Back contact solar cell and preparation method thereof
By forming a P-type doped monocrystalline silicon layer and an N-type semiconductor structure on the back side of the silicon substrate of a back-contact solar cell, and forming electrodes on its surface, and then forming an ohmic contact through laser sintering, the problems of low efficiency and complex process of back-contact solar cells are solved, and efficient and low-cost cell fabrication is achieved.
Patent Information
- Application Number
- CN202410530559.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-29
- Publication Date
- 2025-11-04
AI Technical Summary
In existing back-contact solar cells, both P-type and N-type doped polycrystalline silicon are placed on the back of the cell, resulting in a high recombination rate of positive and negative charges and low efficiency. Furthermore, the existing selective passivation contact structure has complex processes, high costs, and poor uniformity.
P-type and N-type semiconductor structures with P-type doped single-crystal silicon layers are formed on the back side of a silicon substrate, and electrodes are formed on their surface. Ohmic contacts are formed by laser sintering, which simplifies the process and reduces contact resistance.
This improved the on-state voltage and efficiency of back-contact solar cells, simplified the process, and reduced costs.
Smart Images
Figure CN120897543A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of solar cell preparation, and particularly relates to a back contact solar cell and a preparation method thereof. BACKGROUND
[0002] With the development of solar cell technology, the reliability of solar cells is more concerned. In order to improve the conversion efficiency of the cell to light, the back contact solar cell (IBC) cell emerges as the times require. The IBC cell is a kind of solar cell in which P-type doped polysilicon and N-type doped polysilicon are placed on the back surface of the cell, thereby reducing the shading to sunlight. However, since the P-type doped polysilicon and N-type doped polysilicon of the IBC cell are placed on the back surface of the cell, the recombination rate of positive and negative charges is high, thereby resulting in low efficiency of the cell.
[0003] In order to reduce the recombination rate of the cell surface, there is a back contact solar cell in the prior art, in which the N pole and the P pole are both selective passivation contact structures, that is, the N pole is a phosphorus-doped tunnel oxide layer and a polysilicon layer, and the P pole is a boron-doped tunnel oxide layer and a polysilicon layer, so that the transmission distance of the current can be reduced and the recombination rate can be reduced. However, the technology is complex, the cost is high, and the uniformity is poor. At the same time, since the solid solubility of boron atoms in polysilicon is low, the contact resistance of the P pole is much higher than that of the N pole, and the efficiency of the back contact solar cell is still not ideal. SUMMARY
[0004] The present application provides a back contact solar cell and a preparation method thereof to solve the problems existing in the prior art, reduce the contact resistance between the electrode and the semiconductor, and be beneficial to improve the open voltage of the back contact solar cell, thereby improving the efficiency of the back contact solar cell, and at the same time, be beneficial to simplify the process and save the cost.
[0005] In a first aspect, the present application provides a preparation method of a back contact solar cell, comprising:
[0006] providing a silicon substrate; the silicon substrate has opposite front and back surfaces;
[0007] forming a P-type semiconductor structure and an N-type semiconductor structure on the back surface of the silicon substrate; the P-type semiconductor structure comprises a P-type doped silicon layer;
[0008] forming a first electrode on the surface of the P-type semiconductor structure and a second electrode on the surface of the N-type semiconductor structure to form a cell precursor;
[0009] performing laser sintering on the cell precursor to form an ohmic contact between the first electrode and the P-type semiconductor structure.
[0010] Optionally, the N-type semiconductor structure comprises an N-type doped tunneling oxide layer and a polysilicon layer.
[0011] Optionally, the laser sintering of the battery precursor comprises:
[0012] The back surface of the battery precursor is irradiated by a first laser, and a reverse voltage is applied between the first electrode and the second electrode.
[0013] Optionally, the method for preparing the back contact solar cell further comprises:
[0014] The front surface of the battery precursor is irradiated by a second laser, and a reverse voltage is applied between the first electrode and the second electrode.
[0015] Optionally, the reverse voltage U has a voltage range of 5V≤U≤12V.
[0016] Optionally, a first electrode is formed on the surface of the P-type semiconductor structure, and a second electrode is formed on the surface of the N-type semiconductor structure, comprising:
[0017] A screen printing process is used to print a first electrode paste on the surface of the P-type semiconductor structure, and a second electrode paste is printed on the surface of the N-type semiconductor structure;
[0018] The first electrode paste and the second electrode paste are subjected to a sintering process; the sintering process has a temperature range of 500℃≤T≤600℃.
