Preparation method of TOPCon battery

Abstract

The invention relates to a preparation method of a TOPCon cell, and belongs to the technical field of solar cell manufacturing. Comprising the following steps: double-sided alkali texturing; carrying out a boron diffusion process on the textured silicon wafer; in the boron diffusion process, the reaction temperature after the source is introduced is 825-845 DEG C, the propelling temperature is 860-890 DEG C, and boron is supplemented after propelling is finished; sE preparation is carried out; performing high-temperature oxidation on the silicon wafer, removing the boron-rich layer, and growing BSG; the oxidized silicon wafer is subjected to BSG removal and alkali polishing; entering a PE-poly process to carry out in-situ phosphorus doping; crystallizing the silicon wafer through an annealing process; and a PSG-RCA removal process is carried out. By optimizing the reaction temperature of the source feeding step and the reaction temperature of the propelling step in the boron diffusion process and adding the boron supplementing operation, the concentration of the SE doped region can be improved, and it is ensured that the overall change of the doping concentration of the non-SE region is not large, so that the conversion efficiency of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell manufacturing, and particularly to a preparation method of a TOPCon cell. Background Art

[0002] As an ideal clean energy source, solar energy has been increasingly emphasized by countries around the world. With the progress of technology and the reduction of costs, photovoltaic power generation has become economically competitive with other renewable energy sources. The TOPCon cell, fully known as Tunnel Oxide Passivated Contact cell, is a solar cell based on the principle of selective carriers with tunneling oxide passivated contacts. In recent years, due to its obvious advantages such as high conversion efficiency, low attenuation performance, and high cost performance, it has been gradually adopted by the industry.

[0003] During the preparation process of TOPCon cells, PERC SE is doped with phosphorus, while TOPCon SE is doped with boron. Due to the different segregation coefficients of boron and phosphorus, phosphorus is more likely to diffuse from silicon dioxide to silicon, while boron is more likely to diffuse from silicon to silicon dioxide, and more energy is required to promote doping. However, excessive laser energy is likely to cause damage to the silicon wafer. Therefore, it is more difficult to dope boron into silicon. Compared with the traditional boron diffusion process, the TOPCon cell stacking SE technology can theoretically achieve an efficiency increase of 0.5%, while in actual mass production, an efficiency increase of 0.2 - 0.4% can be achieved.

[0004] Emitter doping has a great influence on the conversion efficiency of solar cells. High-concentration doping can reduce the contact resistance between the silicon wafer and the electrode, thereby reducing the series resistance of the cell, but it will cause an increase in carrier recombination and a decrease in the minority carrier lifetime, affecting the open-circuit voltage and short-circuit current of the cell, while low-concentration doping has the opposite effect.

[0005] Therefore, how to control the boron doping concentration problem in the front SE region and non-SE region of TOPCon cells and ensure a high phosphorus doping concentration on the back surface is the core problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a preparation method of a TOPCon cell. The technical solution of the present invention is as follows:

[0007] A preparation method of a TOPCon cell, which includes:

[0008] S1, select an N-type original silicon wafer with a resistivity of 0.6 - 1.6 Ω, and perform double-sided alkaline texturing on the N-type original silicon wafer to form a textured surface;

[0009] S2. Load the textured silicon wafers into a quartz boat through an automated robot and send them into the furnace tube for the boron diffusion process. In the boron diffusion process, the reaction temperature after the source is introduced is 825 - 845 °C, the advancing temperature is 860 - 890 °C, and boron supplementation is carried out after the advancement ends.

[0010] S3. After the boron diffusion is completed, SE is prepared to form a laser heavily doped region P++ layer.

[0011] S4. After SE, the silicon wafers are subjected to high-temperature oxidation to remove the boron-rich layer and grow BSG.

[0012] S5. After oxidation, the silicon wafers are subjected to BSG-alkali polishing to perform alkali polishing on the back of the battery.

[0013] S6. After alkali polishing, the silicon wafers enter the PE-poly process for in-situ phosphorus doping to form a silicon oxide film.

[0014] S7. After the PE-poly process, the silicon wafers are crystallized through an annealing process.

[0015] S8. After annealing, the silicon wafers are subjected to the PSG-RCA process to remove various mask layers on the front and back of the wafers.

[0016] Optionally, S2 includes:

[0017] S21. Send the quartz boat loaded with silicon wafers into the furnace tube through a slurry rod. After the slurry rod withdraws, the furnace door is closed and vacuum pumping starts until the low pressure is reached, and at the same time, the furnace tube is preheated to 780 °C.

[0018] S22. After the preheating ends, start leak detection of the furnace tube.

[0019] S23. When the leak detection result meets the process requirements, continue to heat up the furnace tube to 820 °C, and at the same time, control the pressure inside the furnace tube to reach 160 mbar and keep it constant through a diaphragm pump.

[0020] S24. Introduce nitrogen into the furnace tube at a flow rate of 1500 sccm and oxygen at a flow rate of 2000 sccm. After 5 minutes of pre-oxidation deposition, a layer of silicon oxide is deposited on the surface of the silicon wafers.

