Heterojunction solar cell and preparation method and application thereof
By using a four-layer boron-doped p-type microcrystalline silicon layer structure and optimizing the boron doping gradient design, the problem of insufficient boron doping concentration in silicon heterojunction solar cells is solved, improving carrier mobility and cell efficiency, and making it suitable for various cell types.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 嘉兴阿特斯阳光能源科技有限公司
- Filing Date
- 2024-10-12
- Publication Date
- 2026-04-14
AI Technical Summary
In the prior art, the boron doping concentration in the microcrystalline silicon thin film of silicon heterojunction solar cells is not optimized enough, resulting in low carrier mobility, which affects cell efficiency, especially the increase in hole tunneling contact and the reduction of fill factor.
A four-layer boron-doped p-type microcrystalline silicon layer structure is adopted. By controlling the boron source flow ratio between each layer, the doping gradient is designed to ensure the built-in electric field strength and doping concentration, enhance hole extraction and carrier transport, and reduce back hole tunneling contact.
It significantly improves the cell efficiency of solar cells, reduces hole tunneling resistivity, and enhances the fill factor, making it suitable for heterojunction, Topcon, and IBC back contact cells.
Smart Images
Figure CN121865741A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of silicon solar cell technology, specifically relating to a heterojunction solar cell, its preparation method, and its application. Background Technology
[0002] Silicon heterojunction (HJT) solar cells have attracted much attention due to their advantages such as high turn-on voltage, high conversion efficiency, and low temperature coefficient. Boron-doped amorphous or microcrystalline silicon thin films are a crucial component in achieving high conversion efficiency. By changing the boron doping concentration, the electrical characteristics of the emitter can be adjusted, directly affecting the cell's conversion efficiency. High-efficiency HJT cells require the highest possible conductivity to increase field-effect passivation, while simultaneously achieving the lowest possible defect state density to improve film quality and increase the fill factor (FF). This necessitates appropriate optimization of the doping concentration to prevent excessive boron atom incorporation, which would render boron atoms in an inactive state, affecting the crystallinity of the microcrystalline film, preventing them from contributing to conductivity, and creating neutral scattering centers that reduce carrier mobility within the film, thus impacting cell efficiency.
[0003] Therefore, there is an urgent need to provide a process that can effectively optimize the boron doping concentration in microcrystalline silicon thin films, thereby improving interfacial contact, enhancing the quality of microcrystalline silicon thin films, increasing carrier mobility, and improving battery efficiency. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to provide a heterojunction solar cell, its fabrication method, and its applications. The invention designs four boron-doped p-type microcrystalline silicon layers and achieves the doping gradient design by controlling the boron source flux ratio between each layer. This ensures that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration, while the third and fourth boron-doped p-type microcrystalline silicon layers further enhance hole extraction and improve carrier transport. The four layers work synergistically to significantly reduce back-side hole tunneling contact and improve cell efficiency. This optimized process is applicable not only to heterojunction solar cells but also to Topcon, IBC back-contact, and other types of cells.
[0005] To achieve this objective, the present invention employs the following technical solution:
[0006] In a first aspect, the present invention provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0007] An intrinsic amorphous silicon layer is deposited on each of the opposite sides of an n-type silicon wafer, namely the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer.
[0008] A first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, and a fourth boron-doped p-type microcrystalline silicon layer are sequentially deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer.
[0009] The ratio of boron source flux for depositing the first boron-doped p-type microcrystalline silicon layer to the second boron-doped p-type microcrystalline silicon layer is 1:(2.5-3), and the ratio of boron source flux for depositing the third boron-doped p-type microcrystalline silicon layer to the fourth boron-doped p-type microcrystalline silicon layer is 1:(20-30).
[0010] A phosphorus-doped n-type microcrystalline silicon layer is deposited on the intrinsic amorphous silicon layer on the front side. Then, transparent conductive layers are deposited on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer, respectively. Subsequently, metal electrodes are fabricated on the transparent conductive layers on the front and back sides of the n-type silicon wafer to obtain the heterojunction solar cell.
[0011] It should be noted that effective hole collection is a combination of the tunneling effect between c-Si and pa-Si:H (P-type microcrystalline silicon) and the transparent electrode / pa-Si:H interface. Hole extraction in c-Si is mainly related to the work function matching between ia-Si:H (intrinsic amorphous silicon) and pa-Si:H, and between the transparent electrode and pa-Si:H.
[0012] Therefore, this invention designs a four-layer boron-doped p-type microcrystalline silicon system and achieves the doping gradient design by controlling the boron source flow ratio between each layer. This ensures that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under high gradient doping ratios (by controlling the boron source flow ratio), the third and fourth boron-doped p-type microcrystalline silicon layers enhance the upward band bending, leading to more efficient hole tunneling through ia-Si:H. This results in hole accumulation at the transparent electrode / pa-Si:H heterojunction. The accumulated holes can easily recombine with electrons in the transparent electrode through increased trap states, leading to a decrease in hole tunneling resistivity and an increase in the cell fill factor (FF). Furthermore, the enhanced upward band bending also allows electrons to be repelled from the c-Si / pa-Si:H interface. Therefore, the above process optimization further enhances hole extraction, improves carrier transport, and the synergistic effect of the four layers significantly reduces back-side hole tunneling contact, thereby improving cell efficiency.
[0013] The optimized process for the four-layer boron-doped p-type microcrystalline silicon layer provided by this invention is applicable not only to heterojunction solar cells, but also to Topcon, IBC back contact, and other types of cells.
[0014] In this invention, the ratio of boron source flux for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:(2.5-3), for example, it can be 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, etc. If the boron source flux ratio is too small, an effective doping concentration and field-effect passivation effect cannot be formed; if the boron source flux ratio is too large, Auger recombination will be increased, affecting the battery efficiency.
[0015] In this invention, the boron source flux ratio between the deposited third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:(20-30), for example, it can be 1:20, 1:22, 1:24, 1:26, 1:28, or 1:30. High-gradient doping conditions are beneficial for further enhancing hole extraction and improving carrier transport. If the boron source flux ratio is too small, carrier transport cannot be effectively improved; if the boron source flux ratio is too large, it leads to severe surface recombination and waste of dopant gas.
[0016] Preferably, the deposition method of the intrinsic amorphous silicon layer includes PECVD.
[0017] Preferably, the deposition methods for both the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are PECVD, and the specific parameters for each layer independently include:
[0018] The reaction gases include a silicon source and hydrogen, with a reaction gas pressure of 0.4-0.6 Torr, such as 0.4 Torr, 0.5 Torr, or 0.6 Torr. The deposition power is 100-200 W, such as 100 W, 150 W, or 200 W. The deposition temperature is 160-220℃, such as 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, or 220℃.
