A method for testing the number of pinholes in a tunnel oxide layer of a topcon cell

Abstract

The present application belongs to the field of Topcon battery, and relates to a method for testing the pinhole quantity of a tunneling oxide layer of a Topcon battery piece, which comprises the following steps: exposing the tunneling oxide layer in the Topcon battery piece to an alkali etching solution, allowing the alkali etching solution to corrode the silicon substrate through the pinhole to generate bubbles, and counting the quantity of the bubble generation positions as the pinhole quantity. The method for testing the pinhole quantity of the tunneling oxide layer of the Topcon battery piece has the characteristics of simplicity, convenience and effectiveness, and can visually detect the pinhole quantity of a large-area tunneling oxide layer.

Description

Technical Field

[0001] This invention belongs to the field of Topcon batteries and relates to a method for testing the number of pinholes in the tunnel oxide layer of Topcon battery cells. Background Technology

[0002] Passivated tunneling Topcon cells have become the next generation of cells after PERC cells. One of the core aspects of Topcon cells is the thickness of the silicon oxide tunneling layer and the quality of the silicon oxide film. The quality of the oxide film is mainly determined by two factors: the growth conditions and the high-temperature process. Currently, there are two technical routes for Topcon cells: one is LpcVd (Liquid Perceptual Void Diffusion) to grow the tunneling layer and polycrystalline silicon layer, and the other is PecVd (PecVd) to grow the tunneling layer and polycrystalline silicon layer. LpcVd forms the oxide film through a thermal oxidation process, while PecVd forms the oxide film on the surface of the silicon oxide wafer after ionization with nitrous oxide. However, both routes require a high-temperature process. The LpcVd route requires high-temperature phosphorus diffusion to form the doped polycrystalline silicon layer, while PecVd requires high-temperature annealing to crystallize the amorphous silicon and activate phosphorus atoms. This high-temperature process affects the quality of the oxide film. During the high-temperature process, because the oxide film contains crystalline silicon on both sides with different coefficients of thermal expansion, and the oxide film is usually thin, the large thermal stress causes some areas of the oxide film to form voids to release stress; these voids are called pinholes. The number of pinholes can affect electron transport capability, the passivation of the silicon surface by the oxide film, and ultimately the efficiency of solar cells. However, there is currently no particularly effective method to characterize the number of pinholes on large-area silicon wafers, so the specific influencing factors and the control of the number of pinholes cannot be effectively studied. This invention provides a convenient and effective method for testing the number of pinholes, providing an important tool for pinhole research, a basis for further research on related theories, and contributing to the further improvement of solar energy efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a method for testing the number of pinholes in the tunneling oxide layer of Topcon solar cells. This method is simple and easy to implement, and can visually detect the number of pinholes in a large area of ​​tunneling oxide layer. This is beneficial for further research on the relevant theories of pinholes and plays an important role in improving Topcon solar energy. Furthermore, this invention also provides a silicon oxide protective agent that can significantly reduce the corrosion rate of the tunneling oxide layer by alkaline etching solutions, thus being effectively used in the method of this invention.

[0004] The present invention will achieve the above objectives through the following technical solutions:

[0005] Topcon solar cells include a tunneling oxide layer located on the back of a silicon substrate. This invention provides a method for testing the number of pinholes in the tunneling oxide layer of the aforementioned Topcon solar cell, comprising the following steps: exposing the tunneling oxide layer in the Topcon solar cell to an alkaline etching solution, allowing the alkaline etching solution to corrode the silicon substrate through the pinholes to generate bubbles, and counting the number of locations where bubbles are generated is the number of pinholes.

[0006] When alkaline etching solution etches a silicon substrate, it will generate bubbles. However, it will not generate bubbles when etching the tunneling oxide layer, i.e., silicon oxide. When alkaline etching solution etches the silicon substrate through the pinholes on the surface of the tunneling oxide layer, bubbles will be generated at the locations containing the pinholes. The number of locations where bubbles are generated is the number of pinholes.

[0007] Specifically, the alkaline corrosion solution is a 1-3 wt% sodium hydroxide solution with a corrosion temperature of 55-65℃.

[0008] Specifically, the edges of the Topcon solar cell and the surface of the silicon substrate are protected with paraffin to prevent corrosion, that is, only the tunneling oxide layer is exposed to the alkaline etching solution; the tunneling oxide layer is protected by adding a silicon oxide protective agent to slow down its corrosion rate.

[0009] According to another aspect of the present invention, a silica protective agent for the above-described method is provided, the silica protective agent comprising the following components by mass percentage: 0.5-1.5% silane coupling agent, 0.05-0.1% sodium dodecyl sulfate, 0.01-0.05% phenol, 2-4% 4 wt% aqueous solution of silica, and the balance being deionized water. This silica protective agent utilizes chemical bonding and physical adsorption to allow the above components to act on the silica surface, thereby protecting the silica and slowing down corrosion, without affecting the corrosion rate of silicon. The silica protective agent constitutes 1-2% of the volume of the alkaline etching solution.