[0021] S25. After the pre-oxidation ends, introduce nitrogen into the furnace tube at a flow rate of 3500 sccm, oxygen at a flow rate of 500 sccm, and boron trichloride at a flow rate of 90 - 120 sccm. After 3 - 3.5 minutes of source introduction, a p+ layer is formed.

[0022] S26. After the source introduction ends, purge the furnace tube and continue heating to raise its temperature to 825 - 845 °C.

[0023] After the temperature stabilizes in S27, a secondary gas supply is carried out: nitrogen is introduced into the furnace tube at a flow rate of 3500 sccm, oxygen is introduced at a flow rate of 500 sccm, and boron trichloride is introduced at a flow rate of 90 - 120 sccm. It is introduced for 3 - 3.5 minutes to form an enhanced p+ layer;

[0024] After the secondary gas supply in S28 ends, the furnace tube is purged and heating is continued for advancement, raising the temperature of the furnace tube to 860 - 890 °C, and the advancement is maintained for 6 - 10 minutes;

[0025] After the advancement in S29 ends, the furnace tube is cooled to 830 - 850 °C and boron supplementation is carried out for 2 - 5 minutes: nitrogen is introduced into the furnace tube at a flow rate of 3500 sccm, oxygen is introduced at a flow rate of 500 sccm, and boron trichloride is introduced at a flow rate of 90 - 120 sccm;

[0026] After the boron supplementation in S210 ends, the furnace tube and pipeline are purged with nitrogen, and at the same time, the furnace tube is continuously cooled to 800 °C;

[0027] While cooling, nitrogen is flushed into the furnace tube at a flow rate of 5000 sccm to restore the pressure inside the furnace tube to normal atmospheric pressure;

[0028] Open the furnace door, and extend the slurry rod into the furnace tube to take out the quartz boat from the furnace tube.

[0029] Optionally, the said S6 includes:

[0030] S61, Boat entry: The graphite boat loaded with silicon wafers is sent into the furnace tube through the slurry rod, and after the slurry rod withdraws from the furnace tube, the furnace door is closed;

[0031] S62, Vacuum pumping: Start vacuum pumping and start auxiliary heating to preheat the furnace tube to 420 - 460 °C;

[0032] S63, Leak detection: Check the leak rate of the furnace tube to keep it within the normal range;

[0033] S64, Pre - deposition of the tunneling layer: Nitrous oxide is introduced into the furnace tube at a flow rate of 10000 - 12000 sccm, and the pressure inside the furnace is controlled to be 1800 - 2000 mTorr and kept constant. The pre - deposition time is 30 - 60 s to complete the pre - deposition;

[0034] S65, Deposition of the tunneling oxide layer: Glow discharge is carried out on the silicon wafers inside the furnace tube through a radio - frequency power supply, with a power of 13000 - 15000 w and a deposition time of 90 - 100 s to form the tunneling oxide layer;

[0035] S66, Vacuum pumping: After the glow discharge is completed, the residual gas inside the furnace tube is evacuated;

[0036] S67, Pre - deposition of Poly - 1 layer: Introduce silane into the furnace tube at a flow rate of 3100 - 3300 sccm, introduce hydrogen into the furnace tube at a flow rate of 9000 - 9500 sccm, introduce phosphine into the furnace tube at a flow rate of 280 - 300 sccm, control the furnace pressure to be 2850 - 2950 mTorr and keep it constant, with a pre - deposition time of 30 - 60 s to complete the pre - deposition;

[0037] S68, Deposition of Poly - 1 layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio - frequency power supply, with a power of 12000 - 14000 w and a deposition time of 125 - 150 s to form the Poly - 1 layer;

[0038] S69, Vacuum pumping: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0039] S610, Pre - deposition of molecular sieve layer: Introduce nitrous oxide into the furnace tube at a flow rate of 10000 - 12000 sccm, control the furnace pressure to be 1800 - 2000 mTorr and keep it constant, with a pre - deposition time of 30 - 60 s to complete the pre - deposition;

[0040] S611, Deposition of molecular sieve layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio - frequency power supply, with a radio - frequency power supply power of 13000 - 15000 w and a deposition time of 30 - 100 s to form the molecular sieve layer;

[0041] S612, Vacuum pumping: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0042] S613, Pre - deposition of Poly - 2 layer: Introduce silane into the furnace tube at a flow rate of 3100 - 3300 sccm, introduce hydrogen into the furnace tube at a flow rate of 9000 - 9500 sccm, introduce phosphine into the furnace tube at a flow rate of 850 - 1200 sccm, control the furnace pressure to be 2850 - 2950 mTorrr and keep it constant, with a pre - deposition time of 30 s to complete the pre - deposition;

[0043] S614, Deposition of Poly - 2 layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio - frequency power supply, with a power of 12000 - 14000 w and a deposition time of 390 - 550 s to form the Poly - 2 layer;

[0044] S615, Vacuum pumping: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0045] S616, Pre - deposition of mask layer: Introduce silane into the furnace tube at a flow rate of 1600 - 2000 sccm, introduce nitrous oxide into the furnace tube at a flow rate of 7000 - 9800 sccm, and control the furnace pressure to be 1750 - 2000 mTorr and keep it constant;

[0046] S617, Deposition of masking layer: Glow discharge is carried out on the silicon wafer in the furnace tube through a radio frequency power supply. The power of the radio frequency power supply is 13,000 w and the deposition time is 60 s to form a masking layer;

[0047] S618, Vacuum pumping: After the glow discharge is completed, the residual gas in the furnace tube is evacuated;

[0048] S619, Gas filling and boat removal: After the pressure in the furnace tube returns to normal atmospheric pressure, the furnace door is opened, and the paddle rod is extended to take out the graphite boat from the furnace tube.

