Preparation method of oxygen-doped polycrystalline silicon and application of oxygen-doped polycrystalline silicon in preparation of TOPCon battery

Abstract

The invention belongs to the technical field of solar photovoltaic cells, and particularly relates to a preparation method of oxygen-doped polycrystalline silicon and application of the oxygen-doped polycrystalline silicon in preparation of a TOPCon cell, and the preparation method of the oxygen-doped polycrystalline silicon comprises the following steps: S1, completing preparation of a tunneling oxide layer; s2, preparing an oxygen-containing amorphous silicon layer on the tunneling oxide layer by adopting LPCVD (Low Pressure Chemical Vapor Deposition) equipment through a multi-cycle process of alternately carrying out SiH4 deposition and O2 oxidation; each cycle comprises the following steps: introducing SiH4 after vacuumizing, and introducing O2 after vacuumizing; and S3, performing high-temperature doping and crystallization treatment on the oxygen-containing amorphous silicon layer to form an oxygen-doped polycrystalline silicon layer. SiH4 and O2 are introduced in a time-sharing manner, so that the explosion risk caused by direct mixing of SiH4 and O2 is avoided, the limitation that N2O must be used in PECVD is broken through, high-purity oxygen doping is realized, the oxygen doping efficiency is improved, and nitrogen doping interference is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of solar photovoltaic cells, and particularly to a method for preparing oxygen-doped polysilicon and its application in the preparation of TOPCon cells. Background Art

[0002] To increase the proportion of photovoltaic power generation, cost reduction and efficiency improvement are the two main threads in photovoltaic manufacturing. Currently, the mainstream photovoltaic cells are crystalline silicon solar cells. In the manufacturing of crystalline silicon solar cells, the passivated contact structure is one of the key technologies to improve device performance and stability.

[0003] The passivated contact structure forms a protective film under the contact layer to reduce the surface state density, and combines a contact passivation layer and tunneling effect to achieve metal contact while maintaining passivation, thereby reducing the carrier recombination under the metal and improving the electrical performance of the device. Among these structures, polysilicon (polycrystalline silicon) is widely used in the passivated contact technology as an important film layer. However, for crystalline silicon solar cells, the bandgap of the polysilicon film being close to that of silicon will cause serious optical parasitic absorption, which in turn affects the conversion efficiency of the solar cell. Incorporating oxygen atoms into polysilicon can effectively improve the film bandgap and solve the parasitic absorption problem.

[0004] However, there is currently no suitable oxygen-doped polysilicon preparation scheme in the mass production route of crystalline silicon cells. Existing polysilicon doping methods include ion implantation, high-temperature diffusion, in-situ deposition, etc. Among them, the ion implantation technology has expensive equipment, complex and unstable processes, and does not have mass production conditions; the high-temperature diffusion technology can well prepare doped polysilicon thin films with P or B, but it cannot be achieved in terms of oxygen doping; in-situ deposition all adopts plasma-enhanced chemical vapor deposition (PECVD). In this scheme, the doping source and the silicon source need to enter the high-temperature furnace synchronously. Due to the flammable and explosive characteristics of the silicon source (SiH 4 ), the oxygen source cannot use O 2 containing only oxygen atoms and needs to use N 2 O, which will lead to difficult control of the element content in the oxygen-doped polysilicon and also bring difficulties to the subsequent edge removal process.

[0005] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] The first object of the present invention is to propose a method for preparing oxygen-doped polysilicon based on low-pressure chemical vapor deposition, which can meet the performance and mass production requirements of solar cells by preparing oxygen-doped polysilicon through a cyclic oxygen addition method.

[0007] The above technical object of the present invention is achieved by the following technical solutions:

[0008] A method for preparing oxygen-doped polysilicon, characterized by comprising the following steps:

[0009] S1 Complete the preparation of the tunneling oxide layer;

[0010] S2 Use an LPCVD device to prepare an oxygen-containing amorphous silicon layer on the tunneling oxide layer through multiple cycles of alternating SiH 4 deposition and O 2 oxidation; each cycle includes: introducing SiH 4 after evacuation, and introducing O 2 after evacuation;

[0011] In the present invention, an alternating cycle process is adopted, and oxygen elements are incorporated into the formed polysilicon, so that its band gap is widened, avoiding parasitic absorption caused by the relatively narrow band gap of the polysilicon film layer generated at one time when applied to TOPCon crystalline silicon cells.

