Modified tunneling oxide layer and method of making, topcon structure and method of making, and solar cell
By employing ion-free bombardment oxidation and plasma treatment to modify the tunneling oxide layer in the p-type TOPCon structure, the problem of poor passivation quality was solved, enabling the fabrication of high-efficiency solar cells and improving passivation quality and cell performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA SCI & TECH (NINGBO) CO LTD
- Filing Date
- 2022-07-07
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing technology, the passivation quality of the p-type TOPCon structure is poor, which makes it difficult to meet the requirements of high-efficiency solar cells. In addition, the existing silicon oxide thin film preparation methods have problems such as dense oxide layers or many defect states, which leads to a decrease in cell performance.
A SiOx layer was formed on the surface of a semiconductor substrate using an ion-free bombardment oxidation method. The tunneling oxide layer was then modified by plasma treatment with hydrogen and oxygen-containing gases to prepare a modified tunneling oxide layer with a thickness of 1-4 nm and a Si4+ content of more than 18%. The modified tunneling oxide layer was then processed using a PECVD device.
It significantly improved passivation quality, reduced interface state density and boron diffusion rate, enhanced the integrity of the silicon oxide layer and the chemical passivation effect, reduced contact resistivity to 5 mΩcm2, significantly improved battery performance, increased battery efficiency, reduced interface state density and chemical passivation effect, reduced contact resistivity on silicon surface, and significantly improved battery efficiency.
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Figure CN115274404B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of solar cell technology, and more specifically, to a modified tunneling oxide layer and its preparation method, a TOPCon structure and its preparation method, and a solar cell. Background Technology
[0002] The tunneling oxide passivated contact structure (TOPCon) is a novel crystalline silicon solar cell structure proposed by the Fraunhofer Institute in Germany. The core of this structure is the passivation of the silicon wafer surface using an ultrathin silicon oxide layer and a multilayer structure of doped polycrystalline silicon. The passivation mechanism of the tunneling oxide passivated contact structure mainly comes from two aspects: first, the chemical passivation effect of the interface silicon oxide layer; and second, the field passivation effect of the doped atoms. Therefore, improving the integrity of the interface silicon oxide is beneficial to improving the surface chemical passivation effect.
[0003] The fabrication process for TOPCon solar cells is as follows: cleaning and texturing—diffusing boron emitter—etching—backside SiO2 fabrication—PECVD heavily doped polycrystalline silicon—high-temperature annealing—front surface alumina and Si3N4—screen printing. For tunneling silicon oxide passivation contact technology, electron collection uses an n-type phosphorus-doped polycrystalline silicon thin film, while hole collection uses a p-type boron-doped polycrystalline silicon thin film. Due to the superior performance of n-type passivation contact technology, it has been widely accepted as the next-generation high-efficiency crystalline silicon solar cell technology for industrial use.
[0004] Existing technologies use low-pressure chemical vapor deposition (LPCVD) to grow polycrystalline silicon, but LPCVD has the following problems: low in-situ doping film formation rate, requiring secondary doping, and a cumbersome process; long etching time due to plating around the surface; and high cost due to regular equipment maintenance. Plasma-enhanced chemical vapor deposition (PECVD) technology can solve the above problems. Currently, the best-performing n-type TOPCon cells can achieve an efficiency of 25.5%, but the n-type silicon wafers used in n-type TOPCon cells are expensive; and the need to use silver paste on the back of n-type TOPCon cells also increases costs. In contrast, p-type TOPCon cells use low-cost p-type silicon wafers, and low-cost aluminum paste can be used on the back, which can significantly reduce cell costs and improve product competitiveness. However, the main problem in developing p-type TOPCon cells is the poor passivation quality of the p-type TOPCon structure, which is difficult to meet requirements. Developing high-performance p-type TOPCon technology is beneficial to increasing the industry's technology reserves and promoting industrial technology development. In addition, p-type TOPCon technology can also be used in new high-efficiency battery technologies such as TBC cells and tandem cells. Therefore, it is urgent to develop and improve p-type TOPCon technology.
