Diffusion process of TOPCon battery

Abstract

The invention relates to a diffusion process of a TOPCon battery, which comprises the following steps: S1, placing a battery piece in a diffusion furnace tube, performing boron source deposition for multiple times at a preset temperature, and forming a PN junction on the surface of the battery piece; s2, introducing nitrogen into the diffusion furnace tube, propelling for multiple times, propelling the PN junction into the battery piece, and obtaining the battery piece with the PN junction inside; and S3, placing the battery piece with the PN junction inside in a reaction furnace, and introducing oxygen into the reaction furnace to obtain the battery piece with a protective layer on the surface. The preparation steps are optimized, effective boron doping can be formed without SE laser, the diffusion process provided by the invention is simple, the steps are few, the preparation time is short, the production cost is effectively reduced, the low yield caused by high power control difficulty of the SE laser is avoided, and the production efficiency is improved. The cell prepared by the diffusion process provided by the invention is good in doping effect, and the photoelectric conversion efficiency of the cell is high.

Description

Technical Field

[0001] The invention belongs to the technical field of solar photovoltaic power generation, and in particular relates to a diffusion process of a TOPCon cell. Background Art

[0002] TOPCon solar cells are one of the solar cells with the best passivation performance. With the development of the industry, the efficiency and output of TOPCon solar cells continue to improve, showing broad development space and potential.

[0003] The diffusion process is a key process in the production of TOPCon solar cells. In the existing technology, the diffusion process needs to rely on SE laser to achieve effective boron doping in the cell.

[0004] However, SE laser power control is difficult. If the power is too low, it is difficult to form effective boron doping. If the power is too high, it will lead to leakage, high surface recombination, etc. Therefore, providing a diffusion process that can achieve effective boron doping without SE laser has become an urgent problem to be solved. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a diffusion process of a TOPCon battery. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The present invention provides a diffusion process of a TOPCon battery, comprising the following steps:

[0007] S1: placing the cell in a diffusion furnace tube, performing multiple boron source depositions at a preset temperature, and forming a PN junction on the surface of the cell;

[0008] S2: introducing nitrogen into the diffusion furnace tube, pushing the PN junction into the interior of the battery cell for multiple times, and obtaining a battery cell with a PN junction inside;

[0009] S3: placing the battery cell with the PN junction inside in a reaction furnace, introducing oxygen into the reaction furnace, and obtaining a battery cell with a protective layer on the surface.

[0010] In one achievable manner, step S1 includes the following steps:

[0011] S11: placing the cell in a diffusion furnace tube, introducing a mixed gas of nitrogen, oxygen and BCl3 into the diffusion furnace tube, and performing the first boron source deposition at a preset temperature of 830-875°C;

[0012] S12: changing the flow rate of the mixed gas, and performing a second boron source deposition at a preset temperature of 830-875°C.

[0013] In a feasible manner, in the step S11, the flow rate of the nitrogen gas is 1800-2200 sccm, the flow rate of the oxygen gas is 550-750 sccm, the flow rate of the BCl 3 is 150-230 sccm, and the pressure of the nitrogen gas is 95-105 mbar.

[0014] In a feasible manner, in the step S12, the flow rate of the nitrogen gas is 3000-5000 sccm, the flow rate of the oxygen gas is 550-750 sccm, the flow rate of the BCl 3 is 150-230 sccm, and the pressure of the nitrogen gas is 160-200 mbar.

[0015] In an achievable manner, the deposition time of the first boron source deposition is 400 s;

[0016] The deposition time of the second boron source deposition is 300 s.

[0017] In one achievable manner, step S2 comprises the following steps:

[0018] S21: introducing nitrogen into the diffusion furnace tube, and performing the first push under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 300 mbar;

[0019] S22: A second push is performed under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 400 mbar.

[0020] In one achievable manner, the steps between step S2 and step S3 further include:

[0021] The battery cell with the PN junction inside is subjected to a cooling process, and after the battery cell with the PN junction inside is cooled to room temperature, the battery cell with the PN junction inside is taken out of the diffusion furnace tube.

[0022] In one achievable manner, the material of the battery cell includes silicon.

[0023] In one achievable manner, in step S3, the temperature in the reaction furnace is 1040°C.

