Method for preparing solar cell and solar cell

Abstract

The present invention provides a method for preparing a solar cell and a solar cell. The preparation method comprises: providing a silicon substrate having a relative front and back surface; forming a diffusion layer on the front surface; sequentially forming a tunneling layer and a doped polysilicon layer on the back surface; forming an aluminum oxide layer on the side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, wherein the material of the hydrogen treatment layer comprises Al-O-Al bonds; forming an anti-reflection layer on the side of the hydrogen treatment layer away from the aluminum oxide layer; and forming electrodes on the back surface and the front surface, respectively. Through the present application, the problem that the aluminum oxide layer is easily damaged due to hydrogen enrichment in the aluminum oxide passivation film layer in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the field of solar cells, and in particular to a method for preparing a solar cell and a solar cell. Background Art

[0002] In the manufacturing process of conventional single crystal tunnel oxide passivating contact cells (TOPCon), the surface passivation film is formed by the atomic layer deposition (ALD) technology to react trimethylaluminum (TMA) with water (H2O) to form a thin layer of aluminum oxide (Al2O3) on the surface of the silicon substrate. This process is crucial to improving the photoelectric conversion efficiency of the cell because it can reduce surface recombination and improve carrier transport.

[0003] However, the control of water content in this process has a direct and significant impact on the stability of the passivation film layer and the H passivation effect. On the one hand, when the water content participating in the reaction is too much, too many water molecules participating in the reaction will lead to excessive hydrogen (H) enrichment in the aluminum oxide layer. In the subsequent screen printing high-temperature process, these enriched hydrogen will be activated, and the excess hydrogen will overflow from the aluminum oxide layer. During the hydrogen overflow process, tiny channels or pinholes, i.e., pinhole-shaped white spots, will be formed in the aluminum oxide layer. These small white spots destroy the passivation film layer, increase surface recombination, and directly affect the photoelectric conversion efficiency of the battery. On the other hand, when the aluminum oxide layer is generated by the reaction of trimethylaluminum and water, in order to avoid the problem of H content enrichment leading to the destruction of the aluminum oxide layer, the participation of reaction water is usually reduced in the prior art. When the water content participating in the reaction is too little, the ALD reaction may not be able to form a complete aluminum oxide layer, and the growth of the film layer is incomplete, resulting in a reduction in the passivation effect. Summary of the invention

[0004] The main purpose of the present invention is to provide a solar cell and a solar cell to solve the problem in the prior art that hydrogen is easily enriched in the aluminum oxide passivation film layer, resulting in the aluminum oxide layer being destroyed.

[0005] To achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a solar cell is provided, the method comprising: providing a silicon substrate having a relative front side and a back side; forming a diffusion layer on the front side; sequentially forming a tunneling layer and a doped polysilicon layer on the back side; forming an aluminum oxide layer on a side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, the material of the hydrogen treatment layer comprising Al-O-Al bonds; forming an anti-reflection layer on a side of the hydrogen treatment layer away from the aluminum oxide layer; and forming electrodes on the back side and the front side, respectively.

[0006] Furthermore, forming a hydrogen treatment layer on the surface of the aluminum oxide layer includes: placing a silicon substrate having an aluminum oxide layer into a first reaction chamber; and injecting trimethylaluminum into the first reaction chamber at least once to form the hydrogen treatment layer.

[0007] Furthermore, trimethylaluminum is injected into the first reaction chamber at least once to form a hydrogen treatment layer, including: an introduction step, injecting a first preset flow rate of trimethylaluminum into the first reaction chamber; a purging step, after injecting the trimethylaluminum for a preset time, introducing an inert gas into the first reaction chamber to purge the trimethylaluminum that has not chemically reacted in the first reaction chamber; and repeating the introduction step and the purging step at least once until a hydrogen treatment layer of a first preset thickness is formed.

[0008] Furthermore, the preparation method further comprises: forming a nano-aluminum layer between the hydrogen treatment layer and the anti-reflection layer.

[0009] Furthermore, a nano aluminum layer is formed between the hydrogen treatment layer and the anti-reflection layer, including: placing the silicon substrate with the hydrogen treatment layer into a second reaction chamber; injecting oxygen-containing gas into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas generate a nano aluminum layer.

[0010] Furthermore, oxygen-containing gas is injected into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas generate a nano-aluminum layer, including: injecting oxygen-containing gas at a second preset flow rate into the second reaction chamber, and ionizing the oxygen-containing gas in the second reaction chamber until a nano-aluminum layer of a second preset thickness is formed.

[0011] Furthermore, the oxygen-containing gas includes at least one of nitrous oxide, oxygen, ozone and carbon dioxide.

[0012] Furthermore, before the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano-aluminum layer, the preparation method also includes: heat treating the silicon substrate with the hydrogen-treated layer in the second reaction chamber at a temperature of 460-550° C. for 15-25 minutes.

[0013] Furthermore, in the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano-aluminum layer, the radio frequency power in the second reaction chamber is 15000-18000w.

