CN105140334B - Solar cell selective doping method based on counter diffusion - Google Patents

Abstract

The invention relates to a method for selective doping of solar cells based on reverse diffusion. The steps are as follows: placing a silicon wafer in an oxygen environment for high-temperature diffusion to form a PN junction, while the upper surface of the silicon wafer is oxidized; removing the top electrode region of the silicon wafer Deposit an intrinsic amorphous silicon layer on the upper surface of the silicon wafer; place the silicon wafer in a wet oxygen environment for high-temperature diffusion, so that the doping elements in the non-top electrode area diffuse reversely into the amorphous silicon layer, and the top The doping element in the oxide layer of the electrode area diffuses to the top electrode area, and at the same time, the surface of the silicon wafer in the amorphous silicon layer and the non-top electrode area is oxidized to form an oxide layer; the oxide layer on the surface of the silicon wafer is removed to complete the reverse diffusion selection of the solar cell Sexual doping. The present invention adopts the method of reverse diffusion, and absorbs the impurities in the non-top electrode region through amorphous silicon, so that the doping concentration of the non-top electrode region is reduced, and at the same time, the top electrode region is doped twice, resulting in the difference between the top electrode region and the non-top electrode region. The doping concentration difference between regions is further increased, which improves the effect of selective doping.

Description

Selective Doping Method for Solar Cells Based on Reverse Diffusion

technical field

The invention relates to a method for selective doping of solar cells based on reverse diffusion, and belongs to the technical field of solar cell manufacturing.

Background technique

With the improvement of people's awareness of environmental protection, the demand for clean energy is increasing. Among the new clean energy researched by people, solar energy, as a clean energy that is not subject to geographical restrictions, has become the main direction of new energy development in the future. Solar cells are the main devices that people use the sun's light energy to convert into electrical energy. However, the conversion efficiency of solar cells cannot meet people's requirements at present. Improving the conversion efficiency of solar cells and reducing the manufacturing cost of solar cells has become a research hotspot.

Selectively doped solar cells are an effective low-cost and high-efficiency solar cell. The structural feature of selectively doped solar cells is that heavy doping is carried out on the top electrode coverage area of the solar cell to reduce the contact resistance of the cell, while light doping is carried out on the non-top electrode area to improve the spectral response of the cell and reduce the photogenerated load in the cell. compound flow. At present, the methods for selective doping of solar cells mainly include: two-step diffusion method, screen printing phosphatization method, diffusion mask method, etc. Among them, the two-step diffusion method is to firstly diffuse the top electrode area, and then lightly diffuse the entire emission area. Control; the screen phosphate slurry method is to use a screen to print a high-concentration phosphate slurry locally. Through its diffusion and volatilization, one diffusion can make the top electrode area form a heavy doping, and other areas form a light doping. However, due to the use of local Phosphorus slurry as a diffusion source will inevitably lead to inhomogeneity of surface diffusion, which will reduce the efficiency of the cell. The diffusion mask method is to lightly dope first, then perform laser or photolithography masking, and then carry out secondary heavy doping on the top electrode area. This method reduces the selectivity of the top electrode area due to light doping first. The difference in impurity concentration between doping and the substrate can better control the selective doping area of the cell, but laser or photolithography is required, which increases the cost and reduces the production efficiency.

To sum up, the current main selective doping methods all have certain defects. Therefore, it is necessary to find a new selective doping solar cell production process.

Contents of the invention

The object of the present invention is to overcome the above-mentioned defects in the prior art, and propose a method for selective doping of solar cells based on reverse diffusion, which has simple process implementation, low production cost, and good performance of the obtained solar cells.

In order to achieve the above object, the solar cell selective doping method based on reverse diffusion proposed by the present invention comprises the following steps:

Step 1. Place the silicon wafer in a humid oxygen environment for high-temperature diffusion to form a PN junction, and at the same time, an oxide layer is formed on the upper surface of the silicon wafer, which contains high-concentration doping elements;

Step 2, removing the oxide layer other than the top electrode region on the upper surface of the silicon wafer;

Step 3, depositing an intrinsic amorphous silicon layer on the upper surface of the silicon wafer;

Step 4, place the silicon wafer in a humid oxygen environment for high temperature diffusion, so that the doping elements in the non-top electrode area of the silicon wafer can diffuse into the amorphous silicon layer, reduce the concentration of doping elements in the non-top electrode area of the silicon wafer, and achieve doping Reverse diffusion of elements; the doping elements in the oxide layer of the top electrode area diffuse to the top electrode area to achieve heavy doping of the top electrode area, and at the same time, the surface of the amorphous silicon layer and the silicon wafer in the non-top electrode area is oxidized to form an oxide layer;

In step 5, the oxide layer on the surface of the silicon wafer is removed, and the reverse diffusion selective doping of the solar cell is completed.

