Solar cell and preparation method thereof

Abstract

The invention discloses a solar cell and a preparation method thereof, and the method comprises the steps: sequentially preparing a tunneling oxide layer and a phosphorus-doped polycrystalline silicon layer on the back surface of a silicon substrate, and enabling the thickness of the phosphorus-doped polycrystalline silicon layer to be not larger than 100 nm; and carrying out laser doping on the whole phosphorus-doped polycrystalline silicon layer. Through the above mode, the lateral transmission resistance can be reduced while the parasitic absorption of the doped polycrystalline silicon layer is reduced, the tunneling passivation structure is prevented from being damaged, and the efficiency of the cell is improved.

Description

Technical Field

[0001] The present application relates to the technical field of solar cell preparation, and in particular to a solar cell and a preparation method thereof. Background Art

[0002] In order to reduce the parasitic absorption of the doped polysilicon layer in the tunnel oxide passivation contact cell, it is often improved by thinning the thickness of the doped polysilicon (poly). However, the doping amount of impurity atoms in the thinner doped polysilicon layer will become lower, and there is a problem of increased lateral transmission resistance during carrier collection; and when the thickness of the poly layer is thinned, there is a problem that the tunnel oxide layer is easily penetrated by doping during the high-temperature and long-term doping process of poly, which affects the improvement of the conversion efficiency of solar cells by thinning the thickness of the doped polysilicon. At present, the preparation methods for thinning the back phosphorus-doped polysilicon layer mainly include wet mask thinning, laser selective thinning, and stacked doped polysilicon layer superimposed with selective removal of poly. Among them, the wet mask method requires first depositing the mask and the patterned poly layer and then removing the mask layer by wet method, which has the problems of complicated process and easy to introduce chemical contamination. Laser selective thinning uses laser to directly remove the poly layer selectively, and directly uses the high energy of the laser to thin the poly layer, which has the problems of large damage and difficult to control. The laminated doped polysilicon method requires combining the preparation of the laminated poly with a mask or laser, and the process is complicated, which is not conducive to industrialization.

[0003] The prior art CN118248785A also provides a solution: prepare a tunneling silicon oxide layer and a phosphorus-doped polysilicon layer on the back of an N-type silicon wafer, use a laser to heat treat a designated area of ​​the phosphorus-doped polysilicon layer on the back of the N-type silicon wafer, and form a phosphorus-doped silicon oxide layer in the laser heat-treated area. The patent mentions that this solution can be applied to low-metal contact recombination on a phosphorus-doped polysilicon layer with a thickness of less than 80nm. However, the patent's solution of forming a phosphorus-doped silicon oxide layer by laser heat treatment does not improve the doping concentration of poly and is not helpful in reducing the lateral transmission resistance. Summary of the invention

[0004] The present application mainly provides a solar cell and a method for preparing the same, in order to solve the influence of a thin doped polysilicon layer on improving the photoelectric conversion efficiency of the solar cell.

[0005] In order to solve the above technical problems, a technical solution adopted in this application is: a method for preparing a solar cell is proposed, comprising:

[0006] A tunneling oxide layer and a phosphorus-doped polysilicon layer are sequentially prepared on the back side of a silicon substrate, wherein the thickness of the phosphorus-doped polysilicon layer is not greater than 100 nm; and the surface doping concentration of the phosphorus-doped polysilicon layer is 3E20 cm -3 ~8E20cm -3, square resistance is 60ohm / sq~80ohm / sq;

[0007] The entire surface of the phosphorus-doped polysilicon layer is laser doped, and the phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer are driven into the silicon crystal grains of the phosphorus-doped polysilicon layer, and the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms. After laser doping, the surface doping concentration of the phosphorus-doped polysilicon layer is 1E21cm -3 Above, the square resistance is 30ohm / sq~60ohm / sq, and the effective electrical activation rate of phosphorus atoms is more than 95%;

[0008] The laser doping parameters include: laser wavelength of 500nm to 1100nm, laser energy density of 0.5J / cm 2 ~1.0J / cm 2 , spot area is 0.01mm 2 ~0.1mm 2 .

[0009] As a further example, the thickness of the phosphorus-doped polysilicon layer is in the range of 60 nm to 80 nm.

[0010] As a further example, the laser type used in the laser doping is continuous laser or pulsed laser.

