Back contact solar cell and preparation method thereof

Abstract

The invention discloses a back contact solar cell and a preparation method thereof, and relates to the technical field of solar cells. The battery comprises a battery substrate, and a first doped region, a second doped region, an isolation region and a buffer region which are positioned on a first main surface of the battery substrate, the isolation region and the buffer region are located between the first doped region and the second doped region, and the buffer region is located between the first doped region and the isolation region; the first doped region is provided with an emitter comprising first doped atoms; the second doped region is provided with a carrier collection layer containing second doped atoms, and the conduction type of the second doped atoms is opposite to that of the first doped atoms; the buffer region is provided with a diffusion layer comprising first doping atoms; the junction depth of the diffusion layer is smaller than that of the emitter. According to the embodiment of the invention, the problem of relatively large carrier recombination loss caused by relatively large height difference between the outer surface of the emitter of the first doped region and the outer surface of the carrier collection layer of the second doped region in the thickness direction of the cell can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a preparation method of a back contact solar cell and the back contact solar cell. BACKGROUND

[0002] In the field of solar cells, the back contact solar cell has become one of the main types of solar cells developed in recent years due to its high light utilization rate. The P-type doped region of the back contact solar cell mainly has two structures, i.e. a structure provided with a P-type doped polysilicon layer and a structure provided with a P + emitter. For the back contact solar cell provided with a P + emitter, the parasitic absorption caused by the P-type doped polysilicon layer can be eliminated, but the carrier recombination between the P-type doped region and the N-type doped region of the back contact solar cell is large, which is not conducive to improving the performance of the back contact solar cell. SUMMARY

[0003] Therefore, the embodiments of the present application provide a back contact solar cell and a preparation method thereof, which can reduce the carrier recombination between the first doped region and the second doped region, and is conducive to improving the performance of the back contact solar cell.

[0004] To achieve the above object, according to an aspect of the embodiments of the present application, a back contact solar cell is provided, comprising:

[0005] a cell substrate, a first doped region, a second doped region, an isolation region and a buffer region located on a first main surface of the cell substrate; wherein,

[0006] the isolation region and the buffer region are located between the first doped region and the second doped region, and the buffer region is located between the first doped region and the isolation region;

[0007] the first doped region is provided with an emitter comprising first doped atoms;

[0008] the second doped region is provided with a carrier collection layer comprising second doped atoms, and the second doped atoms are opposite in conductive type to the first doped atoms;

[0009] the buffer region is provided with a diffusion layer comprising the first doped atoms;

[0010] the diffusion layer has a junction depth smaller than that of the emitter.

[0011] To achieve the above object, according to another aspect of the embodiments of the present application, a preparation method of a back contact solar cell is provided, comprising:

[0012] Step A1, providing a battery substrate, a first main surface of the battery substrate has a first doped region, a second doped region, an isolation region and a buffer region; wherein the isolation region and the buffer region are located between the first doped region and the second doped region; the buffer region is located between the first doped region and the isolation region;

[0013] Step A2, preparing a whole mask layer on the first main surface of the battery substrate;

[0014] Step A3, removing the mask layer corresponding to the first doped region, and performing a diffusion treatment of first doped atoms, forming an emitter containing first doped atoms in the first doped region, forming a diffusion layer containing first doped atoms in the inside of the mask layer of the second doped region, the isolation region and the buffer region, and forming a first doped silicon glass layer outside the emitter and outside the mask layer; wherein the junction depth of the diffusion layer is less than the junction depth of the emitter;

[0015] Step A4, removing the first doped silicon glass layer, the mask layer and the diffusion layer corresponding to the second doped region and the isolation region, and forming a carrier collection layer containing second doped atoms in the second doped region;

[0016] Step A5, removing the first doped silicon glass layer corresponding to the first doped region and the buffer region, and removing the mask layer corresponding to the buffer region.

[0017] An embodiment of the above-mentioned application has the following advantages or beneficial effects: by setting a buffer region including a diffusion layer between the first doped region and the second doped region, and the junction depth of the first doped atoms in the diffusion layer being less than the junction depth of the emitter, the barrier energy between the first doped region and the second doped region is reduced, and the influence on the lateral transport of carriers is reduced. By setting the buffer region, the first doped region and the second doped region have a gradual change in the junction depth of the first doped atoms, the electric field is relieved, the barrier energy required to be overcome by the lateral transport of carriers is reduced, the transport path of the carriers is optimized, the carriers are guided to transport along the direction of low recombination and short path, the recombination of the carriers is reduced, the loss of the lateral transport of the carriers is reduced, and the performance of the back contact solar cell is improved.

[0018] By setting the emitter in the first doped region, compared with the battery structure of setting a polysilicon layer doped with first doped atoms in the first doped region, the parasitic absorption caused by the polysilicon layer doped with first doped atoms is eliminated, the short circuit current is larger, the bifaciality is higher, and the passivation performance is more excellent.

[0019] Further, the height difference between the outer surface of the emitter of the first doped region and the outer surface of the carrier collecting layer of the second doped region can be reduced, thereby reducing the structural defects of the height difference region, reducing the recombination loss caused by the structural defects, and improving the photoelectric conversion efficiency of the cell.

[0020] Further effects of the above-described non-conventional optional modes will be described below in conjunction with the specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings are used to better understand the present application and do not constitute an improper limitation on the present application. Among them:

[0022] Figure 1 is a structural schematic diagram of a back contact solar cell according to an embodiment of the present application;

[0023] Figure 2 is a flowchart of a preparation method of a back contact solar cell according to an embodiment of the present application;

[0024] Figure 3 is a structural schematic diagram of a cell substrate after step A2 according to an embodiment of the present application;

[0025] Figure 4 is a structural schematic diagram of a cell substrate after a first texturing treatment according to an embodiment of the present application;

[0026] Figure 5 is a structural schematic diagram of a cell substrate after a diffusion treatment according to an embodiment of the present application;

[0027] Figure 6 is a structural schematic diagram of a cell substrate after a polishing treatment according to an embodiment of the present application;

[0028] Figure 7 is a structural schematic diagram of a cell substrate after a second texturing treatment according to an embodiment of the present application;

[0029] Figure 8 is a structural schematic diagram of a cell substrate after a doping treatment according to an embodiment of the present application;

[0030] Figure 9 is a structural schematic diagram of a cell substrate after forming a first passivation anti-reflection layer and a second passivation anti-reflection layer according to an embodiment of the present application;

[0031] Figure 10 is a photoluminescence test image of a partial structure of a back contact solar cell M according to Embodiment 1;

[0032] Figure 11 is a photoluminescence test image of a partial structure of a back contact solar cell L according to Comparative Example 1.

[0033] Reference signs:

[0034] 1 - base of the cell; 11 - first doped region; 111 - emitter; 112 - first metal electrode; 12 - second doped region; 121 - tunneling passivation layer; 122 - doped polysilicon layer; 123 - second metal electrode; 13 - isolation region; 14 - buffer region; 141 - diffusion layer; 15 - base of silicon; 16 - first passivation anti-reflection layer; 17 - second passivation anti-reflection layer; 18 - mask layer; 19 - first doped silicon glass layer; 20 - second doped silicon glass layer; DETAILED DESCRIPTION

[0035] At present, the emitter of the back contact solar cell is generally formed by directly doping and diffusing on the surface of the silicon base. In particular, for the back contact solar cell provided with P + emitter, in order to control the sheet resistance of the P + emitter, a larger junction depth is required for the P + emitter. Although the P + emitter with larger junction depth can be formed by adjusting the diffusion parameters of the P-type doping atoms, this will cause the P-type doping atoms to diffuse into the inside of the silicon base corresponding to the N-type doped region during the diffusion process, forming a part containing P-type doping atoms, resulting in higher recombination of the N-type doped region, thereby affecting the cell efficiency. In order to reduce the recombination of the N-type doped region, in the existing process, a higher height difference is generally provided between the P+ emitter and the N-type doped region. This is because, in the existing production process, the above-mentioned part containing P-type doping atoms of the N-type doped region is removed by laser before the functional film layer of the N-type doped region is prepared. In order to remove the P-type doping atoms in the N-type doped region as completely as possible, the depth of laser etching needs to be increased, which will eventually result in a larger height difference between the outer surface of the P+ emitter of the P-type doped region and the outer surface of the doped polysilicon layer of the N-type doped region, resulting in an increase in the lateral transport distance of the carriers. When the carriers move between the P-type doped region and the N-type doped region, they need to overcome a higher potential barrier energy, and the "step" position structure with height difference is not flat, which may have local doping overlap or vacancy, has more structural defects, and the recombination of the carriers is increased; and laser damage parts are also generated, causing the carriers to recombine at this position, reducing the short-circuit current, affecting the fill factor of the solar cell, and the edge of the N-type doped region will show a "black edge" with large structural defects on the photoluminescence test image.

