Method for improving the winding degree of single-sided aluminum oxide of photovoltaic cell, photovoltaic cell and preparation method thereof

Abstract

The present invention discloses a method for improving the winding degree of aluminum oxide on one side of a photovoltaic cell, a photovoltaic cell and a preparation method thereof, and belongs to the technical field of photovoltaic cell preparation. The method of the present invention comprises: after texturing, boron diffusion, back etching, tunneling oxide layer and doping amorphous silicon, annealing, de-winding plating, double insertion of aluminum oxide, and deposition of silicon nitride on the front side of a silicon wafer, a silicon oxide mask is prepared on the non-winding plating area on the back side of the silicon wafer, and then plasma etching is performed to remove the aluminum oxide in the winding plating area, and then oxygen is introduced for treatment to obtain a silicon wafer with a silicon oxide layer on the surface; finally, a silicon nitride layer is grown on the surface of the silicon oxide layer. The present invention uses a mask in combination with plasma etching, and only grows a silicon oxide mask on the poly surface of the non-winding plating area to protect the poly from being etched, and then uses plasma to etch the aluminum oxide in the winding plating area, and grows silicon oxide on the etched surface to obtain a silicon wafer with a whole surface of silicon nitride on the surface, which solves the appearance abnormality caused by the back winding plating, improves sintering, and improves battery efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic cell preparation, and in particular relates to a method for improving the winding degree of single-sided aluminum oxide of a photovoltaic cell, a photovoltaic cell and a preparation method thereof. Background Art

[0002] In the past two years, the production capacity of photovoltaic cells has gradually expanded, competition has gradually intensified, and the industry's demand for cost reduction and efficiency improvement has increased. The current mainstream production technologies are P-type PERC cells and N-type TOPCon cells. For the two mainstream production technology routes, ALD (atomic layer deposition technology) to prepare aluminum oxide is one of the key processes for preparing passivation films. For the ALD process, there are two modes: single insertion and double insertion. The single insertion capacity is relatively low, and the double insertion will cause more serious aluminum oxide plating.

[0003] The double-insertion mode mainly reduces the winding plating situation by clamping the device or uses process gas to blow two adjacent silicon wafers apart to make the winding plating area larger and closer to the entire surface.

[0004] Wrap plating will inevitably cause serious appearance abnormalities. At the same time, the requirements for printing paste and sintering in the wrap plating and non-wrap plating areas are different, which will cause efficiency losses. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for improving the winding degree of aluminum oxide on one side of a photovoltaic cell, a photovoltaic cell and a preparation method thereof. The present invention uses a mask combined with a plasma etching method before depositing silicon nitride on the back side, grows a layer of silicon oxide mask only on the poly (polycrystalline silicon) surface of the non-winding area to protect the poly from being etched, then uses plasma to etch the aluminum oxide in the winding area, and then grows silicon oxide on the etched surface to obtain a silicon wafer with a whole surface of silicon nitride on the surface, thereby solving the problem of abnormal appearance caused by winding plating on the back side, improving sintering, and improving cell efficiency.

[0006] The technical solution of the present invention is as follows:

[0007] The first aspect of the present invention provides a method for improving the winding degree of single-sided aluminum oxide of a photovoltaic cell, the method comprising the following steps:

[0008] S1: The silicon wafer is textured, boron diffused, back-etched, the oxide layer and phosphorus-doped amorphous silicon are tunneled, annealed, de-plated, double-inserted with aluminum oxide, and silicon nitride is deposited on the front to complete the positive film.

[0009] S2: Place the silicon wafer after positive coating with its back side facing outwards in a back coating furnace tube for heating, constant temperature, leak detection and constant pressure treatment.

[0010] S3: Prepare a silicon oxide mask on the back side of the silicon wafer.

[0011] S4: Plasma etching is performed on the silicon wafer containing the silicon oxide mask to remove the aluminum oxide around the plating area.

[0012] S5: After the back film furnace tube is evacuated and maintained at a constant pressure, oxygen is introduced to treat the back film furnace tube, thereby obtaining a silicon wafer with a silicon oxide layer on the surface.

[0013] S6: growing a silicon nitride layer on the back side of the silicon wafer in step S5.

[0014] Preferably, in step S3, preparing a silicon oxide mask on the back side of the silicon wafer refers to preparing a silicon oxide mask in a non-plating area on the back side of the silicon wafer.

[0015] Preferably, the specific preparation process of the silicon oxide mask is as follows: after oxygen is introduced into the back film furnace tube, discharge treatment is performed, the poly part of the non-plating area is oxidized to form a silicon oxide mask, and the aluminum oxide in the plating area is not affected.

[0016] Preferably, the flow rate of the oxidizing oxygen is 1000-2000sccm, the time is 5-500s, the pressure is 50-400Pa, and the power is 5000-20000w.

[0017] Preferably, in step S4, the plasma etching includes chemical plasma etching.

[0018] Preferably, in step S4, the plasma etching is performed by introducing CCl4 and discharging to perform plasma etching. After the plasma etching, the aluminum oxide in the surrounding plating area is etched away, and the poly in the non-surrounding plating area is not etched under the protection of the silicon oxide mask.

[0019] Preferably, the flow rate of CCl4 is 1000-30000sccm, the time of plasma etching is 10-300s, the pressure is 100-500pa, and the power is 5000-30000w.