[0011] As a further example, the step of preparing a phosphorus-doped polysilicon layer on the back side of a silicon substrate includes:

[0012] Depositing an intrinsic polysilicon layer on the tunnel oxide layer for a deposition time of 10 to 20 minutes;

[0013] Phosphorus is diffused into the intrinsic polysilicon layer at a temperature of 850° C. to 900° C. to form a phosphorus-doped polysilicon layer.

[0014] As a further example, after laser doping the entire phosphorus-doped polysilicon layer, the method further includes:

[0015] Preparing a first electrode and a second electrode on the back side and the front side of the silicon substrate respectively;

[0016] The method for preparing the first electrode includes: transferring a low-corrosion slurry to a preset electrode area on the back side of the silicon substrate.

[0017] As a further example, the first electrode and the second electrode are pre-sintered, and the pre-sintered first electrode and the second electrode are laser induced sintered.

[0018] As a further example, before sequentially preparing a tunneling oxide layer and a phosphorus-doped polysilicon layer on the back side of the silicon substrate, the process further includes:

[0019] Performing double-sided texturing on the cleaned silicon substrate to form a velvet surface;

[0020] Diffusion of boron is performed on the front surface of the silicon substrate after texturing to form a boron diffusion layer;

[0021] Cleaning the back side of the silicon substrate to remove the wrap-around on the back side, and performing alkali polishing on the back side of the silicon substrate;

[0022] After sequentially preparing a tunneling oxide layer and a phosphorus-doped polysilicon layer on the back side of the silicon substrate, the method further comprises:

[0023] Preparing a first passivation anti-reflection layer on the phosphorus-doped polysilicon layer, and preparing a second passivation anti-reflection layer on the boron diffusion layer;

[0024] A first electrode and a second electrode are respectively prepared on the back side and the front side of the silicon substrate.

[0025] As a further example, before preparing the first passivation anti-reflection layer on the phosphorus-doped polysilicon layer and preparing the second passivation anti-reflection layer on the boron diffusion layer, the method further includes:

[0026] preparing an aluminum oxide layer on the boron diffusion layer;

[0027] The step of preparing a second passivation anti-reflection layer on the boron diffusion layer comprises:

[0028] The second passivation anti-reflection layer is prepared on the aluminum oxide layer.

[0029] In order to solve the above technical problem, another technical solution adopted in the present application is: a solar cell, wherein the solar cell is prepared by the above-mentioned method for preparing the solar cell.

[0030] In order to solve the above technical problems, another technical solution adopted in the present application is: a solar cell, comprising:

[0031] Silicon substrate;

[0032] A tunneling oxide layer, a phosphorus-doped polysilicon layer, a first passivation anti-reflection layer, and a first electrode located on the back side of the silicon substrate;

[0033] A boron diffusion layer, a second passivation anti-reflection layer, and a second electrode located on the front side of the silicon substrate;

[0034] The thickness of the phosphorus-doped polysilicon layer is not greater than 100 nm, the phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer are driven into the silicon crystal grains of the phosphorus-doped polysilicon layer, and the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms, and the surface doping concentration is greater than 1E21cm -3 , the square resistance is 30ohm / sq~60ohm / sq.

[0035] The beneficial effects of the present application are as follows: Different from the prior art, the present application discloses a method for preparing a solar cell, wherein a tunneling oxide layer and a phosphorus-doped polysilicon layer are sequentially prepared on the back of a silicon substrate to form a thin phosphorus-doped polysilicon layer with a thickness of less than 100 nm, and the phosphorus-doped polysilicon layer is subjected to laser irradiation on the entire surface with a laser wavelength of 500 nm to 1100 nm and a laser energy density of 0.5 J / cm 2 ~1.0J / cm 2 , spot area is 0.01mm 2 ~0.1mm 2 Laser doping is used to drive the phosphorus atoms gathered at the grain boundaries between the phosphorus-doped polysilicon layers into the silicon crystal grains, and to make the phosphorus atoms in the phosphorus-doped polysilicon layer that are not effectively electrically activated replace the silicon atoms to form electrically activated replacement phosphorus atoms, thereby increasing the effective electrical activation rate of the phosphorus atoms from 85% to more than 95%, and increasing the surface doping concentration of the laser-doped area to 1E21cm -3 Above, the square resistance is reduced to 30ohm / sq~60ohm / sq. It effectively reduces the parasitic absorption of light by doped polysilicon, increases the current, and is beneficial to improving the conversion efficiency of solar cells. It also solves the limitation that the thin doped polysilicon layer structure maintains a high doping concentration while being easy to dope through the tunneling oxide layer during the conventional high-temperature and long-term doping process. Only one laser process is added after the preparation of phosphorus-doped polysilicon to increase the doping concentration on its surface and reduce the square resistance. This process method has a simple process and can be easily mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work, among which:

