Passivated contact battery and preparation method thereof

Abstract

The invention discloses a passivation contact cell and a preparation method thereof, and relates to the technical field of solar cell manufacturing, and the preparation method comprises the steps: preparing a tunneling oxide layer and an intrinsic amorphous silicon layer on a first main surface of a silicon substrate from inside to outside in sequence; irradiating a metalized region of the intrinsic amorphous silicon layer by using laser; diffusion of a first doping element is synchronously carried out on the intrinsic amorphous silicon layer and the silicon substrate, and a first doping region corresponding to the metallization region and a second doping region corresponding to other regions are formed on the first main surface of the silicon substrate; the doping concentration of the first doped region is higher than the doping concentration of the second doped region. According to the embodiment, the doping concentration of the first doped region, corresponding to the metallization region, of the silicon substrate is higher than that of the second doped region corresponding to other regions, field passivation, chemical passivation and Auger recombination are balanced, the passivation performance is maintained, meanwhile, the contact resistance is reduced, and the overall contact performance of the solar cell is improved.

Description

Technical Field

[0001] The invention relates to the technical field of solar cell manufacturing, and in particular to a passivation contact cell and a preparation method thereof. Background Art

[0002] In the existing passivation contact cell preparation process, after some doping elements diffuse into the silicon substrate through the tunneling oxide layer, the doping concentration of some areas on the surface of the silicon substrate will be increased. After matching the film layer such as SiNx, the passivation performance of the battery will not deteriorate, but will improve its conductivity due to the increase in doping concentration. Therefore, in order to improve the conductivity of the metallized area, the prior art will adopt laser doping or increase the number of gate lines to increase the doping concentration of the metallized area on the surface of the silicon substrate, but the high energy density of the laser will greatly destroy the tunneling oxide layer in the metallized area. Although the conductivity is improved, the passivation performance is significantly reduced, which is not conducive to the improvement of the overall performance of the battery. The method of increasing the number of gate lines will undoubtedly increase the consumption of raw materials when printing the gate lines, raising the cost. Summary of the invention

[0003] In view of this, an embodiment of the present invention provides a passivated contact cell and a preparation method thereof. After preparing a tunneling oxide layer, a laser is used to irradiate the metallized region of a silicon substrate, so that the first porosity corresponding to the metallized region in the tunneling oxide layer is higher than the second porosity corresponding to other regions in the tunneling oxide layer, thereby increasing the penetration of the first element in the subsequent first element doping process, thereby achieving a doping concentration of the first doping region corresponding to the metallized region on the first main surface of the silicon substrate higher than the doping concentration of the second doping region corresponding to other regions. Field passivation, chemical passivation and Auger recombination are balanced, and while maintaining the passivation performance, the concentration difference between the first doping region and the second doping region on the surface of the silicon substrate is ensured, and while reducing the contact resistance, the overall contact performance of the solar cell is improved.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a passivated contact solar cell, comprising:

[0006] Step 1, preparing a tunneling oxide layer and an intrinsic amorphous silicon layer in sequence from inside to outside on a first main surface of a silicon substrate;

[0007] Step 2, irradiating the metallized region of the intrinsic amorphous silicon layer with a laser, so that a first porosity of a portion of the tunneling oxide layer corresponding to the metallized region is higher than a second porosity of a portion of the tunneling oxide layer corresponding to other regions;

[0008] Step 3, simultaneously diffusing the first doping element into the intrinsic amorphous silicon layer and the silicon substrate to form a doped polysilicon layer, and at the same time, forming a first doping region corresponding to the metallization region and a second doping region corresponding to other regions on the first main surface of the silicon substrate; wherein the doping concentration of the first doping region is higher than the doping concentration of the second doping region.

[0009] Optionally, step 2 comprises: using a power density of 0.1-100 mJ / cm 2 The metallized area is irradiated with a laser.

[0010] Optionally, the first porosity is 1.2 to 12 times the second porosity;

[0011] Optionally, the first porosity is 1.2 to 1.3 times the second porosity; and / or, the first porosity is 20-60%; and / or, the second porosity is 5-50%.

[0012] Optionally, the doping concentration of the first doping region is 8E 17 -1E 19 atoms / cm 3 ; and / or, the doping concentration of the second doping region is 5E 17 -5E 18 atoms / cm 3 .

