Solar cell and preparation method thereof
By employing multiple passivation layers with varying densities in solar cells and controlling the amount of precursor introduced and the alternating pulse time, the problem of poor passivation effect in existing ALD processes has been solved, thereby improving the conversion efficiency and passivation effect of solar cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-28
- Publication Date
- 2026-03-13
AI Technical Summary
The alumina film structure prepared by the existing ALD process is simple, resulting in poor passivation effect and affecting the conversion efficiency of solar cells.
By employing multiple passivation layers with varying densities, and by adjusting the proportion of precursor injection and the alternating pulse time, a first passivation layer with high density and a second passivation layer with low density are formed. Combined with a tunneling passivation contact structure, the passivation effect is enhanced.
It improves the conversion efficiency of solar cells, enhances the field passivation and chemical passivation effects, and improves the operability of the ALD process.
Smart Images
Figure CN121665751A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of solar cell technology, specifically relating to a solar cell and a method for preparing a solar cell. Background Technology
[0002] In the solar cell manufacturing process, atomic layer deposition (ALD) is a crucial step. It's a deposition method that deposits materials onto a substrate surface layer by layer in the form of single atomic layers. By alternately introducing precursors onto the substrate, an aluminum oxide film is deposited on the front side of the cell, providing both chemical and field passivation. This improves the cell's on-state voltage and fill factor, thereby enhancing its conversion efficiency.
[0003] In traditional ALD (Alternating Current Deposition) processes, the alumina film structure is uniform, with virtually no differences within the entire alumina film. Therefore, alumina films prepared using existing ALD processes suffer from drawbacks such as simple structure, poor operability, and inadequate passivation, which negatively impact battery conversion efficiency.
[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention
[0005] The purpose of this invention is to provide a solar cell and a method for preparing a solar cell, which improves the passivation effect and increases the conversion efficiency of the cell by setting multiple passivation layers with different densities.
[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:
[0007] A solar cell, comprising:
[0008] A silicon substrate having a first surface and a second surface disposed opposite to each other;
[0009] A first doped layer is formed on the first surface;
[0010] A passivation structure is formed on the first doped layer. The passivation structure includes at least a first passivation layer and a second passivation layer, wherein the density of the first passivation layer is higher than the density of the second passivation layer.
[0011] In one or more embodiments of the present invention, the first passivation layer includes a first alumina layer, the second passivation layer includes a second alumina layer, and the porosity of the first alumina layer is lower than that of the second alumina layer.
[0012] In one or more embodiments of the present invention, the solar cell further includes:
[0013] A tunneling passivation contact structure is formed on the second surface, the tunneling passivation contact structure comprising a tunneling layer and a second doped layer stacked sequentially;
[0014] A first electrode is formed on the first surface and is in contact with the first doped layer; and
[0015] The second electrode is formed on the second surface and is in contact with the second doped layer.
[0016] A method for preparing a solar cell, the method comprising the following steps:
[0017] A silicon substrate is provided, the silicon substrate having a first surface and a second surface disposed opposite to each other;
[0018] A first doped layer is formed on the first surface;
[0019] A passivation structure is formed on the first doped layer, the passivation structure comprising at least a first passivation layer and a second passivation layer, wherein the density of the first passivation layer is higher than the density of the second passivation layer.
[0020] In one or more embodiments of the present invention, the density of the passivation layer is controlled by adjusting the proportion of different precursors introduced to form the passivation layer.
[0021] In one or more embodiments of the present invention, the proportion of different precursors introduced is controlled by adjusting the alternating pulse introduction time and / or alternating pulse introduction flow rate of different precursors forming the passivation layer.
[0022] In one or more embodiments of the present invention, the precursor includes a first precursor containing aluminum and a surface-reacted oxygen of the first aluminum precursor;
[0023] The proportion of the first precursor inlet is adjusted to be greater than half of the total precursor inlet to form the first passivation layer.
[0024] The proportion of the first precursor ingress is adjusted to be less than or equal to half of the total precursor ingress to form the second passivation layer.
[0025] The density of the first passivation layer is higher than that of the second passivation layer.