[0037] Figure 1 It is a schematic diagram of a process of an embodiment of a method for preparing a solar cell provided in the present application;

[0038] Figure 2 Yes Figure 1A schematic diagram of the structure after executing steps 10, 20 and 30 in the method shown;

[0039] Figure 3 Yes Figure 1 A schematic diagram of the structure after executing steps 40 and 50 in the method shown;

[0040] Figure 4 Yes Figure 1 A schematic flow chart of an embodiment of step 40 in the method shown;

[0041] Figure 5 Yes Figure 1 A schematic diagram of the structure after executing step 60 in the method shown;

[0042] Figure 6 Yes Figure 3 A schematic diagram of the structure after executing steps 61 and 62 in the structure shown;

[0043] Figure 7 Yes Figure 1 The schematic diagram of the structure after executing steps 70 and 80 in the method shown.

[0044] Description of reference numerals:

[0045] 100-silicon substrate; 200-boron diffusion layer; 300-tunneling oxide layer; 400-phosphorus-doped polysilicon layer; 500-first passivation anti-reflection layer; 600-second passivation anti-reflection layer; 610-passivation layer; 700-first metal layer; 800-second metal layer; 1000-solar cell. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0047] The terms "first", "second", "third" in the embodiments of the present application are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second", "third" can expressly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0048] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0049] The present application proposes a method for preparing a solar cell, comprising:

[0050] A tunneling oxide layer and a phosphorus-doped polysilicon layer are sequentially prepared on the back side of the silicon substrate, wherein the thickness of the phosphorus-doped polysilicon layer is not greater than 100 nm; the surface doping concentration of the phosphorus-doped polysilicon layer is 3E20 cm -3 ~8E20cm -3 , the square resistance is 60ohm / sq~80ohm / sq, and the effective electrical activation rate of phosphorus atoms is 85%;

[0051] The entire phosphorus-doped polysilicon layer is laser doped. The phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer are driven into the silicon crystal grains of the phosphorus-doped polysilicon layer, and the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms. The surface doping concentration of the phosphorus-doped polysilicon layer after laser doping is 1E21cm -3 Above, the square resistance is 30ohm / sq~60ohm / sq, and the effective electrical activation rate of phosphorus atoms is more than 95%;

[0052] The entire phosphorus-doped polysilicon layer is laser doped. The laser doping parameters include: laser wavelength of 500nm to 1100nm, laser energy density of 0.5J / cm 2 ~1.0J / cm 2 , spot area is 0.01mm2～ 0.1mm 2 .

[0053] Specifically, laser doping drives the phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer into the silicon crystal grains. The phosphorus atoms originally gathered at the grain boundaries between the grains act as recombination centers, causing electron holes to be captured and then recombine. The phosphorus atoms driven into the silicon crystal grains act as doping sources in the silicon crystal, and can effectively improve the conductivity after being activated.

[0054] Specifically, after the initial effective electrical activation rate of phosphorus atoms of 85% is increased to an effective electrical activation rate of more than 95%, under such activation conditions, the effective doping concentration of the doped polysilicon layer is increased, which is conducive to forming an ohmic contact.

[0055] The solar cell preparation method proposed in this application, based on the above laser doping parameters, helps to solve the problem of thin poly structure while maintaining high doping concentration to easily penetrate the tunnel oxide layer. And compared with the prior art, only one laser process is added after preparing phosphorus-doped polysilicon, so that the doping concentration on its surface is increased and the lateral transmission resistance is reduced. This process method has a simple process and can be easily mass-produced.

[0056] Embodiment 1

[0057] See also Figure 1 , Figure 1 1 is a schematic diagram of a process of an embodiment of a method for preparing a solar cell provided in the present application, wherein the method for preparing a solar cell comprises:

[0058] Step 10: Perform double-sided texturing on the cleaned silicon substrate 100 to form a textured surface.