[0013] Optionally, before step 1, the method further includes: step 0, preparing an emitter doped with a second doping element on the second main surface of the silicon substrate, and polishing the first main surface.

[0014] Optionally, the method further comprises:

[0015] Step 4, preparing a passivation layer on the outer side of the emitter, and preparing a passivation anti-reflection layer on the outer side of the doped polysilicon layer;

[0016] Step 5: Prepare metal electrodes on the first main surface and the second main surface respectively; wherein the metal electrodes correspond to the metallized areas.

[0017] Optionally, the thickness of the tunnel oxide layer is 0.2 nm-2 nm; and / or the thickness of the intrinsic amorphous silicon layer is 30 nm-300 nm.

[0018] In a second aspect, the present invention provides a passivated contact solar cell, comprising: a silicon substrate; wherein a metallization region and other regions excluding the metallization region are arranged on the silicon substrate; a tunneling oxide layer and a doped polysilicon layer are sequentially arranged on the first main surface of the silicon substrate from the inside to the outside; wherein a first porosity of the tunneling oxide layer corresponding to the metallization region is higher than a second porosity of the tunneling oxide layer corresponding to other regions; a first doped region and a second doped region doped with a first doping element are respectively formed on the surface of the silicon substrate corresponding to the metallization region and other regions; wherein the doping concentration of the first doped region is higher than the doping concentration of the second doped region.

[0019] The technical solution of the first aspect of the above invention has the following advantages or beneficial effects: after preparing the tunneling oxide layer, the metallized area of ​​the silicon substrate is irradiated with laser, so that the first porosity corresponding to the metallized area in the tunneling oxide layer is higher than the second porosity corresponding to other areas in the tunneling oxide layer, thereby increasing the penetration of the first element in the subsequent first element doping process, thereby achieving a doping concentration of the first doping area corresponding to the metallized area on the first main surface of the silicon substrate higher than the doping concentration of the second doping area corresponding to other areas. The damage to the tunneling oxide layer caused by laser doping in the prior art is avoided, while ensuring the concentration difference between the first doping area and the second doping area on the surface of the silicon substrate, reducing the contact resistance while improving the overall contact performance of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to better understand the present invention and do not constitute an improper limitation of the present invention.

[0021] Figure 1 is a schematic flow chart of a method for preparing a passivated contact solar cell according to an embodiment of the present invention;

[0022] Figure 2 is a schematic diagram of a cross-sectional structure of a silicon substrate formed after step S101 according to an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of a cross-sectional structure of a silicon substrate formed after step S102 according to an embodiment of the present invention;

[0024] Figure 4 is a schematic diagram of a cross-sectional structure of a silicon substrate formed after step S103 according to an embodiment of the present invention;

[0025] Figure 5 is a schematic flow chart of another method for preparing a passivated contact solar cell according to an embodiment of the present invention;

[0026] Figure 6Schematic diagram of the cross-sectional structure of a silicon substrate formed after step S502 according to an embodiment of the present invention.

[0027] The reference numerals are as follows:

[0028] 1-silicon substrate; 11-metallization area; 12-other areas; 110-first doped area; 120-second doped area; 2-tunneling silicon oxide layer; 31-intrinsic amorphous silicon layer; 32-doped polysilicon layer; 4-emitter; 41-silicon glass layer; 5-passivation layer; 6-passivation anti-reflection layer; 7-metal electrode. DETAILED DESCRIPTION

[0029] A solar cell is a photoelectric semiconductor sheet that uses sunlight to generate electricity directly. It is also called a "solar chip" or "photovoltaic cell". As long as it is illuminated by light that meets certain illumination conditions, it can instantly output voltage and generate current in the presence of a circuit. In physics, it is called solar photovoltaic (PV), or photovoltaic for short. In order to conveniently and clearly describe the method for preparing a solar cell and the solar cell of the present invention, the following exemplary embodiments of the present invention are described in conjunction with the accompanying drawings, which include various details of the embodiments of the present invention to facilitate understanding, and they should be considered as merely exemplary. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0030] The excellent passivation effect of Tunnel oxide and passivated contact (TOPCon) solar cells comes from the construction of ultra-thin tunnel oxide layer / doped polysilicon layer structure, in which the density and thickness of the tunnel oxide layer, the thickness of the doping layer and the doping concentration have a significant impact on the passivation and contact performance of the cell. For passivated contact solar cells with only a tunnel oxide layer on the back, the development focus of existing technologies is on how to improve the contact performance and passivation performance of the back structure.

