Metal contact structure and preparation method thereof, and photovoltaic cell and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, and discloses a metal contact structure of a photovoltaic cell, a preparation method of the metal contact structure, the photovoltaic cell and a preparation method of the photovoltaic cell. The preparation method of the metal contact structure comprises the following steps: preparing a tunneling passivation contact structure on the outer surface of a silicon substrate; the tunneling passivation contact structure comprises a tunneling silicon oxide layer and a doped polycrystalline silicon layer which are sequentially prepared on the outer surface of the silicon substrate; preparing thin silicon oxide with a tunneling electron function on the outer surface of the doped polycrystalline silicon layer; and preparing a conductive metal layer on the outer surface of the thin silicon oxide layer. By preparing the metal contact structure, the generation of a recombination center can be effectively avoided, the transmission loss of electrons can be reduced, the contact resistance can be reduced, the light reflection and reabsorption utilization rate of the cell can be improved, the doping concentration of phosphorus elements of the doped polycrystalline silicon layer can be properly reduced, the generation of Auger recombination center can be avoided, and the service life of the cell can be prolonged. Therefore, the electrical performance of the cell can be optimized, and the photoelectric conversion efficiency of the cell is further improved.

Description

Technical Field

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

[0002] The core of the Topcon (Tunnel Oxide Passivating Contacts) cell is to deposit a tunneling silicon oxide layer and a doped polysilicon layer (such as a phosphorus-doped polysilicon layer) in sequence on the back of the silicon substrate; the tunneling silicon oxide layer passivates the silicon substrate, and the field passivation capability of the doped polysilicon layer further improves its passivation performance, while high doping can also achieve excellent metal-semiconductor (such as metal electrode and doped polysilicon layer) contact on the back without damaging the silicon substrate. Therefore, as shown in publication number CN118213439A, the Topcon cell helps to improve the photoelectric conversion efficiency of the cell through its excellent passivation and contact performance. However, the high doping of the phosphorus-doped polysilicon layer will cause some phosphorus atoms to diffuse into the silicon substrate, resulting in the formation of Auger recombination centers.

[0003] Based on this, the prior art, as shown in publication number CN216980577U, sequentially arranges a first tunneling oxide layer, a first n+ polysilicon doping layer, a second tunneling oxide layer, and a second n+ polysilicon doping layer on the back side of the silicon wafer to achieve step-by-step doping passivation, enhance the passivation effect, and reduce the internal diffusion of phosphorus atoms inside the silicon wafer during the phosphorus diffusion process, thereby improving battery efficiency.

[0004] However, the step-by-step doping passivation method shown in publication number CN216980577U not only needs to improve the conductivity and metal contact ability of the back side, but also the second n+ polysilicon doping layer increases the total thickness of the back polysilicon layer, which is likely to bring new problems: such as increasing parasitic light absorption losses, etc.; all of which are not conducive to further improving the photoelectric conversion efficiency of the battery. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a metal contact structure of a photovoltaic cell and a preparation method thereof, a photovoltaic cell and a preparation method thereof.

[0006] Based on this, the present invention discloses a method for preparing a metal contact structure of a photovoltaic cell, comprising the following preparation steps:

[0007] S1. Preparing a tunneling passivation contact structure on the outer surface of a silicon substrate; wherein the tunneling passivation contact structure comprises a tunneling silicon oxide layer and a doped polysilicon layer sequentially prepared on the outer surface of the silicon substrate;

[0008] S2, preparing a thin layer of silicon oxide having a tunneling electron function on the outer surface of the doped polysilicon layer;

[0009] S3. Prepare a conductive metal layer on the outer surface of the thin layer of silicon oxide.

[0010] Preferably, in step S1, the tunnel passivation contact structure is prepared by physical vapor deposition or plasma enhanced chemical vapor deposition.

[0011] Further preferably, in step S1, the thickness of the tunneling silicon oxide layer is 2-3 nm, and the thickness of the doped polysilicon layer is 120-190 nm;

[0012] The doping concentration of the doped polysilicon layer is less than or equal to 1*10e 19 .

[0013] Preferably, in step S2, the thin layer of silicon oxide is prepared by physical vapor deposition or plasma enhanced chemical vapor deposition.

