Back contact cell and preparation method thereof, and photovoltaic module

Abstract

The application discloses a back contact cell and a preparation method and a photovoltaic module thereof, and relates to the technical field of solar cells. The back contact cell comprises a silicon substrate, a first doped layer and a second doped layer on the back surface of the silicon substrate, the first doped layer and the second doped layer are alternately arranged to form a third region with intervals, and a leakage channel structure comprising a first direction heavy doped region and a second direction light doped region is formed by laser induction; the potential barrier height of the first direction heavy doped region and the second doped layer is higher than the potential barrier height of the second direction light doped region and the second doped layer, and the potential barrier height of the second direction light doped region and the second doped layer is higher than the potential barrier height of the second direction light doped region and the undoped third region; a second metal electrode extends to the leakage channel structure and covers part of the first direction heavy doped region; the application also discloses a preparation method and a photovoltaic module comprising the cell. The application enhances the anti-hot spot capability and improves the photoelectric conversion efficiency through the gradient doped leakage channel and the electrode extension design, and the photovoltaic module also has excellent performance.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a back-contact cell and a preparation method thereof, and a photovoltaic module. Background Art

[0002] Back-contact cells have become a research hotspot in the solar cell field because they have no front electrodes obstructing them, resulting in low optical losses and high photoelectric conversion efficiency. However, they face the challenge of the hot spot effect: when part of the cell is shaded, it loses current, causing voltage to rise and forming localized hot spots, which can affect component lifespan and even pose safety risks.

[0003] The hot spot effect occurs when certain cells in a solar cell module are shaded, resulting in an increase in voltage due to the inability to output current. This in turn creates localized hot spots on the cells, triggering the hot spot effect. To prevent the hot spot effect, existing back-contact solar cells typically use the Zener breakdown principle, overlapping portions of the first doped layer and the second doped layer to form leakage channels to release heat. However, this approach requires a large number of leakage channels to effectively prevent hot spots, and a large number of leakage channels can lead to increased carrier recombination during normal operation, reducing photoelectric conversion efficiency.

[0004] Traditional back-contact cells create leakage points in local PN regions to combat the hot spot effect caused by shadowing. However, existing technologies have the following drawbacks:

[0005] 1. A large number of leakage points need to be densely arranged to meet the requirements of hot spot prevention, resulting in an excessive number of leakage channels;

[0006] 2. The leakage channel will cause carrier recombination during normal operation, significantly reducing the photoelectric conversion efficiency;

[0007] 3. The reverse current transmission path is long and the leakage efficiency is limited.

[0008] Therefore, how to achieve efficient hot spot prevention in back-contact batteries while avoiding efficiency loss caused by excessive leakage channels has become a technical problem that needs to be solved urgently. Summary of the Invention

[0009] The present invention aims to solve the problem that it is difficult to strike a balance between the anti-hot spot capability and the photoelectric conversion efficiency of existing back-contact cells, and provides a back-contact cell and a preparation method thereof, and a photovoltaic module.

[0010] The technical solution of this application is:

[0011] A back-contact battery comprising:

[0012] a silicon substrate having a front side and a back side;

[0013] A first doped layer and a second doped layer are provided on the back surface; wherein the first doped layer forms a first region, the second doped layer forms a second region, and the second doped layer and the first doped layer have opposite conductivity types; the first doped layer and the second doped layer are alternately arranged, and the interval region between the first doped layer and the second doped layer is a third region;

[0014] At an edge portion of the first region close to the second region and at a position in the third region, the first doped layer and the second doped layer are in composite contact to form a leakage channel structure, and the region where the leakage channel structure is located is the fourth region;

[0015] The leakage channel structure comprises a laser-induced heavily doped region in a first direction and a lightly doped region in a second direction; wherein the barrier height formed by the heavily doped region in the first direction and the second doped layer is higher than the barrier height formed by the lightly doped region in the second direction and the second doped layer, and the barrier height formed by the lightly doped region in the second direction and the second doped layer is higher than the barrier height formed by the lightly doped region in the second direction and the undoped third region;

[0016] A first metal electrode and a second metal electrode are correspondingly arranged on the first doped layer and the second doped layer; wherein, the second metal electrode extends toward the fourth region and covers a portion of the surface of the heavily doped region in the first direction, and the extended portion of the metal electrode is a third metal electrode; the proportion of the second metal electrode covering the length of the surface of the heavily doped region in the first direction is ≥20%.

[0017] The third metal electrode is the part of the leakage channel structure that extends from the second metal electrode to the fourth region and overlaps it. Its main function is to prevent current from passing through the leakage channel when there is a shadow (that is, when a reverse bias is applied at both ends of the battery cell). With this third electrode extending to the leakage channel, the reverse current can pass directly through the third electrode after passing through the leakage channel, thereby shortening the transmission path of the reverse current and thus having a better anti-hot spot effect.

[0018] Furthermore, the doping concentration of the heavily doped region in the first direction is ≥1×10 21 cm -3 , the depth in the first direction is 10nm~40nm; the doping concentration of the lightly doped region in the second direction increases from 1×10 21 cm -3 Gradually decrease to 1×10 17 cm -3 , the depth in the first direction is 100nm~300nm.

[0019] Furthermore, the height of the first barrier formed by the heavily doped region in the first direction and the second doped layer is Φ1, the height of the second barrier formed by the lightly doped region in the second direction and the second doped layer is Φ2, and the height of the third barrier formed by the lightly doped region in the second direction and the undoped third region is Φ3; wherein, Φ1-Φ2=0.1eV~0.5eV, Φ2-Φ3=0.1eV~0.3eV.

[0020] Furthermore, the ratio of the first-direction high-doping conductivity C1 to the second-direction low-doping conductivity C2 of the leakage channel is: C2 / C1=0.01-2.

[0021] Furthermore, on the plane where the second direction and the third direction are located, the area of ​​a single heavily doped region in the first direction is ≥ 0.02 mm 2 ; and the ratio of the area of ​​the heavily doped region in the first direction to the cross-sectional area of ​​the composite contact between the first doped layer and the second doped layer in the plane where the first direction and the third direction are located is greater than 50.