[0020] Preferably, in step S5, the oxygen flow rate of the oxygen treatment is 1000-20000sccm, the treatment time is 100-600s, the pressure is 100-500pa, and the power is 5000-20000w; the difference in silicon oxide thickness between the mask area and the non-mask area of ​​the silicon wafer is ≤0.5mm; and the average thickness of the silicon oxide layer is 5-8nm.

[0021] The second aspect of the present invention provides a method for preparing a photovoltaic cell, comprising the following steps: preparing a silicon wafer according to the method described in the first aspect; screen printing and sintering light injection on the prepared silicon wafer to obtain a photovoltaic cell.

[0022] The third aspect of the present invention protects a photovoltaic cell prepared by the preparation method described in the second aspect.

[0023] The beneficial technical effects of the present invention are:

[0024] The present invention uses oxygen ion oxidation before depositing back silicon nitride, and only grows a layer of silicon oxide mask on the poly surface of the non-plating area to protect the poly from being etched, and then uses plasma etching to remove the aluminum oxide plating. After etching, oxygen is used to grow a uniform silicon oxide layer, thereby avoiding the color difference caused by the aluminum oxide plating and solving the problem of abnormal appearance of the back side plating. At the same time, the damage is repaired, the sintering is improved, and the battery efficiency can be improved.

[0025] Furthermore, the plasma etching used in the present invention is chemical etching, which can avoid bombardment damage caused by physical etching and reduce the loss of battery efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a silicon wafer coated with aluminum oxide in the preparation process of the present invention.

[0027] Figure 2 Schematic diagram of a silicon wafer containing a mask in the preparation process of the present invention.

[0028] Figure 3 It is a schematic diagram of a silicon wafer containing a mask after etching aluminum oxide in the preparation process of the present invention.

[0029] Figure 4 Schematic diagram of a silicon wafer containing full-surface silicon oxide and silicon nitride in the preparation process of the present invention.

[0030] Figure 5 Schematic diagram of a silicon wafer coated with aluminum oxide in the prior art.

[0031] Figure 6 Schematic diagram of directly preparing a silicon nitride layer on a silicon wafer in an existing process.

[0032] Figure 7 This is the surface of the silicon wafer in Example 1 of the present invention.

[0033] Figure 8 This is the surface of the silicon wafer in Comparative Example 1 of the present invention.

[0034] Fig. 9 These are IQE test diagrams of Example 2 and Comparative Example 2 of the present invention.

[0035] Fig.10 These are IQE test diagrams of Example 3 and Comparative Example 3 of the present invention.

[0036] Fig.11 It is a comparison chart of the reflectivity of Example 3 of the present invention and Comparative Example 3.

[0037] Figure 1-Figure 6Middle: 1. Aluminum oxide coating area; 2. Silicon substrate; 3. Silicon oxide mask in non-coated area; 4. Entire silicon oxide layer; 5. Silicon nitride layer. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0039] A first aspect of the present invention provides a method for improving the winding of a single-sided aluminum oxide of a photovoltaic cell, the method comprising the following steps:

[0040] S1: After texturing, boron diffusion, back etching, tunneling oxide layer and phosphorus-doped amorphous silicon, annealing, de-coating, and double insertion of aluminum oxide, silicon nitride is deposited on the front to complete the positive film.

[0041] S2: Place the silicon wafer after positive coating with its back side facing outwards in a back coating furnace tube for heating, constant temperature, leak detection and constant pressure treatment.

[0042] S3: Prepare a silicon oxide mask on the back side of the silicon wafer.

[0043] S4: Plasma etching is performed on the silicon wafer containing the silicon oxide mask to remove the aluminum oxide in the non-bypass coating area.

[0044] S5: After the back film furnace tube is evacuated and maintained at a constant pressure, oxygen is introduced to treat the back film furnace tube, thereby obtaining a silicon wafer with a silicon oxide layer on the surface.

[0045] S6: growing a silicon nitride layer on the surface of the silicon wafer in step S5.

[0046] In some embodiments, in step S1, the silicon wafer includes one of CZ-Si and FZ-Si. Preferably, the silicon wafer is N-type Cz-Si. Compared with other silicon wafers, CZ-Si has the highest production capacity and the lowest cost.

[0047] In some embodiments, step S1 specifically includes the following steps: after double-sided texturing of the silicon wafer, boron diffusion on the front side and etching on the back side, removing the back side plating, and then sequentially preparing a tunneling oxide layer and phosphorus-doped amorphous silicon on the back side of the silicon wafer, annealing and removing the plating; using double-insertion aluminum oxide to form an aluminum oxide layer on the front side of the silicon wafer, and finally depositing silicon nitride on the front side to complete the positive film.

[0048] It is understandable that when the aluminum oxide layer is formed, aluminum oxide coating will inevitably occur on the back of the silicon wafer, which will affect the final product. Therefore, the aluminum oxide coating needs to be removed.

[0049] It is understandable that the process described in step S1 is a conventional process, and any solution that can achieve the purpose of the present invention is within the scope of protection of the present invention. As an example, the front boron diffusion is specifically: pressure 50-500mbar, BCl3 flow rate 50-500sccm, oxygen flow rate 100-2000sccm, nitrogen flow rate 500-5000sccm, source temperature 800-920℃, time 20-1500s, and finally temperature rise and constant temperature advancement, pressure 100-1010mbar, constant temperature advancement temperature 900-1000℃, oxidation advancement 1020-1035℃, oxygen flow rate 2000-30000sccm, time 30-6000s.