[0059] See also Figure 2 , Figure 2 Yes Figure 1 A schematic diagram of the structure after executing steps 10, 20 and 30 in the method shown.

[0060] In this embodiment, the silicon substrate 100 is an N-type silicon wafer.

[0061] Before the double-sided texturing treatment is performed on the silicon substrate 100 , the silicon substrate 100 needs to be pre-treated to remove dirt and damage on the surface of the silicon substrate 100 .

[0062] Specifically, the silicon substrate 100 may be treated by wet processing, for example, the N-type silicon wafer is placed in a wet processing tank to clean the surface oil and mechanical damage layer. Subsequently, the silicon substrate 100 is textured by alkali etching or other methods to form a pyramid-shaped texture surface.

[0063] Step 20 : Boron is diffused on the front side of the textured silicon substrate 100 to form a boron diffusion layer 200 .

[0064] Boron diffusion is performed on the front side of the silicon substrate 100 by introducing a boron source BBr3 or BCl3 and O2 to form a boron diffusion layer 200 covering the entire front side.

[0065] Specifically, the process parameters of boron diffusion include: reaction temperature of 900° C. to 1050° C., reaction time of 3 h to 4 h, and sheet resistance of 300 ohm / sq to 400 ohm / sq.

[0066] Step 30 : Clean the back side of the silicon substrate 100 to remove the PSG and wrap-around on the side and back side, and perform alkali polishing on the back side of the silicon substrate 100 .

[0067] The back side of the silicon substrate 100 is subjected to surface alkali polishing at 60° C. to 80° C. using 10 wt % to 40 wt % of alkali and additives to form a smooth and flat back side.

[0068] Optionally, the back side of the silicon substrate 100 is cleaned using hydrofluoric acid.

[0069] See also Figure 3 , Figure 3 Yes Figure 1 The schematic diagram of the structure after executing steps 40 and 50 in the method shown.

[0070] Step 40: a tunneling oxide layer 300 and a phosphorus-doped polysilicon layer 400 are sequentially prepared on the back side of the silicon substrate 100 , wherein the thickness of the phosphorus-doped polysilicon layer 400 is not greater than 100 nm.

[0071] After the back side of the silicon substrate 100 is polished, a tunneling oxide layer 300 and a phosphorus-doped polysilicon layer 400 are sequentially formed on the back side of the silicon substrate 100 .

[0072] The phosphorus-doped polysilicon layer 400 may be deposited by LPCVD (Low Pressure Chemical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition) or PVD (Physical Vapor Deposition).

[0073] In some embodiments of the present application, the phosphorus-doped polysilicon layer 400 may be prepared by LPCVD (Low Pressure Chemical Vapor Deposition), specifically, depositing an intrinsic polysilicon layer on the tunneling oxide layer 300 and diffusing phosphorus in the intrinsic polysilicon layer to form the phosphorus-doped polysilicon layer 400 .

[0074] Specifically, see Figure 4 , step 40 further comprises:

[0075] Step 41: depositing an intrinsic polysilicon layer on the tunnel oxide layer 300 for a deposition time of 10 min to 20 min, so that the thickness of the intrinsic polysilicon layer is not greater than 100 nm.

[0076] Step 42 : Phosphorus is diffused into the intrinsic polysilicon layer at a temperature of 850° C. to 900° C. to form a phosphorus-doped polysilicon layer 400 .

[0077] Further, the thickness of the tunnel oxide layer 300 is in the range of 0.5 nm to 2.0 nm, and the thickness of the phosphorus-doped polysilicon layer 400 is in the range of 60 nm to 80 nm.

[0078] Specifically, the thickness of the tunnel oxide layer 300 may be 0.5 nm, 0.8 nm, 1.0 nm, 1.2 nm, 1.3 nm, 1.5 nm, 1.7 nm or 2.0 nm, etc.; the thickness of the phosphorus-doped polysilicon layer 400 may be 60 nm, 65 nm, 68 nm, 70 nm, 75 nm, 80 nm, etc.

[0079] In this embodiment, an N-type silicon wafer is used, and phosphorus diffusion is used to prepare the phosphorus-doped polysilicon layer 400.

