A diffusion process for improving high sheet resistance uniformity of solar cells

Abstract

The application provides a diffusion process for improving high sheet resistance uniformity of a solar cell, comprising the following steps: pressure extraction; pre-oxidation; first deposition of large and small nitrogen and oxygen, pressure reduction by 10 mbar, and constant temperature; second deposition of large and small nitrogen and oxygen, temperature increase by 10 DEG C, and constant pressure; first pushing, stop of air supply, pressure increase by 10 mbar, and temperature increase by 70 DEG C; second pushing, oxygen supply, constant pressure and temperature; third pushing, stop of air supply, constant pressure and temperature; fourth pushing, temperature decrease by 70 DEG C, and constant pressure; third deposition of large and small nitrogen and oxygen, pressure reduction by 10 mbar, and constant temperature; fifth pushing, stop of air supply, pressure increase by 10 mbar, and constant temperature; phosphorus supplement, large and small nitrogen and oxygen supply, constant pressure and temperature; post-oxidation; and pressure return. The scheme realizes high sheet resistance of large-size cell pieces and improves the uniformity of high sheet resistance by optimizing the diffusion process, and achieves the optimization of cell efficiency distribution and the improvement of cell efficiency.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic cell manufacturing, and particularly relates to a diffusion process for improving the uniformity of high sheet resistance in solar cells. Background Technology

[0002] The increase in silicon wafer size has become a major trend in the photovoltaic industry. Companies in the industry have generally established product routes for large-size cells and modules. This is because, on the manufacturing side, large-size silicon wafers can increase the output of silicon wafers, cells, and modules, thereby reducing the production cost per watt. On the product side, large-size silicon wafers can effectively increase module power and improve module efficiency by optimizing cell and module design. On the system side, as the power and efficiency of individual modules increase, large-size silicon wafers can reduce the costs of brackets, combiner boxes, cables, land, etc., thereby reducing the cost per watt of system.

[0003] In battery manufacturing, high sheet resistance emitter solar cells can effectively improve the conversion efficiency of solar cells due to their good short-wavelength spectral response and carrier recombination characteristics. However, the increase in silicon wafer size and the increase in emitter sheet resistance make it difficult to control the uniformity of diffusion sheet resistance to a certain extent. The uniformity of diffusion sheet resistance not only affects the conversion efficiency of the cell, but also affects the distribution of the cell efficiency. Therefore, research on the uniformity of large-size high sheet resistance solar cells is crucial. Summary of the Invention

[0004] In view of the above, this invention provides a diffusion process for improving the uniformity of high sheet resistance in solar cells. By optimizing the diffusion process parameters, it achieves large-size, high sheet resistance cells while simultaneously improving the uniformity of high sheet resistance, thereby optimizing the cell efficiency distribution and improving cell efficiency. The specific technical solution is as follows.

[0005] A diffusion process for improving the uniformity of high sheet resistance in solar cells, characterized by the following steps:

[0006] Step 1, Pressure Pumping: A quartz boat filled with qualified texturized silicon wafers is introduced into the furnace tube. After the furnace door is closed, the pressure is set to 65 mbar, and air leakage is checked.

[0007] Step 2, Pre-oxidation: Keep the pressure setting unchanged, continuously introduce oxygen into the furnace tube, and set the temperature to 770-790℃.

[0008] Step 3, First gas deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, reduce the pressure setting by 10 mbar, and keep the temperature unchanged.

[0009] Step 4, Second High-Temperature Gas Deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, increase the temperature by 10°C, and keep the pressure setting unchanged.

[0010] Step 5, First push: Stop gas supply, increase pressure by 10 mbar, increase temperature by 70°C, and continue for a period of time.

[0011] Step 6, Second push: Continuously introduce oxygen into the furnace tube, keeping the pressure and temperature unchanged.

[0012] Step 7, Third push: Stop gas supply, keep the pressure and temperature unchanged, and continue for a period of time.

[0013] Step 8, Fourth push: Adjust the temperature to drop by 70°C, keep the pressure setting unchanged, and continue for a period of time.

[0014] Step 9, Third Gas Deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, reduce the pressure setting by 10 mbar, and keep the temperature unchanged.