[0012] In each cycle, SiH 4 is first introduced to generate an amorphous silicon layer (SiH 4 →Si + 2H 2 ↑), then the residual gas is evacuated, and then O 2 is introduced to oxidize the surface amorphous silicon (Si + O 2 →SiO 2 ). Oxygen is introduced layer by layer through multiple cycles to avoid the oxygen concentration gradient caused by single oxidation (for example, rich oxygen on the surface layer and poor oxygen on the bottom layer); SiH 4 and O 2 are introduced step by step to avoid explosion caused by the coexistence of two gases in traditional PECVD (such as spontaneous combustion of SiH 4 in O 2 ); the evacuation step removes unreacted SiH 4 and O 2 by-products (such as H 2 O, SiOxHy) to prevent the formation of heterophases.

[0013] S3 Perform high-temperature doping and crystallization treatment on the oxygen-containing amorphous silicon layer to form an oxygen-doped polysilicon layer.

[0014] Specifically, phosphorus / boron doping (POCl 3 or BCl 3 ) is introduced synchronously during the crystallization treatment, and the diffusion of doping elements and crystallization are completed in one step by using high temperature (800 - 1100 °C), avoiding the accumulation of interface defects caused by multiple steps in traditional processes; oxygen elements are locked at the grain boundaries of polysilicon during the crystallization process, inhibiting migration and escape, and finally forming an oxygen-doped polysilicon layer with high oxygen content and uniform distribution.

[0015] Preferably, in step S1, an LPCVD device is used, and O with a flow rate of 10 - 30 SLM is introduced at 580 - 630 °C 2 , for 1 - 5 minutes, to complete the preparation of the tunneling oxide layer. At high temperature, O 2 reacts with the silicon substrate to form a thin and dense tunneling oxide layer (Si + O 2 → SiO 2 ). 580 - 630 °C can avoid the loose structure caused by low-temperature oxidation, and it is completed in the same device as the subsequent LPCVD cycle process, reducing the pollution risk caused by equipment switching.

[0016] Preferably, in step S2, the thickness of the oxygen-containing amorphous silicon layer is adjusted by the number of cycles. Specifically, a fixed thickness is deposited in each cycle, and the total thickness is the single-cycle thickness × the number of cycles. Specifically, the thickness of the amorphous silicon deposited in a single cycle is about 5 - 15 nm. For example, if 5 nm is deposited in a single cycle, cycling 8 - 13 times directly corresponds to a final thickness of 40 - 65 nm, without the need to introduce complex real-time thickness monitoring equipment.

[0017] The oxygen content of the oxygen-containing amorphous silicon layer is adjusted by the time of introducing O 2 and SiH 4 in a single cycle. Prolonging the introduction time of O 2 in a single cycle increases the oxidation depth, and prolonging the introduction time of SiH4 increases the deposition amount of amorphous silicon. By adjusting the O 2 / SiH 4 time ratio in each layer, uniform doping of oxygen atoms in the amorphous silicon layer is achieved.

[0018] Preferably, the number of cycles of the cycle process is 8 - 13 times. If the number of cycles is insufficient, the oxygen-containing amorphous silicon layer is too thin and is prone to fracture after high-temperature crystallization; if the number of cycles is too large, the layer thickness is too thick, and the diffusion path of the doping atoms (P / B) to the underlying tunneling oxide layer increases, resulting in a decrease in doping efficiency. Balancing the thickness and doping efficiency within the range of 8 - 13 times ensures that the final oxygen-doped polysilicon layer has both high conductivity and good passivation performance.