[0050] In some embodiments of the present invention, the present invention may adopt conventional methods in the art for back etching, and any solution that can achieve the effect of the present invention is within the scope of protection of the present invention. Exemplarily, the back etching is performed by acid etching. The back borosilicate glass (BSG) etching treatment is performed on the silicon wafer to remove the doped silicon glass formed on the back and periphery of the silicon wafer due to doping diffusion, and at the same time, the PN junction on the back and side of the silicon wafer can be removed to achieve surface polishing, which can increase the back reflectivity.

[0051] In some embodiments, the process of performing tunneling oxide layer and phosphorus-doped amorphous silicon and annealing after back etching is exemplified as follows: placing the etched silicon wafer in a PECVD furnace tube, tunneling oxidation pressure 50-400pa, NO2 flow 200-20000sccm, discharge power 500-30000W, temperature 400-500°C, time 20-200s, phosphorus-doped amorphous silicon deposition pressure 50-600pa, SiH4 flow 200-5000sccm, PH3 flow 200-3000sccm, hydrogen flow 1000-20000sccm, discharge power 500-30000W, temperature 400-500°C, time 100-2000s. The thickness of the tunneling oxide layer is 1-3nm, and the thickness of the phosphorus-doped amorphous silicon is 90-150nm. The annealing temperature is 800-1000° C. and the annealing time is 5-100 min.

[0052] In some embodiments, the wrap-around plating is removed after annealing; then, an aluminum oxide layer is formed on the front side of the silicon wafer using dual-insertion aluminum oxide, and finally, silicon nitride is deposited on the front side using conventional methods in the art. Wrap-around plating is performed on the silicon wafer to remove the wrap-around plating layer caused by phosphorus doping and remove the phosphorus silicon glass (PSG) formed by phosphorus doping.

[0053] It can be understood that the present invention does not limit step S2, and any conditions that can achieve the purpose of the present invention are within the protection scope of the present invention. Through step S2, the security of the processing system can be guaranteed.

[0054] In some embodiments, Figure 1-Figure 2 As shown, in step S3, preparing a silicon oxide mask on the back of the silicon wafer refers to Figure 1 The non-coating area on the back of the silicon wafer shown in the figure is used to prepare a silicon oxide mask. The non-coating area is the concave area in the figure, that is, the blank space between the aluminum oxide coating areas, which is not marked in the figure. It should be noted that Figure 1-Figure 6 It is only a schematic diagram of the structure related to the back aluminum oxide wrapping process and cannot be regarded as a limitation of the present invention. The structure of the silicon substrate 2 is not specifically drawn. It can be understood that the silicon substrate 2 is a silicon wafer that needs to be improved by the back aluminum oxide wrapping process after the previous process. For example, the silicon substrate 2 is a schematic diagram of the silicon wafer containing aluminum oxide wrapping obtained after the silicon wafer is subjected to texturing, boron diffusion, back etching, tunneling oxide layer and phosphorus-doped amorphous silicon, annealing, de-wrapping, and dual insertion of aluminum oxide, and then silicon nitride is deposited on the front.

[0055] In some embodiments, the specific preparation process of the silicon oxide mask is as follows: oxygen is introduced into the back film furnace tube and then discharged, the poly portion of the non-plating area is oxidized to form a silicon oxide mask, and the aluminum oxide in the plating area is not affected.

[0056] In some embodiments, the oxidation flow rate is 1000-2000 sccm, the time is 5-500 s, the pressure is 50-400 Pa, and the power is 5000-20000 w.

[0057] In some embodiments, in step S4, the plasma etching includes chemical plasma etching. Figure 3 shown.

[0058] In some embodiments, the plasma etching is performed by introducing CCl4 and discharging to perform plasma etching. After the plasma etching, the aluminum oxide in the surrounding plating area is etched away, and the poly in the non-surrounding plating area is not etched under the protection of the silicon oxide mask.

[0059] In some embodiments, the flow rate of CCl4 is 1000-30000 sccm, the plasma etching time is 10-300 s, the pressure is 100-500 Pa, and the power is 5000-30000 W.

[0060] It is understandable that the plasma etching used in the present invention is preferably chemical etching, which can avoid bombardment damage caused by physical etching and reduce the loss of battery efficiency.

[0061] In some embodiments, in step S5, the oxygen flow rate of the oxygen treatment is 1000-20000sccm, the treatment time is 100-600s, the pressure is 100-500pa, and the power is 5000-20000w; the absolute value of the difference in silicon oxide thickness between the mask area and the non-mask area of ​​the silicon wafer is ≤0.5mm; and the average thickness of the silicon oxide layer is 5-8nm.

[0062] The present invention first uses oxygen ion oxidation before depositing the back silicon nitride, and only grows a layer of silicon oxide mask on the surface of the poly in the non-wrap-plating area to protect the poly from being etched, and uses plasma etching to remove the aluminum oxide wrap-plating, and uses oxygen to grow a uniform silicon oxide layer after etching, thereby avoiding the color difference caused by the aluminum oxide wrap-plating and solving the problem of abnormal appearance of the back wrap-plating. At the same time, silicon oxide can passivate and repair damage, and after the aluminum oxide wrap-plating is removed, sintering can be improved, and wrap-plating will hinder sintering. That is, the damage is repaired, sintering is improved, and battery efficiency can be improved.

