WO2021012710A1

WO2021012710A1 - Method for preparing n-type crystalline silicon battery

Info

Publication number: WO2021012710A1
Application number: PCT/CN2020/083205
Authority: WO
Inventors: 倪志春; 杨智; 张树德; 魏青竹
Original assignee: 苏州腾晖光伏技术有限公司
Priority date: 2019-07-24
Filing date: 2020-04-03
Publication date: 2021-01-28
Also published as: CN110571302A; FI20205765A1

Abstract

A method for preparing an N-type crystalline silicon battery. The method sequentially comprises the following steps: A. doping one surface of a textured N-type crystalline silicon wafer (5) with boron; B. placing the N-type crystalline silicon wafer (5), with the boron-doped surface facing upwards, into a first solution in a floating manner to conduct treatment; C. growing a thin oxide layer (6) on the other surface of the N-type crystalline silicon wafer (5); D. depositing a polysilicon layer (7) on the thin oxide layer (6) and doping the polysilicon layer (7) with phosphorus; E. placing the N-type crystalline silicon wafer (5), with the phosphorus-doped surface facing upwards, into a second solution in a floating manner to conduct treatment; F. placing the second-solution-treated N-type crystalline silicon wafer (5) in an alkaline solution to conduct treatment; G. removing the phosphosilicate glass and borosilicate glass on the surface of the N-type crystalline silicon wafer (5); H. oxidizing the surface of N-type crystalline silicon wafer (5); I. depositing passivation anti-reflection layers (2, 8) and a passivation layer on the N-type crystalline silicon wafer (5); and J. performing a metallization process. The above preparation method solves an electric leakage problem of N-type crystalline silicon batteries.

Description

A preparation method of N-type crystalline silicon battery

This application claims the priority of a Chinese patent application filed with the State Intellectual Property Office of China with application number 201910671184.7 on July 24, 2019, the entire content of which is incorporated in this application by reference.

Technical field

The invention belongs to the field of solar cells and relates to a method for preparing an N-type crystalline silicon cell.

Background technique

Conventional fossil fuels are increasingly depleted. Among all sustainable energy sources, solar energy is undoubtedly the cleanest, most common and most potential alternative energy source. At present, silicon solar cells occupy an important position in the photovoltaic field. This is due to the extremely rich reserves of silicon materials in the earth's crust. At the same time, compared with other types of solar cells, silicon solar cells have excellent electrical and mechanical properties. Therefore, the research and development of cost-effective silicon solar cells has become the main research direction of photovoltaic companies in various countries.

The silicon wafer substrates used in existing silicon solar cells mainly include P-type and N-type silicon wafers. However, light-induced attenuation is widespread in P-type single crystal silicon. This is due to the existence of boron-oxygen complex defects and carbon-oxygen complex defects of P-type single crystal silicon, which reduces the minority carrier life and diffusion length, thereby reducing the battery The conversion efficiency. Compared with solar cells made with P-type silicon wafers as the base, solar cells made with N-type silicon wafers as the base have no obvious light attenuation due to the absence of boron-oxygen composite pairs in N-type silicon wafers. The minority carrier lifetime of silicon wafers is higher than that of P-type silicon wafers, so N-type silicon solar cells have received more and more attention.

The existing crystalline silicon solar cells mainly include single-sided solar cells and double-sided solar cells. Among them, only the front side of the single-sided solar cell can absorb sunlight and perform photoelectric conversion, and the back side of the cell is covered by metal aluminum. Therefore, the sunlight that reaches the back of the battery through reflection and scattering is blocked by aluminum and cannot penetrate to the silicon substrate. Therefore, the sunlight that reaches the back of the battery cannot be effectively absorbed. In order to further improve the absorption of sunlight by crystalline silicon solar cells, the photovoltaic industry has gradually begun to develop crystalline silicon solar cells that can absorb sunlight on both sides, that is, crystalline silicon double-sided solar cells.

The back surface of the current mainstream N-type crystalline silicon double-sided battery is phosphorus-doped surface, which is mainly passivated by SiOx and SiNx. Although the non-metal area on the back side can have a better passivation effect, the metalized area still has a relatively high passivation effect. High carrier recombination. This higher carrier recombination limits the further improvement of the photoelectric conversion efficiency of crystalline silicon solar cells. In order to continue to improve the photoelectric conversion efficiency of crystalline silicon solar cells, a carrier selective structure can be used to reduce the carrier recombination in the metalized area on the back of the N-type crystalline silicon double-sided battery, and the back of the N-type crystalline silicon double-sided battery is non-metallic. The recombination of chemical regions can also be further reduced.

However, when preparing a carrier selective structure on the back of an N-type crystalline silicon cell, whether in-situ doping or thermal diffusion doping is used, the doping elements will be diffracted to the non-doped surface during the doping process, making the cell The positive electrode and the negative electrode are directly connected together without insulation, resulting in leakage.

Summary of the invention

In view of the above technical problems, the present invention aims to provide a method for preparing an N-type crystalline silicon battery, which solves the leakage problem of the N-type crystalline silicon backside carrier selective structure battery.

