxidation, polishing, annealing, back-side passivation film coating, front-side coating, laser grooving, screen printing and sintering on a silicon wafer, wherein the laser grooving is performed according to the cell laser grooving method provided in the first aspect.

[0021] In the above technical scheme, thermal oxidation is carried out after diffusion and SE laser doping. In the thermal oxidation process, a phosphorus source is first introduced to allow the silicon wafer to diffuse again, thereby enhancing the diffusion performance of the battery and providing better protection for the heavily doped area formed by the SE laser, thereby reducing the influence of acid and alkali during subsequent processing of the silicon wafer. Moreover, the spacing of the laser spots is controlled during SE laser doping and laser grooving to reduce possible damage to the silicon wafer during the process. This is particularly suitable for the production of thin-film batteries, thereby ensuring the conversion efficiency of the thin-film batteries and reducing the proportion of defective fragments.

[0022] In one possible implementation, the back side passivation film is deposited by using PECVD (Plasma Enhanced Chemical Vapor Deposition) to deposit Al on the back side of the annealed silicon wafer using ozone and trimethylaluminum. 2 O 3 Thin film, then use silane and ammonia in Al 2 O 3 A SiN film is deposited on the surface of the film.

[0023] In the above technical solution, aluminum oxide is deposited as the bottom passivation structure, and silicon nitride is used for protection to achieve a good back passivation effect. The back passivation film can effectively enhance the passivation and incident light comprehensive utilization rate, reduce the loss of unbalanced carriers caused by surface defects, increase the short-circuit current and open-circuit voltage of the battery, and at the same time improve the anti-light decay, anti-PID performance and reliability of the battery with this structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic diagram of a light spot arrangement method provided in an embodiment of the present application;

[0026] Figure 2 This is the spot morphology diagram in Example 1;

[0027] Figure 3 This is the spot morphology diagram in Comparative Example 1. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0029] The following is a detailed description of the cell laser grooving method and photovoltaic cell manufacturing method according to the embodiments of the present application.

[0030] The embodiment of the present application provides a method for laser grooving of a cell, wherein a laser engraving is used to remove part of the passivation film on the back of a silicon wafer to form a light spot. The silicon wafer can be a 166mm single crystal silicon wafer, the number of gate lines can be 150, and the passivation film is Al2O3 superimposed on the back of the silicon wafer in sequence. 2 O 3 The total thickness of the Si film and the passivation film is 90-100nm, and the refractive index is 2.08-2.09.

[0031] During the laser engraving process, the power of the laser is 28-32W. As an implementation method, the set power of the laser is 35W and the set efficiency is 80%-90%.

[0032] Laser engraving is designed according to the following spot arrangement: Figure 1 As shown, the light spots formed by laser engraving are arranged continuously to form multiple solid lines ( Figure 1 The black line segments in the figure), the light spots in the same solid line are sequentially tangent, the solid lines are arranged at intervals along the line type, and the adjacent solid lines on the same line type form a dotted line, the length of each solid line is 0.9-0.95mm, and the length of each dotted line is 0.75-0.85mm; the virtual-to-real ratio is 48%-52%, the virtual-to-real ratio = the actual laser punching length (the punching length in the dotted line) / the total design length (the total length of the solid line + the dotted line); the number of light spots on each solid line is 25-28. All solid lines are arranged to form multiple parallel lines, and the solid lines on adjacent line types are staggered, that is, the solid lines on one line type correspond to the dotted lines on the adjacent line types in parallel. The opening rate of the same line type formed by laser engraving is 1.6%-1.75%, that is, the ratio of the total area of ​​the light spot on the same line type to the area of ​​the line type (the length of the line type × the diameter of the light spot); the opening rate of the same silicon wafer is 0.14%-0.18%, that is, the ratio of the total area of ​​the light spot on the same silicon wafer to the area of ​​the silicon wafer.

[0033] During the laser engraving process, the engraving speed is 40000-42000mm / s; the marking time (total time for engraving the graphics) is 0.68-0.7ms / psc.