[0063] In some embodiments, in step S6, the specific method for growing the silicon nitride layer is: after vacuuming and constant pressure treatment, ammonia and silane are introduced for discharge, so that a silicon nitride film can be grown on the surface of the silicon oxide layer. Further, in the present invention, the silicon nitride is obtained by secondary deposition; the specific conditions of the secondary deposition are: first, the flow rate of the silane is 500-3000sccm, the flow rate of the ammonia is 5000-20000sccm, the discharge time is 50-400s, the pressure is 150-400pa, and the power is 10000-30000w. After deposition, the gas flow rate is changed, and the second layer of silicon nitride is deposited again. In the second deposition, the flow rate of the silane is 450-2800sccm, the flow rate of the ammonia is 6000-22000sccm, the discharge time is 50-400s, the pressure is 150-400pa, and the power is 10000-30000w. After steps S5-S6, the structure diagram of the silicon wafer containing the silicon oxide layer and the silicon nitride layer is obtained as shown in FIG. Figure 4 shown.

[0064] Figure 1-Figure 4 A schematic diagram of the present invention for improving the single-sided aluminum oxide coating process. Figure 5-Figure 6 It is a conventional back film process. Figure 1-Figure 6 It can be seen from the comparison that the solution of the present invention adds masking, plasma etching, and full-surface silicon oxidation steps to prepare a silicon wafer containing a full layer of silicon oxide and silicon nitride.

[0065] It is understandable that, after the positive film treatment of the silicon wafer, the present invention discharges by introducing oxygen, the poly part of the non-wrap-coating area is oxidized to form a silicon oxide mask, and the wrap-coating area is aluminum oxide, which is not affected by oxygen. The specific reaction process is as follows:

[0066] Si+2N2O→SiO2+2N2(1).

[0067] Then, plasma etching is performed by introducing CCl4 to react with aluminum oxide to generate aluminum chloride, thereby etching the aluminum oxide area. The poly layer in the non-coated area is not affected by plasma etching because it is protected by silicon oxide.

[0068] 2Al2O3+3CCl4→2AlCl3+3CO2 (2).

[0069] It can be understood that the present invention uses CCl4 gas to achieve etching through chemical reaction. Compared with physical etching, the surface protection is stronger, the surface smoothness is better, and the damage is reduced compared with physical etching, which requires bombardment.

[0070] The second aspect of the present invention provides a method for preparing a photovoltaic cell, comprising the following steps: preparing a silicon wafer according to the method described in the first aspect; screen printing and sintering light injection on the prepared silicon wafer to obtain a photovoltaic cell.

[0071] The third aspect of the present invention protects a photovoltaic cell prepared by the preparation method described in the second aspect.

[0072] The present invention will be further described below by way of examples and the like.

[0073] Example 1

[0074] A method for preparing a TOPCon photovoltaic cell comprises the following steps:

[0075] First: Texturing the silicon substrate: Use a potassium hydroxide solution with a volume concentration of 2% for texturing, then perform circulating water washing and acid washing, and then dry.

[0076] Second: single-sided boron diffusion doping and oxidation treatment is performed on the front side of the silicon wafer after texturing: boron source is applied to the silicon wafer, with a pressure of 200mbar, a BCl3 flow rate of 200sccm, an oxygen flow rate of 700sccm, a nitrogen flow rate of 3000sccm, a source temperature of 900℃, and a time of 200s. Finally, the temperature is increased and the constant temperature is promoted, with a pressure of 500mbar, a constant temperature promotion temperature of 930℃, an oxidation promotion of 1030℃, an oxygen flow rate of 20000sccm, and a time of 2400s.

[0077] Third: Etching on the back side of the silicon substrate;

[0078] Fourth: Prepare tunneling oxide layer and phosphorus-doped amorphous silicon on the back of silicon wafer, then anneal and remove winding plating: Place the etched silicon wafer in PECVD furnace tube, deposit tunneling oxide silicon and phosphorus-doped amorphous silicon on the back, tunneling oxide pressure 150pa, NO2 flow 10000sccm, discharge power 18000W, temperature 420℃, time 100s, phosphorus-doped amorphous silicon deposition pressure 400pa, SiH4 flow 3000sccm, PH3 flow 600sccm, hydrogen flow 10000sccm, discharge power 20000W, temperature 420℃, time 700s. Then put the finished n-poly silicon wafer into annealing furnace tube, heat to 880℃, pressure 300mbar, N2 flow 10000sccm, time 40min, then cool down and exit the tube, and then remove winding plating.

[0079] Fifth: Use dual-insertion aluminum oxide to form an aluminum oxide layer on the front of the silicon wafer, and then deposit silicon nitride to complete the positive film. The thickness of the aluminum oxide layer is 3.5nm, and the thickness of the silicon nitride layer is 78nm.

[0080] Sixth: Alumina de-plating and back film, specifically including the following steps:

[0081] (1) The back of the silicon wafer after positive film is sent to the back film furnace tube with the back side facing outward, and the temperature is increased, the temperature is kept constant, leak detection is performed, and the pressure is kept constant;

[0082] (2) Mask: Then oxygen is introduced and discharge is performed. The poly in the non-plating area is oxidized into silicon oxide to form a mask, while the aluminum oxide in the plating area is not affected. The oxygen flow rate is 10,000 sccm, the time is 200 s, the pressure is 150 Pa, and the power is 15,000 W.