[0014] To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a solar cell, which is prepared by any of the above-mentioned preparation methods, and the solar cell comprises: a silicon substrate having a front side and a back side opposite to each other; a diffusion layer, an aluminum oxide layer and an anti-reflection layer located on the front side, the aluminum oxide layer being located on a side of the diffusion layer away from the silicon substrate, and the anti-reflection layer being located on a side of the aluminum oxide layer away from the diffusion layer; a tunneling layer and a doped polysilicon layer located on the back side, the doped polysilicon layer being located on a side of the tunneling layer away from the silicon substrate; a hydrogen treatment layer located between the aluminum oxide layer and the anti-reflection layer, the material of the hydrogen treatment layer comprising Al-O-Al bonds; and a nano-aluminum layer located between the hydrogen treatment layer and the anti-reflection layer.

[0015] The technical solution of the present invention is applied to provide a method for preparing a solar cell, the method comprising: providing a silicon substrate having a front side and a back side opposite to each other; forming a diffusion layer on the front side; sequentially forming a tunneling layer and a doped polysilicon layer on the back side; forming an aluminum oxide layer on the side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, the material of the hydrogen treatment layer including an Al-O-Al bond; forming an anti-reflection layer on the side of the hydrogen treatment layer away from the aluminum oxide layer; and forming electrodes on the back side and the front side, respectively. In the present solution, during the process of forming the hydrogen treatment layer on the surface of the aluminum oxide layer, a dehydrogenation reaction will occur on the hydroxyl group on the surface of the aluminum oxide layer, and the oxygen atoms in the hydroxyl group will form a hydrogen treatment layer with an Al-O-Al bond on the surface of the aluminum oxide layer, and the hydrogen atoms in the hydroxyl group can form volatile byproducts, which will be removed later, thereby realizing the removal of hydrogen atoms from the surface of the aluminum oxide, and solving the problem that the aluminum oxide layer is destroyed due to the enrichment of H content in the aluminum oxide layer when the aluminum oxide layer is generated by the reaction of trimethylaluminum and water. In addition, this solution can avoid hydrogen enrichment without reducing the participation of water, thereby avoiding the problem of poor H passivation effect on the surface of the silicon substrate caused by reducing the amount of water involved in the preparation process of the aluminum oxide layer in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 A flow chart of a method for preparing a solar cell provided according to an embodiment of the present application is shown;

[0018] Figure 2 A flow chart showing a method for preparing a solar cell according to an embodiment of the present application, in which a hydrogen treatment layer is formed on the surface of an aluminum oxide layer;

[0019] Figure 3A flow chart is shown of a method for preparing a solar cell provided in an embodiment of the present application, in which trimethylaluminum is injected into a first reaction chamber at least once to form a hydrogen treatment layer. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so as to describe the embodiments of the present invention described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0023] In the field of solar cells, especially in Passivated Emitter and Rear Cell (PERC) and Tunnel Oxide Passivating Contact (TOPCon), aluminum oxide is usually used as a passivation film on the surface of solar cells. It forms a thin film through methods such as atomic layer deposition (ALD), which can effectively reduce non-radiative recombination on the silicon surface, increase the effective life of carriers, and thus improve cell efficiency.

[0024] As introduced in the background technology, the formation process of the passivation film in the prior art will cause excessive hydrogen (H) to accumulate in the aluminum oxide layer, resulting in the destruction of the aluminum oxide layer. In order to solve the above technical problems, the present application proposes a method for preparing a solar cell and a solar cell.

[0025] like Figure 1 As shown, Figure 1A schematic flow chart of a method for preparing a solar cell provided in an embodiment of the present application includes:

[0026] S1, providing a silicon substrate having opposite front and back surfaces;

[0027] S2, forming a diffusion layer on the front side;

[0028] S3, sequentially forming a tunneling layer and a doped polysilicon layer on the back side;

[0029] S4, forming an aluminum oxide layer on a side of the diffusion layer away from the silicon substrate;

[0030] S5, forming a hydrogen treatment layer on the surface of the aluminum oxide layer, wherein the material of the hydrogen treatment layer includes Al-O-Al bonds;

[0031] S6, forming an anti-reflection layer on a side of the hydrogen-treated layer away from the aluminum oxide layer;

[0032] S7, forming electrodes on the back side and the front side respectively.

[0033] In the process of preparing the aluminum oxide layer by ALD, water is used as an oxidant to form the aluminum oxide layer. Excess water vapor or insufficient water vapor will affect the passivation effect of the aluminum oxide layer on the silicon substrate in the solar cell. For example, excess water vapor reacts additionally with Al or Al-O intermediates, thereby introducing more hydrogen atoms (H) into the aluminum oxide layer. These hydrogen atoms may become unstable in subsequent high-temperature processes, affecting the performance of the battery. Insufficient water vapor will cause the reaction between TMA and water to be insufficient, and the hydrogen content in the generated Al2O3 film may be insufficient, resulting in poor passivation effect.