[0019] Preferably, in step S2, the cycle process is carried out at 550 - 630 °C, the flow rate of SiH 4 introduced is 100 - 400 sccm, the time is 2 - 8 minutes, the reaction pressure is controlled at 100 - 400 mtorr, and the flow rate of O 2 introduced is 300 - 5000 sccm, and the time is 1 - 5 minutes. The deposition rate of amorphous silicon is most controllable at 550 - 630 °C, and no local small crystals are formed, which is conducive to the incorporation of oxygen and subsequent crystallization. SiH 4 and O 2The flow rate is based on the experimental verification results of the flow rate designed for normal mass production equipment. The definition of vacuum is to pump the equipment to its background vacuum. By adjusting the parameter combination, the dynamic balance of the deposition-oxidation rate is achieved.

[0020] Preferably, in step S3, the oxygen-containing amorphous silicon layer is subjected to high-temperature doping and crystallization treatment to form an oxygen-doped polycrystalline silicon layer. At high temperature, the doping source reacts with the oxygen-containing amorphous silicon layer, and P / B atoms diffuse into the amorphous silicon lattice, while inducing the transformation of amorphous silicon into a polycrystalline silicon structure. High temperature (>800 °C) promotes the rapid diffusion of P / B doping atoms and the stabilization of oxygen at grain boundaries; during the crystallization process, oxygen atoms preferentially occupy grain boundary sites, passivate dangling bonds, and reduce the interface recombination rate. Specifically, N-type oxygen-doped polycrystalline silicon is suitable for the back field of TOPCon, and P-type is mainly applied to the emitter on the front side of TOPCon.

[0021] Preferably, it specifically includes:

[0022] In a vacuum environment and at a temperature of 800 - 900 °C, nitrogen is used as a carrier gas to introduce POCl 3 as a reaction precursor, and doping and crystallization are achieved by phosphorus diffusion on the oxygen-containing amorphous silicon layer to form an N-type oxygen-doped polycrystalline silicon layer; P atoms diffuse into the oxygen-containing amorphous silicon layer to replace Si sites, and at the same time O 2 further oxidizes the residual silicon dangling bonds.

[0023] Or, in a vacuum environment and at a temperature of 800 - 1100 °C, nitrogen is used as a carrier gas to introduce BCl 3 or BBr 3 as a reaction precursor, and doping and crystallization are achieved by boron diffusion on the oxygen-containing amorphous silicon layer to form a P-type oxygen-doped polycrystalline silicon layer. B atoms occupy Si positions to form P-type doping, and at the same time high temperature promotes the crystallization of amorphous silicon.

[0024] The second object of the present invention is to propose a preparation method of a TOPCon battery, and the above method is used to prepare the oxygen-doped polycrystalline silicon layer.

[0025] The above technical object of the present invention is achieved by the following technical solutions:

[0026] A preparation method of a TOPCon battery, characterized by comprising:

[0027] A1 Pretreat the monocrystalline silicon wafer, including double-sided texturing, front-side single-sided boron diffusion, and laser doping;

[0028] A2 Perform high-temperature oxidation treatment on the front side of the silicon wafer to form a selective emitter;

[0029] A3 uses the above method to prepare an oxygen-doped polysilicon layer on the back side of the silicon wafer; the oxygen-doped polysilicon layer serves as a back surface field (BSF), and its high conductivity and oxygen passivation of grain boundary characteristics jointly reduce the carrier recombination rate.

[0030] A4 removes the front and back phosphosilicate glass (PSG) and the residual oxide layer;

[0031] A5 deposits a passivation layer on both sides of the silicon wafer, and then performs metallization and sintering to obtain the finished battery.

[0032] Preferably, in step A1, an N-type monocrystalline silicon wafer with a resistivity of 0.3 - 1.5 Ω·cm, a minority carrier lifetime > 2.5 ms, a thickness of 170 μm, a size of 210 mm × 210 mm, 182 mm × 182 mm or various sizes of silicon wafers commonly used in current TOPCon production is selected; the damaged layer on the surface of the silicon wafer is removed in a mixed solution of KOH and H 2 O 2 and then double-sided texturing is performed in a KOH solution, and a pyramid texture surface is formed on the surface, and the height of the pyramid texture surface is 1.8 - 3 μm;

[0033] Preferably, in step A1, after the texturing is completed, pre-oxidation (780 - 830 °C) + deposition (800 - 900 °C, the flow rate ratio of BCl 3 and O 2 is 1:2 - 1:6, and the pressure is 100 - 310 mbar) + push (850 - 950 °C) process is carried out to complete the single-sided low-pressure boron diffusion, and the sheet resistance after treatment is 100 - 250 Ω / sq.