[0026] In one or more embodiments of the present invention, the precursor includes a second precursor containing hydrogen;
[0027] The hydrogen content generated during the formation of the passivation structure can be controlled by adjusting the proportion of the second precursor.
[0028] In one or more embodiments of the present invention, the proportion of the second precursor introduced is adjusted to be less than half of the total amount of the precursor introduced to form the first passivation layer.
[0029] The proportion of the second precursor introduced is adjusted to be greater than or equal to half of the total amount of the precursor introduced, thereby forming the second passivation layer;
[0030] The hydrogen content generated during the formation of the second passivation layer is higher than the hydrogen content generated during the formation of the first passivation layer.
[0031] In one or more embodiments of the present invention, the first precursor comprises gaseous trimethylaluminum, the second precursor comprises gaseous H2O, the first passivation layer comprises a first alumina layer, and the second passivation layer comprises a second alumina layer.
[0032] In one or more embodiments of the present invention, the first alumina layer is formed by increasing the proportion of trimethylaluminum to more than half of the total amount of precursors introduced.
[0033] The second alumina layer is formed by increasing the proportion of H2O introduced to more than half of the total amount of precursor introduced.
[0034] The porosity of the first alumina layer is lower than that of the second alumina layer;
[0035] The hydrogen content generated during the formation of the second alumina layer is higher than the hydrogen content generated during the formation of the first alumina layer.
[0036] In one or more embodiments of the present invention, the first passivation layer and the second passivation layer are prepared using an atomic layer deposition process.
[0037] In one or more embodiments of the present invention, the preparation method further includes:
[0038] A tunneling passivation contact structure is formed on the second surface, the tunneling passivation contact structure comprising a tunneling layer and a second doped layer stacked sequentially.
[0039] A first electrode is formed on the first surface in contact with the first doped layer; and
[0040] A second electrode is formed on the second surface in contact with the second doped layer.
[0041] In one or more embodiments of the present invention, a tunneling passivation contact structure is formed on the second surface, including:
[0042] A tunneling layer is deposited on the second surface;
[0043] An amorphous silicon layer is deposited on the surface of the tunneling layer; and
[0044] The amorphous silicon layer is phosphorus-doped to form a doped polycrystalline silicon layer; or,
[0045] A tunneling passivation contact structure is formed on the second surface, including:
[0046] A tunneling layer is deposited on the second surface;
[0047] A doped amorphous silicon layer is deposited on the surface of the tunneling layer; and
[0048] The doped amorphous silicon layer is annealed to form a doped polycrystalline silicon layer.
[0049] Compared with the prior art, the solar cell and its preparation method of the present invention, by forming multiple passivation layers with different densities, make the ALD process more operable, improve the passivation effect, and increase the conversion efficiency of the cell. Compared with the formation of a single passivation structure in the prior art, the ALD process for forming multiple passivation layers is more operable.
[0050] The solar cell and its preparation method of the present invention have a high negative charge intensity in the passivation layer with relatively high density, which improves the field passivation effect; the passivation layer with relatively low density can increase the H atom content during the preparation process, and the passivation layer with relatively low density can be more easily burned through by the paste for subsequent electrode formation, further improving the chemical passivation effect and the fill factor FF. Attached Figure Description
[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0052] Figure 1 This is a schematic diagram of the structure of a solar cell in one embodiment of the present invention;
[0053] Figures 2a-2g This is a schematic diagram of the process steps of a solar cell in one embodiment of the present invention. Detailed Implementation
[0054] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.
[0055] As mentioned in the background section, the passivation structure of existing solar cells is formed by uniform deposition through the ALD process. The passivation structure is basically indistinguishable inside, which results in disadvantages such as simple structure, weak operability, and poor passivation effect, thus affecting the conversion efficiency of the cell.
[0056] It is understandable that the passivation layer on the front of the battery, preferably an aluminum oxide film layer, has chemical passivation and field passivation effects, which can improve the battery's opening voltage and fill factor, thereby improving the battery's conversion efficiency.