[0034] In the present application, a method for preparing a solar cell is provided, the method comprising: providing a silicon substrate having a front side and a back side opposite to each other; forming a diffusion layer on the front side; sequentially forming a tunneling layer and a doped polysilicon layer on the back side; forming an aluminum oxide layer on the side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, the material of the hydrogen treatment layer comprising an Al-O-Al bond; forming an anti-reflection layer on the side of the hydrogen treatment layer away from the aluminum oxide layer; and forming electrodes on the back side and the front side, respectively. In the present solution, during the process of forming the hydrogen treatment layer on the surface of the aluminum oxide layer, a dehydrogenation reaction will occur on the hydroxyl group on the surface of the aluminum oxide layer, and the oxygen atoms in the hydroxyl group will form a hydrogen treatment layer having an Al-O-Al bond on the surface of the aluminum oxide layer, and the hydrogen atoms in the hydroxyl group can form volatile byproducts, which will be removed later, thereby realizing the removal of hydrogen atoms from the surface of the aluminum oxide, and solving the problem that when the aluminum oxide layer is generated by the reaction of trimethylaluminum and water, the aluminum oxide layer is destroyed due to the enrichment of H content in the aluminum oxide layer. In addition, this solution can avoid hydrogen enrichment without reducing the participation of water, thereby avoiding the problem of poor H passivation effect on the surface of the silicon substrate caused by reducing the amount of water involved in the preparation process of the aluminum oxide layer in the prior art.

[0035] The exemplary embodiments of the method for preparing a solar cell provided in the present application will be described in more detail below. However, these exemplary embodiments can be implemented in a variety of different forms and should not be construed as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0036] Specifically, in step S1, a silicon substrate is provided, which has a front side and a back side opposite to each other.

[0037] In some embodiments, the material of the silicon substrate may be selected from single crystal silicon, polycrystalline silicon, amorphous silicon, or microcrystalline silicon.

[0038] In some embodiments, the doping type of the silicon substrate may be N-type or P-type. The N-type semiconductor substrate is doped with an N-type doping element, which may be any one of the V-group elements such as phosphorus (P), bismuth (Bi), antimony (Sb), or arsenic (As). The P-type semiconductor substrate is doped with a P-type element, which may be any one of the III-group elements such as boron (B), aluminum (Al), gallium (Ga), or indium (In).

[0039] In some embodiments, if the solar cell is a single-sided cell, the front side of the silicon substrate can be used as the light-receiving surface for receiving incident light, and the back side can be used as the backlight surface. If the solar cell is a double-sided cell, both the front side and the back side of the silicon substrate can be used as the light-receiving surface for receiving incident light.

[0040] In some embodiments, the provided silicon substrate may be a silicon substrate that has been subjected to chemical cleaning (including organic solvent cleaning, acid-base cleaning, etc.) to remove surface contaminants and a natural oxide layer; alternatively, the provided silicon substrate may be subjected to chemical cleaning (including organic solvent cleaning, acid-base cleaning, etc.) to remove surface contaminants and a natural oxide layer.

[0041] In some embodiments, in order to reduce the light reflection of the silicon substrate surface to the incident light and increase the light absorption, a texturing treatment can be performed on at least one surface of the silicon substrate of the solar cell (i.e., the front side of the silicon substrate and / or the back side of the silicon substrate). The texturing treatment will form a tiny pyramid-shaped structure on the surface of the silicon wafer. When light is incident on the texturing surface, due to the unevenness of the texturing surface, the incident light will collide with the pyramid-shaped structure multiple times, increasing the path length of the incident light inside the silicon substrate, thereby improving the light absorption rate and reducing the light directly reflected back into the air, thereby improving the photoelectric conversion efficiency of the solar cell.

[0042] For example, when the solar cell is a monofacial cell, the front side of the silicon substrate may be subjected to a texturing process to form a velvet surface on the front side (i.e., the light-receiving side) of the silicon substrate. Furthermore, the back side of the silicon substrate may be subjected to a polishing process to form a polished surface on the back side (i.e., the backlight side) of the silicon substrate. It should be noted that, unlike the monofacial cell, the velvet surface may also be formed on the front side and the back side of the silicon substrate, respectively.

[0043] For example, when the solar cell is a bifacial cell, the front side and the back side of the silicon substrate may be subjected to texturing treatment respectively, so as to form a textured surface on the front side and the back side of the silicon substrate respectively.

[0044] In some embodiments, when the silicon substrate is single crystal silicon, at least one surface of the silicon substrate can be textured using a mixed solution of an alkaline solution and an alcohol solution; when the silicon substrate is polycrystalline silicon, at least one surface of the silicon substrate can be textured using an acid solution.

[0045] Specifically, in step S2, a diffusion layer is formed on the front surface.

