Preparation method of N-type solar cell boron diffusion SE structure

Abstract

The application discloses a preparation method of an N-type solar cell boron diffusion SE structure, and comprises the following steps: preparing an oxide layer on the surface of a silicon substrate, boron doping, annealing, and forming a polysilicon layer; preparing a mask on the surface of the polysilicon layer in a preset grid line area; removing the polysilicon layer and the oxide layer in the non-grid line area on the surface of the silicon substrate; and removing the mask to obtain the N-type solar cell boron diffusion SE structure. Compared with a conventional preparation method, the preparation method of the N-type solar cell boron diffusion SE structure only needs one high-temperature annealing process, causes less loss to the silicon substrate, has the advantages of simple process, convenient operation, low cost, small damage and the like, is beneficial to improving the photoelectric conversion efficiency of the cell, is beneficial to realizing large-scale production, has high use value, and has good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology and relates to a method for preparing a boron-diffused SE structure for N-type solar cells. Background Technology

[0002] With the rapid development of modern society, the importance of energy has become increasingly prominent, and environmentally friendly green energy has received even more attention. Currently, photovoltaic (PV) solar cell technology is one of the mainstream green energy technologies. At the same time, the rapid popularization and marketization of PV solar cells have placed new demands on more efficient solar cell technologies. Among various solar cells, N-type solar cells have attracted widespread attention due to their numerous superior properties. Introducing a selective emitter (SE) structure into N-type solar cells is a method that can effectively improve contact performance and enhance cell efficiency. However, as... Figure 1 As shown, the existing methods for preparing boron-diffused SE structures for N-type solar cells mainly involve a second boron diffusion process after the first boron diffusion, which is achieved by grooving. However, the two high-temperature diffusion processes can easily cause thermal damage to the silicon substrate, resulting in high energy loss and high preparation costs. These methods still suffer from drawbacks such as complex processes, difficulty in control, high costs, and significant damage, which are not conducive to improving the photoelectric conversion efficiency of the cells and make it difficult to achieve large-scale production. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing boron-diffused SE structures for N-type solar cells that is simple in process, convenient in operation, low in cost, and causes little damage.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0005] A method for preparing a boron-diffused SE structure for an N-type solar cell includes the following steps:

[0006] S1. Prepare an oxide layer on the surface of a silicon substrate;

[0007] S2. Boron doping is performed on a silicon substrate with an oxide layer on its surface to form an amorphous silicon layer or microcrystalline silicon layer containing boron on the surface of the oxide layer.

[0008] S3. Anneal the silicon substrate with an amorphous silicon layer or microcrystalline silicon layer on its surface to form a polycrystalline silicon layer until boron is doped into part of the silicon substrate.

[0009] S4. Prepare a mask on the surface of a polysilicon layer by pre-setting a gate line region;

[0010] S5. Remove the polysilicon layer and oxide layer from the non-gateway area of ​​the silicon substrate surface;

[0011] S6. Remove the mask to obtain the boron-diffused SE structure of the N-type solar cell.

[0012] In a further improvement to the above preparation method, in step S3, the thickness of the polycrystalline silicon layer is 50 nm to 150 nm; and the boron doping concentration in the polycrystalline silicon layer is 2E19 to 2E20 cm⁻¹. -3 .

[0013] In a further improvement to the above preparation method, in step S3, the junction depth of boron doping in the silicon substrate is 0.4–1.0 μm; and the boron doping concentration in the silicon substrate is 1E19 cm⁻¹. -3 .

[0014] In a further improvement to the above preparation method, in step S3, the annealing temperature is 1000℃~1050℃; the annealing time is 60min~120min; the annealing process also includes the introduction of nitrogen or oxygen; the flow rate of nitrogen is 5slm~15slm; the flow rate of oxygen is 5slm~15slm.

[0015] In a further improvement to the above preparation method, in step S1, N2O plasma is used to oxidize the surface of the silicon substrate to form an oxide layer with a thickness of 2nm to 10nm.