[0031] In the actual production process, since the oxide layer itself is a porous structure, the diffused doping elements will penetrate through the porous structure to the surface of the silicon substrate and achieve partial doping on the surface of the silicon substrate. In the actual preparation process, after some doping elements diffuse into the silicon substrate through the tunneling oxide layer, the doping concentration of some areas on the surface of the silicon substrate will increase. After matching the SiNx and other film layers, the passivation performance of the battery will not deteriorate. On the contrary, due to the increase in doping concentration, its conductivity will be improved. In theory, the destruction of the oxide layer will affect the tunneling mechanism and thus deteriorate the passivation performance. The main reason for the battery's final opening voltage to remain unchanged is that the energy level structure between the doped area formed by the appropriate amount of doping elements on the surface of the silicon substrate and the tunneling oxide layer and the doped polysilicon layer is more conducive to the directional transmission of charges, which is conducive to the improvement of the opening voltage and fill factor, and the hydrogen in the SiNx film layer can effectively repair the composite effect caused by the diffusion of doping elements to a certain extent. Therefore, controlling the degree of phosphorus atoms in the tunneling oxide layer and the expanded part is of great significance to obtain a passivated contact solar cell with high passivation and high contact performance.

[0032] In one embodiment of the present invention, Figure 1 As shown, this embodiment provides a method for preparing a passivated contact solar cell, and the preparation method may include the following steps:

[0033] Step S101, forming a tunnel oxide layer 2 and an intrinsic amorphous silicon layer 31 on a first main surface of a silicon substrate 1 from inside to outside in sequence;

[0034] Step S102, irradiating the metallized region 11 of the intrinsic amorphous silicon layer 31 with a laser, so that a first porosity of a portion of the tunneling oxide layer 2 corresponding to the metallized region 11 is higher than a second porosity of a portion of the tunneling oxide layer 2 corresponding to other regions 12;

[0035] In step S103, the first doping element is diffused synchronously on the intrinsic amorphous silicon layer 31 and the silicon substrate 1 to form the doped polysilicon layer 3. At the same time, a first doping region 110 corresponding to the metallization region 11 and a second doping region 120 corresponding to other regions 12 are formed on the first main surface of the silicon substrate 1; wherein the doping concentration of the first doping region 110 is higher than the doping concentration of the second doping region 120.

[0036] Among them, for the passivated contact solar cell, the first main surface can be understood as the back side of the silicon substrate. It should be noted that in the actual preparation process, the tunneling oxide layer 2 itself is a porous structure. When not irradiated by laser, the porosity of the tunneling oxide layer 2 formed on the entire surface is consistent. Under laser irradiation, based on the laser irradiation parameters and irradiation time, the porosity will continue to increase until the irradiation stops. In order to achieve the expected doping concentration in the first doped region 110 on the surface of the silicon substrate in an embodiment of the present invention, in an optional embodiment, step S102 specifically includes: using a power density of 0.1-100 mJ / cm 2 The metallized area 11 is irradiated with laser. Compared with the high-energy laser beam of laser doping in the prior art, the embodiment of the present invention can achieve the purpose of improving the porosity by only using low-power laser, effectively avoiding the damage to the tunneling oxide layer 2 during the high-energy laser irradiation process, and ensuring the passivation performance. Moreover, the thermal annealing and hydrogen saturation process of the first doping element diffusion process in step S103 can further eliminate the laser damage caused by the laser irradiation in step S102, thereby further reducing the impact on the passivation performance.

[0037] In addition, it should be noted that the present invention performs laser irradiation on the basis of preparing the tunneling oxide layer 2 and the intrinsic amorphous silicon layer 31 in step S101, that is, the intrinsic amorphous silicon layer 3 is used as a transition for laser irradiation, and the tunneling oxide layer 2 is not directly irradiated. This is because direct irradiation of the tunneling oxide layer 2 will cause greater laser damage and the porosity is difficult to control. Line irradiation of the intrinsic amorphous silicon layer 31 can reduce partial laser penetration, thereby reducing the risk of laser damage.

