TOPCon photovoltaic cell structure and preparation method thereof

Abstract

The invention relates to the technical field of TOPCon solar cells, in particular to a TOPCon photovoltaic cell structure and a preparation method thereof, and the method comprises the steps: preparing a local patterning mask on a tunneling oxide layer through nanometer imprinting; and etching by using a high-selectivity etching agent and depositing a passivation layer, forming a local passivation structure on the polycrystalline silicon substrate, removing a mask material, depositing a polycrystalline silicon emitter layer and preparing an electrode, and forming a TOPCon photovoltaic cell structure. According to the invention, the local patterning mask is prepared on the tunneling oxide layer by using the nano imprinting technology, the high-selectivity etching solution is combined to form the local patterning structure, and finally the passivation layer material is deposited in the etched area to form the local patterning passivation layer, so that the contact interface is optimized, the recombination current between the front electrode and the silicon substrate is reduced, and the performance of the device is improved. Therefore, the open-circuit voltage and the filling factor of the cell are improved, and the photoelectric conversion efficiency is improved.

Description

Technical Field

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

[0002] TOPCon (tunneling oxide passivated contact) solar cells are currently the most advanced N-type silicon-based solar cell technology. Its structural design aims to improve the photoelectric conversion efficiency of the cell by optimizing the contact interface and improving the passivation effect. Its structure usually includes a silicon substrate, a tunneling oxide layer, a doped polysilicon layer, a metallization layer, etc. TOPCon photovoltaic cells use the combination of a tunneling oxide layer and a polysilicon layer to provide an excellent passivation effect and effectively reduce the recombination rate on the silicon surface; at the same time, the passivation contact structure formed by the heavily doped polysilicon layer and the tunneling oxide layer reduces contact recombination and improves the open circuit voltage and fill factor of the cell.

[0003] In the prior art, since the contact interface between the front electrode and the silicon substrate fails to achieve the ideal passivation effect, there is often a large recombination current in the front electrode contact area of ​​the TOPCon cell, which not only increases the recombination rate of carriers, but also limits the improvement of the open circuit voltage and fill factor of the cell, thereby restricting the breakthrough of the TOPCon cell efficiency; in addition, the method of preparing the front fully passivated contact structure in the prior art is often complicated and costly, such as the method of depositing a polysilicon layer on the entire surface and then selectively etching, which not only causes waste of polysilicon materials, but also may introduce new defect sources due to the imperfection of the etching process, further exacerbating the problem of recombination current. Therefore, the present invention provides a TOPCon photovoltaic cell structure and a preparation method thereof to solve the above problems. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a TOPCon photovoltaic cell structure and a preparation method thereof.

[0005] A method for preparing a TOPCon photovoltaic cell structure comprises the following steps:

[0006] (1) Tunneling oxide layer deposition: depositing a tunneling oxide layer on a pretreated polysilicon substrate;

[0007] (2) Preparation of a local patterned mask: A local patterned mask is prepared by using nanoimprinting technology. The mask is covered on the tunneling oxide layer. A nanoimprinting mold is used to imprint the local patterned mask on the surface of polysilicon, and the mask is reinforced by heat treatment and curing.

[0008] (3) Highly selective etching: Use a highly selective etchant to remove the tunnel oxide layer and part of the polysilicon substrate not covered by the mask to form a local patterned structure;

[0009] (4) Deposition of a passivation layer: depositing a passivation layer material in the etched area to form a local patterned passivation layer, wherein the passivation layer includes Al2O3 or SiNx;

[0010] (5) Mask removal: removing the mask material to expose the complete patterned passivation layer structure;

[0011] (6) Preparation of polysilicon emitter layer: depositing a polysilicon emitter layer on the tunneling oxide layer not covered by the patterned passivation layer;

[0012] (7) Electrode preparation and packaging: Prepare positive and negative metal electrodes and connect them to the polysilicon emitter layer and the polysilicon substrate, respectively, to form a local patterned passivation contact structure, namely the TOPCon photovoltaic cell structure, and then perform subsequent packaging processing.

[0013] As a preferred embodiment of the present invention, in the process of preparing the local patterned mask, a quartz or nickel-based nanoimprint mold is selected, the imprint pressure is set to 5-10 MPa, the imprinting is performed at room temperature, and the imprinting time is set to 1-5 min.

[0014] As a preferred embodiment of the present invention, during the preparation process of the locally patterned mask, the heat treatment curing temperature is set to 150-200°C to ensure that the mask material is fully cured, the heating time is 30 minutes to 1 hour, the heat treatment is carried out under nitrogen or inert gas protection, and finally the organic solvent is used for cleaning, and the organic solvent is acetone or isopropanol.