[0016] In a further improvement to the above preparation method, in step S1, the oxide layer is a silicon oxide layer.

[0017] In a further improvement to the above preparation method, in step S1, the silicon substrate is an N-type silicon wafer.

[0018] In a further improvement to the above preparation method, in step S2, boron doping is performed on the silicon substrate with an oxide layer on its surface using PECVD, LPCVD, or APCVD.

[0019] In a further improvement to the above preparation method, in step S4, a mask is prepared on the surface of the polysilicon layer in a pre-defined gate line region using a printing coating method.

[0020] In a further improvement to the above preparation method, in step S5, the polysilicon layer and oxide layer in the non-gateline region of the silicon substrate surface are removed by wet alkaline etching.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] To address the shortcomings of traditional methods for fabricating boron-diffused SE structures for N-type solar cells, such as complex processes, difficulty in control, high costs, and significant damage, this invention creatively proposes a method for fabricating boron-diffused SE structures for N-type solar cells. This method involves boron doping and annealing the silicon substrate surface to form high-concentration boron-doped and low-concentration boron-doped regions. A mask is then fabricated on the surface of the high-concentration boron-doped region to retain the high-concentration boron-doped polycrystalline silicon layer. The polycrystalline silicon layer and oxide layer in the unmasked regions are removed, exposing the low-concentration boron-doped silicon substrate. After removing the mask, the boron-diffused SE structure for N-type solar cells is obtained. The resulting high-concentration boron-doped polycrystalline silicon layer significantly reduces contact resistivity, improves open-circuit voltage, reduces series resistance, and increases efficiency when in contact with metal grid lines. Compared with conventional preparation methods, the method for preparing the boron-diffused SE structure of the N-type solar cell of the present invention only requires one high-temperature annealing process and does not require a second high-temperature diffusion after the first grooving or a second high-temperature activation after laser doping. This reduces one high-temperature process and causes less thermal damage to the silicon substrate. It has the advantages of simple process, convenient operation, low cost and less damage. It is not only conducive to improving the photoelectric conversion efficiency of the cell, but also conducive to large-scale production. It has high use value and good application prospects. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0024] Figure 1 This is a schematic diagram of the fabrication process for the boron-diffused SE structure of an existing N-type solar cell.

[0025] Figure 2 This is a schematic diagram of the fabrication process of the boron-diffused SE structure of the N-type solar cell in Embodiment 1 of the present invention.

[0026] Figure 3 This is a diagram showing the boron doping concentration distribution on the surface of the silicon substrate after annealing in Embodiment 1 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0028] The materials and instruments used in the following examples are all commercially available.

[0029] Example

[0030] like Figure 1As shown, the existing methods for preparing boron-diffused SE structures for N-type solar cells mainly involve a second boron diffusion process after the first boron diffusion, which is achieved by grooving. However, the two high-temperature diffusion processes can easily cause thermal damage to the silicon substrate, resulting in high energy loss and high preparation costs. These methods still suffer from drawbacks such as complex processes, difficulty in control, high costs, and significant damage, which are not conducive to improving the photoelectric conversion efficiency of the cells and make it difficult to achieve large-scale production.

[0031] To address the above problems, this application proposes a method for preparing a boron-diffused SE structure for N-type solar cells, comprising the following steps:

[0032] S1. An oxide layer is prepared on the surface of a silicon substrate, specifically by oxidizing the surface of the silicon substrate with N2O plasma to form an oxide layer with a thickness of 1nm to 5nm, wherein the silicon substrate is an N-type silicon wafer and the oxide layer is a silicon oxide layer.

[0033] S2. Boron doping is performed on the silicon substrate with an oxide layer on its surface to form an amorphous silicon layer or microcrystalline silicon layer containing boron on the oxide layer surface. Specifically, PECVD, LPCVD or APCVD methods are used to perform boron doping on the silicon substrate with an oxide layer on its surface to form an amorphous silicon layer or microcrystalline silicon layer containing boron on the oxide layer surface.