[0083] (3) Plasma etching: After vacuuming and constant pressure, CCl4 discharge is introduced to start plasma etching. The aluminum oxide in the plating area is etched away, and the poly layer on the surface is exposed. The poly in the non-plating area is protected by a silicon oxide mask and is not affected by etching. Among them, the flow rate of CCl4 is 10000sccm, the time is 60s, the pressure is 200pa, and the power is 20000w.

[0084] (4) Whole-surface silicon oxide: After vacuuming and constant pressure again, oxygen is introduced for discharge, so that the exposed poly in the coating area and the non-coated poly with silicon oxide mask area continue to be oxidized. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same, thus forming a whole silicon oxide layer with basically the same thickness. Among them, the oxygen flow rate is 10000sccm, the time is 300s, the pressure is 150pa, and the power is 18000w; the average thickness of the silicon oxide layer is 6nm.

[0085] (5) Silicon nitride: After vacuuming and constant pressure, ammonia and silane are introduced for discharge, and a silicon nitride film is grown on the basis of the silicon oxide film. The specific process of silicon nitride film formation is: silane flow rate 1400sccm, ammonia flow rate 11000sccm, pressure 240pa, power 25000w, discharge for 300s; then change the gas flow rate to deposit silicon nitride again, silane flow rate 1300sccm, ammonia flow rate 14000sccm, time 400s, pressure 245pa, power 25000w. The thickness of the silicon nitride layer is 90nm. The appearance after back filming is as follows Figure 7 shown.

[0086] Seventh: Screen printing and sintering light injection are performed to obtain photovoltaic cells, and the cells are used for IV testing. The results are shown in Table 1.

[0087] Comparative Example 1

[0088] A method for preparing a TOPCon photovoltaic cell, including texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-wrap plating-dual insertion aluminum oxide-front film. The above method is basically the same as Example 1, except that in the sixth step, only the back film is performed in this comparative example, that is,

[0089] Sixth: Back film, specifically including the following steps:

[0090] (1) Place the back of the silicon wafer after positive coating into the back coating furnace tube with the back side facing outward, and heat it up, keep the temperature constant, check for leaks, and keep the pressure constant;

[0091] (2) Silicon nitride: After vacuuming and maintaining constant pressure, ammonia and silane are introduced to discharge, and a layer of silicon nitride film is grown on the basis of the silicon oxide film. The silane flow rate is 1400sccm, the ammonia flow rate is 11000sccm, the time is 320s, the pressure is 260pa, and the power is 25000w. Then the gas flow rate is changed to deposit silicon nitride again. The silane flow rate is 1300sccm, the ammonia flow rate is 14000sccm, the time is 400s, the pressure is 245pa, and the power is 25000w.

[0092] The appearance after back film is as follows Figure 8 shown.

[0093] As in Example 1, after the back film is formed, screen printing and sintering light injection are performed to obtain a photovoltaic cell, and then an IV test is performed. The results are shown in Table 1.

[0094] Example 2

[0095] A method for preparing a TOPCon photovoltaic cell includes texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion alumina-front film. The above method is basically the same as Example 1, except that the sixth step, i.e., the sixth step: de-coating alumina and back film, specifically includes the following steps:

[0096] (1) Place the back of the silicon wafer after positive coating into the back coating furnace tube with the back side facing outward, and heat it up, keep the temperature constant, check for leaks, and keep the pressure constant;

[0097] (2) Mask: Then oxygen is introduced and discharge is performed. The poly in the non-plating area is oxidized into silicon oxide to form a mask, while the aluminum oxide in the plating area is not affected. The oxygen flow rate is 10,000 sccm, the time is 200 s, the pressure is 150 Pa, and the power is 15,000 W.

[0098] (3) Plasma etching: Vacuum and constant pressure, CCl4 discharge to start plasma etching, the aluminum oxide in the plating area is etched away, the poly layer on the surface is exposed, and the poly in the non-plating area is protected by a silicon oxide mask and is not affected by etching. Among them, the CCl4 flow rate is 11000sccm, the time is 60s, the pressure is 200pa, and the power is 20000w.

[0099] (4) Whole-surface silicon oxide: vacuumize again, keep constant pressure, and introduce oxygen discharge to continue to oxidize the exposed poly in the coating area and the non-coated poly with silicon oxide mask area. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same, thus forming a whole silicon oxide layer with basically the same thickness. The oxygen flow rate is 10,000 sccm, the time is 300 s, the pressure is 150 Pa, and the power is 18,000 W; the average thickness of the silicon oxide layer is 6 nm.

[0100] (5) Silicon nitride: vacuum, constant pressure, ammonia and silane discharge, grow a silicon nitride film on the basis of silicon oxide film, the specific process of silicon nitride film formation is: after treatment with silane flow rate of 1400sccm, ammonia flow rate of 11000sccm, time of 300s, pressure of 240pa, power of 25000w; change the gas flow rate to deposit silicon nitride again, silane flow rate of 1300sccm, ammonia flow rate of 14000sccm, time of 400s, pressure of 245pa, power of 25000w. The thickness of the silicon nitride layer is 90nm.

