CN117810306A - Preparation method of solar cell back grid line - Google Patents

Abstract

The invention provides a preparation method of a solar cell back grid line, which comprises the following steps: (1) Performing laser film opening on a back grid line area to be electroplated on the back of the solar cell; (2) Cleaning and removing an oxide layer of a laser film opening area on the back of the solar cell; (3) Taking a laser film opening area on the back of the solar cell as an anode, and performing electrochemical etching on the laser film opening area to increase the roughness of the laser film opening area; and (4) electroplating the back grid line in the laser film opening area. The method has low cost, does not damage the battery body, does not add extra working procedures and does not increase the electroplating process time, and the improvement of the grid line junction force can be realized.

Description

A method for preparing back grid lines of solar cells

Technical field

The invention relates to the field of solar cells, and in particular to a preparation method and application of grid lines on the back side of solar cells.

Background technique

Metallization is one of the key processes in the preparation of photovoltaic cells. The traditional process mainly uses silver paste to make solar cell electrodes. For various high-efficiency battery technologies, the cost of silver paste is the second largest cost ratio after silicon wafers. Especially for TOPCon and HJT technology, the cost of silver paste has increased significantly from 10-11% of PERC to more than 16%-24%, becoming an important factor limiting their industrial promotion.

Electroplating metallization (Ni/Cu/Ag or Cu/Ag) can meet the requirements of this type of solar cell for low-temperature processes, low cell material costs, and highly conductive double-sided metal grids. For TOPCon solar cells, the combination of double-sided laser contact opening (LCO) and Ni/Cu/Ag coating allows the boron emitter on the front surface and TOPCon on the back surface to prepare high-conductivity grid lines with low contact resistance.

The back of the TOPCon battery is polished to reduce the loss of light from the back, but the polished surface is less than the surface during electroplating, resulting in poor grid line bonding.

Currently, for the electroplating of polished surfaces, electroless nickel plating or evaporated nickel is used to improve the bonding strength of the grid lines, and some use secondary laser to increase the surface roughness to improve the bonding strength of the grid lines. However, annealing is required after electroless nickel plating to improve the bonding strength of the coating. This requires adding an annealing furnace after electroless nickel plating, which increases the cost of electroplating. Moreover, electroplating copper after annealing requires adding acid activation to remove the surface oxide layer. The increase in the process cannot be done on one machine. Complete the nickel plating and copper plating solution on the equipment. Evaporating nickel requires adding electron beam evaporation equipment before electroplating. The equipment cost is high, and the evaporated nickel layer in the non-gate line area needs to be removed after nickel plating. In addition, acid activation is required to remove the surface oxide layer before electroplating. The process is complex. . Although the secondary laser method has a simple process, it will increase the laser film opening time and the laser itself will cause damage to the film opening area. Performing the secondary laser will increase the damage.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention provides a preparation method and application of grid lines on the back side of a solar cell.

The invention provides a method for preparing back grid lines of a solar cell. The method includes the following steps:

(1) Laser film opening is performed on the back side of the solar cell in the area where the back grid lines are to be formed;

(2) Clean and remove the oxide layer in the laser-filmed area on the back of the solar cell;

(3) Using the laser film-opening area on the back of the solar cell as the anode, perform electrochemical etching on the laser film-opening area to increase the roughness of the laser film-opening area;

(4) Make back grid lines in the laser film opening area.

According to the method of the present invention, in step (3), the positive electrode of the power supply is connected to the metal grid line of the front structure of the solar cell to form the anode.

According to the method of the present invention, in step (3), the anodic oxidation current density in the electrochemical etching is 0.5A/dm ² to 2A/dm ² , preferably 1A/dm ² to 1.5A/dm ² ;

The temperature of the electrochemical etching is 10°C to 30°C, preferably 18°C to 25°C;

The electrochemical etching time is 30S to 85S, preferably 40S to 60S.