[0038] In an optional embodiment, the first porosity is 1.2 to 12 times the second porosity, preferably the first porosity is 1.2 to 1.3 times the second porosity. By controlling the multiple relationship between the first porosity and the second porosity, the concentration difference of the doping concentration between the first doping region 110 and the second doping region 120 can be indirectly controlled, so the multiple relationship between the first porosity and the second porosity can be defined according to actual needs. Specifically, the first porosity can be 20-60%, such as 20%, 30%, 40%, 50%, 60%, etc.; the second porosity can be 5-50%, such as 5%, 10%, 25%, 40%, 50%, etc. It can be understood that the first porosity and the second porosity are uniformly distributed when laser irradiation is not used, so no matter how the first porosity and the second porosity are taken, the first porosity is always greater than the second porosity. Correspondingly, as the porosity increases, more first doping elements pass through the tunneling oxide layer 2 during the diffusion process, so the concentration of the first doping region 110 formed on the surface of the silicon substrate 1 will be higher than the concentration of the second doping region 120, thereby forming a concentration difference between the first doping region 110 and the second doping region 120.

[0039] It should be noted that the thickness of the tunneling oxide layer 2 and the thickness of the intrinsic amorphous silicon layer 31 will also affect the effect of laser irradiation. Therefore, the embodiment of the present invention limits the thickness of the tunneling oxide layer 2, the thickness of the intrinsic amorphous silicon layer 31, and the doping concentration finally formed in the first doping region 110 and the second doping region 120. Specifically, the thickness of the tunneling oxide layer 2 is 0.2 nm-2 nm, such as 0.2nm, 0.5nm, 1.0nm, 1.2nm, 2nm, etc., the thickness of the intrinsic amorphous silicon layer 31 is 30 nm-300 nm, such as 30nm, 50nm, 100nm, 150nm, 200nm, 300nm, etc., and the doping concentration of the first doping region 110 formed is 8E 17 -1E 19 atoms / cm 3 The doping concentration of the second doped region 120 is 5E 17 -5E 18 atoms / cm 3 It is understandable that the thicker the intrinsic amorphous silicon layer 31 and the tunnel oxide layer 2 are, the higher the absorption of laser energy is, and the porosity change rate will also change accordingly, so the laser irradiation time will also be adjusted accordingly to finally obtain a suitable concentration difference.

[0040] In an optional embodiment, since the structure of the front side of the silicon substrate 1 is relatively simple, the front side of the silicon substrate 1 can be prepared before step S101, specifically including: preparing an emitter 4 doped with a second doping element on the second main surface of the silicon substrate 1, and polishing the first main surface. The second main surface is the front side of the silicon substrate 1. The second doping element is of a different type from the first doping element. When the silicon substrate 1 is an N-type silicon substrate, the first doping element can be phosphorus, and the second doping element can be boron. It can be understood that when preparing the emitter 4 on the second main surface, a silicon glass layer will be simultaneously formed on the outside of the emitter 4. Therefore, the cross-sectional structure of the silicon substrate formed after step S101 can be as follows. Figure 2 As shown. The silicon substrate 1 can be textured first to form a second main surface with a textured structure, and then the first main surface can be polished to obtain a smooth first main surface. At the same time, when preparing the intrinsic amorphous silicon layer 31, it is difficult to avoid the occurrence of plating around. Therefore, in order to simplify the process flow, while preparing the intrinsic amorphous silicon layer 31 on the first main surface, the intrinsic amorphous silicon layer 31 is also formed on the outside of the silicon glass layer 41 on the second main surface.

[0041] For example, the cross-sectional structure of the silicon substrate obtained after step S102 may be as follows: Figure 3 As shown, the metallized regions 11 and other regions 12 are alternately arranged to form a tunnel oxide layer 2. It is understandable that since the intrinsic amorphous silicon layer 31 is an amorphous silicon structure without pores, the laser irradiation has basically no effect on the intrinsic amorphous silicon layer 31, and only affects the tunnel oxide layer 2 with a porous structure.

[0042] In a further optional embodiment, after step S103, it is necessary to remove the excess intrinsic amorphous silicon layer 31 and silicon glass layer 41 on the second main surface of the silicon substrate, and specifically, wet chemical cleaning method can be used to soak the second main surface with acid solution or alkaline solution to remove the excess intrinsic amorphous silicon layer 31 and silicon glass layer 41. For example, the cross-sectional structure of the silicon substrate obtained through the above process can be as follows: Figure 4 As shown. Figure 4 It can be seen that after step S103, the original intrinsic amorphous silicon layer 31 is doped with the first doping element to become a doped polycrystalline silicon layer 32, and as the first doping element is continuously doped upward, a first doping region 110 and a second doping region 120 with different doping concentrations are formed on the surface of the silicon substrate 1, thereby achieving the technical effect to be achieved by the present invention.

