A method for preparing a TOPCon solar cell with a double-layer passivation contact structure

Abstract

The present invention discloses a method for preparing a TOPCon solar cell with a double-layer passivated contact structure, belonging to the field of TOPCon cells. A first tunneling oxide layer and a blocking polysilicon layer are first deposited on the back side of a treated silicon substrate; a second tunneling oxide layer and a doped polysilicon layer are then deposited on the deposited blocking polysilicon layer; the oxygen flow rate is then increased to form a silicon dioxide film mask on the back side; and then back-side phosphorus diffusion is performed. The present invention has the beneficial effects of significantly increasing the propulsion temperature for phosphorus diffusion, improving crystallization capability, and avoiding the increased internal diffusion caused by high-temperature phosphorus diffusion, while maintaining a good tunneling effect and the contact passivation capability of the polysilicon layer and the tunneling layer, ultimately significantly improving the efficiency of the TOPCon cell.

Description

Technical Field

[0001] The present invention relates to the field of TOPCon cells, and in particular to a method for preparing a TOPCon solar cell with a double-layer passivation contact structure. Background Art

[0002] In recent years, high-efficiency, low-cost solar cells have been a research hotspot in the photovoltaic industry. TOPCon solar cells involve first depositing a 1-2nm thick tunneling oxide layer on the back of the cell, followed by a layer of doped polysilicon. Together, these two layers form a passivating contact structure, providing excellent interface passivation for the backside of the silicon wafer. This ultra-thin oxide layer allows majority electrons to tunnel into the polysilicon layer while simultaneously preventing minority carrier-hole recombination. Electrons then travel laterally through the polysilicon layer and are collected by the metal, significantly reducing the metal contact recombination current and improving the cell's open-circuit voltage and short-circuit current.

[0003] The main methods for forming the tunnel oxide layer and doped polysilicon layer in the TOPCon cell manufacturing process include APCVD (atmospheric pressure chemical vapor deposition), LPCVD (low pressure chemical vapor deposition), and PECVD (plasma-enhanced chemical vapor deposition). LPCVD is widely used due to its advantages such as low impurity content, excellent uniformity, superior film density, and high production capacity. Because the polysilicon layer formed on the front side of TOPCon products increases parasitic absorption of light and reduces efficiency, the polysilicon layer is avoided as much as possible on the front side. Instead, a thin polysilicon layer is used on the back side to reduce optical parasitic absorption. To match the thin polysilicon, phosphorus diffusion is promoted through low-temperature deposition to form a good passivation and contact layer. However, the low annealing temperature of phosphorus diffusion can negatively affect the crystallization of the polysilicon layer, increase backside recombination, and reduce electrical output, resulting in low cell conversion efficiency. Improvements are urgently needed.

[0004] In view of this, the inventor conducted in-depth research on this demand, and thus came up with this case. Summary of the Invention

[0005] To address the problem in the prior art that TOPCon cells have low annealing ability due to low temperature during phosphorus diffusion, which results in a decrease in the crystallization rate of the polysilicon layer, increased backside recombination, reduced electrical output, and affected cell conversion efficiency, the present invention provides a method for preparing a TOPCon solar cell with a double-layer passivated contact structure, comprising the following steps:

[0006] Step 1: The silicon substrate is cleaned and textured, and the front side is subjected to boron diffusion and etching and alkaline polishing treatment in sequence;

[0007] Step 2: depositing a first tunneling oxide layer and a blocking polysilicon layer on the back side of the processed silicon substrate;

[0008] Step 3, depositing a second tunneling oxide layer and a doped polysilicon layer again on the deposited barrier polysilicon layer;

[0009] Step 4: Increase the oxygen flow rate to form a silicon dioxide film mask on the back side;

[0010] Step 5: back phosphorus diffusion;

[0011] Step six: cleaning, passivation, screen printing and high-temperature sintering are carried out in sequence.