[0034] In addition, the present invention provides a method for preparing a photovoltaic cell, which comprises the following steps:

[0035] S1. Texturing: Clean the 166mm single crystal silicon wafer and texturing the front side of the silicon wafer.

[0036] S2. Diffusion (light doping): Phosphorus is doped on the silicon wafer after texturing to form a phosphorus-doped N+ emitter junction layer, thereby forming a PN junction.

[0037] S3, SE laser doping (heavy doping): The selective emitter is on a lightly doped silicon wafer, and the heavily doped area of ​​impurity atoms is selectively carried out through a micron-sized laser beam, effectively forming a low surface concentration shallow junction process, while also ensuring ohmic contact in the printed gate line area.

[0038] S4. Thermal oxidation: In a tubular high-temperature device, nitrogen and oxygen carrying a phosphorus source are first introduced for heat treatment; then nitrogen and oxygen are introduced for oxidation.

[0039] S5. Polishing: Cleaning and back-polishing the phosphorus-doped silicon wafer.

[0040] S6. Annealing: Annealing the polished silicon wafer to produce and deposit a layer of graded silicon dioxide layer on the surface of the silicon wafer.

[0041] S7, back passivation film: In the PECVD equipment, ozone and trimethyl aluminum are first used to deposit Al on the back of the annealed silicon wafer. 2 O 3 Thin film, then use silane and ammonia in Al 2 O 3 SiN film is deposited on the surface of the film, Al 2 O 3 The total thickness of the film and SiN film is 90-100nm, and the refractive index is 2.08-2.09.

[0042] S8. Front coating: In the PECVD equipment, silane and ammonia are used as source gases, and after radio frequency reaction, a front silicon nitride layer is deposited.

[0043] S9, laser grooving: This is done according to the above-mentioned cell laser grooving method, which will not be elaborated here.

[0044] S10, screen printing and sintering: Using the screen printing method, silver paste is printed on the front side of the silicon wafer and aluminum paste is printed on the back side according to the screen pattern design. After high-temperature sintering, ohmic contact is formed to produce a PERC battery.

[0045] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0046] Example 1

[0047] This embodiment provides a PERC battery, which is carried out according to the following steps:

[0048] (1) Texturing: The 166 mm single crystal silicon wafer is cleaned and KOH is used to texturize the front side of the silicon wafer to form a pyramid texture surface with a height of 2 μm.

[0049] (2) Diffusion: The silicon wafer after texturing is placed in a diffusion furnace and diffused at a diffusion temperature of 800°C for 40 minutes to deposit phosphorus oxychloride on the front side of the silicon wafer and perform thermal diffusion to obtain a phosphorus-doped N+ emitter junction layer with a thickness of 0.3 μm, thereby forming a PN junction.

[0050] (3) SE laser doping: On a lightly doped silicon wafer, a selective emitter is used to diffuse doping in a local area on the phosphorus-doped N+ emitter junction layer through a micrometer-sized laser beam, so that a phosphorus-doped N++ silicon layer is formed between the N+ emitter junction layer and the silicon wafer. The laser power is 35W, and the light spots generated by the laser treatment are evenly spaced and arranged in a linear pattern. The light spots are square, and the spacing between adjacent light spots is 18μm.

[0051] (4) Thermal oxidation: In a tubular high-temperature device, nitrogen and oxygen carrying a phosphorus source are first introduced for heat treatment, and the process parameters are: temperature of 800°C, oxygen flow rate of 1000sccm, nitrogen flow rate of 600sccm, small nitrogen (phosphorus source) flow rate of 700sccm, and treatment time of 300s; then nitrogen and oxygen are introduced for oxidation, and the process parameters are: temperature of 800°C, oxygen flow rate of 1000sccm, nitrogen flow rate of 1300sccm, and oxidation time of 800s.

[0052] (5) Polishing: Clean and polish the back of the phosphorus-doped silicon wafer.