[0019] Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(1-1.5), for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5, etc.
[0020] It should be noted that the present invention does not limit the type of silicon source. For example, it can be silane, etc., and the same applies below.
[0021] Preferably, the thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer is independently 5-7nm, for example, it can be 5nm, 5.5nm, 6nm, 6.5nm or 7nm, etc.
[0022] Preferably, the deposition method of the first boron-doped p-type microcrystalline silicon layer includes PECVD.
[0023] Preferably, the deposition method of the first boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include:
[0024] The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, for example, 4 Torr, 4.5 Torr or 5 Torr, the deposition power is 5000-7000W, for example, 5000W, 6000W or 7000W, and the deposition temperature is 140-170℃, for example, 140℃, 150℃, 160℃ or 170℃.
[0025] Preferably, the flow rate of the boron source is 25-35 sccm, for example, it can be 25 sccm, 30 sccm or 35 sccm.
[0026] In this invention, the flow rate of the boron source is 25-35 sccm. Within this range, the boron concentration in the first boron-doped p-type microcrystalline silicon layer is conducive to the rapid nucleation of boron-doped microcrystalline silicon.
[0027] It should be noted that the present invention does not limit the type of boron source. For example, it can be borane, etc., and the same applies below.
[0028] Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(350-380), for example, it can be 1:350, 1:360, 1:370, or 1:380. In the process of depositing the first boron-doped p-type microcrystalline silicon layer, a suitable flow rate ratio of silicon source to hydrogen is beneficial to improving the doping effect of the boron-doped microcrystalline silicon.
[0029] Preferably, the thickness of the first boron-doped p-type microcrystalline silicon layer is 1-2 nm, for example, it can be 1 nm, 1.5 nm or 2 nm.
[0030] Preferably, the reactant gas also includes carbon dioxide.
[0031] The purpose of incorporating carbon dioxide into the first boron-doped p-type microcrystalline silicon layer in this invention is to facilitate microcrystalline nucleation and improve the crystallinity of microcrystalline silicon.
[0032] Preferably, the flow rate of the carbon dioxide is 100-200 sccm, for example, it can be 100 sccm, 120 sccm, 140 sccm, 160 sccm, 180 sccm or 200 sccm, etc.
[0033] Preferably, the deposition method of the second boron-doped p-type microcrystalline silicon layer includes PECVD.
[0034] Preferably, the deposition method for the second boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include:
[0035] The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, for example, 4 Torr, 4.5 Torr or 5 Torr, the deposition power is 5000-7000W, for example, 5000W, 6000W or 7000W, and the deposition temperature is 140-170℃, for example, 140℃, 150℃, 155℃, 160℃ or 170℃.
[0036] Preferably, the flow rate of the boron source is 60-80 sccm, for example, it can be 60 sccm, 70 sccm or 80 sccm.
[0037] In this invention, the flow rate of the boron source is 60-80 sccm. Within this range, the boron concentration in the second boron-doped p-type microcrystalline silicon layer is beneficial to increasing the hole accumulation concentration.
[0038] Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340, or 1:350. In the process of depositing the second boron-doped p-type microcrystalline silicon layer, a suitable flow rate ratio of silicon source to hydrogen is beneficial to the conductivity and light transmittance of the microcrystalline silicon film.
[0039] Preferably, the thickness of the second boron-doped p-type microcrystalline silicon layer is 23-28 nm, for example, it can be 23 nm, 24 nm, 25 nm, 26 nm, 27 nm or 28 nm.
[0040] Preferably, the reactant gas also includes carbon dioxide.
[0041] The purpose of incorporating carbon dioxide into the second boron-doped p-type microcrystalline silicon layer in this invention is to facilitate microcrystal nucleation and improve the crystallinity of microcrystalline silicon.
[0042] Preferably, the flow rate of the carbon dioxide is 15-25 sccm, for example, it can be 15 sccm, 20 sccm or 25 sccm.
[0043] Preferably, the deposition method of the third boron-doped p-type microcrystalline silicon layer includes PECVD.
[0044] Preferably, the deposition method of the third boron-doped p-type microcrystalline silicon layer in step (2) is PECVD, and the specific parameters include:
[0045] The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, for example, 4 Torr, 4.5 Torr or 5 Torr, the deposition power is 5000-7000W, for example, 5000W, 6000W or 7000W, and the deposition temperature is 140-170℃, for example, 140℃, 145℃, 150℃, 155℃, 160℃ or 170℃.
[0046] Preferably, the flow rate of the boron source is 10-20 sccm, for example, it can be 10 sccm, 15 sccm or 20 sccm.
[0047] In this invention, the flow rate of the boron source is 10-20 sccm. Within this range, the boron concentration of the third boron-doped p-type microcrystalline silicon layer is conducive to forming a high doping concentration gradient with the fourth boron doping layer, thereby improving carrier transport.
[0048] Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340 or 1:350, etc.
[0049] Preferably, the thickness of the third boron-doped p-type microcrystalline silicon layer is 1-2 nm, for example, it can be 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm or 2 nm.
[0050] In this invention, a low-thickness third boron-doped p-type microcrystalline silicon layer is used, and a lower concentration of boron dopant is also incorporated, which further improves carrier transport.
[0051] Preferably, the reactant gas also includes carbon dioxide.
[0052] The purpose of incorporating carbon dioxide into the second boron-doped p-type microcrystalline silicon layer in this invention is to facilitate microcrystal nucleation and improve the crystallinity of microcrystalline silicon.
[0053] Preferably, the flow rate of the carbon dioxide is 15-25 sccm, for example, it can be 15 sccm, 20 sccm or 25 sccm.
[0054] Preferably, the deposition method of the fourth boron-doped p-type microcrystalline silicon layer includes PECVD.
[0055] Preferably, the deposition method for the fourth boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include:
[0056] The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, for example, 4 Torr, 4.5 Torr or 5 Torr, the deposition power is 5000-7000W, for example, 5000W, 6000W or 7000W, and the deposition temperature is 140-170℃, for example, 140℃, 150℃, 155℃, 160℃ or 170℃.
[0057] It should be noted that carbon dioxide is not used for oxygen doping during the deposition of the fourth boron-doped p-type microcrystalline silicon layer, which is beneficial to improving its contact with the transparent conductive layer.