[0019] Optionally, a P-type semiconductor structure is formed on the back surface of the silicon substrate, comprising:
[0020] A boron diffusion process is used to boron-dope the back surface of the silicon substrate;
[0021] Laser etching is used to remove the borosilicate glass in the P-type semiconductor structure region;
[0022] The laser damage layer and the boron-doped layer in the N-type semiconductor structure region are removed.
[0023] Optionally, an N-type semiconductor structure is formed on the back surface of the silicon substrate, comprising:
[0024] A silicon oxide layer and a polysilicon layer are formed on the back surface of the silicon substrate;
[0025] A phosphorus diffusion process is used to phosphorus-dope the silicon oxide layer and the polysilicon layer;
[0026] Laser etching is used to remove the phosphosilicate glass in the N-type semiconductor structure region;
[0027] Remove the laser damage layer and the phosphorus doped layer of the P-type semiconductor structure region.
[0028] Optionally, before forming the first electrode on the surface of the P-type semiconductor structure and forming the second electrode on the surface of the N-type semiconductor structure, further comprising:
[0029] Forming a first passivation film layer on the front surface of the silicon substrate and forming a second passivation film layer on the back surface of the silicon substrate.
[0030] In a second aspect, the present application provides a back contact solar cell prepared by the preparation method of the back contact solar cell according to any one of the above.
[0031] The technical scheme of the present application, by providing a P-type semiconductor structure including a P-type doped monocrystalline silicon layer on the back surface of the silicon substrate, and an N-type semiconductor structure, and forming a first electrode on the surface of the P-type semiconductor structure and a second electrode on the surface of the N-type semiconductor structure to form a cell precursor, and finally laser sintering the cell precursor, so that the first electrode forms an ohmic contact with the P-type semiconductor structure, so that the contact resistance between the first electrode and the P-type semiconductor is reduced, which is beneficial to improve the open voltage of the back contact solar cell, and further improve the efficiency of the back contact solar cell. In addition, by forming a P-type semiconductor structure including a P-type doped monocrystalline silicon layer on the back surface of the silicon substrate, it is not necessary to form a selective passivation contact structure in the P-type semiconductor region, which is beneficial to simplify the process and save costs.
[0032] It should be understood that the content described in this part is not intended to identify key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS
[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.
[0034] Figure 1 A flow chart of a preparation method of a back contact solar cell provided by the first embodiment of the present application;
[0035] Figure 2 A flow chart of a preparation method of a back contact solar cell provided by the first embodiment of the present application;
[0036] Figure 3 A flow chart of a preparation method of a back contact solar cell provided by the second embodiment of the present application;
[0037] Figure 4 A flow chart of a preparation method of a back contact solar cell provided in Embodiment Three of the present application;
[0038] Figure 5 A structural schematic diagram of a back contact solar cell provided in Embodiment Three of the present application. DETAILED DESCRIPTION
[0039] In order to make the personnel in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.
[0040] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.
[0041] Embodiment One
[0042] The present embodiment provides a preparation method of a back contact solar cell, Figure 1 A flow chart of a preparation method of a back contact solar cell provided in Embodiment One of the present application, Figure 2 A flow chart of a preparation method of a back contact solar cell provided in Embodiment One of the present application, Figure 1 and Figure 2 The preparation method of the back contact solar cell comprises:
[0043] S110, providing a silicon substrate.
[0044] The silicon substrate 1 has opposite front and back surfaces. In an optional embodiment, the front surface of the silicon substrate 1 is the light-receiving surface of the back contact solar cell.
[0045] In an optional embodiment, the silicon substrate 1 comprises a P-type silicon substrate 1; in other embodiments, the silicon substrate 1 comprises an N-type silicon substrate 1.
[0046] In an optional embodiment, the providing the silicon substrate 1 comprises: providing an initial silicon substrate 1, and cleaning and texturing the initial silicon substrate 1 to remove mechanical damage layer and metal ions on the surface of the initial silicon substrate 1, and to form "pyramid" appearance on the front side of the initial silicon substrate 1, which is beneficial to improve the light trapping effect of the back contact solar cell, thereby further improving the efficiency of the back contact solar cell. For example, the cleaning and texturing of the initial silicon substrate 1 comprises the following steps: a. pre-cleaning with a mixed solution of HCL and H2O2 with a concentration of 0.2-0.5%; b. alkaline solution texturing with NaOH or KOH with a concentration of 0.4-2% and texturing additives, and the texturing time is 50-60 min; c. post-cleaning with HF solution with a concentration of 0.1-0.3%; d. deionized water rinsing.