In order to achieve the above objective, the technical solutions adopted by the present invention are as follows:

A method for preparing an N-type crystalline silicon battery includes the following steps in sequence:

A. Doping with boron on one side of the textured N-type crystalline silicon wafer;

B. Place the boron-doped N-type crystalline silicon wafer with the boron-doped side up and float it into the first solution for processing. The first solution includes a mixed solution composed of HF and HNO ₃ , or HF , A mixed solution composed of HNO ₃ and H ₂ SO ₄ ;

C. Grow a thin oxide layer on the other side of the N-type crystalline silicon wafer;

D. Deposit a polysilicon layer on the thin oxide layer and dope with phosphorus;

E. Put the phosphorus-doped surface on the N-type crystalline silicon wafer upward and float it into the second solution for processing, and the second solution includes HF;

F. Put the N-type crystalline silicon wafer treated by the second solution in an alkaline solution for treatment;

G. Remove the phosphosilicate glass and borosilicate glass on the surface of the N-type crystal silicon wafer treated with the alkaline solution;

H. Oxidize the surface of the N-type crystalline silicon wafer after the above step G treatment;

I. Deposit a first passivation anti-reflection layer on the boron-doped surface of the N-type crystalline silicon wafer, and deposit a second passivation anti-reflection layer on the phosphorus-doped surface;

J. Perform a metallization process to form a front metal electrode and a back metal electrode.

Preferably, in the step B, a water film is first formed on the boron-doped surface of the N-type crystalline silicon wafer, and then placed in the first solution in a floating manner; A water film is formed on the phosphorus-doped surface of the sheet, which is then placed in the second solution in a floating manner for processing. Specifically, a water film is formed by spraying.

In a preferred embodiment, the step B is specifically implemented as follows: a water film is formed on the boron-doped surface of the N-type crystalline silicon wafer, and the N-type crystalline silicon wafer is transmitted by a chain transmission device to make the N-type crystalline silicon wafer The boron doped face upwards and passes through the first solution in a floating manner.

More preferably, the first solution is a mixed solution composed of HF, HNO ₃ and deionized water, or the first solution is a mixed solution composed of HF, HNO ₃ , H ₂ SO ₄ and deionized water, so The transmission speed of the chain transmission device is 1.8～2.2m/s. Specifically, the volume ratio of HF, HNO ₃ , H ₂ SO ₄ and deionized water is (10-20): (80-130): (40-60): 100.

Further, the transmission speed of the chain transmission device is 1.8-2.2 m/s.

In a preferred embodiment, the step E is specifically implemented as follows: a water film is formed on the phosphorus-doped surface of the N-type crystalline silicon wafer, and the N-type crystalline silicon wafer is transmitted by a chain transmission device to make the N-type crystalline silicon wafer The phosphorous doped face upwards and passes through the second solution in a floating manner. Specifically, a water film is formed by spraying.

More preferably, the second solution is a solution composed of HF and deionized water, the volume concentration of HF in the second solution is 3 to 7%, and the transmission speed of the chain transmission device is 1.6 to 2.0 m/s .

Preferably, the alkaline solution in step F is NaOH, KOH, TMAH or NH ₄ OH. More preferably, the alkaline solution is a KOH solution with a volume concentration of 2 to 5%.

Preferably, the thin oxide layer in step C is a thin silicon oxide layer; in step D, phosphorus is doped during the deposition of the polysilicon layer or after the polysilicon layer is deposited.

Preferably, the step H is specifically implemented as follows: the N-type crystalline silicon wafer is oxidized, the oxide on the surface is removed, and then the surface of the N-type crystalline silicon wafer is oxidized.

More preferably, in the step H, the N-type crystalline silicon wafer is first oxidized by an ozone solution or a HNO ₃ solution, and then placed in an HF solution to remove the oxide layer on the surface, and then the N-type crystalline silicon wafer is removed by an ozone solution or HNO ₃ solution The surface of the crystalline silicon wafer is oxidized.

Preferably, the thickness of the water film formed on the boron-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.

Preferably, the thickness of the water film formed on the phosphorus-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.

Preferably, if the first solution is a mixed solution consisting of HF and HNO _3, HF and the volume ratio of HNO ₃ is 1: (5-8), wherein the volume concentration of HF of 49%, HNO ₃ of The volume concentration is 68%.

Preferably, if the first solution is HF, HNO ₃ and a mixed solution composed of H ₂ SO _4, HF, HNO ₃ and H ₂ SO _4, the volume ratio of the above three: (10 ~ 20) :( 80 -130): (40-60), wherein the volume concentration of HF is 49%, the volume concentration of HNO ₃ is 68%, and the volume concentration of H ₂ SO ₄ is 96%.

In a specific and preferred embodiment, the preparation method sequentially includes the following steps:

(1) N-type crystal silicon wafers are made into texturing (the surface forms a pyramid-shaped suede);

(2) Doping with boron on one side of the N-type crystalline silicon wafer after texturing;

(3) After boron-doped silicon wafer, a water film is formed on the boron-doped surface, which is transported in a chain, and the doped surface passes through the first solution in a floating manner. The first solution contains HF, deionized water, and HNO. ₃ and H ₂ SO ₄ ;

(4) Grow a thin layer of SiOx on the back of the N-type crystalline silicon wafer;

(5) Deposit a Polysilicon layer on the back of the N-type crystalline silicon wafer;

(6) Phosphorus is doped in-situ during the deposition of the Polysilicon polysilicon layer, or phosphorus is doped after the deposition of the Polysilicon polysilicon layer;

(7) Phosphorus-doped N-type crystalline silicon wafers, forming a water film on the phosphorus-doped surface, and using chain transport, the phosphorus-doped surface floats through the second solution, where the second solution contains HF;

(8) Place the N-type crystalline silicon wafer in an alkaline solution and react with the silicon through the alkaline solution to remove the doped layer on the edge of the silicon wafer to prevent leakage; the alkaline solution can contain NaOH, KOH, TMAH or NH ₄ OH At least one of and deionized water;

(9) Put the N-type crystalline silicon wafer in a mixed solution of HF and deionized water to remove the phosphorous silicate glass and borosilicate glass on the surface;

(10) The N-type crystalline silicon wafer is oxidized, and the oxidation process can be realized by ozone solution or HNO ₃ solution;

(11) Place the N-type crystalline silicon wafer in a mixed solution of HF and deionization to remove the oxide layer on the surface;

(12) Oxidize the surface of the N-type crystalline silicon wafer. The oxidation process can be achieved by ozone solution or HNO ₃ solution;

(13) Deposit an aluminum oxide layer on the boron-doped surface of the N-type crystalline silicon wafer;

(14) Deposit SiNx layers on the boron-doped surface and phosphorus-doped surface of the N-type crystal silicon wafer;

(15) A metallization process is performed on the surface of the N-type crystal silicon wafer.