[0034] S3. Anneal the silicon substrate with an amorphous silicon layer or microcrystalline silicon layer on its surface to form a polycrystalline silicon layer until boron is doped into part of the silicon substrate. The thickness of the polycrystalline silicon layer is 50 nm to 150 nm, and the boron doping concentration in the polycrystalline silicon layer is 2E19 to 2E20 cm⁻¹. -3 More preferably, the junction depth of boron doping in the silicon substrate is 0.4–1.0 μm; the boron doping concentration in the silicon substrate is 1E19cm⁻¹. -3 The annealing temperature is 1000℃~1050℃, and the time is 60min~120min; the annealing process also includes the introduction of nitrogen or oxygen; the flow rate of nitrogen is 5slm~15slm; the flow rate of oxygen is 5slm~15slm.

[0035] S4. Prepare a mask in the pre-defined gate line area on the surface of the polysilicon layer, specifically by using a printing and coating method to prepare a mask in the pre-defined gate line area on the surface of the polysilicon layer.

[0036] S5. Remove the polysilicon layer and oxide layer in the non-gate area on the surface of the silicon substrate, specifically by using wet alkaline etching to remove the polysilicon layer and oxide layer in the non-gate area on the surface of the silicon substrate.

[0037] S6. Remove the mask to obtain the boron-diffused SE structure of the N-type solar cell.

[0038] For ease of understanding, this invention provides a method for preparing a boron-diffused SE structure for an N-type solar cell, the process flow diagram of which is shown below. Figure 2 As shown, it includes the following steps:

[0039] S1. Texturing the surface of the silicon substrate (silicon wafer) to form a textured surface; preparing an oxide layer on the textured silicon substrate (silicon wafer) surface, specifically: using N2O plasma to oxidize the silicon wafer surface to form a silicon oxide (SiOx) layer with a thickness of 2nm.

[0040] S2. Boron doping is performed on a silicon substrate with an oxide layer on its surface using the PECVD method to form an amorphous silicon layer containing boron on the oxide layer surface. The PECVD process parameters are: temperature 480℃, SiH4 flow rate 1000sccm, B2H6 flow rate 900sccm, and power 10000W.

[0041] S3. Place the silicon substrate with an amorphous silicon layer on its surface in an annealing furnace and anneal it to form a polycrystalline silicon layer with a thickness of 110 nm and a boron doping concentration of 2E19cm⁻¹. -3 / atom, while boron is doped into the oxide layer and lightly doped into part of the silicon substrate, and as Figure 2 As shown, the junction depth of boron-doped silicon substrate is 0.4–1.0 μm, and the boron doping concentration in the silicon substrate is 1E19cm⁻¹. -3 In this step, the annealing temperature is 1000℃ and the time is 60 minutes. The annealing process also includes the introduction of nitrogen or oxygen, with the nitrogen flow rate being 10 slm and the oxygen flow rate being 10 slm.

[0042] S4. An electrode stencil pattern mask is prepared on the surface of a polycrystalline silicon layer by pre-setting a gate line area using a printing coating method (the material of the mask is printing ink containing 2-butoxyethanol as a binder), wherein the mask area is the highly doped area of ​​the polycrystalline silicon oxide layer, and the non-mask area is the low-doped area of ​​the silicon substrate after annealing.

[0043] S5. The polysilicon layer and oxide layer in the non-gateway area of ​​the silicon substrate surface are removed by wet alkaline etching. Specifically, the surface oxide layer is removed by using a 10% hydrofluoric acid solution, and then the Poly-Si part formed by annealing is removed by alkaline etching with a 30% KOH solution. Then, the crystalline silicon SiOx is further removed by using a low-concentration hydrofluoric acid / hydrochloric acid (1:1) mixed solution (in which the mass concentration of hydrofluoric acid and hydrochloric acid is 1%).