[0047] S120, forming a P-type semiconductor structure and an N-type semiconductor structure on the back side of the silicon substrate.
[0048] The P-type semiconductor structure 2 comprises a P-type doped silicon layer. The P-type doping can comprise, but is not limited to, boron atom doping. Specifically, the P-type semiconductor structure 2 is obtained by directly P-type doping the silicon substrate 1.
[0049] The N-type semiconductor structure 3 can comprise, but is not limited to, an N-type doped selective passivation contact structure. The N-type doping can comprise, but is not limited to, phosphorus atom doping.
[0050] S130, forming a first passivation film layer on the front side of the silicon substrate, and forming a second passivation film layer on the back side of the silicon substrate.
[0051] The first passivation film layer 4 and the second passivation film layer 5 can be single layer or multiple layers. In an optional embodiment, the first passivation film layer 4 comprises a stack of aluminum oxide layer and silicon nitride layer; in other embodiments, the first passivation film layer 4 comprises a stack of aluminum oxide layer, silicon nitride layer and silicon oxide layer; in other embodiments, the first passivation film layer 4 comprises a stack of aluminum oxide layer and silicon oxynitride layer. The second passivation film layer 5 comprises a stack of aluminum oxide layer and silicon nitride layer.
[0052] It should be noted that the first passivation film layer 4 and the second passivation film layer 5 can be formed simultaneously or at different times. In an exemplary embodiment, first, an aluminum oxide film layer is deposited on the front surface and the back surface of the silicon substrate 1 by using an atomic layer deposition (ALD) technology, and the thickness of the deposited aluminum oxide film layer ranges from 1 nm to 10 nm; then, a silicon nitride layer, or a silicon nitride and silicon oxide stack, or a silicon oxynitride layer is deposited on the front surface of the silicon substrate 1 by using a plasma enhanced chemical vapor deposition (PECVD), and the thickness of the deposited film layer ranges from 50 nm to 120 nm; finally, a silicon nitride layer is deposited on the back surface of the silicon substrate 1 by using a PECVD, and the thickness of the deposited film layer ranges from 50 nm to 120 nm.
[0053] S140, forming a first electrode on the surface of the P-type semiconductor structure and forming a second electrode on the surface of the N-type semiconductor structure to form a battery precursor.
[0054] The first electrode 6 is in contact with the surface of the P-type semiconductor structure 2, and the second electrode 7 is in contact with the surface of the N-type semiconductor structure 3. The first electrode 6 and the second electrode 7 serve to collect electric charges. The materials of the first electrode 6 and the second electrode 7 include conductive metals and the like, and the specific materials can be selected according to actual needs. In an optional embodiment, the first electrode 6 includes one of a silver grid line, a copper grid line, or a gold grid line, and the second electrode 7 includes one of a silver grid line, a copper grid line, or a gold grid line. In an optional embodiment, the first electrode 6 and the second electrode 7 are respectively formed by screen printing and sintering using corresponding conductive pastes.
[0055] It should be noted that the formation of the first electrode 6 on the surface of the P-type semiconductor structure 2 and the formation of the second electrode 7 on the surface of the N-type semiconductor structure 3 can be performed in the following two ways: first, the first electrode 6 is formed on the surface of the P-type semiconductor structure 2, and then the second electrode 7 is formed on the surface of the N-type semiconductor structure 3; or second, the first electrode 6 is formed on the surface of the P-type semiconductor structure 2 at the same time as the second electrode 7 is formed on the surface of the N-type semiconductor structure 3. The present embodiment does not specifically limit the order of preparation of the first electrode 6 and the second electrode 7.
[0056] S150, performing laser sintering on the battery precursor to form an ohmic contact between the first electrode and the P-type semiconductor structure.
[0057] The laser sintering is also called laser enhanced contact optimization. The specific method comprises the following steps: irradiating the battery precursor with laser, so that the battery precursor can absorb a large number of photons, a large number of carriers are generated in the silicon wafer, and when a voltage is applied to the battery precursor, the generated carriers move directionally to generate a large current, thereby forming a breakdown at a place with low series resistance, and a local high temperature is generated instantaneously, so that the first electrode 6 and the P-type semiconductor structure 2 form an ohmic contact.