According to the method of the present invention, step (2) and/or step (3) is completed in hydrofluoric acid electrolyte;

Preferably, a cathode is added to the hydrofluoric acid electrolyte, and the cathode is preferably a titanium cathode;

More preferably, the surface of the titanium cathode is plated with platinum or rhodium-iridium alloy.

According to the method of the present invention, the hydrofluoric acid concentration of the hydrofluoric acid electrolyte is 1wt% to 3wt%, preferably 1.4wt% to 1.8wt%; and/or

NH ₄ F is used to adjust the pH value of the hydrofluoric acid electrolyte to 3 to 4, preferably 3.4 to 3.8.

According to the method of the present invention, in step (2), the temperature for cleaning and removing the oxide layer is 10°C to 30°C, preferably 18°C to 25°C;

The cleaning and removal time of the oxide layer is 25S to 60S, preferably 30S to 50S.

According to the method of the present invention, in step (1), the width of the pattern formed in the laser film opening area is 35 μm to 60 μm, preferably 40 μm to 45 μm.

According to the method of the present invention, the solar cell is a TOPCon cell or a HJT cell.

According to the method of the present invention, in step (4), the material of the back gate line is selected from one or more of the following: Ag, Cu, Ni, Sn.

The preparation method of the present invention can have but is not limited to the following beneficial effects:

The preparation method of the present invention adds a power source and anode and cathode to the original hydrofluoric acid tank for electroplating to remove the oxide layer, and increases the surface roughness in the laser film-opening area through electrolytic etching. The method of the present invention is low in cost, does not cause damage to the battery body, does not add additional processes, and does not increase the electroplating process time, and can achieve the improvement of the gate line bonding force.

Description of drawings

Figure 1 shows a schematic diagram of electrochemical etching of the doped polysilicon layer in the laser film-opening area in Embodiment 1.

Figure 2 shows a partial enlarged view corresponding to area a in Figure 1.

FIG3 is a schematic diagram showing the battery structure after electrochemical etching in Example 1.

Figure 4 shows a partial enlarged view corresponding to area b in Figure 3.

FIG. 5 shows a schematic diagram of the front grid structure of the battery in Embodiment 1.

Figure 6 shows a transmission electron microscope image of the laser film-opening area before electrochemical etching in Example 1.

Figure 7 shows a transmission electron microscope image of the laser film-opening area after electrochemical etching in Example 1.

Explanation of reference symbols:

1. Power supply; 2. Anode; 3. Cathode; 4. Laser opening area before electrochemical etching; 5. Front grid line of battery; 6. Electrolyte; 7. Side of TOPCon battery; 8. After electrochemical etching The laser film opening area; 9. The front grid structure of the TOPCon battery; 10. The main grid on the front of the battery; 11. The fine grid on the front of the battery; 12. PAD points.

Detailed ways

The present application will be further described in detail below through the drawings and examples. Through these descriptions, the features and advantages of the present application will become clearer.

The word "exemplary" as used herein means "serving as an example, example, or illustrative." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or superior to other embodiments. Although various aspects of the embodiments are illustrated in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

Before elaborating the technical solutions of the present invention, the terms used in this article are defined as follows:

The term "TOPCon battery" refers to: Tunnel Oxide Passivated Contact Cell, tunnel oxide layer passivated contact cell.

The term "HJT battery" refers to: Hereto-junction with Intrinsic Thin-layer Cell, heterojunction battery.

The invention provides a method for preparing back grid lines of a solar cell. The method includes the following steps:

(1) Laser film opening is performed on the back side of the solar cell in the area where the back grid lines are to be formed;

(2) Clean and remove the oxide layer in the laser-filmed area on the back of the solar cell;

(3) Using the laser film-opening area on the back of the solar cell as the anode, perform electrochemical etching on the laser film-opening area to increase the roughness of the laser film-opening area;

(4) Electroplating is performed in the laser-opened area to form backside gate lines.