[0043] In a further optional embodiment, in the above Figure 4 After the silicon substrate cross-section structure is prepared, it can also be Figure 5 As shown, including:

[0044] Step S501: preparing a passivation layer 5 on the outer side of the emitter 4, and preparing a passivation anti-reflection layer 6 on the outer side of the doped polysilicon layer 32;

[0045] Step S502 , preparing metal electrodes 7 on the first main surface and the second main surface respectively; wherein the metal electrodes 7 correspond to the metallized regions 11 .

[0046] For example, the silicon substrate structure obtained after step S501 and step S502 is as follows: Figure 6 As shown, from Figure 6 It can be seen that the metal electrode 7 arranged on the first main surface is electrically connected to the doped polysilicon layer 32 through the passivation anti-reflection layer 6, and the metal electrode 7 arranged on the second main surface is electrically connected to the emitter 4 through the passivation layer 5, thereby realizing the extraction of current.

[0047] In summary, the preparation method of the passivated contact solar cell provided by the embodiment of the present invention, after preparing the tunneling oxide layer, uses laser to irradiate the metallized area of ​​the silicon substrate, so that the first porosity corresponding to the metallized area portion in the tunneling oxide layer is higher than the second porosity corresponding to other areas in the tunneling oxide layer, thereby increasing the penetration of the first element in the subsequent first element doping process, thereby achieving that the doping concentration of the first doping area corresponding to the metallized area on the first main surface of the silicon substrate is higher than the doping concentration of the second doping area corresponding to other areas. The damage to the tunneling oxide layer caused by laser doping in the prior art is avoided, while ensuring the concentration difference between the first doping area and the second doping area on the surface of the silicon substrate, reducing the contact resistance while improving the overall contact performance of the solar cell.

[0048] Still Figure 6 Taking as an example, the structure of the passivated contact solar cell provided by the present invention is specifically described. Specifically, the passivated contact solar cell provided by the present invention includes: a silicon substrate 1; wherein a metallization area 11 and other areas 12 excluding the metallization area 11 are arranged on the silicon substrate 1; a tunneling oxide layer 2 and a doped polysilicon layer 32 are sequentially arranged on the first main surface of the silicon substrate 1 from the inside to the outside; wherein the first porosity of the tunneling oxide layer 2 corresponding to the metallization area 11 is higher than the second porosity of the tunneling oxide layer 2 corresponding to the other areas 12; a first doped area 110 and a second doped area 120 doped with a first doping element are respectively formed on the surface of the silicon substrate 1 corresponding to the metallization area 11 and the other areas 12; wherein the doping concentration of the first doped area 110 is higher than the doping concentration of the second doped area 120.

[0049] It should be noted that, since the degree to which the first doping element passes through the tunneling oxide layer 2 is directly related to the tunneling mechanism, it has a great influence on the overall passivation performance of the solar cell. Therefore, the embodiment of the present invention only modifies a small area of ​​the metallized region, and there is no need to improve the entire tunneling oxide layer 2. Specifically, the ratio of the area of ​​the metallized region 11 to the total area of ​​the first main surface is 1-10%, which can ensure the tunneling structure and passivation performance of the first main surface as much as possible, and can effectively ensure the battery yield during the production line production process.

[0050] In an optional embodiment, the thickness of the doped polysilicon layer 32 is 30 nm-300 nm, for example, 30nm, 80nm, 150nm, 200nm, 250nm, 300nm, etc.; the thickness of the silicon substrate 1 is 50μm-500μm, for example, 50μm, 100μm, 200μm, 350μm, 450μm, 500μm, etc.

[0051] Furthermore, the passivated contact solar cell provided by the present invention also includes: an emitter 4 doped with a second doping element and arranged on the second main surface of the silicon substrate 1; and a passivation layer 5 arranged on the outside of the emitter 4, a passivation anti-reflection layer 6 arranged on the outside of the doped polysilicon layer 32, and metal electrodes 7 respectively arranged on the first main surface and the second main surface; wherein the metal electrode 7 is arranged corresponding to the metallization area 11.