The present invention adopts the above scheme and has the following advantages compared with the prior art:

The preparation method of the N-type crystalline silicon battery of the present invention can effectively protect the boron-doped surface and the phosphorus-doped surface of the N-type crystalline silicon battery, solve the problem of battery edge leakage, and significantly reduce the reverse of the N-type crystalline silicon battery. Voltage leakage; the preparation method is simple and suitable for popularization and application.

Description of the drawings

In order to explain the technical solution of the present invention more clearly, the following will briefly introduce the drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. Ordinary technicians can obtain other drawings based on these drawings without creative work.

1 is a schematic diagram of the structure of an N-type crystalline silicon wafer doped with boron in an embodiment of the application;

FIG. 2 is a schematic diagram of the structure of the N-type crystalline silicon wafer after removing the borosilicate oxide generated on the back and side surfaces in FIG. 1;

3 is a schematic diagram of the structure of an N-type crystalline silicon wafer after phosphorus doping in an embodiment of the application;

4 is a schematic diagram of the structure of the N-type crystalline silicon wafer after removing the phosphorous silicon oxide formed on the side surface in FIG. 3;

Fig. 5 is a schematic diagram of the structure of the N-type crystalline silicon wafer obtained after processing Fig. 4 in an alkaline solution;

FIG. 6 is a schematic structural diagram of an N-type crystalline silicon battery prepared in an embodiment of this application;

7 is a schematic diagram of the structure of an N-type crystalline silicon battery prepared in Example 1.

Among them, 1. Front metal electrode; 2. SiNx layer; 3. AlOx layer; 4. Boron doped layer; 5. N-type crystalline silicon wafer; 6. SiO ₂ layer; 7. Polysilicon layer; 8. SiNx layer; 9. The back metal electrode.

Detailed ways

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted here that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

The embodiment of the application provides a method for preparing an N-type crystalline silicon battery, which includes the following steps:

Step 1, doping with boron on one side of the N-type crystalline silicon wafer 5 after texturing.

That is to say, in step 1, the N-type crystalline silicon wafer 5 after texturing is doped with boron on one side.

In the embodiment of the present application, the method for texturing the N-type crystalline silicon wafer 5 may be any feasible method in the prior art, which is not limited in the present application. For example, the front side of the N-type crystalline silicon wafer 5 can be immersed in a texturing solution composed of KOH, texturing additives and deionized water. After erosion, an uneven suede surface is formed on the front side of the N-type crystalline silicon wafer 5, such as , Forming a pyramid suede. The purpose of texturing the surface of the N-type crystalline silicon wafer 5 is mainly to reduce the reflectivity of sunlight on the N-type crystalline silicon wafer 5 and increase the absorption of solar light by the N-type crystalline silicon wafer 5. Among them, the volume concentration of KOH in the texturing solution can be 1%-10%, and the texturing time can be 500 seconds to 2000 seconds. More preferably, the volume concentration of KOH in the texturing solution is 3%, and the texturing time is 800 seconds. second. When the volume concentration of KOH in the texturing solution is 3% and the texturing time is 800 seconds, the degree of erosion of the N-type crystalline silicon wafer by the texturing solution can be better controlled, thereby obtaining an ideal suede.

In the embodiments of the present application, any feasible boron doping treatment method in the prior art can be used, which is not limited in the present application. For example, a thermal diffusion method can be used for the boron doping treatment. After the texture surface of the N-type crystalline silicon wafer 5 is doped with boron elements, a boron doped surface is formed on the texture surface of the N-type crystalline silicon wafer 5.

In the embodiments of the present application, for ease of description, the side of the N-type crystalline silicon wafer 5 subjected to the single-sided boron doping treatment is called the front side, and the other side is called the back side.

It should also be noted that no matter what doping treatment method in the prior art is adopted, gas assisted doping is usually required. For example, in the thermal diffusion method, the N-type crystalline silicon wafer 5 is placed in a diffusion furnace to raise the temperature to a preset temperature, and a boron source, oxygen and nitrogen are introduced to deposit the surface of the N-type crystalline silicon wafer 5. Specifically, the doping source, that is, the boron source can be N2 carrying BBr ₃ , where the flow of N2 carrying BBr ₃ can be 150 sccm, the flow of nitrogen without the source can be 30 SLM, the flow of oxygen can be 600 sccm, and the source time can be 25min, the thermal diffusion temperature can be 900℃. It can be seen that, as shown in Figure 1, in the process of doping the front side of the N-type crystalline silicon wafer 5 with boron, due to the effect of gas, the boron element is not only doped on the front side of the N-type crystalline silicon wafer, but also boron doping is formed. On the surface, the back and sides of the N-type crystalline silicon wafer (that is, the edge of the N-type crystalline silicon wafer) will also be doped with part of boron, and a layer of borosilicate oxide will be formed on the back and side of the N-type crystalline silicon wafer. And, there is a borosilicate impurity layer between the back surface of the N-type crystalline silicon wafer and the borosilicate oxide layer, and between the side surface and the borosilicate oxide.

Step 2: Put the boron-doped N-type crystalline silicon wafer with the boron-doped side up and float it into the first solution for processing, and the first solution includes a mixed solution composed of HF and HNO ₃ , or, A mixed solution composed of HF, HNO ₃ and H ₂ SO ₄ .

