Annealing process to reduce poly-silicon doped blowhole

Abstract

The application discloses an annealing process for reducing polycrystalline silicon doping film explosion. The existing TOPCon cell has a tunneling oxide layer and a polycrystalline silicon doping layer on the back surface of a silicon wafer; generally, in order to ensure the conversion efficiency and reduce the internal resistance, the polycrystalline silicon doping layer has a high doping concentration, so that the back surface of the TOPCon cell has a large number of recombination centers, and the film explosion is easy to occur, thereby reducing the photoelectric conversion efficiency of the cell. The application discloses an annealing process for reducing polycrystalline silicon doping film explosion, by strictly controlling the process parameters such as temperature, pressure, nitrogen filling flow rate and the like, the problem of serious carrier recombination on the back surface of the TOPCon cell is solved, the phenomenon of film explosion on the back surface of the silicon wafer is reduced, and the photoelectric conversion efficiency of the cell is improved.

Description

Technical Field

[0001] This invention relates to the technical field of solar cells, and in particular to an annealing process for reducing polycrystalline silicon doping and film cracking. Background Technology

[0002] Existing TOPCon solar cells (tunneling oxide passivation cells) have a tunneling oxide layer and a polycrystalline silicon doped layer on the back of the silicon wafer. Generally, to ensure conversion efficiency and reduce internal resistance, the polycrystalline silicon doped layer has a high doping concentration. However, this increased doping concentration also results in larger recombination centers on the back of the TOPCon cell, leading to film bursting and reducing the cell's photoelectric conversion efficiency. This invention discloses an annealing process to reduce polycrystalline silicon doping film bursting, which can effectively reduce the phenomenon of film bursting on the back of the silicon wafer, thereby improving the photoelectric conversion efficiency of the solar cell. Summary of the Invention

[0003] Purpose of the invention

[0004] To address the problem of polycrystalline silicon doping layer increasing doping concentration in existing TOPCon cells, which leads to larger recombination centers on the back side of the TOPCon cell and causes film explosion, this invention proposes an annealing process to reduce polycrystalline silicon doping film explosion.

[0005] Technical solution

[0006] An annealing process for reducing polysilicon doping film explosion includes the following steps:

[0007] S1. Nitrogen purging and boat loading: The silicon wafers after the back polycrystalline silicon passivation film process are loaded into a quartz boat and placed on silicon carbide slurry. The boat loading temperature is maintained at 770 to 790°C, and the wafers are fed into the furnace tube at a speed of 120 mm / s. Under positive pressure conditions of nitrogen flow rate of 10000 sccm and tube pressure of 1060 Pa, the boat loading time is 600 s.

[0008] S2. Low-pressure heating: Maintain the set temperature of the carrier boat at 810 to 830°C. Under a negative pressure environment of 400 Pa, heat the inside of the quartz boat to 810 to 830°C at a rate of 5°C / min for 480 seconds.

[0009] S3. Constant temperature purging: Purging at a constant temperature of 810 to 830℃, a pressure of 400 Pa, a nitrogen flow rate of 6000 sccm, and a constant purging time of 300 s.

[0010] S4. Temperature-changing push-bonding: Under the conditions of nitrogen flow rate of 6000 sccm and pressure of 600 Pa, the temperature inside the quartz boat is increased from 810 to 830℃ to 910 to 930℃, and the temperature change time is 900s.

[0011] S5. High-temperature passivation: Passivation treatment is performed at a temperature of 910 to 930°C, a nitrogen flow rate of 8000 sccm, and a pressure of 600 Pa for 2700 seconds.

[0012] S6. Cooling and depressurization: Set the target state to a temperature of 800℃ and a pressure of 1060pa. Supplement nitrogen with nitrogen at a flow rate of 10000sccm to lower the temperature and increase the pressure inside the quartz boat. The process takes 1800s.

[0013] S7. Nitrogen purging and unloading: Place the quartz boat containing the processed silicon wafer onto the silicon carbide slurry, maintain the unloading temperature at 770 to 790°C, and feed it out of the furnace tube at a speed of 120 mm / s. Purge nitrogen gas at a rate of 10,000 sccm to ensure a positive pressure inside the tube. The unloading time is 600 s.

[0014] Beneficial effects

[0015] This invention provides an annealing process to reduce polycrystalline silicon doping film explosion. By precisely controlling the process temperature, it reduces carrier recombination on the back of the TOPCon cell and reduces film explosion on the back of the silicon wafer, thereby improving the photoelectric conversion efficiency of the cell. Attached Figure Description

[0016] Figure 1 This is a microscopic observation of control sample one in an embodiment of the present invention;

[0017] Figure 2 This is a microscopic observation of control sample two in an embodiment of the present invention;

[0018] Figure 3 This is a microscopic observation of sample one from the experimental group of an embodiment of the present invention;

[0019] Figure 4 This is a microscopic observation of sample two in the experimental group of an embodiment of the present invention;

[0020] Figure 5 This is an observation diagram of the PL testing machine for control group sample one in an embodiment of the present invention;

[0021] Figure 6 This is an observation diagram of the PL tester for control group sample two in an embodiment of the present invention;

[0022] Figure 7 This is an observation diagram of the PL testing machine for experimental group sample one in an embodiment of the present invention;

[0023] Figure 8 This is an observation diagram of the PL testing machine for experimental sample two in an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present invention, the invention will now be further described in conjunction with the accompanying drawings and specific embodiments. Example

[0025] An annealing process for reducing polysilicon doping film explosion includes the following steps:

[0026] S1. Nitrogen purging and boat loading: The silicon wafers after the back polycrystalline silicon passivation film process are loaded into a quartz boat and placed on silicon carbide slurry. The boat loading temperature is maintained at 780℃, and the wafers are fed into the furnace tube at a speed of 120mm / s. Under the positive pressure conditions of nitrogen flow rate of 10000sccm and tube pressure of 1060pa, the boat loading time is 600s.