[0015] As a preferred embodiment of the present invention, in the highly selective etching step, the highly selective etchant is a mixture of acetic acid and hydrofluoric acid, the mixing volume ratio is 1-3:1, and the etching time is between 30s-2min.

[0016] As a preferred embodiment of the present invention, the high-selectivity etching step also includes plasma-assisted etching, selecting an inductively coupled plasma source, a plasma power range of 200-500W, a flow volume ratio of etching gases CF4 and O2 of 10-20:1, a total flow rate of 50-100sccm, and an etching chamber pressure between 10-100Pa.

[0017] As a preferred embodiment of the present invention, during the deposition of the passivation layer, PECVD technology is used, and the deposition rate range is 0.5-1.5 nm / s.

[0018] As a preferred embodiment of the present invention, in the passivation layer deposition step, the pattern shape of the locally patterned passivation layer includes one or more combinations of circular, square or honeycomb, the circular pattern diameter ranges from 1-3 μm, the square pattern side length ranges from 1-2 μm, and the spacing between patterns is between 0.5-1 μm.

[0019] As a preferred embodiment of the present invention, in the tunnel oxide layer deposition step, the tunnel oxide layer is deposited using PECVD technology.

[0020] As a preferred embodiment of the present invention, in the tunnel oxide layer deposition, the pretreatment includes cleaning the surface of the polysilicon substrate using a standard RCA cleaning process, and forming a micro-nano structure on the substrate surface by wet or dry etching technology.

[0021] A TOPCon photovoltaic cell structure is prepared by the preparation method of the TOPCon photovoltaic cell structure.

[0022] The beneficial effects achieved by the present invention are as follows: 1. The present invention prepares a front local polysilicon passivation contact structure by a method of combining a local mask with selective etching, prepares a local patterned mask on the tunneling oxide layer using nano-imprinting technology, and uses a highly selective etching solution to remove the tunneling oxide layer and part of the polysilicon substrate not covered by the mask to form a local patterned structure, and finally deposits a passivation layer material in the etched area to form a local patterned passivation layer, thereby optimizing the contact interface, reducing the recombination current between the front electrode and the silicon substrate, and reducing the recombination rate of carriers, thereby improving the open circuit voltage and fill factor of the battery and improving the photoelectric conversion efficiency.

[0023] 2. The present invention provides excellent passivation effect by locally patterning the passivation layer, and also reduces contact recombination by reducing the contact area, thereby further enhancing the performance of the battery, so that the combination of the tunnel oxide layer and the polysilicon layer can fully exert its passivation advantage.

[0024] 3. Compared with the traditional method of depositing a polysilicon layer on the entire surface and then selectively etching, the present invention is simpler and more efficient. The preparation and removal process of the local patterned mask simplifies the process flow, reduces the waste of polysilicon materials, and reduces the risk of introducing new defects due to imperfect etching process, thereby reducing production costs.

[0025] 4. The present invention adopts nano-imprinting technology to prepare local patterned masks, combined with high-precision, high-hardness nano-imprinting molds, so that the patterning process has a high degree of controllability and repeatability, which helps to ensure that each battery has consistent performance and improve the product yield and reliability.

[0026] 5. Through sophisticated preparation technology and optimized structural design, the TOPCon photovoltaic cell prepared in the present invention exhibits higher stability under changes in environmental factors such as light and temperature. The local patterned passivation layer can effectively resist external corrosion, extend the service life of the battery, and provide strong guarantee for the long-term stable operation of the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1The figure is a schematic diagram of the process of preparing the TOPCon photovoltaic cell structure adopted in the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with specific embodiments.

[0029] Some steps in the following embodiments are supplemented:

[0030] 1. Pretreatment of polysilicon substrate

[0031] The RCA cleaning process includes SC-1 cleaning, SC-2 cleaning, and hydrofluoric acid treatment;

[0032] The wet etching to form the micro-nano structure uses 3% potassium hydroxide solution to etch the silicon substrate, and the dry etching uses inductively coupled plasma-reactive ion etching.

[0033] 2. Local patterned mask

[0034] The mask material includes SU-8 photoresist, polymethyl methacrylate PMMA, silicon dioxide SiO2, silicon nitride Si3N4, etc., and the embodiment uses SU-8 photoresist;

[0035] The imprinting mold was cleaned with deionized water and isopropyl alcohol (IPA) in sequence and dried with nitrogen gas.