[0057] However, the factors affecting the chemical passivation and field passivation effects of alumina films include the density of the alumina film and the amount of hydrogen atoms generated during its formation. These two factors exhibit an inverse relationship: if a high density of the alumina film is prioritized during formation, the amount of hydrogen atoms generated will decrease. This results in dangling bonds on the silicon substrate surface not being saturated with hydrogen atoms, thus failing to reduce interface defects and consequently reducing the effectiveness of chemical passivation. Conversely, increasing the amount of hydrogen atoms generated during alumina film formation will decrease the density of the resulting alumina film, thereby reducing its field passivation effect.
[0058] This invention provides a solar cell and a method for fabricating a solar cell. By forming multiple passivation layers with different densities, the chemical passivation and field passivation effects of the passivation layers are balanced, making the ALD process more operable, improving the passivation effect, and increasing the cell's conversion efficiency. In the process of fabricating different passivation layers, fabricating a high-density passivation layer enhances the field passivation effect, while fabricating a low-density passivation layer increases the hydrogen atom content generated during the fabrication process, enhancing the chemical passivation effect, thereby improving the cell's conversion efficiency.
[0059] The method for fabricating a solar cell according to the present invention can control the density of the formed passivation layer by adjusting the proportion of different precursors introduced during the fabrication of a passivation structure comprising multiple passivation layers. For example, the proportion of different precursors introduced can be adjusted by controlling the alternating pulse introduction time and / or alternating pulse introduction flow rate of the different precursors, thereby controlling the density of the formed passivation layer.
[0060] In a preferred embodiment, the precursor includes a first precursor containing aluminum and a second precursor containing hydrogen. The second precursor may contain surface reactive oxygen of the first precursor of aluminum. The proportion of the first precursor introduced is adjusted to be greater than half of the total amount of the precursor introduced, and the proportion of the second precursor introduced is adjusted to be less than or equal to half of the total amount of the precursor introduced to form a first passivation layer with high density; the proportion of the first precursor introduced is adjusted to be less than or equal to half of the total amount of the precursor introduced, and the proportion of the second precursor introduced is adjusted to be greater than half of the total amount of the precursor introduced to form a second passivation layer with low density, and at the same time, a higher content of hydrogen atoms is generated. These hydrogen atoms can saturate the dangling bonds on the surface of the silicon substrate, reduce interface state defects, and after sintering and promotion, these hydrogen atoms enter the silicon substrate to passivate the grain boundary defects inside the silicon substrate. The formation of the second passivation layer with low density can also make the subsequent paste of the first electrode easier to burn through, so that the paste of the first electrode is easier to contact the first doped layer (i.e., the emitter) on the front surface of the silicon substrate, improving the fill factor FF.
[0061] The present invention will be further described below in conjunction with specific embodiments.
[0062] As Figure 1 shown, a TOPCon solar cell in an embodiment of the present invention includes a silicon substrate 10. Combining Figure 2a shown, the silicon substrate 10 includes a first surface S1 and a second surface S2 arranged oppositely. The first surface S1 is the front surface (i.e., the light-receiving surface) of the silicon substrate 10, and the second surface S2 is the back surface (i.e., the backlight surface) of the silicon substrate 10.
[0063] Furthermore, a light-trapping structure (not shown in the figure) is formed on the first surface S1 of the silicon substrate 10. For example, a pyramid light-trapping structure can be formed on the first surface S1 of the silicon substrate 10 by alkaline texturing.
[0064] In this embodiment, a first doped layer 11 (i.e., the emitter) is formed on the first surface S1 of the silicon substrate 10 by a diffusion process or a PECVD process. Exemplarily, the first doped layer 11 is a P-type doped layer (i.e., a P+ emitter) formed by a boron doping process. The boron source can be BBr3 or BCl3.
[0065] Refer Figure 1 shown, a tunneling passivation contact structure 20 is formed on the second surface S2 of the silicon substrate 10 in this embodiment. The tunneling passivation contact structure 20 includes a tunneling layer 21 and a second doped layer 22 stacked in sequence. Among them, the tunneling layer 21 is preferably a silicon oxide layer with a thickness of 1 nm to 2 nm. The second doped layer 22 is a phosphorus-doped polysilicon layer, which can be prepared by an LPCVD (low-pressure chemical vapor deposition) or a PECVD (plasma-enhanced chemical vapor deposition) process.
