A topcon cell and a preparation method thereof

Abstract

The application relates to the field of solar cell manufacturing, and particularly discloses a TOPCon cell and a preparation method thereof. A front surface oxidation layer is obtained by front surface oxidation of a silicon substrate; a back surface oxidation layer and a polysilicon layer are sequentially arranged on the back surface of the silicon substrate; a SE area of the front surface oxidation layer is laser grooved to obtain a diffusion precursor, grooves on the front surface of the diffusion precursor penetrate the front surface oxidation layer; boron diffusion is performed on the front surface of the diffusion precursor to obtain a cell precursor; after back surface phosphorus diffusion, surface passivation and electrode arrangement are performed on the cell precursor, the TOPCon cell is obtained. The TOPCon cell is produced by only one diffusion, so that the process flow is simplified, the service life of a reaction furnace is greatly prolonged, the demand for boron diffusion reagents in the production process is reduced, and the production cost is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar cell manufacturing, in particular to a TOPCon cell and a preparation method thereof. BACKGROUND

[0002] With the continuous upgrading of photovoltaic cells, new efficiency improvement technologies are constantly emerging in the market, and TOPCon (Tunnel Oxide Passivated Contacts) technology is one of them.

[0003] The existing TOPCon cell adopts a secondary diffusion method to realize the difference in sheet resistance between the emitter region and the non-emitter region, that is, first uniformly diffusing dopants on the surface of the cell, then slotting the emitter region, and then diffusing the dopants again on the surface after slotting. This is equivalent to diffusing the dopants once in the emitter region and twice in the non-emitter region, so as to achieve the effect that the sheet resistance of the emitter region is greater than that of the non-emitter region.

[0004] However, it should be noted that during the diffusion of dopants, high temperatures are often accompanied by the generation of many by-products on the reaction furnace, resulting in uncontrollable stress on the furnace wall. Under the action of stress and high temperature, the service life of the reaction furnace is greatly shortened, the production cost is greatly increased, and at the same time, the production process is greatly complicated by the need for two diffusion processes.

[0005] Therefore, how to find a TOPCon cell and a preparation method thereof that takes into account low cost and simple process has become a problem to be solved in the prior art. SUMMARY

[0006] The purpose of the present application is to provide a TOPCon cell and a preparation method thereof to solve the problem of complex production process and high production cost of the TOPCon cell in the prior art.

[0007] To solve the above technical problems, the present application provides a preparation method of a TOPCon cell, comprising:

[0008] Oxidizing the front surface of the silicon substrate to obtain a front surface oxidation layer;

[0009] A back surface oxidation layer and a polysilicon layer are sequentially arranged on the back surface of the silicon substrate;

[0010] Laser slotting is performed on the SE region of the front surface oxidation layer to obtain a diffusion precursor, and the recess on the front surface of the diffusion precursor penetrates the front surface oxidation layer;

[0011] Boron diffusion is performed on the front surface of the diffusion precursor to obtain a cell precursor;

[0012] After performing backside phosphorus diffusion, surface passivation, and electrode placement on the battery preform, the TOPCon battery is obtained.

[0013] Optionally, in the method for preparing the TOPCon battery, before performing backside phosphorus diffusion on the battery preform, the method further includes:

[0014] The battery preform is acid-washed.

[0015] Optionally, in the method for fabricating the TOPCon cell, the step of sequentially depositing a back oxide layer and a polycrystalline silicon layer on the back side of the silicon substrate includes:

[0016] Two silicon substrates with the front oxide layer are bonded together and placed in a basket, and then oxidized and polysilicon is applied in sequence to obtain the back oxide layer and polysilicon layer of the two silicon substrates respectively.

[0017] Optionally, in the method for preparing the TOPCon battery, after obtaining the front oxide layer, the method further includes:

[0018] The back side of the silicon substrate is acid-washed to remove oxide impurities.

[0019] Optionally, in the method for fabricating the TOPCon battery, after acid washing the back side of the silicon substrate, the method further includes:

[0020] The back side of the acid-washed silicon substrate is then subjected to alkaline polishing.

[0021] Optionally, in the method for fabricating the TOPCon battery, the depth of the groove ranges from 0.01 micrometers to 1.00 micrometers, including the endpoint value.

[0022] Optionally, in the method for preparing the TOPCon battery, the sheet resistance of the SE region of the battery preform ranges from 60 Ω / sq to 150 Ω / sq, including the endpoint values.

[0023] Optionally, in the method for preparing the TOPCon battery, the diffusion temperature for boron diffusion on the front side of the diffusion preform ranges from 900 degrees Celsius to 1050 degrees Celsius, including the endpoint values.