The method of the present invention increases the surface roughness of the laser-opened film area on the back of the battery by electrolytic etching, thereby improving the bonding strength between the back of the battery and the metal grid line. In a specific embodiment, the laser-opened film area on the back of the battery is electrochemically etched by adding a power supply and anodes and cathodes to the original hydrofluoric acid tank for removing the oxide layer. Compared with traditional chemical nickel plating, nickel evaporation and secondary laser methods, this method is low in cost, does not add additional processes and equipment, does not increase the electroplating process time, does not damage the battery body, and can achieve the improvement of grid line bonding strength using the original equipment.

According to one embodiment of the present invention, in step (3), the positive electrode of the power supply is connected to the metal grid line of the front structure of the solar cell to form the anode.

Taking the TOPCon battery as an example, a cathode is added to the electrolyte tank, so that the cathode is connected to the negative electrode of the power supply, and the metal grid on the front of the TOPCon battery is connected to the positive electrode of the power supply. Since the passivation layer on the back of the TOPCon battery is not conductive, the electrolysis anode reaction The surface roughness of the doped polysilicon layer in the laser-opened area on the back of the TOPCon cell increases through electrochemical etching, improving its bonding with the metal grid lines generated in the subsequent electroplating steps. force.

According to an embodiment of the present invention, in step (3), the anodic oxidation current density in the electrochemical etching is 0.5A/dm ² ~2A/dm ² , preferably 1A/dm ² ~1.5A/dm ² ;

The temperature of the electrochemical etching is 10°C to 30°C, preferably 18°C to 25°C;

The electrochemical etching time is 30S to 85S, preferably 40S to 60S.

By controlling the anodizing current density, etching temperature and etching time of electrochemical etching, the inventors successfully controlled the surface roughness of the doped polysilicon layer in the laser-opened area on the back of the solar cell.

According to an embodiment of the present invention, step (2) and/or step (3) is completed in hydrofluoric acid electrolyte;

Preferably, a cathode is added to the hydrofluoric acid electrolyte, and the cathode is preferably a titanium cathode;

More preferably, the surface of the titanium cathode is plated with platinum or rhodium-iridium alloy.

In a specific embodiment, the method of the present invention uses the same hydrofluoric acid electrolyte in the same electrolyte tank to successively complete the removal steps of the oxide layer in the laser film opening area and the doping polysilicon layer in the laser film opening area. Surface roughening, this method is easy to operate, low cost, and does not damage the battery itself.

According to one embodiment of the present invention, in step (2), the hydrofluoric acid concentration of the hydrofluoric acid electrolyte is 1wt% to 3wt%, preferably 1.4wt% to 1.8wt%;

NH ₄ F is used to adjust the pH value of the hydrofluoric acid electrolyte to 3 to 4, preferably 3.4 to 3.8.

When the hydrofluoric acid content in the electrolyte is less than 1wt%, the electrochemical etching efficiency is slow; when the hydrofluoric acid content in the electrolyte is higher than 3wt%, the electrolyte corrodes the non-laser film-opening area of the cell.

According to an embodiment of the present invention, in step (2), the temperature for cleaning and removing the oxide layer is 10°C to 30°C, preferably 18°C to 25°C;

The cleaning and removal time of the oxide layer is 25S to 60S, preferably 30S to 50S.

During the laser film opening process of step (1), while removing the passivation layer, oxides will be generated on the surface of the doped polycrystalline layer. Hydrofluoric acid electrolyte is used to remove the oxides, exposing the doped polycrystalline layer. out to facilitate subsequent electrochemical etching.

According to an embodiment of the present invention, in step (1), the width of the pattern formed in the laser film-opening area is 35 μm to 60 μm, preferably 40 μm to 45 μm.

Since the width of the pattern formed by laser film opening is small, using a secondary laser to open the film again will cause great damage to the film opening area. However, the electrochemical etching method of the present invention overcomes this defect and has no effect on the battery itself. Damage can improve the bonding strength of the grid lines.

According to an embodiment of the present invention, the solar cell is a TOPCon cell or a HJT cell. Preferably, in step (4), the material of the backside gate line is selected from one or more of the following: Ag, Cu, Ni, Sn.

After the electrochemical etching in step (3), the surface roughness of the doped polysilicon layer in the laser film-opening area increases. At this time, metal gate lines are electroplated in this area to obtain better gate line bonding force.