[0058] Preferably, the flow rate of the boron source is 300-400 sccm, for example, it can be 300 sccm, 350 sccm or 400 sccm.
[0059] In this invention, the flow rate of the boron source is 300-400 sccm. Within this range, the boron concentration in the fourth boron-doped p-type microcrystalline silicon layer is conducive to forming a suitable concentration gradient with the third boron-doped p-type microcrystalline silicon layer.
[0060] Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350), for example, it can be 1:300, 1:310, 1:320, 1:330, 1:340 or 1:350, etc.
[0061] Preferably, the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 4-6 nm, for example, it can be 4 nm, 4.5 nm, 5 nm, 5.5 nm or 6 nm.
[0062] In this invention, a low-thickness fourth p-type microcrystalline silicon layer is used, along with a high concentration of boron dopant, which can further enhance hole extraction, more effectively improve carrier transport, and significantly improve battery efficiency.
[0063] Preferably, the total thickness of the first boron-doped p-type microcrystalline silicon layer, the second boron-doped p-type microcrystalline silicon layer, the third boron-doped microcrystalline silicon layer, and the fourth boron-doped p-type microcrystalline silicon layer is 30-35 nm, for example, it can be 30 nm, 31 nm, 32 nm, 33 nm, 34 nm, or 35 nm.
[0064] Preferably, the preparation method includes the following steps:
[0065] A 5-7 nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer using PECVD. The specific steps include: introducing hydrogen and a silicon source as reaction gases into a reaction chamber, wherein the flow rate of hydrogen is 800-1200 sccm (e.g., 800 sccm, 900 sccm, 1000 sccm, 1100 sccm, or 1200 sccm, etc.), the flow rate of silicon source is 800-1000 sccm (e.g., 800 sccm, 900 sccm, or 1000 sccm, etc.), the flow rate ratio of silicon source to hydrogen is 1:(1-1.5), the preset deposition power is 100-200 W, the deposition temperature is 180-220 °C, and the reaction gas pressure is 0.4-0.6 Torr.
[0066] A 5-7 nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include: introducing hydrogen and a silicon source as reaction gases into a reaction chamber, wherein the flow rate of hydrogen is 800-1200 sccm (e.g., 800 sccm, 900 sccm, 1000 sccm, 1100 sccm, or 1200 sccm, etc.), the flow rate of silicon source is 800-1000 sccm (e.g., 800 sccm, 900 sccm, or 1000 sccm, etc.), the flow rate ratio of silicon source to hydrogen is 1:(1-1.5), the preset deposition power is 100-200 W, the deposition temperature is 180-220 °C, and the reaction gas pressure is 0.4-0.6 Torr.
[0067] A first boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm is deposited on the intrinsic amorphous silicon layer on the back side along the direction away from the n-type silicon wafer using PECVD. The specific steps include: introducing a silicon source, a boron source, hydrogen gas, and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm (e.g., 50 sccm, 60 sccm, 70 sccm, or 80 sccm, etc.), the flow rate of the boron source is 25-35 sccm, the flow rate of the hydrogen gas is 25000-29000 sccm (e.g., 25000 sccm, 27000 sccm, or 29000 sccm, etc.), the flow rate of the carbon dioxide gas is 100-200 sccm, the flow rate ratio of silicon source to hydrogen gas is 1:(350-380), the preset deposition power is 5000-7000W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr.
[0068] The deposition of a second boron-doped p-type microcrystalline silicon layer with a thickness of 23-28 nm on a first boron-doped p-type microcrystalline silicon layer is performed by PECVD. The specific steps include: introducing a silicon source, a boron source, hydrogen gas, and carbon dioxide into a reaction chamber. The flow rate of the silicon source is 50-80 sccm (e.g., 50 sccm, 60 sccm, 70 sccm, or 80 sccm), the flow rate of the boron source is 60-80 sccm, the flow rate of the hydrogen gas is 15000-28000 sccm (e.g., 15000 sccm, 20000 sccm, 25000 sccm, or 28000 sccm), and the flow rate of the carbon dioxide gas is 15-25 sccm. The flow rate ratio of the silicon source to the hydrogen gas is 1:(300-350). The preset deposition power is 5000-7000 W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr.
[0069] A third boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm is deposited on a second boron-doped p-type microcrystalline silicon layer using PECVD. The specific steps include: introducing a silicon source, a boron source, hydrogen gas, and carbon dioxide into a reaction chamber. The flow rate of the silicon source is 50-80 sccm (e.g., 50 sccm, 60 sccm, 70 sccm, or 80 sccm), the flow rate of the boron source is 10-20 sccm, the flow rate of the hydrogen gas is 15000-28000 sccm (e.g., 15000 sccm, 20000 sccm, 25000 sccm, or 28000 sccm), and the flow rate of the carbon dioxide gas is 15-25 sccm. The flow rate ratio of the silicon source to the hydrogen gas is 1:(300-350). The preset deposition power is 5000-7000 W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr.
[0070] A fourth boron-doped p-type microcrystalline silicon layer with a thickness of 4-6 nm was deposited on a third boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps included: introducing a silicon source, a boron source, and hydrogen gas into a reaction chamber, wherein the flow rate of the silicon source was 50-80 sccm (e.g., 50 sccm, 60 sccm, 70 sccm, or 80 sccm, etc.), the flow rate of the boron source was 300-400 sccm, and the flow rate of the hydrogen gas was 15000-28000 sccm (e.g., 15000 sccm, 20000 sccm, 25000 sccm, or 28000 sccm, etc.), the flow rate ratio of silicon source to hydrogen gas was 1:(300-350), the preset deposition power was 5000-7000 W, the deposition temperature was 140-170℃, and the reaction gas pressure was 4-5 Torr.
[0071] A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 25-30 nm (e.g., 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, or 30 nm) is deposited on the intrinsic amorphous silicon layer on the front side in a direction away from the n-type silicon wafer using PECVD. The specific steps include: introducing a silicon source, a phosphorus source, and hydrogen gas into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the phosphorus source is 300-800 sccm, the flow rate of the hydrogen gas is 8000-12000 sccm, the preset deposition power is 4000-6000 W, the deposition temperature is 180-200 °C, and the reaction gas pressure is 4-6 Torr.
[0072] ITO (indium tin oxide) transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively using magnetron sputtering. The thickness of each layer was independently 80-110 nm (e.g., 80 nm, 85 nm, 100 nm or 110 nm).
[0073] The heterojunction solar cell is obtained by fabricating metal electrodes (e.g., silver electrodes) on the transparent conductive layers on the front and back sides of an n-type silicon wafer using screen printing.