[0046] In some embodiments, the diffusion layer may be an N-type diffusion layer or a P-type diffusion layer. It should be noted that after selecting silicon substrates of different doping types, the diffusion layer formed on the front side of the silicon substrate will be different. Wherein, when the doping type of the silicon substrate is N-type, the diffusion layer is a P-type diffusion layer, and the P-type diffusion layer serves as an emitter to form a PN junction with the silicon substrate; when the doping type of the silicon substrate is P-type, the diffusion layer is an N-type diffusion layer, and the N-type diffusion layer serves as an emitter to form a PN junction with the silicon substrate.

[0047] The formation of PN junction is the basis of solar cell operation. When sunlight shines on the solar cell, the photon energy is absorbed by the silicon substrate, generating electron-hole pairs. In the presence of PN junction, electrons move to the N-type region under the action of the electric field, and holes move to the P-type region, thus achieving charge separation.

[0048] Specifically, in the case where the silicon substrate is an N-type silicon substrate, a P-type diffusion is performed on the front side of the N-type silicon substrate to form a P-type diffusion layer. Exemplarily, the texturized silicon wafer and the boron source are placed in a diffusion furnace (a diffusion furnace is a high-temperature, atmosphere-controlled device used to diffuse dopants on the silicon wafer). When the diffusion furnace is heated to a predetermined temperature, boron atoms begin to evaporate from the boron source, enter the silicon lattice through the surface of the silicon wafer, and are then absorbed by the surface of the silicon wafer to form P-type doping. In some embodiments, the boron source includes but is not limited to boric acid (H3BO3), trifluoroboric acid (BF3) or an organic compound of boron such as borohydride.

[0049] Specifically, when the silicon substrate is an N-type silicon substrate, N-type diffusion is performed on the front side of the P-type silicon substrate to form an N-type diffusion layer. Exemplarily, the texturized silicon wafer and the phosphorus source are placed in a diffusion furnace together. When the diffusion furnace is heated to a predetermined temperature, phosphorus atoms begin to evaporate from the phosphorus source, enter the silicon lattice through the surface of the silicon substrate, and are then absorbed by the surface of the silicon substrate to form N-type doping. In some optional embodiments, the phosphorus source includes but is not limited to sodium hypophosphite (NaH2PO2).

[0050] Specifically, in step S3, a tunneling layer and a doped polysilicon layer are sequentially formed on the back side.

[0051] In some embodiments, the diffusion process of the diffusion layer will form a diffusion layer (peripheral diffusion layer) on the front side, the back side, and the periphery other than the front side and the back side of the silicon substrate. The peripheral diffusion layer is prone to short circuit, and the diffusion layer on the back side of the silicon substrate will affect the subsequent passivation. Therefore, after the step of forming the diffusion layer and before the step of forming the tunneling layer, the method for preparing a solar cell may further include: removing the peripheral diffusion layer and the back diffusion layer.

[0052] In some embodiments, a wet etching method may be used to first remove the peripheral diffusion layer in an inline device and then remove the diffusion layer on the back side of the silicon substrate.

[0053] In some embodiments, after the step of removing the peripheral diffusion layer and the diffusion layer located on the back side of the silicon substrate and before the step of forming the tunneling layer, in order to make the back side of the silicon substrate have a smooth polished surface and enhance the back side passivation effect of the silicon substrate, the method for preparing a solar cell may further include: performing an alkali polishing treatment on the back side of the silicon substrate.

[0054] In the step of forming a diffusion layer on the back side of the silicon substrate, when the dopant (boron source, usually boric acid or boron trifluoride, etc.) contacts the silicon substrate under high temperature conditions, the doping atoms (boron atoms) diffuse into the silicon substrate to form a highly doped silicon layer (P-type silicon layer), namely the emitter (P + Emitter). At the same time, this process will also form a silicon-based glass layer (BSG, borosilicate glass) on the front side of the silicon substrate, which will hinder the formation of metal contacts, because metal contacts need to directly contact the silicon wafer in order to establish good ohmic contacts. In addition, the silicon-based glass layer will also affect the subsequent film deposition, resulting in a decrease in the quality of the film. Therefore, in some embodiments, after the step of alkali polishing the back side of the silicon substrate and before the step of forming the tunneling layer, the method for preparing a solar cell further includes: removing the silicon glass layer on the front side of the silicon substrate in a chain device.

[0055] In some embodiments, the material of the tunneling layer may include, but is not limited to, at least one of silicon oxide, silicon nitride, silicon oxynitride, or silicon carbide.

[0056] In some embodiments, the tunneling layer is located on the surface of the silicon substrate, which can saturate the dangling bonds on the surface of the silicon substrate, reduce the defect state density of the silicon substrate, and reduce the recombination centers on the surface of the silicon substrate to reduce the carrier recombination rate, so that the interface state density on the surface of the silicon substrate is larger. The increase in the interface state density will promote the recombination of photogenerated carriers, increase the fill factor, short-circuit current and open-circuit voltage of the solar cell, so as to improve the photoelectric conversion efficiency of the solar cell.

[0057] In some embodiments, the tunnel layer formation process may include but is not limited to a chemical vapor deposition process, a physical vapor deposition process, or an atomic layer deposition process.