[0101] Same as Example 1, after back filming, screen printing, sintering, light injection and IV test were performed, and the results are shown in Table 1. IQE test was also performed, and the results are shown in Table 1. Fig. 9 .

[0102] Comparative Example 2

[0103] A method for preparing a TOPCon photovoltaic cell includes texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion aluminum oxide-positive film. The above method is basically the same as Example 2, except that in the sixth step, CCl4 is not introduced in this comparative example, but Ar is used, as follows:

[0104] Sixth: Alumina de-plating and back film

[0105] (1) The back of the silicon wafer after positive film coating is sent into the back film furnace tube with the back side facing outward, and the temperature is increased, the temperature is kept constant, leak detection is carried out, and the pressure is kept constant.

[0106] (2) Mask: Then oxygen is introduced and discharge is performed. The poly in the non-plating area is oxidized into silicon oxide to form a mask, while the aluminum oxide in the plating area is not affected. Oxygen flow rate is 10000sccm, time is 200s, pressure is 150pa, and power is 15000w.

[0107] (3) Plasma etching: Vacuum and constant pressure, introduce Ar discharge to start plasma etching, the aluminum oxide in the plating area is etched away, and the poly in the non-plating area is protected by a silicon oxide mask and is not affected by etching. Ar flow rate 10000sccm, time 60s, pressure 240pa, power 25000w.

[0108] (4) Whole-surface silicon oxide: vacuum, constant pressure, oxygen discharge, so that the exposed poly in the coating area and the non-coating poly with silicon oxide mask area continue to be oxidized. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same. Among them, the oxygen flow rate is 10000sccm, the time is 300s, the pressure is 150pa, and the power is 18000w; the average thickness of the silicon oxide layer is 6nm.

[0109] (5) Silicon nitride: Vacuum and constant pressure were applied, and ammonia and silane were introduced for discharge. A silicon nitride film was grown on the basis of the silicon oxide film. The silane flow rate was 1400 sccm, the ammonia flow rate was 11000 sccm, the time was 300 s, the pressure was 240 Pa, and the power was 25000 W. Then, the gas flow rate was changed to deposit silicon nitride again. The silane flow rate was 1300 sccm, the ammonia flow rate was 14000 sccm, the time was 400 s, the pressure was 245 Pa, and the power was 25000 W. The thickness of the silicon nitride layer was 90 nm.

[0110] Same as Example 1, after back filming, screen printing, sintering, light injection and IV test were performed, the results are shown in Table 1, and IQE test was performed, the results are shown in Table 1. Fig. 9 .

[0111] Example 3

[0112] A method for preparing a TOPCon photovoltaic cell includes texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion alumina-front film. The above method is basically the same as Example 1, except that the sixth step, i.e., the sixth step: de-coating alumina and back film, specifically includes the following steps:

[0113] (1) Place the back of the silicon wafer after positive coating into the back coating furnace tube with the back side facing outward, and heat it up, keep the temperature constant, check for leaks, and keep the pressure constant;

[0114] (2) Mask: Then oxygen is introduced and discharge is performed. The poly in the non-plating area is oxidized into silicon oxide to form a mask, while the aluminum oxide in the plating area is not affected. The oxygen flow rate is 10,000 sccm, the time is 200 s, the pressure is 150 Pa, and the power is 15,000 W.

[0115] (3) Plasma etching: Vacuum and constant pressure are applied, and CCl4 is introduced to discharge and plasma etching is started. The aluminum oxide in the plating area is etched away, and the poly layer on the surface is exposed. The poly in the non-plating area is protected by a silicon oxide mask and is not affected by etching. The flow rate of CCl4 is 12000sccm, the time is 60s, the pressure is 200pa, and the power is 20000w.

[0116] (4) Whole-surface silicon oxide: vacuum, constant pressure, oxygen discharge, so that the exposed poly in the coating area and the non-coated poly with silicon oxide mask area continue to be oxidized. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same, thus forming a whole silicon oxide layer with basically the same thickness. Oxygen flow rate is 10000sccm, time is 300s, pressure is 150pa, power is 18000w; the average thickness of the silicon oxide layer is 6nm.

[0117] (5) Silicon nitride: vacuum, constant pressure, ammonia and silane discharge, grow a silicon nitride film on the basis of silicon oxide film, the specific process of silicon nitride film formation is: after treatment with silane flow rate of 1400sccm, ammonia flow rate of 11000sccm, time of 300s, pressure of 240pa, power of 25000w; change the gas flow rate to deposit silicon nitride again, silane flow rate of 1300sccm, ammonia flow rate of 14000sccm, time of 400s, pressure of 245pa, power of 25000w. The thickness of the silicon nitride layer is 90nm.

[0118] Same as Example 1, after back filming, screen printing, sintering, light injection and IV test were performed, the results are shown in Table 1, and IQE test was performed, the results are shown in Table 1. Fig.10 , and the reflectivity test was performed. The results are as follows Fig.11 .

[0119] Comparative Example 3

[0120] A method for preparing a TOPCon photovoltaic cell, including texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion aluminum oxide-front film. The above method is basically the same as Example 3, except that there is no mask and full-surface silicon nitride preparation step in the sixth step, that is, the sixth step: aluminum oxide de-coating and back film, specifically includes the following steps:

[0121] (1) Place the back of the silicon wafer after positive coating into the back coating furnace tube with the back side facing outward, and heat it up, keep the temperature constant, check for leaks, and keep the pressure constant;

[0122] (2) Plasma etching: vacuum, constant pressure, CCl4 discharge to start plasma etching, aluminum oxide in the plating area is etched away, and poly in the non-plating area is not affected by etching. Among them, the CCl4 flow rate is 12000sccm, the time is 60s, the pressure is 200pa, and the power is 20000w.