[0053] (6) Annealing: The polished silicon wafer is placed in an annealing furnace at a temperature of 800°C. A certain amount of oxygen is introduced during annealing to grow a front silicon dioxide layer with a thickness of 4 nm on the phosphorus-doped N+ emitter junction layer.

[0054] (7) Back-side passivation film: In the PECVD equipment, ozone and trimethyl aluminum are first used to deposit Al on the back side of the annealed silicon wafer. 2 O 3 Thin film, then use silane and ammonia in Al 2 O 3 SiN film is deposited on the surface of the film, Al 2 O 3 The total thickness of the film and SiN film is 95, and the refractive index is 2.09.

[0055] (8) Front coating: In the PECVD equipment, silane and ammonia are used as source gases, and a radio frequency reaction is introduced to form a front silicon nitride layer. The thickness is controlled at 75nm and the refractive index is controlled at 2.14.

[0056] (9) Laser grooving: Laser engraving is used to remove part of the passivation film on the back of the silicon wafer to form a light spot. During the laser engraving process, the set power of the laser is 35W, the set efficiency is 80%, and the actual output power of the laser is 29W; the engraving speed is 40000mm / s; and the marking time is 0.68ms / psc.

[0057] Laser engraving is designed according to the following spot arrangement: Figure 1 As shown, the light spots formed by laser engraving are arranged continuously to form multiple solid lines. The light spots in the same solid line are tangent in sequence. The solid lines are arranged at intervals along the line type. The dotted lines are formed between the adjacent solid lines on the same line type. The length of each solid line is 0.9mm, and the length of each dotted line is 0.85mm; the ratio of virtual to real is 51.43%; the number of light spots on each solid line is 28. All solid lines are arranged to form multiple parallel lines, and the solid lines on adjacent lines are staggered. The opening rate of the same line type formed by laser engraving is 1.75%; the opening rate of the same silicon wafer is 0.18%.

[0058] The spot morphology obtained by laser grooving is shown in the figure below. Figure 2 As shown by Figure 2 It can be seen that the edges of the light spots are relatively neat and round, there is basically no diffraction, the overlap is good, and the light spots in the same solid line are tangent to each other in sequence.

[0059] (10) Screen printing and sintering: Using the screen printing method, silver paste is printed on the front side of the silicon wafer and aluminum paste is printed on the back side according to the screen pattern design. After high-temperature sintering, ohmic contact is formed to produce a PERC cell.

[0060] Comparative Example 1

[0061] This comparative example provides a PERC battery, and its preparation method is different from that of Example 1 in that: in this comparative example, during the laser engraving process, the set power of the laser is 35W, the set efficiency is 80%, and the actual output power of the laser is 29W; the engraving speed is 48000mm / s; and the marking time is 0.72ms / psc.

[0062] Laser engraving is designed according to the following spot arrangement: Figure 1As shown in the figure, the light spots formed by laser engraving are arranged continuously to form multiple solid lines. The light spots in the same solid line are tangent to each other in sequence. The solid lines are arranged at intervals along the line type. The dotted lines are formed between the adjacent solid lines on the same line type. The length of each solid line is 0.7mm, and the length of each dotted line is 0.85mm; the ratio of virtual to real is 45.2%; the number of light spots on each solid line is 21. All solid lines are arranged to form multiple parallel lines, and the solid lines on adjacent lines are staggered. The opening rate of the same line type formed by laser engraving is 1.53%; the opening rate of the same silicon wafer is 0.12%.

[0063] The spot morphology obtained by laser grooving is shown in the figure below. Figure 3 As shown by Figure 3 It can be seen that the edge of the light spot has serious diffraction and burrs. The white area of ​​the light spot in the figure is the normal area, and the areas outside the white area are all diffraction areas, and the light spots are separated from each other.

[0064] Comparative Example 2

[0065] This comparative example provides a PERC cell, and its preparation method is different from that of Example 1 in that: in this comparative example, during the laser engraving process, the set power of the laser is 35W, the set efficiency is 60%, and the actual output power of the laser is 20.2W.