In order to eliminate the influence of boron doping on the back and side surfaces of the N-type crystalline silicon wafer in step 1 above, firstly, in step 2, the boro-silicon oxide and boro-silicon impurity layer generated on the back and side surfaces of the N-type crystalline silicon wafer are removed to obtain The structure shown in Figure 2. Specifically, the boron-doped N-type crystalline silicon wafer prepared in step 1 is floated in the first solution, wherein the boron-doped surface of the N-type crystalline silicon wafer does not contact the first solution. In a feasible manner, the first solution is contained in a containing tank provided with a chain transmission device, and the N-type crystal silicon wafer doped with boron is placed on the chain transmission device. Wherein, the boron-doped surface faces upward and does not contact the first solution, so that the first solution only contacts the back and side surfaces of the N-type crystalline silicon wafer.

The first solution is used to remove the borosilicate oxide and borosilicate impurity layers generated on the back and sides of the N-type crystalline silicon wafer. The first solution may be a mixed solution composed of HF and HNO ₃ or a mixed solution composed of HF, HNO ₃ and H ₂ SO ₄ .

If the first solution is a mixed solution composed of HF and HNO ₃ , correspondingly, the volume ratio of HF and HNO ₃ is 1: (5-8), where the volume concentration of HF is 49%, and the volume concentration of HNO ₃ Is 68%. HF is mainly used to remove the borosilicate oxide formed on the back and sides of N-type crystalline silicon wafers, and HNO _{3 is} mainly used to remove the borosilicon impurity layer generated on the back and sides of N-type crystalline silicon wafers. When the volume ratio of HF and HNO ₃ is 1: (5-8), the reaction speed of the first solution and the borosilicate oxide and borosilicate impurity layer on the back and side surfaces of the N-type crystalline silicon wafer can be well controlled to Adapt to the requirements of large-scale industrial production.

If the first solution is a mixed solution composed of HF, HNO ₃ and H ₂ SO ₄ , correspondingly, HF, HNO 3 and H ₂ SO ₄ , the volume ratio of the above three is: (10-20): (80- 130): (40-60), wherein the volume concentration of HF is 49%, the volume concentration of HNO ₃ is 68%, and the volume concentration of H ₂ SO ₄ is 96%. HF is mainly used to remove the borosilicate oxide formed on the back and sides of the N-type crystalline silicon wafer, and HNO ₃ and H ₂ SO ₄ are mainly used to remove the borosilicate impurity layer generated on the back and side of the N-type crystalline silicon wafer. On the one hand, the experimental data shows that the back and sides of the N-type crystalline silicon wafer prepared in step 1 above are cleaned in the first solution containing H ₂ SO ₄ , and the 12V reverse voltage leakage value of the finally prepared battery can reach 0.03-0.09A. On the other hand, in the case of using the above-mentioned volume concentration of H ₂ SO ₄ , H ₂ SO ₄ will weaken the acidity of HNO _{3 to} a certain extent, thereby slowing the erosion rate of the borosilicate impurity layer.

Slowing down the erosion rate of the borosilicate impurity layer can bring about the following benefits: the transmission speed of the N-type crystal silicon wafer driven by the chain transmission device can reach 1.8-4.2m/s, if the first solution is HF, HNO ₃ And H ₂ SO ₄ , and the volume ratio of the above three is: (10-20): (80-130): (40-60), in which the volume concentration of HF is 49%, and that of HNO ₃ The volume concentration is 68%, and the volume concentration of H ₂ SO ₄ is 96%. After the back and side surfaces of the N-type crystalline silicon wafer are processed in the first solution at the above-mentioned transmission speed, the back side of the N-type crystalline silicon wafer is obtained. The borosilicate impurity layer on the side and the side is just completely removed, and will not cause excessive erosion.

When the chain transmission device drives the N-type crystal silicon wafer to move, when the transmission speed of the chain transmission device exceeds 0.5m/s, the first solution will splash to the front of the N-type crystal silicon wafer, thereby destroying the boron doping Borosilicate oxide on the surface. Therefore, it is possible to first form a water film on the boron-doped surface, and then process it in the first solution by means of a chain transfer device, so that the first solution is in contact with the back and side surfaces of the N-type crystalline silicon wafer instead of boron. Doped surface contact. This can eliminate the influence on the back and side surfaces of the N-type crystal silicon wafer during the boron doping treatment in step 1, and can also protect the boron doped surface from being corroded by the first solution. Among them, the method of forming a water film on the boron-doped surface of the N-type crystalline silicon wafer can be a water spray method, for example, a spray device is used to spray water on the boron-doped surface to form a water film.

In a preferred embodiment, the thickness of the water film formed on the boron-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.

If the thickness of the water film formed on the boron-doped surface is less than 0.1mm, when the chain transmission device drives the N-type crystal silicon wafer to move, the splashed first solution will destroy the water film with a thickness of less than 0.1mm, and then erode the water. The boron-doped surface under the film; if the thickness of the water film formed by the boron-doped surface is greater than 5mm, the weight of the water film is too large. With the rapid movement of the chain transmission device, due to the effect of inertia, the boron-doped surface The water film will fall off, and the splashed first solution will attack the boron-doped surface under the water film. If the thickness of the water film formed on the boron-doped surface is 0.1-5mm, which can satisfy the transmission speed of the chain transmission device at 1.8-4.2m/s, the water film will not be damaged by the splashed first solution, nor It will not fall off automatically, thereby ensuring the processing quality of the above step 2 and the processing speed of the above step 2.

Step 3: Prepare a thin oxide layer 6 on the back of the N-type crystalline silicon wafer.

In the embodiments of the present application, the function of the thin oxide layer 6 is mainly to increase the conversion rate of sunlight energy. The oxide thin layer 6 may be a silicon dioxide thin layer or a molybdenum oxide thin layer, etc., which is not limited in this application.

The embodiments of the present application do not limit the method for preparing the thin oxide layer. For example, a thin oxide layer 6 can be directly grown on the back of an N-type crystalline silicon wafer under suitable temperature and atmosphere conditions; another example, a thin oxide layer 6 can be deposited on the back of an N-type crystalline silicon wafer.