[0123] (3) Silicon nitride: Vacuum and constant pressure are applied, and ammonia and silane are discharged to grow a layer of silicon nitride film on the basis of the silicon oxide film. The silane flow rate is 1400sccm, the ammonia flow rate is 11000sccm, the time is 300s, the pressure is 240Pa, and the power is 25000W. Then the gas flow rate is changed to deposit silicon nitride again. The silane flow rate is 1300sccm, the ammonia flow rate is 14000sccm, the time is 400s, the pressure is 245Pa, and the power is 25000W.

[0124] Same as Example 1, after back filming, screen printing, sintering light injection and IV test were performed, the results are shown in Table 1, and IQE test was performed, the results are shown in Table 1. Fig.10 , and the reflectivity test was performed. The results are as follows Fig.11 .

[0125] Example 4

[0126] A method for preparing a TOPCon photovoltaic cell includes texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion alumina-front film. The above method is basically the same as Example 1, except that the sixth step, i.e., the sixth step: de-coating alumina and back film, specifically includes the following steps:

[0127] (1) Place the back of the silicon wafer after positive coating into the back coating furnace tube with the back side facing outward, and heat it up, keep the temperature constant, check for leaks, and keep the pressure constant;

[0128] (2) Mask: Then oxygen is introduced and discharge is performed. The poly in the non-plating area is oxidized into silicon oxide to form a mask, while the aluminum oxide in the plating area is not affected. The oxygen flow rate is 10,000 sccm, the time is 200 s, the pressure is 150 Pa, and the power is 15,000 W.

[0129] (3) Plasma etching: vacuum, constant pressure, CCl4 discharge to start plasma etching, aluminum oxide in the plating area is etched away, the poly layer on the surface is exposed, and the poly in the non-plating area is protected by a silicon oxide mask and is not affected by etching. Among them, the CCl4 flow rate is 13000sccm, the time is 60s, the pressure is 200pa, and the power is 20000w.

[0130] (4) Whole-surface silicon oxide: vacuum, constant pressure, oxygen discharge, so that the exposed poly in the coating area and the non-coated poly with silicon oxide mask area continue to be oxidized. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same, thus forming a whole silicon oxide layer with basically the same thickness. Oxygen flow rate is 10000sccm, time is 300s, pressure is 150pa, power is 18000w; the average thickness of the silicon oxide layer is 6nm.

[0131] (5) Silicon nitride: Vacuum and constant pressure are applied, and ammonia and silane are introduced for discharge. A layer of silicon nitride film is grown on the basis of the silicon oxide film. The specific process of silicon nitride film formation is as follows: after treatment with a silane flow rate of 1400sccm, an ammonia flow rate of 11000sccm, a time of 300s, a pressure of 240Pa, and a power of 25000W; the gas flow rate is changed to deposit silicon nitride again, with a silane flow rate of 1300sccm, an ammonia flow rate of 14000sccm, a time of 400s, a pressure of 245Pa, and a power of 25000W.

[0132] The same as Example 1, after back filming, screen printing, sintering light injection and IV testing were carried out. The results are shown in Table 1.

[0133] Comparative Example 4

[0134] A method for preparing a TOPCon photovoltaic cell, including texturing-boron diffusion-back etching-tunneling oxide layer and phosphorus-doped amorphous silicon-annealing-de-coating-dual insertion alumina-front film. The above method is basically the same as Example 4, except that there is no mask preparation in the sixth step, that is, the sixth step: alumina de-coating and back film, specifically including the following steps:

[0135] (1) The back of the silicon wafer after positive film coating is sent into the back film furnace tube with the back side facing outward, and the temperature is increased, the temperature is kept constant, leak detection is carried out, and the pressure is kept constant.

[0136] (2) Plasma etching: vacuum, constant pressure, CCl4 discharge to start plasma etching, aluminum oxide in the plating area is etched away, and poly in the non-plating area is not affected by etching. CCl4 flow rate 13000sccm, time 60s, pressure 200pa, power 20000w.

[0137] (3) Whole-surface silicon oxide: vacuum, constant pressure, oxygen discharge, so that the exposed poly in the wrap-around area and the non-wrapped poly with silicon oxide mask area continue to be oxidized. The thicker the silicon oxide, the slower the oxidation rate. Finally, the silicon oxide thickness in the masked area and the unmasked area will be close to the same. Among them, the oxygen flow rate is 10000sccm, the time is 300s, the pressure is 150pa, and the power is 18000w.

[0138] (4) Silicon nitride: Vacuum and constant pressure are applied, and ammonia and silane are introduced for discharge. A layer of silicon nitride film is grown on the basis of the silicon oxide film. The specific process of silicon nitride film formation is as follows: after treatment with a silane flow rate of 1400sccm, an ammonia flow rate of 11000sccm, a time of 300s, a pressure of 240Pa, and a power of 25000W; the gas flow rate is changed to deposit silicon nitride again, with a silane flow rate of 1300sccm, an ammonia flow rate of 14000sccm, a time of 400s, a pressure of 245Pa, and a power of 25000W.