[0036] According to the problems in the prior art, the embodiments of the present application provide a back contact solar cell and a preparation method thereof.

[0037] Exemplary embodiments of the present application are described herein with reference to the accompanying drawings, which are meant to be exemplary in nature, and include various specific details to facilitate understanding, and are to be considered in the context of the description. One skilled in the art will realize that the embodiments described herein are not the only ones that can be employed, and that the intent and parameters of the present application can vary from those described. Accordingly, various modifications and changes can be made to the embodiments described without departing from the scope and spirit of the present application. Also, for the purpose of clarity and the brevity of description, the description below omits the description of well-known functions and structures.

[0038] It should be noted that the first main surface referred to in the embodiments of the present application means the side of the solar cell that faces away from sunlight when the solar cell is in operation, and correspondingly, the second main surface referred to in the embodiments of the present application means the side of the solar cell that faces towards sunlight when the solar cell is in operation. The inside to outside referred to in the embodiments of the present application means the direction from the surface of the silicon substrate to the direction away from the silicon substrate. The inside referred to in the embodiments of the present application means the side of the corresponding functional film layer that is close to the silicon substrate, and correspondingly, the outside referred to in the embodiments of the present application means the side of the corresponding functional film layer that is away from the silicon substrate.

[0039] It should be noted that the outer surface referred to in the embodiments of the present application means the side of the functional film layer that is away from the silicon substrate.

[0040] It should be noted that the embodiments of the present application and the technical features in the embodiments can be combined with each other without conflict.

[0041] Figure 1 is a structural schematic diagram of a back contact solar cell according to the embodiments of the present application. As shown in Figure 1 the back contact solar cell according to the embodiments of the present application mainly comprises: a cell substrate 1, a first doped region 11, a second doped region 12, an isolation region 13 and a buffer region 14 located on the first main surface of the cell substrate 1.

[0042] The conductive type of the first doped region 11 and the second doped region 12 is opposite. As an example, when the conductive type of the first doped region 11 is N type, the conductive type of the second doped region 12 is P type; when the conductive type of the first doped region 11 is P type, the conductive type of the second doped region 12 is N type.

[0043] Optionally, in the direction parallel to the first main surface, the proportion of the area of the first doped region 11 to the total area of the first main surface is 17.5% to 46%; the proportion of the area of the second doped region 12 to the total area of the first main surface is 40% to 60%. For example, the proportion of the area of the first doped region 11 to the total area of the first main surface can be 17.5%, 20%, 23%, 27%, 32%, 36%, 40% or 46%; the proportion of the area of the second doped region 12 to the total area of the first main surface can be 40%, 43%, 47%, 50%, 55% or 60%. By controlling the proportion of the area of the first doped region 11 and the second doped region 12 in the first main surface, the area of the first doped region 11 and the second doped region 12 is reasonably distributed, which can ensure the total amount of photo-generated carriers, reduce the recombination loss caused by surface recombination centers, and improve the carrier collection efficiency.

[0044] The isolation region 13 and the buffer region 14 are located between the first doped region 11 and the second doped region 12, and the buffer region 14 is located between the first doped region 11 and the isolation region 13. The isolation region 13 is used to isolate the first doped region 11 and the second doped region 12.

[0045] Optionally, in the direction parallel to the first main surface, the proportion of the area of the isolation region 13 to the total area of the first main surface is 10% to 30%; the proportion of the area of the buffer region 14 to the total area of the first main surface is 4% to 12.5%. For example, the proportion of the area of the isolation region 13 to the total area of the first main surface can be 10%, 15%, 18%, 20%, 25% or 30%; the proportion of the area of the buffer region 14 to the total area of the first main surface can be 4%, 5.0%, 6.0%, 8.0%, 10.0% or 12.5%. By controlling the proportion of the area of the isolation region 13 in the first main surface, the short circuit between the first doped region 11 and the second doped region 12 or the first metal electrode 112 and the second metal electrode 123 can be effectively prevented while avoiding the reduction of the effective light absorption area of the battery, and the leakage can be avoided. By setting the buffer region 14 between the first doped region 11 and the second doped region 12 and adjusting the proportion of the area of the buffer region 14 in the first main surface, in the hole carrier transport process, the problem of insufficient diffusion distance and large structural defects caused by direct movement between the first doped region 11 and the second doped region 12 to cause large recombination loss is avoided, the doping concentration of the first doped region 11 and the second doped region 12 is relieved, and the carrier lateral transport process only needs to overcome a lower barrier energy, thereby optimizing the transport path.

[0046] In addition, the battery base 1 can further include a silicon base 15. The silicon base 15 can adopt an N-type silicon base or a P-type silicon base. Specifically, the conductivity type of the silicon base 15 is opposite to that of the first doped region 11 and the same as that of the second doped region 12. As an example, when the silicon base 15 adopts an N-type silicon base, the conductivity type of the first doped region 11 can be P-type, and the conductivity type of the second doped region 12 can be N-type.

[0047] Optionally, the resistivity of the silicon base 15 can be 0.1 Ω·cm~100 Ω·cm; and the thickness of the silicon base 15 can be 100 μm~500 μm. As an example, the resistivity of the silicon base 15 can be 0.1 Ω·cm, 0.5 Ω·cm, 1.0 Ω·cm, 10 Ω·cm, 30 Ω·cm, 50 Ω·cm, 80 Ω·cm or 100 Ω·cm, etc.; and the thickness of the silicon base 15 can be 100 μm, 150 μm, 200 μm, 220 μm, 260 μm, 300 μm, 350 μm, 400 μm or 500 μm, etc. By selecting a silicon base 15 with appropriate resistivity and thickness to prepare the back contact solar cell, the light absorption and material cost can be balanced, the internal resistance of the cell can be reduced, and the carrier collection efficiency can be improved.

[0048] The first doped region 11 is provided with an emitter 111 including first doped atoms. The first doped atoms can be P-type doped atoms or N-type doped atoms. The P-type doped atoms refer to atoms of trivalent doped elements, such as boron atoms, aluminum atoms, etc.; and the N-type doped atoms refer to atoms of pentavalent doped elements, such as phosphorus atoms, arsenic atoms, antimony atoms, etc. Preferably, the first doped atoms can be P-type doped atoms.

[0049] Optionally, the junction depth of the emitter 111 is 1 μm~2 μm; the sheet resistance of the emitter 111 is 200 Ω~400 Ω; and the peak concentration of the first doped atoms in the emitter 111 is 3×10 18 atoms / cm 3 ~9×10 18 atoms / cm 3 . As an example, the junction depth of the emitter 111 can be 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.7 μm or 2 μm, etc.; the sheet resistance of the emitter 111 can be 200 Ω, 230 Ω, 250 Ω, 280 Ω, 300 Ω, 350 Ω or 400 Ω, etc.; and the peak concentration of the first doped atoms in the emitter 111 can be 3×10 18 atoms / cm 3 , 5×10 18 atoms / cm 3 , 6×10 18 atoms / cm 3, 7 x 10 18 atoms / cm 3 , 8 x 10 18 atoms / cm 3 or 9 x 10 18 atoms / cm 3 , etc. The junction depth of the emitter 111 refers to the distance between the geometric position of the PN junction formed by the diffusion of the first dopant atoms in the silicon substrate 15 and the surface of the emitter 111. By setting the junction depth, sheet resistance and peak concentration of the first dopant atoms in the above-mentioned optimal parameter range, it is beneficial to form a sufficient built-in electric field, promote the separation of carriers and improve the fill factor of the solar cell. The second doped region 12 is provided with a carrier collection layer containing second dopant atoms, and the second dopant atoms are opposite in conductivity type to the first dopant atoms.

[0050] The second dopant atoms can be P-type or N-type dopant atoms. The types of the first and second dopant atoms are different, i.e. when the first dopant atoms are P-type, the second dopant atoms are N-type; when the first dopant atoms are N-type, the second dopant atoms are P-type. Preferably, the silicon substrate 15 is an N-type silicon substrate, the first dopant atoms are P-type, and the second dopant atoms are N-type.