[0034] Preferably, the above diffused sample is subjected to laser local doping treatment to achieve local heavy doping, and the local sheet resistance after laser treatment is 30 - 90 Ω / sq.

[0035] Preferably, in step A2, the parameters of the oxidation treatment are: the temperature is set at 950 °C - 1050 °C, the pressure is set at 400 - 800 mbar, the oxygen flow rate is 20000 - 40000 sccm, and the oxidation time is 3000 - 4500 s;

[0036] After the oxidation treatment, the sheet resistance of the lightly doped region is 300 - 500 Ω / sq, and the sheet resistance of the heavily doped region is 100 - 300 Ω / sq, obtaining a silicon wafer containing a selective emitter. After removing the BSG on the back side of the silicon wafer, alkali polishing is carried out to make the reflectivity of the back side of the silicon wafer greater than 40%.

[0037] Preferably, in step A4, it includes:

[0038] On the front side, after removing the front phosphosilicate glass (PSG) by chain HF, NaOH is used to remove the front side plating, and then the residual oxide layer on the front and back sides is removed in a tank-type HF;

[0039] Deposit aluminum oxide with a thickness of 3 - 10 nm on both sides of the silicon wafer using ALD, and prepare silicon nitride with a thickness of 75 - 80 nm using PECVD; deposit silicon nitride with a thickness of 70 - 100 nm on the back of the silicon wafer to complete the preparation of the battery precursor.

[0040] Perform surface passivation on the battery precursor. After the surface passivation is completed, open the film in the contact area between the fine grid and the main grid on the front side of the silicon wafer and complete the printing of the main grid. Metalize the back side, and then sinter and LECO to complete the battery preparation.

[0041] Beneficial effects:

[0042] The present invention uses low-pressure chemical vapor deposition (LPCVD), directly uses O 2 as the oxygen source, and through multiple cycles of SiH 4 deposition and O 2 oxidation steps, avoids the explosion risk of the coexistence of SiH 4 and O 2 in PECVD; compared with the problem of nitrogen atom residue caused by relying on N 2 O as the oxygen source in the prior art, the present invention can ensure that oxygen atoms enter the amorphous silicon layer in a single chemical state (Si-O bond), avoiding the interference of nitrogen pollution on the performance of the subsequent passivation layer. At the same time, the alternating operation of the cyclic process of "deposition - oxidation - vacuum pumping", in a single cycle, by adjusting the feeding time and flow rate of O 2 / SiH 4 realizes the atomic-level uniform distribution of oxygen elements in the amorphous silicon layer, and the oxygen content accuracy can be controlled within ±0.5 at%. Effectively inhibits the interface state defects caused by oxygen aggregation at the grain boundaries.

[0043] In step S1 of the present invention, a tunneling oxide layer is prepared by low-temperature LPCVD, avoiding the thermal damage to the silicon substrate caused by the traditional thermal oxidation process. In step S2, the deposition temperature of amorphous silicon further reduces the thermal budget, forming a low-temperature synergy with the process of step S1 to ensure the structural integrity of the tunneling oxide layer. Subsequently, in step S3, the integrated treatment of high-temperature doping and crystallization not only activates the diffusion doping of phosphorus / boron atoms, but also realizes the transformation of amorphous silicon to polycrystalline silicon through high-temperature annealing, synchronously completing the improvement of conductivity and the optimization of crystal structure. This step-by-step design of "low-temperature deposition - high-temperature crystallization" solves the interface defect problem caused by excessive migration of oxygen atoms during the crystallization stage in the traditional high-temperature continuous deposition process.