[0044] S6. The mask is removed using an alkaline (KOH) solution containing diethylene glycol butyl ether (both diethylene glycol butyl ether and KOH have a mass concentration of 5%) to obtain the boron-diffused SE structure of the N-type solar cell.

[0045] In this invention, boron doping and annealing are performed on the surface of a silicon substrate to form high-concentration boron-doped regions and low-concentration boron-doped regions on the silicon wafer surface. A mask is then prepared on the surface of the high-concentration boron-doped regions to retain the high-concentration boron-doped polycrystalline silicon layer. The polycrystalline silicon layer and oxide layer in the unmasked regions are removed, exposing the low-concentration boron-doped silicon substrate. After removing the mask, a boron-diffused SE structure for N-type solar cells is obtained. The resulting high-concentration boron-doped polycrystalline silicon layer significantly reduces contact resistivity when in contact with metal grid lines, improving the cell's open-circuit voltage, reducing series resistance, and increasing efficiency. Compared to conventional methods, this invention's method for preparing the boron-diffused SE structure for N-type solar cells requires only one high-temperature annealing process, causing less thermal damage to the silicon substrate. It offers advantages such as simple process, convenient operation, low cost, and minimal damage, which is beneficial for improving the photoelectric conversion efficiency of the cell, facilitating large-scale production, and demonstrating high practical value and promising application prospects.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a boron-diffused SE structure for an N-type solar cell, characterized in that, Includes the following steps: S1. Prepare an oxide layer on the surface of a silicon substrate; S2. Boron doping is performed on a silicon substrate with an oxide layer on its surface to form an amorphous silicon layer or microcrystalline silicon layer containing boron on the surface of the oxide layer. S3. Anneal the silicon substrate with an amorphous silicon layer or microcrystalline silicon layer on its surface to form a polycrystalline silicon layer until boron is doped into a portion of the silicon substrate; the thickness of the polycrystalline silicon layer is 110 nm to 150 nm; the boron doping concentration in the polycrystalline silicon layer is 2E19 to 2E20 cm⁻¹. -3 The boron-doped junction depth in the silicon substrate is 0.4–1.0 μm; the boron doping concentration in the silicon substrate is 1E19cm⁻¹. -3 ; S4. A mask is prepared on the surface of a polycrystalline silicon layer with a pre-defined gate line region; the mask is made of printing ink containing 2-butoxyethanol as a binder. S5. The polysilicon layer and oxide layer in the non-gate area of ​​the silicon substrate are removed by wet alkaline etching. Specifically, the surface oxide layer is removed by using a 10% hydrofluoric acid solution, the Poly-Si part formed by annealing is removed by alkaline etching with a 30% KOH solution, and the crystalline silicon SiOx is removed by using a mixed solution of hydrofluoric acid / hydrochloric acid. S6. Remove the mask to obtain the boron-diffused SE structure of the N-type solar cell.

2. The preparation method according to claim 1, characterized in that, In step S3, the annealing temperature is 1000℃~1050℃; the annealing time is 60min~120min; the annealing process also includes the introduction of nitrogen or oxygen; the flow rate of nitrogen is 5slm~15slm; the flow rate of oxygen is 5slm~15slm.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, N2O plasma is used to oxidize the surface of the silicon substrate to form an oxide layer with a thickness of 1 nm to 5 nm.

4. The preparation method according to claim 3, characterized in that, In step S1, the oxide layer is a silicon oxide layer.

5. The preparation method according to claim 4, characterized in that, In step S1, the silicon substrate is an N-type silicon wafer.

6. The preparation method according to claim 1 or 2, characterized in that, In step S2, boron doping is performed on the silicon substrate with an oxide layer on its surface using PECVD, LPCVD, or APCVD.

7. The preparation method according to claim 1 or 2, characterized in that, In step S4, a mask is prepared on the surface of the polysilicon layer in a pre-defined gate line area using a printing coating method.

Images