[0080] Specifically, in the preparation process of the phosphorus-doped polysilicon layer 400, for example, an intrinsic polysilicon layer is first deposited by LPCVD for 10 to 20 minutes, so that the thickness of the intrinsic polysilicon layer is not greater than 100 nm. Then, phosphorus is diffused on the intrinsic polysilicon layer at 850°C to 900°C to form a phosphorus-doped polysilicon layer 400 doped on the entire surface. At this time, the surface doping concentration of the phosphorus-doped polysilicon layer 400 is 3E20cm -3 ~8E20cm -3, the square resistance is 60ohm / sq~80ohm / sq, and the effective electrical activation rate of phosphorus atoms is 85%. The phosphorus diffusion time is controlled to be shorter to avoid the problem that the tunneling oxide layer is easily penetrated by doping during the doping process. More specifically, the square resistance of the phosphorus-doped polysilicon layer 400 can be 60ohm / sq, 62ohm / sq, 63ohm / sq, 65ohm / sq, 68ohm / sq, 70ohm / sq, 75ohm / sq, 78ohm / sq, 80ohm / sq.

[0081] In some embodiments of the present application, PECVD (Plasma Enhanced Chemical Vapor Deposition) can also be used to prepare phosphorus-doped polysilicon 400, and a tunneling oxide layer 300 and an in-situ doped polysilicon layer are sequentially deposited on the back side, and the in-situ doped polysilicon is annealed at a high temperature to form a phosphorus-doped polysilicon layer 400.

[0082] It should be noted that in the present application, the phosphorus-doped polysilicon layer 400 is prepared in step 40, and the parameters affecting the doping concentration, such as the doping source amount and / or the doping time, are controlled within a relatively small range to prevent high-temperature doping from penetrating the tunneling oxide layer, destroying the tunneling passivation structure, and affecting the photoelectric conversion efficiency of the solar cell. Controlling the parameters affecting the doping concentration within a relatively small range is conventional in the art and is not limited here.

[0083] The thinned phosphorus-doped polysilicon layer 400 can reduce its absorption of light energy, thereby reducing parasitic absorption. In this way, more light energy can be absorbed by other parts of the battery and converted into electrical energy, thereby improving the photoelectric conversion efficiency of the battery; at the same time, by optimizing the thickness of the phosphorus-doped polysilicon layer 400, the solar cell can maintain a good passivation contact effect, while reducing parasitic absorption and maintaining high efficiency of the battery.

[0084] Step 50 : performing laser doping on the entire phosphorus-doped polysilicon layer 400 .

[0085] The phosphorus-doped polysilicon layer 400 formed in the above manner has a layer of phosphorus-rich phosphosilicate glass (PSG) on its surface. The phosphorus-doped polysilicon layer 400 is doped with a laser, and the phosphorus-rich phosphosilicate glass (PSG) can further increase the doping concentration in the phosphorus-doped polysilicon layer 400.

[0086] Specifically, the process parameters of laser doping include: laser wavelength of 500nm to 1100nm, laser energy density of 0.5J / cm 2 ~1.0J / cm 2 , spot area is 0.01mm 2～ 0.1mm 2The laser type used can be either continuous laser or pulsed laser. When it is pulsed laser, the pulse width can be 5ns to 100ns. The laser wavelength is, for example, 532nm, 1064nm, etc. The laser energy density is, for example, 0.5J / cm 2 , 0.6J / cm 2 , 0.7J / cm 2 , 0.8J / cm 2 , 0.9J / cm 2 , 1.0J / cm 2 etc.; the spot area is, for example, 0.01 mm 2 , 0.02mm 2 , 0.04mm 2 , 0.06mm 2 、0.08mm 2 、0.09mm 2 , 0.1mm 2 wait.

[0087] Laser doping drives the phosphorus atoms gathered at the grain boundaries between the grains into the silicon crystal grains, and makes the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms. After laser doping, the surface doping concentration of the phosphorus-doped polysilicon layer 400 is 1E21cm -3 The square resistance is 30 ohm / sq to 60 ohm / sq, and the effective electrical activation rate of phosphorus atoms is more than 95%. More specifically, the square resistance of the phosphorus-doped polysilicon layer 400 can be 30 ohm / sq, 32 ohm / sq, 33 ohm / sq, 35 ohm / sq, 40 ohm / sq, 45 ohm / sq, 50 ohm / sq, 55 ohm / sq, 57 ohm / sq, 58 ohm / sq, or 60 ohm / sq.