[0051] The carrier collection layer includes a tunneling passivation layer 121 and a doped polysilicon layer 122 containing second dopant atoms arranged from inside to outside. The tunneling passivation layer 121 can include silicon oxide.

[0052] Optionally, the thickness of the tunneling passivation layer 121 is 0.5 nm to 2.5 nm; the thickness of the doped polysilicon layer 122 is 100 nm to 300 nm; and the doping concentration of the second dopant atoms in the doped polysilicon layer 122 is 3 x 10 20 atoms / cm 3 ~1 x 10 21 atoms / cm 3 . As an example, the thickness of the tunneling passivation layer 121 can be 0.5 nm, 0.8 nm, 1.0 nm, 1.5 nm, 1.7 nm, 2.0 nm or 2.5 nm, etc.; the thickness of the doped polysilicon layer 122 can be 100 nm, 130 nm, 150 nm, 180 nm, 200 nm, 240 nm, 270 nm or 300 nm, etc. The doping concentration of the second dopant atoms in the doped polysilicon layer 122 can be 3 x 10 20 atoms / cm 3 , 5 x 10 20 atoms / cm 3 , 6 x 1020 atoms / cm 3 atoms / cm 20 atoms / cm 3 atoms / cm 21 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm atoms / cm

[0053] The buffer region 14 is provided with a diffusion layer 141 containing the first dopant atoms. The diffusion layer 141 has a junction depth less than that of the emitter 111. The type of dopant element in the diffusion layer 141 is the same as that of the emitter 111.

[0054] Due to the presence of the diffusion layer 141 with a shallow junction depth and high sheet resistance in the isolation region 13, the processing depth is shallow during the polishing process, and the laser damage and polishing damage to the silicon substrate 15 and the side surface of the buffer region 14 is small, reducing the impact on the minority carrier lifetime and preventing the presence of a "black edge" representing structural defects at the edge of the second doped region 12 in the photoluminescence test image of the prepared back contact solar cell.

[0055] Optionally, the diffusion layer 141 has a junction depth of 0.3 μm to 0.8 μm; the diffusion layer 141 has a sheet resistance of 400 Ω to 800 Ω; and the diffusion layer 141 has a peak concentration of the first dopant atoms of 1 × 10 18 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 18 atoms / cm 3 atoms / cm 17 atoms / cm 3 atoms / cm 18 atoms / cm 3By adjusting the junction depth, sheet resistance and peak depth of the first dopant atoms of the diffusion layer 141, the junction depth of the first dopant atoms of the emitter 111 and the diffusion layer 141 can be made to vary in gradient, the carrier transport path can be optimized, and surface recombination can be reduced.

[0056] In an optional embodiment, the height difference between the outer surface of the carrier collection layer of the second doped region 12 and the outer surface of the diffusion layer 141 corresponding to the buffer region 14 is 1 μm to 5 μm; wherein the outer surface of the carrier collection layer of the second doped region 12 is closer to the second main surface of the battery substrate 1 than the outer surface of the diffusion layer 141 corresponding to the buffer region 14. As an example, the height difference between the outer surface of the carrier collection layer of the second doped region 12 and the outer surface of the diffusion layer 141 can be 1 μm, 2 μm, 2.5 μm, 3 μm, 4 μm or 5 μm, etc.

[0057] The outer surface of the carrier collection layer refers to the outer surface of the doped polysilicon layer 122.

[0058] By adjusting the height difference between the outer surface of the diffusion layer 141 corresponding to the buffer region 14 and the outer surface of the carrier collection layer of the second doped region 12, the height difference between the two is kept within an appropriate range, avoiding the problem that the height difference between the two is too large and the buffering effect is not obvious, and enhancing the effect of the buffer region in relieving the abrupt change in doping concentration between the first doped region and the second doped region. By relieving the abrupt change in doping concentration through the buffer region, the carrier can pass through the height difference area by overcoming a smaller barrier energy, reducing the resistance of the carrier lateral transport, reducing carrier recombination, and optimizing the carrier transport path.

[0059] In an optional embodiment, the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the carrier collection layer of the second doped region 12 is 0.1 μm to 3 μm; wherein the outer surface of the carrier collection layer of the second doped region 12 is closer to the second main surface of the battery substrate 1 than the outer surface of the emitter 111 of the first doped region 11. As an example, the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the carrier collection layer of the second doped region 12 can be 0.1 μm, 0.5 μm, 0.8 μm, 1.2 μm, 1.5 μm, 1.9 μm, 2.3 μm, 2.7 μm or 3 μm, etc. By adjusting the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the carrier collection layer of the second doped region 12, the height difference between the two can be reduced relative to the prior art, the lateral transport distance of the carrier can be shortened, the carrier transport path can be optimized, and the problem of uneven film deposition at the "step" of the height difference, resulting in a large number of structural defects, can be reduced, and carrier recombination can be reduced.

[0060] In an optional embodiment, the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the diffusion layer 141 corresponding to the buffer region 14 is 0.9 μm to 4.9 μm; wherein the outer surface of the emitter 111 of the first doped region 11 is closer to the second main surface of the battery substrate 1 than the outer surface of the diffusion layer 141 corresponding to the buffer region 14. For example, the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the diffusion layer 141 corresponding to the buffer region 14 is 0.9 μm, 1.5 μm, 2.0 μm, 3.0 μm, 3.8 μm, 4.3 μm or 4.9 μm, etc. By adjusting the height difference between the outer surface of the diffusion layer 141 corresponding to the buffer region 14 and the outer surface of the emitter 111 of the first doped region 11, the height difference between them is in the appropriate range, avoiding the problem that the buffer effect is not obvious when the height difference between them is large, and enhancing the effect of the buffer region in relieving the abrupt change of the doping concentration between the first doped region and the second doped region. By relieving the abrupt change of the doping concentration through the buffer region, the carrier can overcome a smaller barrier energy to pass through the height difference area, reducing the resistance of the carrier lateral transport, reducing the carrier recombination, and optimizing the carrier transport path.

[0061] In an optional embodiment, the height difference between the first main surface of the battery substrate 1 corresponding to the isolation region 13 and the outer surface of the emitter 111 of the first doped region 11 is 0.5 μm to 10 μm; the height difference between the first main surface of the battery substrate 1 corresponding to the isolation region 13 and the outer surface of the carrier collection layer of the second doped region 12 is 0.5 μm to 10 μm. For example, the height difference between the first main surface of the battery substrate 1 corresponding to the isolation region 13 and the outer surface of the emitter 111 of the first doped region 11 can be 0.5 μm, 0.8 μm, 1 μm, 3 μm, 5 μm, 7 μm or 10 μm, etc.; the height difference between the first main surface of the battery substrate 1 corresponding to the isolation region 13 and the outer surface of the carrier collection layer of the second doped region 12 can be 0.5 μm, 0.9 μm, 2 μm, 4 μm, 5.5 μm, 8 μm or 10 μm, etc. By adjusting the height difference between the first main surface of the battery substrate 1 corresponding to the isolation region 13 and the outer surface of the emitter 111 of the first doped region 11 or the outer surface of the carrier collection layer of the second doped region 12, the high recombination center formed by the step edge of the isolation region 13 and the first doped region 11 or the second doped region 12 can be reduced, thereby reducing the impact on the lateral transport of the carrier.

[0062] In an alternative embodiment, the back contact solar cell further comprises a first passivation and anti-reflection layer 16 disposed on the first doped region 11, the second doped region 12, the isolation region 13 and the buffer region 14. Specifically, the first passivation and anti-reflection layer 16 is disposed on the outer side of the emitter 111 of the first doped region 11, the outer side of the doped polysilicon layer 122 of the second doped region 12, the outer side of the diffusion layer 141 of the buffer region 14 and the isolation region 13, and the first passivation and anti-reflection layers 16 of different regions are connected as a whole. The first passivation and anti-reflection layer 16 can include aluminum oxide, silicon nitride, etc., but is not limited thereto. The first passivation and anti-reflection layer 16 has the effects of passivating surface defects, reducing light reflection and resisting oxidation, and can also protect the silicon substrate 15 of the isolation region 13 from direct exposure.