[0022] Furthermore, the dark field reverse resistance RshuntDr of the back contact battery is ≤3Ω.

[0023] Furthermore, under the condition that the reverse voltage applied across the back-contact battery is 7V, the leakage current of the back-contact battery is greater than or equal to the short-circuit current.

[0024] The present invention also provides a method for preparing the above-mentioned back-contact battery, comprising the following steps:

[0025] S1. The silicon substrate having a first conductivity type is placed in an alkaline solution for polishing;

[0026] S2. A first tunnel passivation layer, a first doped layer, and a BSG layer are sequentially deposited on the back of the silicon substrate, wherein the first doped layer has a second conductivity type;

[0027] S3. First laser ablation: using a first laser to perform spaced ablation on the back of the silicon substrate, and etching the silicon substrate using an alkaline solution to form an unablated first region, a second region of the exposed silicon substrate, and a third region of the exposed silicon substrate;

[0028] S4. Second laser doping: Irradiating the residual BSG layer at the predetermined fourth region with a second laser, modifying the BSG layer while doping the residual BSG layer in the thickness direction using the remaining BSG layer as a boron source. After the second laser irradiation, the boron element in the BSG layer diffuses toward the first doped layer in the first direction, forming a heavily doped region in the first direction and a lightly doped region in the second direction.

[0029] S5. Annealing: Annealing the second laser-doped region to redistribute the boron element within the first doped layer while optimizing the lattice structure after the second laser doping;

[0030] S6. Depositing a second tunnel passivation layer, a second doped layer, and a phosphosilicate glass layer on the back side of the silicon substrate, wherein the second doped layer has a first conductivity type;

[0031] S7. Third laser ablation: ablating the PSG layer in the first and third regions on the back side of the silicon substrate using a third laser, and etching the front and side surfaces of the silicon substrate using a strong acid to expose the silicon substrate on the front and side surfaces, respectively;

[0032] S8. Using alkaline solution and strong acid to sequentially clean the front and side surfaces of the silicon substrate and the first, second, and fourth regions, and performing a texturing treatment on the third region and the front surface;

[0033] S9. depositing a passivation layer on the front and back sides of the silicon substrate;

[0034] S10. Depositing an anti-reflection layer on the front and back surfaces of the silicon substrate;

[0035] S11. Print metal electrodes and perform sintering treatment; wherein, the metal electrode of the second doping layer needs to be introduced into the first direction heavily doped region of the fourth region and cover at least 20% of the length of the surface of the first direction heavily doped region.

[0036] Furthermore, in the above S3, the first laser is a pulsed laser with a pulse width of 5ps to 30ps, a wavelength of 355nm or 532nm, a spot size of 150μm to 300μm, and an energy density of 4×10 3 J / m 2 ~9×10 3 J / m 2 , the overlap rate is 10-80%; and / or, in said S4, the second laser is a pulsed laser with a pulse width of 5ps-30ps, a wavelength of 355nm or 532nm, a spot size of 150μm-300μm, and an energy density of 3.55×10 3 J / m 2 ~6.5×10 3 J / m 2 , the overlap rate is 10%~80%; and / or, in S7, the third laser is a pulsed laser with a pulse width of 5ps~30ps, a wavelength of 355nm or 532nm, a spot size of 150μm~300μm, and an energy density of 2×10 3 J / m 2 ~4×10 3 J / m 2 , the overlap rate is 10%~50%.

[0037] Furthermore, the thickness of the BSG layer is 50nm~100nm; the thickness of the PSG layer is 50nm~100nm; the thickness of the passivation layer is 4nm~10nm; and the thickness of the anti-reflection layer is 50nm~100nm.

[0038] Furthermore, in S3, after etching with NaOH using alkaline solution, a BSG layer of 10 nm to 40 nm still exists on the surface of the first region, and the surface height of the first region is 1 μm to 5 μm higher than the surface height of the second region.

[0039] Furthermore, in S8, after texturing, the reflectivity of the textured surface on the front side of the silicon substrate is 5% to 10%, and the surface height of the second region is 1 μm to 5 μm higher than the surface height of the third region.

[0040] Furthermore, in S5, the annealing temperature is 800° C. to 1000° C., and the annealing time is 30 min to 90 min.

[0041] The present invention also provides a photovoltaic module, comprising: a cell string, the cell string being formed by connecting a plurality of the above-mentioned back-contact cells or back-contact cells prepared using the above-mentioned back-contact cell preparation method; and an encapsulation layer, the encapsulation layer being used to cover the surface of the cell string.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) This application uses laser induction to dope the doped region near the leakage channel to form a heavily doped region in the first direction and a lightly doped region in the second direction, so that the leakage capacity of a single leakage channel is significantly enhanced, thereby reducing the number of required leakage channels while also reducing the carrier recombination during normal operation of a single leakage channel, thereby achieving the goals of efficient hot spot prevention and high photoelectric conversion efficiency.

[0044] (2) This application not only shortens the reverse current transmission path and further improves the conductivity of a single leakage channel by extending the metal electrode, but also the extended electrode can collect carriers in the covered area, including the heavily doped area, under normal working conditions, thereby improving the conversion efficiency of the battery cell.

[0045] (3) The leakage channel structure of the present application is formed by laser induction, and the process is simple and controllable. It can accurately control the doping concentration and regional distribution, which is conducive to improving the consistency of battery performance.

[0046] (4) The preparation method of the present application can effectively control the formation of heavily doped regions in the first direction and lightly doped regions in the second direction by optimizing laser parameters, annealing process, etc., thereby ensuring the stability and reliability of the leakage channel structure, while simplifying the production process and reducing production costs.