[0058] In an optional embodiment, when the battery precursor is laser sintered, only the first electrode 6 can be irradiated with laser, and a bias voltage is applied between the first electrode 6 and the second electrode 7, so that the first electrode 6 and the P-type semiconductor structure 2 form an ohmic contact, thereby reducing the contact resistance between the first electrode 6 and the P-type semiconductor structure 2. In other embodiments, when the battery precursor is laser sintered, the first electrode 6 and the second electrode 7 can be irradiated with laser at the same time, and a bias voltage is applied between one electrode and the second electrode 7, so that the first electrode 6 and the P-type semiconductor structure 2 form an ohmic contact at the same time, and the second electrode 7 and the N-type semiconductor structure 3 also form an ohmic contact, thereby reducing the contact resistance between the first electrode 6 and the P-type semiconductor structure 2, and the contact resistance between the second electrode 7 and the N-type semiconductor structure 3.
[0059] In this embodiment, the P-type semiconductor structure comprising a P-type doped monocrystalline silicon layer is formed on the back surface of the provided silicon substrate, and the N-type semiconductor structure is formed, and the first electrode is formed on the surface of the P-type semiconductor structure, and the second electrode is formed on the surface of the N-type semiconductor structure, to form a battery precursor, and finally the battery precursor is laser sintered, so that the first electrode and the P-type semiconductor structure form an ohmic contact, so that the contact resistance between the first electrode and the P-type semiconductor is reduced, which is beneficial to improve the open voltage of the back contact solar cell, and further improve the efficiency of the back contact solar cell. In addition, by forming the P-type semiconductor structure comprising a P-type doped monocrystalline silicon layer on the back surface of the silicon substrate, it is not necessary to form a selective passivation contact structure in the P-type semiconductor region, which is beneficial to simplify the process and save costs.
[0060] Embodiment two
[0061] Figure 3 A flowchart of a preparation method of a back contact solar cell provided in the second embodiment of the present application. Based on the above-mentioned embodiment, the present embodiment further increases the step of how to laser sinter the battery precursor. As shown in the figure, the preparation method comprises the following steps: Figure 3
[0062] S210, providing a silicon substrate.
[0063] The silicon substrate 1 has opposite front and back surfaces.
[0064] S220, forming a P-type semiconductor structure and an N-type semiconductor structure on the back surface of the silicon substrate.
[0065] The P-type semiconductor structure 2 comprises a P-type doped silicon layer.
[0066] S230, forming a first passivation film layer on the front surface of the silicon substrate, and forming a second passivation film layer on the back surface of the silicon substrate.
[0067] S240, forming a first electrode on the surface of the P-type semiconductor structure, and forming a second electrode on the surface of the N-type semiconductor structure 3, to form a battery precursor.
[0068] S250, irradiating the back surface of the battery precursor with a first laser, and applying a reverse voltage between the first electrode and the second electrode.
[0069] The back surface of the battery precursor can be understood as the back surface of the silicon substrate 1. The back surface of the battery precursor is irradiated with the first laser, so that the back surface of the battery precursor absorbs a large number of photons, and a large number of carriers are generated at the position irradiated by the laser. The intensity of the first laser can be set according to actual needs, which needs to ensure that the battery precursor can sufficiently absorb photons, and will not cause damage to the battery precursor.
[0070] The application of the reverse voltage between the first electrode 6 and the second electrode 7 makes the carriers generated by the laser irradiation directional move to generate current, so that at the place where the series resistance is low, a breakdown is formed, a local high temperature is generated instantaneously, and the first electrode 6 forms an ohmic contact with the P-type semiconductor structure 2, the second electrode 7 and the N-type semiconductor structure, so as to reduce the contact resistance between the first electrode 6 and the P-type semiconductor structure 2, and between the second electrode 7 and the N-type semiconductor structure 3.
[0071] Since the first electrode 6 and the second electrode 7 are both formed on the back surface of the silicon substrate 1, the back surface of the silicon substrate 1 is irradiated with the first laser, so that the generated carriers are close to the first electrode 6 and the second electrode 7, thereby making the transmission distance of the current generated by the directional movement of the carriers shorter, which is beneficial to reduce the recombination of the carriers, so that a smaller energy laser and a smaller reverse voltage can form an ohmic contact, which is beneficial to save energy.
[0072] The voltage range of the reverse voltage can be set according to actual conditions. In an optional embodiment, the voltage range of the reverse voltage U is 5V≤U≤12V. When the reverse voltage is less than 5V, the current generated by the directional movement of the carriers generated by the laser irradiation is too small, so that the local high temperature cannot be generated instantaneously, and the first electrode 6 and the P-type semiconductor structure 2, the second electrode 7 and the N-type semiconductor structure cannot form an alloy to form an ohmic contact. When the reverse voltage is greater than 12V, the current generated by the directional movement of the carriers generated by the laser irradiation is too large, which will cause damage to the battery precursor.
