Method for manufacturing solar cell secondary grid through laser 3D printing

Abstract

The invention discloses a method for manufacturing a solar cell secondary grid through laser 3D printing, and the method comprises the steps: firstly carrying out the grooving of a passivation layer of a cell through a first laser, then conveying metal powder to a position above the groove through a nozzle in a powder airflow manner, carrying out the instantaneous hot melting sintering of the metal powder on the cell through a second laser, and carrying out the cooling to form a metal electrode, and the first laser, the nozzle and the second laser synchronously and continuously move on the battery piece according to the pattern of the auxiliary grid to form the auxiliary grid. The method has the advantages that the auxiliary grid electrode is accurately prepared and formed on the battery piece at a time through the laser 3D printing method by adopting the metal powder, the influence on the battery efficiency can be reduced, the height-width ratio of the auxiliary grid can exceed 100%, shielding on the surface of the battery piece is reduced, the battery efficiency can be improved, and compared with silk-screen printing, the technology is few and environmentally friendly, and the cost is low. The production cost is reduced.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a secondary grid of a solar cell. Background Art

[0002] Solar cells convert solar energy into electrical energy and are one of the important clean energy sources, and electrodes are the key to exporting electrons. At present, the main grid and auxiliary grid electrodes of solar cells are mainly made by screen printing. The principle of screen printing is: first, the slurry is coated on the screen, and the screen has some mesh holes according to the designed pattern. Then the screen is squeezed by a scraper, and the slurry is leaked through some mesh holes of the screen to the silicon wafer. The rest of the screen without forming a pattern has no mesh holes and cannot pass through the slurry, so a blank is formed on the silicon wafer, and the printing of the electrode is completed. The slurry is generally composed of a conductive functional phase, an inorganic phase, an organic solvent and other additives.

[0003] The sintering principle is to apply the slurry on the silicon wafer and dry it to completely volatilize the organic solvent. The film layer shrinks to become a solid and adheres tightly to the silicon wafer. When the electrode metal material and semiconductor silicon are heated to the eutectic temperature, silicon atoms dissolve into the molten alloy electrode material in a certain proportion. The temperature drops, the system cools to form a recrystallization layer, and the silicon atoms dissolved in the electrode metal material crystallize out in a solid form again, and an epitaxial layer grows on the contact interface between the metal and the crystal to form an ohmic contact. During the electrode sintering process, when the temperature is greater than 400°C, the glass begins to soften, and when it reaches above 600°C, the slurry melts, and the lead borosilicate glass sinks under the silver electrode, wets and corrodes the anti-reflection film, and then contacts and reacts with the silicon surface, because the lead oxide in the glass can undergo an oxidation-reduction reaction with silicon. In this process, a large amount of silver and etched silicon are dissolved in the glass phase; the silver particles begin to sinter or condense through mutual diffusion at the contact points between each other.

[0004] The current common screen printing technology in the industry requires many auxiliary materials such as special screens, slurries and scrapers, which leads to high costs. In addition, screen printing also has problems such as broken grids, slurry blocking the screen, false printing, poor sintering and over-burning, which will lead to low efficiency and yield of solar cells. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for producing a solar cell sub-grid by laser 3D printing, so as to accurately produce the sub-grid and improve the cell conversion efficiency.

[0006] Technical solution: A method for laser 3D printing to produce a solar cell sub-grid, first using a first laser to groove the cell passivation layer, then using a nozzle to transport metal powder to the top of the groove in a powder airflow, and then using a second laser to instantly heat-melt and sinter the metal powder on the cell, forming a metal electrode after cooling, and forming a sub-grid as the first laser, nozzle, and second laser move continuously on the cell synchronously according to the sub-grid pattern.

[0007] Furthermore, the first laser and the second laser are blue lasers, the laser power is 10-100W, the laser frequency is 400-1500KHz, and the spot size is 10-60μm.

[0008] Furthermore, the temperature of the first laser and the second laser irradiating the battery cell is 50-1000°C.