Step 4, deposit a polysilicon layer 7 on the thin oxide layer 6, and dope with phosphorus.

Polysilicon has a high conversion rate and mobility, and its photoelectric efficiency will not decay as the illumination time continues.

Further, the phosphorous element may be doped during the deposition of the polysilicon layer 7 or after the polysilicon layer 7 is deposited.

First of all, it should be noted that in step 1, after doping boron on the front side of the N-type crystal silicon wafer, the boron-doped surface obtained includes not only the doped boron element but also the generated boron silicon oxide. In 2, the boron-doped surface is not treated, so the boron silicon oxide on the boron-doped surface will not be damaged. Therefore, as shown in Figure 3, when the polysilicon layer is doped with phosphorus, only the side surface of the N-type crystalline silicon wafer will be affected. Part of the phosphorus is doped to produce phosphorus silicon oxide and phosphorus silicon impurity layer. The boron silicon oxide on the doped surface will block the influence of phosphorus on the boron-doped surface, that is, the boron-doped surface will not be doped with phosphorus.

In addition, for the method of doping phosphorus in step 4, please refer to the method of doping boron in step 1. The main difference is that the doping source and doping conditions are different. When doping phosphorus, the doping source should be Phosphorus source.

Step 5: Put the phosphorus-doped surface on the N-type crystalline silicon wafer upward and float it into a second solution for processing, and the second solution includes HF.

In the above step 4, after phosphorus is doped on the polysilicon layer 7, a phosphorus doped surface is formed. In order to remove the phosphorous silicon oxide generated on the side surface of the N-type crystal silicon wafer and the boron-silicon oxide on the boron-doped surface without destroying the boron-silicon doped layer on the boron-doped surface, the N-type crystal doped with phosphorus The silicon wafer floats in HF, where the phosphorus-doped surface of the N-type crystalline silicon wafer is not in contact with the second solution, and the structure shown in FIG. 4 is obtained after processing. In a feasible way, referring to step 2, the second solution is placed in the containing tank provided with the chain transmission device, and the N-type crystal silicon wafer doped with phosphorus is placed on the chain transmission device. The phosphorous doped surface faces upwards and does not contact the second solution, so that the second solution only contacts the front and side surfaces of the N-type crystalline silicon wafer.

The thickness of the water film formed on the phosphorus-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.

If the thickness of the water film formed on the phosphorus-doped surface is less than 0.1 mm, the second solution splashed by the chain transmission device will drive the N-type crystal silicon wafer to move, which will destroy the water film with a thickness of less than 0.1 mm, and then erode the water. The phosphorus-doped surface under the film; if the thickness of the water film formed by the phosphorus-doped surface is greater than 5mm, the weight of the water film is too large. With the rapid movement of the chain transmission device, due to the effect of inertia, the phosphorus-doped surface The water film will fall off, and the splashed first solution will erode the phosphorus-doped surface under the water film. If the thickness of the water film formed on the phosphorus-doped surface is 0.1-5mm, which can meet the transmission speed of the chain transmission device at 1.8-4.2m/s, the water film will not be destroyed by the splashed first solution, nor It will not fall off automatically, thereby ensuring the processing quality of the above step 5 and the processing speed of the above step 5.

The second solution is used to remove the phosphorous silicon oxide generated on the side surface of the N-type crystal silicon wafer on the one hand, and on the other hand, it can remove the borosilicate oxide on the boron-doped surface and clean the boron-doped surface more cleanly. The volume concentration of HF in the second solution can be 3 to 7%.

Step 6, putting the N-type crystalline silicon wafer treated with the second solution in an alkaline solution for treatment.

After the above steps are processed, in order to prevent some phosphorous silicon impurity layer from remaining on the side of the N-type crystalline silicon wafer, the N-type crystalline silicon wafer processed by the second solution is placed in an alkaline solution for processing. Alkaline solution can react with silicon, but not with oxide. Therefore, only the exposed silicon on the side of the N-type crystalline silicon wafer reacts with the alkaline solution, and the phosphorous silicon impurity layer on the side can be removed, as shown in Figure 5. , The alkaline solution will erode the side of the N-type crystalline silicon wafer with a certain thickness, so that the boron-doped surface on the front side of the N-type crystalline silicon wafer is separated from the phosphorus-doped surface on the back, that is, the boron-doped surface and the phosphorus The doped surface is completely isolated by the N-type crystal silicon wafer in the middle, so there will be no leakage.

Among them, the alkaline solution can be NaOH, KOH, TMAH or NH ₄ OH, which is not limited in this application. Preferably, the alkaline solution is a KOH solution with a volume concentration of 2 to 5%. Since the function of the alkaline solution in step 6 is to erode a certain thickness of silicon and completely isolate the boron-doped surface from the phosphorus-doped surface on the back. Therefore, if the concentration of the alkaline solution is too low, the erosion will be too slow, To be effective, if the concentration of the alkaline solution is too high, the erosion will be too fast, and the solution will cause excessive erosion. When the alkaline solution is a KOH solution with a volume concentration of 2 to 5%, it can not only achieve the effect of erosion, but also control the rate of erosion by way of excessive erosion.

Step 7, removing the phosphosilicate glass and the borosilicate glass on the surface of the N-type crystalline silicon wafer treated with the alkaline solution.

Further, HF can be used to remove the phosphorous silicate glass on the phosphorus-doped surface and the borosilicate glass on the boron-doped surface. Phosphosilicate glass and borosilicate glass refer to phosphorous silicon oxide and borosilicate oxide, respectively. After removing the phosphorous silicate glass and the borosilicate glass, the boron-doped surface is silicon doped only with boron element, and the phosphorus-doped surface is silicon doped only with phosphorus element.

Step 8, oxidize the surface of the N-type crystalline silicon wafer processed in Step 7.