[0074] In a second aspect, the present invention provides a heterojunction solar cell, wherein the heterojunction solar cell is prepared by the preparation method described in the first aspect, and the heterojunction solar cell includes a back metal electrode, a back transparent conductive layer, a fourth boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a first boron-doped p-type microcrystalline silicon layer, a back intrinsic amorphous silicon layer, an n-type silicon wafer, a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer, and a front metal electrode.
[0075] Thirdly, the present invention provides a silicon solar cell, the silicon solar cell comprising the heterojunction solar cell as described in the second aspect.
[0076] The numerical range described in this invention includes not only the point values listed above, but also any point values within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values included in the range.
[0077] Compared with the prior art, the present invention has the following beneficial effects:
[0078] (1) This invention designs a four-layer boron-doped p-type microcrystalline silicon layer and completes the doping gradient design by controlling the boron source flux ratio between each layer. This ensures that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under the condition of high gradient boron doping ratio, the third and fourth boron-doped p-type microcrystalline silicon layers enhance the upward band bending, resulting in more efficient hole tunneling through ia-Si:H. This leads to hole accumulation at the transparent electrode / pa-Si:H hetero interface. The accumulated holes can easily recombine with electrons in the transparent electrode through the increased trap states, which leads to a decrease in hole tunneling resistivity and an increase in the battery fill factor FF. In addition, the enhanced upward band bending also allows electrons to be repelled from the c-Si / pa-Si:H interface. Therefore, the above process optimization further enhances hole extraction, improves carrier transport, and the four layers work together to significantly reduce back-side hole tunneling contact and improve battery efficiency.
[0079] (2) The optimized process of the four boron-doped p-type microcrystalline silicon layer provided by the present invention is not only applicable to heterojunction solar cells, but also to Topcon, IBC back contact and other cells. Attached Figure Description
[0080] Figure 1 This is a schematic diagram of the structure of the heterojunction solar cell provided in Embodiment 1 of the present invention.
[0081] Figure 2 This is a schematic diagram of the heterojunction solar cell provided in Comparative Example 1 of the present invention.
[0082] Figure 3 This is a schematic diagram of the heterojunction solar cell provided in Comparative Example 2 of the present invention.
[0083] Among them, 1-n-type silicon wafer; 2-backside intrinsic amorphous silicon layer; 3-frontside intrinsic amorphous silicon layer; 41-first boron-doped p-type microcrystalline silicon layer; 42-backside boron-doped p-type microcrystalline silicon layer; 43-low concentration boron-doped p-type microcrystalline silicon layer; 51-second boron-doped p-type microcrystalline silicon layer; 52-medium concentration boron-doped p-type microcrystalline silicon layer; 61-third boron-doped p-type microcrystalline silicon layer; 62-high concentration boron-doped p-type microcrystalline silicon layer; 7-fourth boron-doped p-type microcrystalline silicon layer; 8-phosphorus-doped n-type microcrystalline silicon layer; 91-backside transparent conductive layer; 92-frontside transparent conductive layer; 101-backside metal electrode; 102-frontside metal electrode. Detailed Implementation
[0084] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.
[0085] Example 1
[0086] This embodiment provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0087] (1) A 6 nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer by PECVD. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, the flow rate ratio of silane to hydrogen is 1:1.11, the preset deposition power is 150 W, the deposition temperature is 180 °C, and the reaction gas pressure is 0.5 Torr.
[0088] A 6nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include:
[0089] Hydrogen and silane were introduced into the reaction chamber as reaction gases, with a hydrogen flow rate of 1000 sccm and a silane flow rate of 900 sccm. The flow rate ratio of silane to hydrogen was 1:1.11. The preset deposition power was 150 W, the deposition temperature was 180 °C, and the reaction gas pressure was 0.5 Torr.
[0090] (2) A first boron-doped p-type microcrystalline silicon layer with a thickness of 1.5 nm is deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0091] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 75 sccm, borane is 25 sccm, hydrogen is 27000 sccm, and carbon dioxide is 150 sccm. The flow ratio of silane to hydrogen is 1:360. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0092] (3) A second boron-doped p-type microcrystalline silicon layer with a thickness of 26 nm was deposited on the first boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0093] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane and borane are 70 sccm, the flow rates of hydrogen are 23100 sccm, and the flow rates of carbon dioxide are 10 sccm. The flow rate ratio of silane to hydrogen is 1:330. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0094] The borane flow rate ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:2.8.
[0095] (4) A third boron-doped p-type microcrystalline silicon layer with a thickness of 1.5 nm is deposited on the second boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0096] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 65 sccm, borane is 15 sccm, hydrogen is 21450 sccm, and carbon dioxide is 20 sccm. The flow ratio of silane to hydrogen is 1:330. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0097] (5) A fourth boron-doped p-type microcrystalline silicon layer with a thickness of 5 nm is deposited on the third boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0098] Silane, borane, and hydrogen are introduced into the reaction chamber, with a flow rate of 65 sccm for silane, 375 ccm for borane, and 21450 sccm for hydrogen. The flow rate ratio of silane to hydrogen is 1:330. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0099] The borane flow rate ratio of the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:25.
[0100] (6) A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 28 nm is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0101] Silane, phosphine, and hydrogen are introduced into the reaction chamber, with a flow rate of 55 sccm for silane, 400 sccm for phosphine, and 10000 sccm for hydrogen. The preset deposition power is 4000 W, the deposition temperature is 180 °C, and the reaction gas pressure is 4.5 Torr.
[0102] (7) ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively by magnetron sputtering, with a thickness of 95 nm for both layers.
[0103] (8) Silver grid electrodes with a thickness of 15 μm were fabricated on the ITO transparent conductive layer on the front and back sides of the n-type silicon wafer using screen printing to obtain the heterojunction solar cell, the structural schematic diagram of which is shown below. Figure 1As shown, the structure includes a back metal electrode 101, a back transparent conductive layer 91, a fourth boron-doped p-type microcrystalline silicon layer 7, a third boron-doped p-type microcrystalline silicon layer 61, a second boron-doped p-type microcrystalline silicon layer 51, a first boron-doped p-type microcrystalline silicon layer 41, a back intrinsic amorphous silicon layer 2, an n-type silicon wafer 1, a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92, and a front metal electrode 102, all stacked together.
[0104] Example 2
[0105] This embodiment provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0106] (1) A 5nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer by PECVD. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 800 sccm, the flow rate of silane is 800 sccm, the flow rate ratio of silane to hydrogen is 1:1, the preset deposition power is 100W, the deposition temperature is 185℃, and the reaction gas pressure is 0.4 Torr.