[0063] In an alternative embodiment, the back contact solar cell further comprises a second passivation and anti-reflection layer 17 disposed on the second major surface of the cell substrate 1. The second passivation and anti-reflection layer 17 can include aluminum oxide, silicon nitride, etc., but is not limited thereto, and can be the same as or different from the first passivation and anti-reflection layer 16. The second passivation and anti-reflection layer 17 has the effects of passivating surface defects of the second major surface, reducing light reflection and resisting oxidation, and can also serve as a physical barrier to protect the silicon substrate 15 of the second major surface from direct exposure.

[0064] In an alternative embodiment, the back contact solar cell further comprises a first metal electrode 112 disposed on the first doped region 11 and in ohmic contact with the emitter 111, and a second metal electrode 123 disposed on the second doped region 12 and in ohmic contact with the carrier collection layer. The electrode paste used to prepare the first metal electrode 112 and the second metal electrode 123 can be the same or different. Alternatively, the electrode paste used to prepare the first metal electrode 112 can include silver paste or silver-aluminum paste, and the electrode paste used to prepare the second metal electrode 123 can include silver paste.

[0065] It can be understood that, in the first major surface of the cell substrate 1, the plurality of first doped regions 11, the plurality of buffer regions 14, the plurality of isolation regions 13 and the plurality of second doped regions 12 are arranged alternately, Figure 1 Only one first doped region 11, one second doped region 12, one isolation region 13 and one buffer region 14 are shown by way of example. The number of first doped regions 11, buffer regions 14, isolation regions 13 and second doped regions 12 in the first major surface of each cell substrate 1 can be set according to actual conditions, and is not specifically limited herein.

[0066] According to the back contact solar cell of the embodiment of the present application, by arranging the buffer zone 14 including the diffusion layer 141 between the first doped zone 11 and the second doped zone 12, and the junction depth of the first doped atoms in the diffusion layer 141 is less than the junction depth of the first doped atoms in the emitter 111, the carrier recombination loss in the height difference region can be reduced, the potential barrier energy between the first doped zone 11 and the second doped zone 12 can be reduced, the influence on the carrier lateral transfer can be reduced, the buffer zone 14 is arranged to make the first doped zone 11 and the second doped zone 12 have a gradual change of the junction depth of the first doped atoms, the electric field change is relieved, the potential barrier energy to be overcome by the carrier lateral transfer is reduced, the carrier transfer path is optimized, the carrier is guided to transfer along the direction of low recombination and short path, the carrier recombination is reduced, and the loss of the carrier lateral transfer is reduced.

[0067] Meanwhile, the height difference between the outer surface of the emitter 111 of the first doped zone 11 and the outer surface of the carrier collection layer of the second doped zone 12 is reduced, the structural defects in the height difference region are reduced, the recombination loss is reduced, and the cell performance is improved.

[0068] By arranging the emitter 111 in the first doped zone 11, compared with the cell structure in which a polysilicon layer doped with the first doped atoms is arranged in the first doped zone 11, the parasitic absorption caused by the polysilicon layer doped with the first doped atoms is eliminated, the short-circuit current is larger, the bifaciality is higher, and the passivation performance is more excellent.

[0069] Figure 2 is a flowchart of the preparation method of the back contact solar cell according to the embodiment of the present application. As shown in Figure 2 the preparation method of the back contact solar cell according to the embodiment of the present application includes the following steps A1-A5:

[0070] Step A1, providing a cell substrate 1, the first main surface of the cell substrate 1 has a first doped zone 11, a second doped zone 12, an isolation zone 13 and a buffer zone 14; wherein the isolation zone 13 and the buffer zone 14 are located between the first doped zone 11 and the second doped zone 12; the buffer zone 14 is located between the first doped zone 11 and the isolation zone 13;

[0071] At this time, since the positions corresponding to the first doped zone 11, the second doped zone 12, the isolation zone 13 and the buffer zone 14 on the cell substrate 1 have not been provided with the corresponding functional film layer, the cell substrate 1 mainly includes a silicon substrate 15. The first main surface and the second main surface of the silicon substrate 15 can be subjected to texturing and polishing treatment.

[0072] It is worth mentioning that the first doped region 11, the second doped region 12, the isolation region 13 and the buffer region 14 are divided based on the differences of the subsequent functional film layers, and the main surface of the battery substrate 1 itself does not contain the first doped region 11, the second doped region 12, the isolation region 13 and the buffer region 14, which are only defined for the convenience of subsequent description of each region.

[0073] The embodiment of the present application provides the drawing taking the polished surface of the silicon substrate 15 as an example for description, and those skilled in the art can know that the silicon substrate 15 can be a textured surface based on the polished surface.

[0074] Step A2, preparing a whole mask layer 18 on the first main surface of the battery substrate 1;

[0075] Meanwhile, a whole mask layer 18 is prepared on the second main surface. After step A2, the structure of the battery substrate 1 as shown in FIG. 1A is obtained, which includes the silicon substrate 15 and the mask layer 18 on the two main surfaces. Figure 3

[0076] Optionally, the mask layer 18 can include any one of the following: a stack of an oxidation layer and an intrinsic crystalline silicon layer arranged from inside to outside, a silicon carbide layer, a silicon nitride layer or a stack of silicon carbide and silicon nitride. The oxidation layer can include silicon oxide. The thickness of the mask layer 18 is 10 nm to 100 nm. For example, the thickness of the mask layer 18 can be 10 nm, 25 nm, 40 nm, 55 nm, 78 nm, 90 nm or 100 nm, etc. By adjusting the material and thickness of the mask layer 18, the concentration and junction depth of the first doped atoms penetrating into the silicon substrate 15 during the subsequent diffusion process can be controlled.

[0077] Step A3, removing the mask layer 18 corresponding to the first doped region 11, and performing diffusion treatment of the first doped atoms to form an emitter 111 containing the first doped atoms in the first doped region 11, to form a diffusion layer 141 containing the first doped atoms in the inside of the mask layer 18 of the second doped region 12, the isolation region 13 and the buffer region 14, and to form a first doped silicon glass layer 19 outside the emitter 111 and outside the mask layer 18; wherein the junction depth of the diffusion layer 141 is less than the junction depth of the emitter 111;

[0078] Optionally, the step A3 can specifically include: removing the mask layer 18 corresponding to the first doped region 11 by first laser processing, and performing first texturing processing on the silicon substrate 15 corresponding to the first doped region 11 to obtain a structure as shown in FIG. 1B. Figure 4 ​The first laser treatment has a power of 10w-50w, the first texturing treatment uses an alkali solution with a mass fraction of 5%-50%, and the first texturing treatment has a time of 5s-300s. For example, the power of the first laser treatment can be 10w, 15w, 20w, 25w, 30w, 40w, or 50w, etc.; the mass fraction of the alkali solution used in the first texturing treatment can be 5%, 10%, 15%, 22%, 30%, 40%, or 50%, etc.; and the time of the first texturing treatment can be 5s, 20s, 50s, 90s, 150s, 200s, 250s, or 300s, etc. Alternatively, the alkali solution used in the first texturing treatment can be a potassium hydroxide solution, but is not limited thereto. By adjusting the power of the first laser treatment, the mass fraction of the alkali solution used in the first texturing treatment, and the treatment time, etc., laser damage caused by the first laser treatment can be reduced, and the texturing quality can be improved.

[0079] After the diffusion treatment of the first dopant atoms, a structure as shown in Figure 5 is obtained, wherein the first doped region 11 forms an emitter 111, and the first dopant atoms diffuse into the silicon substrate 15 to form a diffusion layer 141 at the inside of the mask layer 18, corresponding to the positions of the second doped region 12, the buffer region 14, and the isolation region 13, and the second major surface, due to the blocking of the mask layer 18. Meanwhile, a first doped silicon glass layer 19 containing the first dopant atoms is formed outside the emitter 111 and outside the mask layer 18.

[0080] wherein the sheet resistance of the diffusion layer 141 is higher than that of the emitter 111.

[0081] Step A4, removing the first doped silicon glass layer 19, the mask layer 18, and the diffusion layer 141 corresponding to the second doped region 12 and the isolation region 13, and forming a carrier collection layer containing second dopant atoms on the second doped region 12;

[0082] Before removing the first doped silicon glass layer 19 corresponding to the second doped region 12 and the isolation region 13, the step A4 can further include: single-sidedly etching the first doped silicon glass layer 19 on the second major surface of the cell substrate 1.