Example 1

This embodiment takes a TOPCon cell as an example to illustrate the method for preparing the back grid line of a solar cell of the present invention.

(1) Prepare a front-side structure of the cell including metal gate lines on the front side of the TOPCon cell substrate, and sequentially prepare a tunnel oxide layer, a doped polysilicon layer and a passivation layer on the back side of the TOPCon cell substrate.

In a specific implementation, the metal grid lines of the TOPCon battery front structure are arranged on the pyramid texture structure on the substrate. Figure 3 shows a schematic diagram of the battery front grid structure. As shown in Figure 3, the TOPCon battery front grid structure 9 includes a plurality of battery front main grids 10, a plurality of battery front fine grids 11 and a plurality of connecting main grids and fine grids. Gate PAD point 12.

(2) Laser film removal to remove the passivation layer at the grid line position on the back of the TOPCon battery.

Wherein, the width of the pattern formed in the laser film-opening area is 35 μm to 60 μm, preferably 40 μm to 45 μm.

In a specific implementation, the width of the pattern formed in the laser film opening area is 42 μm.

(3) Clean and remove the oxide layer in the laser-opened area on the back of the battery.

During the laser film opening process in step (2), while removing the passivation layer, oxides will be generated on the surface of the doped polycrystalline layer, and the oxides will be removed by cleaning to expose the doped polycrystalline layer.

Preferably, hydrofluoric acid is used to remove the oxide layer.

Wherein, the hydrofluoric acid concentration of the hydrofluoric acid electrolyte is 1 to 3 wt%, preferably 1.4 to 1.8 wt%.

NH ₄ F is used to adjust the pH value of the hydrofluoric acid electrolyte to 3 to 4, preferably 3.4 to 3.8.

In a specific embodiment, the hydrofluoric acid concentration of the hydrofluoric acid electrolyte is 1.5 wt %, and NH ₄ F is used to adjust the pH value of the hydrofluoric acid electrolyte to 3.6.

Wherein, the temperature for cleaning and removing the oxide layer is 10°C to 30°C, preferably 18°C to 25°C;

The time for cleaning and removing the oxide layer is 25S to 60S, preferably 30S to 50S.

In a specific embodiment, the temperature for cleaning the oxide layer is 22° C., and the time for cleaning the oxide layer is 45 seconds.

(4) Use the laser-opened area on the back of the battery as the anode to electrochemically etch the doped polysilicon layer in the laser-opened area.

Figure 1 shows a schematic diagram of electrochemical etching of the doped polysilicon layer in the laser film-opening area. As shown in Figure 1 and its partial enlarged view in Figure 2, after the cleaning and removal of the oxide layer in step (3), there is no need to replace the tank body and electrolyte 6. Only the cathode 3 is added to the electrolyte tank body and the cathode 3 is connected to the electrolyte tank. The negative electrode of power supply 1 is connected, and the positive electrode of power supply 1 is connected to the grid line 5 on the front of the battery to form anode 2. Since the passivation layer on the back of the TOPCon battery is not conductive, the electrolytic anode reaction occurs in the doping of the laser-opened film area on the back of the TOPCon battery. The polysilicon layer is electrolytically etched to increase the roughness of the laser film-opening area.

Figure 3 shows a schematic diagram of the battery structure after electrochemical etching in Embodiment 1. As shown in Figure 3 and its partial enlarged view in Figure 4, observe the side 7 of the TOPCon battery. The laser film opening area 8 after electrochemical etching is relative to the electrochemical etching. The laser opening area 4 before chemical etching increases the roughness.

In a preferred embodiment, both steps (3) and (4) are completed in a hydrofluoric acid electrolyte tank.

Wherein, the tank body also includes a cathode.

In a specific embodiment, a titanium electrode with a surface plated with platinum or rhodium-iridium alloy is used as the cathode plate.

By controlling the anodizing current density, etching temperature and etching time of electrochemical etching, the surface roughness of the doped polysilicon layer in the laser-opened area on the back of the TOPCon cell is controlled.