[0088] Laser doping effectively reduces the parasitic absorption by thinning the doped polysilicon while reducing the lateral transmission resistance of the battery. Compared with the laser doping process of designated areas used in the prior art, the whole surface laser doping method is better controlled, has a high precision tolerance, and is conducive to industrial production.

[0089] It should be noted that since the laser doping can increase the doping concentration in a short time, for example, the laser local processing time is no more than 10 μs, it can be avoided that the doping penetrates the tunneling oxide layer and destroys the tunneling passivation structure.

[0090] Among them, the main purpose of the laser doping process is to increase the surface doping concentration of the phosphorus-doped polysilicon layer 400. Before completing the laser doping process, other substances such as PSG layer, oxide layer, etc. will be formed on the surface of the phosphorus-doped polysilicon layer 400. The new substances generated can be removed by wet cleaning and other methods in subsequent steps. It should be noted that if there is no laser doping step here, the subsequent steps in the prior art still need to be removed by cleaning and other methods such as the phosphorus-doped polysilicon layer and other previous processes. By-products that are not beneficial to the battery structure, therefore, adding laser doping does not involve an additional cleaning step, and the present application scheme is conducive to industrial application and promotion.

[0091] See also Figure 5 , Figure 5 Yes Figure 1 The schematic diagram of the structure after executing step 60 in the method shown.

[0092] Step 60 : preparing a first passivation anti-reflection layer 500 on the phosphorus-doped polysilicon layer 400 , and preparing a second passivation anti-reflection layer 600 on the boron diffusion layer 200 on the front side of the silicon substrate 100 .

[0093] First, the phosphorus-doped polysilicon layer 400 after laser doping is cleaned to remove the wrap-around plating on the side and front side, and remove the BSG on the front side and the PSG on the back side.

[0094] After cleaning, a first passivation anti-reflection layer 500 is formed on the phosphorus-doped polysilicon layer 400 , and a second passivation anti-reflection layer 600 is formed on the boron diffusion layer 200 on the front side of the silicon substrate 100 .

[0095] The first passivation anti-reflection layer 500 is prepared on the phosphorus-doped polysilicon layer 400. The first passivation anti-reflection layer 500 can be one or more layers of silicon nitride film with a thickness of 70-80nm; the second passivation anti-reflection layer 600 is prepared on the boron diffusion layer 200. The second passivation anti-reflection layer 600 can be one or more layers of silicon nitride film with a thickness of 70-80nm and a refractive index of 2.0 to 2.15.

[0096] Optionally, see Figure 6 Before forming the second passivation anti-reflection layer 600 on the boron diffusion layer 200 , the method further includes: forming an aluminum oxide layer 610 on the boron diffusion layer 200 .

[0097] An aluminum oxide layer 610 may be grown on the boron diffusion layer 200 by atomic layer deposition (ALD). The thickness of the aluminum oxide layer 610 is 3 nm to 10 nm.

[0098] After the aluminum oxide layer 610 is formed, a second passivation anti-reflection layer 600 is formed on the aluminum oxide layer 610 .

[0099] One or more silicon nitride films may be deposited on the aluminum oxide layer 610 by PECVD plasma enhanced chemical vapor deposition to form the second passivation anti-reflection layer 600 . The second passivation anti-reflection layer 600 has a thickness of 70 nm to 80 nm and a refractive index of 2.0 to 2.15.

[0100] See also Figure 7 , Figure 7 Yes Figure 1 The schematic diagram of the structure after executing step 70 and step 80 in the method shown.

[0101] Step 70: Prepare a first electrode 700 and a second electrode 800 on the back and front sides of the silicon substrate 100 respectively; the method for preparing the first electrode 700 includes: transferring a low-corrosion slurry to a preset electrode area on the back side of the silicon substrate 100, the preset electrode area being the area where the first electrode 700 is finally expected to be prepared.

[0102] The method of transferring the low-corrosion slurry includes, for example, screen printing or laser transfer. Further, as one example, the first passivation anti-reflection layer 500 may be grooved in advance at a position corresponding to a preset electrode region, and then the low-corrosion slurry may be transferred into the groove.

[0103] Specifically, after conventionally sintered metal paste burns through the second passivation anti-reflection layer 600 on the back side, it is easy to continue to burn through the phosphorus-doped polysilicon layer 400 and contact the tunneling oxide layer 300, thereby destroying the tunneling passivation structure and affecting the photoelectric conversion efficiency of the solar cell. Therefore, the present application further adopts a low-corrosion paste.