[0044] The present invention can adjust the film layer according to the battery requirements. The thickness of polycrystalline silicon can be adjusted by the number of cycles, and the oxygen and SiH 4Oxygen content in the time-adjusting film layer; the problem of parasitic absorption is solved by introducing oxygen-doped polysilicon, which can be directly used to replace the existing polysilicon film layer, effectively improving the current density and thus enhancing the battery performance. At the same time, it also enables the polysilicon-based passivation contact structure to be applied to the front side of the battery, realizing a double-sided passivation contact battery; using an LPCVD device, the device is simple and is a mature device in current solar cell production; suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments or the prior description. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 ECV test results of oxygen-doped polysilicon (taking the N-type as an example).

[0047] Figure 2 Transmittance test results of oxygen-doped polysilicon.

[0048] Figure 3 Bandgap test results of oxygen-doped polysilicon. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] To further elaborate on the technical means and effects adopted by the present invention to achieve the intended invention purpose, for a method for preparing oxygen-doped polysilicon provided by the present invention, its specific implementation manners, features and effects are described in detail as follows.

[0050] Example 1

[0051] The application of a preparation scheme of oxygen-doped polysilicon that can be mass-produced based on low-pressure chemical vapor deposition in TOPCon cells includes the following steps:

[0052] S1. Select an N-type single-crystal silicon wafer with a resistivity of 1.0 - 1.5 Ω·cm, a minority carrier lifetime > 2.5 ms, a thickness of 170 μm, and a size of 210 mm × 210 mm; remove the damaged layer on the surface of the silicon wafer in a mixed solution of KOH and H 2 O 2 and then perform double-sided texturing in a KOH solution to form a pyramid texture on the surface, with the height of the pyramid texture being 3 μm;

[0053] S2. After the texturing is completed, perform pre-oxidation (780 - 800 °C) + deposition (800 - 900 °C, BCl 3 and O 2The single-sided low-pressure boron diffusion is completed by the process of (flow ratio 1:2 to 1:5, pressure 100 to 300 mbar) + propulsion (850 to 950 °C). The sheet resistance after boron diffusion treatment is 100 to 250 Ω / sq;

[0054] S3. Perform laser local doping treatment on the above-diffused samples to achieve local heavy doping. The local sheet resistance after laser treatment is 30 to 80 Ω / sq;

[0055] S4. Place the laser-treated samples in a low-pressure furnace tube for oxidation treatment. Oxidation treatment parameters: temperature is set at 950 °C to 1050 °C, pressure is set at 400 to 800 mbar, oxygen flow rate is 20000 to 40000 sccm, and oxidation time is 3000 to 4500 s. After oxidation treatment, the sheet resistance of the lightly doped region is 300 to 500 Ω / sq, and the sheet resistance of the heavily doped region is 100 to 200 Ω / sq, obtaining a silicon wafer containing a selective emitter. After removing BSG on the back of the silicon wafer, perform alkaline polishing to make the reflectivity of the back of the silicon wafer greater than 40%;

[0056] S5. In the LPCVD, introduce oxygen with a flow rate of 10 SLM for 5 min at 580 °C on the back of the silicon wafer to prepare a tunneling layer (1 to 2 nm). After completing the evacuation, introduce SiH with a flow rate of 150 sccm at 600 °C 4 for 3 min, control the reaction pressure at 130 mtorr to complete the deposition of the first layer of amorphous silicon. Evacuate again, keep the temperature unchanged and introduce O with a flow rate of 200 sccm 2 for 5 min. After completing the introduction of oxygen, evacuate again. The above four steps are one cycle. After 8 cycles, perform high-temperature phosphorus diffusion at 900 °C to complete high-temperature crystallization and diffusion, obtaining oxygen-doped polysilicon with a thickness of 80 to 90 nm;

[0057] S6. Remove the front-side phosphosilicate glass (PSG) on the front side through chain HF, then remove the front-side plating with NaOH, and then remove the remaining oxide layers on the front and back sides in a tank-type HF;

[0058] S7. Deposit aluminum oxide with a thickness of 3 to 10 nm on both sides of the silicon wafer using ALD, and prepare silicon nitride with a thickness of 75 to 80 nm using PECVD; deposit silicon nitride with a thickness of 70 to 100 nm on the back of the silicon wafer to complete the preparation of the battery precursor;

[0059] S8. Perform surface passivation on the battery precursor. After surface passivation, open the film in the contact area between the fine grid and the main grid on the front side of the silicon wafer and complete the printing of the main grid. Metallize the back side, and then sinter and perform LECO to complete the battery preparation.