[0005] PECVD technology is a suitable route for preparing boron-doped polycrystalline silicon. However, existing silicon oxide preparation techniques still have several problems, and high-performance p-type TOPCon structures cannot be obtained when combined with PECVD. Existing methods for preparing silicon oxide thin films include plasma-assisted nitrous oxide oxidation, nitric acid oxidation, and thermo-oxidative oxidation. Using plasma N₂O oxidation, oxygen plasma bombardment introduces numerous defects at the interface, resulting in poor passivation. Using nitric acid oxidation, the silicon oxide surface is relatively porous, leading to damage during cleaning and transport. While thermo-oxidative oxidation produces better silicon oxide quality, the resulting thickness leads to poor contact. Ultimately, the optimal passivation effect of silicon oxide prepared by these three methods in p-TOPCon is only 700mV-705mV, corresponding to a single-sided saturation current density (J₀) typically around 15fA / cm². 2 In the subsequent sintering process of the printed electrode, iV oc This will further reduce performance, leading to a decrease in the final device's performance. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is how to improve the passivation quality of the TOPCon structure, thereby enabling the fabrication of high-efficiency solar cells.
[0007] To address the aforementioned problems, the first aspect of this invention provides a modified tunneling oxide layer, which is SiO₂ surface-treated by plasma. x Si 4+ Content in SiO x The proportion of them is greater than or equal to 18%.
[0008] Furthermore, the thickness of the modified tunneling oxide layer is 1–4 nm.
[0009] A second aspect of the present invention provides a method for preparing the above-mentioned modified tunneling oxide layer, comprising the following steps:
[0010] S1. SiO is formed on the surface of a semiconductor substrate using an ion-free bombardment oxidation method. x layer;
[0011] S2. Using hydrogen and oxygen-containing gases as the treatment atmosphere, plasma is used to treat SiO2. x A modified tunneling oxide layer is obtained on the surface.
[0012] Furthermore, the non-ion bombardment oxidation method in step S1 is selected from any one of the following: oxidizing gas oxidation method, low temperature oxidation method, and chemical reagent oxidation method.
[0013] Furthermore, step S2 is performed in a PECVD apparatus.
[0014] Furthermore, the plasma treatment method in step S2 is either continuous plasma treatment or pulsed plasma treatment.
[0015] Furthermore, the oxygen-containing gas is selected from any one of the following: N2O, CO2, O2.
[0016] A third aspect of the present invention provides a TOPCon structure comprising the modified tunneling oxide layer described above.
[0017] The fourth aspect of the present invention provides a method for preparing a TOPCon structure, comprising the following steps: cleaning a semiconductor substrate, preparing a modified tunneling oxide layer, preparing a doped amorphous silicon layer, and annealing; wherein the modified tunneling oxide layer is prepared using the above-described preparation method.
[0018] A fifth aspect of the present invention provides a solar cell including the TOPCon structure described above.
[0019] Compared with the prior art, the present invention has the following beneficial effects:
[0020] Si in the modified tunneling oxide layer of the present invention 4+ Content in SiO x The proportion of boron in the modified silicon oxide layer reaches more than 18%. After plasma surface treatment, the interface state density is reduced. Compared with the silicon oxide layer prepared by existing technology, the diffusion rate of boron in the modified silicon oxide layer is low, which effectively reduces the destructive effect of boron on the tunneling oxide layer, improves the integrity of the silicon oxide layer, and maintains the chemical passivation effect.
[0021] This invention employs a two-step method to prepare a tunneling oxide layer. First, a silicon oxide layer without bombardment damage is prepared. This method significantly reduces ion bombardment damage in the subsequent second step, thereby significantly improving passivation quality. This method effectively reduces interface state defects; the interface state count obtained by conventional plasma nitrous oxide oxidation methods is typically 1×10⁻⁶. 12 eV -1 *cm -2 When using this novel preparation method, the density of defect states can be reduced to 0.5 × 10⁻⁶. 12 eV -1 *cm -2 .
[0022] The method of this invention uses hydrogen and oxygen-containing gas to react with SiO2. x The surface of the layer is modified; hydrogen plasma has a heating effect on the surface, increasing the energy of oxygen and nitrogen atoms and improving bonding quality; hydrogen plasma can also etch SiO. x The weak bonds on the surface make the valence bonds in silicon oxide more stable. These two effects make SiO... x By retaining more stable Si-O, performance is improved.