[0010] Furthermore, the Topcon solar cell of the present invention also includes a polycrystalline silicon layer and a silicon oxide passivation film on the back side of the tunneling oxide layer. In this case, the polycrystalline silicon layer and the silicon oxide passivation film need to be removed to expose the tunneling oxide layer to an alkaline etching solution.

[0011] Specifically, the method for testing the number of pinholes in the tunneling oxide layer of the Topcon solar cell containing polycrystalline silicon and a passivation film includes: placing the Topcon solar cell in a hydrofluoric acid aqueous solution to remove the silicon oxide passivation film; placing the Topcon solar cell after removing the silicon oxide passivation film in an alkaline etching solution to remove the polycrystalline silicon layer, exposing the tunneling oxide layer to the alkaline etching solution; the alkaline etching solution continuing to etch the silicon substrate through the pinholes to generate bubbles; and counting the number of locations where bubbles are generated at this time is the number of pinholes.

[0012] The beneficial effects of this invention are as follows: This invention proposes a method for testing the number of pinholes in the tunneling oxide layer of Topcon solar cells. This method is convenient, effective, simple and easy to implement. It can visualize the number of pinholes in a large area of ​​tunneling oxide layer, which is conducive to further research on the relevant theories of pinholes and plays an important role in improving the efficiency of Topcon solar energy. Attached Figure Description

[0013] Figure 1 : A schematic diagram of the Topcon battery cell structure in an embodiment of the present invention.

[0014] Figure 2 Photograph of pinhole bubbles on the surface of the silicon oxide tunneling layer in Example 1 of this invention.

[0015] Figure 3 Photograph of pinhole bubbles on the surface of the silicon oxide tunneling layer in Example 2 of this invention.

[0016] Figure 4 Statistical analysis of the number of pinholes on the surface of the silicon oxide tunneling layer in Example 2 of this invention. Detailed Implementation

[0017] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but this is not intended to limit the scope of protection of the present invention.

[0018] It should be noted in advance that the Topcon battery cells used in the embodiments of the present invention have the following characteristics: Figure 1 The structure shown includes a silicon oxide tunneling layer 2 on the back side of a silicon substrate 1, a polycrystalline silicon layer 3 on the back side of the silicon oxide tunneling layer 2, and a silicon oxide passivation layer 5 on the back side of the polycrystalline silicon layer 3. The silicon oxide tunneling layer 2 contains a pinhole 4.

[0019] Example 1:

[0020] A method for testing the number of pinholes in the tunneling oxide layer of a small-area Topcon solar cell includes the following steps:

[0021] S1. Protect the silicon substrate surface and sides of the above-mentioned Topcon solar cell with paraffin wax to prevent it from being corroded in alkaline etching solution;

[0022] S2. The Topcon solar cell after step S1 is immersed in a 5 vol% aqueous solution of hydrofluoric acid to remove the silicon oxide passivation layer on the surface of the polycrystalline silicon.

[0023] S3. Thoroughly mix 1 wt% sodium hydroxide solution with silicon dioxide protective agent, the volume of silicon dioxide protective agent being 1% of the volume of alkaline corrosion solution, heat to 55°C, and place the Topcon battery cell treated in step S2 into the above mixture; the silicon dioxide protective agent is composed of the following components calculated by mass percentage: 0.5% silane coupling agent, 0.05% sodium dodecyl sulfate, 0.01% phenol, 2% 4 wt% aqueous solution of silica, and the balance being deionized water.

[0024] S4. When the polysilicon has been completely etched clean, the alkaline etching solution continues to etch the silicon substrate through the pinholes and generate bubbles. The bubbles emerge through the pinholes and tunnel through the oxide layer surface. The number of locations where bubbles are generated at this time is the number of pinholes.

[0025] In Example 1, after the Topcon solar cell with the silicon oxide passivation layer removed is placed in a mixture of sodium hydroxide solution and silicon oxide protective agent, a large number of hydrogen bubbles are initially formed. As the reaction proceeds, the polycrystalline silicon is completely etched away after 2 minutes. The alkaline etching solution continues to etch the silicon substrate through the pinholes. The number of locations where bubbles are generated on the surface of the silicon oxide tunneling layer at this time is the number of pinholes in the silicon oxide tunneling layer. Figure 2 As shown, visible bubbles are generated at the pinholes on the surface of the silicon oxide tunneling layer, and the number of pinholes can be counted at this time.

[0026] Example 2:

[0027] A method for testing the number of pinholes in the tunneling oxide layer of a large-area Topcon solar cell includes the following steps:

[0028] S1. Protect the silicon substrate surface and sides of the above-mentioned Topcon solar cell with paraffin wax to prevent it from being corroded in alkaline etching solution;

[0029] S2. The Topcon solar cell after step S1 is immersed in a 5 vol% aqueous solution of hydrofluoric acid to remove the silicon oxide passivation layer on the surface of the polycrystalline silicon.