[0012] Compared with conventional production line processes, in order to achieve a higher level of improvement in the tunneling effect, the present invention has developed a new type of stacked structure process. By depositing a stacked structure of a first tunneling oxide layer - a blocking polysilicon layer - a second tunneling oxide layer - a doped polysilicon layer on the back of a silicon substrate, the advancement temperature of phosphorus diffusion can be greatly increased, thereby improving the crystallization ability. At the same time, it can avoid the increased internal expansion caused by high-temperature phosphorus diffusion, maintain a good tunneling effect unchanged, maintain the contact passivation ability of the polysilicon layer and the tunneling layer, and ultimately significantly improve the efficiency of the TOPCon battery.

[0013] Preferably, in step 1, the silicon substrate is textured on both sides to obtain a textured silicon wafer, thereby removing surface damage and forming a surface pyramid light-trapping structure. Boron diffusion is performed on the front surface of the textured silicon wafer to form the P+ doped layer and the borosilicate glass layer. The borosilicate glass layer is then removed by etching, and the back surface of the crystalline silicon substrate is polished using an alkali polishing process to remove the phosphosilicate glass layer formed during the boron diffusion process.

[0014] Preferably, in the step 2, LPCVD equipment is used, oxygen is introduced under normal pressure, and the reaction is carried out at a temperature of 600~620°C for 950~1200s to form a first tunneling oxide layer on the surface of the silicon substrate. Subsequently, a blocking polysilicon layer is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 200~300mtorr and a temperature of 590~630°C for 200~400s.

[0015] Preferably, the thickness of the first tunneling oxide layer is 1-1.5 nm, and the thickness of the blocking polysilicon layer is 20-40 nm.

[0016] Preferably, in the step three, LPCVD equipment is used, oxygen is introduced under normal pressure, and the reaction is carried out at a temperature of 590~630°C for 200~400s to form a second tunneling oxide layer on the surface of the silicon substrate. Subsequently, a doped polysilicon layer is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 200~300mtorr and a temperature of 590~630°C for 1000-1400s.

[0017] Preferably, the thickness of the second tunneling oxide layer is 0.3-0.5 nm, and the thickness of the doped polysilicon layer is 100-130 nm.

[0018] The present invention adopts the Doe experimental design to verify the gradient of oxide layers and polysilicon layers with different thicknesses, and obtains that the thickness result of the first tunneling oxide layer (1~1.5nm) - blocking polysilicon layer (20~40nm) - second tunneling oxide layer (0.3~0.5nm) - doped polysilicon layer (100~130nm) is the optimal.

[0019] Preferably, in step 4, a low-pressure diffusion deposition device is used to form a silicon dioxide masking film by low-pressure oxidation with an oxygen flow rate of 1100-1400 sccm and a reaction time of 200-300 seconds.

[0020] In step 4, by increasing the oxygen flow rate to 1100-1400 sccm, a thicker silicon dioxide masking film is formed on the back of the TOPCon cell. At high temperatures, the solubility of phosphorus atoms in SiO2 and silicon differs significantly, and the diffusion rate of phosphorus in silicon is much faster than that in silicon dioxide. Therefore, adding a silicon dioxide masking film before phosphorus diffusion can slow the diffusion of phosphorus and prevent it from penetrating.

[0021] Preferably, in the step five, POCl3 is used for phosphorus diffusion, firstly low-temperature deposition, then staged advancement, POCl3 is used again for source supplement diffusion, and finally a post-oxidation annealing process is performed.

[0022] Preferably, in the step five, POCl3 is used for phosphorus diffusion with a flow rate of 1500~1600sccm, and low-temperature deposition is performed first, the deposition temperature is 750~850℃, and the time is 900~1200s; then the process is advanced in stages, first at a temperature of 860~930℃ for 10~20min, and then at a temperature of 800~860℃ for 10~20min; then POCl3 is used for source diffusion again, with a flow rate of 1500~1600sccm, a deposition temperature of 830~860℃, and a time of 120~180s, and finally an oxidation annealing process is performed for 1200~1500s, and the temperature is lowered to 720~750℃.