[0015] Step 10, Fifth push: Stop gas supply, increase pressure by 10 mbar, keep temperature unchanged, and continue for a period of time.

[0016] Step 11, Phosphorus replenishment: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, increase the flow rate of small nitrogen, and keep the pressure and temperature unchanged.

[0017] Step 12, Post-oxidation: Continuously introduce oxygen into the furnace tube, keep the pressure setting unchanged, and reduce the temperature by 10°C.

[0018] Step 13, back pressure: Continuously introduce large amounts of nitrogen into the furnace tube and set the pressure to 1060 mbar.

[0019] Furthermore, the pumping time is 300s, and the pre-oxidation time is 100-200s.

[0020] Furthermore, the initial gas deposition process involves a high nitrogen flow rate of 350 ml / min, a low nitrogen flow rate of 1060 ml / min, an oxygen flow rate of 600 ml / min, and a duration of 240 s.

[0021] Furthermore, the flow rate of the large nitrogen in the second high-temperature gas deposition is 350 ml / min, the flow rate of the small nitrogen is 1060 ml / min, the flow rate of oxygen is 600 ml / min, and the duration is 210 s.

[0022] Furthermore, the duration of the first thrust is 300 seconds, the duration of the second thrust is 120 seconds, the duration of the third thrust is 360 seconds, and the duration of the fourth thrust is 1000 seconds.

[0023] Furthermore, the third gas deposition process involves a large nitrogen flow rate of 200 ml / min, a small nitrogen flow rate of 1200 ml / min, an oxygen flow rate of 600 ml / min, and a duration of 60 s.

[0024] Furthermore, the duration of the fifth thrust is 180 seconds.

[0025] Furthermore, the nitrogen flow rate for phosphorus supplementation is 200 ml / min, the nitrogen flow rate is 1300 ml / min, the oxygen flow rate is 600 ml / min, and the duration is 660 s.

[0026] Furthermore, the oxygen flow rate introduced during the post-oxidation process is 1400 ml / min, and the duration is 100-200 s.

[0027] Furthermore, the high nitrogen flow rate introduced under back pressure is 20,000 ml / min, and the duration is 300 s.

[0028] The diffusion process of this invention, which improves the uniformity of sheet resistance in solar cells, optimizes the diffusion steps and adjusts the pressure, pump speed, gas flow rate, and temperature at different stages of the process. This makes the reaction between gases in the furnace tube more complete and uniform throughout the diffusion process, and the reaction state more stable. Without the need for additional equipment, the large-size solar cells produced can achieve both high sheet resistance and low sheet resistance uniformity. This effectively improves the conversion efficiency of the solar cells after optimized diffusion, and makes the distribution of solar cell conversion efficiency levels more concentrated.

[0029] Additional aspects and advantages of the invention will be further set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. Attached Figure Description

[0030] Figure 1 This is a flowchart of the method of the present invention;

[0031] Figure 2 The TI temperature range sheet resistance map is shown for the experimental and control groups.

[0032] Figure 3 T2 temperature range sheet resistance map for the experimental and control groups;

[0033] Figure 4 T3 temperature range sheet resistance map for the experimental and control groups;

[0034] Figure 5 T4 temperature range sheet resistance map for the experimental and control groups;

[0035] Figure 6 T5 temperature range sheet resistance map for the experimental and control groups;

[0036] Figure 7 The sheet resistance map for the T6 temperature range is shown for the experimental and control groups. Detailed Implementation

[0037] The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0038] Example 1

[0039] In this embodiment, refer to Figure 1 The diffusion process for improving the uniformity of high sheet resistance in solar cells includes the following steps:

[0040] Step 1, Pressure Pumping: A quartz boat filled with qualified texturized silicon wafers is placed into the furnace tube. After the furnace door is closed, the pressure is set to 65 mbar, the pressure pumping time is 300 seconds, and air leakage is checked.

[0041] Step 2, Pre-oxidation: The pressure setting remains unchanged at 65 mbar. Oxygen is continuously introduced into the furnace tube at a flow rate of 1150 ml / min for 150 seconds, and the temperature is set to 770℃.