[0049] Optionally, the said S8 includes:

[0050] S81, After annealing, the silicon wafer faces down and passes through a chain PSG cleaning machine to remove the oxide layer in the edge area of the front side of the silicon wafer by reacting with HF acid, exposing the amorphous silicon deposited by the PE-poly process and loading the silicon wafer into a flower basket;

[0051] S82, The flower basket is grabbed by a manipulator and fed into the positive etching tank for positive etching. The reaction is carried out for 330 s at 75 °C. In the positive etching tank, the volume ratio of sodium hydroxide solution, poly-removing additive and water is 14:3.5:675, and the concentration of the sodium hydroxide solution is 48%;

[0052] S83, After positive etching, the silicon wafer enters the water tank for a first water wash for 90 s;

[0053] S84, After the first water wash, the silicon wafer enters the alkali wash tank for alkali washing. The reaction is carried out for 120 s at 65 °C. In the alkali wash tank, the volume ratio of sodium hydroxide solution, hydrogen peroxide and water is 6:25:670, the concentration of the sodium hydroxide solution is 48%, and the concentration of hydrogen peroxide is 30%;

[0054] S85, After alkali washing, the silicon wafer enters the water tank for a second water wash for 100 s;

[0055] S86, After water washing, the silicon wafer enters the first pickling tank for a first pickling for 230 s. In the first pickling tank, the volume ratio of hydrofluoric acid solution and water is = 110:590, and the concentration of the hydrofluoric acid solution is 49%;

[0056] S87, After the first pickling, the silicon wafer enters the water tank for a third water wash for 100 s;

[0057] S88, After the third water wash, the silicon wafer enters the second pickling tank for a second pickling for 130 s. In the second pickling tank, the volume ratio of hydrochloric acid solution, hydrofluoric acid solution and water is 10:50:645, the concentration of the hydrochloric acid solution is 37%, and the concentration of the hydrofluoric acid solution is 49%;

[0058] S89, After the second pickling, the silicon wafer enters the water tank for a fourth water wash for 100 s;

[0059] In S810, after four - time water washing, the silicon wafer enters the slow - lift tank for dehydration;

[0060] In S811, after dehydration, the silicon wafer enters the drying tank for drying, and is dried for 800 s under the temperature condition of 95 °C.

[0061] Optionally, the reflectivity of the surface texture formed by double - sided alkaline texturing in S1 is 9.5%.

[0062] Optionally, the thickness of BSG in S4 is 60 - 120 nm.

[0063] Optionally, the size of the tower base formed by alkaline polishing in S5 is 6 - 12 μm.

[0064] Optionally, the thickness of the silicon oxide film in S6 is 1 - 2.5 nm.

[0065] Optionally, the reaction temperature after source - feeding in S2 is 830 °C, and the pushing temperature is 890 °C.

[0066] All of the above - mentioned optional technical solutions can be arbitrarily combined, and the present invention does not elaborate on the structures after combined one by one.

[0067] By means of the above - mentioned scheme, the beneficial effects of the present invention are as follows:

[0068] By optimizing the reaction temperatures of the source - feeding step and the pushing step in the boron diffusion process and adding boron - supplementing operation, the concentration of the SE doping region can be increased, and the overall change in the doping concentration of the non - SE region can be ensured to be small, so as to improve the conversion efficiency of the battery.

[0069] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following takes the preferred embodiments of the present invention and combines with the drawings to elaborate in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 is a flowchart of the preparation method of the TOPCon battery provided by the embodiment of the present invention.

[0071] Figure 2 is a flowchart of the boron diffusion process in the embodiment of the present invention.

[0072] Figure 3 is a flowchart of the boron diffusion process of the prior art.

[0073] Figure 4 is a flowchart of the prior - art PSG - RCA removal process.

[0074] Figure 5It is a flowchart of the PSG-RCA process in the embodiments of the present invention.

[0075] Figure 6 It is a schematic diagram of the ECV comparison results of the heavily doped SE regions in the experimental group and the control group.

[0076] Figure 7 It is a schematic diagram of the ECV comparison results of the non-SE regions in the experimental group and the control group.

[0077] Figure 8 It is a schematic diagram of the ECV comparison results of the front side of the silicon wafer before and after RCA.

[0078] Figure 9 It is a schematic diagram of the ECV comparison results of the back side of the silicon wafer after annealing and after RCA. Detailed implementation manners

[0079] The following combines the drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but do not limit the scope of the present invention.