Specifically, the N-type crystalline silicon wafer can be first placed in a mixed solution of HF and deionized to remove the surface oxide layer; then the surface of the N-type crystalline silicon wafer can be oxidized. The oxidation process can be achieved by an ozone solution or a HNO ₃ solution.

Further, an aluminum oxide layer is deposited on the boron-doped surface of the N-type crystalline silicon wafer after surface oxidation.

Depositing an oxide layer on the boron-doped surface can improve the conversion efficiency of solar energy. For example, a layer of aluminum oxide is deposited on the boron-doped surface, and the thickness of the aluminum oxide layer may be 6 nm.

Step 9, deposit a first passivation anti-reflection layer 2 on the boron-doped surface of the N-type crystal silicon wafer, and deposit a second passivation anti-reflection layer 8 on the phosphorus-doped surface.

In the embodiment of the present application, the materials of the first passivation anti-reflection layer 2 and the second passivation anti-reflection layer 8 are not limited. The materials of the first passivation anti-reflection layer 2 and the second passivation anti-reflection layer 8 are The structure can be the same or different. The first passivation anti-reflection layer 2 and the second passivation anti-reflection layer 8 may be a single-layer structure or a multi-layer composite structure. The materials of the first passivation anti-reflection layer 2 and the second passivation anti-reflection layer 8 can be any material that can be used for anti-reflection in the prior art, such as silicon nitride.

Step 10: Perform a metallization process to form a front metal electrode and a back metal electrode.

In the embodiments of the present application, any method of preparing metal electrodes in the prior art can be used, for example, silver paste is printed on the first passivation anti-reflection layer 2 and dried at a drying temperature of 300°C; The anti-reflection layer 8 is brushed with aluminum paste and sintered, and the sintering temperature is 900°C.

It should be noted that both the front metal electrode and the back metal electrode adopt conductive metal materials, such as copper, silver, iron, etc., which are not limited in this application.

In summary, the method for preparing an N-type crystalline silicon battery provided by the implementation of this application firstly dope the front surface of the N-type crystalline silicon wafer with boron, and then remove the side of the N-type crystalline silicon wafer in a floating manner in the first solution. And the borosilicate oxide on the back side, and then dope the back of the N-type crystalline silicon wafer with phosphorus, and then float the phosphorus-silicon oxide on the side of the N-type crystalline silicon wafer in the second solution. After the N-type crystalline silicon wafer treated by the second solution is put into an alkaline solution for processing, the boron-doped surface and the phosphorus-doped surface are completely isolated by the middle N-type crystalline silicon wafer, so there will be no leakage . Therefore, as shown in FIG. 6, using the N-type crystalline silicon wafer whose boron-doped surface is completely isolated from the phosphorus-doped surface, the prepared N-type crystalline silicon cell will not leak.

Example one

Figure 7 shows an N-type crystalline silicon battery prepared in this embodiment, including a front metal electrode 1, a SiNx layer 2, an AlOx layer 3, a boron-doped layer 4, an N-type crystalline silicon wafer 5, and a SiO ₂ layer 6. , Polysilicon polysilicon layer 7, SiNx layer 8, and back metal electrode 9, including SiNx layer 2, AlOx layer 3, boron doped layer 4, N-type crystalline silicon wafer 5, SiO ₂ layer 6, Polysilicon polysilicon layer 7 and SiNx layer 8 Stacked sequentially from top to bottom, the front metal electrode 1 passes through the SiNx layer 2 and the AlOx layer 3 to form an ohmic contact with the boron doped layer 4, and the back metal electrode 9 passes through the SiNx layer 8 to form an ohmic contact with the Polysilicon layer 7.

Among them, the SiNx layer 2 refers to a silicon nitride layer, and the AlOx layer 3 refers to an aluminum oxide layer.

Use the following steps to prepare the N-type crystalline silicon battery as shown in Figure 7, prepare a set of N-type crystalline silicon wafers (50 pieces) for the following treatment:

(1) The N-type crystalline silicon wafer is texturized, and the surface of the silicon wafer forms a pyramid texture. The texturing solution uses KOH, texturing additives and deionized water, the volume concentration of KOH is 3%, and the texturing time is 800 seconds;

(2) with boron diffusion tube of doped N-type silicon single-sided, as the dopant source carrying BBr3 ₃ N _2, wherein N ₂ flow carrying BBr3 ₃ 150 sccm, flow rate of 30 SLM do not carry a source of nitrogen, oxygen flow was 600sccm , The source time is 25min, the temperature is 900℃;

(3) A water film is formed on the boron-doped surface, which is transported in a chain, with the water film facing upwards, and floats through the first solution composed of HF, HNO ₃ , H ₂ SO ₄ and deionized water, in which 30L of HF solution , HNO ₃ solution 230L, H ₂ SO ₄ solution 60L, deionized water 200L, solution temperature 16°C, conveyor speed 2m/s;

(4) Using LPCVD to grow a thin layer of SiOx on the non-boron-doped surface of an N-type crystal silicon wafer;

(5) Use LPCVD to deposit a Polysilicon layer on the non-boron-doped surface of an N-type crystal silicon wafer;

(6) using N-type phosphorus diffusion tube of non-crystal boron-doped silicon surface phosphorus is doped, dopant source carrying POCl N ₂ _3, wherein the carrying POCl N ₂ flow rate of 100 sccm _3, carry no flow of nitrogen source 5SLM , The oxygen flow rate is 600sccm, the source time is 30min, and the temperature is 880℃;

(7) Using a chain cleaner to form a water film on the phosphorus-doped surface, and float through the mixed solution of HF and deionized water, the HF solubility is 5%, and the transmission speed is 1.8m/s;

(8) Place the N-type crystalline silicon wafer in the KOH alkaline solution, the KOH volume concentration is 3%, and the reaction time is 600 seconds;

(9) Place the N-type crystal silicon wafer in the HF solution, the volume concentration of the HF solution is 5%, and the reaction time is 300 seconds;