The present invention proposes a selective doping method of reverse diffusion, which absorbs impurities in the non-electrode region through amorphous silicon, so that the doping concentration of the non-electrode region is reduced, and at the same time, the electrode region is doped twice, causing the electrode region to be separated from the electrode region. The doping concentration difference in the non-electrode area is further increased, which improves the effect of selective doping; and when the reverse diffusion process is carried out, due to the protection of the oxide layer, the oxidation degree of the silicon wafer surface in the electrode area is low, and the oxidation degree of the silicon wafer in the non-electrode area is low. The silicon surface is oxidized to form an oxide layer, so that after the oxide layer is removed, the electrode area is convex to a certain extent, which is conducive to the positioning of subsequent electrodes.

The further improvement of the present invention is:

1. The silicon wafer is P-type single crystal silicon. In the first step, the silicon wafer is first placed in a wet oxygen environment for high-temperature pre-diffusion, so that phosphorus element diffuses into the silicon wafer to form a PN junction, and the surface of the silicon wafer is oxidized at the same time Phosphosilicate glass is formed.

2. In step 1, the thickness of the oxide layer is about 0.05 microns, the concentration of phosphorus in the oxide layer is about 1e19/cm ³ , the process temperature of high temperature pre-diffusion is 1000°C, and the duration is 30 minutes.

3. The silicon wafer is N-type single crystal silicon. In the first step, the silicon wafer is first placed in a humid oxygen environment for high-temperature pre-diffusion, so that boron element diffuses into the silicon wafer to form a PN junction, and at the same time, the surface of the silicon wafer is covered with Oxidation forms borosilicate glass.

4. In step 1, the thickness of the oxide layer is about 0.05 microns, the concentration of boron in the silicon thin layer is about 1e19/cm ³ , the process temperature of high temperature pre-diffusion is 1000°C, and the duration is 30 minutes.

5. In the second step, the oxide layer in the top electrode area is retained by screen printing, and the oxide layer in other areas on the silicon wafer is removed by hydrofluoric acid buffer.

6. In the third step, the thickness of the deposited intrinsic amorphous silicon layer is about 40-50 nm.

7. In the fourth step, the process temperature of high-temperature diffusion is 900°C-1100°C, and the duration is 30-2 minutes.

8. In the fifth step, a hydrofluoric acid buffer solution is used to remove the oxide layer on the surface of the silicon wafer.

The feature of this processing method of the present invention is:

1. Different from the traditional selective doping process, the whole chip is heavily doped first, and then the impurities on the light-receiving surface are diffused backwards to reduce the doping concentration of impurities on the light-receiving surface.

2. The intrinsic amorphous silicon film is used to absorb the impurities in the doped area on the surface of the battery, so that the surface of the battery will not be polluted by other different elements.

3. The phosphosilicate glass in the electrode area is reserved as the electrode impurity protection layer in the high-temperature impurity reverse diffusion process, which ensures the heavy doping of the electrode area.

4. The method of wet oxidation is adopted in the impurity reverse diffusion process to oxidize the amorphous silicon layer, which reduces the steps of removing the amorphous silicon film and improves the production efficiency.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Fig. 1 is a schematic process flow diagram of the method of the present invention.

FIG. 2 is a schematic diagram of a simulation of impurity distribution on a silicon wafer obtained by a method according to Embodiment 1 of the present invention.

FIG. 3 is a schematic diagram of a simulation of impurity distribution on a silicon wafer obtained by the method in Embodiment 2 of the present invention.

FIG. 4 is a schematic diagram of a simulation of impurity distribution on a silicon wafer obtained by the method of Embodiment 3 of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Embodiment one

As shown in Figure 1, it is a schematic flow chart of the method for selective doping of solar cells based on reverse diffusion in the present invention, which specifically includes the following steps:

1a. Place the P-type monocrystalline silicon wafer in a humid oxygen environment for high-temperature pre-diffusion, so that phosphorus element diffuses into the silicon wafer to form a PN junction. At the same time, a phosphosilicate glass layer 1 with a thickness of about 0.05 microns is formed on the silicon wafer surface. The concentration of phosphorus in the glass layer 1 is about 1e19/cm ³ ; the process temperature of high temperature pre-diffusion is 1000°C, and the duration is 30 minutes;

2a. Retain the phosphosilicate glass in the top electrode area by screen printing, and remove the phosphosilicate glass in other areas on the silicon wafer with hydrofluoric acid buffer;

3a. Depositing an intrinsic amorphous silicon layer 2 with a thickness of about 40 nm on the upper surface of the silicon wafer;

4a. Place the silicon wafer in a humid oxygen environment for high-temperature diffusion, so that the doping elements (phosphorus) in the non-top electrode area of the silicon wafer can diffuse into the amorphous silicon layer, reducing the concentration of doping elements in the non-top electrode area of the silicon wafer, and realizing Reverse diffusion of doping elements; the doping element (phosphorus) in the oxide layer of the top electrode area diffuses to the top electrode area to achieve heavy doping of the top electrode area, and at the same time, the surface of the amorphous silicon layer and the silicon wafer in the non-top electrode area is oxidized Forming the phosphosilicate glass layer 1; the process temperature of high-temperature diffusion is 900° C., and the duration is 30 minutes;

5a. Using a hydrofluoric acid buffer solution to remove the phosphosilicate glass on the surface of the silicon wafer to complete the reverse diffusion selective doping of the solar cell.