[0024] In an achievable manner, the square resistance of the battery cell having a PN junction inside is 150-300Ω / sq;

[0025] The sheet resistance of the battery sheet with the protective layer on the surface is 300-350Ω / sq.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] A diffusion process for a TOPCon battery of the present invention optimizes the preparation steps and adjusts the flow rate, temperature and pressure of the gas in the diffusion process to achieve effective boron doping without the need for an SE laser. The diffusion process provided by the present invention is simple, has fewer steps, and shortens the preparation time, thereby effectively reducing the production cost and avoiding the low yield caused by the high difficulty in controlling the power of the SE laser. The battery cell prepared by the diffusion process provided by the present invention has good doping effect and high battery photoelectric conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the steps of a diffusion process of a TOPCon battery provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0030] Embodiment 1

[0031] See also Figure 1 , Figure 1 yes Figure 1 It is a flow chart of the steps of a diffusion process of a TOPCon battery provided in an embodiment of the present invention.

[0032] The diffusion process of a TOPCon cell provided in this embodiment includes the following steps:

[0033] S1: Place the cell in a diffusion furnace tube and perform multiple boron source depositions at a preset temperature to form a PN junction on the surface of the cell.

[0034] Specifically, the material of the battery cell includes silicon.

[0035] In this embodiment, step S1 includes the following steps:

[0036] S11: placing the battery cell in a diffusion furnace tube, introducing a mixed gas of nitrogen, oxygen and BCl3 into the diffusion furnace tube, and performing the first boron source deposition at a preset temperature of 830-875°C.

[0037] Specifically, in step S11, the flow rate of nitrogen is 1800-2200 sccm, the flow rate of oxygen is 550-750 sccm, the flow rate of BCl3 is 150-230 sccm, and the pressure of nitrogen is 95-105 mbar. The deposition time of the first boron source deposition is 400 s.

[0038] S12: changing the flow rate of the mixed gas, and performing a second boron source deposition at a preset temperature of 830-875° C.

[0039] Specifically, in step S12, the flow rate of nitrogen is 3000-5000 sccm, the flow rate of oxygen is 550-750 sccm, the flow rate of BCl3 is 150-230 sccm, and the pressure of nitrogen is 160-200 mbar. The deposition time of the second boron source deposition is 300 s.

[0040] S2: nitrogen is introduced into the diffusion furnace tube, and multiple pushes are performed to push the PN junction into the interior of the battery cell, thereby obtaining a battery cell with a PN junction inside.

[0041] Specifically, step S2 includes the following steps:

[0042] S21: nitrogen is introduced into the diffusion furnace tube, and the first push is performed under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 300 mbar.

[0043] S22: Perform a second push under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 400 mbar.

[0044] Specifically, after the second advancement, the PN junction is advanced to the pre-determined depth inside the cell. In this embodiment, the square resistance of the cell with the PN junction inside obtained in step S2 is 150-300Ω / sq.

[0045] Specifically, between step S2 and step S3, the following is also included:

[0046] The battery cell with the PN junction inside is subjected to a cooling process. After the battery cell with the PN junction inside is cooled to room temperature, the battery cell with the PN junction inside is taken out of the diffusion furnace tube.

[0047] S3: placing a battery cell having a PN junction inside in a reaction furnace, introducing oxygen into the reaction furnace, and obtaining a battery cell having a protective layer on the surface.

[0048] Specifically, in step S3, the temperature in the reaction furnace is 1040°C. Oxygen reacts with the Si material on the surface of the cell to form a BSG protective layer rich in SiO2 on the surface of the cell to protect the PN junction inside the cell. In this embodiment, the cell with a protective layer on the surface obtained in step S3 has a square resistance of 300-350Ω / sq.

[0049] The present embodiment provides a diffusion process for a TOPCon battery. By optimizing the preparation steps and adjusting the flow rate, temperature and pressure of the gas in the diffusion process, effective boron doping can be achieved without the need for an SE laser. The diffusion process is simple, has fewer steps and a shorter preparation time, which effectively reduces production costs and avoids the low yield caused by the high difficulty in controlling the power of the SE laser. The battery cell prepared by the diffusion process provided in the present embodiment has good doping effect and high battery photoelectric conversion efficiency.

[0050] Embodiment 2

[0051] Based on the first embodiment, this embodiment provides a diffusion process of a TOPCon cell, including the following steps:

[0052] Step 1: Get the cell after texturing, put it into the diffusion furnace tube, introduce nitrogen, oxygen and BCl3 mixed gas into the diffusion furnace tube, and perform the first PN junction deposition at a temperature of 875°C for 400s. Among them, the flow rate of BCl3 is 210sccm, the flow rate of oxygen is 650sccm, the flow rate of nitrogen is 2000sccm, and the nitrogen pressure is 100mbar. After the first PN junction deposition, adjust the flow rate of BCl3 to 180sccm, the flow rate of oxygen to 650sccm, the flow rate of nitrogen to 4000sccm, and the nitrogen pressure to 180mbar. Perform the second PN junction deposition at a temperature of 875°C for 300s.

