Preparation method of BC battery without mask

Abstract

The invention relates to the technical field of solar cells, and particularly discloses a preparation method of a BC cell without a mask, and the method comprises the steps: sequentially depositing a P-type amorphous silicon layer and an N-type amorphous silicon layer, and then carrying out the boron doping propelling of a P region through laser, and carrying out the high-temperature phosphorus doping junction propelling. High energy and high heat energy are provided for a P-type amorphous silicon layer in a P region while patterning is carried out, so that boron atoms penetrate into a silicon substrate, and a blocking layer similar to bubbles is formed to block immersion of phosphorus atoms; on the other hand, the high temperature of 800-820 DEG C (not reaching the diffusion temperature of boron atoms) is selected to carry out phosphorus diffusion on the N region, phosphorus atoms penetrate through the P-type amorphous silicon layer to reach the silicon substrate to carry out doping diffusion, and simultaneous preparation of the P region and the N region on the back surface can be realized without a mask, so that the production cost is reduced, the environmental pollution is reduced, and the environmental friendliness of the cell is improved; and the production efficiency and quality of the battery can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a method for preparing a mask-free BC cell. Background Art

[0002] Currently, P-type PERC monocrystalline solar cells are the cell type with the largest market share in photovoltaic cells. However, due to the limitations of technical mechanisms, the conversion efficiency of P-type PERC monocrystalline solar cells has reached a bottleneck. As the oldest crystalline silicon cell technology, BC cell technology not only has a cell structure with the highest conversion efficiency potential, but also has the ability to be inclusive and continuously absorb the process advantages and passivation technologies of other crystalline silicon technology routes to continuously improve conversion efficiency.

[0003] Currently, BC batteries need to repeatedly use masks (twice) when preparing the back P and N regions to control the distribution and shape of the material to improve the performance of the battery, and the mask needs to be repeatedly removed by laser + wet method, which not only increases the preparation cost and complexity of the battery, but may also introduce additional pollution and defects, affecting the performance and life of the battery.

[0004] Therefore, it is particularly important to develop a mask-free BC battery preparation method to reduce preparation cost and complexity and improve battery performance and life. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a BC battery without a mask, which can significantly shorten the production process of the BC battery and reduce the process steps of the BC battery production. At the same time, it does not require expensive equipment, thereby realizing the feasibility of mass production of the BC battery and effectively improving the conversion efficiency and conversion potential of the battery.

[0006] In order to achieve the above object, the present invention provides a method for preparing a BC battery without a mask, comprising the following steps:

[0007] (1) Double-sided polishing of silicon substrate;

[0008] (2) A layer of P-type amorphous silicon and a layer of N-type amorphous silicon are sequentially deposited on the back of the silicon substrate;

[0009] (3) Laser doping is used on the back of the silicon substrate to promote the doping of the P region and to complete the electrode patterning at the same time;

[0010] (4) A high-temperature furnace tube on the back of the silicon substrate performs doping and push-in of the N region;

[0011] (5) De-plating on the front side of the silicon substrate;

[0012] (6) The silicon substrate is alkali-etched and pickled in sequence, the front side is textured, and the amorphous silicon and poly silicon in the P and N regions are removed from the back side;

[0013] (7) Aluminum oxide is deposited on both sides of the silicon substrate;

[0014] (8) Deposition of silicon nitride film on both sides of silicon substrate;

[0015] (9) Screen printing is performed on the back side of the silicon substrate to produce a BC battery.

[0016] Preferably, in step (1), the reflectivity of the silicon substrate after polishing is controlled at 35%-45%.

[0017] Preferably, the thickness of the P-type amorphous silicon layer in step (2) is 20-60 nm, and the thickness of the N-type amorphous silicon layer is 20-60 nm.

[0018] Preferably, the doping concentration of the doped amorphous silicon in step (2) is 3E20-5E21 atoms / cm 3 .

[0019] Preferably, the laser wavelength in step (3) is 535nm-1064nm, and the laser is used to irradiate the P region on the back side of the substrate, so that the boron atoms continue to diffuse deeply into the silicon base to form a p+ emitter in a local area.

