Tunneling passivation structure, TOPCon battery and preparation method of TOPCon battery

Abstract

The invention relates to a tunneling passivation structure. The tunneling passivation structure comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer and a second doped poly layer which are sequentially arranged on the backlight surface of a silicon substrate. The tunneling passivation structure provided by the invention comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer and a second doped poly layer which are arranged in sequence, on one hand, the thickness of MnTiO3 and the thickness of silicon oxynitride correspond to the change of a band gap, and the change is much smaller than that of silicon dioxide; on the other hand, MnTiO3 serves as a bottom tunneling layer field and is prepared only through a process, thickness control is not affected by other factors of the environment and is more accurate, silicon oxynitride field is prepared only through the process, thickness control is not affected by other factors of the environment and is more accurate; meanwhile, due to the laminated design of the tunneling passivation structure, the propulsion rate of phosphorus is inhibited to a certain extent, and serious compounding caused by excessive propulsion of doping atoms on the silicon substrate is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a tunnel passivation structure and a TOPCon cell and a preparation method thereof. Background Art

[0002] TOPCon cell, full name of tunnel oxide passivation contact cell, is a high-efficiency solar cell technology based on the principle of selective carriers. It was first proposed by the Fraunhofer Institute in Germany around 2013. By around 2015, TOPCon technology began to enter the initial research and development stage, and the cell efficiency reached 25.1%, which showed that it showed significant potential under laboratory conditions. In 2017, the Georgia Institute of Technology in the United States further promoted the improvement of TOPCon cell efficiency to 25.7% through electrical performance simulation. As of 2024, China's TOPCon cell industry has developed rapidly and its production capacity has increased significantly. In 2022, China's TOPCon cell production capacity has exceeded 100GW, including major contributions from many companies, such as JinkoSolar's 35GW production capacity. By 2023, the production capacity has surged to more than 400GW, showing the acceleration of the industrialization process of this technology. So far, the main back structure is a silicon dioxide tunneling layer + doped polysilicon layer structure as a TOPCon tunneling passivation structure.

[0003] However, the thickness of silicon dioxide cannot be effectively monitored in the production line, and the loss of yield efficiency caused by thickness out of control is relatively serious and often occurs. The main reason is that the change in the thickness of silicon dioxide causes the corresponding band gap to change too much: the band gap corresponding to the lower thickness of silicon dioxide is much lower than the band gap of the silicon substrate, which loses the function of carrier selectivity and causes serious carrier recombination; the higher thickness of silicon dioxide will cause the band gap to be too high and carriers cannot pass through. As a result, the thickness of silicon dioxide needs to be controlled at the 0.1nm level on site, and silicon dioxide can grow naturally, which makes on-site control difficult and cannot be effectively monitored. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a tunnel passivation structure and a TOPCon battery and a preparation method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a tunnel passivation structure, which comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer, and a second doped poly layer which are sequentially arranged on the backlight surface of a silicon substrate.

[0007] The tunneling passivation structure proposed by the present invention comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer, and a second doped poly layer arranged in sequence. On the one hand, the change in the band gap corresponding to the thickness of MnTiO3 and silicon oxynitride is much smaller than that of silicon dioxide; on the other hand, MnTiO3 as the bottom tunneling layer is only prepared on-site through a process, and the thickness control is not affected by other environmental factors, which is more accurate; silicon oxynitride is only prepared on-site through a process, and the thickness control is not affected by other environmental factors, which is more accurate; at the same time, the stacking design of the tunneling passivation structure of the present invention suppresses the advancement rate of phosphorus to a certain extent, avoiding excessive advancement of doped atoms in the silicon substrate and serious recombination.

[0008] As a further improvement of the above solution of the present invention, the thickness of the MnTiO3 layer is 2-4 nm.

[0009] As a further improvement of the above solution of the present invention, the thickness of the first doped poly layer is 30-50 nm.

[0010] As a further improvement of the above solution of the present invention, the thickness of the silicon oxynitride layer is 2-4 nm.

[0011] As a further improvement of the above solution of the present invention, the thickness of the second doped poly layer is 100-130 nm.

[0012] The present invention provides a method for preparing the tunnel passivation structure as described above, which comprises the following steps:

[0013] S11. Forming a MnTiO3 layer on the backlight surface of the substrate;

[0014] S12. forming a first doped poly layer, a silicon oxynitride layer, and a second doped poly layer sequentially on the MnTiO3 layer;

[0015] S13: Annealing treatment.