[0107] A 5nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include:
[0108] Hydrogen and silane are introduced into the reaction chamber as reaction gases, with a hydrogen flow rate of 800 sccm and a silane flow rate of 800 sccm. The flow rate ratio of silane to hydrogen is 1:1. The preset deposition power is 100W, the deposition temperature is 185℃, and the reaction gas pressure is 0.4 Torr.
[0109] (2) A first boron-doped p-type microcrystalline silicon layer with a thickness of 2 nm is deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0110] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 80 sccm, borane is 25 sccm, hydrogen is 28000 sccm, and carbon dioxide is 100 sccm. The flow ratio of silane to hydrogen is 1:350. The preset deposition power is 5000W, the deposition temperature is 160℃, and the reaction gas pressure is 4 Torr.
[0111] (3) A second boron-doped p-type microcrystalline silicon layer with a thickness of 23 nm was deposited on the first boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0112] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 50 sccm, borane is 62.5 sccm, hydrogen is 15000 sccm, and carbon dioxide is 15 sccm. The flow ratio of silane to hydrogen is 1:300. The preset deposition power is 5000W, the deposition temperature is 160℃, and the reaction gas pressure is 4 Torr.
[0113] The borane flow rate ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:2.5.
[0114] (4) A third boron-doped p-type microcrystalline silicon layer with a thickness of 2 nm is deposited on the second boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0115] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 50 sccm, borane is 10 sccm, hydrogen is 15000 sccm, and carbon dioxide is 15 sccm. The flow ratio of silane to hydrogen is 1:300. The preset deposition power is 5000W, the deposition temperature is 160℃, and the reaction gas pressure is 4 Torr.
[0116] (5) A fourth boron-doped p-type microcrystalline silicon layer with a thickness of 4 nm is deposited on the third boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0117] Silane, borane, and hydrogen are introduced into the reaction chamber, with a flow rate of 50 sccm for silane, 300 sccm for borane, and 15000 sccm for hydrogen. The flow rate ratio of silane to hydrogen is 1:300. The preset deposition power is 5000W, the deposition temperature is 160℃, and the reaction gas pressure is 4 Torr.
[0118] The borane flow rate ratio of the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:30.
[0119] (6) A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 25 nm is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0120] Silane, phosphine, and hydrogen are introduced into the reaction chamber, with a flow rate of 60 sccm for silane, 480 sccm for phosphine, and 11000 sccm for hydrogen. The preset deposition power is 4500 W, the deposition temperature is 195 °C, and the reaction gas pressure is 4.5 Torr.
[0121] (7) ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively by magnetron sputtering, with a thickness of 100 nm for both layers.
[0122] (8) Silver grid electrodes with a thickness of 15 μm were fabricated on the ITO transparent conductive layer on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell.
[0123] Example 3
[0124] This embodiment provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0125] (1) A 7nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer by PECVD. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1200sccm, the flow rate of silane is 800sccm, the flow rate ratio of silane to hydrogen is 1:1.5, the preset deposition power is 200W, the deposition temperature is 195℃, and the reaction gas pressure is 0.6Torr.
[0126] A 7nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include:
[0127] Hydrogen and silane were introduced into the reaction chamber as reaction gases, with a hydrogen flow rate of 1200 sccm and a silane flow rate of 800 sccm. The flow rate ratio of silane to hydrogen was 1:1.5. The preset deposition power was 200 W, the deposition temperature was 195 °C, and the reaction gas pressure was 0.6 Torr.
[0128] (2) A first boron-doped p-type microcrystalline silicon layer with a thickness of 1 nm is deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0129] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 78 sccm, borane is 27 sccm, hydrogen is 29000 sccm, and carbon dioxide is 200 sccm. The flow rate ratio of silane to hydrogen is 1:372. The preset deposition power is 7000W, the deposition temperature is 160℃, and the reaction gas pressure is 5 Torr.
[0130] (3) A second boron-doped p-type microcrystalline silicon layer with a thickness of 27 nm was deposited on the first boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0131] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane and borane are 80 sccm, the flow rates of hydrogen are 28000 sccm, and the flow rates of carbon dioxide are 25 sccm. The flow rate ratio of silane to hydrogen is 1:350. The preset deposition power is 7000W, the deposition temperature is 160℃, and the reaction gas pressure is 5 Torr.
[0132] The ratio of borane flow rate for depositing the first boron-doped p-type microcrystalline silicon layer to the second boron-doped p-type microcrystalline silicon layer is 1:3.
[0133] (4) A third boron-doped p-type microcrystalline silicon layer with a thickness of 1 nm is deposited on the second boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0134] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 80 sccm, borane is 14 sccm, hydrogen is 28000 sccm, and carbon dioxide is 25 sccm. The flow ratio of silane to hydrogen is 1:350. The preset deposition power is 7000W, the deposition temperature is 160℃, and the reaction gas pressure is 5 Torr.
[0135] (5) A fourth boron-doped p-type microcrystalline silicon layer with a thickness of 6 nm is deposited on the third boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0136] Silane, borane, and hydrogen are introduced into the reaction chamber, with a flow rate of 80 sccm for silane, 400 sccm for borane, and 28000 sccm for hydrogen. The flow rate ratio of silane to hydrogen is 1:350. The preset deposition power is 7000W, the deposition temperature is 160℃, and the reaction gas pressure is 5 Torr.
[0137] The borane flow rate ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:29.
[0138] (6) A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 30 nm is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0139] Silane, phosphine, and hydrogen are introduced into the reaction chamber, with a flow rate of 40 sccm for silane, 380 sccm for phosphine, and 8500 sccm for hydrogen. The preset deposition power is 4500 W, the deposition temperature is 190 °C, and the reaction gas pressure is 4.5 Torr.
[0140] (7) ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively by magnetron sputtering, with a thickness of 90 nm for both layers.
[0141] (8) Silver grid electrodes with a thickness of 15 μm were fabricated on the ITO transparent conductive layer on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell.
[0142] Example 4
[0143] The difference between this embodiment and embodiment 1 is that the thickness of the third boron-doped p-type microcrystalline silicon layer in step (4) is 5 nm.
[0144] The remaining preparation methods and parameters are consistent with those in Example 1.
[0145] Example 5
[0146] The difference between this embodiment and embodiment 1 is that the thickness of the fourth boron-doped p-type microcrystalline silicon layer in step (4) is 10 nm.