[0080] As Figure 1 shown, the preparation method of the TOPCon battery provided by the embodiments of the present invention includes the following steps S1 to S8:

[0081] S1, select an N-type original silicon wafer with a resistivity of 0.6 - 1.6 Ω, and perform double-sided alkaline texturing on the N-type original silicon wafer to form a textured surface.

[0082] In a specific embodiment, the reflectivity of the double-sided alkaline texturing to form a textured surface in S1 is 9.5%.

[0083] S2, load the textured silicon wafer into a quartz boat through an automated robot and send it into the furnace tube for boron diffusion process; in the boron diffusion process, the reaction temperature after the source is introduced is 825 - 845 °C, the pushing temperature is 860 - 890 °C, and boron supplementation is performed after the pushing ends.

[0084] In a specific embodiment, S2 includes:

[0085] S21, send the quartz boat loaded with the silicon wafer into the furnace tube through a silicon carbide slurry rod, close the furnace door after the slurry rod exits and start pumping vacuum to a low pressure (100 mbar), and at the same time preheat the furnace tube to 780 °C;

[0086] S22, start leak detection of the furnace tube after the preheating ends;

[0087] S23, when the leak detection result meets the process requirements (leak rate ≤ 2 mbar / min), continue to heat up the furnace tube to 820 °C, and at the same time control the pressure in the furnace tube to reach 160 mbar and keep it constant through a diaphragm pump;

[0088] S24, Introduce nitrogen into the furnace tube at a flow rate of 1500 sccm and oxygen at a flow rate of 2000 sccm. After pre-oxidation deposition for 5 minutes, a layer of silicon oxide is deposited on the surface of the silicon wafer.

[0089] S25, After the pre-oxidation ends, introduce nitrogen into the furnace tube at a flow rate of 3500 sccm, oxygen at a flow rate of 500 sccm, and boron trichloride at a flow rate of 90 - 120 sccm. Pass the source for 3 - 3.5 minutes to form a p+ layer.

[0090] S26, After passing the source ends, purge the furnace tube and continue heating to raise the temperature to 825 - 845 °C.

[0091] S27, After the temperature stabilizes, conduct secondary source passing: introduce nitrogen into the furnace tube at a flow rate of 3500 sccm, oxygen at a flow rate of 500 sccm, and boron trichloride at a flow rate of 90 - 120 sccm. Pass for 3 - 3.5 minutes to form a strengthened p+ layer.

[0092] S28, After the secondary source passing ends, purge the furnace tube and continue heating for propulsion to raise the temperature of the furnace tube to 860 - 890 °C, and maintain the propulsion for 6 - 10 minutes.

[0093] S29, After the propulsion ends, cool the furnace tube to 830 - 850 °C and conduct boron supplementation for 2 - 5 minutes: introduce nitrogen into the furnace tube at a flow rate of 3500 sccm, oxygen at a flow rate of 500 sccm, and boron trichloride at a flow rate of 90 - 120 sccm.

[0094] S210, After the boron supplementation ends, use nitrogen to purge the furnace tube and the pipeline, and at the same time continue to cool the furnace tube to 800 °C.

[0095] S211, While cooling, introduce nitrogen into the furnace tube at a flow rate of 5000 sccm to restore the pressure inside the furnace tube to normal atmospheric pressure.

[0096] S212, Open the furnace door, insert the silicon carbide slurry rod into the furnace tube to take out the quartz boat from the furnace tube.

[0097] As Figure 2 and Figure 3 shown, they are respectively the flowcharts of the boron diffusion process in the embodiment of the present invention and the prior art. By comparing Figure 2 and Figure 3 it can be seen that in the boron diffusion process of the embodiment of the present invention, compared with the prior boron diffusion process, the reaction temperature of the source passing step and the propulsion step is optimized in the boron diffusion process, and boron supplementation operation is added, which can increase the concentration of the SE doping region and ensure that the doping concentration in the non-SE region changes little as a whole, so as to improve the conversion efficiency of the battery.

[0098] In a preferred embodiment, the reaction temperature after the source introduction in S2 is 830 °C, and the advancing temperature is 890 °C.

[0099] S3. After the boron diffusion is completed, SE (selective emitter) preparation is carried out to form a laser heavily doped region P++ layer.

[0100] This step is used to reduce the contact resistance, increase the open-circuit voltage Voc and fill factor FF of the solar cell, and improve the cell conversion efficiency.

[0101] S4. After SE, the silicon wafer is subjected to high-temperature oxidation to remove the boron-rich layer and grow BSG.

[0102] Among them, the purpose of removing the boron-rich layer is to form a suitable surface concentration and junction depth.

[0103] In a specific embodiment, the thickness of the BSG in S4 is 60 - 120 nm.

[0104] S5. After oxidation, the silicon wafer undergoes BSG removal - alkali polishing to perform alkali polishing on the back of the cell.

[0105] In a specific embodiment, the size of the tower base formed by the alkali polishing in S5 is 6 - 12 μm.

[0106] S6. After alkali polishing, the silicon wafer enters the PE - poly process for in-situ phosphorus doping to form a silicon oxide film.