[0083] Alternatively, the step A4 can specifically include: removing the first doped silicon glass layer 19 corresponding to the second doped region 12 and the isolation region 13 by a second laser treatment, and removing the mask layer 18 and the diffusion layer 141 corresponding to the second doped region 12 and the isolation region 13 on the second major surface, and the first doped silicon glass layer 19 on the second major surface by a polishing treatment, so as to form a polishing surface on the second major surface and the surface of the silicon substrate 15 corresponding to the second doped region 12 and the isolation region 13.

[0084] The power of the second laser treatment is 30w-50w, the polishing treatment uses an alkali solution with a mass fraction of 5%-50%, and the polishing treatment time is 100s-300s. The polishing treatment depth is greater than or equal to 0.1μm and less than or equal to 1.5μm. As an example, the power of the second laser treatment can be 30w, 35w, 37w, 40w, 43w, 48w or 50w, etc. The mass fraction of the alkali solution used in the polishing treatment can be 5%, 10%, 15%, 22%, 30%, 40% or 50%, etc. The polishing treatment time can be 100s, 120s, 150s, 190s, 200s, 240s, 260s or 300s, etc. Alternatively, the alkali solution used in the polishing treatment can be a potassium hydroxide solution, but is not limited thereto.

[0085] The second doped region 12 forms a carrier collection layer containing second doped atoms, which can specifically include: forming a tunneling passivation layer 121 and an intrinsic polysilicon layer in the first doped region 11, the second doped region 12, the isolation region 13 and the buffer region 14 from the inside to the outside in turn, and performing a doping treatment of the second doped atoms, so that the intrinsic polysilicon layer forms a doped polysilicon layer 122.

[0086] Due to the existence of the shallow-junction-deep-high-resistance diffusion layer 141 in the second doped region 12 and the isolation region 13, the processing depth is shallow during the second laser treatment and the polishing treatment, and the laser damage and the polishing damage to the silicon substrate 15 and the buffer region 14 side are small, which reduces the influence on the minority carrier lifetime and does not cause the “black edge” representing structural defects to exist at the edge of the second doped region 12 in the photoluminescence test image of the prepared back contact solar cell.

[0087] After the polishing treatment, a structure as shown in Figure 6 is obtained, and the electrode substrate second main surface does not have a functional film layer. In the first main surface, the first doped region 11 includes an emitter 111 and a first doped silicon glass layer 19 arranged from the inside to the outside in turn, the buffer region 14 includes a diffusion layer 141, a mask layer 18 and a first doped silicon glass layer 19 arranged from the inside to the outside in turn, and the second doped region 12 and the isolation region 13 do not have a functional film layer.

[0088] Then, a tunneling passivation layer 121 and a doped polysilicon layer 122 containing second doped atoms are formed in the second doped region 12 from the inside to the outside in turn.

[0089] Step A5: removing the first doped silicon glass layer 19 corresponding to the first doped region 11 and the buffer region 14, and removing the mask layer 18 corresponding to the buffer region 14.

[0090] Optionally, hydrofluoric acid solution can be used to remove the first doped silicon glass layer 19 corresponding to the first doped region 11 and the buffer zone 14.

[0091] Furthermore, the silicon substrate 15 exposed on the isolation region 13 and the second main surface can be texturized to form a textured surface structure.

[0092] After step A5, the result is as follows: Figure 7 In the structure shown, the second main surface of the electrode substrate does not have a functional film layer; in the first main surface, the first doped region 11 includes an emitter 111, the buffer zone 14 includes a diffusion layer 141, and the second doped region 12 includes a tunneling passivation layer 121 and a doped polysilicon layer 122 arranged sequentially from the inside to the outside. The isolation region 13 does not have a functional film layer.

[0093] In an optional embodiment of the present invention, step A4 may include: a tunneling passivation layer 121 and an intrinsic polysilicon layer are simultaneously formed on the outer side of the first doped region 11, the second doped region 12, the buffer zone 14 and the isolation region 13, as well as on the second main surface. After doping treatment with second doping atoms, a doped polysilicon layer 122 is formed on the intrinsic polysilicon layer of the first main surface and the second main surface of the battery substrate 1. Furthermore, while the doped polysilicon layer 122 is formed on the intrinsic polysilicon layer, a second doped silicon glass layer 20 is formed on the outer side of the doped polysilicon layer 122.

[0094] After doping, the following can be obtained: Figure 8 The structure shown includes a second main surface of the battery substrate 1 comprising a tunneling passivation layer 121, a doped polycrystalline silicon layer 122, and a second doped silicon glass layer 20 arranged sequentially from the inside to the outside; and a first doped region 11 comprising an emitter 111, a first doped silicon glass layer 19, a tunneling passivation layer 121, a doped polycrystalline silicon layer 122, and a second doped silicon glass layer 20 arranged sequentially from the inside to the outside; a buffer zone 14 comprising a diffusion layer 141, a mask layer 18, a first doped silicon glass layer 19, a tunneling passivation layer 121, a doped polycrystalline silicon layer 122, and a second doped silicon glass layer 20 arranged sequentially from the inside to the outside; and an isolation region 13 and a second doped region 12 comprising a tunneling passivation layer 121, a doped polycrystalline silicon layer 122, and a second doped silicon glass layer 20 arranged sequentially from the inside to the outside.

[0095] Step A4 above may further include: removing the portion of the second doped silicon glass layer 20 corresponding to the first doped region 11, the isolation region 13 and the buffer zone 14 by a third laser process.

[0096] Based on this, the step A5 can further include: single-sided etching the second major surface to remove the second doped silicon glass layer 20 of the second major surface; removing the tunneling passivation layer 121 and the doped polysilicon layer 122 corresponding to the first doped region 11, the buffer region 14 and the isolation region 13, and the tunneling passivation layer 121 and the doped polysilicon layer 122 of the second major surface by the second texturing treatment, and performing the texturing treatment on the silicon base 15 exposed by the isolation region 13 and the second major surface to form a textured structure on the silicon base 15 corresponding to the isolation region 13 and the second major surface, removing the first doped silicon glass layer 19 corresponding to the first doped region 11 and the buffer region 14 and the second doped silicon glass layer 20 corresponding to the second doped region 12 by using a hydrofluoric acid solution, and removing the mask layer 18 corresponding to the buffer region 14 by acid etching to obtain a structure as shown in Figure 7 The power of the third laser treatment can be 10w, 15w, 28w, 30w, 33w, 37w, 42w or 50w, etc.; the mass fraction of the alkali solution used in the second texturing treatment can be 5%, 10%, 15%, 22%, 30%, 40% or 50%, etc.; and the time of the second texturing treatment can be 100s, 120s, 150s, 190s, 200s, 240s, 260s or 300s, etc. Alternatively, the alkali solution used in the second texturing treatment can be a potassium hydroxide solution, but is not limited thereto.

[0097] In an alternative embodiment of the present application, after the step A5, the method can further include: forming a first passivation and anti-reflection layer 16 on the first doped region 11, the second doped region 12, the isolation region 13 and the buffer region 14. Specifically, the first passivation and anti-reflection layer 16 is formed on the outside of the emitter 111 of the first doped region 11, the outside of the doped polysilicon layer 122 of the second doped region 12, the outside of the diffusion layer 141 of the buffer region 14 and the isolation region 13, and all the first passivation and anti-reflection layers 16 on the first major surface are connected as a whole. The first passivation and anti-reflection layer 16 can include aluminum oxide, silicon nitride, etc., but is not limited thereto.

[0098] In addition, the method can further include: forming a second passivation and anti-reflection layer 17 on the second major surface of the cell base 1. The second passivation and anti-reflection layer 17 can include aluminum oxide, silicon nitride, etc., but is not limited thereto, and can be the same as or different from the first passivation and anti-reflection layer 16.

[0099] After the first passivation and anti-reflection layer 16 and the second passivation and anti-reflection layer 17 are formed, a structure as shown in Figure 9The structure is shown. By forming the first passivation anti-reflection layer 16 on the first main surface and the second passivation anti-reflection layer 17 on the second main surface, the surface defects can be passivated, the reflection of light can be reduced, and the isolation region 13 and the silicon substrate 15 of the second main surface can be protected as a physical barrier to avoid direct exposure.

[0100] In an alternative embodiment of the present application, the above method can further include: forming the first metal electrode 112 in ohmic contact with the emitter 111 on the first doped region 11; and forming the second metal electrode 123 in ohmic contact with the carrier collection layer on the second doped region 12.