[0066] In this embodiment, a passivation structure 30 is formed on the first surface S1 of the silicon substrate 10. The passivation structure 30 is preferably disposed on the first doping layer 11 and includes multiple passivation layers stacked in sequence.
[0067] In this embodiment, the multiple passivation layers include two layers, namely a first passivation layer 31 and a second passivation layer 32. The density of the first passivation layer 31 is higher than that of the second passivation layer 32. The first passivation layer 31 and the second passivation layer 32 can be prepared by an atomic layer chemical vapor deposition process. Both the first passivation layer 31 and the second passivation layer 32 are alumina layers, and the porosity of the alumina in the first passivation layer 31 (defined as the first alumina layer) is lower than the porosity of the alumina in the second passivation layer 32 (defined as the second alumina layer).
[0068] Specifically, by alternately pulsing the gas-phase precursors TMA (trimethylaluminum) and H2O into the reaction chamber, a multi-layer alumina layer is chemically adsorbed and deposited on the front surface of the silicon substrate 10. By controlling the alternate pulsing time and / or the flow rate of the gas-phase precursors TMA (trimethylaluminum) and H2O, the density of the formed alumina layer is controlled, and at the same time, the content of H atoms generated during the formation of alumina is controlled. For example Figure 1 As shown, in this embodiment, the two-layer alumina layer, where the first alumina layer (the first passivation layer 31) is prepared by increasing the proportion of the precursor TMA, and the second alumina layer (the second passivation layer 32) is prepared by increasing the proportion of the precursor H2O.
[0069] It can be understood that in other embodiments, there may be more than two passivation layers, and among them, the density of at least one passivation layer is higher than that of the remaining passivation layers.
[0070] Preferably, a first antireflection layer 41 is further disposed on the first surface S1 of the silicon substrate 10 in this embodiment, and a second antireflection layer 42 is further disposed on the second surface S2 of the silicon substrate 10. Exemplarily, the first antireflection layer 41 and the second antireflection layer 42 can be a stacked film formed by any one or more of a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer.
[0071] In addition, the first electrode 51 in this embodiment is located on the first surface S1 of the silicon substrate 10 and is in contact with the first doping layer 11, and the second electrode 52 is located on the second surface S2 of the silicon substrate 10 and is in contact with the second doping layer 22.
[0072] The preparation method of the solar cell in this embodiment specifically includes the following steps:
[0073] 1. Double-sided texturing
[0074] Refer Figure 2aAs shown, a silicon substrate 10 is provided. The silicon substrate includes a first surface S1 and a second surface S2 which are oppositely arranged. The first surface S1 is the front surface (i.e., the light-receiving surface) of the silicon substrate 10, and the second surface S2 is the back surface (i.e., the backlight surface) of the silicon substrate 10.
[0075] In this embodiment, a pyramid-shaped light-trapping structure is formed on the first surface S1 and the second surface S2 of the silicon substrate 10 through an alkaline texturing process. Among them, the alkaline solution can include NaOH or KOH.
[0076] 2. Boron diffusion
[0077] As Figure 2b shown, a first doped layer (i.e., P+ emitter) 11 with P-type doping is formed on the first surface S1 of the silicon substrate 10 through a boron diffusion process. Specifically, the diffusion is carried out by using a boron source deposition and push method in a high-temperature furnace tube. Exemplarily, the silicon substrate 10 is placed in the furnace tube, and when heated to a certain temperature, an impurity boron source gas (BBr3 or BCl3) is introduced. Under the action of oxygen, the boron source gas reacts with the silicon substrate 10 to form P-type silicon (the first doped layer 11) and borosilicate glass (BSG12), forming a PN junction (the silicon substrate 10 is N-type). In the boron diffusion process, BSG (not shown) is also formed on the second surface S2 and the edge of the silicon substrate 10.