[0047] (5) The back contact battery of the present application has a lower dark field reverse resistance and a higher reverse leakage current. Under a reverse voltage of 7V, the leakage current is greater than or equal to the short-circuit current, which can effectively protect the battery from damage under abnormal operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present application or the technical solutions of the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0049] Figure 1 A flow chart of the preparation process of a back-contact battery provided in Examples 1-3 of the present application;

[0050] Figure 2 Schematic diagram of a laser doping gradient structure of a back contact cell provided in Examples 1-3 of the present application; wherein the horizontal axis (depth): the unit is micrometer (μm), reflecting the distance extending from the semiconductor surface to the inside; the vertical axis (doping concentration): the unit is atoms per cubic centimeter (atoms / cm 3 ), reflecting the number density of doping atoms at different depths;

[0051] Figure 3 A comparison diagram of the energy band structure of a leakage channel structure in a back-contact battery provided in Examples 1-3 of the present application;

[0052] Figure 4 A top view of the planar structure of a back-contact battery provided in Examples 1-3 of the present application;

[0053] Figure 5 A side view of the planar structure of a back-contact battery provided in Examples 1-3 of the present application.

[0054] Description of main reference numerals:

[0055] 1. Silicon substrate; 2. First region; 3. Second region; 4. Third region; 5. Fourth region; 6. First doped layer; 7. Second doped layer; 8. Leakage channel structure; 8.1. Heavily doped region in the first direction; 8.2. Lightly doped region in the second direction; 9. First tunneling passivation layer; 10. Second tunneling passivation layer; 11. First metal electrode; 12. Second metal electrode; 13. Third metal electrode; 14. Passivation layer; 15. Anti-reflection layer. DETAILED DESCRIPTION

[0056] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that these specific details are not necessarily required to practice the present application. In other embodiments, well-known materials or methods are not specifically described to avoid obscuring the present application.

[0057] Throughout this specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment of the present invention. Thus, appearances of the phrases "one embodiment," "an embodiment," "an example," or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combinations and / or subcombinations in one or more embodiments or examples. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0058] Glossary: ​​BSG: borosilicate glass, PSG: phosphosilicate glass, PECVD: plasma-enhanced chemical vapor deposition, ALD: atomic layer deposition.

[0059] The following will clearly and completely describe the technical solutions of the present invention in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0060] Example 1

[0061] like Figure 4 and Figure 5 As shown, a back contact battery comprises:

[0062] An N-type silicon substrate 1 having a front surface and a back surface;

[0063] A first doped layer (P-type) 6 and an N-type second doped layer (N-type) 7 are provided on the back surface. The first doped layer 6 forms a first region 2, and the second doped layer 7 forms a second region 3. The first doped layers 6 and the second doped layers 7 are arranged alternately, and the interval between the first doped layers 6 and the second doped layers 7 is a third region 4.

[0064] At the edge of the first region 2 close to the second region 3 and the third region 4, the first doped layer 6 and the second doped layer 7 are in composite contact to form a leakage channel structure 8. The region where the leakage channel structure 8 is located is the fourth region 5.

[0065] The leakage channel structure 8 includes a laser-induced heavily doped region 8.1 in the first direction and a lightly doped region 8.2 in the second direction. The barrier height formed between the heavily doped region 8.1 in the first direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7. The barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the undoped third region 4.

[0066] A first metal electrode 11 and a second metal electrode 12 are correspondingly arranged on the first doped layer 6 and the second doped layer 7 ; wherein the second metal electrode 12 extends toward the fourth region 5 and covers part of the surface of the first direction heavily doped region 8 . 1 , and the extended part of the metal electrode is the third metal electrode 13 .

[0067] This embodiment provides a method for preparing a back contact battery. Figure 1 As shown, the preparation method comprises the following steps:

[0068] Step 1: Select a silicon substrate 1 (N-type) with a size of 210 mm × 182 mm and a resistivity of 15 Ω·cm and polish it with a bath-type alkali solution (NaOH).

[0069] Step 2: Deposit a 5 nm first tunnel passivation layer (SiO x ) 9; deposit a 300nm first doping layer 6 on the first tunnel passivation layer 9, the first doping layer 6 is a P-type polysilicon layer, and the doping element is B; the B concentration is 6e+19cm -3 ; A 70nm BSG layer (borosilicate glass layer) is deposited on the back of the silicon substrate 1 as an isolation layer and a boron diffusion source;

[0070] Step 3: Use the first laser to selectively ablate the BSG layer in the second area 3 and the third area 4; use a picosecond pulsed laser with a pulse width of 15ps, a wavelength of 532nm, a spot size of 220um, and an energy density of 7*10 3 J / m 2, the overlap rate is 50%; the second region 3 and the third region 4 irradiated by the first laser are etched by NaOH to expose the silicon substrate 1 in these two regions. At this time, the surface height difference between the first region 2 and the second region 3 is 3 μm, and a 25 nm BSG layer remains in the first region 2 and the fourth region 5;

[0071] Step 4: Use the second laser to irradiate the residual BSG layer in the preset fourth region 5, modify the BSG layer, and dope the residual BSG layer as a B source in the thickness direction; so that the boron element in the BSG layer diffuses toward the first doping layer 6 in the first direction under the action of the second laser, forming a first direction heavily doped region 8.1; wherein the area of ​​the first direction heavily doped region 8.1 is 0.27mm 2 (0.45mm*0.6mm rectangle); Second laser: 15ps pulsed laser, spot size 220um, wavelength 532nm, energy density: 5*10 3 J / m 2 The overlap ratio is 50%. Outside the 20 nm range of the first direction heavily doped region 8.1, due to the action of the second laser, the doped layer of the first region 2 is also subject to a certain degree of boron diffusion, forming the second direction lightly doped region 8.2. At this time, the surface concentration of the first direction heavily doped region 8.1 is about 1.1e+21 cm -3 The second direction lightly doped region 8.2 extends about 35nm from the surface of the first direction heavily doped region 8.1 at a distance of 8.7e+19 cm -3 The concentration of α begins to decrease gradually along the first direction until it reaches a point about 300 nm from the surface of the heavily doped region, where the concentration is about 6.1e+19 cm -3 .

[0072] Step 5: Performing a high-temperature annealing treatment on the second laser-doped region to redistribute the boron element within the first-direction heavily-doped region 8.1 and optimize the lattice structure after the second laser doping. The annealing temperature is 900° C. and the annealing time is 60 minutes.