[0139] The same as in Example 1, after back filming, screen printing, sintering light injection and IV testing were performed. The testing method was as follows: using a conventional Halm tester, under standard test conditions (25°C, 1000W / m 2 The results are shown in Table 1.

[0140] Table 1 Performance tests of embodiments and comparative examples

[0141]

[0142] Combined with Table 1, Figure 7-Figure 8 The data are analyzed for Example 1 and Comparative Example 1, and it can be seen that the present invention can solve the aluminum oxide plating problem by plasma etching and improve the battery efficiency.

[0143] Combined with Table 1, Fig. 9 The data of Example 2 and Comparative Example 2 are analyzed, and it can be seen that the IQE long-wave band of the present invention is better than that of argon physical etching, indicating that the back side passivation is better. At the same time, the battery electrical performance is higher in terms of voltage and efficiency. Therefore, the chemical etching used in the present invention causes less damage to the silicon wafer than physical etching.

[0144] Combined with Table 1, Figure 10-11 From the data, we analyze Example 3 and Comparative Example 3 and can see that for the battery with a silicon oxide film layer, the back reflectivity is greater, which is more conducive to light absorption, and the corresponding battery short-circuit current is higher. At the same time, Example 3 with the presence of a silicon oxide film layer has a better long-wave IQE, indicating that the back passivation is better, and silicon oxide has the function of repairing and improving the back passivation.

[0145] By analyzing Example 4 and Comparative Example 4 in combination with the data in Table 1, it can be seen that in the absence of the silicon oxide mask, the battery exhibits poor opening voltage and efficiency. In the method described in the present invention, the silicon oxide mask can play a role in protecting poly.

[0146] In summary, in combination with all the embodiments, comparative examples and the results obtained, it can be seen that the present invention can remove the aluminum oxide coating on the back side and solve the appearance problem caused by aluminum oxide on the back side. At the same time, the CCl4 used is more inclined to chemical etching, which can reduce the damage caused by bombardment compared to physical etching. The silicon oxide mask can protect poly and reduce the damage caused by etching, and the use of oxygen ion oxidation can ensure that silicon oxide is only grown in the non-coating area and will not interfere with the etching of aluminum oxide in the coating area. The silicon oxide film grown after the final etching can effectively repair the etching damage and passivate the interface effect. At the same time, it can improve the back reflection efficiency and achieve the purpose of improving the battery efficiency. This solution only adds three steps of masking, etching, and silicon oxide to the original back film process. It will not add additional processes, is easy to popularize on a large scale, and can improve battery efficiency and appearance yield, which is conducive to improving product competitiveness.

[0147] It should be noted that the method described in the present invention can also be applied to battery processes such as PERC and BC that use single-sided aluminum oxide.

[0148] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A method for improving the winding degree of single-sided aluminum oxide of photovoltaic cells, characterized in that: The method comprises the following steps: S1: Texturing, boron diffusion, back etching, tunneling oxide layer and phosphorus-doped amorphous silicon, annealing, de-plating, double insertion of aluminum oxide, front deposition of silicon nitride, and completion of positive film; S2: Place the back of the silicon wafer after positive coating outward in a back coating furnace tube for heating, constant temperature, leak detection and constant pressure treatment; S3: preparing a silicon oxide mask on the back side of the silicon wafer; S4: Plasma etching is performed on the silicon wafer containing the silicon oxide mask to remove the aluminum oxide around the plating area; S5: After the back film furnace tube is evacuated and kept at a constant pressure, oxygen is introduced to obtain a silicon wafer with a silicon oxide layer on the surface; S6: growing a silicon nitride layer on the back side of the silicon wafer in step S5; In step S3, the step of preparing a silicon oxide mask on the back side of the silicon wafer refers to preparing a silicon oxide mask on a non-plating area on the back side of the silicon wafer; The specific preparation process of the silicon oxide mask is as follows: after oxygen is introduced into the back film furnace tube, a discharge treatment is performed, and the upper layer of the poly in the non-plating area is oxidized to form a silicon oxide mask, and the aluminum oxide in the plating area is not affected; In step S4, the plasma etching is performed by introducing CCl4 and discharging to perform plasma etching; after the plasma etching, the aluminum oxide in the surrounding plating area is etched away, and the unoxidized poly part in the non-surrounding plating area is not etched under the protection of the silicon oxide mask.

2. The method according to claim 1, characterized in that The flow rate of the oxidizing oxygen is 1000-2000sccm, the time is 5-500s, the pressure is 50-400Pa, and the power is 5000-20000w.

3. The method according to claim 1, characterized in that The flow rate of CCl4 is 1000-30000sccm, the time of plasma etching is 10-300s, the pressure is 100-500pa, and the power is 5000-30000w.

4. The method according to claim 1, characterized in that: In step S5, the oxygen flow rate of the oxygen treatment is 1000-20000sccm, the treatment time is 100-600s, the pressure is 100-500pa, and the power is 5000-20000w; the average thickness of the silicon oxide layer is 5-8nm.

5. A method for preparing a photovoltaic cell, characterized in that: The steps include: Prepare a silicon wafer according to the method according to any one of claims 1 to 4; The prepared silicon wafer is subjected to screen printing, sintering and light injection to obtain a photovoltaic cell.

6. A photovoltaic cell prepared by the preparation method according to claim 5.

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