[0101] Specifically, by printing electrode paste for preparing the first metal electrode 112 on the first doped region 11 and printing electrode paste for preparing the second metal electrode 123 on the second doped region 12, the first metal electrode 112 and the second metal electrode 123 are formed respectively after drying and sintering, and the structure of the back contact solar cell is as shown. Figure 1 The first metal electrode 112 passes through the first passivation anti-reflection layer 16 of the first doped region 11 and is electrically connected with the doped polysilicon layer 122, and the second metal electrode 123 passes through the first passivation anti-reflection layer 16 of the second doped region 12 and is electrically connected with the emitter 111.

[0102] The electrode paste for preparing the first metal electrode 112 and the second metal electrode 123 can be the same or different. Alternatively, the electrode paste for preparing the first metal electrode 112 includes silver paste or silver-aluminum paste, and the electrode paste for preparing the second metal electrode 123 includes silver paste.

[0103] According to the preparation method of the back contact solar cell of the embodiment of the present application, by preparing the mask layer 18, the diffusion layer 141 can be formed inside the mask layer 18 during the diffusion treatment, so as to form the buffer region 14 including the diffusion layer 141 between the first doped region 11 and the second doped region 12. Due to the blockage of the mask layer 18, the junction depth of the diffusion layer 141 is smaller than the junction depth of the emitter 111. By the buffer region 14, the abrupt change of the doping concentration between the first doped region 11 and the second doped region 12 is alleviated, the carrier recombination loss of the height difference region is reduced, the potential barrier energy between the first doped region 11 and the second doped region 12 is reduced, and the influence on the carrier lateral transport is reduced. By setting the buffer region 14, the junction depth of the first doped atoms between the first doped region 11 and the second doped region 12 is gradually changed, the electric field abrupt change is alleviated, the potential barrier energy to be overcome by the carrier lateral transport is reduced, the carrier transport path is optimized, the carrier is guided to transport along the direction of low recombination and short path, the carrier recombination is reduced, and the loss of carrier lateral transport is reduced.

[0104] Meanwhile, the height difference between the outer surface of the emitter 111 of the first doped region 11 and the outer surface of the carrier collection layer of the second doped region 12 is reduced, the structural defects in the height difference area are reduced, the recombination loss is reduced, and the cell performance is improved.

[0105] Furthermore, due to the existence of the shallow-junction high-sheet-resistance diffusion layer 141, in the process of the second laser treatment and the polishing treatment, the treatment depth is shallow, the laser damage and the polishing damage to the silicon substrate 15 and the side surface of the buffer region 14 are small, the influence on the minority carrier lifetime is reduced, and the "black edge" representing the structural defects does not exist in the second doped region 12 edge in the photoluminescence test image of the prepared back contact solar cell.

[0106] The back contact solar cell and the preparation method thereof are further described below through specific embodiments.

[0107] Embodiment 1

[0108] An N-type silicon substrate with a resistivity of 20 Ω·cm and a thickness of 150 μm is used, and the silicon substrate is subjected to texturing and polishing treatment.

[0109] A silicon dioxide layer with a thickness of 80 nm is grown on the first main surface and the second main surface of the silicon substrate 15 by using a plasma-enhanced chemical vapor deposition (PECVD) device at a temperature of 500 ℃, as a mask layer 18.

[0110] The mask layer 18 corresponding to the first doped region 11 is removed by the first laser treatment, so that the silicon substrate 15 corresponding to the first doped region 11 is exposed, and the exposed silicon substrate 15 is subjected to first texturing treatment to form a textured structure. The power of the first laser treatment is 20 W, and the first texturing treatment uses an alkali solution with a mass fraction of 30%, and the time of the above first texturing treatment is 200 s.

[0111] The diffusion treatment of boron atoms (first doped atoms) is performed, and a P+emitter (emitter 111) with a sheet resistance of 300 Ω, a doping concentration of 5×10 18 atoms / cm 3 , and a junction depth of 1.2 μm is formed in the first doped region 11. In the direction parallel to the first main surface, the area of the first doped region 11 accounts for 40% of the total area of the first main surface. The buffer region 14 accounts for 6% of the total area of the first main surface. Due to the blockage of the mask layer 18, the boron atoms diffused into the silicon substrate 15 below the mask layer 18 are less in the second doped region 12, the buffer region 14, the isolation region 13, and the second main surface, and a P+emitter with a sheet resistance of 600 Ω and a concentration of 1×10 18atoms / cm 3 The diffusion layer 141 has a junction depth of 0.5 μm, and a borosilicate glass layer (first doped silicon glass layer 19) is formed outside the P+ emitter and outside the entire mask layer 18.

[0112] The borosilicate glass layer on the second main surface is removed by single-side etching. The borosilicate glass layer corresponding to the second doped region 12 and the isolation region 13 is removed by a second laser treatment, and the mask layer 18 and the diffusion layer 141 corresponding to the second doped region 12 and the isolation region 13 are removed by polishing. The cell substrate 1 after polishing is dried to form a polished surface on the silicon substrate 15 corresponding to the second doped region 12 and the isolation region 13. The polishing is performed using an alkali solution having a mass fraction of 20% for a time of 200 s and a depth of 1 μm.

[0113] The dried cell substrate 1 is placed in a quartz boat, heated to 600°C under low pressure, and 2000 seem of oxygen is introduced to grow a tunneling passivation layer 121 having a thickness of 1.5 nm on both the first main surface and the second main surface. Subsequently, silane is introduced to grow an intrinsic polysilicon layer having a thickness of 250 nm outside the tunneling passivation layer 121 on both the first main surface and the second main surface. The temperature is raised to introduce a phosphorus source for phosphorus atom (second doping atom) doping treatment. The concentration of the doped phosphorus atoms is 5 x 1019 atoms / cm3. 20 atoms / cm 3 The intrinsic polysilicon layer is converted into a doped polysilicon layer 122, and a phosphosilicate glass layer (second doped silicon glass layer 20) is formed outside the doped polysilicon layer 122.

[0114] The phosphosilicate glass layer corresponding to the first doped region 11 and the buffer region 14 and the phosphosilicate glass layer of the isolation region 13 are removed by a third laser treatment. The power of the third laser treatment is 30 W. The second main surface is etched by single-side etching using a hydrofluoric acid solution having a mass fraction of 5% to remove the phosphosilicate glass layer on the second main surface. The tunneling passivation layer 121 and the doped polysilicon layer 122 corresponding to the first doped region 11, the buffer region 14, and the isolation region 13 and the tunneling passivation layer 121 and the doped polysilicon layer 122 on the second main surface are removed by a second texturing treatment, and the silicon substrate 15 exposed by the isolation region 13 and the second main surface is subjected to the texturing treatment to form a textured structure.

[0115] The first doped region 11 and the above-mentioned first doped silicon glass layer 19 corresponding to the above-mentioned buffer region 14 and the second doped silicon glass layer 20 corresponding to the second doped region 12 are removed by using a 10% hydrofluoric acid solution, and the mask layer 18 corresponding to the buffer region 14 is removed by using an acid solution with the same mass fraction as that used for removing the boron silicon glass layer. Finally, the proportion of the area of the second doped region 12 to the total area of the above-mentioned first main surface in the direction parallel to the first main surface is 43%, and the proportion of the isolation region 13 to the total area of the above-mentioned first main surface is 11%.

[0116] At 250°C, trimethylaluminum and water are introduced to grow an aluminum oxide film with a thickness of 6 nm on the first main surface and the second main surface. In a PECVD device, silane and ammonia are introduced at a temperature of 540°C to deposit a silicon nitride film with a thickness of 75 nm on the first main surface and the second main surface, so as to take the aluminum oxide film and the silicon nitride film on the first main surface as the first passivation anti-reflection layer 16 and take the aluminum oxide film and the silicon nitride film on the second main surface as the second passivation anti-reflection layer 17.

[0117] Silver paste is printed on the first doped region 11 and the second doped region 12 by using screen printing, and is subjected to drying and high-temperature sintering to realize metallization, so as to form the first metal electrode 112 on the first doped region 11 and form the second metal electrode 123 on the second doped region 12. After light injection treatment, the back contact solar cell M is obtained.