[0058] In some embodiments, a polysilicon layer is first formed on the side of the tunneling layer away from the silicon substrate to increase the migration rate of electrons while suppressing the migration rate of holes. Next, the polysilicon layer is doped to form a doped polysilicon layer. Finally, the tunneling layer and the doped polysilicon layer form a passivation contact structure.

[0059] In some embodiments, the doping type of the doped polysilicon layer is the same as the doping type of the silicon substrate.

[0060] In some embodiments, the polysilicon layer may be formed by low pressure chemical vapor deposition (LPCVD).

[0061] In some optional embodiments, the tunneling layer and the polysilicon layer can be deposited sequentially by LPCVD double insertion. It should be noted that the LPCVD double insertion means that during the deposition of the tunneling layer and the polysilicon layer, the silicon substrate will be inserted into the reaction chamber twice. The first insertion is to deposit the tunneling layer, and then the silicon substrate is taken out, cooled or chemically cleaned, and then inserted into the reaction chamber again to deposit the polysilicon layer.

[0062] In some embodiments, the doped polysilicon layer can be formed by phosphorus doping annealing on the back of the silicon substrate having the tunneling layer and the polysilicon layer in a double insertion manner. It should be noted that the double insertion method means that during the manufacturing process, the silicon substrate having the tunneling layer and the polysilicon layer will be inserted into a high-temperature annealing furnace (diffusion furnace) twice for processing. The first insertion is to deposit a film layer containing a phosphorus source on the back of the silicon substrate having the tunneling layer and the polysilicon layer, usually a phosphorus silane (PH3-SiH4) mixed gas or other forms of phosphorus; the second insertion is to perform high-temperature annealing so that the phosphorus atoms can be effectively incorporated into the polysilicon layer to form an n-type polysilicon doped layer.

[0063] In some embodiments, during the step of forming the doped polysilicon layer, the phosphorus source (such as phosphine, phosphoramide, etc.) reacts with the silicon oxide (SiO2) on the surface of the silicon wafer to form a layer of glassy substance containing phosphorus, namely, phosphosilicate glass (PSG). This layer of PSG will affect the subsequent metallization process, resulting in poor contact between the metal gate line and the silicon wafer, increasing the contact resistance and reducing the battery efficiency. Therefore, the PSG on the back of the silicon substrate can also be removed in the chain device.

[0064] In some embodiments, after forming a layer of metal contacts on the front side of the silicon substrate to facilitate battery connection and conduction and forming a doped polysilicon layer, the method for preparing a solar cell further includes: performing a wrap-around plating process on the front side of the silicon substrate.

[0065] Specifically, in step S4, an aluminum oxide layer is formed on a side of the diffusion layer away from the silicon substrate.

[0066] Take the method of forming an aluminum oxide passivation film by atomic layer deposition (ALD) as an example. The aluminum oxide layer is formed by the atomic layer deposition process, which can achieve high-quality Al2O3 thin films while maintaining low surface roughness and high minority carrier lifetime, thereby significantly improving the edge passivation effect of the battery. It should be noted that the aluminum oxide passivation film can be prepared by chemical vapor deposition.

[0067] In some embodiments, the silicon substrate having the above passivation contact structure and the diffusion layer may be first loaded into an aluminum boat, and an aluminum oxide layer may be prepared by an atomic layer deposition (ALD) method. The ALD process may include:

[0068] The first step is to inject a metal source (usually trimethylaluminum TMA) to react. The TMA molecules will be adsorbed on the front surface of the silicon substrate to form a layer of aluminum precursor. After that, an oxidant (usually water vapor H2O) is injected to react with the TMA adsorbed on the surface to generate an aluminum oxide film and volatile byproducts. This process will be repeated many times to achieve the desired film thickness.

[0069] Optionally, during the ALD process, TMA is injected at a flow rate of 18-22 sccm and a pulse time of 6-8 s.

[0070] Optionally, during the ALD process, H2O is injected at a flow rate of 18-22 sccm and a pulse time of 4-6 s.

[0071] Optionally, the reaction of H2O with TMA adsorbed on the surface includes at least one reaction, and after each chemical reaction of TMA and H2O, the reaction chamber is purged with an inert gas (such as nitrogen N2) to remove unreacted precursors and byproducts, prevent cross contamination, and prepare for the next round of pulses.

[0072] Exemplarily, in order to form an aluminum oxide layer with a thickness of 4 to 5 nm, the above-mentioned reaction of H2O with TMA adsorbed on the surface and the preparation process of purging the reaction chamber with an inert gas after each chemical reaction of TMA and H2O can be cycled 18 to 22 times.

[0073] In some embodiments, before the step of injecting the metal source, water vapor (H2O) may be injected to clean the front surface of the silicon substrate, and then nitrogen purge may be performed to remove excess water vapor. Further, in order to ensure a clean surface, the process step may be cycled 3 to 7 times. In each cycle, water vapor (H2O) may be injected at a flow rate of 18 to 22 sccm and a time pulse of 4 to 6 s.