[0030] S3. Thoroughly mix 2wt% sodium hydroxide solution with silicon dioxide protective agent, the volume of silicon dioxide protective agent being 2% of the volume of alkaline corrosion solution, heat to 60°C, and place the Topcon battery cell treated in step S2 into the above mixture; the silicon dioxide protective agent is composed of the following components calculated by mass percentage: 1% silane coupling agent, 0.06% sodium dodecyl sulfate, 0.03% phenol, 3% 4wt% aqueous solution of silica, and the balance being deionized water.

[0031] S4. When the polysilicon has been completely etched clean, the alkaline etching solution continues to etch the silicon substrate through the pinholes and generate bubbles. The bubbles emerge through the pinholes and tunnel through the oxide layer surface. The number of locations where bubbles are generated at this time is the number of pinholes.

[0032] In Example 2, after the Topcon solar cell with the silicon oxide passivation layer removed is placed in a mixture of sodium hydroxide solution and silicon oxide protective agent, a large number of hydrogen bubbles are initially formed. As the reaction proceeds, the polycrystalline silicon is completely etched away after 2 minutes. The alkaline etching solution continues to etch the silicon substrate through the pinholes. The number of locations where bubbles are generated on the surface of the silicon oxide tunneling layer at this time is the number of pinholes in the silicon oxide tunneling layer. Figure 3 As shown, visible bubbles are generated at the pinholes on the surface of the silicon oxide tunneling layer. The number of pinholes can then be counted by marking the locations of the bubbles on the photograph. Figure 4 As shown, there are 15 pinholes.

[0033] It is understood that the above specific embodiments are all further illustrations of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, all other modifications and refinements obtained without creative effort are within the scope of protection of the present invention.

Claims

1. A method for testing the number of pinholes in a tunneling oxide layer of a Topcon solar cell, wherein the Topcon solar cell includes a tunneling oxide layer located on the back side of a silicon substrate, characterized in that, Includes the following steps: S1. Protect the edges of the Topcon solar cell and the surface of the silicon substrate with paraffin wax; S2. Thoroughly mix the alkaline etching solution with the silica protective agent to obtain a mixed solution; wherein the volume of the silica protective agent accounts for 1% or 2% of the volume of the alkaline etching solution; the alkaline etching solution is a 1-3 wt% sodium hydroxide solution; the silica protective agent comprises the following components calculated by mass percentage: 0.5-1.5% silane coupling agent, 0.05-0.1% sodium dodecyl sulfate, 0.01-0.05% phenol, 2-4% 4 wt% aqueous solution of silica, and the balance being deionized water; S3. Expose the Topcon solar cell after step S1 to the above mixture, so that the alkaline etching solution corrodes the silicon substrate through the pinhole to generate bubbles. The number of locations where bubbles are generated at this time is the number of pinholes.

2. The method for testing the number of pinholes in the tunneling oxide layer of a Topcon solar cell according to claim 1, characterized in that, The corrosion temperature in step S3 is 55-65℃.

3. A method for testing the number of pinholes in the tunneling oxide layer of a Topcon solar cell, wherein the Topcon solar cell comprises a tunneling oxide layer located on the back side of a silicon substrate, a polycrystalline silicon layer located on the back side of the tunneling oxide layer, and a silicon oxide passivation film located on the back side of the polycrystalline silicon layer, characterized in that, Includes the following steps: a. Protect the edges of the Topcon solar cell and the surface of the silicon substrate with paraffin wax; b. Place the Topcon battery cell treated in step a in an aqueous hydrofluoric acid solution to remove the silicon oxide passivation film; c. Thoroughly mix the alkaline etching solution with the silica protective agent to obtain a mixture; wherein the volume of the silica protective agent accounts for 1% or 2% of the volume of the alkaline etching solution; the alkaline etching solution is a 1-3 wt% sodium hydroxide solution; the silica protective agent comprises the following components calculated by mass percentage: 0.5-1.5% silane coupling agent, 0.05-0.1% sodium dodecyl sulfate, 0.01-0.05% phenol, 2-4% 4 wt% aqueous solution of silica, and the balance being deionized water; d. Expose the Topcon solar cell after step b to the above mixture, so that the alkaline etching solution can etch the polycrystalline silicon layer. When the polycrystalline silicon layer is completely etched, the alkaline etching solution continues to etch the silicon substrate through the pinhole to generate bubbles. The number of locations where bubbles are generated at this time is the number of pinholes.

4. The method for testing the number of pinholes in the tunneling oxide layer of a Topcon solar cell according to claim 3, characterized in that, The corrosion temperature for step d is 55-65℃.

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