[0042] Step 3, First gas deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, set the pressure to 55 mbar, keep the temperature at 770℃, the flow rate of large nitrogen is 350 ml / min, the flow rate of small nitrogen is 1060 ml / min, the flow rate of oxygen is 600 ml / min, and the duration is 240 s.

[0043] Step 4, Second High-Temperature Gas Deposition: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube. Set the temperature to 780℃, the pressure to 55mbar, the flow rate of large nitrogen to 350ml / min, the flow rate of small nitrogen to 1060ml / min, and the flow rate of oxygen to 600ml / min for 210s.

[0044] Step 5, First push: Stop gas supply, set the pressure to 65 mbar, raise the temperature to 850℃, and continue for 300 seconds.

[0045] Step 6, Second push: Continue to introduce oxygen into the furnace tube, keeping the pressure and temperature settings unchanged, the same as the first push in the previous step, for 120 seconds, with an oxygen flow rate of 700 ml / min.

[0046] Step 7, Third push: Stop gas supply, keep the pressure and temperature settings unchanged, the same as the second push in the previous step, for 360 seconds.

[0047] Step 8, Fourth push: Adjust the temperature to drop from 70°C to 780°C, set the pressure to 65 mbar, and continue for 1000 seconds.

[0048] Step 9, Third Gas Deposition: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube, keep the temperature at 780℃, reduce the pressure setting by 10mbar to 55mbar, and introduce large nitrogen at a flow rate of 200ml / min, small nitrogen at a flow rate of 1200ml / min, and oxygen at a flow rate of 600ml / min for 60s.

[0049] Step 10, Fifth push: Stop gas supply, increase pressure by 10 mbar to 65 mbar, keep temperature at 780℃, and continue for 180 seconds.

[0050] Step 11, Phosphorus replenishment: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube, increase the flow rate of small nitrogen, set the pressure to 65 mbar, keep the temperature at 780℃, and introduce large nitrogen at a flow rate of 200 ml / min, small nitrogen at a flow rate of 1300 ml / min, and oxygen at a flow rate of 600 ml / min for 660 seconds.

[0051] Step 12, Post-oxidation: Continuously introduce oxygen into the furnace tube, keep the pressure setting unchanged, reduce the temperature by 10°C to 770°C, and introduce oxygen at a flow rate of 1400 ml / min for 150 seconds.

[0052] Step 13, back pressure: Continuously introduce nitrogen into the furnace tube at a flow rate of 20,000 ml / min, and set the pressure to 1060 mbar for 300 seconds.

[0053] Example 2

[0054] The diffusion process for improving the uniformity of high sheet resistance in solar cells in this embodiment includes the following steps:

[0055] Step 1, Pressure Pumping: A quartz boat filled with qualified texturized silicon wafers is placed into the furnace tube. After the furnace door is closed, the pressure is set to 65 mbar, the pressure pumping time is 300 seconds, and air leakage is checked.

[0056] Step 2, Pre-oxidation: The pressure setting remains unchanged at 65 mbar. Oxygen is continuously introduced into the furnace tube at a flow rate of 1000 ml / min for 200 seconds, and the temperature is set to 770℃.

[0057] Step 3, First gas deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, set the pressure to 55 mbar, keep the temperature at 770℃, the flow rate of large nitrogen is 350 ml / min, the flow rate of small nitrogen is 1060 ml / min, the flow rate of oxygen is 600 ml / min, and the duration is 240 s.

[0058] Step 4, Second High-Temperature Gas Deposition: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube. Set the temperature to 780℃, the pressure to 55mbar, the flow rate of large nitrogen to 350ml / min, the flow rate of small nitrogen to 1060ml / min, and the flow rate of oxygen to 600ml / min for 210s.

[0059] Step 5, First push: Stop gas supply, set the pressure to 65 mbar, raise the temperature to 850℃, and continue for 300 seconds.

[0060] Step 6, Second push: Continue to introduce oxygen into the furnace tube, keeping the pressure and temperature settings unchanged, the same as the first push in the previous step, for 120 seconds, with an oxygen flow rate of 700 ml / min.