Among them, the anodizing current density in electrochemical etching is 0.5A/dm ² to 2A/dm ² , preferably 1A/dm ² to 1.5A/dm ² ;

The temperature of electrochemical etching is 10°C to 30°C, preferably 18°C to 25°C;

The electrochemical etching time is 30S to 85S, preferably 40S to 60S.

In a specific embodiment, the electrochemical etching anodic oxidation current density is ^1.2dm2 , the electrochemical etching temperature is 22°C, and the electrochemical etching time is 45S. Figures 6 and 7 respectively show the transmission electron microscope images of the laser film opening area before and after electrochemical etching. It can be seen from the figures that after electrochemical etching, the roughness of the laser film opening area (grid line area) is significantly improved, which is conducive to increasing the grid line bonding force and improving the grid line pull-off force.

(5) After the electrochemical etching in step (4) is completed, electroplating back metal grid lines is performed on the roughened laser film-opening area.

In a specific embodiment, Ni-Cu-Ag gate lines are electroplated in the laser-opened area, and the electroplating conditions are: nickel plating current 400mA, electroplating time 2.5min, copper plating current 1600mA, electroplating time 4min, chemical silver plating 1min.

After roughening the laser film-opening area, the bonding force of the back grid lines is strengthened, without increasing the plating process time, and without the need for additional plating equipment and processes.

The present application has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve only as an illustration. On this basis, various replacements and improvements can be made to the present application, all of which fall within the scope of protection of the present application.

Claims (10)

1. The preparation method of the back grid line of the solar cell is characterized by comprising the following steps of:

(1) Performing laser film opening on an area of the back surface of the solar cell where a back surface grid line is to be formed;

(2) Cleaning and removing an oxide layer of a laser film opening area on the back of the solar cell;

(3) Taking a laser film opening area on the back of the solar cell as an anode, and performing electrochemical etching on the laser film opening area to increase the roughness of the laser film opening area;

(4) And manufacturing a back grid line in the laser film opening area.

2. The method of claim 1, wherein in step (3), the anode is formed by connecting a power source positive electrode to a metal grid line of a front side structure of the solar cell.

3. The method according to claim 1 or 2, wherein in step (3), the anodic oxidation current density in the electrochemical etching is 0.5A/dm ² ～2A/dm ² Preferably 1A/dm ² ～1.5A/dm ² ；

The temperature of the electrochemical etching is 10-30 ℃, preferably 18-25 ℃;

the time of the electrochemical etching is 30S-85S, preferably 40S-60S.

4. A method according to any one of claims 1 to 3, wherein step (2) and/or step (3) is carried out in a hydrofluoric acid electrolyte.

5. The method according to claim 4, characterized in that a cathode, preferably a titanium cathode, is added to the hydrofluoric acid electrolyte;

more preferably, the surface of the titanium cathode is plated with platinum or rhodium iridium alloy.

6. The method according to claim 4 or 5, characterized in that the hydrofluoric acid concentration of the hydrofluoric acid electrolyte is 1wt% to 3wt%, preferably 1.4wt% to 1.8wt%; and/or

Using NH ₄ F, adjusting the pH value of the hydrofluoric acid electrolyte to be3 to 4, preferably 3.4 to 3.8.

7. The method according to any one of claims 4 to 6, wherein in step (2) the temperature at which the oxide layer is removed by washing is between 10 ℃ and 30 ℃, preferably between 18 ℃ and 25 ℃;

the time for cleaning and removing the oxide layer is 25S-60S, preferably 30S-50S.

8. The method according to any one of claims 1 to 7, wherein in step (1), the laser-opened regions are formed with a pattern width of 35 μm to 60 μm, preferably 40 μm to 45 μm.

9. The method according to any one of claims 1 to 8, wherein the solar cell is a TOPCon cell or a HJT cell.

10. The method according to any one of claims 1 to 9, wherein in step (4), the material of the back gate line is selected from one or more of the following: ag. Cu, ni and Sn.