[0074] Specifically, in step S5, a hydrogen treatment layer is formed on the surface of the aluminum oxide layer, and the material of the hydrogen treatment layer includes Al-O-Al bonds.

[0075] In some embodiments, the process of forming the hydrogen treatment layer can remove the residual hydrogen atoms in the aluminum oxide layer. In addition, the hydrogen treatment layer can have a hydrogen passivation effect, and the Al-O-Al bonds in the material can combine with the residual hydrogen atoms in the aluminum oxide layer to form a more stable chemical bond, thereby fixing the hydrogen atoms in the film layer, reducing the movement and escape of hydrogen, and thus enhancing the hydrogen passivation effect.

[0076] In some embodiments, Figure 2As shown, a hydrogen treatment layer is formed on the surface of the aluminum oxide layer, including: S51, placing a silicon substrate with an aluminum oxide layer into a first reaction chamber; S52, injecting trimethylaluminum into the first reaction chamber at least once to form a hydrogen treatment layer.

[0077] In some embodiments, the first reaction chamber may be a reaction chamber of an atomic deposition process. That is, the aluminum oxide layer is prepared by placing a silicon substrate having a passivation contact structure and a diffusion layer in the first reaction chamber during the preparation process using the atomic layer deposition process.

[0078] Specifically, after the aluminum oxide layer is formed in the first reaction chamber, trimethylaluminum can be directly injected into the first reaction chamber without injecting an oxidant. At this time, the uninjected oxidant chemically reacts with the injected trimethylaluminum, so the trimethylaluminum is adsorbed on the surface of the aluminum oxide layer facing away from the silicon substrate, and the trimethylaluminum chemically reacts with the active sites (such as hydroxyl groups) on the surface of the aluminum oxide layer, causing the methyl groups in the trimethylaluminum to fall off, and the hydroxyl groups on the surface of the aluminum oxide layer undergo a dehydrogenation reaction, so that the detached methyl groups and the detached hydrogen atoms escape from the surface of the aluminum oxide layer in the form of methane gas, and the aluminum atoms in the trimethylaluminum can form Al-O-Al bonds with the oxygen atoms in the hydroxyl groups, and finally the trimethylaluminum located on the side of the aluminum oxide layer facing away from the silicon substrate is converted into a hydrogen treatment layer.

[0079] In some embodiments, trimethylaluminum may be injected into the first reaction chamber 3 to 5 times. In the atomic layer deposition process, each deposition cycle may form an atomic-level thin film on the surface of aluminum oxide, and multiple cycles may be constructed layer by layer to form a non-porous, uniform thin film. By injecting trimethylaluminum 3 to 5 times, the film quality of the formed hydrogen treatment layer is better.

[0080] In some embodiments, Figure 3 As shown, trimethylaluminum is injected into the first reaction chamber at least once to form a hydrogen treatment layer, including: S521, an introduction step, injecting a first preset flow rate of trimethylaluminum into the first reaction chamber; S522, a purging step, after injecting trimethylaluminum for a preset time, introducing an inert gas into the first reaction chamber to purge the trimethylaluminum that has not chemically reacted in the first reaction chamber; S523, repeating the introduction step and the purging step at least once until a hydrogen treatment layer of a first preset thickness is formed.

[0081] In the above embodiment, a more compact and uniform hydrogen passivation layer can be constructed by introducing trimethylaluminum multiple times and purging with an inert gas. In addition, by purging after each injection of trimethylaluminum, unreacted trimethylaluminum and byproducts in the first reaction chamber can be effectively removed, avoiding the accumulation of unreacted trimethylaluminum and byproducts in the first reaction chamber, causing contamination or affecting subsequent deposition cycles, thereby improving the consistency of the process and the repeatability of the battery performance.

[0082] In some embodiments, the atomic layer deposition process is based on the principle of saturated adsorption. In order to ensure that the trimethylaluminum molecules are evenly distributed on the surface of the aluminum oxide layer and reach saturated adsorption, the first preset flow rate can be 18~22sccm, and the preset time can be 6~8s.

[0083] In addition, when the trimethylaluminum is injected at the first preset flow rate and the preset time, the step can be repeated 3 to 5 times to form a hydrogen treatment layer with a first preset thickness. The first preset thickness can be 1 to 2 nm.

[0084] In some embodiments, the preparation method further includes: forming a nano-aluminum layer between the hydrogen treatment layer and the anti-reflection layer. The formation of the nano-aluminum layer is usually accompanied by the capture and fixation of hydrogen. In other words, the formation of the nano-aluminum layer can reduce the overflow of hydrogen in the aluminum oxide layer, avoid the small white spot defects caused by the overflow of hydrogen, and further improve the passivation effect. In addition, the nano-aluminum layer, as a conductive material layer, can reduce the ohmic contact resistance of the front metal grid line.

[0085] In some embodiments, forming a nano aluminum layer between the hydrogen treatment layer and the anti-reflection layer includes: placing a silicon substrate with the hydrogen treatment layer into a second reaction chamber; injecting an oxygen-containing gas into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas generate a nano aluminum layer.