[0078] 3. Removal of BSG + polishing
[0079] As Figure 2c shown, the boron-diffused silicon substrate 10 is washed with an acid solution to remove the BSG12 on the back surface and the edge, then washed with an alkaline solution to remove the PN junction on the back surface while polishing the back surface, and finally cleaned again.
[0080] 4. Preparation of the back surface tunneling passivation contact structure
[0081] As Figure 2d shown, a tunneling layer 21, a second doped layer 22, and an oxide layer 23 are sequentially stacked on the second surface S2. The second doped layer 22 is preferably a phosphorus-doped polysilicon layer.
[0082] Exemplarily, in this embodiment, the LPCVD (low-pressure chemical vapor deposition) process can be used. Under the state of low pressure and high temperature, oxygen is introduced to form an ultra-thin tunneling layer SiO2 with a thickness of about 1 nm to 2 nm on the back surface of the silicon substrate 10, then SiH4 is introduced to form an amorphous silicon layer, and finally a gas containing a phosphorus source, such as POCl3, is introduced. Under the action of high temperature, the amorphous silicon layer is crystallized to form a highly doped polysilicon layer.
[0083] Exemplarily, in this embodiment, a PECVD (Plasma Enhanced Chemical Vapor Deposition) process can also be used. Under the action of high temperature and radio frequency glow discharge, N2O is introduced to form an ultra-thin tunneling layer SiO2 on the back surface of the silicon substrate 10, with a thickness of about 1 nm to 2 nm. Then, SiH4 and PH3 are introduced to form highly doped amorphous silicon, and finally, high-temperature annealing is performed to form a highly doped polycrystalline silicon layer.
[0084] The oxide layer can be SiO X , SiO X N Y or SiN X .
[0085] 5. Removal of overplating and RCA cleaning
[0086] As shown in the reference Figure 2e , the phosphosilicate glass (PSG) on the front surface and edge of the silicon substrate 10 is washed off with an acid solution, then the tunneling passivation contact structure (overplating) on the front surface and edge of the silicon substrate 10 is washed off with an alkaline solution, then the BSG on the front surface and the PSG on the back surface of the silicon substrate 10 are washed off with an acid solution, and finally, RCA cleaning is performed to remove the oxide layer. RCA cleaning is a prior art and will not be elaborated here.
[0087] 6. Preparation of the passivation structure
[0088] As shown in the reference Figure 2f , an atomic layer chemical vapor deposition process (ALD process) is used to prepare a passivation structure 30 with multiple passivation layers stacked on the first surface S1 of the silicon substrate 10.
[0089] In this embodiment, the passivation structure 30 includes two passivation layers, namely a first passivation layer 31 and a second passivation layer 32. The density of the first passivation layer 31 is higher than that of the second passivation layer 32, and the porosity of the first passivation layer 31 is lower than that of the second passivation layer 32. Density and porosity are inversely proportional to each other. The first passivation layer 31 is disposed on the surface of the first doping layer 11, and the second passivation layer 32 is disposed on the surface of the first passivation layer 31. Both the first passivation layer 31 and the second passivation layer 32 are alumina layers. By alternately pulsing the gas-phase precursors TMA (trimethylaluminum) and H2O into the reaction chamber, an alumina layer is chemically adsorbed and deposited on the front surface of the silicon substrate 10. By controlling the alternate pulsing time and / or the flow rate of the gas-phase precursors TMA (trimethylaluminum) and H2O, the density and porosity of the formed alumina layer are controlled, and at the same time, the content of H atoms generated during the formation of alumina is controlled.
[0090] As Figure 1As shown, the first alumina layer (the first passivation layer 31) is prepared by increasing the proportion of the precursor TMA (trimethylaluminum) in TMA and H2O. Preferably, the proportion of the introduced amount of TMA is increased to be greater than half of the total introduced amount of the precursors. For example, when the unit flow rates of TMA (trimethylaluminum) and H2O are the same, the introduction time can be adjusted so that TMA:H2O = (7 - 9):(4 - 6), thereby increasing the density of the formed first alumina layer (the first passivation layer 31) and reducing the porosity of the first alumina layer (the first passivation layer 31). The second alumina layer (the second passivation layer 32) is prepared by increasing the proportion of H2O in the precursor TMA (trimethylaluminum) and H2O. Preferably, the proportion of the introduced amount of H2O is increased to be greater than half of the total introduced amount of the precursors. For example, when the unit flow rates of TMA (trimethylaluminum) and H2O are the same, the introduction time can be adjusted so that TMA:H2O = (4 - 6):(7 - 9), thereby reducing the density of the formed second alumina layer (the second passivation layer 32) and increasing the porosity of the second alumina layer (the second passivation layer 32), and at the same time generating more H atoms that can saturate the dangling bonds on the surface of the silicon substrate 10.