[0073] Specifically, the first laser is used to irradiate the back surface of the battery precursor and apply a reverse voltage between the first electrode 6 and the second electrode 7. After the battery precursor absorbs the photons and converts them into electrons, the local channel of the battery sheet is broken down. Due to the high temperature generated during the breakdown process, the silicon in the battery precursor and the metal of the first electrode 6 or the second electrode 7 form an alloy, which is conducive to the formation of an ohmic contact between the first electrode 6 and the P-type semiconductor structure 2, the second electrode 7 and the N-type semiconductor structure 3.
[0074] In an optional embodiment, the preparation method of the back contact solar cell further comprises using a second laser to irradiate the front surface of the battery precursor and applying a reverse voltage between the first electrode 6 and the second electrode 7.
[0075] The front surface of the battery precursor can be understood as the front surface of the silicon substrate 1. The second laser is used to irradiate the front surface of the battery precursor, which can also generate carriers in the battery precursor. The intensity of the second laser can be set according to actual needs, which needs to ensure that the battery precursor can fully absorb photons and will not cause damage to the battery precursor. It is worth noting that the intensity of the first laser and the second laser can be equal or not equal, and the present embodiment does not make specific limitations.
[0076] It should be noted that the laser sintering of the battery precursor can specifically include only using the first laser to irradiate the back surface of the battery precursor, and applying a reverse voltage between the first electrode 6 and the second electrode 7, or only using the second laser to irradiate the front surface of the battery precursor, and applying a reverse voltage between the first electrode 6 and the second electrode 7, or using the first laser to irradiate the back surface of the battery precursor, and using the second laser to irradiate the front surface of the battery precursor, while applying a reverse voltage between the first electrode 6 and the second electrode 7. When the first laser is used to irradiate the back surface of the battery precursor, and the second laser is used to irradiate the front surface of the battery precursor, while a reverse voltage is applied between the first electrode 6 and the second electrode 7, more carriers will be generated in the battery precursor, so that the first laser and / or the second laser with smaller energy can form an ohmic contact between the electrode and the silicon, which is beneficial to reduce the requirements for the laser generating device and save costs.
[0077] In the embodiment, after the first electrode and the second electrode are formed, the back surface of the battery precursor is irradiated by the first laser, and a reverse voltage is applied between the first electrode and the second electrode, so that the back surface of the battery precursor absorbs a large number of photons, and a large number of carriers are generated at the position of laser irradiation. The carriers move directionally under the action of the reverse bias to generate current, so that a breakdown occurs at a place with low series resistance, and a local high temperature is generated instantaneously, so that the first electrode and the P-type semiconductor structure, the second electrode and the N-type semiconductor structure form an ohmic contact, so as to reduce the contact resistance between the first electrode and the P-type semiconductor structure, and between the second electrode and the N-type semiconductor structure.
[0078] Embodiment three
[0079] Figure 4 A flowchart of a preparation method of a back contact solar cell is provided for the third embodiment of the present application. Based on the above-mentioned embodiments, the embodiment further increases the steps of how to form the P-type semiconductor structure and the N-type semiconductor structure on the back surface of the silicon substrate, and how to form the first electrode on the surface of the P-type semiconductor structure and the second electrode on the surface of the N-type semiconductor structure. Referring to FIG. 6, the preparation method has the following steps: Figure 4
[0080] S310, providing a silicon substrate.
[0081] The silicon substrate 1 has opposite front and back surfaces. The silicon substrate is a polished or textured silicon substrate.
[0082] S320, using a boron diffusion process to boron-dope the back surface of the silicon substrate.
[0083] The concentration of the boron doping ranges from 1e18 to 1e19 cm 3 .
[0084] The boron diffusion process can include, but is not limited to, three steps of low-temperature deposition, high-temperature propulsion and post-oxidation. In an optional embodiment, the silicon substrate is sent into a furnace tube to diffuse boron on the back surface of the silicon substrate. In the boron diffusion process, the gas for the low-temperature deposition step is BCl3 and O2, the BCl3 concentration is 100-300 sccm, the ratio of BCl3 to O2 is 1:2-1:5, the deposition temperature is 800-900°C, and the deposition time is less than 50 min. After the low-temperature deposition is completed, the gas supply is stopped, and the cavity temperature is maintained at 900-1000°C. After the high-temperature propulsion is completed, post-oxidation is performed. In the post-oxidation step, the oxygen flow is 1000-10000 sccm, and the post-oxidation time is less than 30 min. It should be noted that after the boron diffusion process is performed for boron doping, boron silicon glass (BSG) with a thickness of 40-200 nm is formed.