[0009] Furthermore, the metal powder is silver powder or copper powder, and the particle size is 0.5 to 1.2 μm.

[0010] Furthermore, the powder delivery rate of the powder airflow is 5 to 50 g / min, and the carrier gas flow rate is 5 to 30 L / min.

[0011] Furthermore, the width of the secondary gate is 10-50 μm, the height is 4-20 μm, and the aspect ratio is 30-150%.

[0012] Furthermore, the synchronous movement speed of the first laser, the nozzle and the second laser is 2000-6000 mm / s.

[0013] Furthermore, the manufacturing process is carried out in a vacuum environment or an inert gas environment.

[0014] Beneficial effect: The advantages of the present invention are: the secondary grid electrode can be accurately prepared on the battery cell at one time using metal powder through the laser 3D printing method, which can reduce the impact on the battery efficiency. The aspect ratio of the secondary grid can exceed 100%, reducing the obstruction of the battery cell surface, which is beneficial to improving the battery efficiency. Compared with screen printing, it has fewer processes and is environmentally friendly, and the production cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the process of manufacturing a solar cell sub-grid using the laser 3D printing method of the present invention;

[0016] Figure 2 A schematic diagram of the secondary grid produced by the traditional screen printing method;

[0017] Figure 3 Schematic diagram of the secondary grid produced by the laser 3D printing method of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further illustrated below in conjunction with specific embodiments.

[0019] After the solar cell has gone through the previous processes, such as: cleaning and texturing → boron diffusion (forming PN junction) → alkali polishing → tunneling oxide layer + doped polysilicon layer → front etching → aluminum oxide preparation → front and back silicon nitride, it enters the gate line production process and the solar cell sub-gate is produced through the laser 3D printing method of this application.

[0020] Combined with Figure 1 As shown, the cell 4 is fixed on a temperature-controlled stage and remains stationary. According to the position of the secondary grid pattern, the first laser 1 is used to groove the passivation layer of the cell to expose the silicon substrate. Then, the metal powder 21 is delivered to the top of the groove through a fine nozzle 2. The powder amount and airflow of the nozzle are adjusted to form a powder airflow near the surface area of ​​the cell, and the metal powder is accurately delivered into the groove to contact with the silicon substrate. Then, the second laser 3 is used to instantly melt and sinter the metal powder falling into the groove on the cell. The metal powder and the contacted silicon substrate fuse with each other to form an ohmic contact. After cooling and solidification, a metal electrode is formed on the surface of the cell.

[0021] The first laser performs grooving according to the secondary grid pattern. The angles and distances between the first laser, nozzle, second laser and the battery cell are adjustable. However, during the manufacturing process, the first laser, nozzle and second laser are fixed at a certain angle and distance, and the order of grooving by the first laser, powder feeding by the nozzle and melting of powder by the second laser is always maintained. Then, as the first laser, nozzle and second laser move continuously and synchronously in a straight line on the battery cell according to the secondary grid pattern, the continuously formed metal electrode forms the secondary grid 5.

[0022] The metal powder is silver powder or copper powder, etc., with a particle size of 0.5 to 1.2 μm. The powder delivery rate of the powder airflow is 5 to 50 g / min, and the carrier gas flow rate is 5 to 30 L / min. The first laser and the second laser can use infrared light, green light, and blue light, preferably blue laser, with a laser power of 10 to 100W, a laser frequency of 400 to 1500KHz, and a spot size of 10 to 60μm. Compared with red light, the first laser uses blue laser, which can reduce damage to the film layer below the passivation layer when grooving. The second laser uses blue laser, which is more easily absorbed by metal powder during melting powder, and easily forms instantaneous metal melting. The blue laser is absorbed by the battery cell in the surface layer, which will not cause serious thermal impact on the surface of the battery cell, and has less impact on the layer below the surface. The process is well controllable, especially the temperature is controlled during the second laser irradiation process, so that the temperature irradiated on the battery cell is controlled within 50 to 1000°C, which can effectively prevent the metal electrode from burning through the PN junction due to excessive temperature and protect the silicon nitride layer in the area without gate line coverage. The synchronous movement speed of the first laser, the nozzle, and the second laser is 2000 to 6000mm / s.