[0091] In other embodiments, more than two passivation layers can be prepared, but one of the above-mentioned first passivation layer 31 and one of the above-mentioned second passivation layer 32 need to be included. The relative distances of the first passivation layer 31 and the second passivation layer 32 from the first doping layer 11 are not limited, that is, the first passivation layer 31 can be relatively closer to the first doping layer 11, or the second passivation layer 32 can be relatively closer to the first doping layer 11.
[0092] 7. Preparation of the antireflection layer
[0093] Refer to Figure 2g As shown, a first antireflection layer 41 and a second antireflection layer 42 are respectively prepared on the first surface S1 and the second surface S2 of the silicon substrate 10. The first antireflection layer 31 and the second antireflection layer 32 can be a stacked film formed by any one or more of a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer.
[0094] Exemplarily, under the action of high temperature and radio frequency glow discharge, a silicon nitride thin film can be formed by introducing SiH4 and NH3; a silicon oxynitride thin film can be formed by introducing SiH4, NH3 and N2O; a silicon oxide thin film can be formed by introducing SiH4 and N2O.
[0095] 8. Printing metal electrodes
[0096] Refer to Figure 1As shown, a fine circuit is fabricated by printing a first electrode 51 (including the front main gate and the front sub-gate) and a second electrode 52 (including the back main gate and the back sub-gate) on the front and back sides of a silicon substrate 10 using silver or silver-aluminum. The printing sequence is back main gate → back sub-gate → front main gate → front sub-gate. The cell is then sintered and subjected to light injection or electrical injection treatment. Finally, the front sub-gate position of the cell is subjected to LIF laser treatment to obtain the finished solar cell.
[0097] Example 1:
[0098] N-type silicon wafers are texturized in NaOH solution to form a pyramid light-trapping structure.
[0099] An N-type silicon wafer is placed in a furnace tube and heated to a certain temperature. BCl3 is then introduced, and under the action of oxygen, it reacts with the silicon wafer to form P-type silicon and borosilicate glass (BSG), thus forming a PN junction.
[0100] The BSG on the back and edges of the silicon wafer is removed with an acid solution, and then the PN junction on the back is removed with an alkaline solution while the back is polished.
[0101] Under high temperature and radio frequency glow discharge, N2O is introduced to form a tunneling layer on the back of the silicon wafer, then SiH4 and PH3 are introduced to form highly doped amorphous silicon, and finally high temperature annealing is performed to form a highly doped polycrystalline silicon layer.
[0102] The PSG on the front and edges of the silicon wafer is removed by acid washing, then the plating on the front and edges is removed by alkaline washing, then the BSG on the front and the PSG on the back are removed by acid washing, and finally RCA cleaning is performed.
[0103] By alternately introducing gaseous precursor TMA (trimethylaluminum) and H2O pulses (time ratio TMA:H2O = 8:6) into the reaction chamber, high-density AlO2 is chemically adsorbed and deposited on the front side of the silicon wafer. X Film layer (16 turns); A gaseous precursor TMA and H2O pulses (time ratio TMA:H2O = 6:8) are alternately introduced into the reaction chamber to chemically adsorb and deposit a loose-density AlO2 layer on the front side of the silicon wafer. X Film layer (36 turns).
[0104] Under high temperature and radio frequency glow discharge, SiH4 and NH3 are introduced into the front side of the silicon wafer to form a silicon nitride film, and SiH4, NH3 and N2O are introduced to form a silicon oxynitride film. SiH4 and NH3 are introduced into the back side of the silicon wafer to form a silicon nitride film.