[0014] Further preferably, the thin layer of silicon oxide is prepared by physical vapor deposition;

[0015] Oxygen is introduced into the reaction chamber for oxidation, the oxygen flow rate is 200-600 sccm, and the oxidation temperature is 200-300° C., so as to obtain the thin layer of silicon oxide with a thickness of 1-2 nm on the outer surface of the doped polysilicon layer.

[0016] Preferably, in step S3, the conductive metal layer is prepared by physical vapor deposition.

[0017] Further preferably, the deposition power of the conductive metal layer is 20-35KW, and the deposition temperature is 200-300°C, so as to deposit the conductive metal layer with a thickness of 50-500nm on the outer surface of the thin layer of silicon oxide;

[0018] The conductive metal layer is made of copper or nickel.

[0019] The present invention also discloses a metal contact structure of a photovoltaic cell, which is prepared by the preparation method of the metal contact structure of a photovoltaic cell described above in the present invention; the metal contact structure includes a tunneling passivation contact structure, a thin layer of silicon oxide and a conductive metal layer sequentially arranged on the surface of a silicon substrate.

[0020] The present invention also discloses a method for preparing a photovoltaic cell, comprising the following preparation steps:

[0021] Step 1: Perform double-sided texturing on the silicon substrate;

[0022] Step 2: preparing an emitter on the front side of the silicon substrate;

[0023] Step 3, cleaning the silicon substrate after the treatment in step 2, and then polishing the back side of the silicon substrate;

[0024] Step 4: using the method for preparing a metal contact structure of a photovoltaic cell described above in the present invention, prepare the metal contact structure on the back of the silicon substrate treated in step 3; the metal contact structure comprises a tunnel passivation contact structure, a thin layer of silicon oxide and a conductive metal layer sequentially arranged on the back of the silicon substrate;

[0025] Step 5: prepare a front passivation anti-reflection layer on the front side of the emitter, and prepare a back anti-reflection layer on the back side of the conductive metal layer;

[0026] Step 6: Prepare a front metal electrode and a back metal electrode on the front and back sides of the silicon substrate processed in step 5, respectively, so that the front metal electrode makes ohmic contact with the emitter, and the back metal electrode makes ohmic contact with the conductive metal layer.

[0027] The present invention also discloses a photovoltaic cell, which is a Topcon cell, which is prepared by the photovoltaic cell preparation method described above in the present invention.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] The present invention sequentially deposits a thin layer of silicon oxide and a conductive metal layer such as copper or nickel on the back side of a tunnel passivation contact structure (which includes a tunnel silicon oxide layer and a doped polysilicon layer sequentially deposited on the back side of a silicon substrate), which has the following advantages:

[0030] (1) Both the thin silicon oxide layer and the conductive metal layer can prevent metal diffusion. Therefore, after metallization sintering, the back metal paste will not burn through the conductive metal layer. In addition, due to the barrier effect of the thin silicon oxide layer and the conductive metal layer, the back metal paste will not directly contact the doped polysilicon layer. Therefore, the generation of recombination centers can be effectively avoided, which helps to improve the open circuit voltage and photoelectric conversion efficiency.

[0031] (2) The thin layer of silicon oxide also has the function of tunneling electrons. The lateral and longitudinal electron transmission capabilities of the conductive metal layer are much higher than those of the doped polysilicon layer. The lateral and longitudinal electron transmission capabilities of the conductive metal layer are extremely strong, and it has high conductivity. Moreover, the contact resistance of the conductive metal layer is low, and it has excellent contact performance. The contact resistance of the metal-metal contact with the back metal electrode through the conductive metal layer (such as copper or nickel) is extremely low. Therefore, the doped polysilicon layer transfers electrons to the conductive metal layer through the thin layer of silicon oxide, and then through the metal-metal contact, it can reduce the transmission loss of electrons, reduce the contact resistance, reduce the loss of electrical performance, and optimize the electrical performance of the battery.

[0032] (3) Due to the addition of a thin layer of silicon oxide and a conductive metal layer such as copper or nickel, the high doping concentration requirement for the doped polysilicon layer can be reduced, and the doping concentration of elements such as phosphorus can be appropriately reduced, thereby reducing the possibility of phosphorus diffusion into the silicon substrate to avoid the generation of Auger recombination centers, which helps to improve the photoelectric conversion efficiency of the battery.

[0033] (4) The high light reflection ability of the conductive metal layer can improve the battery's light reflection and reabsorption utilization rate, which can further improve the battery's photoelectric conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 1 in a method for preparing a Topcon battery in this embodiment.