[0060] Example 2

[0061] The application of the preparation scheme of oxygen-doped polysilicon mass-produced by low-pressure chemical vapor deposition method in TOPCon cells includes the following steps:

[0062] S1. Select N-type monocrystalline silicon wafers with a resistivity of 0.3 - 0.9 Ω·cm, a minority carrier lifetime > 2.5 ms, a thickness of 170 μm, and a size of 182 mm × 182 mm;

[0063] In the KOH and H 2 O 2 mixed solution, remove the damaged layer on the surface of the silicon wafer, and then perform double-sided texturing in the KOH solution to form a pyramid-shaped textured surface on the surface, with the height of the pyramid-shaped textured surface being 1.8 - 2.2 μm;

[0064] S2. After the texturing is completed, perform pre-oxidation (810 - 830 °C) + deposition (850 - 900 °C, the flow ratio of BCl 3 and O 2 is 1:3 - 1:6, and the pressure is 120 - 310 mbar) + propulsion (850 - 950 °C) process in a tube-type high-temperature equipment to complete single-sided low-pressure boron diffusion, and the sheet resistance after boron diffusion treatment is 100 - 250 Ω / sq;

[0065] S3. Perform laser local doping treatment on the diffused sample above to achieve local heavy doping, and the local sheet resistance after laser treatment is 50 - 90 Ω / sq;

[0066] S4. Place the laser-treated sample in a low-pressure furnace tube for oxidation treatment. The oxidation treatment parameters are: the temperature is set at 950 °C - 1050 °C, the pressure is set at 400 - 800 mbar, the oxygen flow rate is 20000 - 40000 sccm, and the oxidation time is 3000 - 4500 s. After oxidation treatment, the sheet resistance of the lightly doped region is 350 - 500 Ω / sq, and the sheet resistance of the heavily doped region is 150 - 300 Ω / sq, obtaining a silicon wafer containing a selective emitter. After removing BSG on the back of the silicon wafer, perform alkaline polishing to make the reflectivity of the back of the silicon wafer greater than 40%;

[0067] S5. Pass oxygen with a flow rate of 30 SLM for 3 min at 620 °C on one side of the back of the silicon wafer in LPCVD to prepare a tunneling layer (1 - 2 nm). After completing the evacuation, pass SiH 4 with a flow rate of 300 sccm for 3 min at 610 °C, control the reaction pressure to 280 mtorr to complete the deposition of the first layer of amorphous silicon. Evacuate again, keep the temperature unchanged and then pass O 2 with a flow rate of 4000 sccm for 1 min. After completing the oxygen introduction, evacuate again. The above four steps are one cycle, and after performing 10 cycles, perform high-temperature phosphorus diffusion at 900 °C to complete high-temperature crystallization and diffusion, obtaining oxygen-doped polysilicon with a thickness of 110 - 130 nm;

[0068] S6. After removing the front phosphorus silicate glass (PSG) through chain HF on the front side, NaOH is used to remove the front side overplating, and then the remaining oxide layers on the front and back sides are removed in a trough-type HF.

[0069] S7. Aluminum oxide with a thickness of 3 - 10 nm is deposited on both sides of the silicon wafer using ALD, and silicon nitride with a thickness of 75 - 80 nm is prepared using PECVD; silicon nitride with a thickness of 70 - 100 nm is deposited on the back side of the silicon wafer to complete the preparation of the battery precursor.

[0070] S8. Surface passivation is performed on the battery precursor. After the surface passivation is completed, the film is opened in the contact area between the fine grid and the main grid on the front side of the silicon wafer and the main grid printing is completed. Metallization is performed on the back side, and then sintering and LECO are carried out to complete the battery preparation.