[0105] Fine circuits are fabricated on the front and back sides of a silicon wafer using silver or silver-aluminum, followed by sintering and light injection. Finally, the sub-gate position on the front side of the cell is subjected to LIF laser to obtain the finished cell.
[0106] Comparative Example 1:
[0107] N-type silicon wafers are texturized in NaOH solution to form a pyramid light-trapping structure.
[0108] An N-type silicon wafer is placed in a furnace tube and heated to a certain temperature. BCl3 is then introduced, and under the action of oxygen, it reacts with the silicon wafer to form P-type silicon and borosilicate glass (BSG), thus forming a PN junction.
[0109] The BSG on the back and edges of the silicon wafer is removed with an acid solution, and then the PN junction on the back is removed with an alkaline solution while the back is polished.
[0110] Under high temperature and radio frequency glow discharge, N2O is introduced to form a tunneling layer on the back of the silicon wafer, then SiH4 and PH3 are introduced to form highly doped amorphous silicon, and finally high temperature annealing is performed to form a highly doped polycrystalline silicon layer.
[0111] The PSG on the front and edges of the silicon wafer is removed by acid washing, then the plating on the front and edges is removed by alkaline washing, then the BSG on the front and the PSG on the back are removed by acid washing, and finally RCA cleaning is performed.
[0112] AlO was chemically adsorbed and deposited on the front side of a silicon wafer by alternately introducing gaseous precursor TMA and H2O pulses (time ratio TMA:H2O = 6:7) into the reaction chamber. X Film layer (52 turns).
[0113] Under high temperature and radio frequency glow discharge, SiH4 and NH3 are introduced into the front side of the silicon wafer to form a silicon nitride film, and SiH4, NH3 and N2O are introduced to form a silicon oxynitride film. SiH4 and NH3 are introduced into the back side of the silicon wafer to form a silicon nitride film.
[0114] Fine circuits are fabricated on the front and back sides of a silicon wafer using silver or silver-aluminum, followed by sintering and light injection. Finally, the sub-gate position on the front side of the cell is subjected to LIF laser to obtain the finished cell.
[0115] The electrical performance of individual solar cells in Example 1 and Comparative Example 1 was tested, and the test results are shown in the table below:
[0116] Table 1: Electrical Performance Parameters of Solar Cells
[0117] Grouping Eta(%) Uoc(V) Isc(A) FF (%) Quantity (pcs) Comparative Example 1 26.01 0.7353 7.297 84.58 3698 Example 1 26.04 0.7357 7.294 84.68 1150
[0118] Referring to Table 1, the efficiency Eta of the cell in Example 1 was increased by 0.03% compared to that of Comparative Example 1, mainly reflected in a 0.4mV increase in opening voltage and a 0.1% increase in fill factor. These results indicate that photovoltaic cells with passivation layers of varying density exhibit better passivation performance.
[0119] Compared with the prior art, the solar cell and its preparation method of the present invention, by forming multiple passivation layers with different densities, make the ALD process more operable, improve the passivation effect, and increase the conversion efficiency of the cell. Compared with the formation of a single passivation structure in the prior art, the ALD process for forming multiple passivation layers is more operable.
[0120] The solar cell and its preparation method of the present invention have a high negative charge intensity in the passivation layer with relatively high density, which improves the field passivation effect; the passivation layer with relatively low density can increase the H atom content during the preparation process, and the passivation layer with relatively low density can be more easily burned through by the paste for subsequent electrode formation, further improving the chemical passivation effect and the fill factor FF.
[0121] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0122] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A solar cell, characterized in that, include: A silicon substrate having a first surface and a second surface disposed opposite to each other; A first doped layer is formed on the first surface; A passivation structure is formed on the first doped layer. The passivation structure includes at least a first passivation layer and a second passivation layer, wherein the density of the first passivation layer is higher than the density of the second passivation layer.
2. The solar cell according to claim 1, characterized in that, The first passivation layer includes a first alumina layer, and the second passivation layer includes a second alumina layer, wherein the porosity of the first alumina layer is lower than that of the second alumina layer.