[0107] In a specific embodiment, S6 includes:

[0108] S61. Loading the boat: The graphite boat loaded with silicon wafers is sent into the furnace tube through a silicon carbide slurry rod, and the furnace door is closed after the slurry rod exits the furnace tube;

[0109] S62. Vacuum pumping: Start vacuum pumping and turn on the auxiliary heating to preheat the furnace tube to 420 - 460 °C;

[0110] S63. Leak detection: Check the leak rate of the furnace tube to make it within the normal range (leak rate ≤ 2 mbar / min);

[0111] S64. Pre - depositing the tunneling layer: Nitrous oxide is introduced into the furnace tube at a flow rate of 10000 - 12000 sccm, and the pressure in the furnace is controlled to be 1800 - 2000 mTorr and kept constant. The pre - deposition time is 30 - 60 s to complete the pre - deposition;

[0112] S65. Depositing the tunneling oxide layer: Glow discharge is carried out on the silicon wafer in the furnace tube through a radio - frequency power supply with a power of 13000 - 15000 w and a deposition time of 90 - 100 s to form a tunneling oxide layer;

[0113] S66, Evacuation: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0114] S67, Pre-deposition of Poly-1 layer: Introduce silane into the furnace tube at a flow rate of 3100 - 3300 sccm, introduce hydrogen into the furnace tube at a flow rate of 9000 - 9500 sccm, introduce phosphine into the furnace tube at a flow rate of 280 - 300 sccm, control the furnace pressure to be 2850 - 2950 mTorr and keep it constant, and the pre-deposition time is 30 - 60 s to complete the pre-deposition;

[0115] S68, Deposition of Poly-1 layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio frequency power supply with a power of 12000 - 14000 w and a deposition time of 125 - 150 s to form a Poly-1 layer;

[0116] S69, Evacuation: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0117] S610, Pre-deposition of molecular sieve layer: Introduce nitrous oxide into the furnace tube at a flow rate of 10000 - 12000 sccm, control the furnace pressure to be 1800 - 2000 mTorr and keep it constant, and the pre-deposition time is 30 - 60 s to complete the pre-deposition;

[0118] S611, Deposition of molecular sieve layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio frequency power supply with a power of 13000 - 15000 w and a deposition time of 30 - 100 s to form a molecular sieve layer;

[0119] S612, Evacuation: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0120] S613, Pre-deposition of Poly-2 layer: Introduce silane into the furnace tube at a flow rate of 3100 - 3300 sccm, introduce hydrogen into the furnace tube at a flow rate of 9000 - 9500 sccm, introduce phosphine into the furnace tube at a flow rate of 850 - 1200 sccm, control the furnace pressure to be 2850 - 2950 mTorrr and keep it constant, and the pre-deposition time is 30 s to complete the pre-deposition;

[0121] S614, Deposition of Poly-2 layer: Perform glow discharge on the silicon wafer in the furnace tube through a radio frequency power supply with a power of 12000 - 14000 w and a deposition time of 390 - 550 s to form a Poly-2 layer;

[0122] S615, Evacuation: After the glow discharge is completed, evacuate the residual gas in the furnace tube;

[0123] S616, Pre - deposition mask layer: Silane is introduced into the furnace tube at a flow rate of 1600 - 2000 sccm, and nitrous oxide is introduced into the furnace tube at a flow rate of 7000 - 9800 sccm. The pressure inside the furnace is controlled to be 1750 - 2000 mTorr and kept constant;

[0124] S617, Deposition mask layer: Glow discharge is carried out on the silicon wafer inside the furnace tube through a radio - frequency power supply. The power of the radio - frequency power supply is 13000 w, and the deposition time is 60 s to form a mask layer;

[0125] S618, Vacuum pumping: After the glow discharge is completed, the residual gas inside the furnace tube is evacuated;

[0126] S619, Gas filling and boat extraction: After the pressure inside the furnace tube returns to normal atmospheric pressure, the furnace door is opened, and the silicon carbide paddle is extended to take out the graphite boat from the furnace tube.

[0127] In the embodiment of the present invention, by optimizing the interface defects of the SiOx thin film and the doping concentration of the Poly layer, the doped Poly layer can obtain good passivation performance and low contact resistivity. While realizing the high - surface Poly doping process, by controlling the doping source flow rate and annealing conditions, precise control of the doping concentration and distribution is achieved, the passivation effect on the battery surface is enhanced, the surface recombination rate is reduced, and the conversion efficiency and stability of the battery are improved.

[0128] In a specific embodiment, the thickness of the silicon oxide thin film in S6 is 1 - 2.5 nm.

[0129] S7, After the PE - poly process, the silicon wafer is crystallized through an annealing process.

[0130] The purpose of this step is: ① to convert the amorphous silicon grown by PECVD into microcrystalline silicon or polycrystalline silicon; ② to activate phosphorus atoms and push the junction depth; ③ to form pinholes (tiny voids).

[0131] S8, After annealing, the silicon wafer undergoes the PSG - RCA removal process to remove various mask layers on the front and back sides of the silicon wafer.

[0132] Through this step, the high - quality boron doping on the front side and the thickness and concentration of the high - surface phosphorus doping on the back side can be perfectly retained without being thinned.