[0023] The sub-gate manufacturing process is carried out in a vacuum environment or an inert gas environment such as nitrogen or argon.

[0024] The secondary grid obtained by the laser 3D printing method of the present invention, the movement speed of the nozzle and the laser relative to the battery cell, the amount of powder and the size of the airflow, and the laser spot size all determine the size of the secondary grid electrode obtained. The secondary grid has a width of 10 to 50 μm, a height of 4 to 20 μm, and an aspect ratio of 30 to 150%.

[0025] Attached Figure 2 The figure shows a schematic diagram of the auxiliary grid produced by the traditional screen printing method. Over-burning or poor sintering may occur during the sintering process. The auxiliary grid indicated by red is over-burned, which is equivalent to burning through the PN junction, which will cause leakage. The auxiliary grid indicated by green is poorly sintered and does not form a good ohmic contact with the silicon substrate, thus affecting the battery efficiency.

[0026] Attached Figure 3 The figure shows a schematic diagram of a sub-gate produced by the laser 3D printing method of the present invention, which can achieve precise grooving and precise sintering, thereby reducing damage to the passivation layer of the silicon wafer outside the grooving area, and also can achieve better ohmic contact.

[0027] Traditional screen printing achieves ohmic contact by corroding the passivation layer with lead-containing glass powder metal paste. However, it is difficult to accurately control the sintering temperature and the melting point of the glass powder, which can easily cause composite current and reduce battery efficiency. In addition, the metal electrode prepared by metal paste printing has a relatively small aspect ratio and blocks the surface to a large extent.

[0028] The laser 3D printing method of the present invention can reduce the impact on battery efficiency by accurately preparing the sub-grid electrode through laser. The aspect ratio of the sub-grid can exceed 100%, reducing the shielding of the battery cell surface, which is beneficial to improving battery efficiency.

[0029] The present invention adopts a laser 3D printing method to prepare a secondary grid electrode on a battery cell at one time using metal powder. No organic solvent, glass powder or other additives are required to prepare the metal slurry. The printing equipment, drying equipment, annealing equipment, and auxiliary materials such as metal slurry, screen, and scraper of screen printing can be omitted, which can greatly reduce the investment in production equipment and is conducive to reducing production costs. In addition, the use of lead-containing glass powder and organic solvents is reduced, which is more environmentally friendly.

Claims

1. A method for manufacturing a solar cell subgrid by laser 3D printing, characterized in that: First, the first laser is used to groove the passivation layer of the battery cell, and then the metal powder is transported to the top of the groove through the nozzle in the powder airflow. The second laser is then used to instantly heat-melt and sinter the metal powder on the battery cell. After cooling, a metal electrode is formed. As the first laser, nozzle, and second laser move continuously on the battery cell in synchronization according to the secondary grid pattern, a secondary grid is formed.

2. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The first laser and the second laser are blue lasers, the laser power is 10-100W, the laser frequency is 400-1500KHz, and the spot size is 10-60μm.

3. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The temperature of the first laser and the second laser irradiating the battery cell is 50-1000°C.

4. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The metal powder is silver powder or copper powder, and the particle size is 0.5 to 1.2 μm.

5. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The powder delivery rate of the powder airflow is 5 to 50 g / min, and the carrier gas flow rate is 5 to 30 L / min.

6. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The synchronous movement speed of the first laser, the nozzle and the second laser is 2000-6000 mm / s.

7. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The width of the auxiliary grid is 10 to 50 μm, the height is 4 to 20 μm, and the aspect ratio is 30 to 150%.

8. The method for manufacturing a solar cell subgrid by laser 3D printing according to claim 1, characterized in that: The manufacturing process is carried out in a vacuum environment or an inert gas environment.

Images