[0036] In the mask patterning process, after the mask material is coated on the substrate surface, the mold is aligned and contacted with the substrate, and nanoimprinting is performed under pressure to transfer the mold pattern to the mask material.

[0037] 3. Highly selective etching

[0038] During the etching process, the etching tank is placed in a temperature control system, the etching temperature is set according to the etchant and material system, the substrate covered with a local patterned mask is placed in the etching tank, and the etching liquid is started to be stirred. After the etching is completed, it is quickly taken out, soaked in deionized water for cleaning, and finally gently blown dry with nitrogen.

[0039] Example 1: A method for preparing a TOPCon photovoltaic cell structure, such as Figure 1 As shown, the following steps are included:

[0040] (1) Tunnel oxide layer deposition: using PECVD technology to deposit a tunnel oxide layer on the pretreated polysilicon substrate with a thickness controlled at 18 nm;

[0041] The pretreatment includes cleaning the surface of the polysilicon substrate using a standard RCA cleaning process and forming a micro-nano structure on the substrate surface using a wet etching technique;

[0042] (2) Preparation of local patterned mask: A local patterned mask was prepared by nanoimprinting technology and covered on the tunneling oxide layer. A high-precision quartz nanoimprinting mold was selected, the imprinting pressure was set to 7 MPa, and the imprinting was performed at room temperature for 3 min.

[0043] Curing at 180°C for 45 minutes through heat treatment, nitrogen protection, to ensure that the mask material is fully cured, and acetone is used for cleaning to remove mold release agent and other residues;

[0044] (3) Highly selective etching: using a mixture of acetic acid and hydrofluoric acid in a volume ratio of 2:1 as an etchant to remove the tunnel oxide layer and part of the polysilicon substrate not covered by the mask. The etching time is 1 min to form a local patterned structure.

[0045] Assisted by inductively coupled plasma etching, plasma power 300W, CF4 and O2 flow ratio 15:1, total flow 75sccm, chamber pressure 50Pa;

[0046] (4) Passivation layer deposition: Al2O3 was deposited as a passivation layer in the etched area using PECVD technology at a deposition rate of 1 nm / s to form a locally patterned passivation layer with a circular pattern, a diameter of 2 μm, and a spacing of 0.75 μm;

[0047] (5) Mask removal: removing the mask material to expose the complete patterned passivation layer structure;

[0048] (6) Preparation of polysilicon emitter layer: depositing a polysilicon emitter layer on the tunneling oxide layer not covered by the patterned passivation layer;

[0049] (7) Electrode preparation and packaging: Prepare positive and negative metal electrodes, connect them to the polysilicon emitter layer and the polysilicon substrate respectively, form a local patterned passivation contact structure, namely the TOPCon photovoltaic cell structure, and then perform packaging processing.

[0050] Example 2: A method for preparing a TOPCon photovoltaic cell structure, such as Figure 1 As shown, the following steps are included:

[0051] (1) Tunnel oxide layer deposition: The tunnel oxide layer is deposited on the pretreated polysilicon substrate using PECVD technology with a thickness controlled at 15 nm;

[0052] The pretreatment includes cleaning the surface of the polysilicon substrate using a standard RCA cleaning process and forming a micro-nano structure on the substrate surface using a dry etching technique;

[0053] (2) Preparation of local patterned mask: A local patterned mask was prepared by nanoimprinting technology and covered on the tunneling oxide layer. A high-precision quartz nanoimprint mold was selected, the imprinting pressure was set to 8 MPa, and the imprinting was performed at room temperature for 2 min.

[0054] Curing at 170°C for 1h with nitrogen protection to ensure that the mask material is fully cured, and cleaning with isopropyl alcohol to remove mold release agent and other residues;

[0055] (3) Highly selective etching: using a mixture of acetic acid and hydrofluoric acid in a volume ratio of 1:1 as an etchant to remove the tunnel oxide layer and part of the polysilicon substrate not covered by the mask. The etching time is 90 seconds to form a local patterned structure.