[0133] In a specific embodiment, S8 includes:

[0134] S81, After annealing, the silicon wafer is placed face - down in a chain - type PSG removal cleaning machine. The oxide layer in the edge area on the front side of the silicon wafer is removed by reacting with HF acid (concentration of 49%), the amorphous silicon deposited by the PE - poly process is exposed, and the silicon wafer is loaded into a flower basket;

[0135] S82. The flower basket is grabbed by a manipulator and fed into the positive etching tank for positive etching. The reaction is carried out for 330 s under the condition of 75 °C. In the positive etching tank, the volume ratio of sodium hydroxide solution, de-poly additive and water is 14:3.5:675, and the concentration of the sodium hydroxide solution is 48%.

[0136] Among them, the de-poly additive includes sodium benzoate, surfactant (sodium dodecyl sulfate), catalyst (sodium diacetate), other chemical components (sodium lactate) and deionized water, and their mass percentages are 2%, 4%, 8%, 8% and 78% respectively.

[0137] S83. After positive etching, the silicon wafer enters the water tank for the first water wash for 90 s.

[0138] S84. After the first water wash, the silicon wafer enters the alkali wash tank for alkali washing. The reaction is carried out for 120 s under the condition of 65 °C. In the alkali wash tank, the volume ratio of sodium hydroxide solution, hydrogen peroxide and water is 6:25:670, the concentration of the sodium hydroxide solution is 48%, and the concentration of hydrogen peroxide is 30%.

[0139] S85. After alkali washing, the silicon wafer enters the water tank for the second water wash for 100 s.

[0140] S86. After water washing, the silicon wafer enters the first pickling tank for the first pickling for 230 s. In the first pickling tank, the volume ratio of hydrofluoric acid solution and water is = 110:590, and the concentration of the hydrofluoric acid solution is 49%.

[0141] S87. After the first pickling, the silicon wafer enters the water tank for the third water wash for 100 s.

[0142] S88. After the third water wash, the silicon wafer enters the second pickling tank for the second pickling for 130 s. In the second pickling tank, the volume ratio of hydrochloric acid solution, hydrofluoric acid solution and water is 10:50:645, the concentration of the hydrochloric acid solution is 37%, and the concentration of the hydrofluoric acid solution is 49%.

[0143] S89. After the second pickling, the silicon wafer enters the water tank for the fourth water wash for 100 s.

[0144] S810. After the fourth water wash, the silicon wafer enters the slow lifting tank for dehydration.

[0145] S811. After dehydration, the silicon wafer enters the drying tank for drying. It is dried for 800 s under the temperature condition of 95 °C.

[0146] As Figure 4 and Figure 5 shown, they are the flowcharts of the prior art and the PSG-RCA process in the embodiment of the present invention respectively. Compare Figure 4 and Figure 5It can be seen that the PSG-RCA process provided by the embodiments of the present invention reduces an alkali washing process to ensure that the doping structures on the front and back sides are not damaged, thereby ensuring a stable gain in efficiency.

[0147] To verify the beneficial effects of the method provided by the embodiments of the present invention, the following comparative experiments shown in Table 1 below are provided:

[0148] Table 1

[0149]

[0150] Furthermore, the embodiments of the present invention performed Sinton and efficiency tests on the battery performances obtained by the experimental group and the control group, and the test results are shown in Table 2 and Table 3 respectively.

[0151] Table 2

[0152]

[0153] Table 3

[0154]

[0155] The above-mentioned Sinton test includes the potential open-circuit voltage (iVoc), potential fill factor (iFF), reverse saturation current (J0), and minority carrier lifetime (Lifetime) under a standard solar intensity. The higher the minority carrier lifetime, the higher the potential open-circuit voltage, the higher the potential fill factor, and the lower the reverse saturation current under a standard solar intensity, indicating a higher passivation level and higher efficiency of the silicon wafer.

[0156] Referring to Table 2, the battery passivation level prepared by the embodiments of the present invention has an advantage; referring to Table 3, the efficiency (Eta) of the embodiments of the present invention is higher. Overall, it shows that the battery structure prepared by the present invention improves the conversion efficiency of TOPCon solar cells.

[0157] As Figure 6 and Figure 7 shown, they are respectively the schematic diagrams of the ECV comparison results of the heavily doped SE region and the non-SE region for the experimental group and the control group. From Figure 6 and Figure 7 it can be seen that through the boron diffusion process provided by the embodiments of the present invention, the concentration of the SE doping region can be increased, and the overall change in the doping concentration of the non-SE region can be ensured to be small.

[0158] As Figure 8 and Figure 9 shown, they are respectively the schematic diagrams of the ECV comparison results of the front side of the silicon wafer before and after RCA and the ECV comparison results of the back side of the silicon wafer after annealing and after RCA. From Figure 8 and Figure 9It can be seen that the PSG-RCA removal process in the embodiments of the present invention has an obvious protective effect on the doping structures on the front and back sides, perfectly retaining the doping concentration and depth formed in the previous processes, providing guarantee for high-quality doping, and thus playing a great role in stabilizing the battery efficiency.