[0024] Optionally, in the method for preparing the TOPCon battery, the diffusion time of the boron diffusion ranges from 120 minutes to 240 minutes, including the endpoint value.

[0025] A TOPCon battery, wherein the TOPCon battery is a solar cell obtained by any of the above-described methods for preparing a TOPCon battery.

[0026] The method for fabricating a TOPCon battery provided by this invention involves oxidizing the front side of a silicon substrate to obtain a front oxide layer; sequentially depositing a back oxide layer and a polycrystalline silicon layer on the back side of the silicon substrate; laser-grooving the SE region of the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer; performing boron diffusion on the front side of the diffusion preform to obtain a battery preform; and performing back phosphorus diffusion, surface passivation, and electrode placement on the battery preform to obtain the TOPCon battery.

[0027] This invention first forms an oxide layer on the front side of a silicon substrate, then removes the oxide layer in the SE (sediment-exposed) region by trenching, exposing the underlying silicon substrate. This requires only one boron diffusion step. Due to the obstruction of the front oxide layer in the non-SE regions, the diffusion rate in the non-SE regions is significantly slower than in the SE regions, thus creating a sheet resistance difference between the SE and non-SE regions. The fact that TOPCon cell production requires only one diffusion step not only simplifies the process but also greatly extends the reactor's lifespan and reduces the demand for boron diffusion reagents during production, thereby significantly lowering production costs. This invention also provides a TOPCon cell with the aforementioned beneficial effects. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic flowchart illustrating a specific embodiment of the TOPCon battery fabrication method provided by the present invention;

[0030] Figure 2 A schematic flowchart illustrating another specific embodiment of the TOPCon battery preparation method provided by the present invention;

[0031] Figure 3 This is a flowchart illustrating another specific embodiment of the TOPCon battery preparation method provided by the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The core of this invention is to provide a method for preparing a TOPCon battery, and a flowchart of one specific embodiment is shown below. Figure 1 As shown, this is referred to as Specific Implementation Method One, which includes:

[0034] S101: The front side of the silicon substrate is oxidized to obtain the front oxide layer.

[0035] After obtaining the aforementioned front oxide layer, the process further includes:

[0036] The back side of the silicon substrate is acid-washed to remove oxide impurities.

[0037] During the front-side oxidation process, other areas of the silicon substrate also undergo oxidation to varying degrees. Therefore, acid etching is added after the front-side oxidation process to remove oxides from other locations, which can significantly improve the epitaxial quality of subsequent epitaxial layers. Furthermore, hydrofluoric acid is used to etch the back-side.

[0038] Before front-side oxidation, the front side of the silicon substrate can be further texturized.

[0039] The specific process of the front oxidation is as follows: the silicon substrate is loaded into the diffusion furnace, heated to 765℃~785℃ and maintained at 765℃~785℃, and nitrogen gas with a flow rate of 700sccm~900sccm and oxygen gas with a flow rate of 1000sccm~1200sccm are introduced into the diffusion furnace for pre-oxidation for 250s~400s.

[0040] Furthermore, after acid washing the back side of the silicon substrate, the process further includes:

[0041] The back side of the acid-washed silicon substrate is then subjected to alkaline polishing. Similar to the acid washing process, alkaline polishing results in a smoother and flatter back side of the silicon substrate, reducing stress concentration defects and significantly improving the quality of subsequent epitaxial layers. It also reduces carrier recombination centers, thereby enhancing photoelectric conversion efficiency.

[0042] S102: A back oxide layer and a polycrystalline silicon layer are sequentially disposed on the back side of the silicon substrate.

[0043] In this step, the back side of the silicon substrate is oxidized to obtain the back oxide layer, and polycrystalline silicon is deposited on the surface of the back oxide layer to obtain the polycrystalline silicon layer. The process temperature range is 300℃ to 700℃, the reaction time is 120min-210min, and the process is completed under low pressure.

[0044] S103: Laser grooving is performed on the SE area of ​​the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer.

[0045] Specifically, the depth of the groove ranges from 0.01 micrometers to 1.00 micrometers, including endpoint values ​​such as 0.010 micrometers, 0.562 micrometers, or 1.000 micrometers. Within the aforementioned groove depth range, the sheet resistance difference between the formed SE region and the non-SE region is most suitable, which best improves the photoelectric conversion efficiency of the battery, while also improving the contact resistance and pull force between the metal electrode and silicon, further enhancing efficiency.

[0046] The laser used for laser grooving has a wavelength range of 532nm or 266nm, a laser energy of ≥25MJ, a pulse frequency range of 5Hz to 20Hz, and a pulse width of ≤100ps.

[0047] S104: Boron diffusion is performed on the front side of the diffusion preform to obtain a battery preform.