[0073] Step 6: Deposit a 5 nm second tunnel passivation layer (SiO x ) 10, 250nm second doped layer 7 (N-type polysilicon layer, P concentration 1e+21 cm -3 )), a 50nm PSG layer (phosphosilicate glass layer); during the deposition process, the PN junction barrier formed by the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the barrier formed by the lightly doped region 8.2 in the second direction and the second doped layer 7; the Zener breakdown effect between the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the Zener breakdown effect between the lightly doped region 8.2 in the second direction and the second doped layer 7;

[0074] Step 7: Use the third laser to selectively ablate the PSG layer in the first region 2 and the third region 4; in this step, the cross-sectional area of ​​the first doping layer 6 and the second doping layer 7 composite contact is reserved to be 0.000135 mm 2 (0.45mm*0.0003mm rectangle); the third laser is: 15ps pulsed laser, spot size is 220um, wavelength is 355nm, energy density: 3*10 3 J / m 2 , the overlap rate is 30%;

[0075] Step 8: Use a strong acid mixture of HF and HNO3 to remove the various film layers formed on the front and side surfaces of the silicon substrate 1, exposing the silicon substrate on the front and side surfaces. Use an alkaline solution (KOH) and a strong acid HF to texture the front surface and the third region 4, and clean the second doped layer 7 in the first region 2 and the PSG layer in the second and fourth regions 3 and 4. At this point, the textured reflectivity of the front surface is 10%, and the surface height of the second region 3 is 3 μm higher than that of the third region 4.

[0076] Step 9: Use ALD process to deposit a 7nm passivation layer on the front and back of the battery (AL x O y layer) 14;

[0077] Step 10: Use PECVD process to deposit 70nm anti-reflection layer (SiN x Layer) 15, at this time the suede reflectivity on the front side is 2%.

[0078] Step 11: Print the metal electrode using screen printing technology, wherein the metal electrode of the second region 3 is extended to cover 50% of the length of the first direction heavily doped region 8.1, and the extended metal electrode is the third metal electrode 13; then perform sintering.

[0079] Example 2

[0080] like Figure 4 and Figure 5 As shown, a back contact battery comprises:

[0081] An N-type silicon substrate 1 having a front surface and a back surface;

[0082] A first doped layer (P-type) 6 and an N-type second doped layer (N-type) 7 are provided on the back surface. The first doped layer 6 forms a first region 2, and the second doped layer 7 forms a second region 3. The first doped layers 6 and the second doped layers 7 are arranged alternately, and the interval between the first doped layers 6 and the second doped layers 7 is a third region 4.

[0083] At the edge of the first region 2 close to the second region 3 and the third region 4, the first doped layer 6 and the second doped layer 7 are in composite contact to form a leakage channel structure 8. The region where the leakage channel structure 8 is located is the fourth region 5.

[0084] The leakage channel structure 8 includes a laser-induced heavily doped region 8.1 in the first direction and a lightly doped region 8.2 in the second direction. The barrier height formed between the heavily doped region 8.1 in the first direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7. The barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the undoped third region 4.

[0085] A first metal electrode 11 and a second metal electrode 12 are correspondingly arranged on the first doped layer 6 and the second doped layer 7 ; wherein the second metal electrode 12 extends toward the fourth region 5 and covers part of the surface of the first direction heavily doped region 8 . 1 , and the extended part of the metal electrode is the third metal electrode 13 .

[0086] This embodiment provides a method for preparing a back contact battery. Figure 1 As shown, the preparation method comprises the following steps:

[0087] Step 1: Select a silicon substrate 1 (N-type) with a size of 210 mm × 182 mm and a resistivity of 15 Ω·cm and polish it with a bath-type alkali solution (NaOH).

[0088] Step 2: Deposit a 5 nm first tunnel passivation layer (SiO x ) 9; deposit a 300nm first doping layer 6 on the first tunnel passivation layer 9, the first doping layer 6 is a P-type polysilicon layer, and the doping element is B; the B concentration is 6e+19cm -3 ; A 50nm BSG layer (borosilicate glass layer) is deposited on the back of the silicon substrate 1 as an isolation layer and a boron diffusion source;

[0089] Step 3: Use the first laser to selectively ablate the BSG layer in the second area 3 and the third area 4; use a picosecond pulsed laser with a pulse width of 5ps, a wavelength of 355nm, a spot size of 250um, and an energy density of 4*10 3 J / m 2 , an overlap rate of 10%; the second region 3 and the third region 4 irradiated by the first laser are etched by NaOH to expose the silicon substrate 1 in these two regions. At this time, the surface height difference between the first region 2 and the second region 3 is 1 μm, and a 10 nm BSG layer remains in the first region 2 and the fourth region 5;

[0090] Step 4: Use the second laser to irradiate the residual BSG layer in the preset fourth region 5, modify the BSG layer, and dope the residual BSG layer as a B source in the thickness direction; so that the boron element in the BSG layer diffuses toward the first doping layer 6 in the first direction under the action of the second laser, forming a first direction heavily doped region 8.1; wherein the area of ​​the first direction heavily doped region 8.1 is 0.27mm 2 (0.45mm*0.6mm rectangle); Second laser: 5ps pulsed laser, spot size 150um, wavelength 355nm, energy density: 3.55*10 3 J / m 2 The overlap ratio is 10%. Outside the 20 nm range of the first direction heavily doped region 8.1, due to the action of the second laser, the doped layer of the first region 2 is also subject to a certain degree of boron diffusion, forming the second direction lightly doped region 8.2. At this time, the surface concentration of the first direction heavily doped region 8.1 is about 1.9e+21 cm -3 The second direction lightly doped region 8.2 extends from the surface of the first direction heavily doped region 8.1 by about 35nm in the first direction at a distance of 8.35e+19cm. -3 The concentration of α gradually decreases along the first direction until it reaches a point about 300 nm from the surface of the heavily doped region, where the concentration is about 5e+19 cm -3 .

[0091] Step 5: Performing a high-temperature annealing treatment on the second laser-doped region to redistribute the boron element within the first-direction heavily-doped region 8.1 and optimize the lattice structure after the second laser doping. The annealing temperature is 800° C. and the annealing time is 30 minutes.