[0159] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a TOPCon battery, characterized in that: include: S1, selecting an N-type original silicon wafer with a resistivity of 0.6-1.6Ω, and performing double-sided alkali texturing on the N-type original silicon wafer to form a textured surface; S2, loading the textured silicon wafer into a quartz boat through an automated robot, and sending it into a furnace tube for a boron diffusion process; in the boron diffusion process, the reaction temperature after the source is 825-845°C, the advancing temperature is 860-890°C, and boron supplementation is performed after the advancement is completed; S3, after the boron diffusion is completed, SE preparation is performed to form a laser heavily doped region P++ layer; S4, after SE, the silicon wafer is subjected to high temperature oxidation to remove the boron-rich layer and grow BSG; S5, the oxidized silicon wafer is subjected to BSG removal-alkaline polishing, and the back side of the cell is alkaline polished; S6, after alkali polishing, the silicon wafer enters the PE-poly process for in-situ phosphorus doping to form a silicon oxide film; S7, after the PE-poly process, the silicon wafer is crystallized by an annealing process; S8, after annealing, the silicon wafer undergoes a PSG-RCA removal process to remove various mask layers on the front and back sides of the silicon wafer.

2. The method for preparing a TOPCon battery according to claim 1, characterized in that: The S2 includes: S21, the quartz boat loaded with silicon wafers is sent into the furnace tube through the slurry rod. After the slurry rod is withdrawn, the furnace door is closed and vacuum is started to be drawn to the bottom pressure, and the furnace tube is preheated to 780°C at the same time; S22, after the preheating is completed, the furnace tube is started to be leak tested; S23, when the leak detection result meets the process requirements, the furnace tube is further heated to 820°C, and the pressure in the furnace tube is controlled by a diaphragm pump to reach 160 mbar and kept constant; S24, nitrogen gas is introduced into the furnace tube at a flow rate of 1500 sccm and oxygen gas is introduced at a flow rate of 2000 sccm, and a pre-oxidation deposition is performed for 5 minutes, so that a layer of silicon oxide is deposited on the surface of the silicon wafer; S25, after the pre-oxidation is completed, nitrogen gas is introduced into the furnace tube at a flow rate of 3500 sccm, oxygen gas is introduced at a flow rate of 500 sccm, and boron trichloride is introduced at a flow rate of 90-120 sccm for 3-3.5 minutes to form a p+ layer; S26, after the source is passed, the furnace tube is purged and heated continuously to raise the temperature to 825-845°C; S27, after the temperature is stabilized, a secondary source is introduced: nitrogen is introduced into the furnace tube at a flow rate of 3500 sccm, oxygen is introduced at a flow rate of 500 sccm, and boron trichloride is introduced at a flow rate of 90-120 sccm for 3-3.5 minutes to form an enhanced p+ layer; S28, after the secondary source is completed, the furnace tube is purged and heated continuously to raise the temperature of the furnace tube to 860-890°C and maintained for 6-10 minutes; S29, after the advancement is completed, the furnace tube is cooled to 830-850°C and boron is supplemented for 2-5 minutes: nitrogen is introduced into the furnace tube at a flow rate of 3500sccm, oxygen is introduced at a flow rate of 500sccm, and boron trichloride is introduced at a flow rate of 90-120sccm; S210, after the boron supplementation is completed, the furnace tube and pipeline are purged with nitrogen, and the furnace tube is further cooled to 800°C; S211, while cooling, nitrogen is flushed into the furnace tube at a flow rate of 5000 sccm to restore the pressure inside the furnace tube to normal atmospheric pressure; S212, open the furnace door, and extend the slurry rod into the furnace tube to take the quartz boat out of the furnace tube.