[0147] The remaining preparation methods and parameters are consistent with those in Example 1.
[0148] Comparative Example 1
[0149] This comparative example provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0150] (1) A 6 nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer by PECVD. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, the flow rate ratio of silane to hydrogen is 1:1.11, the preset deposition power is 150 W, the deposition temperature is 180 °C, and the reaction gas pressure is 0.5 Torr.
[0151] A 6nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include:
[0152] Hydrogen and silane were introduced into the reaction chamber as reaction gases, with a hydrogen flow rate of 1000 sccm and a silane flow rate of 900 sccm. The flow rate ratio of silane to hydrogen was 1:1.11. The preset deposition power was 150 W, the deposition temperature was 180 °C, and the reaction gas pressure was 0.5 Torr.
[0153] (2) A boron-doped p-type microcrystalline silicon layer with a thickness of 34 nm is deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0154] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 75 sccm, borane is 60 sccm, hydrogen is 27000 sccm, and carbon dioxide is 20 sccm. The flow ratio of silane to hydrogen is 1:360. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0155] (3) A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 28 nm is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0156] Silane, phosphine, and hydrogen are introduced into the reaction chamber, with a flow rate of 55 sccm for silane, 380 sccm for phosphine, and 10000 sccm for hydrogen. The preset deposition power is 4500 W, the deposition temperature is 190 °C, and the reaction gas pressure is 4.5 Torr.
[0157] (4) ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively by magnetron sputtering, with a thickness of 95 nm for both layers.
[0158] (5) Silver grid electrodes with a thickness of 15 μm were fabricated on the ITO transparent conductive layer on the front and back sides of the n-type silicon wafer using screen printing to obtain the heterojunction solar cell, the structural schematic diagram of which is shown below. Figure 2 As shown, it includes a back metal electrode 101, a back transparent conductive layer 91, a back boron-doped p-type microcrystalline silicon layer 42, a back intrinsic amorphous silicon layer 2, an n-type silicon wafer 1, a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92, and a front metal electrode 102, all stacked together.
[0159] Comparative Example 2
[0160] This comparative example provides a method for fabricating a heterojunction solar cell, the method comprising the following steps:
[0161] (1) A 6 nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer by PECVD. The specific steps include: introducing hydrogen and silane as reaction gases into the reaction chamber, wherein the flow rate of hydrogen is 1000 sccm, the flow rate of silane is 900 sccm, the flow rate ratio of silane to hydrogen is 1:1.11, the preset deposition power is 150 W, the deposition temperature is 155 °C, and the reaction gas pressure is 0.5 Torr.
[0162] A 6nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include:
[0163] Hydrogen and silane were introduced into the reaction chamber as reaction gases, with a hydrogen flow rate of 1000 sccm and a silane flow rate of 900 sccm. The flow rate ratio of silane to hydrogen was 1:1.11. The preset deposition power was 150 W, the deposition temperature was 185 °C, and the reaction gas pressure was 0.5 Torr.
[0164] (2) A low-concentration boron-doped p-type microcrystalline silicon layer with a thickness of 1 nm is deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0165] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 75 sccm, borane is 25 sccm, hydrogen is 27000 sccm, and carbon dioxide is 20 sccm. The flow rate ratio of silane to hydrogen is 1:360. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0166] (3) A medium-concentration boron-doped p-type microcrystalline silicon layer with a thickness of 15 nm was deposited on a low-concentration boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0167] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 75 sccm, borane is 60 sccm, hydrogen is 27000 sccm, and carbon dioxide is 20 sccm. The flow ratio of silane to hydrogen is 1:360. The preset deposition power is 6000W, the deposition temperature is 160℃, and the reaction gas pressure is 4.5 Torr.
[0168] (4) A high-concentration boron-doped p-type microcrystalline silicon layer with a thickness of 4 nm was deposited on a medium-concentration boron-doped p-type microcrystalline silicon layer by PECVD. The specific steps include:
[0169] Silane, borane, hydrogen, and carbon dioxide are introduced into the reaction chamber. The flow rates of silane are 75 sccm, borane is 90 sccm, hydrogen is 27000 sccm, and carbon dioxide is 20 sccm. The flow ratio of silane to hydrogen is 1:360. The preset deposition power is 6000W, the deposition temperature is 155℃, and the reaction gas pressure is 4.5 Torr.
[0170] (5) A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 28 nm is deposited on the front intrinsic amorphous silicon layer in a direction away from the n-type silicon wafer by PECVD. The specific steps include:
[0171] Silane, phosphine, and hydrogen are introduced into the reaction chamber, with a flow rate of 55 sccm for silane, 380 sccm for phosphine, and 11000 sccm for hydrogen. The preset deposition power is 4500 W, the deposition temperature is 190 °C, and the reaction gas pressure is 4.5 Torr.
[0172] (6) ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively by magnetron sputtering, with a thickness of 95 nm for both layers.
[0173] (7) Silver grid electrodes with a thickness of 15 μm were fabricated on the ITO transparent conductive layer on the front and back sides of the n-type silicon wafer by screen printing to obtain the heterojunction solar cell, the structural schematic diagram of which is shown below. Figure 3 As shown, the structure includes a back metal electrode 101, a back transparent conductive layer 91, a high-concentration boron-doped p-type microcrystalline silicon layer 62, a medium-concentration boron-doped p-type microcrystalline silicon layer 52, a low-concentration boron-doped p-type microcrystalline silicon layer 43, a back intrinsic amorphous silicon layer 2, an n-type silicon wafer 1, a front intrinsic amorphous silicon layer 3, a phosphorus-doped n-type microcrystalline silicon layer 8, a front transparent conductive layer 92, and a front metal electrode 102, all stacked together.
[0174] Comparative Example 3
[0175] The difference between this comparative example and Example 1 is that the flow rate of borane in step (2) or step (3) is adjusted so that the flow rate ratio of borane for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:2.
[0176] The remaining preparation methods and parameters are consistent with those in Example 1.
[0177] Comparative Example 4
[0178] The difference between this comparative example and Example 1 is that the flow rate of borane in step (2) or step (3) is adjusted so that the ratio of borane flow rates for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:3.5.
[0179] The remaining preparation methods and parameters are consistent with those in Example 1.
[0180] Comparative Example 5
[0181] The difference between this comparative example and Example 1 is that the flow rate of borane in step (4) or step (5) is adjusted so that the flow rate ratio of borane for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:15.
[0182] The remaining preparation methods and parameters are consistent with those in Example 1.