[0061] Step 7, Third push: Stop gas supply, keep the pressure and temperature settings unchanged, the same as the second push in the previous step, for 360 seconds.

[0062] Step 8, Fourth push: Adjust the temperature to drop from 70°C to 780°C, set the pressure to 65 mbar, and continue for 1000 seconds.

[0063] Step 9, Third Gas Deposition: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube, keep the temperature at 780℃, reduce the pressure setting by 10mbar to 55mbar, and introduce large nitrogen at a flow rate of 200ml / min, small nitrogen at a flow rate of 1200ml / min, and oxygen at a flow rate of 600ml / min for 60s.

[0064] Step 10, Fifth push: Stop gas supply, increase pressure by 10 mbar to 65 mbar, keep temperature at 780℃, and continue for 180 seconds.

[0065] Step 11, Phosphorus replenishment: Continuously introduce large nitrogen, small nitrogen, and oxygen into the furnace tube, increase the flow rate of small nitrogen, set the pressure to 65 mbar, keep the temperature at 780℃, and introduce large nitrogen at a flow rate of 200 ml / min, small nitrogen at a flow rate of 1300 ml / min, and oxygen at a flow rate of 600 ml / min for 660 seconds.

[0066] Step 12, Post-oxidation: Continuously introduce oxygen into the furnace tube, keep the pressure setting unchanged, reduce the temperature by 10°C to 770°C, and introduce oxygen at a flow rate of 1400 ml / min for 150 seconds.

[0067] Step 13, back pressure: Continuously introduce nitrogen into the furnace tube at a flow rate of 20,000 ml / min, and set the pressure to 1060 mbar for 300 seconds.

[0068] Experimental verification of the diffusion process of this invention was conducted. First, 2800 gallium-doped single-crystal silicon wafers with dimensions of 182mm × 182mm × 155µm were selected. The resistivity of the silicon wafers was 0.4–1.1Ω, and the thickness was 150µm–155µm. The selected silicon wafers underwent conventional texturing using the same texturing machine. After texturing, the silicon wafers were divided into two groups and pushed into a diffusion furnace tube with a diameter of 420mm, serving as the control group and the experimental group, respectively. The control group maintained a constant pressure of 65mbar throughout the diffusion process, and a high nitrogen gas flow rate of 32L / min was introduced during the pushing process. The experimental group is Example 1 of this application. After diffusion was completed in both groups, one wafer was extracted from the middle position of each of the six isothermal zones corresponding to the diffusion furnace tube on the quartz boat. The six isothermal zones are furnace opening T1, secondary furnace opening T2, furnace middle T3, secondary furnace middle T4, secondary furnace tail T5, and furnace tail T6. Therefore, a total of 6 wafers were extracted. The sheet resistance of the silicon wafer at the center point and the four corners was measured using a four-probe sheet resistance meter. The standard deviation (STD) of the wafer was calculated. The high sheet resistance value and uniformity test results of the low-concentration doped region after optimized diffusion are shown in Table 1 below (unit: Ω / □):

[0069]

[0070] Combining Table 1 above and Figures 2-7 It can be seen that the sheet resistance distribution on the silicon wafer is higher at the top and lower at the bottom in the control group, while it is higher in the middle and lower around the edges in the experimental group. The sheet resistance distribution in the experimental group is more concentrated, and the non-uniformity is reduced by 1.15%.

[0071] Further processing was performed on the experimental and control groups until they were manufactured into monocrystalline PERC solar cells. The resulting monocrystalline PERC laser-doped solar cells were then tested for conversion efficiency using an IV tester, and the distribution of conversion efficiency levels was analyzed. The conversion efficiency test results (average values) of the monocrystalline PERC laser-doped solar cells obtained in the embodiments of this invention are shown in Table 2 below:

[0072]

[0073] In the large-size high sheet resistance battery after diffusion, the sheet resistance non-uniformity of the experimental group using the process of the present invention is reduced, and the sheet resistance distribution is more concentrated. As shown in Table 2, compared with the control group, the experimental group using the present invention has a higher concentration of cell conversion efficiency levels, and the cell conversion efficiency is improved by 0.03%.