[0104] Specifically, in the low-corrosion slurry, the softening point of the glass powder in the slurry can be reduced by adding TeO2, and the amount of lead can be reduced after adding, thereby reducing the corrosiveness of the glass. For example, when the TeO2 content is 20wt% to 50wt%, the glass material has good stability and mild corrosion characteristics. Of course, other glass materials such as Sb2O3, B2O3 and other components also have a certain degree of influence on the softening temperature and corrosiveness of the glass material. The above methods are applicable to the low-corrosion slurry of this application, and this application does not make specific restrictions on this.

[0105] Because the doped polysilicon layer has strong parasitic absorption, the polysilicon is thinned to reduce the parasitic absorption of light by the polysilicon layer. When the thinned polysilicon is printed with metallization paste, the conventional TOPCon paste burns through the first passivation anti-reflection layer 500 and contacts the thin phosphorus-doped polysilicon layer 400, which is easy to burn through and contact the tunneling oxide layer 300, destroying the tunneling passivation structure and producing a larger metal composite. Therefore, a low-corrosive paste is used for printing to prevent the paste from corroding through the phosphorus-doped polysilicon layer 400. The thinned phosphorus-doped polysilicon layer 400 is combined with the low-corrosive paste, which can reduce the parasitic absorption of light by the polysilicon layer while preventing the paste from corroding through the phosphorus-doped polysilicon layer and destroying the tunneling passivation structure, thereby improving the efficiency of the battery.

[0106] Step 80: pre-sintering the first electrode and the second electrode, and performing laser induced sintering on the pre-sintered first electrode and the second electrode.

[0107] The first electrode 700 and the second electrode 800 are pre-sintered so that the second electrode 800 and the first electrode 700 form a stable chemical bond with the silicon substrate 100 at a high temperature, and the material is sintered by laser induced sintering using the high energy density of the laser beam, thereby improving the contact quality and the conversion efficiency of the solar cell.

[0108] Embodiment 2

[0109] The present application also provides a solar cell, which is prepared by the method described in Example 1.

[0110] Embodiment 3

[0111] The present application also proposes a solar cell, which may be a TOPCon cell, including:

[0112] Silicon substrate 100;

[0113] A tunneling oxide layer 300, a phosphorus-doped polysilicon layer 400, a first passivation anti-reflection layer 500 disposed on the phosphorus-doped polysilicon layer 400, and a first electrode 700 disposed on the first passivation anti-reflection layer 500, located on the back side of the silicon substrate 100;

[0114] A boron diffusion layer 200 disposed on the front side of the silicon substrate 100, a second passivation anti-reflection layer 600 disposed on the boron diffusion layer 200, and a second electrode 800 disposed on the second passivation anti-reflection layer 600;

[0115] The phosphorus-doped polysilicon layer 400 is laser doped on the entire surface, and the thickness is not greater than 100 nm; phosphorus atoms gathered at grain boundaries between grains in the phosphorus-doped polysilicon layer 400 are driven into the crystal grains by the laser beam of the laser doping, and phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer 400 replace silicon atoms to form electrically activated replacement phosphorus atoms, and the effective electrical activation rate of phosphorus atoms in the phosphorus-doped polysilicon layer 400 is greater than 95%, and the surface phosphorus doping concentration is greater than 1E21cm -3 , the square resistance is 30ohm / sq~60ohm / sq.

[0116] The present application provides a solar cell and a method for preparing the same, which directly performs laser doping on the entire phosphorus-doped polysilicon layer to increase the phosphorus doping concentration on the surface, and matches the low-corrosive slurry to achieve better metal contact, thereby solving the limitation of thin doped polysilicon layer structure while maintaining high doping concentration to easily penetrate the tunnel oxide layer. This invention uses a thin doped polysilicon layer thickness to reduce parasitic absorption loss while maintaining a high doping concentration on the surface, improving the problem of increased lateral transmission resistance caused by the thin doped polysilicon layer structure, avoiding damage to the tunnel passivation structure, and improving the photoelectric conversion efficiency of the battery.