[0035] Figure 2 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 2 in the preparation method of a Topcon battery in this embodiment.

[0036] Figure 3 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 4 in the preparation method of a Topcon battery in this embodiment.

[0037] Figure 4 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 5 in the preparation method of a Topcon battery in this embodiment.

[0038] Figure 5 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 7 in the preparation method of a Topcon battery in this embodiment.

[0039] Figure 6 This is a schematic diagram of the cross-sectional structure of a silicon substrate after being processed in step 8 in the preparation method of a Topcon battery in this embodiment.

[0040] Figure 7 Schematic diagram of the cross-sectional structure of a Topcon battery of this embodiment.

[0041] Explanation of the accompanying drawings: silicon substrate 1; p+ emitter 2; tunneling silicon oxide layer 3; doped polysilicon layer 4; aluminum oxide film 5; front silicon nitride film 6; thin layer of silicon oxide 7; conductive metal layer 8; back silicon nitride film 9; front metal electrode 10; back metal electrode 11. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] Example

[0044] A method for preparing a Topcon battery in this embodiment is shown in Figure 1-7 , comprising the following preparation steps:

[0045] Step 1. Perform double-sided texturing on the silicon substrate 1 to form pyramid texturing surfaces on both the front and back surfaces of the silicon substrate 1. The structure of the silicon substrate after step 1 is as follows: Figure 1 shown.

[0046] In step 1, it is preferred to use an alkaline solution for double-sided texturing treatment, and the alkaline solution includes but is not limited to a NaOH solution or a KOH solution.

[0047] Step 2. Perform a single-sided boron diffusion treatment on the silicon substrate 1 after the treatment in step 1 to prepare a p+ emitter 2 on the front side of the silicon substrate 1. The structure of the silicon substrate after the treatment in step 2 is as follows: Figure 2 shown.

[0048] In step 2, a single-sided boron diffusion process is performed in a diffusion furnace, and the doping source used to prepare the p+ emitter 2 includes but is not limited to BBr3 or BCl3.

[0049] In practice, during the single-sided boron diffusion process in step 2, a wrap-around layer is easily generated on the edge and local areas of the back side of the silicon substrate 1, and borosilicate glass (BSG) is also formed on the outer surface of the p+ emitter 2 and the wrap-around layer.

[0050] Step 3: Clean the silicon substrate 1 after the treatment in step 2 to etch and remove the edge and the back side coating layer and BSG of the silicon substrate 1.

[0051] In step 3, preferably, a mixed solution of HF and HNO 3 is used for the cleaning process.

[0052] Step 4. Polish the back side of the silicon substrate 1 after the treatment in step 3 to remove the pyramid velvet surface on the back side, thereby forming a flat morphology on the back side of the silicon substrate 1. The structure of the silicon substrate after the treatment in step 4 is as follows: Figure 3 shown.

[0053] In step 4, it is preferred to use an alkaline solution for polishing, and the alkaline solution is preferably a TMAH (tetramethylammonium hydroxide) solution.

[0054] Step 5. A tunneling silicon oxide layer 3 and a doped polysilicon layer 4 (such as a phosphorus-doped polysilicon layer) are sequentially deposited on the back of the silicon substrate 1 after being processed in step 4 to obtain a tunneling passivation contact structure on the back of the silicon substrate 1. The silicon substrate structure after processing in step 5 is as follows: Figure 4 shown.

[0055] In step 5, the deposition method of the tunneling silicon oxide layer 3 and the doped polysilicon layer 4 is preferably a PVD (physical vapor deposition) method or a PECVD (plasma enhanced chemical vapor deposition) method. The thickness of the tunneling silicon oxide layer 3 is preferably 2-3nm (such as 2nm, 2.5nm or 3nm), and the thickness of the doped polysilicon layer 4 is preferably 120-190nm (such as 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or 190nm).

[0056] In step 5 of this embodiment, the doping concentration of the doped polysilicon layer 4 is reduced to 1*10e 19 Therefore, by reducing the doping concentration of the doped polysilicon layer 4, the doping concentration of the doped polysilicon layer 4 can be reduced to avoid the generation of Auger recombination, which helps to improve the photoelectric conversion efficiency of the battery.

[0057] Step 6: Deposit a thin layer of silicon oxide 7 on the back surface of the doped polysilicon layer 4.