[0183] Comparative Example 6
[0184] The difference between this comparative example and Example 1 is that the flow rate of borane in step (4) or step (5) is adjusted so that the flow rate ratio of borane for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:35.
[0185] The remaining preparation methods and parameters are consistent with those in Example 1.
[0186] Comparative Example 7
[0187] The difference between this comparative example and Example 1 is that steps (2) and (3) are reversed with steps (4) and (5). Specifically, a third boron-doped p-type microcrystalline silicon layer and a fourth boron-doped p-type microcrystalline silicon layer are deposited first on the intrinsic amorphous silicon layer on the back side, and then a first boron-doped p-type microcrystalline silicon layer and a second boron-doped p-type microcrystalline silicon layer are deposited.
[0188] The remaining preparation methods and parameters are consistent with those in Example 1.
[0189] Performance testing
[0190] The heterojunction solar cells provided in the above embodiments and comparative examples were tested for back hole tunneling contact resistivity and photoelectric performance.
[0191] The testing conditions were as follows: electrodes were printed on glass using a special metal mask, and the contact was then tested. Photoelectric performance was tested using an IV testing machine under one day's sunlight.
[0192] The test results are shown in Table 1.
[0193] Table 1
[0194]
[0195]
[0196] analyze:
[0197] As shown in the table above, this invention designs a four-layer boron-doped p-type microcrystalline silicon system. The doping gradient is designed by controlling the boron source flux ratio between each layer, ensuring that the first and second boron-doped p-type microcrystalline silicon layers provide sufficient built-in electric field strength and doping concentration. Under high doping gradient conditions, the third and fourth boron-doped p-type microcrystalline silicon layers exhibit enhanced upward band bending, leading to more efficient hole tunneling through ia-Si:H. This results in hole accumulation at the transparent electrode / pa-Si:H heterojunction. The accumulated holes can easily recombine with electrons in the transparent electrode through increased trap states, leading to a decrease in hole tunneling resistivity and an increase in the cell fill factor (FF). Furthermore, the enhanced upward band bending also allows electrons to be repelled from the c-Si / pa-Si:H interface. Therefore, the above process optimization further enhances hole extraction, improves carrier transport, and the synergistic effect of the four layers significantly reduces back-side hole tunneling contact, thereby improving cell efficiency.
[0198] As can be seen from Examples 1 and 4-5, if the thickness of the third boron-doped p-type microcrystalline silicon layer is too thick, it will affect the passivation performance; if the thickness of the fourth boron-doped p-type microcrystalline silicon layer is too thick, it will result in excessive doping and increased recombination.
[0199] As can be seen from Example 1 and Comparative Examples 1-2, if the boron-doped p-type microcrystalline silicon layer is a single-layer film, effective doping cannot be formed, thus increasing the contact. If the boron-doped p-type microcrystalline silicon layer adopts a three-layer structure composed of low, medium, and high concentrations of boron doping, the hole concentration is low.
[0200] As can be seen from Example 1 and Comparative Examples 3-4, if the borane flow rate ratio of the deposited first boron-doped p-type microcrystalline silicon layer to the second boron-doped p-type microcrystalline silicon layer is too high, the doping concentration will be too high, leading to increased recombination. If the borane flow rate ratio of the deposited first boron-doped p-type microcrystalline silicon layer to the second boron-doped p-type microcrystalline silicon layer is too low, effective doping cannot be achieved.
[0201] As can be seen from Example 1 and Comparative Examples 5-6, if the borane flow rate ratio between the deposited third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is too high, carrier recombination increases. If the borane flow rate ratio between the deposited third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is too low, hole accumulation cannot be effectively formed.
[0202] As can be seen from Example 1 and Comparative Example 7, if a third boron-doped p-type microcrystalline silicon layer and a fourth boron-doped p-type microcrystalline silicon layer are deposited first on the intrinsic amorphous silicon layer on the back side, and then a first boron-doped p-type microcrystalline silicon layer and a second boron-doped p-type microcrystalline silicon layer are deposited, it is not conducive to hole tunneling and increases the contact.
[0203] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.
Claims
1. A method for fabricating a heterojunction solar cell, characterized in that, The preparation method includes the following steps: An intrinsic amorphous silicon layer is deposited on each of the opposite surfaces of an n-type silicon wafer, namely the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer. A first boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, and a fourth boron-doped p-type microcrystalline silicon layer are sequentially deposited on the intrinsic amorphous silicon layer on the back side in a direction away from the n-type silicon wafer; wherein, the boron source flux ratio for depositing the first boron-doped p-type microcrystalline silicon layer and the second boron-doped p-type microcrystalline silicon layer is 1:(2.5-3), and the boron source flux ratio for depositing the third boron-doped p-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer is 1:(20-30); A phosphorus-doped n-type microcrystalline silicon layer is deposited on the intrinsic amorphous silicon layer on the front side. Then, transparent conductive layers are deposited on the phosphorus-doped n-type microcrystalline silicon layer and the fourth boron-doped p-type microcrystalline silicon layer, respectively. Subsequently, metal electrodes are fabricated on the transparent conductive layers on the front and back sides of the n-type silicon wafer to obtain the heterojunction solar cell.
2. The preparation method according to claim 1, characterized in that, The deposition method of the intrinsic amorphous silicon layer includes PECVD; Preferably, the deposition methods for both the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer are PECVD, and the specific parameters for each layer independently include: The reaction gases include silicon source and hydrogen, the reaction gas pressure is 0.4-0.6 Torr, the deposition power is 100-200W, and the deposition temperature is 180-220℃; Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(1-1.5); Preferably, the thickness of the front intrinsic amorphous silicon layer and the back intrinsic amorphous silicon layer is independently 5-7 nm.
3. The preparation method according to claim 1, characterized in that, The deposition method for the first boron-doped p-type microcrystalline silicon layer includes PECVD. Preferably, the deposition method of the first boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include: The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, the deposition power is 5000-7000W, and the deposition temperature is 140-170℃. Preferably, the flow rate of the boron source is 25-35 sccm; Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(350-380); Preferably, the thickness of the first boron-doped p-type microcrystalline silicon layer is 1-2 nm.
4. The preparation method according to claim 3, characterized in that, The reactant gases also include carbon dioxide; Preferably, the flow rate of the carbon dioxide is 100-200 sccm.