[0023] As the high-temperature advancement process progresses, the phosphorus source deposited on the silicon wafer surface in the deposition step is consumed, and the surface concentration decreases. In step five, the temperature of the heating advancement is increased, and the source is turned on again at the end, POCl3 is added for diffusion, and the surface concentration is appropriately increased, thereby improving the crystallization ability and optimizing the band gap width, achieving the purpose of increasing the opening voltage and improving the efficiency, maintaining a good tunneling layer, and maintaining the original passivation and contact capabilities of the single-layer polysilicon.

[0024] Preferably, in step six, RCA is used to clean the back oxide layer, the N+ layer generated on the front and edge during phosphorus diffusion, and the front borosilicate glass layer and the front phosphosilicate glass layer are removed; then, aluminum oxide atomic layer deposition is performed on the front to form an aluminum oxide passivation layer; SiN is deposited on the front and back surfaces. x , forming a front anti-reflection layer and a back anti-reflection layer; then forming an ohmic contact by printing electrodes and high-temperature sintering.

[0025] The present invention also provides a TOPCon solar cell obtained by adopting the above preparation method.

[0026] Preferably, the above-mentioned TOPCon solar cell includes an N-type silicon wafer, the front side of which is sequentially provided with a P+ diffusion layer, an aluminum oxide passivation layer, a front anti-reflection layer and a front metal electrode, and the back side of which is sequentially provided with a first tunneling oxide layer, a blocking polysilicon layer, a second tunneling oxide layer, a doped polysilicon layer, a back anti-reflection layer and a back metal electrode; the front metal electrode penetrates the front anti-reflection layer and the aluminum oxide passivation layer to form an ohmic contact with the P+ diffusion layer; the back metal electrode penetrates the back anti-reflection layer to form an ohmic contact with the doped polysilicon layer.

[0027] The beneficial effects produced by the technical solution of the present invention are as follows:

[0028] (1) By depositing a stacked structure of the first tunneling oxide layer - blocking polysilicon layer - second tunneling oxide layer - doped polysilicon layer on the back of the silicon substrate, the advancement temperature of phosphorus diffusion can be greatly increased, thereby improving the crystallization ability. At the same time, it can avoid the increase in internal expansion caused by high-temperature phosphorus diffusion, maintain a good tunneling effect, maintain the contact passivation ability of the polysilicon layer and the tunneling layer, and ultimately greatly improve the efficiency of the TOPCon battery.

[0029] (2) By adopting the Doe experimental design, the gradient of oxide layers and polysilicon layers with different thicknesses was verified, and the thickness was obtained as the first tunneling oxide layer (1~1.5nm) - blocking polysilicon layer (20~40nm) - second tunneling oxide layer (0.3~0.5nm) - doped polysilicon layer (100~130nm), thereby greatly increasing the advancement temperature of phosphorus diffusion and improving the crystallization ability.

[0030] (3) By increasing the oxygen flow rate before phosphorus diffuses, a thicker silicon dioxide film mask is formed on the back of the battery, which can slow down the diffusion rate of phosphorus and prevent the solubility of phosphorus atoms in SiO2 and Si from being too different at high temperatures. The diffusion rate of phosphorus in silicon is also much greater than the diffusion rate in silicon dioxide, resulting in P diffusion.

[0031] (4) By increasing the temperature of the heating process and passing the source again at the end, adding POCl3 for diffusion, and appropriately increasing the surface concentration, the crystallization ability is improved, the band gap width is optimized, and the purpose of increasing the opening voltage and improving the efficiency is achieved. A good tunneling layer is maintained, and the original passivation and contact capabilities of the single-layer polysilicon are also maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 It is a schematic flow chart of the preparation method of the TOPCon solar cell with a double-layer passivated contact structure in the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] This embodiment uses a double-layer passivation contact structure on the TOPCon solar cell, increases the oxygen flow rate before the phosphorus diffusion process, forms a thicker silicon dioxide film mask, reduces the phosphorus source flow rate in the early stage of phosphorus diffusion, significantly increases the advancement temperature and improves the crystallization ability, and then performs a source replenishment process after the advancement is completed to increase the phosphorus diffusion surface concentration, ultimately significantly improving the efficiency of the TOPCon cell. The specific implementation method is as follows:

[0036] like Figure 1 As shown, a method for preparing a TOPCon solar cell with a double-layer passivation contact structure includes the following steps:

[0037] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0038] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at a temperature of 600-620°C for 950-1200 seconds to form a first tunneling oxide layer with a thickness of 1-1.5 nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 20-40 nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 200-300 mtorr and a temperature of 590-630°C for 200-400 seconds.

[0039] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at a temperature of 590-630°C for 200-400 seconds to form a second tunneling oxide layer with a thickness of 0.3-0.5 nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 100-130 nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 200-300 mtorr and a temperature of 590-630°C for 1000-1400 seconds.

[0040] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1100-1400 sccm for 200-300 seconds to form a thicker silicon dioxide masking film.

[0041] Step five, use POCl3 for phosphorus diffusion with a flow rate of 1500~1600sccm, first perform low-temperature deposition, the deposition temperature is 750~850℃, and the time is 900~1200s; then advance in stages, first heat up and advance at a temperature of 860~930℃ for 10~20min, then cool down and advance at 800~860℃ for 10~20min; then use POCl3 for source diffusion again, with a flow rate of 1500~1600sccm, the deposition temperature is 830~860℃, and the time is 120~180s, and finally perform an oxidation annealing process for 1200~1500s, and cool to 720~750℃.

[0042] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0043] The present invention also provides a TOPCon solar cell obtained by adopting the above preparation method.

[0044] As a preferred embodiment, the above-mentioned TOPCon solar cell includes an N-type silicon wafer, the front side of which is sequentially provided with a P+ diffusion layer, an aluminum oxide passivation layer, a front anti-reflection layer and a front metal electrode, and the back side of which is sequentially provided with a first tunneling oxide layer, a blocking polysilicon layer, a second tunneling oxide layer, a doped polysilicon layer, a back anti-reflection layer and a back metal electrode; the front metal electrode penetrates the front anti-reflection layer and the aluminum oxide passivation layer to form an ohmic contact with the P+ diffusion layer; and the back metal electrode penetrates the back anti-reflection layer to form an ohmic contact with the doped polysilicon layer.

[0045] The beneficial effects of the method for preparing a TOPCon solar cell with a double-layer passivation contact structure in the present invention are further reviewed below through several groups of examples.

[0046] Example 1:

[0047] In this embodiment, a method for preparing a TOPCon solar cell with a double-layer passivated contact structure includes the following steps:

[0048] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0049] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 620°C for 1200s to form a first tunneling oxide layer with a thickness of 1.5nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 40nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 300mtorr and a temperature of 630°C for 400s.

[0050] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 630°C for 400s to form a second tunneling oxide layer with a thickness of 0.5nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 130nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 300mtorr and a temperature of 630°C for 1400s.

[0051] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1400 sccm for 300 seconds to form a thicker silicon dioxide masking film.

[0052] Step 5: Phosphorus diffusion is performed using POCl3 at a flow rate of 1600 sccm. Low-temperature deposition is performed first, with a deposition temperature of 850°C and a time of 1200s. The process is then advanced in stages, first at a temperature of 930°C for 20min, then at a temperature of 860°C for 10min. POCl3 is then used for source diffusion again at a flow rate of 1600 sccm, a deposition temperature of 860°C, and a time of 180s. Finally, an oxidation annealing process is performed for 1500s, followed by cooling to 750°C.

[0053] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0054] Comparative Example 1:

[0055] In the preparation method of Comparative Example 1, the phosphorus diffusion process in step 5 only includes deposition and oxidation annealing, specifically:

[0056] POCl3 was used as the diffusion source with a flow rate of 1600 sccm, a temperature of 850°C, and a time of 35 min. Finally, an oxidation annealing process was performed for 1500 s and the temperature was lowered to 750°C.