[0092] Step 6: Deposit a 5 nm second tunnel passivation layer (SiO x ) 10, 250nm second doped layer 7 (N-type polysilicon layer, P concentration 1e+21 cm -3 )), a 50nm PSG layer (phosphosilicate glass layer); during the deposition process, the PN junction barrier formed by the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the barrier formed by the lightly doped region 8.2 in the second direction and the second doped layer 7; the Zener breakdown effect between the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the Zener breakdown effect between the lightly doped region 8.2 in the second direction and the second doped layer 7;

[0093] Step 7: Use the third laser to selectively ablate the PSG layer in the first region 2 and the third region 4; in this step, the cross-sectional area of ​​the first doping layer 6 and the second doping layer 7 composite contact is reserved to be 0.000135 mm 2(0.45mm*0.0003mm rectangle); the third laser is: 5ps pulsed laser, spot size is 150um, wavelength is 532nm, energy density is 2*10 3 J / m 2 , the overlap rate is 10%;

[0094] Step 8: Use a strong acid mixture of HF and HNO3 to remove the various film layers formed on the front and side surfaces of the silicon substrate 1, exposing the silicon substrate on the front and side surfaces. Use an alkaline solution (KOH) and a strong acid HF to texture the front surface and the third region 4 and clean the second doped layer 7 in the first region 2 and the PSG layer in the second and fourth regions 3 and 4. At this point, the textured reflectivity of the front surface is 10%, and the surface height of the second region 3 is 2 μm higher than that of the third region 4.

[0095] Step 9: Use ALD process to deposit a 4nm passivation layer on the front and back of the battery (AL x O y layer) 14;

[0096] Step 10: Use PECVD process to deposit 50nm anti-reflection layer (SiN x Layer) 15, at this time the suede reflectivity on the front side is 2%.

[0097] Step 11: Use screen printing technology to print metal electrodes, wherein the metal electrode of the second region 3 is extended to cover 25% of the length of the first direction heavily doped region 8.1, and the extended metal electrode is the third metal electrode 13; then sintering is performed.

[0098] Example 3

[0099] like Figure 4 and Figure 5 As shown, a back contact battery comprises:

[0100] An N-type silicon substrate 1 having a front surface and a back surface;

[0101] A first doped layer (P-type) 6 and an N-type second doped layer (N-type) 7 are provided on the back surface. The first doped layer 6 forms a first region 2, and the second doped layer 7 forms a second region 3. The first doped layers 6 and the second doped layers 7 are arranged alternately, and the interval between the first doped layers 6 and the second doped layers 7 is a third region 4.

[0102] At the edge of the first region 2 close to the second region 3 and the third region 4, the first doped layer 6 and the second doped layer 7 are in composite contact to form a leakage channel structure 8. The region where the leakage channel structure 8 is located is the fourth region 5.

[0103] The leakage channel structure 8 includes a laser-induced heavily doped region 8.1 in the first direction and a lightly doped region 8.2 in the second direction. The barrier height formed between the heavily doped region 8.1 in the first direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7. The barrier height between the lightly doped region 8.2 in the second direction and the second doped layer 7 is higher than the barrier height between the lightly doped region 8.2 in the second direction and the undoped third region 4.

[0104] A first metal electrode 11 and a second metal electrode 12 are correspondingly arranged on the first doped layer 6 and the second doped layer 7 ; wherein the second metal electrode 12 extends toward the fourth region 5 and covers part of the surface of the first direction heavily doped region 8 . 1 , and the extended part of the metal electrode is the third metal electrode 13 .

[0105] This embodiment provides a method for preparing a back contact battery. Figure 1 As shown, the preparation method comprises the following steps:

[0106] Step 1: Select a silicon substrate 1 (N-type) with a size of 210 mm × 182 mm and a resistivity of 15 Ω·cm and polish it with a bath-type alkali solution (NaOH).

[0107] Step 2: Deposit a 5 nm first tunnel passivation layer (SiO x ) 9; deposit a 300nm first doping layer 6 on the first tunnel passivation layer 9, the first doping layer 6 is a P-type polysilicon layer, and the doping element is B; the B concentration is 6e+19cm -3 ; A 100nm BSG layer (borosilicate glass layer) is deposited on the back of the silicon substrate 1 as an isolation layer and a boron diffusion source;

[0108] Step 3: Use the first laser to selectively ablate the BSG layer in the second area 3 and the third area 4; the first laser: a picosecond pulsed laser with a pulse width of 30ps, a wavelength of 355nm, a spot size of 300um, and an energy density of 9*10 3 J / m 2 , the overlap rate is 80%; the second region 3 and the third region 4 irradiated by the first laser are etched by NaOH to expose the silicon substrate 1 in these two regions. At this time, the surface height difference between the first region 2 and the second region 3 is 5 μm, and a 40 nm BSG layer remains in the first region 2 and the fourth region 5;

[0109] Step 4: Use the second laser to irradiate the residual BSG layer in the preset fourth region 5, modify the BSG layer, and dope the residual BSG layer as a B source in the thickness direction; so that the boron element in the BSG layer diffuses toward the first doping layer 6 in the first direction under the action of the second laser, forming a first direction heavily doped region 8.1; wherein the area of ​​the first direction heavily doped region 8.1 is 0.27mm 2 (0.45mm*0.6mm rectangle); Second laser: 30ps pulsed laser, spot size 300um, wavelength 355nm, energy density: 6.5*10 3 J / m 2 The overlap ratio is 80%. Outside the 20 nm range of the heavily doped region 8.1 in the first direction, the doped layer of the first region 2 is also subject to a certain degree of boron diffusion due to the action of the second laser, forming a lightly doped region 8.2 in the second direction. At this time, the surface concentration of the heavily doped region 8.1 in the first direction is about 3e+21 cm -3 The second direction lightly doped region 8.2 extends from the surface of the first direction heavily doped region 8.1 by about 35nm in the first direction at a distance of 9.5e+19 cm -3 The concentration of α begins to decrease gradually along the first direction until it reaches a point about 300 nm from the surface of the heavily doped region, where the concentration is about 7.6e+19 cm -3 .