[0066] The obtained spot morphology shows that the edges of the spots are neat and slightly separated, and the brightness of the spots is darker.

[0067] Comparative Example 3

[0068] This comparative example provides a PERC cell, and its preparation method is different from that of Example 1 in that: in this comparative example, during the laser engraving process, the set power of the laser is 35W, the set efficiency is 98%, and the actual output power of the laser is 36.5W.

[0069] The obtained spot morphology shows that the spots are tangent, brighter, with higher energy concentration and slightly ring-shaped edges.

[0070] Comparative Example 4

[0071] This comparative example provides a PERC battery, and its preparation method is different from that of Example 1 in that: the set power in this implementation is 90%, the measured power is 29W, the dotted line length is 0.85mm, the solid line length is 0.95mm, and the dot-to-solid ratio is 52.8%; the engraving speed is 53400mm / s; and the marking time is 0.68ms / psc.

[0072] The performance test results of Example 1 and Comparative Example 1 are shown in Table 1:

[0073] Table 1 Battery performance test results of Example 1 and Comparative Example 1

[0074]

[0075]

[0076] It can be seen from Table 1 that, compared with Comparative Example 1, the marking time of Example 1 is reduced by 0.04 ms / psc, which greatly improves the production capacity; the efficiency gain is 0.035%.

[0077] To sum up, the cell laser grooving method and photovoltaic cell preparation method of the embodiments of the present application can penetrate the back passivation film without causing obvious damage to the silicon wafer, so that the entire silicon wafer substrate is clearly exposed and smooth, without obvious signs of laser pulse corrosion, thereby improving product efficiency.

[0078] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for laser grooving a cell, characterized in that: Laser engraving is used to remove the passivation film in part of the back side of the silicon wafer to form a light spot. The power of the laser is 28-32W, the engraving speed is 40000-42000mm / s, the light spots are arranged continuously to form multiple solid lines, the light spots in the same solid line are tangent to each other in sequence, the solid lines are arranged at intervals along the line type, and dotted lines are formed between adjacent solid lines on the same line type. The length of each solid line is 0.9-0.95mm, and the length of each dotted line is 0.75-0.85mm.

2. The method for laser grooving a cell according to claim 1, characterized in that: The set power of the laser is 35W, and the set efficiency is 80%-90%.

3. The method for laser grooving a cell according to claim 2, characterized in that: The virtual-to-real ratio is 48%-52%; and / or the number of light spots on each solid line is 25-28.

4. The method for laser grooving a cell according to claim 1, characterized in that: The opening rate of the same line type is 1.6%-1.75%; and / or, the opening rate of the same silicon wafer is 0.14%-0.18%.

5. The method for laser grooving a cell according to claim 1, characterized in that: All the solid lines are arranged to form a plurality of mutually parallel lines, and the solid lines on adjacent lines are arranged in a staggered manner.

6. The method for laser grooving a cell according to claim 1, characterized in that: The silicon wafer is a 166mm single crystal silicon wafer; and / or the passivation film is an Al2O3 film and a SiN film sequentially superimposed on the back of the silicon wafer, the total thickness of the passivation film is 90-100nm, and the refractive index is 2.08-2.

09.

7. A method for preparing a photovoltaic cell, characterized in that: The method comprises the following steps: texturing, diffusion, SE laser doping, thermal oxidation, polishing, annealing, back-side passivation film coating, front-side coating, laser grooving, screen printing and sintering of a silicon wafer in sequence, wherein the laser grooving is performed according to the cell laser grooving method as described in any one of claims 1 to 6.

8. The method for preparing a photovoltaic cell according to claim 7, characterized in that: The method of back-coating a passivation film is: using PECVD, first using ozone and trimethylaluminum to deposit an Al2O3 film on the back of the annealed silicon wafer, and then using silane and ammonia to deposit a SiN film on the surface of the Al2O3 film.

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