[0117] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a solar cell, characterized in that: include: A tunneling oxide layer and a phosphorus-doped polysilicon layer are sequentially prepared on the back side of a silicon substrate, wherein the thickness of the phosphorus-doped polysilicon layer is not greater than 100 nm; and the surface doping concentration of the phosphorus-doped polysilicon layer is 3E20 cm -3 ~8E20cm -3 , square resistance is 60ohm / sq~80ohm / sq; The entire surface of the phosphorus-doped polysilicon layer is laser doped, and the phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer are driven into the silicon crystal grains of the phosphorus-doped polysilicon layer, and the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms. After laser doping, the surface doping concentration of the phosphorus-doped polysilicon layer is 1E21cm -3 Above, the square resistance is 30ohm / sq~60ohm / sq; The laser doping parameters include: laser wavelength of 500nm to 1100nm, laser energy density of 0.5J / cm 2 ~1.0J / cm 2 , spot area is 0.01mm 2 ~0.1mm 2 .

2. The method for preparing a solar cell according to claim 1, characterized in that: The thickness of the phosphorus-doped polysilicon layer is in the range of 60nm to 80nm.

3. The method for preparing a solar cell according to claim 1, characterized in that: The laser type used in the laser doping is continuous laser or pulse laser.

4. The method for preparing a solar cell according to claim 1, characterized in that: The method of preparing a phosphorus-doped polysilicon layer on the back side of a silicon substrate comprises: Depositing an intrinsic polysilicon layer on the tunnel oxide layer for a deposition time of 10 to 20 minutes; Phosphorus is diffused into the intrinsic polysilicon layer at a temperature of 850° C. to 900° C. to form a phosphorus-doped polysilicon layer.

5. The method for preparing a solar cell according to claim 1, characterized in that: After laser doping the entire phosphorus-doped polysilicon layer, the method further comprises: Preparing a first electrode and a second electrode on the back side and the front side of the silicon substrate respectively; The method for preparing the first electrode includes: transferring a low-corrosion slurry to a preset electrode area on the back side of the silicon substrate.

6. The method for preparing a solar cell according to claim 5, characterized in that: The first electrode and the second electrode are pre-sintered, and the pre-sintered first electrode and the second electrode are laser induced sintered.

7. The method for preparing a solar cell according to claim 1, characterized in that: Before sequentially preparing a tunneling oxide layer and a phosphorus-doped polysilicon layer on the back side of the silicon substrate, the method further includes: Performing double-sided texturing on the cleaned silicon substrate to form a velvet surface; Diffusion of boron is performed on the front surface of the silicon substrate after texturing to form a boron diffusion layer; Cleaning the back side of the silicon substrate to remove the wrap-around on the back side, and performing alkali polishing on the back side of the silicon substrate; After sequentially preparing a tunneling oxide layer and a phosphorus-doped polysilicon layer on the back side of the silicon substrate, the method further comprises: Preparing a first passivation anti-reflection layer on the phosphorus-doped polysilicon layer, and preparing a second passivation anti-reflection layer on the boron diffusion layer; A first electrode and a second electrode are respectively prepared on the back side and the front side of the silicon substrate.

8. The method for preparing a solar cell according to claim 7, characterized in that: Before preparing the first passivation anti-reflection layer on the phosphorus-doped polysilicon layer and preparing the second passivation anti-reflection layer on the boron diffusion layer, the method further includes: preparing an aluminum oxide layer on the boron diffusion layer; The step of preparing a second passivation anti-reflection layer on the boron diffusion layer comprises: The second passivation anti-reflection layer is prepared on the aluminum oxide layer.

9. A solar cell, characterized in that: The solar cell is prepared by the method for preparing a solar cell according to any one of claims 1 to 8.

10. A solar cell, characterized in that: include: Silicon substrate; A tunneling oxide layer, a phosphorus-doped polysilicon layer, a first passivation anti-reflection layer, and a first electrode located on the back side of the silicon substrate; A boron diffusion layer, a second passivation anti-reflection layer, and a second electrode located on the front side of the silicon substrate; The thickness of the phosphorus-doped polysilicon layer is not greater than 100 nm, the phosphorus atoms gathered at the grain boundaries between the grains of the phosphorus-doped polysilicon layer are driven into the silicon crystal grains of the phosphorus-doped polysilicon layer, and the phosphorus atoms that are not effectively electrically activated in the phosphorus-doped polysilicon layer replace the silicon atoms to form electrically activated replacement phosphorus atoms, and the surface doping concentration is greater than 1E21cm -3 , the square resistance is 30ohm / sq~60ohm / sq.

Images