[0085] S330, laser etching is used to remove the boron silicon glass in the P-type semiconductor structure region.
[0086] The back surface of the silicon substrate 1 includes a P-type semiconductor structure 2 region and an N-type semiconductor structure 3 region, the P-type semiconductor structure 2 is formed in the P-type semiconductor structure 2 region, and the N-type semiconductor structure 3 is formed in the N-type semiconductor structure 3 region. The conditions of laser etching can be set according to actual needs, and the boron silicon glass in the P-type semiconductor structure 2 region can be removed; in an optional embodiment, the laser etching laser power is 15W-55W, and the speed is 3000-50000mm / s. It should be noted that after laser etching, a laser damage layer with a certain thickness is generated.
[0087] In an optional embodiment, after the boron silicon glass in the P-type semiconductor structure 2 region is removed, a step of chain acid washing the silicon substrate 1 is further included to remove the thin boron silicon glass on the surface of the silicon substrate 1. For example, a HF solution with a mass percentage of 5%-30% is used to perform chain acid washing on the silicon substrate 1 after boron doping, which can effectively remove the thin BSG film on the front and back surfaces of the silicon substrate.
[0088] S340, removing the laser damage layer and the boron doping layer outside the P-type semiconductor structure region.
[0089] In an optional embodiment, a groove tank is used to perform double-sided alkali etching on the silicon substrate after chain acid washing by using an alkali solution, so as to remove the laser damage layer and the boron doping layer outside the P-type semiconductor structure region, and form a silicon substrate 1 without boron doping outside the P-type semiconductor structure region. For example, the double-sided etching solution is a NaOH or KOH solution added with an etchant, the mass percentage of NaOH or KOH is 3%-10%, the etching temperature is 60-90°C, and the etching time is 150s-600s.
[0090] S350, forming a silicon oxide layer and a polysilicon layer on the back surface of the silicon substrate.
[0091] In an optional embodiment, a stack structure of the silicon oxide layer and the polysilicon layer is deposited on the back surface of the silicon substrate 1 by low pressure chemical vapor deposition (LPCVD), wherein the thickness of the silicon oxide layer is 1-2 nm, for example, 1.5 nm; the total thickness of the silicon oxide layer and the polysilicon layer is 100-300 nm, for example, one of 100 nm, 150 nm, 200 nm, 250 nm, 300 nm or a range value of any two thereof. For example, the reaction gas for depositing the silicon oxide layer is oxygen, the oxygen flow is 10000-30000 sccm, the reaction gas for depositing the polysilicon layer is silane, the flow of silane is 100-400 sccm, and the reaction temperature is 550-600°C.
[0092] S360, phosphorus doping is performed on the silicon oxide layer and the polysilicon layer by a phosphorus diffusion process,
[0093] wherein the concentration of the phosphorus doping ranges from 3e20 to 7e20 cm 3 .
[0094] wherein the phosphorus doping process may, but is not limited to, include three steps of low-temperature deposition and high-temperature promotion and post-oxidation. In an optional embodiment, after the silicon oxide layer and the polysilicon layer are prepared, the silicon substrate is sent into a furnace tube to perform phosphorus diffusion on the polysilicon layer. In the phosphorus diffusion process, the gas for the low-temperature deposition step is O2 and POCl3, and nitrogen is used as a protective gas, wherein the ratio of N2:O2 is between 1:2 and 1:7, the deposition temperature is 850-900°C, and the deposition time is less than 50 min. After the low-temperature deposition is completed, the gas supply is stopped, the temperature of the cavity is maintained at 850-950°C, and the constant-temperature promotion is performed for 10-60 min. After the high-temperature promotion is completed, post-oxidation is performed. In the post-oxidation step, the oxygen flow is 8000-15000 sccm, the post-oxidation time is less than 30 min, and the post-oxidation temperature is 700-850°C. It should be noted that after the phosphorus doping by the phosphorus diffusion process, a phosphosilicate glass (PSG) with a thickness of 40-80 nm is formed.
[0095] S370, laser etching is used to remove the phosphosilicate glass in the N-type semiconductor structure region.
[0096] wherein the conditions of the laser etching can be set according to actual needs, and the borosilicate glass in the N-type semiconductor structure 3 region can be removed; in an optional embodiment, the laser power of the laser etching is 15-55 W, and the speed is 3000-50000 mm / s. It should be noted that after the laser etching, a laser damage layer with a certain thickness is generated.