(10) Place the N-type crystal silicon wafer in the HNO ₃ solution, the volume concentration of the HNO ₃ solution is 67%, and the reaction time is 300 seconds;

(11) Place the N-type crystal silicon wafer in the HF solution, the volume concentration of the HF solution is 5%, and the reaction time is 300 seconds;

(12) Place the N-type crystalline silicon wafer in the HNO ₃ solution, the volume concentration of the HNO ₃ solution is 67%, and the reaction time is 300 seconds;

(13) Using atomic layer deposition (ALD) to deposit an AlOx layer on the boron-doped surface of the N-type crystalline silicon wafer, the thickness of the AlOx layer is 6nm;

(14) Deposit SiNx layers on the back and front sides of the N-type crystalline silicon wafer, the thickness of the SiNx layer is 90nm, and the refractive index is 2.05;

(15) Silver paste is printed on the phosphorus-doped surface of the N-type crystal silicon wafer and dried at a temperature of 300°C;

(16) Brush aluminum paste on the boron-doped surface of the N-type crystalline silicon wafer and sinter, and the maximum sintering temperature is 900℃.

Example two

The second embodiment is basically the same as the first embodiment above, except that the first solution in step (3) of the second embodiment is composed of HF, HNO ₃ , H ₂ SO ₄ and deionized water. Among them, the HF solution is 18L, HNO ₃ 121L of solution, 60L of H ₂ SO ₄ solution, 140L of deionized water, solution temperature of 16°C, and conveyor speed of 2m/s.

Example three

The third embodiment is basically the same as the above-mentioned first embodiment. The difference is that in step (3) of the third embodiment, the first solution is composed of HF, HNO ₃ , H ₂ SO ₄ and deionized water, wherein the HF solution is 20L, HNO ₃ 150L of solution, 66L of H ₂ SO ₄ solution, 150L of deionized water, solution temperature of 16°C, and conveyor speed of 2m/s.

Example four

The fourth embodiment is basically the same as the first embodiment above. The difference is that the first solution in step (3) of the fourth embodiment is composed of HF, HNO ₃ , H ₂ SO ₄ and deionized water. Among them, 40L of HF solution, HNO ₃ Solution 200L, H ₂ SO ₄ solution 76L, deionized water 286L, solution temperature 16°C, conveyor speed 2m/s.

Example five

The fifth embodiment is basically the same as the first embodiment above. The difference is that the first solution in step (3) of the fourth embodiment is composed of HF, HNO ₃ and deionized water. Among them, 30L of HF solution and 200L of HNO ₃ solution are used to remove Ionized water 200L, solution temperature 16°C, conveyor speed 2m/s.

Example Six

The sixth embodiment is basically the same as the above-mentioned first embodiment. The difference is that in step (3) of the sixth embodiment, the first solution is composed of HF, HNO ₃ and deionized water. Among them, 18L of HF solution and 120L of HNO ₃ solution are used. Ionized water 130L, solution temperature 16°C, conveyor speed 2m/s.

Example Seven

The seventh embodiment is basically the same as the above-mentioned first embodiment. The difference is that in step (3) of the seventh embodiment, the first solution is composed of HF, HNO ₃ and deionized water. Among them, 40L of HF solution and 200L of HNO ₃ solution are used. Ionized water is 260L, the solution temperature is 16℃, and the conveyor speed is 2m/s.

Comparative example one

Use the following steps to prepare N-type crystalline silicon cells, prepare a set of N-type crystalline silicon wafers (50 pieces) for the following treatments:

(2) using the N-type boron diffusion tube sided crystal silicon wafer doped, dopant source carrying BBr3 ₃ N _2, wherein N ₂ flow carrying BBr3 ₃ 150 sccm, flow rate of 30 SLM do not carry a source of nitrogen, oxygen flow is 600sccm, source time 25min, temperature 900℃;

(3) Using LPCVD to grow a thin SiOx layer on the non-boron-doped surface of an N-type crystal silicon wafer;

(4) Use LPCVD to deposit a Polysilicon layer on the non-boron-doped surface of an N-type crystal silicon wafer;

(5) a non-boron-doped N-type silicon doped with phosphorus is phosphorus surface diffuser, doped source carrying POCl N ₂ _3, wherein the carrying POCl N ₂ flow rate of 100 sccm _3, 5 SLM do not carry a source of nitrogen flow, the oxygen Flow 600sccm, source time 30min, temperature 880℃;

(6) Place the N-type crystal silicon wafer in the HF solution, the volume concentration of the HF solution is 5%, and the reaction time is 300 seconds;

(7) Place the N-type crystalline silicon wafer in the HNO ₃ solution, the volume concentration of the HNO ₃ solution is 67%, and the reaction time is 300 seconds;

(8) Place the N-type crystalline silicon wafer in the HF solution, the volume concentration of the HF solution is 5%, and the reaction time is 300 seconds;

(9) Place the N-type crystalline silicon wafer in the HNO ₃ solution, the volume concentration of the HNO ₃ solution is 67%, and the reaction time is 300 seconds;

(10) Using atomic layer deposition (ALD) to deposit an AlOx layer on the boron-doped surface of the N-type crystalline silicon wafer, the thickness of the AlOx layer is 6nm;

(11) Deposit SiNx layers on the back and front sides of the N-type crystalline silicon wafer, with a thickness of 90nm and a refractive index of 2.05;

(12) Silver paste is printed on the phosphorus-doped surface of the N-type crystalline silicon wafer, and the drying process is carried out at a drying temperature of 300°C;

(13) The silver-aluminum paste is printed on the boron-doped surface of the N-type crystal silicon wafer, and the sintering process is carried out. The maximum sintering temperature is 900°C.