[0020] Preferably, the temperature of the high-temperature furnace tube in step (4) is 800-820°C; the temperature does not reach the diffusion temperature of boron atoms, and can allow phosphorus atoms to diffuse deeply into the silicon base through the P-type amorphous silicon layer to form n+BSF in a local area.

[0021] Preferably, the de-plating in step (5) adopts chain equipment, and the front BSG, PSG, poly, amorphous silicon and other layers are removed by pickling; the pickling uses a mixed solution of HNO3, HF, and H2O2 in a volume ratio of 4:2:3.

[0022] Preferably, the alkaline etching in step (6) uses sodium hydroxide solution or potassium hydroxide solution as the alkaline polishing solution to grow a velvet layer on the front side of the silicon substrate and remove the amorphous silicon and poly silicon in the P and N regions on the back side of the silicon substrate.

[0023] Preferably, the pickling in step (6) uses HF to perform secondary treatment on the rounded chamfers of the pyramid spires and the pyramid grooves of the velvet surface.

[0024] Preferably, in step (6), the suede reflectivity of the front side of the silicon substrate after alkali etching and acid washing is 7%-10%, and the tower base size is 1-5 μm.

[0025] Preferably, the thickness of the aluminum oxide in step (7) is 3-10 nm.

[0026] Preferably, the thickness of the silicon nitride in step (8) is 70-90 nm.

[0027] BC battery prepared by the above method.

[0028] Compared with the existing technology, the present invention has the following advantages:

[0029] The present invention uses an AP-CVD device capable of low-temperature plasma treatment to sequentially deposit P-type and N-type amorphous silicon layers, and then uses a laser to irradiate the P region on the back of the substrate, with the focus on the P-type amorphous silicon layer. Boron atoms are stimulated by the power of the laser to continue to diffuse into the silicon base to form a p+emitter, and at the same time, the laser focus will be expanded to form a bubble-like barrier layer to block the infiltration of phosphorus atoms in the N-type amorphous silicon layer. Then, a high temperature of 800-820°C is selected to diffuse the N region, which reaches the diffusion temperature of phosphorus atoms (does not reach the diffusion temperature of boron atoms). Phosphorus atoms easily pass through the P-type amorphous silicon layer to reach the silicon base for doping diffusion, thereby realizing a preparation method without a mask when the P region and the N region are prepared on the back at the same time, which can not only reduce environmental pollution, improve the environmental friendliness of the battery, reduce the cost of the battery, and improve the market competitiveness of the battery, but also improve the production efficiency and quality of the battery. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0031] Example 1

[0032] The present invention provides a method for preparing a mask-free BC battery, comprising the following steps:

[0033] (1) Double-sided polishing of the silicon substrate

[0034] An N-type single crystal silicon wafer is selected, and a groove polishing device is used to perform double-sided polishing on the front and back sides of the silicon substrate.

[0035] In this embodiment, the loss layer on the surface of the silicon wafer is first removed in a mixed solution of KOH and H2O2, and then polished in a sodium hydroxide solution or a potassium hydroxide solution. The surface of the silicon wafer is smooth and the reflectivity is controlled at 40%±2%.

[0036] (2) Deposition on the back side of the silicon substrate: a layer of P-type amorphous silicon and a layer of N-type amorphous silicon are deposited in sequence.

[0037] In this embodiment, an AP-CVD device is used to generate a layer of P-type amorphous silicon (thickness 25nm) and a layer of N-type amorphous silicon (thickness 40nm) on the back of the silicon wafer. The doping concentration of the amorphous silicon is 1.5E21atoms / cm 3 .

[0038] (3) Laser selective doping of the P region on the back side of the silicon substrate.

[0039] In this example, laser is used to irradiate the P region on the back side of the substrate, so that the boron atoms continue to diffuse deeper into the silicon base. At the same time, the laser focus will expand around to form a bubble-like barrier layer, which can block the infiltration of phosphorus in the N-type amorphous silicon layer and form a p+emitter in the local area. The laser wavelength is 535nm, and the electrode patterning can be completed at the same time.