[0110] Step 5: Performing a high-temperature annealing treatment on the second laser-doped region to redistribute the boron element within the first-direction heavily-doped region 8.1 and optimize the lattice structure after the second laser doping. The annealing temperature is 1000° C. and the annealing time is 90 minutes.

[0111] Step 6: Deposit a 5 nm second tunnel passivation layer (SiO x ) 10, 250nm second doped layer 7 (N-type polysilicon layer, P concentration 1e+21 cm -3 )), a 100nm PSG layer (phosphosilicate glass layer); during the deposition process, the PN junction barrier formed by the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the barrier formed by the lightly doped region 8.2 in the second direction and the second doped layer 7; the Zener breakdown effect between the heavily doped region 8.1 in the first direction and the second doped layer 7 is significantly higher than the Zener breakdown effect between the lightly doped region 8.2 in the second direction and the second doped layer 7;

[0112] Step 7: Use the third laser to selectively ablate the PSG layer in the first region 2 and the third region 4; in this step, the cross-sectional area of ​​the first doping layer 6 and the second doping layer 7 composite contact is reserved to be 0.000135 mm 2(0.45mm*0.0003mm rectangle); the third laser is: 30ps pulsed laser, spot size is 300um, wavelength is 532nm, energy density: 4*10 3 J / m 2 , the overlap rate is 50%;

[0113] Step 8: Use a strong acid mixture of HF and HNO3 to remove the various film layers formed on the front and side surfaces of the silicon substrate 1, exposing the silicon substrate on the front and side surfaces. Use an alkaline solution (KOH) and a strong acid HF to texture the front surface and the third region 4, and clean the second doped layer 7 in the first region 2 and the PSG layer in the second and fourth regions 3 and 4. At this point, the textured reflectivity of the front surface is 10%, and the surface height of the second region 3 is 5 μm higher than that of the third region 4.

[0114] Step 9: Use ALD process to deposit a 10nm passivation layer on the front and back of the battery (AL x O y layer) 14;

[0115] Step 10: Use PECVD process to deposit 100nm anti-reflection layer (SiN x Layer) 15, at this time the suede reflectivity on the front side is 2%.

[0116] Step 11: Use screen printing technology to print metal electrodes, wherein the metal electrode of the second region 3 is extended to cover 80% of the length of the first direction heavily doped region 8.1, and the extended metal electrode is the third metal electrode 13; then sintering is performed.

[0117] Comparative Example 1

[0118] This comparative example provides a method for preparing a back-contact battery, which differs from Example 1 in that, in step 4, the BSG layer of the second region 3, the third region 4 and the fourth region 5 is selectively ablated by using a first laser; the second region 3, the third region 4 and the fourth region 5 irradiated by the first laser are etched by alkaline solution to expose the silicon substrates of the three regions. At this time, the first region 2 and the fourth region 5 have the same structure, and the height difference between them and the second region 3 is about 2um; at this time, there is still a BSG layer of about 20nm in the first region 2; after etching, the fourth region 5 exposes the silicon substrate 1 without a leakage channel; the rest of the preparation methods and parameters are consistent with Example 1.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing a back-contact battery, which differs from Example 1 in that step 4 (second laser doping) and step 5 (annealing treatment) are omitted; the remaining preparation methods and parameters remain consistent with Example 1.

[0121] Comparative Example 3

[0122] This comparative example provides a method for preparing a back-contact battery, which differs from Example 1 in that, in step 11, the metal electrode of the second region 3 is not extended and does not cover the first-direction heavily doped region 8.1; the rest of the preparation method and parameters remain consistent with Example 1.

[0123] Comparative Example 4

[0124] This comparative example provides a method for preparing a back-contact battery, which differs from Example 1 in that, in step 11, the metal electrode of the second region 3 is extended to cover an area that is 18% of the length of the heavily doped region 8.1 in the first direction; the rest of the preparation methods and parameters remain consistent with Example 1.

[0125] Performance Testing

[0126] The electrical performance of the back-contact cells prepared in Examples 1-3 and Comparative Examples 1-4 was tested.

[0127] The test method is: using an IV tester and measuring the following parameters of the solar cell under completely shielded conditions. The results are shown in Table 1.

[0128] Table 1 Test results of batteries of Examples and Comparative Examples

[0129] EFF (%) Jsc(A) Voc(mV) FF(%) RshDr (Ω) RshDf(ohm) <![CDATA[U -7V Leakage Current (A) Hot spot temperature (℃) Example 1 26.76 16.065 747.5 85.5 1.2 2012 26.1 88 Example 2 26.74 16.062 747.2 85.48 1.5 2136 24.9 92 Example 3 26.78 16.076 747.8 85.46 0.8 1893 28.4 82 Comparative Example 1 26.73 16.055 747.5 85.47 2267 2764 0.02 158 Comparative Example 2 26.48 16.057 744.2 85.02 2.1 2586 18.7 115 Comparative Example 3 26.69 16.052 746.8 85.4 1.8 2276 21.5 102 Comparative Example 4 26.72 16.057 747.1 85.45 1.7 2209 22.6 99

[0130] Performance test data conclusion analysis:

[0131] 1. Comparative Analysis of Performance of Examples 1-3

[0132] Examples 1-3 all adopt the leakage channel structure designed in this application, including a heavily doped region in the first direction and a lightly doped region in the second direction. The second metal electrode extends to cover part of the heavily doped region in the first direction. The only differences are in details such as laser parameters, annealing conditions, and electrode coverage ratio. The overall performance is excellent:

[0133] Photoelectric conversion efficiency (EFF): maintained above 26.74%;

[0134] Reverse leakage characteristics: Dark field reverse resistance (RshDr) is ≤1.5Ω, and leakage current is ≥24A at 7V reverse voltage, which is much larger than the short-circuit current (16A). The leakage current is ≥ the short-circuit current, ensuring that energy can be released in time under reverse bias.

[0135] Hot spot temperature: All temperatures were controlled below 100°C (≤92°C), which was lower than the control temperature (102-158°C), verifying the inhibitory effect of the leakage channel structure on the hot spot effect.

[0136] The core reason for the performance difference is that due to the inconsistent thickness of the remaining BSG, which serves as the diffusion source, the doping concentrations in the heavily doped and lightly doped areas of the leakage channel are different, which in turn makes the reverse conductivity of the leakage channel and the electrical performance of the battery cell different.