[0048] Corresponding to the depth range of the aforementioned groove, the sheet resistance of the SE region of the battery preform after the boron diffusion ranges from 60 Ω / sq to 150 Ω / sq, including endpoint values ​​such as any one of 60.0 Ω / sq, 95.3 Ω / sq, or 150.0 Ω / sq.

[0049] S105: After performing backside phosphorus diffusion, surface passivation, and electrode placement on the battery preform, the TOPCon battery is obtained.

[0050] In one specific implementation, the diffusion temperature for boron diffusion on the front side of the diffusion pretreatment material ranges from 900 degrees Celsius to 1050 degrees Celsius, including endpoint values ​​such as any one of 900.0 degrees Celsius, 952.3 degrees Celsius, or 1050.0 degrees Celsius. Correspondingly, the diffusion time for boron diffusion ranges from 120 minutes to 240 minutes, including endpoint values ​​such as another one of 120.0 minutes, 201.3 minutes, or 240.0 minutes.

[0051] The TOPCon battery fabrication method provided by this invention involves oxidizing the front side of a silicon substrate to obtain a front oxide layer; sequentially depositing a back oxide layer and a polycrystalline silicon layer on the back side of the silicon substrate; laser-grooving the SE region of the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer; performing boron diffusion on the front side of the diffusion preform to obtain a battery preform; and performing back phosphorus diffusion, surface passivation, and electrode placement on the battery preform to obtain the TOPCon battery. This invention first deposits an oxide layer on the front side of the silicon substrate, then removes the oxide layer in the SE region by grooving to expose the underlying silicon substrate. This requires only one boron diffusion step. Due to the obstruction of the front oxide layer in the non-SE region, the diffusion rate in the non-SE region is significantly slower than in the SE region, thus creating a sheet resistance difference between the SE and non-SE regions. The fact that only one diffusion step is needed to produce TOPCon batteries not only simplifies the process but also greatly extends the lifespan of the reactor and reduces the demand for boron diffusion reagents during production, thereby significantly reducing production costs.

[0052] Based on Specific Implementation Method 1, the battery preform is further processed to obtain Specific Implementation Method 2, the flowchart of which is shown below. Figure 2 As shown, it includes:

[0053] S201: The front side of the silicon substrate is oxidized to obtain the front oxide layer.

[0054] S202: A back oxide layer and a polycrystalline silicon layer are sequentially disposed on the back side of the silicon substrate.

[0055] S203: Laser grooving is performed on the SE region of the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer.

[0056] S204: Boron diffusion is performed on the front side of the diffusion preform to obtain a battery preform.

[0057] S205: Acid washing is performed on the battery preform.

[0058] Specifically, pickling is performed using hydrofluoric acid, the concentration of which ranges from 30% to 70%.

[0059] S206: After performing backside phosphorus diffusion, surface passivation, and electrode placement on the battery preform, the TOPCon battery is obtained.

[0060] The difference between this specific embodiment and the above specific embodiment is that, after obtaining the battery preform, this specific embodiment further performs acid washing on the battery preform. The remaining steps are the same as those in the above specific embodiment, and will not be described in detail here.

[0061] In this specific embodiment, the battery preform that has undergone boron diffusion is acid-washed (specifically, HF acid can be used). The acid-washing process will remove some boron from the non-SE region, which is equivalent to further reducing the diffusion concentration in the non-SE region and increasing the sheet resistance in the non-SE region. However, the diffusion concentration in the SE region will hardly change after acid washing. This means that the difference between the sheet resistance of the SE region and the sheet resistance of the non-SE region of the silicon wafer after acid washing is further increased, thereby improving the battery efficiency.

[0062] Based on Specific Embodiment Two, the method for preparing the epitaxial layer on the back side of the silicon substrate is further specified to obtain Specific Embodiment Three, the flowchart of which is shown below. Figure 3 As shown, it includes:

[0063] S301: The front side of the silicon substrate is oxidized to obtain the front oxide layer.

[0064] S302: The two silicon substrates with the front oxide layer are bonded together and placed in a basket, and oxidation and polysilicon deposition are performed in sequence to obtain the back oxide layer and polysilicon layer of the two silicon substrates respectively.

[0065] S303: Laser grooving is performed on the SE area of ​​the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer.

[0066] S304: Boron diffusion is performed on the front side of the diffusion preform to obtain a battery preform.

[0067] S305: Acid washing is performed on the battery preform.

[0068] S306: After performing backside phosphorus diffusion, surface passivation, and electrode placement on the battery preform, the TOPCon battery is obtained.

[0069] The difference between this specific embodiment and the above specific embodiment is that this specific embodiment limits the arrangement of the oxide layer and the polysilicon layer on the back of the silicon substrate. The remaining steps are the same as those in the above specific embodiment, and will not be described in detail here.