3. The solar cell according to claim 1, characterized in that, The solar cell also includes: A tunneling passivation contact structure is formed on the second surface, the tunneling passivation contact structure comprising a tunneling layer and a second doped layer stacked sequentially; A first electrode is formed on the first surface and is in contact with the first doped layer; and The second electrode is formed on the second surface and is in contact with the second doped layer.
4. A method for preparing a solar cell, characterized in that, The preparation method includes the following steps: A silicon substrate is provided, the silicon substrate having a first surface and a second surface disposed opposite to each other; A first doped layer is formed on the first surface; A passivation structure is formed on the first doped layer, the passivation structure comprising at least a first passivation layer and a second passivation layer, wherein the density of the first passivation layer is higher than the density of the second passivation layer.
5. The method for preparing a solar cell according to claim 1, characterized in that, The density of the passivation layer is controlled by adjusting the proportion of different precursors introduced to form the passivation layer.
6. The method for preparing a solar cell according to claim 5, characterized in that, The proportion of different precursors introduced can be controlled by adjusting the alternating pulse introduction time and / or alternating pulse introduction flow rate of different precursors forming the passivation layer.
7. The method for preparing a solar cell according to claim 5, characterized in that, The precursor includes a first precursor containing aluminum and a surface-reacted oxygen of the first aluminum precursor; The proportion of the first precursor inlet is adjusted to be greater than half of the total precursor inlet to form the first passivation layer. The proportion of the first precursor ingress is adjusted to be less than or equal to half of the total precursor ingress to form the second passivation layer. The density of the first passivation layer is higher than that of the second passivation layer.
8. The method for preparing a solar cell according to claim 7, characterized in that, The precursor includes a second precursor containing hydrogen; The hydrogen content generated during the formation of the passivation structure can be controlled by adjusting the proportion of the second precursor.
9. The method for preparing a solar cell according to claim 8, characterized in that, The proportion of the second precursor introduced is adjusted to be less than half of the total amount of the precursor introduced, thereby forming the first passivation layer; The proportion of the second precursor introduced is adjusted to be greater than or equal to half of the total amount of the precursor introduced, thereby forming the second passivation layer; The hydrogen content generated during the formation of the second passivation layer is higher than the hydrogen content generated during the formation of the first passivation layer.
10. The method for preparing a solar cell according to claim 8, characterized in that, The first precursor comprises gaseous trimethylaluminum, the second precursor comprises gaseous H2O, the first passivation layer comprises a first alumina layer, and the second passivation layer comprises a second alumina layer.
11. The method for preparing a solar cell according to claim 10, characterized in that, The first alumina layer is formed by increasing the proportion of trimethylaluminum to more than half of the total amount of precursors introduced. The second alumina layer is formed by increasing the proportion of H2O introduced to more than half of the total amount of precursor introduced. The porosity of the first alumina layer is lower than that of the second alumina layer; The hydrogen content generated during the formation of the second alumina layer is higher than the hydrogen content generated during the formation of the first alumina layer.
12. The method for preparing a solar cell according to claim 4, characterized in that, The first passivation layer and the second passivation layer are prepared using an atomic layer deposition process.
13. The method for preparing a solar cell according to claim 4, characterized in that, The preparation method further includes: A tunneling passivation contact structure is formed on the second surface, the tunneling passivation contact structure comprising a tunneling layer and a second doped layer stacked sequentially. A first electrode is formed on the first surface in contact with the first doped layer; and A second electrode is formed on the second surface in contact with the second doped layer.
14. The method for preparing a solar cell according to claim 13, characterized in that, A tunneling passivation contact structure is formed on the second surface, including: A tunneling layer is deposited on the second surface; An amorphous silicon layer is deposited on the surface of the tunneling layer; and The amorphous silicon layer is phosphorus-doped to form a doped polycrystalline silicon layer; or, A tunneling passivation contact structure is formed on the second surface, including: A tunneling layer is deposited on the second surface; A doped amorphous silicon layer is deposited on the surface of the tunneling layer; and The doped amorphous silicon layer is annealed to form a doped polycrystalline silicon layer.