[0016] As a further improvement of the above scheme of the present invention, the specific process of step S1 is: titanate nanowires, MnCl2 solution, NaF solution, NaOH solution, and water are mixed uniformly in a molar ratio of 20:20:5:6:200 to form a reaction solution, the reaction solution is heated to 80-120°C, and the silicon substrate is immersed in the reaction solution for 100-300s to form a MnTiO3 layer on the backlight surface of the substrate.

[0017] As a further improvement of the above solution of the present invention, the specific process of step S2 is:

[0018] Put the silicon substrate with a MnTiO3 layer formed on the backlight side into a furnace tube, and after the furnace tube is evacuated, introduce phosphine and silane at 320-400°C, with a volume ratio of phosphine to silane of 0.01-0.1:1, and a process time of 100-300s, to form a first doped poly layer on the surface of the MnTiO3 layer;

[0019] Then, the furnace tube is evacuated, and SiH4, N2O, NH3 and N2 are introduced at 320-400° C., wherein the volume ratio of SiH4, N2O, NH3 and N2 in the furnace tube is (1-3): (4-8): (4-8): (250-350), and the process time is 6-10 minutes, so that a silicon oxynitride layer can be formed on the surface of the first doped poly layer;

[0020] Then, the furnace tube is evacuated, and phosphine and silane are introduced at 320-400° C., the volume ratio of phosphine to silane is 0.1-0.2:1, and the process time is 300-500 seconds, so that a second doped poly layer can be formed on the surface of the silicon oxynitride layer.

[0021] The present invention provides a TOPCon battery, which includes the tunneling passivation structure as described above.

[0022] The present invention provides a method for preparing the TOPCon battery as described above, which comprises the following steps:

[0023] S21. Pre-treating the silicon substrate, sequentially depositing a boron diffusion layer, a front passivation layer, and a front anti-reflection film layer on the front side of the silicon substrate, and sequentially depositing a tunnel passivation structure and a back anti-reflection film layer on the backlight side of the silicon substrate;

[0024] S22. Metallization treatment;

[0025] S23. Sintering.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The tunneling passivation structure proposed in the present invention comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer, and a second doped poly layer arranged in sequence. On the one hand, the change in the band gap corresponding to the thickness of MnTiO3 and silicon oxynitride is much smaller than that of silicon dioxide; on the other hand, MnTiO3 as the bottom tunneling layer is only prepared on-site by a process, and the thickness control is not affected by other environmental factors, which is more accurate; silicon oxynitride is only prepared on-site by a process, and the thickness control is not affected by other environmental factors, which is more accurate; at the same time, the stacking design of the tunneling passivation structure of the present invention suppresses the advancement rate of phosphorus to a certain extent, avoiding excessive advancement of doped atoms in the silicon substrate and serious recombination.

[0028] 2. In the present invention, the MnTiO3 layer is prepared by a hydrothermal method. Since it is doped with F element, F is the element with the highest electronegativity and can combine with photogenerated electrons, thereby inhibiting the recombination of photogenerated electrons and holes, thereby improving efficiency. The preparation method is safe, rapid and highly stable.

[0029] 3. In the present invention, PECVD is used to introduce different proportions of N2O, SiH4, NH3 and N2 to prepare silicon oxynitride as the intermediate tunneling layer of the TOPCon battery. The N / O ratio is changed by adjusting the content of N2O, SiH4, NH3 and N2. Changing the N / O ratio will affect the SiO x N y The band gap of SiO2 leads to the change of band bending, which affects the carriers passing through SiO2. x N y The capacity of the layer is increased, and N2 is used to reduce the gas density to slow down the reaction rate, so that the production line can be easily controlled.

[0030] 4. The tunnel passivation structure proposed by the present invention is simple to prepare and easy to control, and the ability of selective carriers is more stable, which is more guaranteed for the efficiency and yield of the site. Under the premise of ensuring that the carriers selectively pass through the tunneling layer, the process is easier to control, more stable for the process, and the yield efficiency is more guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of the structure of a TOPCon battery provided in an embodiment of the present invention;

[0032] Figure 2 A preparation process of a tunnel passivation structure in a TOPCon battery provided in an embodiment of the present invention;

[0033] Figure 3 It is the ECV curve diagram of the embodiment and the comparative example.

[0034] Figure numerals: 1, silicon substrate; 2, MnTiO3 layer; 3, first doped poly layer; 4, silicon oxynitride layer; 5, second doped poly layer; 6, boron diffusion layer; 7, front oxide layer; 8, front anti-reflection film layer; 9, back anti-reflection film layer. DETAILED DESCRIPTION

[0035] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0037] Example

[0038] Reference Figure 1 This embodiment proposes a TOPCon cell, which includes a silicon substrate 1, and a boron diffusion layer 6, a front passivation layer 7, and a front anti-reflection film layer 8 sequentially deposited on the front side of the silicon substrate 1, and a tunneling passivation structure and a back anti-reflection film layer 9 sequentially deposited on the backlight side of the silicon substrate 1. The tunneling passivation structure includes a 3nm thick MnTiO3 layer 2, a 40nm thick first doped poly layer 3, a 3nm thick silicon oxynitride layer 4, and a 120nm thick second doped poly layer 5 sequentially arranged on the backlight side of the silicon substrate.