[0057] Other steps are the same as in Example 1.

[0058] Example 2:

[0059] In this embodiment, a method for preparing a TOPCon solar cell with a double-layer passivated contact structure includes the following steps:

[0060] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0061] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 610°C for 1100s to form a first tunneling oxide layer with a thickness of 1.3nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 30nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 260mtorr and a temperature of 620°C for 300s.

[0062] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 610°C for 300 seconds to form a second tunneling oxide layer with a thickness of 0.4 nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 120 nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 260 mtorr and a temperature of 620°C for 1300 seconds.

[0063] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1300 sccm for 280 seconds to form a thicker silicon dioxide masking film.

[0064] Step 5: Phosphorus diffusion is performed using POCl3 at a flow rate of 1550 sccm. Low-temperature deposition is performed first, with a deposition temperature of 830°C and a time of 1100s. The process is then staged, with a temperature increase at 910°C for 18 minutes, followed by a temperature decrease at 840°C for 18 minutes. POCl3 is then used for source diffusion again at a flow rate of 1550 sccm, a deposition temperature of 850°C, and a time of 160s. Finally, an oxidation annealing process is performed for 1400s, followed by cooling to 740°C.

[0065] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0066] Comparative Example 2:

[0067] In the preparation method of this comparative example 2, the phosphorus diffusion process in step 5 only includes deposition, high-temperature driving and oxidation annealing, specifically:

[0068] Using POCl3 as the diffusion source with a flow rate of 1550sccm, low-temperature deposition is first performed at a deposition temperature of 830°C for 1100s; then it is advanced in stages, first at a temperature of 910°C for 18min, then at a temperature of 840°C for 18min; finally, an oxidation annealing process is performed for 1400s, and the temperature is lowered to 740°C.

[0069] Other steps are the same as in Example 2.

[0070] Example 3:

[0071] In this embodiment, a method for preparing a TOPCon solar cell with a double-layer passivated contact structure includes the following steps:

[0072] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0073] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 610°C for 1000s to form a first tunneling oxide layer with a thickness of 1.2nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 30nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 240mtorr and a temperature of 600°C for 300s.

[0074] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 610°C for 300 seconds to form a second tunneling oxide layer with a thickness of 0.4 nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 110 nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 240 mtorr and a temperature of 600°C for 1200 seconds.

[0075] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1200 sccm for 260 seconds to form a thicker silicon dioxide masking film.

[0076] Step 5: Phosphorus diffusion is performed using POCl3 at a flow rate of 1550 sccm. Low-temperature deposition is performed first, with a deposition temperature of 800°C and a time of 1000s. The process is then advanced in stages, first at a temperature of 880°C for 16 minutes, then at a temperature of 820°C for 16 minutes. POCl3 is then used for source diffusion again at a flow rate of 1550 sccm, a deposition temperature of 840°C, and a time of 150s. Finally, an oxidation annealing process is performed for 1300s, followed by cooling to 730°C.

[0077] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0078] Comparative Example 3:

[0079] In the preparation method of this comparative example 3, step 4 uses a low-pressure diffusion deposition device to form a thicker silicon dioxide mask film by low-pressure oxidation with an oxygen flow rate of 1000 sccm for 260 seconds. The other steps are the same as those in Example 3.

[0080] Example 4:

[0081] In this embodiment, a method for preparing a TOPCon solar cell with a double-layer passivated contact structure includes the following steps:

[0082] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0083] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 600°C for 950 seconds to form a first tunneling oxide layer with a thickness of 1 nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 20 nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 200 mtorr and a temperature of 590°C for 200 seconds.

[0084] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 590°C for 200 seconds to form a second tunneling oxide layer with a thickness of 0.3 nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 100 nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 200 mtorr and a temperature of 590°C for 1000 seconds.

[0085] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1100 sccm for 200 seconds to form a thicker silicon dioxide masking film.