[0137] 2. Performance Difference Analysis between Examples and Comparative Examples:

[0138] 1. Comparing Example 1 and Comparative Example 1, Comparative Example 1 does not have a leakage channel structure, resulting in:

[0139] The dark field reverse resistance is as high as 2267Ω, and the reverse leakage current at 7V is only 0.02A, which is much smaller than the short-circuit current. The energy generated by the shading cannot be released, and the hot spot temperature soars to 158°C.

[0140] The efficiency is slightly lower than that of Example 1 (26.73% vs 26.76%). This is due to the lack of extended metal electrodes to collect current and the fact that the leakage channel of Example 1 is compensated for to a certain extent by laser doping to increase the barrier, which makes its efficiency slightly lower than that of Example 1 (especially reflected in the short-circuit current value).

[0141] This directly proves that the leakage channel structure is the core design to improve the reverse leakage characteristics and suppress the hot spot effect. Its gradient doping (heavy doping in the first direction + light doping in the second direction) can take into account both reverse high leakage and forward low recombination.

[0142] 2. Comparing Example 1 with Comparative Example 2, the second laser doping and annealing steps are omitted in Comparative Example 2, and a complete first-direction heavily doped region and a second-direction lightly doped region are not formed, resulting in:

[0143] The dark field reverse resistance (2.1Ω) is higher than that of Example 1 (1.2Ω), the 7V leakage current (18.7A) is lower than that of Example 1 (26.1A), and the hot spot temperature (115°C) is significantly increased;

[0144] The efficiency (26.48%) is lower than that of Example 1 because the potential barrier of the leakage channel is low due to the lack of laser doping. Under forward bias conditions, carriers easily cross the potential barrier, resulting in carrier recombination and lowering the photoelectric conversion efficiency.

[0145] This shows that laser-induced doping (second laser) and annealing are key processes for forming gradient-doped leakage channels, which can precisely control the doping concentration and regional distribution, thereby increasing the potential barrier at the leakage channel and improving the effectiveness and stability of the leakage channel.

[0146] 3. Comparing Example 1 and Comparative Example 3, the second metal electrode of Comparative Example 3 does not extend to cover the heavily doped region in the first direction, resulting in:

[0147] The dark field reverse resistance (1.8Ω) is higher than that of Example 1 (1.2Ω), the 7V leakage current (21.5A) is lower than that of Example 1 (26.1A), and the hot spot temperature (102°C) is significantly increased;

[0148] The efficiency is slightly lower than that of Example 1 (26.69% vs 26.76%). Due to the lack of an extension of the second metal electrode (the third electrode), its short-circuit current is significantly lower than that of Example 1.

[0149] 4. Performance data analysis of Comparative Example 4: The maximum offset during screen printing is approximately 20% of the length of the heavily doped region in the second direction. When the extended electrode coverage length is less than 20%, due to a certain offset during the actual screen printing process, the offset is very likely to reduce or even eliminate the coverage of half of the extended electrode in the heavily doped region, resulting in poor hot spot reduction. For example, Comparative Example 4 is designed to have an 18% extended coverage length, but in practice, the offset is approximately 20% (Examples 1-3 all have a 20% offset), resulting in approximately half of the metal electrode not covering the heavily doped region. This results in a decrease in hot spot temperature compared to Comparative Example 3 without metal electrode extension, but the increase is small, only about 3°C. Comparing Example 2 with Comparative Example 3, the hot spot temperature drops by about 10°C. Assuming that Example 2 only extends 1 / 3 of the extended electrode compared to Comparative Example 4, the hot spot temperature drop is more than three times that of Comparative Example 4.

[0150] This verifies that the second metal electrode extension (third electrode) design can shorten the reverse current transmission path, reduce transmission resistance (and increase the short-circuit current of the battery cell under normal working conditions to balance efficiency loss), and is an important auxiliary design for improving hot spot prevention capabilities; however, if the extension length is too short, it will also lead to poor hot spot reduction effect.

[0151] In summary, the present application achieves the synergistic optimization of "high-efficiency reverse leakage" and "low forward recombination loss" through the gradient-doped leakage channel (heavy doping in the first direction + light doping in the second direction) and electrode extension design: the photoelectric conversion efficiency is ≥26.7%, the dark field reverse resistance is ≤1.5Ω, and the leakage current under a reverse voltage of 7V is greater than the short-circuit current, the 7V reverse leakage current is ≥24 A, and the hot spot temperature is ≤100°C, which solves the contradiction between hot spot prevention and efficiency in traditional structures; the present application significantly improves the reverse leakage characteristics of the battery and reduces the hot spot temperature by reasonably designing the leakage channel structure of the back-contact battery and adopting the corresponding preparation method, while maintaining a photoelectric conversion efficiency of more than 26.7%, solving the problem of balancing hot spot prevention and efficiency in the existing technology, and improving the safety and reliability of photovoltaic modules.

[0152] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in this field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A back contact battery, characterized in that: include: a silicon substrate having a front side and a back side; A first doped layer and a second doped layer are provided on the back surface; wherein the first doped layer forms a first region, the second doped layer forms a second region, and the second doped layer and the first doped layer have opposite conductivity types; the first doped layer and the second doped layer are alternately arranged, and the interval region between the first doped layer and the second doped layer is a third region; At an edge portion of the first region close to the second region and at a position in the third region, the first doped layer and the second doped layer are in composite contact to form a leakage channel structure, and the region where the leakage channel structure is located is the fourth region; The leakage channel structure comprises a laser-induced heavily doped region in a first direction and a lightly doped region in a second direction; wherein the barrier height formed by the heavily doped region in the first direction and the second doped layer is higher than the barrier height formed by the lightly doped region in the second direction and the second doped layer, and the barrier height formed by the lightly doped region in the second direction and the second doped layer is higher than the barrier height formed by the lightly doped region in the second direction and the undoped third region; A first metal electrode and a second metal electrode are provided on the first doped layer and the second doped layer respectively; wherein the second metal electrode extends toward the fourth region and covers a portion of the surface of the heavily doped region in the first direction, and the extended portion of the metal electrode serves as a third metal electrode; and a proportion of the length of the surface of the heavily doped region in the first direction covered by the second metal electrode is ≥ 20%; The doping concentration of the heavily doped region in the first direction is ≥1×10 21 cm -3 The doping concentration of the lightly doped region in the second direction increases from 1×10 21 cm -3 Gradually decrease to 1×10 17 cm -3 .