[0118] In the back contact solar cell M, the height difference between the outer surface of the P+ emitter of the first doped region and the first main surface of the silicon base 15 corresponding to the isolation region is 4.1 μm, the height difference between the outer surface of the doped polysilicon layer 122 of the second doped region and the first main surface of the cell base 1 corresponding to the isolation region is 3.78 μm, and the height difference between the first main surface of the silicon base 15 corresponding to the buffer region and the first main surface of the silicon base 15 corresponding to the isolation region is 5.65 μm. The height difference between the outer surface of the P+ emitter of the first doped region and the first main surface of the silicon base 15 corresponding to the buffer region is 1.55 μm, the height difference between the outer surface of the P+ emitter of the first doped region and the outer surface of the doped polysilicon layer 122 of the second doped region is 0.32 μm, and the height difference between the outer surface of the doped polysilicon layer 122 of the second doped region and the first main surface of the silicon base 15 corresponding to the buffer region is 1.87 μm. Among them, the distance from the second main surface of the cell base 1 is sorted from small to large as follows: isolation region < second doped region < first doped region < buffer region.

[0119] Example 2

[0120] The difference from Example 1 is that the mask layer 18 is different. Specifically, the silicon substrate 15 after texturing and polishing is placed in a hot oxygen environment at a temperature of 600°C to grow a 1 nm thick silicon oxide layer, and an intrinsic crystalline silicon layer with a thickness of 50 nm is grown outside the silicon oxide layer at 600°C by low pressure chemical vapor deposition (LPCVD), so as to take the silicon oxide layer and the intrinsic crystalline silicon layer as the mask layer 18. Other process conditions and procedures are the same. A back contact solar cell N is prepared.

[0121] In the back contact solar cell N, the height difference between the outer surface of the P+ emitter of the first doped region and the first main surface of the silicon substrate 15 corresponding to the isolation region is 4.56 μm, the height difference between the outer surface of the doped polysilicon layer 122 of the second doped region and the first main surface of the silicon substrate 15 corresponding to the isolation region is 3.17 μm, and the height difference between the first main surface of the silicon substrate 15 corresponding to the buffer region and the first main surface of the silicon substrate 15 corresponding to the isolation region is 5.56 μm. The height difference between the outer surface of the P+ emitter of the first doped region and the first main surface of the silicon substrate 15 corresponding to the buffer region is 1 μm, the height difference between the outer surface of the P+ emitter of the first doped region and the outer surface of the doped polysilicon layer 122 of the second doped region is 1.39 μm, and the height difference between the outer surface of the doped polysilicon layer 122 of the second doped region and the first main surface of the silicon substrate 15 corresponding to the buffer region is 2.39 μm. Among them, in order from small to large distance from the second main surface of the cell substrate 1: isolation region < second doped region < first doped region < buffer region.

[0122] Comparative Example 1

[0123] The difference from Example 1 is that the mask layer 18 is not formed, and there is no buffer region 14, so that a P+ emitter with a sheet resistance of 300 Ω, a doping concentration of 5 x 10 18 atoms / cm 3 , and a junction depth of 1.2 μm is formed on the first main surface and the second main surface. The borosilicate glass layer corresponding to the isolation region 13 and the second doped region 12 is removed by a green skin laser with a power of 40 w, and the P+ emitter corresponding to the second doped region 12 and the isolation region 13 is removed by polishing. The cell substrate 1 after polishing is dried. The depth of the polishing treatment is 5 μm. Other process conditions and procedures are the same. A back contact solar cell L without a buffer region 14 is prepared.

[0124] In the back contact solar cell N, the height difference between the outer surface of the P+ emitter of the first doped region and the first main surface of the silicon base 15 corresponding to the isolation region is 5.85 μm, and the height difference between the outer surface of the doped polysilicon layer 122 of the second doped region and the first main surface of the silicon base 15 corresponding to the isolation region is 3.84 μm. The height difference between the first doped region and the second doped region is 2.01 μm. Among them, in order of increasing distance from the second main surface of the cell base 1, the order is: isolation region < second doped region < first doped region.

[0125] Performance parameter test

[0126] The above back contact solar cell M, back contact solar cell N and back contact solar cell L were tested under the same conditions to obtain the performance test data shown in Table 1 below.

[0127]

[0128] Note: EFF represents photoelectric conversion efficiency; Voc represents open circuit voltage; Isc represents short circuit current; FF represents fill factor.

[0129] From Table 1 above, it can be found that the back contact solar cell M and the back contact solar cell N with the buffer region 14 have certain improvement in photoelectric conversion efficiency, open circuit voltage, short circuit current and fill factor compared with the back contact solar cell L without the buffer region 14. This is because in the back contact solar cell L without the buffer region 14, the outer surface of the P+ emitter of the first doped region 11 and the outer surface of the doped polysilicon layer 122 of the second doped region 12 have a large height difference in the thickness direction of the cell, which affects the transport path of the carriers, and the height difference region between the outer surface of the P+ emitter of the first doped region 11 and the outer surface of the doped polysilicon layer 122 of the second doped region 12 has more structural defects and higher potential barrier energy, which increases the carrier recombination loss. The back contact solar cell M and the back contact solar cell N with the buffer region 14 form a boron atom junction depth gradient between the first doped region 11, the buffer region 14 and the second doped region 12, which relieves the electric field mutation, reduces the potential barrier energy, optimizes the transport path of the carriers, reduces the carrier recombination, reduces the loss of carrier lateral transport, and reduces the structural defects in the height difference region, thereby improving the cell performance.

[0130] Although the height difference between the outer surface of the P+ emitter of the first doped region 11 and the outer surface of the doped polycrystalline silicon layer 122 of the second doped region 12 is larger in the back-contact solar cell N compared to the back-contact solar cell L, the back-contact solar cell N incorporates a buffer zone 14 that mitigates abrupt changes in doping concentration between the first and second doped regions 11 and 12. This buffer zone 14 reduces the electric field abruptness and lowers the barrier energy for carrier transport between the first and second doped regions 11 and 12, effectively reducing carrier recombination. Therefore, the back-contact solar cell N exhibits superior performance compared to the back-contact solar cell L.

[0131] Photoluminescence test

[0132] Photoluminescence tests were performed on back-contact solar cells M and L, and the results were as follows: Figure 10 The photoluminescence test image of the local structure of the back-contact solar cell M shown and as follows Figure 11 The image shows a photoluminescence test image of a local structure of the back-contact solar cell L. It can be observed that for the back-contact solar cell L without the buffer zone 14, Figure 11 The lighter-colored area on the right represents the second doped region 12, surrounded by a "black border" indicating larger structural defects; this is for the back-contact solar cell M with a buffer zone 14. Figure 10 The light-colored area in the upper right corner represents the second doped region 12, and its edges do not have the "black border" that indicates a large structural defect. Therefore, the back-contact solar cell M with the buffer zone 14 has fewer structural defects in the height difference region, which can reduce carrier recombination losses in this region.

[0133] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A back-contact solar cell, characterized in that, include: A battery substrate (1) includes a first doped region (11), a second doped region (12), an isolation region (13), and a buffer zone (14) located on the first main surface of the battery substrate (1); wherein, The isolation region (13) and the buffer region (14) are located between the first doped region (11) and the second doped region (12), and the buffer region (14) is located between the first doped region (11) and the isolation region (13); The first doped region (11) is provided with an emitter (111) including a first doped atom; The second doped region (12) is provided with a carrier collection layer containing second doped atoms, the second doped atoms having the opposite conductivity type to the first doped atoms; The buffer (14) is provided with a diffusion layer (141) including the first doped atom. The junction depth of the diffusion layer (141) is less than the junction depth of the emitter (111).

2. The back-contact solar cell according to claim 1, characterized in that, The carrier collection layer includes: a tunneling passivation layer (121) disposed from the inside out and a doped polysilicon layer (122) including the second doped atom; Preferably, the thickness of the tunneling passivation layer (121) is 0.5 nm to 2.5 nm; Preferably, the thickness of the doped polycrystalline silicon layer (122) is 100 nm to 300 nm; Preferably, the doping concentration of the second doped atom in the doped polycrystalline silicon layer (122) is 3 × 10⁻⁶. 20 atoms / cm 3 ~1×10 21 atoms / cm 3 ; Preferably, The height difference between the outer surface of the carrier collection layer of the second doped region (12) and the outer surface of the diffusion layer (141) is 1 μm to 5 μm; wherein, compared with the outer surface of the diffusion layer (141), the outer surface of the carrier collection layer of the second doped region (12) is closer to the second main surface of the battery substrate (1); Preferably, The height difference between the outer surface of the emitter (111) of the first doped region (11) and the outer surface of the carrier collection layer of the second doped region (12) is 0.1 μm to 3 μm; wherein, compared with the outer surface of the emitter (111) of the first doped region (11), the outer surface of the carrier collection layer of the second doped region (12) is closer to the second main surface of the battery substrate (1); Preferably, The height difference between the outer surface of the emitter (111) of the first doped region (11) and the outer surface of the diffusion layer (141) is 0.9 μm to 4.9 μm; wherein, compared with the outer surface of the diffusion layer (141), the outer surface of the emitter (111) of the first doped region (11) is closer to the second main surface of the battery substrate (1).