[0058] In step 6, the deposition method of the thin layer of silicon oxide 7 is preferably a PVD method or a PECVD method. Taking the deposition of the thin layer of silicon oxide 7 by the PVD method as an example, oxygen is introduced into the reaction chamber for oxidation, the oxygen flow rate is 200-600sccm (such as 350sccm), and the oxidation temperature is 200-300°C (such as 260°C), so as to deposit a thin layer of silicon oxide 7 with a thickness of 1-2nm (such as 1.5nm) on the back surface of the doped polysilicon layer 4.

[0059] Step 7. Deposit a conductive metal layer 8 on the back surface of the thin layer of silicon oxide 7. The structure of the silicon substrate after step 7 is as follows: Figure 5 shown.

[0060] In step 7, the deposition method of the conductive metal layer 8 is preferably a PVD method, the deposition power of the conductive metal layer 8 is 20-35KW (such as 25KW), and the deposition temperature is 200-300°C (such as 230°C), so as to deposit a conductive metal layer 8 with a thickness of 50-500nm (such as 200nm) on the back surface of the thin layer of silicon oxide 7. The conductive metal layer 8 is made of copper or nickel.

[0061] Compared with other deposition methods, the advantage of using PVD method for the conductive metal layer 8 is that the PVD method can deposit the conductive metal layer 8 under low temperature conditions, so it can ensure that the metal (copper or nickel) is not oxidized during the deposition process. Moreover, during the deposition process of the PVD method, the metal will not be plated around the front side of the silicon substrate 1; therefore, there is no need to add an additional process for removing the plating, which can simplify the process and reduce costs.

[0062] In step 7, if the thickness of the conductive metal layer 8 is less than 50nm, the probability of sunlight passing through the conductive metal layer 8 increases, which will reduce the light reflection ability of the conductive metal layer 8, resulting in the difficulty of sunlight passing through the front through the light reflection of the conductive metal layer 8 and being reflected back to the silicon substrate 1 again, and then being absorbed and utilized by the silicon substrate 1 again, which is not conducive to the improvement of light absorption and light utilization rate; moreover, if the thickness of the conductive metal layer 8 is too small, it will also reduce the conductivity of the conductive metal layer 8, which is not conducive to the improvement of the lateral and longitudinal transmission ability of electrons, and then increase the transmission loss of electrons; all of these are not conducive to the improvement of the photoelectric conversion efficiency of the battery. If the thickness of the conductive metal layer 8 is 500nm, the deposition time of the conductive metal layer 8 will be increased, causing the silicon substrate 1 to be easily bent and deformed, and the cost will also be increased.

[0063] The preparation method of the metal contact structure of a photovoltaic cell of this embodiment includes the above steps 5-7. Therefore, the metal contact structure of a photovoltaic cell of this embodiment includes the silicon substrate 1, the tunneling passivation contact structure, the thin silicon oxide 7 and the conductive metal layer 8 described above; the tunneling passivation contact structure includes the tunneling silicon oxide layer 3 and the doped polysilicon layer 4 sequentially arranged on the outer surface of the silicon substrate 1; the thin silicon oxide 7 is arranged on the outer surface of the doped polysilicon layer 4 for tunneling electrons; the conductive metal layer 8 is arranged on the outer surface of the thin silicon oxide 7.

[0064] Step 8. Deposit a front passivation anti-reflection layer and a back anti-reflection layer on the front and back of the silicon substrate 1 after being processed in step 7. The structure of the silicon substrate after being processed in step 8 is as follows: Figure 6 shown.

[0065] In step 8, the front passivation anti-reflection layer includes an aluminum oxide film 5 and a front silicon nitride film 6 deposited sequentially on the front of the p+ emitter 2. The back anti-reflection layer is a back silicon nitride film 9 deposited on the back of the conductive metal layer 8. Among them, the deposition method of the aluminum oxide film 5 is preferably ALD (atomic layer deposition). The deposition method of the front silicon nitride film 6 and the back silicon nitride film 9 is preferably PECVD.

[0066] Step 9. Prepare a front metal electrode 10 and a back metal electrode 11 on the front and back of the silicon substrate 1 after the treatment in step 8, respectively, to obtain the Topcon battery of this embodiment. The structure of the Topcon battery is as follows: Figure 7 shown.