[0070] After obtaining the front oxide layer, a back oxide layer and a polycrystalline silicon layer need to be formed on the back surface of the silicon substrate. In this specific embodiment, the front oxide layers of the two silicon substrates are bonded together, and the two bonded silicon substrates are loaded onto a boat together. After loading, only the side and back of the silicon substrate are exposed on the outside. Under these circumstances, the formation of the back oxide layer and the polycrystalline silicon layer can avoid contamination of the front side of the silicon substrate and improve the quality of the epitaxial layer. At the same time, since the epitaxial layer is formed on two wafers at the same time, the production efficiency of the solar cell is also improved.

[0071] This invention also provides a TOPCon battery, which is a solar cell obtained by any of the above-described methods for fabricating TOPCon batteries. The method for fabricating a TOPCon battery provided by this invention involves: oxidizing the front side of a silicon substrate to obtain a front oxide layer; sequentially depositing a back oxide layer and a polycrystalline silicon layer on the back side of the silicon substrate; laser-grooving the SE region of the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer; performing boron diffusion on the front side of the diffusion preform to obtain a battery preform; and performing back phosphorus diffusion, surface passivation, and electrode placement on the battery preform to obtain the TOPCon battery. This invention first sets an oxide layer on the front side of the silicon substrate, and then removes the oxide layer in the SE region by grooving to expose the underlying silicon substrate. This requires only one boron diffusion. Due to the obstruction of the front oxide layer in the non-SE region, the diffusion rate in the non-SE region is significantly slower than that in the SE region, thus forming a sheet resistance difference between the SE and non-SE regions. The production of TOPCon cells only requires one diffusion, which not only simplifies the process but also greatly extends the service life of the reactor. At the same time, it reduces the demand for boron diffusion reagents during the production process, thereby greatly reducing production costs.

[0072] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0073] It should be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0074] The TOPCon battery and its preparation method provided by this invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for preparing a TOPCon battery, characterized in that, include: The front side of the silicon substrate is oxidized to obtain the front oxide layer; A back oxide layer and a polycrystalline silicon layer are sequentially disposed on the back side of the silicon substrate; Laser grooving is performed on the SE region of the front oxide layer to obtain a diffusion preform, wherein the groove on the front side of the diffusion preform penetrates the front oxide layer; The front oxide layer of the SE region is removed by the groove to expose the silicon substrate; Boron diffusion is performed on the front side of the diffusion preform to obtain a battery preform. After performing backside phosphorus diffusion, surface passivation, and electrode placement on the battery preform, the TOPCon battery is obtained. The depth of the groove ranges from 0.01 micrometers to 1.00 micrometers, including the endpoint values; The laser used for laser grooving has a wavelength range of 532nm or 266nm, a laser energy of ≥25MJ, a pulse frequency range of 5Hz to 20Hz, and a pulse width of ≤100ps. Prior to backside phosphorus diffusion on the battery preform, the process further includes: The battery preform was acid-washed with HF acid to reduce the boron diffusion concentration in the non-SE region.

2. The method for preparing a TOPCon battery as described in claim 1, characterized in that, The step of sequentially depositing a back oxide layer and a polycrystalline silicon layer on the back side of the silicon substrate includes: Two silicon substrates with the front oxide layer are bonded together and placed in a basket, and then oxidized and polysilicon is applied in sequence to obtain the back oxide layer and polysilicon layer of the two silicon substrates respectively.

3. The method for preparing a TOPCon battery as described in claim 1, characterized in that, After obtaining the aforementioned front oxide layer, the process further includes: The back side of the silicon substrate is acid-washed to remove oxide impurities.

4. The method for preparing a TOPCon battery as described in claim 1, characterized in that, After acid washing the back side of the silicon substrate, the process further includes: The back side of the acid-washed silicon substrate is then subjected to alkaline polishing.

5. The method for preparing a TOPCon battery according to any one of claims 1 to 4, characterized in that, The sheet resistance of the SE region of the battery preform ranges from 60 Ω / sq to 150 Ω / sq, including the endpoint values.

6. The method for preparing a TOPCon battery as described in claim 5, characterized in that, The diffusion temperature range for boron diffusion on the front side of the diffusion preform is 900 degrees Celsius to 1050 degrees Celsius, including the endpoint values.

7. The method for preparing a TOPCon battery as described in claim 6, characterized in that, The diffusion time for the boron diffusion ranges from 120 minutes to 240 minutes, including the endpoint values.

8. A TOPCon battery, characterized in that, The TOPCon cell is a solar cell obtained by the preparation method of the TOPCon cell according to any one of claims 1 to 7.

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