3. The back-contact solar cell according to claim 1, characterized in that, The junction depth of the diffusion layer (141) is 0.3 μm to 0.8 μm; And / or, The sheet resistance of the diffusion layer (141) is 400Ω~800Ω; And / or, The peak concentration of the first doped atom in the diffusion layer (141) is 1×10⁻⁶. 18 atoms / cm 3 ~3×10 18 atoms / cm 3 ; And / or, The junction depth of the emitter (111) is 1 μm to 2 μm; And / or, The sheet resistance of the emitter (111) is 200Ω~400Ω; And / or, The peak concentration of the first doped atom in the emitter (111) is 3 × 10⁻⁶. 18 atoms / cm 3 ~9×10 18 atoms / cm 3 .

4. The back-contact solar cell according to claim 1, characterized in that, The height difference between the first main surface of the battery substrate (1) corresponding to the isolation region (13) and the outer surface of the emitter (111) of the first doped region (11) is 0.5 μm to 10 μm; And / or, The height difference between the first main surface of the battery substrate (1) corresponding to the isolation region (13) and the outer surface of the carrier collection layer of the second doped region (12) is 0.5 μm to 10 μm.

5. The back-contact solar cell according to claim 1, characterized in that, Along a direction parallel to the first main surface, the area of ​​the first doped region (11) accounts for 17.5% to 46% of the total area of ​​the first main surface; And / or, Along a direction parallel to the first main surface, the area of ​​the second doped region (12) accounts for 40% to 60% of the total area of ​​the first main surface; And / or, Along a direction parallel to the first main surface, the area of ​​the isolation region (13) accounts for 10% to 30% of the total area of ​​the first main surface; And / or, Along a direction parallel to the first main surface, the area of ​​the buffer zone (14) accounts for 4% to 12.5% ​​of the total area of ​​the first main surface.

6. The back-contact solar cell according to claim 1, characterized in that, The back-contact solar cell also includes: A first passivation antireflection layer (16) is disposed in the first doped region (11), the second doped region (12), the isolation region (13) and the buffer zone (14). And / or, A second passivation and antireflection layer (17) is disposed on the second main surface of the battery substrate (1). And / or, The first metal electrode (112) is disposed in the first doped region (11) and is in ohmic contact with the emitter (111). And / or, The second metal electrode (123) is disposed in the second doped region (12) and in ohmic contact with the carrier collection layer. Preferably, The battery substrate (1) includes a silicon substrate (15); the resistivity of the silicon substrate (15) is 0.1 Ω·cm to 100 Ω·cm; Preferably, the thickness of the silicon substrate (15) is 100 μm to 500 μm; Preferably, the silicon substrate (15) is an N-type silicon substrate, the first doped atom is a P-type doped atom, and the second doped atom is an N-type doped atom.

7. A method for fabricating a back-contact solar cell, characterized in that, include: Step A1: Provide a battery substrate (1), wherein the first main surface of the battery substrate (1) has a first doped region (11), a second doped region (12), an isolation region (13), and a buffer region (14); wherein the isolation region (13) and the buffer region (14) are located between the first doped region (11) and the second doped region (12); and the buffer region (14) is located between the first doped region (11) and the isolation region (13). Step A2: Prepare a full-surface mask layer (18) on the first main surface of the battery substrate (1); Step A3: Remove the mask layer (18) corresponding to the first doped region (11) and perform diffusion treatment of the first doped atoms to form an emitter (111) containing the first doped atoms in the first doped region (11). A diffusion layer (141) containing the first doped atoms is formed inside the mask layer (18) of the second doped region (12), the isolation region (13) and the buffer zone (14). A first doped silicon glass layer (19) is formed outside the emitter (111) and outside the mask layer (18). The junction depth of the diffusion layer (141) is smaller than the junction depth of the emitter (111). Step A4: Remove the first doped silicon glass layer (19), the mask layer (18), and the diffusion layer (141) corresponding to the second doped region (12) and the isolation region (13) to form a carrier collection layer containing second doped atoms in the second doped region (12); Step A5: Remove the first doped silicon glass layer (19) corresponding to the first doped region (11) and the buffer (14), and remove the mask layer (18) corresponding to the buffer (14).

8. The method for preparing a back-contact solar cell according to claim 7, characterized in that, Step A4 includes: forming a tunneling passivation layer (121) and an intrinsic polysilicon layer sequentially from the inside to the outside in the first doped region (11), the second doped region (12), the isolation region (13) and the buffer zone (14), and performing a doping treatment of the second doped atom so that the intrinsic polysilicon layer forms a doped polysilicon layer (122). And / or, Following step A5, the method further includes: A first passivation antireflection layer (16) is formed in the first doped region (11), the second doped region (12), the isolation region (13) and the buffer zone (14). And / or, Compared to the outer surface of the diffusion layer (141), the outer surface of the carrier collection layer of the second doped region (12) is closer to the second main surface of the battery substrate (1); And / or, Compared with the outer surface of the emitter (111) of the first doped region (11), the outer surface of the carrier collection layer of the second doped region (12) is closer to the second main surface of the battery substrate (1); And / or, Compared to the outer surface of the diffusion layer (141), the outer surface of the emitter (111) of the first doped region (11) is closer to the second main surface of the battery substrate (1).

9. The method for preparing a back-contact solar cell according to claim 7, characterized in that, The method further includes: A first metal electrode (112) is formed in the first doped region (11) to make ohmic contact with the emitter (111). A second metal electrode (123) is formed in the second doped region (12) to make ohmic contact with the carrier collection layer. Preferably, the electrode paste used to prepare the first metal electrode (112) includes silver paste and silver-aluminum paste; The electrode paste used to prepare the second metal electrode (123) includes silver paste; Preferably, the method further includes: A second passivation antireflection layer (17) is formed on the second main surface of the battery substrate (1); Preferably, The mask layer (18) may include any one of the following: a stack of oxide layers and intrinsic crystalline silicon layers from the inside out, a silicon carbide layer or a silicon nitride layer; And / or, The thickness of the mask layer (18) is 10nm~100nm; Preferably, the battery substrate (1) includes a silicon substrate (15). Step A3 includes: The mask layer (18) corresponding to the first doped region (11) is removed by a first laser treatment, and the silicon substrate (15) corresponding to the first doped region (11) is subjected to a first texturing treatment; wherein, the power of the first laser treatment is 10w~50w, the first texturing treatment uses an alkaline solution with a mass fraction of 5%~50%, and the time of the first texturing treatment is 5s~300s.

10. The method for preparing a back-contact solar cell according to claim 7, characterized in that, Step A4 includes: The first doped silicon glass layer (19) corresponding to the second doped region (12) and the isolation region (13) is removed by a second laser process, and the mask layer (18) and the diffusion layer (141) corresponding to the second doped region (12) and the isolation region (13) are removed by a polishing process. Preferably, the power of the second laser treatment is 30W~50W; Preferably, the polishing treatment uses an alkaline solution with a mass fraction of 5% to 50%, and the polishing treatment time is 100s to 300s; Preferably, the depth of the polishing process is greater than or equal to 0.1 μm and less than or equal to 1.5 μm; Preferably, While forming the doped polysilicon layer (122) in the intrinsic polysilicon layer, step A4 further includes: forming a second doped silicon glass layer (20) outside the doped polysilicon layer (122); removing the portion of the second doped silicon glass layer (20) corresponding to the first doped region (11), the isolation region (13) and the buffer zone (14); After removing the first doped silicon glass layer (19) corresponding to the first doped region (11) and the buffer zone (14), step A5 further includes removing the second doped silicon glass layer (20) of the second doped region (12).

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