[0086] Step 5: Phosphorus diffusion is performed using POCl3 at a flow rate of 1500sccm. Low-temperature deposition is performed first, with a deposition temperature of 750°C and a time of 900s. The process is then advanced in stages, first at a temperature of 860°C for 10min, then at a temperature of 800°C for 20min. POCl3 is then used for source diffusion again at a flow rate of 1500sccm, a deposition temperature of 830°C, and a time of 120s. Finally, an oxidation annealing process is performed for 1200s, followed by cooling to 720°C.

[0087] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0088] Comparative Example 4:

[0089] In the preparation method of this comparative example 4, step 4 uses a low-pressure diffusion deposition device to form a thicker silicon dioxide mask film by low-pressure oxidation using an oxygen flow rate of 1500 sccm for 200 seconds. The other steps are the same as those in Example 4.

[0090] The TOPCon solar cells obtained in the above four groups of examples and comparative examples were subjected to performance tests, and the results are as follows:

[0091] Table 1 TOPCon solar cell performance test results of Examples 1 to 4 and Comparative Examples 1 to 4

[0092]

[0093] As can be seen from Table 1, the TOPCon solar cells prepared in Examples 1 to 4 of the present application adopt a double-layer passivation contact structure + increased oxygen flow before phosphorus diffusion + optimized source quantity and advancement temperature process for phosphorus diffusion + re-source replenishment, respectively, compared with their comparative examples 1 to 4, the voltage, current and photoelectric conversion efficiency of the battery are improved, and the advancement temperature of phosphorus diffusion can be greatly increased to improve the crystallization ability.

[0094] Example 5:

[0095] In this embodiment, a method for preparing a TOPCon solar cell with a double-layer passivated contact structure includes the following steps:

[0096] Step 1: Select an n-type silicon substrate and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatments in sequence;

[0097] Step 2: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 610°C for 1100 seconds to form a first tunneling oxide layer with a thickness of 1.3nm on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer with a thickness of 30nm is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 240mtorr and a temperature of 600°C for 300 seconds.

[0098] Step 3: Using LPCVD equipment, oxygen is introduced under normal pressure and reacted at 600°C for 300 seconds to form a second tunneling oxide layer with a thickness of 0.4 nm on the surface of the silicon substrate. Subsequently, a doped polysilicon layer with a thickness of 120 nm is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 240 mtorr and a temperature of 600°C for 1200 seconds.

[0099] Step 4: Using a low-pressure diffusion deposition device, low-pressure oxidation is performed with an oxygen flow rate of 1400 sccm for 300 seconds to form a thicker silicon dioxide masking film.

[0100] Step 5: Phosphorus diffusion is performed using POCl3 at a flow rate of 1550 sccm. Low-temperature deposition is performed first, with a deposition temperature of 830°C and a time of 1000s. The process is then staged, with the temperature being raised at 930°C for 20min and then lowered at 860°C for 20min. POCl3 is then used for source diffusion again at a flow rate of 1550 sccm, a deposition temperature of 850°C and a time of 180s. Finally, an oxidation annealing process is performed for 1500s, followed by cooling to 750°C.

[0101] Step six: finally, cleaning, passivation treatment, screen printing and high-temperature sintering are carried out in sequence to make a battery.

[0102] Comparative Example 5:

[0103] In the preparation method of this comparative example 5, steps 2 and 3 form a first tunneling oxide layer (0.8 nm) - a blocking polysilicon layer (18 nm) - a second tunneling oxide layer (0.4 nm) - a doped polysilicon layer (120 nm), and the other steps are the same as those in Example 5.

[0104] Comparative Example 6:

[0105] The preparation method in this comparative example 6 is the same as that in Example 5 except that steps 2 and 3 form the first tunneling oxide layer (1.8 nm) - blocking polysilicon layer (45 nm) - second tunneling oxide layer (0.4 nm) - doped polysilicon layer (120 nm).

[0106] Comparative Example 7:

[0107] The preparation method in this comparative example 7 is the same as that in Example 5 except that steps 2 and 3 form the first tunneling oxide layer (1.3 nm) - blocking polysilicon layer (30 nm) - second tunneling oxide layer (0.2 nm) - doped polysilicon layer (90 nm).