[0086] In the above embodiment, the nano aluminum layer is prepared in the second reaction chamber. After the oxygen-containing gas is injected into the second reaction chamber, the oxygen ions in the oxygen-containing gas react with the material on the surface of the hydrogen treatment layer, thereby breaking the Al-O-Al bonds in the hydrogen treatment layer to obtain Al-O bonds and generate free aluminum atoms. These aluminum atoms are rearranged in the second reaction chamber to obtain a nano aluminum layer.

[0087] In some embodiments, injecting an oxygen-containing gas into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas generate a nano-aluminum layer includes: injecting an oxygen-containing gas at a second preset flow rate into the second reaction chamber, and ionizing the oxygen-containing gas in the second reaction chamber until a nano-aluminum layer of a second preset thickness is formed. The second preset thickness may be 1-2 nm.

[0088] In the above embodiment, the oxygen-containing gas can be ionized to obtain oxygen ions. In order to make the ionized oxygen ions react with the material of the hydrogen treatment layer to form the nano-aluminum layer, a plasma enhanced chemical vapor deposition process can be used to prepare the nano-aluminum layer. In this case, the second reaction chamber can be a reaction chamber of the plasma enhanced chemical vapor deposition process.

[0089] In some embodiments, the oxygen-containing gas includes at least one of nitrous oxide, oxygen, ozone, and carbon dioxide.

[0090] In some embodiments, the second preset flow rate may be 3000-6000 sccm.

[0091] In some embodiments, before the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano aluminum layer, in order to activate the activity of the material in the hydrogen treatment layer so that the oxygen ions can react with the material of the hydrogen treatment layer, the preparation method also includes: heat treating the silicon substrate with the hydrogen treatment layer in the second reaction chamber, the heat treatment temperature is 460~550℃, and the heat treatment time is 15~25min.

[0092] In some embodiments, in the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano-aluminum layer, in order to maintain the number of high-energy ions and accelerate the chemical reaction process, the radio frequency power in the second reaction chamber is 15000~18000w.

[0093] Specifically, in step S6, an anti-reflection layer is formed on a side of the hydrogen-treated layer away from the aluminum oxide layer.

[0094] In some embodiments, the anti-reflection layer may include at least one of silicon nitride, silicon oxynitride, or silicon oxide.

[0095] Specifically, in step S7, electrodes are formed on the back side and the front side respectively.

[0096] In some embodiments, the electrodes may be formed on the back side and the front side of the silicon substrate respectively by using a screen printing process.

[0097] The embodiment of the present application also provides a solar cell, which can be prepared by the above-mentioned method for preparing a solar cell. Specifically, a solar cell includes: a silicon substrate having a relative front and back side; a diffusion layer, an aluminum oxide layer and an anti-reflection layer located on the front side, the aluminum oxide layer is located on the side of the diffusion layer away from the silicon substrate, and the anti-reflection layer is located on the side of the aluminum oxide layer away from the diffusion layer; a tunneling layer and a doped polysilicon layer located on the back side, the doped polysilicon layer is located on the side of the tunneling layer away from the silicon substrate; a hydrogen treatment layer, located between the aluminum oxide layer and the anti-reflection layer, and the material of the hydrogen treatment layer includes Al-O-Al bonds. Further, the solar cell also includes a nano-aluminum layer, located between the hydrogen treatment layer and the anti-reflection layer.

[0098] In some embodiments, the solar cell may be a TOPCon cell.

[0099] Experiments have shown that compared with the solar cells in the prior art that do not form the above-mentioned hydrogen treatment layer and nano-aluminum layer, the photoelectric conversion efficiency of the solar cells in this scheme can be improved by 0.01~0.03%, the open circuit voltage can be improved by 0.3~1 millivolts, and the fill factor can be improved by 0.05~0.1.

[0100] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0101] 1. The preparation method of the solar cell of the present application comprises: providing a silicon substrate having a front side and a back side opposite to each other; forming a diffusion layer on the front side; sequentially forming a tunneling layer and a doped polysilicon layer on the back side; forming an aluminum oxide layer on the side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, wherein the material of the hydrogen treatment layer comprises an Al-O-Al bond; forming an anti-reflection layer on the side of the hydrogen treatment layer away from the aluminum oxide layer; and forming electrodes on the back side and the front side, respectively. In the present solution, during the process of forming the hydrogen treatment layer on the surface of the aluminum oxide layer, the hydroxyl groups on the surface of the aluminum oxide layer will undergo a dehydrogenation reaction, and the oxygen atoms in the hydroxyl groups will form a hydrogen treatment layer having an Al-O-Al bond on the surface of the aluminum oxide layer, and the hydrogen atoms in the hydroxyl groups can form volatile byproducts, which will be removed subsequently, thereby achieving the removal of hydrogen atoms from the surface of the aluminum oxide, thereby solving the problem that when the aluminum oxide layer is generated by the reaction of trimethylaluminum and water, the aluminum oxide layer is destroyed due to the enrichment of H content in the aluminum oxide layer. In addition, this solution can avoid hydrogen enrichment without reducing the participation of water, thereby avoiding the problem of poor H passivation effect on the surface of the silicon substrate caused by reducing the amount of water involved in the preparation process of the aluminum oxide layer in the prior art.