[0040] (4) A high-temperature furnace tube is used on the back side of the silicon substrate to dope the N region.

[0041] In this embodiment, the high-temperature phosphorus diffusion temperature is 800-820° C., which does not reach the high temperature of the diffusion of boron atoms, and can make the phosphorus atoms diffuse deeply into the silicon base through the P-type amorphous silicon layer to form n+BSF in local areas.

[0042] (5) Use chain equipment to pickle and remove the plating on the front side of the silicon substrate

[0043] In this example, pickling uses a mixture of HNO3 (concentration of 12%), HF (concentration of 4%), and H2O2 (concentration of 9%) in a volume ratio of 4:2:3.

[0044] (6) The front side of the silicon substrate is etched with alkaline to form a texture, and the back side is pickled to remove the amorphous silicon or poly silicon in the P and N regions.

[0045] In this embodiment, sodium hydroxide solution or potassium hydroxide solution is used for alkaline etching to make the texture, and then HF (concentration of 4%) is used for secondary treatment of the top of the pyramid and the rounded chamfer of the groove of the textured surface, so that a layer of texture is grown on the front side of the silicon substrate with a reflectivity of 7-10% and a tower base size of 1-5μm, and the amorphous silicon and poly silicon in the P and N zones on the back side of the silicon substrate are removed.

[0046] (7) Aluminum oxide film is deposited on the front

[0047] In this embodiment, an ALD device is used to deposit an aluminum oxide film on the front and back sides of an N-type single crystal silicon wafer, with a thickness of 8-10 nm.

[0048] (8) Silicon nitride film is deposited on both sides.

[0049] In this embodiment, a PECVD device is used to deposit a silicon nitride film on the front and back sides of an N-type single crystal silicon wafer, with a thickness of 70-80 nm.

[0050] (9) Screen printing is performed on the back side of the substrate to produce a BC battery.

[0051] Comparative Example 1

[0052] (1) double-sided polishing of the silicon substrate is performed in the same manner as step (1) of Example 1;

[0053] (2) A layer of P-type amorphous silicon is deposited on the back with a thickness of 70 nm and a doping concentration of 1.5E21 atoms / cm 3 ;

[0054] (3) Perform high-temperature boron diffusion and crystallization on the back of the silicon substrate and form a BSG mask at a temperature of 1050°C ±50°C;

[0055] (4) Using a laser to pattern the N region on the back of the silicon substrate and remove the mask of the N region;

[0056] (5) Chain + alkali polishing, the chain equipment pickles to remove the BSG on the front side, and the tank equipment polishes the front side poly + the POLY layer of the back N area with sodium hydroxide solution or potassium hydroxide solution;

[0057] (6) A layer of N-type amorphous silicon is deposited on the back with a thickness of 60 nm and a doping concentration of 1.5E21 atoms / cm 3 ;

[0058] (7) Perform high-temperature phosphorus diffusion on the back of the silicon substrate and form a PSG mask at a temperature of 1000°C ± 50°C and a doping concentration of 1.5E21 atoms / cm 3 .

[0059] (8) Using laser to pattern the P region on the back of the silicon substrate and remove the mask of the P region;

[0060] (9) Chain type + polishing (including texturing), the chain type equipment uses pickling to remove the PSG plated on the front side, and the tank type equipment uses sodium hydroxide solution or potassium hydroxide solution to polish the front side poly plated + the POLY layer of the back N zone + front texturing.

[0061] (10) depositing an aluminum oxide film on the front surface with a thickness of 8-10 nm;

[0062] (11) double-sided deposition of silicon nitride film with a thickness of 70-80 nm;

[0063] (12) Screen printing is performed on the back to produce a BC battery.

[0064] The performance of the batteries prepared in the examples and comparative examples is shown in Table 1 below.