[0052] In summary, the passivated contact solar cell provided by the embodiment of the present invention sets the first porosity of the tunneling oxide layer corresponding to the metallized region to be higher than the second porosity of the tunneling oxide layer corresponding to other regions, so that after the doping diffusion process of the first element, the doping concentration of the first doped region formed on the first main surface of the silicon substrate corresponding to the metallized region is higher than the doping concentration of the second doped region formed corresponding to other regions. The damage to the tunneling oxide layer caused by laser doping in the prior art is avoided, while ensuring the concentration difference between the first doped region and the second doped region on the surface of the silicon substrate, reducing the contact resistance while improving the overall contact performance of the solar cell.

[0053] Example

[0054] Step a, performing a texturing treatment on an N-type silicon substrate having a resistivity of 1 Ω cm and a thickness of 135 μm to form a suede structure;

[0055] Step b, loading the textured silicon substrate into an LPCVD quartz boat, introducing a boron source to complete the boron diffusion process, and forming an emitter and a borosilicate glass layer BSG on the front side of the silicon substrate;

[0056] Step c, washing away the BSG with a 10% HF solution, and polishing the back of the silicon substrate to obtain a surface with a 10 μm tower base;

[0057] Step d, placing the dried silicon substrate in a quartz boat, heating it to 600°C under low pressure, introducing 2000sccm of oxygen to prepare a tunneling oxide layer (SiO2) with a thickness of 1.5nm and a porosity of 40%, and then introducing silane to prepare an intrinsic amorphous silicon layer with a thickness of 150nm on the outside of the tunneling oxide layer 2;

[0058] Step e, using a power density of 1 mJ / cm 2 2. The metallized area of ​​the intrinsic amorphous silicon layer is irradiated with an ultraviolet pulse laser having a wavelength of 254 nm, so that the porosity of the part of the tunnel oxide layer corresponding to the metallized area increases to 50%;

[0059] Step f, introducing phosphorus oxychloride pentachloride and oxygen at 890°C to simultaneously diffuse phosphorus into the intrinsic amorphous silicon layer and the silicon substrate to obtain a doping concentration of 5E 20 atoms / cm 3 The doping concentrations of the doped polysilicon layer and the silicon substrate surface are 8E 17 and 2E 18 atoms / cm 3 a first doped region and a second doped region;

[0060] Step g, performing wet chemical cleaning on the phosphosilicate glass layer PSG formed on the front, side, and back of the silicon substrate and the BSG on the front;

[0061] Step h, Al2O3 coating is performed on the front side of the silicon substrate. Trimethylaluminum and water are introduced at 250°C to prepare an Al2O3 layer with a thickness of 6 nm on the front side. Silane and ammonia are introduced at 540°C in a plasma enhanced chemical vapor deposition device to complete the SiN coating on both sides. x The film is deposited with a thickness of 75 nm. Then, the silver paste is printed on the front and back sides of the silicon wafer by screen printing to form a passivation layer outside the emitter and a passivation anti-reflection layer outside the doped polysilicon layer.

[0062] Step i: coating a metal fine grid with a width of 15 μm on the front metallization area and coating a metal fine grid with a width of 20 μm on the back metallization area, and sintering at a high temperature to form a metal electrode.

[0063] Comparative Example 1

[0064] Step a, performing a texturing treatment on an N-type silicon substrate having a resistivity of 1 Ω cm and a thickness of 135 μm to form a suede structure;

[0065] Step b, loading the textured silicon substrate into an LPCVD quartz boat, introducing a boron source to complete the boron diffusion process, and forming an emitter and a borosilicate glass layer BSG on the front side of the silicon substrate;

[0066] Step c, washing away the BSG with a 10% HF solution, and polishing the back of the silicon substrate to obtain a surface with a 10 μm tower base;

[0067] Step d, placing the dried silicon substrate in a quartz boat, heating it to 600°C under low pressure, introducing 2000sccm of oxygen to prepare a tunneling oxide layer (SiO2) with a thickness of 1.5nm and a porosity of 40%, and then introducing silane to prepare an intrinsic amorphous silicon layer with a thickness of 150nm on the outside of the tunneling oxide layer 2;