[0071] Comparative Example 1

[0072] The battery preparation in this case is the same as that in Example 1, except that oxygen-doped polysilicon prepared by the scheme of Example 1 is not used, but conventional non-oxygen-doped polysilicon is used. The specific preparation process is as follows:

[0073] S1. Select N-type monocrystalline silicon wafers with a resistivity of 0.6 - 2.0 Ω·cm, a minority carrier lifetime > 2.5 ms, a thickness of 130 ± 8 μm, and a size of 182 mm × 182 mm;

[0074] In the mixed solution of KOH and H2O 2 The damaged layer on the surface of the silicon wafer is removed, and then double-sided texturing is performed in a KOH solution to form a pyramid texture on the surface. The height of the pyramid texture is 1 - 3 μm;

[0075] S2. After the texturing is completed, pre-oxidation (780 - 800 °C) + deposition (800 - 900 °C, the flow ratio of BCl 3 and O 2 is 1:2 - 1:5, pressure 100 - 300 mbar) + push (850 - 950 °C) process is carried out to complete single-sided low-pressure boron diffusion. The sheet resistance after boron diffusion treatment is 100 - 250 Ω / sq;

[0076] S3. Laser local doping treatment is performed on the above-diffused samples to achieve local heavy doping. The local sheet resistance after laser treatment is 30 - 80 Ω / sq;

[0077] S4. Place the laser-treated sample in a low-pressure furnace tube for oxidation treatment. The oxidation treatment parameters are as follows: the temperature is set at 950°C - 1050°C, the pressure is set at 400 - 800 mbar, the oxygen flow rate is 20000 - 40000 sccm, and the oxidation time is 3000 - 4500 s. After oxidation treatment, the sheet resistance of the lightly doped region is 300 - 500 Ω / sq, and the sheet resistance of the heavily doped region is 100 - 200 Ω / sq, obtaining a silicon wafer with a selective emitter. After removing BSG from the back of the silicon wafer, perform alkaline polishing to make the reflectivity of the back of the silicon wafer greater than 40%;

[0078] S5. Pass oxygen with a flow rate of 20 SLM into the back of the silicon wafer in LPCVD at 610°C for 4 min to prepare a tunneling layer (1 - 2 nm). After completing the evacuation, pass SiH with a flow rate of 280 sccm at 605°C 4 for 30 min, control the reaction pressure at 230 mtorr to complete the amorphous silicon deposition, and use high-temperature phosphorus diffusion at 800 - 910°C to complete high-temperature crystallization and diffusion, obtaining polycrystalline silicon with a thickness of 100 - 130 nm;

[0079] S6. Remove the front phosphorus silicate glass (PSG) on the front side of the silicon wafer through chain HF, then use NaOH to remove the front side overplating, and then remove the remaining oxide layers on the front and back sides in a tank-type HF;

[0080] S7. Deposit aluminum oxide with a thickness of 3 - 10 nm on both sides of the silicon wafer using ALD, and use PECVD to prepare silicon nitride with a thickness of 75 - 80 nm; deposit silicon nitride with a thickness of 70 - 100 nm on the back of the silicon wafer to complete the preparation of the battery precursor.

[0081] S8. Perform surface passivation on the battery precursor. After completing the surface passivation, open the film in the contact area between the fine grid and the main grid on the front side of the silicon wafer and complete the main grid printing, perform metallization on the back side, and then sinter and LECO to complete the battery preparation.

[0082] Perform electrical performance tests on the batteries prepared in the above Examples 1 - 2 and Comparative Example 1. Prepare 100 batteries for each case and take the average value. The results are shown in Table 1.

[0083] Table 1 Electrical performance of batteries in each case

[0084]

[0085] As can be seen from Table 1, compared with the batteries in the comparative example, Examples 1 and 2 use the oxygen-doped polycrystalline silicon prepared by the proposed solution in this patent as the back passivation contact structure of the TOPCon battery, and both obtain better Uoc and Jsc, resulting in a significant improvement in the battery conversion efficiency.

[0086] As Figure 1, by adopting the way of cyclic oxygen supply proposed in this patent, through increasing the number of cycles and reducing the time of introducing silane in a single cycle, and cooperating with the high-temperature crystallization process debugging, a certain thickness of oxygen-doped Poly-Si is obtained; as Figures 2 - 3 , it is proved by transmittance and UPS tests that the oxygen-doped Poly-Si has better transmittance and larger bandgap, thus solving the parasitic absorption problem to a certain extent.