[0074] In summary, this invention, by comprehensively adjusting the diffusion process and parameters, and redesigning the corresponding ratios of pressure, temperature, gas flow, and time throughout the diffusion process, enables the solar cell to retain a high sheet resistance value while effectively improving the uniformity of the high sheet resistance. This results in solar cells with good sheet resistance uniformity, a more concentrated efficiency distribution within the solar cell, and an effective improvement in efficiency.

[0075] Although specific embodiments of the invention have been described in detail with reference to illustrative examples, it should be understood that those skilled in the art can devise various other modifications and embodiments that fall within the spirit and scope of the invention. Specifically, reasonable variations and modifications can be made to the arrangement of components and / or dependent combinations within the scope of the foregoing disclosure, drawings, and claims without departing from the spirit of the invention. The scope of these variations and modifications, except for those concerning components and / or layout, is defined by the appended claims and their equivalents.

Claims

1. A diffusion process for improving the uniformity of high sheet resistance in solar cells, characterized in that, The diffusion process includes the following steps: Step 1, Pressure Pumping: A quartz boat filled with qualified texturized silicon wafers is placed into the furnace tube. After the furnace door is closed, the pressure is set to 65 mbar, the pressure pumping time is 300 seconds, and air leakage is checked. Step 2, Pre-oxidation: Keep the pressure setting unchanged, continuously introduce oxygen into the furnace tube at a flow rate of 1000-1150 ml / min for 150-200 seconds, and set the temperature to 770℃; Step 3, First gas deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, reduce the pressure setting by 10 mbar, keep the temperature unchanged, the flow rate of large nitrogen is 350 ml / min, the flow rate of small nitrogen is 1060 ml / min, the flow rate of oxygen is 600 ml / min, and the duration is 240 s. Step 4, Second High-Temperature Gas Deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, increase the temperature by 10°, keep the pressure setting unchanged, and introduce large nitrogen at a flow rate of 350 ml / min, small nitrogen at a flow rate of 1060 ml / min and oxygen at a flow rate of 600 ml / min for a duration of 210 s. Step 5, First push: Stop gas supply, increase pressure by 10 mbar, increase temperature by 70°C, and continue for 300 seconds; Step 6, Second push: Continuously introduce oxygen into the furnace tube, keeping the pressure and temperature unchanged, for 120 seconds, with an oxygen flow rate of 700 ml / min. Step 7, Third push: Stop gas supply, keep pressure and temperature unchanged, and continue for 360 seconds; Step 8, Fourth push: Adjust the temperature to drop by 70°C, keep the pressure setting unchanged, and continue for 1000 seconds; Step 9, Third gas deposition: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, temperature 780℃, pressure set reduced by 10mbar, temperature unchanged, large nitrogen flow rate is 200ml / min, small nitrogen flow rate is 1200ml / min, oxygen flow rate is 600ml / min, for 60s. Step 10, Fifth push: Stop gas supply, increase pressure by 10 mbar, keep temperature unchanged, and continue for 180 seconds; Step 11, Phosphorus supplementation: Continuously introduce large nitrogen, small nitrogen and oxygen into the furnace tube, increase the flow rate of small nitrogen, keep the pressure setting and temperature unchanged, the flow rate of large nitrogen is 200ml / min, the flow rate of small nitrogen is 1300ml / min, the flow rate of oxygen is 600ml / min, and continue for 660s. Step 12, Post-oxidation: Continuously introduce oxygen into the furnace tube, keep the pressure setting unchanged, and reduce the temperature by 10°. Step 13, back pressure: Continuously introduce nitrogen into the furnace tube at a flow rate of 20,000 ml / min and set the pressure to 1060 mbar.

2. The diffusion process for improving the uniformity of high sheet resistance in solar cells according to claim 1, characterized in that, The oxygen flow rate introduced during the post-oxidation process is 1400 ml / min, and the duration is 100-200 s.

3. The diffusion process for improving the uniformity of high sheet resistance in solar cells according to claim 1, characterized in that, The duration of the back pressure introducing nitrogen is 300 seconds.

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