[0068] Step e: introducing phosphorus oxychloride pentachloride and oxygen at 890°C to simultaneously diffuse phosphorus into the intrinsic amorphous silicon layer and the silicon substrate to obtain a doping concentration of 5E 20 atoms / cm 3 The doping concentrations of the doped polysilicon layer and the silicon substrate surface are 8E 17 and 2E 18 atoms / cm 3 a first doped region and a second doped region;

[0069] Step f, performing wet chemical cleaning on the phosphosilicate glass layer PSG formed on the front, side, and back of the silicon substrate and the BSG on the front;

[0070] Step g, Al2O3 coating is performed on the front side of the silicon substrate. Trimethylaluminum and water are introduced at 250°C to prepare an Al2O3 layer with a thickness of 6 nm on the front side. Silane and ammonia are introduced at 540°C in a plasma enhanced chemical vapor deposition device to complete the SiN coating on both sides. x The film is deposited with a thickness of 75 nm. Then, the silver paste is printed on the front and back sides of the silicon wafer by screen printing to form a passivation layer outside the emitter and a passivation anti-reflection layer outside the doped polysilicon layer.

[0071] Step h: coating a metal fine grid with a width of 15 μm on the front metallization area and coating a metal fine grid with a width of 20 μm on the back metallization area, and sintering at a high temperature to form a metal electrode.

[0072] Comparative Example 2

[0073] Step a, performing a texturing treatment on an N-type silicon substrate having a resistivity of 1 Ω cm and a thickness of 135 μm to form a suede structure;

[0074] Step b, loading the textured silicon substrate into an LPCVD quartz boat, introducing a boron source to complete the boron diffusion process, and forming an emitter and a borosilicate glass layer BSG on the front side of the silicon substrate;

[0075] Step c, washing away the BSG with a 10% HF solution, and polishing the back of the silicon substrate to obtain a surface with a 10 μm tower base;

[0076] Step d, placing the dried silicon substrate in a quartz boat, heating it to 600°C under low pressure, introducing 2000sccm of oxygen to prepare a tunneling oxide layer (SiO2) with a thickness of 1.5nm and a porosity of 40%, and then introducing silane to prepare an intrinsic amorphous silicon layer with a thickness of 150nm on the outside of the tunneling oxide layer 2;

[0077] Step e, using a power density of 50 mJ / cm 2 2. The ultraviolet pulse laser with a wavelength of 254 nm irradiates the metallized area of ​​the intrinsic amorphous silicon layer, so that the porosity of the part of the tunnel oxide layer corresponding to the metallized area increases to 80%;

[0078] Step f, introducing phosphorus oxychloride pentachloride and oxygen at 890°C to simultaneously diffuse phosphorus into the intrinsic amorphous silicon layer and the silicon substrate to obtain a doping concentration of 5E 20 atoms / cm 3 The doping concentrations of the doped polysilicon layer and the silicon substrate surface are 8E 17 and 2E 18 atoms / cm 3 a first doped region and a second doped region;

[0079] Step g, performing wet chemical cleaning on the phosphosilicate glass layer PSG formed on the front, side, and back of the silicon substrate and the BSG on the front;

[0080] Step h, Al2O3 coating is performed on the front side of the silicon substrate. Trimethylaluminum and water are introduced at 250°C to prepare an Al2O3 layer with a thickness of 6 nm on the front side. Silane and ammonia are introduced at 540°C in a plasma enhanced chemical vapor deposition device to complete the SiN coating on both sides. x The film is deposited with a thickness of 75 nm. Then, the silver paste is printed on the front and back sides of the silicon wafer by screen printing to form a passivation layer outside the emitter and a passivation anti-reflection layer outside the doped polysilicon layer.

[0081] Step i: coating a metal fine grid with a width of 15 μm on the front metallization area and coating a metal fine grid with a width of 20 μm on the back metallization area, and sintering at a high temperature to form a metal electrode.