5. The preparation method according to claim 1, characterized in that, The deposition method for the second boron-doped p-type microcrystalline silicon layer includes PECVD. Preferably, the deposition method for the second boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include: The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, the deposition power is 5000-7000W, and the deposition temperature is 140-170℃. Preferably, the flow rate of the boron source is 60-80 sccm; Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350); Preferably, the thickness of the second boron-doped p-type microcrystalline silicon layer is 23-28 nm; Preferably, the reactant gas further includes carbon dioxide; Preferably, the flow rate of the carbon dioxide is 15-25 sccm.
6. The preparation method according to claim 1, characterized in that, The deposition method for the third boron-doped p-type microcrystalline silicon layer includes PECVD. Preferably, the deposition method of the third boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include: The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, the deposition power is 5000-7000W, and the deposition temperature is 140-170℃. Preferably, the flow rate of the boron source is 10-20 sccm; Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350); Preferably, the thickness of the third boron-doped p-type microcrystalline silicon layer is 1-2 nm; Preferably, the reactant gas further includes carbon dioxide; Preferably, the flow rate of the carbon dioxide is 15-25 sccm.
7. The preparation method according to claim 1, characterized in that, The deposition method for the fourth boron-doped p-type microcrystalline silicon layer includes PECVD. Preferably, the deposition method for the fourth boron-doped p-type microcrystalline silicon layer is PECVD, and the specific parameters include: The reaction gases include silicon source, boron source and hydrogen, the reaction gas pressure is 4-5 Tor, the deposition power is 5000-7000W, and the deposition temperature is 140-170℃. Preferably, the flow rate of the boron source is 300-400 sccm; Preferably, the flow rate ratio of the silicon source to hydrogen is 1:(300-350); Preferably, the thickness of the fourth boron-doped p-type microcrystalline silicon layer is 4-6 nm.
8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: A 5-7 nm thick intrinsic amorphous silicon layer is deposited on the back side of an n-type silicon wafer using PECVD. The specific steps include: introducing hydrogen and a silicon source as reaction gases into a reaction chamber, wherein the flow rate of hydrogen is 800-1200 sccm, the flow rate of silicon source is 800-1000 sccm, the flow rate ratio of silicon source to hydrogen is 1:(1-1.5), the preset deposition power is 100-200W, the deposition temperature is 180-220℃, and the reaction gas pressure is 0.4-0.6 Torr. A 5-7 nm thick intrinsic amorphous silicon layer is deposited on the front side of an n-type silicon wafer using PECVD. The specific steps include: introducing hydrogen and silicon source as reaction gases into a reaction chamber, wherein the flow rate of hydrogen is 800-1200 sccm, the flow rate of silicon source is 800-1000 sccm, the flow rate ratio of silicon source to hydrogen is 1:(1-1.5), the preset deposition power is 100-200W, the deposition temperature is 180-220℃, and the reaction gas pressure is 0.4-0.6 Torr. A first boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm is deposited on the intrinsic amorphous silicon layer on the back side along the direction away from the n-type silicon wafer by PECVD. The specific steps include: introducing a silicon source, a boron source, hydrogen gas and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the boron source is 25-35 sccm, the flow rate of the hydrogen gas is 25000-29000 sccm, the flow rate of the carbon dioxide gas is 100-200 sccm, the flow rate ratio of the silicon source to the hydrogen gas is 1:(350-380), the preset deposition power is 5000-7000W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr. The deposition of a second boron-doped p-type microcrystalline silicon layer with a thickness of 23-28 nm on a first boron-doped p-type microcrystalline silicon layer by PECVD method includes the following steps: introducing a silicon source, a boron source, hydrogen gas, and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the boron source is 60-80 sccm, the flow rate of the hydrogen gas is 15000-28000 sccm, the flow rate of the carbon dioxide gas is 15-25 sccm, the flow rate ratio of the silicon source to the hydrogen gas is 1:(300-350), the preset deposition power is 5000-7000W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr. The deposition of a third boron-doped p-type microcrystalline silicon layer with a thickness of 1-2 nm on a second boron-doped p-type microcrystalline silicon layer by PECVD method includes the following steps: introducing a silicon source, a boron source, hydrogen gas, and carbon dioxide into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the boron source is 10-20 sccm, the flow rate of the hydrogen gas is 15000-28000 sccm, the flow rate of the carbon dioxide gas is 15-25 sccm, the flow rate ratio of the silicon source to the hydrogen gas is 1:(300-350), the preset deposition power is 5000-7000W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr. The deposition of a fourth boron-doped p-type microcrystalline silicon layer with a thickness of 4-6 nm on a third boron-doped p-type microcrystalline silicon layer by PECVD method includes the following steps: introducing a silicon source, a boron source and hydrogen gas into a reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the boron source is 300-400 sccm, the flow rate of the hydrogen gas is 15000-28000 sccm, the flow rate ratio of silicon source to hydrogen gas is 1:(300-350), the preset deposition power is 5000-7000W, the deposition temperature is 140-170℃, and the reaction gas pressure is 4-5 Torr. A phosphorus-doped n-type microcrystalline silicon layer with a thickness of 25-30 nm is deposited on the intrinsic amorphous silicon layer on the front side along the direction away from the n-type silicon wafer by PECVD. The specific steps include: introducing a silicon source, a phosphorus source and hydrogen gas into the reaction chamber, wherein the flow rate of the silicon source is 50-80 sccm, the flow rate of the phosphorus source is 300-800 sccm, the flow rate of the hydrogen gas is 8000-12000 sccm, the preset deposition power is 4000-6000 W, the deposition temperature is 180-200℃, and the reaction gas pressure is 4-6 Torr. ITO transparent conductive layers were deposited on phosphorus-doped n-type microcrystalline silicon layers and fourth boron-doped p-type microcrystalline silicon layers respectively using magnetron sputtering, with thicknesses of 80-110 nm for each layer. The heterojunction solar cell is obtained by fabricating metal electrodes on the transparent conductive layers on the front and back sides of an n-type silicon wafer using screen printing.
9. A heterojunction solar cell, characterized in that, The heterojunction solar cell is prepared using the preparation method described in any one of claims 1-8; The heterojunction solar cell includes a back metal electrode, a back transparent conductive layer, a fourth boron-doped p-type microcrystalline silicon layer, a third boron-doped p-type microcrystalline silicon layer, a second boron-doped p-type microcrystalline silicon layer, a first boron-doped p-type microcrystalline silicon layer, a back intrinsic amorphous silicon layer, an n-type silicon wafer, a front intrinsic amorphous silicon layer, a phosphorus-doped n-type microcrystalline silicon layer, a front transparent conductive layer, and a front metal electrode, all stacked together.
10. A silicon solar cell, characterized in that, The silicon solar cell includes the heterojunction solar cell as described in claim 9.