3. The method for preparing a TOPCon battery according to claim 1, characterized in that: The S6 includes: S61, boat entry: the graphite boat loaded with silicon wafers is sent into the furnace tube by a paddle, and the furnace door is closed after the paddle exits the furnace tube; S62, vacuuming: start vacuuming and start auxiliary heating to preheat the furnace tube to 420-460℃; S63, leak detection: check the furnace tube leakage rate to make it within the normal range; S64, pre-deposition of tunneling layer: introducing laughing gas into the furnace tube at a flow rate of 10000-12000 sccm, and controlling the pressure in the furnace to be 1800-2000 mTorr and keep it constant, the pre-deposition time is 30-60 s, and the pre-deposition is completed; S65, depositing a tunneling oxide layer: glow discharging the silicon wafer in the furnace tube by a radio frequency power supply, the power is 13000-15000w, the deposition time is 90-100s, and a tunneling oxide layer is formed; S66, vacuuming: after the glow discharge is completed, the residual gas in the furnace tube is evacuated; S67, pre-deposition of Poly-1 layer: silane is introduced into the furnace tube at a flow rate of 3100-3300 sccm, hydrogen is introduced into the furnace tube at a flow rate of 9000-9500 sccm, phosphine is introduced into the furnace tube at a flow rate of 280-300 sccm, and the pressure in the furnace is controlled to be 2850-2950 mTorr and kept constant, the pre-deposition time is 30-60 s, and the pre-deposition is completed; S68, depositing a Poly-1 layer: glow discharging the silicon wafer in the furnace tube by a radio frequency power supply, the power is 12000-14000w, the deposition time is 125-150s, and a Poly-1 layer is formed; S69, vacuuming: after the glow discharge is completed, the residual gas in the furnace tube is evacuated; S610, pre-deposition of molecular sieve layer: introducing laughing gas into the furnace tube at a flow rate of 10000-12000 sccm, and controlling the pressure in the furnace to be 1800-2000 mTorr and keep it constant, the pre-deposition time is 30-60 s, and the pre-deposition is completed; S611, depositing a molecular sieve layer: glow discharging the silicon wafer in the furnace tube by a radio frequency power supply, the radio frequency power supply power is 13000-15000w, and the deposition time is 30-100s to form a molecular sieve layer; S612, vacuuming: after the glow discharge is completed, the residual gas in the furnace tube is evacuated; S613, pre-deposition of Poly-2 layer: silane is introduced into the furnace tube at a flow rate of 3100-3300 sccm, hydrogen is introduced into the furnace tube at a flow rate of 9000-9500 sccm, phosphine is introduced into the furnace tube at a flow rate of 850-1200 sccm, and the pressure in the furnace is controlled to be 2850-2950 mTorrr and kept constant, the pre-deposition time is 30 s, and the pre-deposition is completed; S614, depositing a Poly-2 layer: glow discharging the silicon wafer in the furnace tube by a radio frequency power supply, the power is 12000-14000w, the deposition time is 390-550s, and a Poly-2 layer is formed; S615, vacuuming: after the glow discharge is completed, the residual gas in the furnace tube is evacuated; S616, pre-depositing a mask layer: introducing silane into the furnace tube at a flow rate of 1600-2000 sccm, introducing nitrous oxide into the furnace tube at a flow rate of 7000-9800 sccm, and controlling the pressure in the furnace to be 1750-2000 mTorr and keeping it constant; S617, depositing a mask layer: glow discharging the silicon wafer in the furnace tube by a radio frequency power supply, the radio frequency power supply power is 13000w, the deposition time is 60s, and a mask layer is formed; S618, vacuuming: after the glow discharge is completed, the residual gas in the furnace tube is evacuated; S619, Inflate and remove the boat: After the pressure in the furnace tube returns to normal atmospheric pressure, open the furnace door and extend the paddle rod to take the graphite boat out of the furnace tube.

4. The method for preparing a TOPCon battery according to claim 1, characterized in that: The S8 includes: S81, after annealing, the front side of the silicon wafer is passed through a chain PSG removal cleaning machine with the front side facing downward, and the oxide layer in the front edge area of ​​the silicon wafer is removed by reaction with HF acid, exposing the amorphous silicon deposited by the PE-poly process and placing the silicon wafer into a basket; S82, the flower basket is grabbed by a robot and put into the positive etching groove for positive etching, and the reaction is carried out at 75°C for 330s. In the positive etching groove, the volume ratio of sodium hydroxide solution, depoly additive and water is 14:3.5:675, and the concentration of sodium hydroxide solution is 48%; S83, after etching, the silicon wafer enters a water tank for washing for 90 seconds; S84, after the first water washing, the silicon wafer enters the alkaline washing tank for alkaline washing, and reacts for 120 seconds at 65°C. In the alkaline washing tank, the volume ratio of sodium hydroxide solution, hydrogen peroxide and water is 6:25:670, the concentration of sodium hydroxide solution is 48%, and the concentration of hydrogen peroxide is 30%; S85, the silicon wafer after alkali washing enters the water tank for secondary washing for 100s; S86, after water washing, the silicon wafer enters a primary pickling tank for a primary pickling for 230 seconds, in which the volume ratio of the hydrofluoric acid solution to water is 110:590, and the concentration of the hydrofluoric acid solution is 49%; S87, the silicon wafer after the acid wash is put into the water tank for washing three times for 100 seconds; S88, after three water washings, the silicon wafer enters a secondary pickling tank for secondary pickling for 130 seconds, in which the volume ratio of hydrochloric acid solution, hydrofluoric acid solution and water is 10:50:645, the concentration of the hydrochloric acid solution is 37%, and the concentration of the hydrofluoric acid solution is 49%; S89, after the secondary pickling, the silicon wafer enters the water tank for four water washings for 100s; S810, after four water washes, the silicon wafer enters the slow pull tank for dehydration; S811, after dehydration, the silicon wafer enters the drying tank for drying at 95°C for 800s.

5. The method for preparing a TOPCon battery according to claim 1, characterized in that: The reflectivity of the double-sided alkali texturing formed by S1 is 9.5%.

6. The method for preparing a TOPCon battery according to claim 1, characterized in that: The thickness of BSG in the S4 is 60-120 nm.

7. The method for preparing a TOPCon battery according to claim 1, characterized in that: The tower base size formed by alkali polishing in S5 is 6-12 μm.

8. The method for preparing a TOPCon battery according to claim 1, characterized in that: The thickness of the silicon oxide film in S6 is 1-2.5 nm.

9. The method for preparing a TOPCon battery according to claim 1 or 2, characterized in that: The reaction temperature after the source is passed through S2 is 830°C, and the advancing temperature is 890°C.

Images