[0067] In step 9, the preparation process of the front metal electrode 10 and the back metal electrode 11 is as follows: first, the front metal paste and the back metal paste are screen-printed on the front side of the front passivation anti-reflection layer and the back side of the back anti-reflection layer, respectively, and then metallization sintering is performed to obtain the front metal electrode 10 and the back metal electrode 11. Among them, the front metal electrode 10 is in ohmic contact with the p+ emitter 2, and the back metal electrode 11 is in ohmic contact with the conductive metal layer 8.

[0068] A Topcon battery of the present embodiment is prepared by the preparation method of a Topcon battery of the present embodiment. The Topcon battery of the present embodiment comprises: a silicon substrate 1; a p+ emitter 2, a front passivation anti-reflection layer and a front metal electrode 10 are sequentially arranged on the front side of the silicon substrate 1, and one end of the front metal electrode 10 is in ohmic contact with the p+ emitter 2, and the other end of the front metal electrode 10 extends to the top of the front passivation anti-reflection layer; a tunneling silicon oxide layer 3, a doped polysilicon layer 4, a thin silicon oxide layer 7, a conductive metal layer 8, a back anti-reflection layer and a back metal electrode 11 are sequentially arranged on the back side of the silicon substrate 1, and one end of the back metal electrode 11 is in ohmic contact with the conductive metal layer 8, and the other end of the back metal electrode 11 extends to the bottom of the back metal electrode 11.

[0069] It should be noted that the existing step-by-step doping passivation method (i.e., sequentially arranging a first tunneling oxide layer, a first n+ polysilicon doping layer, a second tunneling oxide layer, and a second n+ polysilicon doping layer on the back of a silicon wafer) as shown in publication number CN216980577U has at least the following defects: (1) The conductivity of the polysilicon doping layer is far inferior to that of the conductive metal layer 8 of copper or nickel. (2) Moreover, the semiconductor-metal contact performance of the polysilicon doping layer and the back metal electrode is also inferior to the metal-metal contact performance of the conductive metal layer 8 (such as copper or nickel) and the back metal electrode 11. (3) The second n+ polysilicon doping layer will also increase the total thickness of the back polysilicon layer, which is prone to parasitic light absorption loss; while the present embodiment sequentially deposits a thin layer of silicon oxide 7 and a conductive metal layer 8 such as copper or nickel on the back of the tunneling passivation contact structure, which can effectively avoid parasitic light absorption loss.

[0070] Therefore, compared with the existing stepwise doping passivation method as shown in publication number CN216980577U, the present embodiment sequentially deposits a thin layer of silicon oxide 7 and a conductive metal layer 8 such as copper or nickel on the back side of the tunnel passivation contact structure (including a tunneling silicon oxide layer 3 and a doped polysilicon layer 4 sequentially deposited on the back side of the silicon substrate 1), which has the following advantages:

[0071] (1) The thin silicon oxide layer 7 and the conductive metal layer 8 can both prevent metal diffusion. Therefore, after metallization sintering, the back metal paste will not burn through the conductive metal layer 8. In addition, due to the barrier effect of the thin silicon oxide layer 7 and the conductive metal layer 8, the back metal paste will not directly contact the doped polysilicon layer 4. Therefore, the generation of recombination centers can be effectively avoided, which helps to improve the open circuit voltage and photoelectric conversion efficiency.

[0072] (2) The thin layer of silicon oxide 7 also has the function of tunneling electrons. The lateral and longitudinal electron transmission capabilities of the conductive metal layer 8 are much higher than those of the doped polysilicon layer 4. The lateral and longitudinal electron transmission capabilities of the conductive metal layer 8 are extremely strong, and it has high conductivity. Moreover, the contact resistance of the conductive metal layer 8 is low, and it has excellent contact performance. The contact resistance of the metal-metal contact between the conductive metal layer 8 (such as copper or nickel) and the back metal electrode 11 is extremely low. Therefore, the doped polysilicon layer 4 transmits electrons to the conductive metal layer 8 through the thin layer of silicon oxide 7, and then through the metal-metal contact, the transmission loss of electrons can be reduced, and the contact resistance can be reduced, the loss of electrical performance can be reduced, and the electrical performance of the battery can be optimized.