[0027] S2. Low-pressure heating: Maintain the set temperature of the carrier boat at 820℃, and heat the inside of the quartz boat to 820℃ at a rate of 5℃ / min under a negative pressure environment of 400pa for 480s.

[0028] S3. Constant temperature purging: Purging is carried out at a constant temperature of 820℃, a pressure of 400pa, a nitrogen flow rate of 6000sccm, and a constant purging time of 300s.

[0029] S4. Temperature-changing bonding: Under the conditions of nitrogen flow rate of 6000 sccm and pressure of 600 Pa, the temperature inside the quartz boat is increased from 820°C to 920°C, and the temperature change time is 900 s.

[0030] S5. High-temperature passivation: Passivation treatment is performed at a temperature of 920℃, a nitrogen flow rate of 8000 sccm, and a pressure of 600 Pa for 2700 s.

[0031] S6. Cooling and depressurization: Set the target state to a temperature of 800℃ and a pressure of 1060pa. Supplement nitrogen with nitrogen at a flow rate of 10000sccm to lower the temperature and increase the pressure inside the quartz boat. The process takes 1800s.

[0032] S7. Nitrogen purging and unloading: Place the quartz boat containing the processed silicon wafer onto the silicon carbide slurry, maintain the unloading temperature at 780℃, and feed it out of the furnace tube at a speed of 120mm / s. Purge nitrogen gas at a rate of 10000sccm to ensure a positive pressure inside the tube. The unloading time is 600s.

[0033] After fully executing the above process, TOPCon battery samples processed using this technology were obtained. As a solution group, the polycrystalline silicon doped film bursting at two locations on the back of the solution group samples was observed and recorded using a Keyence 3D microscope. Figure 3 and Figure 4 , Figure 3 and Figure 4The sample showed no burst film and its structure was a complete pyramid base; then, using an Ingel PL tester, PL images of two polycrystalline silicon doped burst films on the back of the sample were observed and recorded, yielding... Figure 7 and Figure 8 It is a bright flake.

[0034] Meanwhile, TOPCon batteries exhibiting film bursting issues were selected from the market as a bursting group. The bursting conditions of two polycrystalline silicon doped areas on the back of the bursting group samples were observed and recorded using a Keyence 3D microscope. Figure 1 and Figure 2 , Figure 1 and Figure 2 The light-colored bright spots in the image represent the film bursting phenomenon; then, using an Ingel PL testing machine, the PL images of two polycrystalline silicon doped bursting areas on the back of the bursting film group sample were observed and recorded to obtain... Figure 5 and Figure 6 , is a dark film.

[0035] Finally, the technical parameters of 391 TOPCon batteries with burst film and 389 TOPCon batteries with solution were tested, and the average values ​​were obtained as shown in Table 1 below.

[0036] Table 1

[0037] Label Title Eta / % Uoc / V Isc / A FF Rs / Ω Rsh / Ω IRev2 / A Membrane bursting group 391 24.7585 0.707 13.3763 86.4163 0.00142 1425.916 0.342 Solution Group 389 25.3567 0.711 13.4289 87.6680 -0.0002 1557.054 0.2608 Gap / 0.5982 0.004 0.0526 1.2517 -0.0016 131.1380 -0.0812

[0038] In the table, Title indicates the number of solar cells tested in the comparative experiment, Eta indicates the energy conversion efficiency, Uoc indicates the open-circuit voltage, Isc indicates the short-circuit current, FF indicates the fill factor, Rs indicates the series resistance of the solar cell, Rsh indicates the parallel resistance of the solar cell, and IRev2 indicates the reverse leakage current. The electrical performance data in the table are average values. The Gap row refers to the difference in various electrical performance values ​​between the bursting group and the solved group. It can be seen that the beneficial indicators of the TOPCon cells treated by this process are improved, ultimately resulting in an increase in conversion efficiency of 0.5982%.

[0039] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An anneal process to reduce poly-silicon doping pop corn, characterized in that, The steps include: S1. N2 in boat, after the back of the silicon wafer loaded in the quartz boat and placed in the silicon slurry, keep the boat temperature 770-790 ℃, with a speed of 120 mm / s into the furnace tube, according to the nitrogen flow 10000 sccm, the pressure 1060 pa in the tube positive pressure state, in the boat time for 600 s; S2. Low pressure heating, keep the boat set temperature 810-830 ℃, according to the pressure 400 pa negative pressure environment, with a rate of 5 ℃ / min to 810-830 ℃ in the quartz boat, heating time 480 s; S3. Constant temperature purge, according to the constant temperature 810-830 ℃, pressure 400 pa, nitrogen flow 6000 sccm purge state, constant purge time 300 s; S4. Temperature push knot, according to the nitrogen flow 6000 sccm, pressure 600 pa, the temperature of the quartz boat from 810-830 ℃ to 910-930 ℃, temperature time 900 s; S5. High temperature passivation, according to the temperature 910-930 ℃, nitrogen flow 8000 sccm, pressure 600 pa, execute passivation treatment, passivation time 2700 s; S6. Cooling back pressure, the target state is set to temperature 800 ℃, pressure 1060 pa, with the nitrogen flow rate of 10000 sccm to supplement the nitrogen, the temperature of the quartz boat to reduce, pressure rise, process time 1800 s; S7. N2 out of the boat, the quartz boat of the silicon wafer after processing is placed on the silicon slurry, keep the boat temperature 770-790 ℃, with a speed of 120 mm / s out of the furnace tube, according to the rate of 10000 sccm into the nitrogen, ensure that the tube is positive pressure state, out of the boat time 600 s.

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