[0023] The preferred oxygen-containing gas is N₂O. H₂ has reducing properties and can activate the silicon oxide surface, allowing N atoms in N₂O to combine with silicon oxide, significantly reducing the concentration of boron on the silicon surface and thus reducing boron defects. N atoms also have a trapping effect on H atoms, effectively reducing H leakage during sintering, thereby improving the efficiency of subsequent sintering processes. oc Maintain a high level.
[0024] This preparation method is compatible with current mass production equipment technology, especially mass production PECVD equipment. The gas consumables used are low-cost, and hardly increase the cost of additional consumables.
[0025] This invention provides a method for preparing high-nitrogen-concentration, low-ion-bombardment-damage, high-performance modified silicon oxide, replacing the traditional silicon oxide layer. This method significantly improves the performance of TOPCon structures, achieving a passivation quality of 730 mV for P-type TOPCon and reducing the contact resistivity to 5 mΩcm. 2 .
[0026] The TOPCon structure has a modified tunneling oxide layer, which can maintain a high level of passivation during subsequent sintering, which is beneficial for the fabrication of high-efficiency solar cells. Attached Figure Description
[0027] Figure 1 This is a microstructure diagram of the modified tunneling oxide layer in Example 1 of the present invention;
[0028] Figure 2 This is a microstructure diagram of the modified tunneling oxide layer in Example 2 of the present invention. Detailed Implementation
[0029] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.
[0030] It should be noted that the endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0031] As mentioned in the background section, current methods for preparing the tunneling oxide layer in TOPCon include nitric acid oxidation, N2O plasma oxidation, thermal oxidation, and ozone oxidation. These methods all utilize strong oxidizing reagents or gases to oxidize the silicon wafer surface, forming an ultrathin SiO2 layer as the tunneling oxide layer. However, after growing P-Poly, these oxide layers may exhibit problems such as excessively dense oxide layers leading to high contact resistivity, or numerous defect states resulting in poor passivation.
[0032] Based on this, a specific embodiment of the present invention provides a method for preparing a TOPCon structure, comprising the following steps: cleaning a semiconductor substrate, preparing a modified tunneling oxide layer, preparing a doped amorphous silicon layer, and annealing.
[0033] The method for preparing the modified tunneling oxide layer includes the following steps: S1, forming a SiOx layer on the surface of a semiconductor substrate using an ion-free bombardment oxidation method; S2, treating the SiOx surface with plasma using hydrogen and oxygen-containing gas as the treatment atmosphere to obtain the modified tunneling oxide layer.
[0034] The ion-free oxidation method in step S1 can be an oxidizing gas oxidation method, a low-temperature oxidation method (100–600°C), or a chemical reagent oxidation method. Typical methods include ozone oxidation and nitric acid oxidation. This step prepares a silicon oxide layer without bombardment damage. This method can significantly reduce ion bombardment damage in the subsequent second step, thereby significantly improving the passivation quality.
[0035] In step S2, the plasma treatment method is either continuous plasma treatment or pulsed plasma treatment. This step is performed in a PECVD apparatus. In a specific embodiment, the plasma treatment power is 5–10 W, and the treatment time is 50–150 s. The flow ratio of hydrogen to oxygen-containing gas is 2:1–8:1. This method uses hydrogen and oxygen-containing gas to treat SiO₂. x The surface of the layer is modified. Hydrogen plasma has a heating effect on the surface, which increases the energy of oxygen, nitrogen and other atoms and improves the bonding quality. Hydrogen plasma can also etch weak bonds on the SiOx surface, making the valence bonds in silicon oxide more stable. These two effects allow SiOx to retain more stable Si-O, thus improving its performance.
[0036] The oxygen-containing gas is N2O or CO2, preferably N2O. The combination of nitrogen atoms with silicon oxide can significantly reduce the concentration of boron on the silicon surface, thereby reducing boron defects. Nitrogen atoms also have a trapping effect on hydrogen atoms, effectively reducing hydrogen overflow during sintering and thus maintaining a high level of iVoc during subsequent sintering processes.