[0102] 2. The solar cell of the present application comprises: a silicon substrate having a front side and a back side opposite to each other; a diffusion layer, an aluminum oxide layer and an anti-reflection layer located on the front side, the aluminum oxide layer being located on the side of the diffusion layer away from the silicon substrate, and the anti-reflection layer being located on the side of the aluminum oxide layer away from the diffusion layer; a tunneling layer and a doped polysilicon layer located on the back side, the doped polysilicon layer being located on the side of the tunneling layer away from the silicon substrate; a hydrogen treatment layer located between the aluminum oxide layer and the anti-reflection layer, the material of the hydrogen treatment layer comprising Al-O-Al bonds. This solution can avoid hydrogen enrichment without reducing the participation of water, and avoids the problem of poor H passivation effect on the surface of the silicon substrate caused by reducing the amount of water involved in the preparation process of the aluminum oxide layer in the prior art.

Claims

1. A method for preparing a solar cell, characterized in that: The preparation method comprises: providing a silicon substrate having opposite front and back surfaces; forming a diffusion layer on the front surface; sequentially forming a tunneling layer and a doped polysilicon layer on the back side; forming an aluminum oxide layer on a side of the diffusion layer away from the silicon substrate; forming a hydrogen treatment layer on the surface of the aluminum oxide layer, wherein the material of the hydrogen treatment layer includes Al-O-Al bonds; forming an anti-reflection layer on a side of the hydrogen-treated layer away from the aluminum oxide layer; forming electrodes on the back side and the front side respectively; Forming a hydrogen treatment layer on the surface of the aluminum oxide layer comprises: placing the silicon substrate having the aluminum oxide layer into a first reaction chamber; In the case of not injecting an oxidant, trimethylaluminum is injected into the first reaction chamber at least once to form the hydrogen treatment layer.

2. The preparation method according to claim 1, characterized in that: Injecting trimethylaluminum into the first reaction chamber at least once to form the hydrogen treatment layer comprises: an introduction step of injecting a first preset flow rate of trimethylaluminum into the first reaction chamber; a purging step, after injecting trimethylaluminum for a preset time, introducing an inert gas into the first reaction chamber to purge the trimethylaluminum that has not chemically reacted in the first reaction chamber; The introducing step and the purging step are repeatedly performed at least once until the hydrogen treatment layer with a first preset thickness is formed.

3. The preparation method according to claim 1 or 2, characterized in that: The preparation method further comprises: A nano-aluminum layer is formed between the hydrogen treatment layer and the anti-reflection layer.

4. The preparation method according to claim 3, characterized in that: Forming a nano-aluminum layer between the hydrogen treatment layer and the anti-reflection layer, comprising: placing the silicon substrate having the hydrogen-treated layer into a second reaction chamber; An oxygen-containing gas is injected into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas form the nano-aluminum layer.

5. The preparation method according to claim 4, characterized in that: Injecting an oxygen-containing gas into the second reaction chamber so that the material of the hydrogen treatment layer and the oxygen-containing gas generate the nano-aluminum layer, comprising: An oxygen-containing gas with a second preset flow rate is injected into the second reaction chamber, and the oxygen-containing gas in the second reaction chamber is ionized until the nano-aluminum layer with a second preset thickness is formed.

6. The preparation method according to claim 4, characterized in that: The oxygen-containing gas includes at least one of nitrous oxide, oxygen, ozone and carbon dioxide.

7. The preparation method according to claim 4, characterized in that: Before the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano-aluminum layer, the preparation method further comprises: The silicon substrate with the hydrogen treatment layer in the second reaction chamber is heat-treated at a temperature of 460-550° C. and a duration of 15-25 minutes.

8. The preparation method according to claim 4, characterized in that: In the step of injecting oxygen-containing gas into the second reaction chamber to obtain the nano-aluminum layer, the radio frequency power in the second reaction chamber is 15000~18000w.

9. A solar cell, characterized in that: The solar cell is prepared by the preparation method according to any one of claims 1 to 8, comprising: a silicon substrate having opposing front and back surfaces; a diffusion layer, an aluminum oxide layer and an anti-reflection layer located on the front side, wherein the aluminum oxide layer is located on a side of the diffusion layer away from the silicon substrate, and the anti-reflection layer is located on a side of the aluminum oxide layer away from the diffusion layer; a tunneling layer and a doped polysilicon layer located on the back side, wherein the doped polysilicon layer is located on a side of the tunneling layer away from the silicon substrate; A hydrogen treatment layer, located between the aluminum oxide layer and the anti-reflection layer, wherein the material of the hydrogen treatment layer includes Al-O-Al bonds; The nano-aluminum layer is located between the hydrogen treatment layer and the anti-reflection layer.

Images