[0087] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing oxygen-doped polysilicon, characterized in that: The steps include: S1 completes the preparation of the tunnel oxide layer; S2 uses LPCVD equipment to prepare an oxygen-containing amorphous silicon layer on the tunnel oxide layer by alternately performing multiple cycles of SiH4 deposition and O2 oxidation; each cycle includes: introducing SiH4 after evacuating the vacuum, and introducing O2 after evacuating the vacuum; S3 performs high temperature doping and crystallization treatment on the oxygen-containing amorphous silicon layer to form an oxygen-doped polycrystalline silicon layer.

2. The method for preparing oxygen-doped polysilicon according to claim 1, characterized in that: In step S1, LPCVD equipment is used to introduce O2 at a flow rate of 10-30 SLM at 580-630° C. for 1-5 min to complete the preparation of the tunnel oxide layer.

3. The method for preparing oxygen-doped polycrystalline silicon according to claim 1, characterized in that: In step S2, the thickness of the oxygen-containing amorphous silicon layer is adjusted by the number of cycles, and the oxygen content of the oxygen-containing amorphous silicon layer is adjusted by the time for which O2 and SiH4 are introduced in a single cycle.

4. The method for preparing oxygen-doped polysilicon according to claim 3, characterized in that: The number of cycles of the cyclic process is 8 to 13 times.

5. The method for preparing oxygen-doped polysilicon according to claim 3, characterized in that: In step S2, the circulation process is carried out at 550-630°C, the SiH4 flow rate is 100-400 sccm, the time is 2-8 min, the reaction pressure is controlled at 100-400 mtorr, the O2 flow rate is 300-5000 sccm, and the time is 1-5 min.

6. The method for preparing oxygen-doped polysilicon according to claim 1, characterized in that: In step S3, the oxygen-containing amorphous silicon layer is subjected to high temperature doping and crystallization treatment to form an oxygen-doped polycrystalline silicon layer, including: In a vacuum environment at a temperature of 800-900° C., nitrogen is used as a carrier gas to introduce POCl3 as a reaction precursor, and phosphorus is diffused on the oxygen-containing amorphous silicon layer to achieve doping and crystallization to form an N-type oxygen-doped polysilicon layer; Alternatively, in a vacuum environment at a temperature of 800-1100° C., nitrogen is used as a carrier gas to introduce BCl 3 or BBr 3 as a reaction precursor, and doping and crystallization are achieved by boron diffusion on the oxygen-containing amorphous silicon layer to form a P-type oxygen-doped polycrystalline silicon layer.

7. A method for preparing a TOPCon battery, characterized in that: include: A1 pre-processes the monocrystalline silicon wafers, including double-sided texturing, front-side single-sided boron diffusion and laser doping; A2 performs high-temperature oxidation on the front side of the silicon wafer to form a selective emitter; A3: preparing an oxygen-doped polysilicon layer on the back side of a silicon wafer by the method described in any one of claims 1 to 6; A4 removes the front and back phosphosilicate glass and residual oxide layer; A5 deposits a passivation layer on both sides of the silicon wafer, and performs metallization and sintering to produce a finished battery.

8. The method for preparing a TOPCon battery according to claim 7, characterized in that: In step A1, the square resistance is 100-250Ω / sq after the single-sided boron diffusion treatment on the front side.

9. The method for preparing a TOPCon battery according to claim 8, characterized in that: The boron diffused sample is subjected to local laser doping treatment, and the local square resistance after the laser treatment is 30-90Ω / sq.

10. The method for preparing a TOPCon battery according to claim 7, characterized in that: In step A2, the parameters of the oxidation treatment are: the temperature is set at 950°C to 1050°C, the pressure is set at 400 to 800 mbar, the oxygen flow rate is 20000 to 40000 sccm, and the oxidation time is 3000 to 4500 s; After oxidation treatment, the square resistance of the lightly doped area is 300-500Ω / sq, and the square resistance of the heavily doped area is 100-300Ω / sq, thereby obtaining a silicon wafer including a selective emitter.

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