[0037] The modified tunneling oxide layer prepared by the above method has a thickness of 1–4 nm, Si 4+ Content in SiOx The proportion of these components reaches over 18%, and the interface state density is less than 0.5 × 10⁻⁶. 12 eV -1 cm -2 Compared to silicon oxide layers prepared by existing technologies, boron has a lower diffusion rate in modified silicon oxide layers, thereby effectively reducing the destructive effect of boron on tunneling oxide layers, improving the integrity of silicon oxide layers, and maintaining the chemical passivation effect.
[0038] The modified tunneling oxide layer described above can be applied to both P-type and N-type TOPCon cells, significantly improving the performance of the TOPCon structure. The passivation quality of the P-type TOPCon reaches over 730 mV, and the corresponding single-sided saturation current density (J0) is reduced to 7 fA / cm². 2 Below, the contact resistivity decreases to 5 mΩcm 2 .
[0039] The present invention will be described in detail below through specific embodiments. The semiconductor substrates used in the following embodiments and comparative examples are 160 μm thick n-type single crystal silicon wafers, chemically polished on both sides, with a resistivity of 0.8 Ω·cm.
[0040] Example 1
[0041] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0042] 1) Cut the silicon wafer into 4cm×4cm sizes and perform standard RCA cleaning.
[0043] 2) Place the silicon wafer in an ozone generator to grow a SiO2 thin film.
[0044] 3) Place the sample into the PECVD apparatus, use N2O and H2 as the treatment atmosphere, with a flow ratio of 4:1, and perform continuous plasma treatment at a power of 5W for 100s.
[0045] 4) Next, a boron-doped amorphous silicon thin film is deposited on both sides of the silicon wafer using a PECVD device.
[0046] 5) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0047] Observe the modified tunneling oxide layer of the p-type tunneling silicon oxide passivation structure, such as Figure 1 As shown, the thickness of the modified tunneling oxide layer is 1.7 nm.
[0048] Example 2
[0049] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0050] 1) Perform standard RCA cleaning on the silicon wafer.
[0051] 2) Place the silicon wafer in an ozone generator to grow a SiO2 thin film.
[0052] 3) Place the sample into the PECVD apparatus, use N2O and H2 as the treatment atmosphere, with a flow ratio of 2:1, and perform continuous plasma treatment at a power of 5W for 100s.
[0053] 4) Next, a boron-doped amorphous silicon thin film is deposited on both sides of the silicon wafer using a PECVD device.
[0054] 5) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0055] Observe the modified tunneling oxide layer of the p-type tunneling silicon oxide passivation structure, such as Figure 2 As shown, the thickness of the modified tunneling oxide layer is 1.6 nm.
[0056] Example 3
[0057] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0058] 1) Perform standard RCA cleaning on the silicon wafer.
[0059] 2) Place the silicon wafer in an ozone generator to grow a SiO2 thin film of about 1.5 nm.
[0060] 3) Place the sample into the PECVD apparatus, use N2O and H2 as the treatment atmosphere, with a flow ratio of 8:1, and perform continuous plasma treatment at a power of 5W for 100s.
[0061] 4) Next, a boron-doped amorphous silicon thin film is deposited on both sides of the silicon wafer using a PECVD device.
[0062] 5) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0063] Example 4
[0064] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0065] 1) Perform standard RCA cleaning on the silicon wafer.
[0066] 2) Place the silicon wafer in an annealing furnace and perform low-temperature oxidation treatment at 200℃, 300℃ and 400℃ to grow a SiO2 thin film of about 1.5nm.
[0067] 3) Place the sample into the PECVD apparatus, use N2O and H2 as the treatment atmosphere, with a flow ratio of 2:1, and perform continuous plasma treatment at a power of 5W for 100s.
[0068] 4) Next, a boron-doped amorphous silicon thin film is deposited on both sides of the silicon wafer using a PECVD device.
[0069] 5) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0070] Example 5
[0071] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0072] 1) Perform standard RCA cleaning on the silicon wafer.
[0073] 2) Place the silicon wafer in nitric acid to grow a SiO2 thin film of about 1.5 nm.