[0053] Step 2: Introduce nitrogen into the diffusion furnace tube for nitrogen purge, adjust the temperature in the diffusion furnace tube to 915°C, adjust the pressure to 300mbar, set the nitrogen flow rate to 4200sccm, and perform the first push. The time for the first push is 300s. After the first push is completed, introduce nitrogen into the diffusion furnace tube again for nitrogen purge, set the temperature in the diffusion furnace tube to 915°C, the pressure to 400mbar, set the nitrogen flow rate to 4200sccm, and perform the second push to obtain a battery cell with a PN junction inside. The time for the second push is 250s. After the second push is completed, cool the battery cell with a PN junction inside to room temperature and then take it out of the diffusion furnace tube.

[0054] Step 3: Place the battery cell with a PN junction inside in a reactor, introduce oxygen at a temperature of 1040°C, so that the oxygen reacts with Si to generate a BSG layer rich in SiO2, and obtain a battery cell with a protective layer on the surface.

[0055] Embodiment 3

[0056] Based on the second embodiment, this embodiment provides a diffusion process of a TOPCon cell, which differs from the second embodiment in that the temperature of the first PN junction deposition and the second PN junction deposition in step 1 are both 870° C. The remaining steps of this embodiment are the same as those of the second embodiment and will not be described again.

[0057] Embodiment 4

[0058] Based on the second embodiment, this embodiment provides a diffusion process of a TOPCon cell, which differs from the second embodiment in that the temperature of the first PN junction deposition and the second PN junction deposition in step 1 are both 850° C. The remaining steps of this embodiment are the same as those of the second embodiment and will not be described again.

[0059] Embodiment 5

[0060] Based on the second embodiment, this embodiment provides a diffusion process of a TOPCon cell, which differs from the second embodiment in that the temperature of the first PN junction deposition and the second PN junction deposition in step 1 are both 830° C. The remaining steps of this embodiment are the same as those of the second embodiment and will not be described again.

[0061] Comparative Example 1

[0062] This comparative example provides a conventional SE laser-assisted diffusion process, including:

[0063] Boron diffusion once: Get the cell after texturing, place it in a diffusion furnace tube, and introduce nitrogen, oxygen and BCl3 mixed gas into the diffusion furnace tube for the first PN junction deposition, and the deposition time is 200s. Among them, the flow rate of BCl3 is 245sccm, the flow rate of oxygen is 1000sccm, the flow rate of nitrogen is 4000sccm, the temperature is 820℃, and the nitrogen pressure is 120mbar. After the first PN junction deposition, introduce nitrogen, oxygen and BCl3 mixed gas into the diffusion furnace tube for the second PN junction deposition, and the deposition time is 350s. During the second PN junction deposition, the flow rate of BCl3 is 245sccm, the flow rate of oxygen is 1000sccm, the flow rate of nitrogen is 3200sccm, the temperature is 820℃, and the nitrogen pressure is 140mbar.

[0064] Purge and push: introduce nitrogen and BCl3 mixed gas for purge, nitrogen pressure is 140mbar, BCl3 flow rate is 300sccm, nitrogen flow rate is 2000sccm, temperature is 920℃, purge for 200s. Then change the nitrogen flow rate from 2000sccm to 3000sccm, push, push time is 480s. After the push is completed, cool down and take out the battery cell.

[0065] SE laser: laser grooves the cells after purging and advancement, with a power range of 40% to 70% and a frequency of 100KHz.

[0066] Secondary boron diffusion: Place the cell after SE laser treatment in a reactor, set the deposition reaction temperature to 1040°C, introduce oxygen, prepare an oxide layer on the surface of the cell, and obtain a cell with a protective layer on the surface.

[0067] Comparative Example 2

[0068] On the basis of comparative example 1, this comparative example provides a conventional SE laser-assisted diffusion process, which differs from comparative example 1 in that the flow rate of BCl3 is 215 sccm during the first PN junction deposition and the second PN junction deposition.

[0069] The doping effect of the cells with PN junctions in Example 2, Example 3, Example 4 and Example 5, and the cells after SE laser treatment in Comparative Example 1 and Comparative Example 2 were characterized, and the results are shown in Table 1.