[0097] In an optional embodiment, after removing the borosilicate glass in the region of the N-type semiconductor structure 3, a step of chain etching the front surface of the silicon substrate is further included to remove the BSG on the front surface of the silicon substrate 1. For example, a 5%-30% HF solution is used to remove the thin BSG film on the front surface of the silicon substrate.
[0098] S380, removing the laser damage layer and the phosphorus doped layer outside the region of the N-type semiconductor structure.
[0099] Specifically, after removing the borosilicate glass in the region of the N-type semiconductor structure 3, the silicon substrate 1 is subjected to alkaline etching and texturing to remove the laser damage layer and the phosphorus doped layer outside the region of the N-type semiconductor structure, so as to expose the P-type semiconductor structure 2 and the N-type semiconductor structure 3 arranged in an interdigital and spaced manner.
[0100] In an optional embodiment, the silicon substrate 1 is subjected to alkaline etching by using 1%-5% NaOH and etching additives, and then subjected to tank texturing by using 0.5%-3% NaOH and texturing additives, so as to form a pyramid texturing pattern on the front and back surfaces of the silicon substrate and in the gap region (PN isolation region). Finally, the silicon substrate is cleaned by using 5%-30% HF and O3 to remove the PSG film on the front surface of the silicon substrate. In this embodiment, the back surface of the silicon substrate is first subjected to alkaline tank etching to remove the regions other than the region of the N-type semiconductor structure (i.e., the region where the borosilicate glass layer has been removed) and the phosphorus doped polysilicon layer on the front surface, and then subjected to texturing tank etching to form a texturing pattern on the front and back surfaces of the silicon substrate. The silicon substrate is further cleaned by using HF and O3 to remove the borosilicate glass layer in the region of the N-type semiconductor structure, the dense oxide layer in the region of the P-type semiconductor structure, and other surface additives, so as to expose the N-type semiconductor region and the P-type semiconductor region arranged in an interdigital and spaced manner.
[0101] In another embodiment, removing the PSG film on the front surface of the silicon substrate can include cleaning the silicon substrate by using a mixed acid including 25%-35% HNO3 and 5%-15% HF. In this embodiment, the mixed acid of nitric acid and hydrofluoric acid is used to remove the borosilicate glass layer on the front surface of the silicon substrate and achieve the etching effect.
[0102] S390, forming a first passivation film layer on the front surface of the silicon substrate and forming a second passivation film layer on the back surface of the silicon substrate.
[0103] S3100, printing a first electrode paste on the surface of the P-type semiconductor structure and printing a second electrode paste on the surface of the N-type semiconductor structure by using a screen printing process.
[0104] The first electrode 6 paste and the second electrode 7 paste can be the same or different. In an optional embodiment, the first electrode 6 paste and / or the second electrode 7 paste comprises a conductive paste such as silver paste or silver-aluminum paste. It can be understood that the printing of the first electrode 6 paste on the surface of the P-type semiconductor structure 2 and the printing of the second electrode 7 paste on the surface of the N-type semiconductor structure 3 can be performed simultaneously or at different times, and the present embodiment does not limit the printing sequence of the first electrode 6 paste and the second electrode 7 paste.
[0105] S3110, performing sintering treatment on the first electrode paste and the second electrode paste.
[0106] The temperature range of the sintering treatment is 500℃≤T≤600℃. Since the first electrode 6 and the second electrode 7 are formed, laser sintering is performed on the battery precursor to form ohmic contact between the first electrode 6 and the P-type semiconductor structure 2 and between the second electrode 7 and the N-type semiconductor structure 3, and thus the temperature of the sintering treatment can be lower than the temperature of the conventional sintering, which is beneficial to cost saving.
[0107] Specifically, after the first electrode 6 paste is printed on the surface of the P-type semiconductor structure 2 and the second electrode 7 paste is printed on the surface of the N-type semiconductor structure 3, due to the limitation of the preparation process and the flowability of the electrode paste, in order to fix the electrode paste on the surface of the P-type semiconductor structure 2 or the N-type semiconductor structure 3, the silicon substrate 1 printed with the electrode paste can be placed in a high-temperature sintering furnace for sintering, so that the organic materials such as organic additives or organic carriers in the electrode paste volatilize in a high-temperature environment, and the electrode paste is solidified. In this way, the movement of the electrode paste can be prevented, and the uniformity of the distribution of the first electrode 6 and the second electrode 7 can be improved.
[0108] S3120, performing laser sintering on the battery precursor to form ohmic contact between the first electrode and the P-type semiconductor structure.