[0074] 3) Place the sample into the PECVD apparatus, use N2O and H2 as the treatment atmosphere, with a flow ratio of 2:1, perform pulsed plasma treatment, with a power of 6W and a duration of 10 seconds, then turn off the plasma and purge with nitrogen for 10 seconds. This is one cycle, and repeat for 10 cycles.
[0075] 4) Next, a boron-doped amorphous silicon thin film is deposited on both sides of the silicon wafer using a PECVD device.
[0076] 5) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0077] Comparative Example 1
[0078] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0079] 1) Cut the silicon wafer into 4cm×4cm sizes and perform standard RCA cleaning.
[0080] 2) The silicon wafer is placed in nitric acid to form a surface oxide layer.
[0081] 3) After cleaning and drying the silicon wafer, boron-doped amorphous silicon thin films are deposited on both sides of the silicon wafer using PECVD.
[0082] 4) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0083] Comparative Example 2
[0084] A double-sided p-type tunneling silicon oxide passivation structure is prepared by the following steps:
[0085] 1) Cut the silicon wafer into 4cm×4cm sizes and perform standard RCA cleaning.
[0086] 2) Place the silicon wafer into a PECVD device for plasma treatment, using N2O as the treatment gas, treat both sides, with a power of 10W and a treatment time of 100S.
[0087] 3) Next, boron-doped amorphous silicon thin films are deposited on both sides of the silicon wafer using PECVD.
[0088] 4) Place the sample in a tube annealing furnace for annealing at a temperature of 800-920℃ for 30 minutes.
[0089] The passivation and contact properties of Examples 1-5 were analyzed and tested, and the passivation properties of Comparative Examples 1 and 2 were analyzed and tested. The test results are shown in Table 1 below.
[0090]
[0091]
[0092] Table 1. Passivation performance of the examples and comparative samples
[0093] The data comparison shows that the p-type tunneling silicon oxide passivation structures in Examples 1-5 have modified tunneling oxide layers, and their passivation performance is significantly better than that of Comparative Examples 1 and 2. The back junction cells prepared using the process of Example 1 can achieve an efficiency of 23.17%.
[0094] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A method for preparing a modified tunneling oxide layer, characterized in that, Includes the following steps: S1. SiO is formed on the surface of a semiconductor substrate using an ion-free bombardment oxidation method. x layer; S2. Using hydrogen and oxygen-containing gases as the treatment atmosphere, plasma is used to treat SiO₂. x A modified tunneling oxide layer is obtained on the surface, wherein the oxygen-containing gas is selected from any one of the following: N2O, CO2, O2, and the Si in the modified tunneling oxide layer is... 4+ The content is greater than or equal to 18%, and the thickness is 1-4 nm.
2. The method for preparing the modified tunneling oxide layer according to claim 1, characterized in that, In step S1, the non-ion bombardment oxidation method is selected from any of the following: oxidizing gas oxidation method, low temperature oxidation method, and chemical reagent oxidation method.
3. The method for preparing the modified tunneling oxide layer according to claim 1, characterized in that, Step S2 is performed in a PECVD apparatus.
4. The method for preparing the modified tunneling oxide layer according to claim 3, characterized in that, The plasma treatment method in step S2 is either continuous plasma treatment or pulsed plasma treatment.
5. A modified tunneling oxide layer, characterized in that, The modified tunneling oxide layer is prepared by any one of the preparation methods described in claims 1-4, wherein the modified tunneling oxide layer is SiO2 that has undergone plasma surface treatment. x The modified tunneling oxide layer Si 4+ The content is greater than or equal to 18%, and the thickness is 1-4 nm.
6. A TOPCon structure, characterized in that, Includes the modified tunneling oxide layer as described in claim 5.
7. A method for preparing a TOPCon structure, characterized in that, Includes the following steps: The semiconductor substrate is cleaned, a modified tunneling oxide layer is prepared, a doped amorphous silicon layer is prepared, and annealing is performed; the modified tunneling oxide layer is prepared using the preparation method described in any one of claims 1-4.
8. A solar cell, characterized in that, Includes the TOPCon structure as described in claim 6.