[0039] The preparation method of the TOPCon battery of this embodiment comprises the following steps:

[0040] S1. Place the original silicon substrate in a sodium hydroxide solution, and form an uneven pyramid velvet surface on the front of the silicon substrate through alkali corrosion to increase light absorption;

[0041] S2. Place the textured silicon substrate into a boron diffusion tube, introduce BCl3 into the boron diffusion tube at high temperature, and form a boron diffusion layer 6 on the silicon substrate;

[0042] S3. Using HF solution to remove the BSG layer on the back of the silicon substrate 1, and then using NaOH solution to etch away the PN junction on the back and edge of the silicon substrate 1, and polishing the back;

[0043] S4. Preparing a tunnel passivation structure on the backlight surface of the silicon substrate 1; combining Figure 2 , the specific steps of preparing the tunnel passivation structure are as follows:

[0044] S41. Titanate nanowires, MnCl2 solution, NaF solution, NaOH solution, and water are mixed in a mass ratio of 20:20:5:6:200 to form a reaction solution, the reaction solution is heated to 100° C., and the silicon substrate 1 is immersed in the reaction solution for 100-300 seconds to form a 3 nm MnTiO3 layer 2 on the backlight surface of the silicon substrate;

[0045] S42. The silicon substrate 1 with the MnTiO3 layer 2 formed on the backlight surface is placed in a furnace tube. After the furnace tube is evacuated, phosphine and silane with a volume ratio of 0.05:1 are introduced into the furnace tube at 350°C for 120 seconds, and a first doped poly layer 3 of 40nm can be formed on the surface of the MnTiO3 layer 2; then the furnace tube is evacuated, SiH4, N2O, NH3 and N2 are introduced at 350°C, and the volume ratio of SiH4, N2O, NH3 and N2 in the furnace tube is 1:6:6:300, and the process time is 8min, so that a 3nm silicon oxynitride layer 4 can be formed on the surface of the first doped poly layer 3; then the furnace tube is evacuated, and phosphine and silane with a volume ratio of 0.15:1 are introduced at 350°C for 400 seconds, and a second doped poly layer 5 of 120nm can be formed on the surface of the silicon oxynitride layer 4;

[0046] S43. After the furnace tube is evacuated and heated to 900 ° C, oxygen is introduced into the furnace tube, the oxygen flow rate is 8000 sccm, and the process time is 6 min; then nitrogen is introduced at 900 ° C, the nitrogen flow rate is 5000 ml, and the process time is 6 min;

[0047] S5. Use chain HF to remove PSG on the front and edge of the silicon substrate, and use RCA to clean the front and edge poly plating as well as the front BSG and back PSG;

[0048] S6. Depositing an aluminum oxide film on the front side of the silicon wafer by atomic layer deposition (ALD) to form a front passivation layer 7 to provide a field passivation effect;

[0049] S7. Depositing a silicon nitride film on both sides of the silicon wafer by PECVD to form a front anti-reflection film layer 8 and a back anti-reflection film layer 9;

[0050] S8. Printing metal grid lines on the front and back of the battery by a printing machine to form front electrodes and back electrodes;

[0051] S9. Through sintering + laser induced sintering, a good ohmic contact is formed, and finally a TOPCon battery is obtained.

[0052] Comparative Example

[0053] A TOPCon cell proposed in the comparative example is different from that in the embodiment in that: in the TOPCon cell in the comparative example, the tunnel passivation structure comprises a 2 nm silicon dioxide layer and a 120 nm doped poly layer sequentially arranged on the backlight surface of the silicon substrate.

[0054] The preparation method of the TOPCon cell in the comparative example is different from that in the embodiment in that the preparation method of the tunnel passivation structure includes the following steps: firstly depositing a 2nm silicon dioxide layer by plasma enhanced chemical vapor deposition (PECVD), and then depositing a 120nm doped poly layer. The remaining steps are the same as those in the embodiment.

[0055] Test Case

[0056] The TOPCon cells prepared in the comparative example were subjected to electrical performance tests under the following test conditions: (1) Light intensity: The sunlight intensity under AM1.5G conditions should be 1000 W / m 2 , that is, the light intensity is 100MW / cm; (2) Temperature: The temperature of the photovoltaic cell is 25°C. The test instrument is an IV tester. The test results are shown in Table 1 below.