[0065] Table 1

[0066] Voc(mV) Isc(A) Rs(Ω) FF(%) Eta(%) Example 1 737 14.10 1.32 83.82 26.37 Comparative Example 1 735 14.08 1.4 83.74 26.24

[0067] The present invention adopts a method of sequentially depositing a P-type amorphous silicon layer and an N-type amorphous silicon, and then using a laser to promote boron doping in the P region and using a high-temperature furnace tube to perform phosphorus doping in the N region to prepare a BC battery. The P region and the N region can be prepared on the back side without a mask, which simplifies the preparation process of the BC battery and reduces the cost.

[0068] The deposition order of P-type amorphous silicon layer and N-type amorphous silicon layer cannot be changed. The reason is that the diffusion temperature of boron is higher than the diffusion temperature of phosphorus. If the N-type amorphous silicon layer is deposited first and the P-type amorphous silicon layer is deposited later, whether the boron of the P-type amorphous silicon layer is penetrated by laser into the N-type amorphous silicon layer and doped into the silicon wafer, or the phosphorus atoms of the N-type amorphous silicon layer are doped by laser first and then the boron atoms are diffused at high temperature, it will cause the phosphorus atoms and boron atoms in the N-type amorphous silicon layer to be doped and diffused at the same time.

[0069] It can be seen from Table 1 that the BC battery prepared by the method of the present invention reduces the damage of the high-temperature step to the passivation layer, making it have a higher efficiency, which is mainly reflected in the opening voltage (Voc) and filling (FF). The current is basically the same, and the opening voltage and filling are improved.

[0070] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0071] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing a mask-free BC battery, characterized in that: The steps include: (1) Double-sided polishing of silicon substrate; (2) A layer of P-type amorphous silicon and a layer of N-type amorphous silicon are sequentially deposited on the back of the silicon substrate; (3) Laser doping is used on the back of the silicon substrate to advance the doping of the P region to form a p+ emitter in a local area and to complete electrode patterning at the same time; (4) A high-temperature furnace tube on the back of the silicon substrate performs doping and push-junction on the N region to form n+BSF in a local area; (5) De-plating on the front side of the silicon substrate; (6) The silicon substrate is alkali-etched and pickled in sequence, the front side is textured, and the amorphous silicon and poly silicon in the P and N regions are removed from the back side; (7) Aluminum oxide is deposited on both sides of the silicon substrate; (8) Deposition of silicon nitride on both sides of a silicon substrate; (9) Screen printing is performed on the back side of the silicon substrate to produce a BC battery.

2. The method for preparing a mask-free BC battery according to claim 1, characterized in that: In step (1), the reflectivity of the silicon substrate after polishing is controlled at 35%-45%.

3. The method for preparing a mask-free BC battery according to claim 1, characterized in that: The thickness of the P-type amorphous silicon layer in step (2) is 20-60nm, and the thickness of the N-type amorphous silicon layer is 20-60nm; the doping concentration of the doped amorphous silicon is 3E20-5E21atoms / cm 3 .

4. The method for preparing a mask-free BC battery according to claim 1, characterized in that: The laser wavelength described in step (3) is 535nm-1064nm.

5. The method for preparing a mask-free BC battery according to claim 1, characterized in that: The temperature of the high-temperature furnace tube in step (4) is 800-820°C.

6. The method for preparing a mask-free BC battery according to claim 1, characterized in that: In step (5), the de-plating is carried out using a chain device, and the front BSG, PSG, poly, amorphous silicon and other layers are removed by pickling; the pickling uses a mixed solution of HNO3, HF, and H2O2 in a volume ratio of 4:2:

3.

7. The method for preparing a mask-free BC battery according to claim 1, characterized in that: The alkaline etching in step (6) uses sodium hydroxide solution or potassium hydroxide solution as the alkaline etching solution; The pickling adopts HF; After the front side of the silicon substrate is alkali-etched and pickled, the suede reflectivity is 7%-10%, and the tower base size is 1-5 μm.

8. The method for preparing a mask-free BC battery according to claim 1, characterized in that: The thickness of the aluminum oxide in step (7) is 3-10 nm.

9. The method for preparing a mask-free BC battery according to claim 1, characterized in that The thickness of the silicon nitride in step (8) is 70-90 nm.

10. A BC battery prepared by the method according to any one of claims 1 to 9.