2. The back contact battery according to claim 1, characterized in that The depth of the first-direction heavily doped region in the first direction is 10 nm to 40 nm; the depth of the second-direction lightly doped region in the first direction is 100 nm to 300 nm.

3. The back contact battery according to claim 1, characterized in that The height of the first barrier formed by the heavily doped region in the first direction and the second doped layer is Φ1, the height of the second barrier formed by the lightly doped region in the second direction and the second doped layer is Φ2, and the height of the third barrier formed by the lightly doped region in the second direction and the undoped third region is Φ3; wherein, Φ1-Φ2=0.1eV~0.5eV, Φ2-Φ3=0.1eV~0.3eV.

4. The back contact battery according to claim 1, characterized in that The ratio of the high-doping conductivity C1 in the first direction to the low-doping conductivity C2 in the second direction of the leakage channel is: C2 / C1=0.01-2.

5. The back contact battery according to claim 1, characterized in that On the plane where the second and third directions are located, the area of ​​a single heavily doped region in the first direction is ≥ 0.02 mm 2 ; and the ratio of the area of ​​the heavily doped region in the first direction to the cross-sectional area of ​​the composite contact between the first doped layer and the second doped layer in the plane where the first direction and the third direction are located is greater than 50.

6. The back contact battery according to claim 1, characterized in that The dark field reverse resistance RshuntDr of the back contact battery is ≤3Ω.

7. The back contact battery according to claim 1, characterized in that Under the condition that the reverse voltage applied across the back-contact battery is 7V, the leakage current of the back-contact battery is greater than or equal to the short-circuit current.

8. A method for preparing a back contact battery according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. The silicon substrate having a first conductivity type is placed in an alkaline solution for polishing; S2. A first tunnel passivation layer, a first doped layer, and a BSG layer are sequentially deposited on the back of the silicon substrate, wherein the first doped layer has a second conductivity type; S3. First laser ablation: using a first laser to perform spaced ablation on the back of the silicon substrate, and etching the silicon substrate using an alkaline solution to form an unablated first region, a second region of the exposed silicon substrate, and a third region of the exposed silicon substrate; S4. Second laser doping: Irradiating the residual BSG layer at the predetermined fourth region with a second laser, modifying the BSG layer while doping the residual BSG layer in the thickness direction using the remaining BSG layer as a boron source. After the second laser irradiation, the boron element in the BSG layer diffuses toward the first doped layer in the first direction, forming a heavily doped region in the first direction and a lightly doped region in the second direction. S5. Annealing: Annealing the second laser-doped region to redistribute the boron element within the first doped layer while optimizing the lattice structure after the second laser doping; S6. Depositing a second tunnel passivation layer, a second doped layer, and a phosphosilicate glass layer on the back side of the silicon substrate, wherein the second doped layer has a first conductivity type; S7. Third laser ablation: ablating the PSG layer in the first and third regions on the back side of the silicon substrate using a third laser, and etching the front and side surfaces of the silicon substrate using a strong acid to expose the silicon substrate on the front and side surfaces, respectively; S8. Using alkaline solution and strong acid to sequentially clean the front and side surfaces of the silicon substrate and the first, second, and fourth regions, and performing a texturing treatment on the third region and the front surface; S9. depositing a passivation layer on the front and back sides of the silicon substrate; S10. Depositing an anti-reflection layer on the front and back surfaces of the silicon substrate; S11. Print metal electrodes and perform sintering treatment; wherein, the metal electrode of the second doping layer needs to be introduced into the first direction heavily doped region of the fourth region and cover at least 20% of the length of the surface of the first direction heavily doped region.

9. The method for preparing a back contact battery according to claim 8, characterized in that: In the above S3, the first laser is a pulsed laser with a pulse width of 5ps to 30ps, a wavelength of 355nm or 532nm, a spot size of 150μm to 300μm, and an energy density of 4×10 3 J / m 2 ~9×10 3 J / m 2 , the overlap rate is 10%~80%; and / or, In S4, the second laser is a pulsed laser with a pulse width of 5ps to 30ps, a wavelength of 355nm or 532nm, a spot size of 150μm to 300μm, and an energy density of 3.55×10 3 J / m 2 ~6.5×10 3 J / m 2 , the overlap rate is 10%~80%; and / or, In S7, the third laser is a pulsed laser with a pulse width of 5ps to 30ps, a wavelength of 355nm or 532nm, a spot size of 150μm to 300μm, and an energy density of 2×10 3 J / m 2 ~4×10 3 J / m 2 , the overlap rate is 10%~50%.

10. The method for preparing a back contact battery according to claim 8, characterized in that: The thickness of the BSG layer is 50nm~100nm; the thickness of the PSG layer is 50nm~100nm; the thickness of the passivation layer is 4nm~10nm; and the thickness of the anti-reflection layer is 50nm~100nm.

11. The method for preparing a back contact battery according to claim 10, characterized in that: In S3 , after etching with NaOH using an alkaline solution, a BSG layer of 10 nm to 40 nm still exists on the surface of the first region, and the surface height of the first region is 1 μm to 5 μm higher than the surface height of the second region.

12. The method for preparing a back contact battery according to claim 8, characterized in that: In S8, after texturing, the reflectivity of the textured surface of the front side of the silicon substrate is 5% to 10%, and the surface height of the second region is 1 μm to 5 μm higher than the surface height of the third region.

13. A photovoltaic module, characterized in that: include: A battery string, the battery string being formed by connecting a plurality of back-contact batteries according to any one of claims 1 to 7 or back-contact batteries prepared by the method for preparing a back-contact battery according to any one of claims 8 to 12; and an encapsulation layer, the encapsulation layer being used to cover the surface of the battery string.

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