[0082] The passivated contact solar cells prepared in the above examples and comparative examples were tested for performance, and the test results are shown in the following table:

[0083]

[0084] It can be seen that compared with Comparative Example 1, the passivated contact solar cell provided by the embodiment of the present invention has a slightly improved porosity of the tunneling layer corresponding to the metal area on the back, resulting in a higher concentration of doped elements on the surface of the silicon substrate, and thus better contact performance, lower series resistance, and an increase of 0.1% in battery efficiency. While achieving a gain of 0.3% in the fill factor, the passivation performance is also enhanced by field passivation, increasing by 0.2mV. In Comparative Example 2, due to the excessive power of the laser radiation, the porosity of the tunneling layer is greatly increased, resulting in the destruction of the tunneling layer after phosphorus diffusion, so the passivation performance is worse, the current is also lost due to increased recombination, and the battery efficiency is reduced. Therefore, in the embodiment of the present invention, not only the porosity of some areas in the tunneling oxide layer is increased by laser irradiation, but also the selection of laser parameters during laser irradiation, the thickness of the intrinsic amorphous silicon layer, and the specific parameters in the phosphorus diffusion process are coordinated to achieve the final technical effect of the embodiment of the present invention.

[0085] The introduction provided in the above steps is only used to help understand the structure, method and core idea of ​​the present invention. For ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also belong to the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a passivated contact solar cell, characterized in that: include: Step 1, preparing a tunneling oxide layer (2) and an intrinsic amorphous silicon layer (31) on a first main surface of a silicon substrate (1) in sequence from the inside to the outside; Step 2, irradiating the metallized region (11) of the intrinsic amorphous silicon layer (31) with a laser, so that a first porosity of a portion of the tunneling oxide layer (2) corresponding to the metallized region (11) is higher than a second porosity of a portion of the tunneling oxide layer (2) corresponding to other regions (12); Step 3, simultaneously diffusing the first doping element into the intrinsic amorphous silicon layer (31) and the silicon substrate (1) to form a doped polysilicon layer (32), and at the same time forming a first doping region (110) corresponding to the metallized region (11) and a second doping region (120) corresponding to other regions (12) on the first main surface of the silicon substrate (1); wherein the doping concentration of the first doping region (110) is higher than the doping concentration of the second doping region (120).

2. The method according to claim 1, characterized in that The step 2 comprises: using a power density of 0.1-100 mJ / cm 2 The laser irradiates the metallized area (11).

3. The method according to claim 1, characterized in that The first porosity is 1.2 to 12 times the second porosity.

4. The method according to claim 3, characterized in that The first porosity is 1.2 to 1.3 times the second porosity; and / or, The first porosity is 20-60%; and / or, The second porosity is 5-50%.

5. The method according to claim 1, characterized in that The doping concentration of the first doping region (110) is 8E 17 -1E 19 atoms / cm 3 ; and / or, The doping concentration of the second doping region (120) is 5E 17 -5E 18 atoms / cm 3 .

6. The method according to claim 1, characterized in that Before step 1, the method further includes: Step 0: preparing an emitter (4) doped with a second doping element on the second main surface of the silicon substrate (1), and performing a polishing process on the first main surface.

7. The method according to claim 6, characterized in that Also includes: Step 4, preparing a passivation layer (5) on the outer side of the emitter (4), and preparing a passivation anti-reflection layer (6) on the outer side of the doped polysilicon layer (32); Step 5: preparing metal electrodes (7) on the first main surface and the second main surface respectively; wherein the metal electrodes (7) correspond to the metallized areas (11).

8. The method according to claim 1, characterized in that Also includes: The thickness of the tunnel oxide layer (2) is 0.2 nm-2 nm; and / or, The intrinsic amorphous silicon layer (31) has a thickness of 30 nm-300 nm.

9. A passivated contact solar cell, characterized in that: include: A silicon substrate (1); wherein a metallized region (11) and other regions (12) excluding the metallized region (11) are provided on the silicon substrate (1); A tunneling oxide layer (2) and a doped polysilicon layer (32) are sequentially arranged on the first main surface of the silicon substrate (1) from the inside to the outside; wherein a first porosity of a portion of the tunneling oxide layer (2) corresponding to the metallized region (11) is higher than a second porosity of a portion of the tunneling oxide layer (2) corresponding to other regions (12); A first doping region (110) and a second doping region (120) doped with a first doping element are formed on the surface of the silicon substrate (1) corresponding to the metallization region (11) and other regions (12), respectively; wherein the doping concentration of the first doping region (110) is higher than the doping concentration of the second doping region (120).

10. The passivated contact solar cell according to claim 9, characterized in that: The ratio of the area of ​​the metallized region (11) to the total area of ​​the first main surface is 1-10%.

Images