[0109] In the present embodiment, after the P-type semiconductor structure and the N-type semiconductor structure are formed on the back surface of the silicon substrate, the first electrode paste is printed on the surface of the P-type semiconductor structure and the second electrode paste is printed on the surface of the N-type semiconductor structure by using the screen printing process. Since the first electrode and the second electrode are formed, laser sintering is performed on the battery precursor to form ohmic contact between the first electrode and the P-type semiconductor structure and between the second electrode and the N-type semiconductor structure, and thus the temperature of the sintering treatment after the printing of the electrode paste can be lower than the temperature of the conventional sintering, which is beneficial to cost saving.
[0110] Embodiment Four
[0111] Based on the same inventive concept, Figure 5 A structure diagram of a back contact solar cell is provided for the third embodiment of the present application, which is described with reference to Figure 5As shown, the embodiment also provides a back contact solar cell prepared by the preparation method of the back contact solar cell provided by any of the above embodiments, wherein the P-type semiconductor structure 2 and the N-type semiconductor structure 3 are arranged in an interdigitated manner on the back surface of the silicon substrate. Since the back contact solar cell provided by the embodiment is prepared by the preparation method of the back contact solar cell provided by any of the embodiments of the present application, it can achieve the beneficial effects of the preparation method of the back contact solar cell provided by the embodiments of the present application, and the same parts can be referred to the description above.
[0112] The above detailed description does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.
Claims
1. A method for fabricating a back-contact solar cell, characterized in that, include: Provide silicon substrate; The silicon substrate has a front side and a back side facing each other; A P-type semiconductor structure and an N-type semiconductor structure are formed on the back side of the silicon substrate; The P-type semiconductor structure includes a P-type doped silicon layer; A first electrode is formed on the surface of the P-type semiconductor structure, and a second electrode is formed on the surface of the N-type semiconductor structure to form a battery precursor; The battery precursor is laser-sintered to form an ohmic contact between the first electrode and the P-type semiconductor structure.
2. The method for preparing a back-contact solar cell according to claim 1, characterized in that, The N-type semiconductor structure includes an N-type doped tunneling oxide layer and a polycrystalline silicon layer.
3. The method for preparing a back-contact solar cell according to claim 1, characterized in that, Laser sintering of the battery precursor includes: The back side of the battery precursor is irradiated with a first laser, and a reverse voltage is applied between the first electrode and the second electrode.
4. The method for preparing a back-contact solar cell according to claim 3, characterized in that, Also includes: The front side of the battery precursor is irradiated with a second laser, and a reverse voltage is applied between the first electrode and the second electrode.
5. The method for preparing a back-contact solar cell according to claim 3 or 4, characterized in that, The reverse voltage U has a voltage range of 5V ≤ U ≤ 12V.
6. The method for fabricating a back-contact solar cell according to claim 1, characterized in that, Forming a first electrode on the surface of the P-type semiconductor structure and a second electrode on the surface of the N-type semiconductor structure includes: A first electrode paste is printed on the surface of the P-type semiconductor structure and a second electrode paste is printed on the surface of the N-type semiconductor structure using a screen printing process. The first electrode slurry and the second electrode slurry are subjected to sintering treatment; the temperature range of the sintering treatment is: 500℃≤T≤600℃.
7. The method for preparing a back-contact solar cell according to claim 1, characterized in that, A P-type semiconductor structure is formed on the back side of the silicon substrate, comprising: The back side of the silicon substrate is boron-doped using a boron diffusion process; Laser etching was used to remove the borosilicate glass from the P-type semiconductor structure region. Remove the boron-doped layer outside the laser-damaged layer and the P-type semiconductor structure region.
8. The method for preparing a back-contact solar cell according to claim 1, characterized in that, An N-type semiconductor structure is formed on the back side of the silicon substrate, comprising: A silicon oxide layer and a polycrystalline silicon layer are formed on the back side of the silicon substrate; The silicon oxide layer and the polycrystalline silicon layer are phosphorus-doped using a phosphorus diffusion process. Laser etching is used to remove the phosphosilicate glass in the N-type semiconductor structure region; Remove the phosphorus-doped layer outside the laser-damaged layer and the N-type semiconductor structure region.
9. The method for preparing a back-contact solar cell according to claim 1, characterized in that, Before forming the first electrode on the surface of the P-type semiconductor structure and the second electrode on the surface of the N-type semiconductor structure, the method further includes: A first passivation film layer is formed on the front side of the silicon substrate, and a second passivation film layer is formed on the back side of the silicon substrate.
10. A back-contact solar cell, characterized in that, It is prepared by the method of any one of claims 1-9 for back contact solar cells.