After using the simulation software to simulate the method of the first embodiment, the impurities in the silicon wafer are shown in FIG. 2 . The curves in the simulation result graph respectively represent the concentration of the doping element (phosphorus) and the position of the PN junction.

Embodiment two

The steps of this example are the same as those of Example 1, the difference lies in the process parameters of high-temperature diffusion in dry oxygen environment in step 4a (the fourth step). In this example, the process temperature of high-temperature diffusion is 1000°C, and the duration is 5 minutes . After using the simulation software to simulate the method of the second embodiment, the impurities in the silicon wafer are shown in FIG. 3 . The curves in the simulation result graph respectively represent the concentration of the doping element (phosphorus) and the position of the PN junction.

Embodiment Three

The steps of this example are the same as those of Example 1, the difference lies in the process parameters of high-temperature diffusion in dry oxygen environment in step 4a (the fourth step). In this example, the process temperature of high-temperature diffusion is 1100°C, and the duration is 2 minutes . After using the simulation software to simulate the method of the third embodiment, the impurities in the silicon wafer are shown in FIG. 4 . The curves in the simulation result graph respectively represent the concentration of the doping element (phosphorus) and the position of the PN junction.

Comparing the three embodiments of the present invention, it can be seen from the simulation results that the PN junction of the battery is continuously deepened with the increase of the high-temperature diffusion temperature of the reverse diffusion process. The impurity concentration on the surface of the battery first increases and then decreases, but the impurity concentration in the top electrode region gradually increases with the increase of temperature. The heavily doped impurities in the top electrode region mainly diffuse into the battery body, and the lateral diffusion is small. This is related to the deposition of the intrinsic amorphous silicon layer on the surface of the battery. Excessive lateral diffusion impurities are absorbed by the amorphous silicon layer. This shows that using the amorphous silicon layer as the reverse diffusion layer of the battery can limit the lateral diffusion of impurities in the heavily doped region. The impurity concentration in the lightly doped region is relatively close, and the lower diffusion temperature can effectively form a shallow junction and improve the short-wave spectral response of the battery. After a comprehensive comparison, it can be seen that in step 4a (the fourth step), the diffusion temperature of 900°C and the diffusion duration 30 minutes is a better impurity reverse diffusion process condition.

The embodiment part of the present invention takes P-type single crystal silicon as an example to describe the process of the present invention in detail. The process and conditions for selective doping of N-type single crystal silicon are similar to it, the only difference is that the doping element is replaced by phosphorus In addition to boron, those skilled in the art can fully realize the reverse diffusion selective doping of N-type single crystal silicon by understanding the part of this embodiment and drawing inferences from facts. Therefore, this article will not repeat them.

In addition to the above-mentioned embodiments, the present invention can also have other implementations. All technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims (3)

1. A method for selective doping of solar cells based on reverse diffusion, comprising the steps of: Step 1. Place the N-type monocrystalline silicon wafer in a wet oxygen environment for high-temperature pre-diffusion, so that boron diffuses into the silicon wafer to form a PN junction, and at the same time, the surface of the silicon wafer is oxidized to form a borosilicate glass layer; in the oxide layer Contains a high concentration of boron, and the thickness of the formed oxide layer is 0.05 microns. The concentration of boron in the oxide layer is about 1e19/cm ³ . The process temperature of high-temperature pre-diffusion is 1000°C, and the duration is 30 minutes; Step 2, removing the oxide layer other than the top electrode region on the upper surface of the silicon wafer; Step 3, depositing an intrinsic amorphous silicon layer with a thickness of 40-50 nm on the surface of the silicon wafer; Step 4: Place the silicon wafer in a wet oxygen environment for high-temperature diffusion, so that the boron element in the non-top electrode area of the silicon wafer can diffuse into the intrinsic amorphous silicon layer, reduce the concentration of boron in the non-top electrode area of the silicon wafer, and realize the boron element Reverse diffusion; the boron element in the oxide layer of the top electrode area diffuses to the top electrode area to realize the heavy doping of the top electrode area, and at the same time, the intrinsic amorphous silicon layer and the silicon wafer surface of the non-top electrode area are oxidized to form an oxide layer; In the fourth step, the process temperature of high-temperature diffusion is 900°C, and the duration is 30 minutes; Step 5: remove all oxide layers on the surface of the silicon wafer, and complete the reverse diffusion selective doping of the solar cell. 2. The method for selective doping of solar cells based on reverse diffusion according to claim 1, characterized in that: in the second step, the oxide layer of the top electrode region is retained by screen printing, and the silicon wafer is The oxide layer in other areas was removed with hydrofluoric acid buffer. 3. The method for selective doping of solar cells based on reverse diffusion according to claim 1, characterized in that: in the fifth step, a hydrofluoric acid buffer solution is used to remove the oxide layer on the surface of the silicon wafer.