[0056] Assisted by inductively coupled plasma etching, plasma power 300W, CF4 and O2 flow ratio 15:1, total flow 75sccm, chamber pressure 50Pa;

[0057] (4) Passivation layer deposition: SiNx was deposited as a passivation layer in the etched area using PECVD technology at a deposition rate of 0.8 nm / s to form a locally patterned passivation layer with a square pattern, a side length of 1.5 μm, and a spacing of 0.5 μm;

[0058] (5) Mask removal: removing the mask material to expose the complete patterned passivation layer structure;

[0059] (6) Preparation of polysilicon emitter layer: depositing a polysilicon emitter layer on the tunneling oxide layer not covered by the patterned passivation layer;

[0060] (7) Electrode preparation and packaging: Prepare positive and negative metal electrodes, connect them to the polysilicon emitter layer and the polysilicon substrate respectively, form a local patterned passivation contact structure, namely the TOPCon photovoltaic cell structure, and then perform packaging processing.

[0061] Example 3: A method for preparing a TOPCon photovoltaic cell structure, such as Figure 1 As shown, the following steps are included:

[0062] (1) Tunnel oxide layer deposition: The tunnel oxide layer is deposited on the pretreated polysilicon substrate using PECVD technology with a thickness controlled at 12 nm;

[0063] The pretreatment includes cleaning the surface of the polysilicon substrate using a standard RCA cleaning process and forming a micro-nano structure on the substrate surface using a wet etching technique;

[0064] (2) Preparation of local patterned mask: A local patterned mask was prepared by nanoimprinting technology and covered on the tunneling oxide layer. A high-precision quartz nanoimprint mold was selected, the imprinting pressure was set to 6 MPa, and the imprinting was performed at room temperature for 4 min.

[0065] Curing at 160°C for 50 minutes with nitrogen protection to ensure that the mask material is fully cured, and cleaning with acetone to remove mold release agent and other residues;

[0066] (3) Highly selective etching: using a mixture of acetic acid and hydrofluoric acid in a volume ratio of 3:1 as an etchant to remove the tunnel oxide layer and part of the polysilicon substrate not covered by the mask. The etching time is 1.5 min to form a local patterned structure.

[0067] Assisted by inductively coupled plasma etching, plasma power 400W, CF4 and O2 flow ratio of 10:1, total flow 80sccm, chamber pressure 30Pa;

[0068] (4) Passivation layer deposition: A composite passivation layer of Al2O3 and SiNx is deposited in the etched area using PECVD technology. Al2O3 is deposited first and then SiNx to form a local patterned passivation layer with a honeycomb pattern. Each unit has a diameter of about 2 μm and a spacing of 0.8 μm.

[0069] (5) Mask removal: removing the mask material to expose the complete patterned passivation layer structure;

[0070] (6) Preparation of polysilicon emitter layer: depositing a polysilicon emitter layer on the tunneling oxide layer not covered by the patterned passivation layer;

[0071] (7) Electrode preparation and packaging: Prepare positive and negative metal electrodes, connect them to the polysilicon emitter layer and the polysilicon substrate respectively, form a local patterned passivation contact structure, namely the TOPCon photovoltaic cell structure, and then perform packaging processing.

[0072] Comparative Example: A conventional method for preparing a TOPCon photovoltaic cell structure comprises the following steps:

[0073] (1) Select a standard polycrystalline silicon solar cell substrate and use a standard RCA cleaning process to remove surface impurities and contaminants;

[0074] (2) using thermal oxidation or PECVD (plasma enhanced chemical vapor deposition) technology to deposit a uniform tunneling oxide layer (SiO2) with a thickness of 12 nm on the pretreated polysilicon substrate;

[0075] (3) depositing a comprehensive passivation layer on the entire tunnel oxide layer, selecting Al2O3 as the passivation material, and depositing it using PECVD technology;

[0076] (4) forming an n-type polysilicon emitter layer on the overall passivation layer by a phosphorus diffusion process, which is carried out at high temperature and the phosphorus source is a liquid phosphorus source;

[0077] (5) using wet etching technology to open a window on the full passivation layer to expose part of the tunnel oxide layer and the emitter layer so as to form a local contact later; depositing metal in the window area as a local contact electrode by screen printing;

[0078] (6) preparing a back electrode on the back side of the polysilicon substrate, also by metal deposition and patterning process;

[0079] (7) After all electrodes are prepared, the battery is packaged.

[0080] Test Example: The TOPCon solar cells with TOPCon solar cell structures obtained in Examples 1 to 3 and the comparative example were subjected to relevant performance tests, and the results are shown in the following table;

[0081]

[0082] As can be seen from the table, compared with the comparative example, the open circuit voltage (Voc) of Example 1, Example 2 and Example 3 has been significantly improved. The open circuit voltage is a measure of the maximum voltage that can be generated at both ends of a solar cell under light conditions but when the circuit is disconnected. Its increase means that the potential difference of the battery in the open circuit state is larger, which is beneficial to improving the output performance of the battery. Specifically, the Voc of Example 1 is the highest, reaching 0.70V, which is about 7% higher than the 0.655V of the comparative example.