After the battery is prepared, 5 pieces are randomly selected from the batteries obtained in Example 1 and Comparative Example 1, and the leakage of the two groups of batteries is tested by a battery IV tester. The leakage test data obtained are shown in Table 1 and Table 2, respectively. Show. Two batteries were randomly selected from each of the battery slices obtained in Example 2 to Example 7. The battery IV tester was used to test the leakage of each group of battery slices. The leakage test data obtained are shown in Table 3, respectively.

Table 1 Leakage test data of the battery slice in Example 1

Table 2 Leakage test data of the battery slice of Comparative Example 1

Table 3 Leakage test data of the battery slices of Example 2 to Example 7

From Table 1, Table 2 and Table 3, it can be seen that the 12V reverse voltage leakage of the cells prepared by the preparation methods of Example 1 to Example 7 are all small, which solves the leakage problem and significantly reduces the N-type crystalline silicon battery. Reverse voltage leakage. It can also be seen from Table 2 that after treating the N-type crystalline silicon wafer with the first solution containing H ₂ SO ₄ , the 12V reverse voltage leakage value of the prepared battery can reach 0.03-0.09A.

The above-mentioned embodiments are only to illustrate the technical concept and features of the present invention, and are a preferred embodiment. The purpose is that those familiar with the technology can understand the content of the present invention and implement it accordingly, and cannot limit the present invention. protected range. All equivalent changes or modifications made according to the principles of the present invention should be covered by the protection scope of the present invention.

Claims

A method for preparing an N-type crystalline silicon battery is characterized in that it sequentially includes the following steps:

A. Doping with boron on one side of the textured N-type crystalline silicon wafer;

B. Place the boron-doped N-type crystalline silicon wafer with the boron-doped side up and float it into the first solution for processing. The first solution includes a mixed solution composed of HF and HNO 3 , or HF , A mixed solution composed of HNO 3 and H 2 SO 4 ;

C. Grow a thin oxide layer on the other side of the N-type crystalline silicon wafer;

D. Deposit a polysilicon layer on the thin oxide layer and dope with phosphorus;

E. Put the phosphorus-doped surface on the N-type crystalline silicon wafer upward and float it into the second solution for processing, and the second solution includes HF;

F. Put the N-type crystalline silicon wafer treated by the second solution in an alkaline solution for treatment;

G. Remove the phosphosilicate glass and borosilicate glass on the surface of the N-type crystal silicon wafer treated with the alkaline solution;

H. Oxidize the surface of the N-type crystalline silicon wafer after the above step G treatment;

I. Deposit a first passivation anti-reflection layer on the boron-doped surface of the N-type crystalline silicon wafer, and deposit a second passivation anti-reflection layer on the phosphorus-doped surface;

J. Perform a metallization process to form a front metal electrode and a back metal electrode.
The preparation method according to claim 1, wherein in the step B, a water film is formed on the boron-doped surface of the N-type crystalline silicon wafer, and then placed in the first solution in a floating manner for processing; In the step E, a water film is formed on the phosphorus-doped surface of the N-type crystalline silicon wafer, and then placed in the second solution in a floating manner for processing.
The preparation method according to claim 1 or 2, wherein the step B is specifically implemented as follows: a water film is formed on the boron-doped surface of an N-type crystalline silicon wafer, and a chain transmission device is used to transport the N-type crystalline silicon wafer , Make the boron-doped N-type crystalline silicon wafer face upward and pass the first solution in a floating manner.
The preparation method according to claim 3, wherein the first solution is a mixed solution composed of HF, HNO 3 and deionized water, or the first solution is HF, HNO 3 , H 2 SO 4 For the mixed solution composed of deionized water, the transmission speed of the chain transmission device is 1.8-2.2 m/s.
The preparation method according to claim 1 or 2, wherein the step E is specifically implemented as follows: a water film is formed on the phosphorus-doped surface of an N-type crystalline silicon wafer, and a chain transmission device is used to transfer the N-type crystalline silicon wafer , Make the phosphorous doped surface of the N-type crystalline silicon wafer upward and pass through the second solution in a floating manner.
The preparation method according to claim 1, wherein the second solution is a solution composed of HF and deionized water, the volume concentration of HF in the second solution is 3 to 7%, and the chain transmission device The transmission speed is 1.6～2.0m/s.
The preparation method according to claim 1, wherein the alkaline solution in step F is a KOH solution with a volume concentration of 2 to 5%.
The preparation method according to claim 1, wherein the thin oxide layer in step C is a thin silicon oxide layer; in step D, during the deposition of the polysilicon layer or after the polysilicon layer is deposited Miscellaneous phosphorus elements.
The preparation method according to claim 1, wherein the step H is specifically implemented as follows: oxidize the N-type crystalline silicon wafer, remove the surface oxide, and then oxidize the surface of the N-type crystalline silicon wafer.
The preparation method according to claim 1, characterized in that, in the step I, an aluminum oxide layer and a silicon nitride layer are sequentially deposited on the boron-doped surface on the N-type crystalline silicon wafer, and A silicon nitride layer is deposited on the phosphorus-doped surface.
The preparation method according to claim 3, wherein the thickness of the water film formed on the boron-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.
The preparation method according to claim 5, wherein the thickness of the water film formed on the phosphorus-doped surface is 0.1-5 mm, and the transmission speed of the chain transmission device is 1.8-4.2 m/s.
The production method according to claim 1, wherein, if the first solution is a mixed solution consisting of HF and HNO 3, HF and the volume ratio of HNO 3 is 1: (5-8), wherein, The volume concentration of HF is 49%, and the volume concentration of HNO 3 is 68%.
The production method according to claim 1, wherein, if the first solution is a mixed solution of HF, HNO 3 and H 2 SO 4 consisting of HF, HNO 3 and H 2 SO 4, more than three volume, The ratio is: (10-20): (80-130): (40-60), where the volume concentration of HF is 49%, the volume concentration of HNO 3 is 68%, and the volume concentration of H 2 SO 4 is 96%. .