[0070] Table 1

[0071] Classification Square resistance (Ω / sq) Boron doping concentration Knot depth Embodiment 2 150 <![CDATA[8.35×10 18 ]]> 1.1 Embodiment 3 180 <![CDATA[8.05×10 18 ]]> 1.05 Embodiment 4 220 <![CDATA[6.14×10 18 ]]> 1.08 Embodiment 5 300 <![CDATA[4.72×10 18 ]]> 1.00 Comparative Example 1 115 <![CDATA[1.5×10 19 ]]> 1.17 Comparative Example 2 125 <![CDATA[1.5×10 19 ]]> 1.15

[0072] From the data in Table 1, it can be seen that the square resistances of Example 2, Example 3, Example 4, and Example 5 are 150Ω, 180Ω, 220Ω, and 300Ω, respectively, and the square resistances of Comparative Example 1 and Comparative Example 2 are 115Ω and 125Ω, respectively. Compared with Examples 2 to 5, as the PN junction deposition temperature decreases, the boron doping concentration decreases, the square resistance increases, and the junction depth decreases.

[0073] The cells with protective layers on the surfaces prepared in Example 2, Example 3, Example 4, Example 5, Comparative Example 1 and Comparative Example 2 were used to prepare N-type Topcon cells to test the photoelectric conversion efficiency, open circuit voltage, short circuit current, fill factor, series resistance and parallel resistance of the cells.

[0074] The preparation steps of N-type Topcon battery include:

[0075] Back polishing: Get the cell with a protective layer on the surface, remove the BSG plated on the back of the cell through a chain machine, retain the front BSG to protect the front PN junction, and enter the alkaline polishing tank. The alkaline solution reacts with the silicon on the back of the cell. After the reaction, the reflectivity of the back of the cell is controlled at 47.5% to 49.5%, and the weight loss is controlled at 0.17g to 0.23g.

[0076] Preparation of tunneling oxide layer and poly-Si: Plasma enhanced chemical vapor deposition (PECVD) is used to prepare tunneling oxide layer and amorphous silicon layer. The thickness of the tunneling oxide layer is 1-2nm. Annealing is then performed to convert the amorphous silicon layer into polycrystalline silicon (poly-Si). After annealing, the square resistance range of the back side of the cell is 50±5Ω.

[0077] RCA removes BSG and PSG on the front and back sides: Through the RCA process, HF is used to remove BSG and PSG on the front and back sides of the battery cell, with a weight reduction range of 0.5g to 0.54g.

[0078] Front and back aluminum oxide deposition: Atomic layer deposition is used to deposit aluminum oxide film on the front and back of the cell at the same time, with the film thickness controlled at 2nm-3nm.

[0079] Front and back SiN X Deposition: Using PECVD method, SiH4, NH3 and other gases are introduced to coat the front and back of the cell with SiN X The film forms hydrogen passivation and promotes light absorption. After deposition, the front film thickness ranges from 67 to 77 nm, the front refractive index ranges from 2.03% to 2.12%, the back film thickness ranges from 73 to 83 nm, and the back refractive index ranges from 2.08% to 2.18%.

[0080] Screen printing and sintering: Complete screen printing in the order of back fine grid → back main grid → front fine grid → front main grid. After sintering, perform laser-assisted sintering LECO. The power of laser-assisted sintering is 30W and the voltage is 14V.

[0081] After completing the preparation steps of the above N-type Topcon cell, light injection was performed and DC was passed. The control conditions were standard spectrum of AM1.5, temperature of 25°C, and light intensity of 1000W / cm 2 The battery was tested with an IV tester for its photoelectric conversion efficiency Eta (%), open circuit voltage Uoc (V), short circuit current Isc (A), fill factor FF (%), series resistance Rs (Ω), and parallel resistance Rsh (Ω). The test results are shown in Table 2.

[0082] Table 2

[0083] Square resistance (Ω / sq) Eta(%) Uoc(V) Isc(A) FF(%) Rs(Ω) Rsh(Ω) Embodiment 2 150 26.259 0.726 13.975 85.339 0.0014 2279 Embodiment 3 180 26.424 0.7294 14.000 85.426 0.0014 2287 Embodiment 4 220 26.515 0.731 13.99 85.53 0.0014 2289 Embodiment 5 300 26.435 0.7311 14.031 85.08 0.0013 2165 Comparative Example 1 125 26.456 0.727 14.02 85.55 0.0012 1746 Comparative Example 2 115 26.485 0.728 14.042 85.49 0.0013 2017

[0084] From the data in Table 2, it can be seen that the photoelectric conversion efficiency of Example 4 is 26.515%, which has the best photoelectric conversion efficiency compared with the other examples and comparative examples.