[0073] (3) Since a thin layer of silicon oxide 7 and a conductive metal layer 8 such as copper or nickel are added, the high doping concentration requirement for the doped polysilicon layer 4 can be reduced, and the doping concentration of elements such as phosphorus can be appropriately reduced, thereby reducing the possibility of phosphorus diffusion into the silicon substrate 1, thereby avoiding the generation of Auger recombination centers, which helps to improve the photoelectric conversion efficiency of the battery.

[0074] (4) The high light reflection capability of the conductive metal layer 8 can improve the reflection and reabsorption of light by the battery, thereby improving the light utilization rate and further improving the photoelectric conversion efficiency of the battery.

[0075] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0076] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a metal contact structure of a photovoltaic cell, characterized in that: The method comprises the following preparation steps: S1. Preparing a tunneling passivation contact structure on the outer surface of a silicon substrate; wherein the tunneling passivation contact structure comprises a tunneling silicon oxide layer and a doped polysilicon layer sequentially prepared on the outer surface of the silicon substrate; S2, preparing a thin layer of silicon oxide having a tunneling electron function on the outer surface of the doped polysilicon layer; S3. Prepare a conductive metal layer on the outer surface of the thin layer of silicon oxide.

2. The method for preparing a metal contact structure of a photovoltaic cell according to claim 1, characterized in that: In step S1, the tunnel passivation contact structure is prepared by physical vapor deposition or plasma enhanced chemical vapor deposition.

3. The method for preparing a metal contact structure of a photovoltaic cell according to claim 1 or 2, characterized in that: In step S1, the thickness of the tunneling silicon oxide layer is 2-3 nm, and the thickness of the doped polysilicon layer is 120-190 nm; The doping concentration of the doped polysilicon layer is less than or equal to 1*10e 19 .

4. The method for preparing a metal contact structure of a photovoltaic cell according to claim 1, characterized in that: In step S2, the thin layer of silicon oxide is prepared by physical vapor deposition or plasma enhanced chemical vapor deposition.

5. The method for preparing a metal contact structure of a photovoltaic cell according to claim 4, characterized in that: The thin layer of silicon oxide is prepared by physical vapor deposition; Oxygen is introduced into the reaction chamber for oxidation, the oxygen flow rate is 200-600 sccm, and the oxidation temperature is 200-300° C., so as to obtain the thin layer of silicon oxide with a thickness of 1-2 nm on the outer surface of the doped polysilicon layer.

6. The method for preparing a metal contact structure of a photovoltaic cell according to claim 1, characterized in that: In step S3, the conductive metal layer is prepared by physical vapor deposition.

7. The method for preparing a metal contact structure of a photovoltaic cell according to claim 6, characterized in that: The deposition power of the conductive metal layer is 20-35KW, and the deposition temperature is 200-300°C, so as to deposit the conductive metal layer with a thickness of 50-500nm on the outer surface of the thin layer of silicon oxide; The conductive metal layer is made of copper or nickel.

8. A metal contact structure of a photovoltaic cell, characterized in that: It is prepared by the method for preparing a metal contact structure of a photovoltaic cell as described in any one of claims 1 to 7; the metal contact structure comprises a tunneling passivation contact structure, a thin layer of silicon oxide and a conductive metal layer which are sequentially arranged on the surface of a silicon substrate.

9. A method for preparing a photovoltaic cell, characterized in that: The method comprises the following preparation steps: Step 1, performing double-sided texturing treatment on the silicon substrate; Step 2: preparing an emitter on the front side of the silicon substrate; Step 3, cleaning the silicon substrate after the treatment in step 2, and then polishing the back side of the silicon substrate; Step 4: using the method for preparing a metal contact structure of a photovoltaic cell according to any one of claims 1 to 7, preparing the metal contact structure on the back of the silicon substrate treated in step 3; the metal contact structure comprises a tunnel passivation contact structure, a thin layer of silicon oxide and a conductive metal layer sequentially arranged on the back of the silicon substrate; Step 5: prepare a front passivation anti-reflection layer on the front side of the emitter, and prepare a back anti-reflection layer on the back side of the conductive metal layer; Step 6: Prepare a front metal electrode and a back metal electrode on the front and back sides of the silicon substrate processed in step 5, respectively, so that the front metal electrode makes ohmic contact with the emitter, and the back metal electrode makes ohmic contact with the conductive metal layer.

10. A photovoltaic cell, characterized in that: It is prepared by the method for preparing a photovoltaic cell as described in claim 9.

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