[0057] Table 1 Electrical performance test results of TOPCon batteries

[0058] Experimental Group quantity Eta Voc / V Isc / A FF / % Rsh / Ω Rser / Ω IRev2 / A Comparative Example 100 26.07％ 0.717 13.904 86.313 2420.8 0.00046 0.114 Example 100 26.08％ 0.719 13.892 86.265 2432.1 0.00053 0.126

[0059] It can be seen from the results in Table 1 that the TOPCon battery of the embodiment of the present invention has the same electrical performance as the conventional TOPCon battery and has certain advantages. After changing the tunnel passivation structure, the embodiment of the present invention can not only reduce the difficulty of on-site maintenance and stability, but also can ensure that there is no loss in conversion efficiency.

[0060] The silicon wafers prepared with tunnel passivation structures in two groups of embodiments (respectively denoted as Embodiment ① and Embodiment ②) and the silicon wafers prepared with tunnel passivation structures in a group of comparative examples were subjected to ECV tests. The test results are shown in FIG. Figure 3 As shown, from Figure 3 It can be seen that the tunneling passivation structure prepared in the embodiment of the present invention effectively suppresses excessive phosphorus internal diffusion and reduces recombination. At the same time, the silicon oxynitride layer has an inhibitory effect on phosphorus atoms, so that the film structure forms a doped passivation layer with high and low concentrations, which increases the conductivity of the film and facilitates the migration of electrons and holes.

[0061] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A tunnel passivation structure, characterized in that: The method comprises a MnTiO3 layer, a first doped poly layer, a silicon oxynitride layer and a second doped poly layer which are sequentially arranged on the backlight surface of a silicon substrate.

2. The tunnel passivation structure according to claim 1, characterized in that: The thickness of the MnTiO3 layer is 2-4 nm.

3. The tunnel passivation structure according to claim 1, characterized in that: The thickness of the first doped poly layer is 30-50 nm.

4. The tunnel passivation structure according to claim 1, characterized in that: The thickness of the silicon oxynitride layer is 2-4 nm.

5. The tunnel passivation structure according to claim 1, characterized in that: The thickness of the second doped poly layer is 100-130 nm.

6. A method for preparing a tunnel passivation structure as claimed in any one of claims 1 to 5, characterized in that: It includes the following steps: S11. Forming a MnTiO3 layer on the backlight surface of the substrate; S12. forming a first doped poly layer, a silicon oxynitride layer, and a second doped poly layer sequentially on the MnTiO3 layer; S13: Annealing treatment.

7. The method for preparing a tunnel passivation structure according to claim 6, characterized in that: The specific process of step S1 is: titanate nanowires, MnCl2 solution, NaF solution, NaOH solution, and water are mixed evenly in a molar ratio of 20:20:5:6:200 to form a reaction solution, the reaction solution is heated to 80-120°C, and the silicon substrate is immersed in the reaction solution for 100-300s to form a MnTiO3 layer on the backlight surface of the substrate.

8. The method for preparing a tunnel passivation structure according to claim 6, characterized in that: The specific process of step S2 is: The silicon substrate with a MnTiO3 layer formed on the backlight side is placed in a furnace tube. After the furnace tube is evacuated, phosphine and silane are introduced at 320-400°C, the volume ratio of phosphine to silane is 0.01-0.1:1, and the process time is 100-140s, so that a first doped poly layer can be formed on the surface of the MnTiO3 layer; Then, the furnace tube is evacuated, and SiH4, N2O, NH3 and N2 are introduced at 320-400° C., wherein the volume ratio of SiH4, N2O, NH3 and N2 in the furnace tube is (1-3): (4-8): (4-8): (250-350), and the process time is 6-10 minutes, so that a silicon oxynitride layer can be formed on the surface of the first doped poly layer; Then, the furnace tube is evacuated, and phosphine and silane are introduced at 320-400° C., the volume ratio of phosphine to silane is 0.1-0.2:1, and the process time is 300-500 seconds, so that a second doped poly layer can be formed on the surface of the silicon oxynitride layer.

9. A TOPCon battery, characterized in that: It comprises the tunnel passivation structure according to any one of claims 1 to 5.

10. A method for preparing the TOPCon battery according to claim 9, characterized in that: It includes the following steps: S21. Pre-treating the silicon substrate, sequentially depositing a boron diffusion layer, a front passivation layer, and a front anti-reflection film layer on the front side of the silicon substrate, and sequentially depositing a tunnel passivation structure and a back anti-reflection film layer on the backlight side of the silicon substrate; S22. Metallization treatment; S23. Sintering.

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