[0085] Compared with Example 5, Example 4 has improved photoelectric conversion efficiency, reduced short-circuit current by 0.04A, increased fill factor, increased series resistance, and increased parallel resistance. This shows that when the boron diffusion deposition temperature is 850°C, the doping concentration and junction depth obtained by boron diffusion are the best. When the reaction temperature is lower than 850°C, the boron doping concentration decreases and the boron doping effect decreases.

[0086] Compared with Comparative Example 1 and Comparative Example 2, the photoelectric conversion efficiency of Example 4 is greater than that of Comparative Example 1 and Comparative Example 2, and the photoelectric conversion efficiency of Example 2, Example 3 and Example 5 is not much different from that of Comparative Example 1 and Comparative Example 2. The experimental results show that under the same process, the performance of the cell prepared by the diffusion process provided by the present invention is equivalent to that of the conventional SE laser assisted diffusion process, and the performance of the cell prepared by the diffusion process of the present invention is better than that of the SE laser assisted diffusion process under the optimal parameters. The diffusion process provided by the present invention can achieve effective doping without SE laser, has a simple process method, short preparation time, and low preparation cost, and can avoid the SE laser from generating defects and recombination centers on the surface of the cell, which leads to a decrease in cell efficiency.

[0087] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A diffusion process for a TOPCon cell, characterized in that: The following steps are involved: S1: placing the cell in a diffusion furnace tube, performing multiple boron source depositions at a preset temperature, and forming a PN junction on the surface of the cell; S2: introducing nitrogen into the diffusion furnace tube, pushing the PN junction into the interior of the battery cell for multiple times, and obtaining a battery cell with a PN junction inside; S3: placing the battery cell with a PN junction inside in a reaction furnace, introducing oxygen into the reaction furnace, and obtaining a battery cell with a protective layer on the surface.

2. The diffusion process of a TOPCon cell according to claim 1, characterized in that: The step S1 comprises the following steps: S11: placing the battery cell in a diffusion furnace tube, introducing a mixed gas of nitrogen, oxygen and BCl3 into the diffusion furnace tube, and performing the first boron source deposition at a preset temperature of 830-875°C; S12: changing the flow rate of the mixed gas, and performing a second boron source deposition at a preset temperature of 830-875°C.

3. The diffusion process of a TOPCon cell according to claim 2, characterized in that: In the step S11, the flow rate of the nitrogen gas is 1800-2200 sccm, the flow rate of the oxygen gas is 550-750 sccm, the flow rate of the BCl 3 is 150-230 sccm, and the pressure of the nitrogen gas is 95-105 mbar.

4. The diffusion process of a TOPCon cell according to claim 2, characterized in that: In the step S12, the flow rate of the nitrogen gas is 3000-5000 sccm, the flow rate of the oxygen gas is 550-750 sccm, the flow rate of the BCl 3 is 150-230 sccm, and the pressure of the nitrogen gas is 160-200 mbar.

5. The diffusion process of a TOPCon cell according to claim 2, characterized in that: The deposition time of the first boron source deposition is 400s; The deposition time of the second boron source deposition is 300 s.

6. The diffusion process of a TOPCon cell according to claim 1, characterized in that: The step S2 comprises the following steps: S21: introducing nitrogen into the diffusion furnace tube, and performing the first push under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 300 mbar; S22: A second push is performed under the conditions of a nitrogen flow rate of 3600-4500 sccm, a temperature of 915° C., and a pressure of 400 mbar.

7. The diffusion process of a TOPCon cell according to claim 1, characterized in that: The steps S2 and S3 also include: The battery cell with the PN junction inside is subjected to a cooling process, and after the battery cell with the PN junction inside is cooled to room temperature, the battery cell with the PN junction inside is taken out of the diffusion furnace tube.

8. The diffusion process of a TOPCon cell according to claim 1, characterized in that: The material of the battery cell includes silicon.

9. The diffusion process of a TOPCon cell according to claim 1, characterized in that: In step S3, the temperature in the reaction furnace is 1040°C.

10. The diffusion process of a TOPCon cell according to claim 1, characterized in that: The square resistance of the battery cell with a PN junction inside is 150-300Ω / sq; The sheet resistance of the battery sheet with the protective layer on the surface is 300-350Ω / sq.

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