[0083] The short-circuit current (Isc) of all embodiments is higher than that of the comparative example, showing a stronger current generation capability. Short-circuit current refers to the current flowing when the positive and negative poles of a solar cell are short-circuited under light conditions. It reflects the maximum current that a battery can generate under ideal conditions. The Isc of embodiment 3 is the highest, reaching 43.2mA / cm2, which is about 5.4% higher than the 41.0mA / cm2 of the comparative example.

[0084] In addition, the conversion efficiency (η) of the embodiments is significantly higher than that of the comparative examples. Conversion efficiency is the ability of solar cells to convert light energy into electrical energy, and is a core indicator for measuring cell performance. The conversion efficiency of Example 3 is the highest, reaching 23.7%, which is about 7.7% higher than the 22.0% of the comparative example. This shows that the front local polysilicon passivation contact structure prepared by the method of local mask combined with selective etching effectively improves the photoelectric conversion efficiency of TOPCon photovoltaic cells.

[0085] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a TOPCon photovoltaic cell structure, characterized in that: The following steps are involved: (1) Tunneling oxide layer deposition: depositing a tunneling oxide layer on a pretreated polysilicon substrate; (2) Preparation of a local patterned mask: A local patterned mask is prepared by using nanoimprinting technology. The mask is covered on the tunneling oxide layer. A nanoimprinting mold is used to imprint the local patterned mask on the surface of polysilicon, and the mask is reinforced by heat treatment and curing. (3) Highly selective etching: Use a highly selective etchant to remove the tunnel oxide layer and part of the polysilicon substrate not covered by the mask to form a local patterned structure; (4) Deposition of a passivation layer: depositing a passivation layer material in the etched area to form a local patterned passivation layer, wherein the passivation layer includes Al2O3 or SiNx; (5) Mask removal: removing the mask material to expose the complete patterned passivation layer structure; (6) Preparation of polysilicon emitter layer: depositing a polysilicon emitter layer on the tunneling oxide layer not covered by the patterned passivation layer; (7) Electrode preparation and packaging: Prepare positive and negative metal electrodes and connect them to the polysilicon emitter layer and the polysilicon substrate, respectively, to form a local patterned passivation contact structure, namely the TOPCon photovoltaic cell structure, and then perform subsequent packaging processing.

2. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: During the preparation of the local patterned mask, a quartz or nickel-based nanoimprint mold is selected, the imprint pressure is set to 5-10 MPa, the imprinting is performed at room temperature, and the imprinting time is set to 1-5 min.

3. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: During the preparation of the local patterned mask, the heat treatment curing temperature is set to 150-200° C., the heating time is 30 minutes to 1 hour, the heat treatment is performed under nitrogen or inert gas protection, and finally the organic solvent is used for cleaning, and the organic solvent is acetone or isopropanol.

4. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: In the highly selective etching step, the highly selective etchant is a mixture of acetic acid and hydrofluoric acid, the mixed volume ratio is 1-3:1, and the etching time is between 30s-2min.

5. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: The highly selective etching step also includes plasma-assisted etching, selecting an inductively coupled plasma source, a plasma power range of 200-500W, a flow volume ratio of etching gas CF4 and O2 of 10-20:1, a total flow of 50-100sccm, and an etching chamber pressure between 10-100Pa.

6. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: During the deposition of the passivation layer, PECVD technology is used with a deposition rate ranging from 0.5 to 1.5 nm / s.

7. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: In the passivation layer deposition step, the pattern shape of the local patterned passivation layer includes one or more combinations of circular, square or honeycomb, the diameter of the circular pattern is in the range of 1-3 μm, the side length of the square pattern is in the range of 1-2 μm, and the spacing between patterns is between 0.5-1 μm.

8. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: In the tunnel oxide layer deposition step, the tunnel oxide layer is deposited using PECVD technology.

9. The method for preparing a TOPCon photovoltaic cell structure according to claim 1, characterized in that: In the tunnel oxide layer deposition, the pretreatment includes cleaning the surface of the polysilicon substrate using a standard RCA cleaning process, and forming a micro-nano structure on the substrate surface by wet or dry etching technology.

10. A TOPCon photovoltaic cell structure, characterized in that: The TOPCon photovoltaic cell structure is prepared by the preparation method of any one of claims 1-9.

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