[0108] Comparative Example 8:

[0109] The preparation method in this comparative example 8 is the same as that in Example 5 except that steps 2 and 3 form the first tunneling oxide layer (1.3 nm) - blocking polysilicon layer (30 nm) - second tunneling oxide layer (0.6 nm) - doped polysilicon layer (140 nm).

[0110] The TOPCon solar cells obtained in Example 5 and Comparative Examples 5 to 8 were subjected to performance tests, and the results are as follows:

[0111] Table 2 TOPCon solar cell performance test results of Example 5 and Comparative Examples 5 to 8

[0112]

[0113] As can be seen from Table 2, the TOPCon solar cell prepared in Example 5 of the present application adopts a double-layer passivation contact structure with a thickness of a first tunneling oxide layer (1~1.5nm)-a blocking polysilicon layer (20~40nm)-a second tunneling oxide layer (0.3~0.5nm)-a doped polysilicon layer (100~130nm). Compared with comparative examples 5~8, the voltage, current and photoelectric conversion efficiency of the battery are also improved.

[0114] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a TOPCon solar cell with a double-layer passivation contact structure, characterized in that: The steps include: Step 1: The silicon substrate is cleaned and textured, and the front side is subjected to boron diffusion and etching and alkaline polishing treatment in sequence; Step 2: depositing a first tunneling oxide layer with a thickness of 1 to 1.5 nm and a blocking polysilicon layer with a thickness of 20 to 40 nm on the back side of the processed silicon substrate; Step 3: depositing a second tunnel oxide layer with a thickness of 0.3-0.5 nm and a doped polysilicon layer with a thickness of 100-130 nm on the deposited blocking polysilicon layer; Step 4: Increase the oxygen flow rate to form a silicon dioxide film mask on the back side; Step 5: Use POCl3 for backside phosphorus diffusion, first low-temperature deposition, then step-by-step advancement, and again use POCl3 for source diffusion, and finally perform post-oxidation annealing process; Step 6: Cleaning, passivation, screen printing and high-temperature sintering are carried out in sequence; In the step five, POCl3 is specifically used for back phosphorus diffusion with a flow rate of 1500~1600sccm, and low-temperature deposition is first performed, the deposition temperature is 750~850℃, and the time is 900~1200s; then it is advanced in stages, first heating and advancing at a temperature of 860~930℃ for 10~20min, and then cooling and advancing at 800~860℃ for 10~20min; then POCl3 is used for source diffusion again, with a flow rate of 1500~1600sccm, a deposition temperature of 830~860℃, and a time of 120~180s, and finally an oxidation annealing process is performed for 1200~1500s, and the temperature is lowered to 720~750℃.

2. The method for preparing a TOPCon solar cell according to claim 1, wherein: In step 2, LPCVD equipment is used to introduce oxygen at normal pressure and react at a temperature of 600-620°C for 950-1200s to form a first tunneling oxide layer on the surface of the silicon substrate. Subsequently, a barrier polysilicon layer is deposited on the surface of the first tunneling oxide layer by reacting at a low pressure of 200-300 mtorr and a temperature of 590-630°C for 200-400s.

3. The method for preparing a TOPCon solar cell according to claim 1, wherein: In step three, LPCVD equipment is used to introduce oxygen at normal pressure and react at a temperature of 590-630°C for 200-400 seconds to form a second tunneling oxide layer on the surface of the silicon substrate. Subsequently, a doped polysilicon layer is deposited on the surface of the second tunneling oxide layer by reacting at a low pressure of 200-300 mtorr and a temperature of 590-630°C for 1000-1400 seconds.

4. The method for preparing a TOPCon solar cell according to claim 1, wherein: In step 4, a low-pressure diffusion deposition device is used, an oxygen flow rate of 1100-1400 sccm is used, and the reaction time is 200-300 seconds to form a silicon dioxide masking film.

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