Back contact battery and preparation method thereof

Abstract

The invention relates to a back contact battery and a preparation method thereof. The cell includes: a silicon substrate; the first region and the second region are alternately arranged on the back surface of the silicon substrate; the first region comprises a first tunneling oxide layer, a first doped polycrystalline silicon layer, a back passivation layer and a first metal electrode; the second region comprises a second tunneling oxide layer, a second doped polycrystalline silicon layer, a back passivation layer and a second metal electrode; the isolation region is located between the first region and the second region; a first identification point and a second identification point are arranged on the back face of the silicon substrate, the second identification point wraps the first identification point or the first identification point wraps the second identification point, and the height difference D between the first identification point and the second identification point is larger than 0 and smaller than or equal to 3 micrometers. By arranging the first identification point and the second identification point with the height difference, effective and accurate identification is facilitated, a guarantee is provided for the printing precision of subsequent overprinting, and the yield of solar cells can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to a back-contact battery and a preparation method thereof. Background Art

[0002] In the solar cell industry, when the number of electrodes on the cell increases, and the structure and technology become more and more complex, precise overprinting is required during electrode printing. The emergence of new cell structures such as TOPCon and xBC requires higher precision in the production process. The laser marking point technology can accurately mark points on the surface of complex cell wafers, providing reliable references for subsequent processing and detection, and meeting the production requirements of these new cell structures.

[0003] Laser marking points can improve production efficiency and precision. Specifically, laser marking points can provide precise positioning information for automated equipment, ensuring the accurate progress of each process, improving production efficiency and consistency. For example, in the welding, encapsulation and other links of cell wafers, precise marking points can help the equipment quickly and accurately find the welding position and encapsulation position, reducing errors and rework.

[0004] For xBC products, the full-back surface patterning has higher requirements for precision. During the manufacturing process, multiple laser processes are required to assist patterning and wafer positioning. However, ordinary lasers cannot make a contrast difference between the marked point area and the normal area, which results in a low recognition precision during the printing overprinting process, easily leading to inaccurate positioning and reducing the product yield. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a back-contact battery and a preparation method thereof, which form an obvious difference between the marked point area and the non-marked point area, accurately and effectively identify the marked points, and improve the alignment precision of the printing process for battery preparation.

[0006] The present invention adopts the following technical solutions:

[0007] A back-contact battery, comprising:

[0008] A silicon substrate having a front surface and a back surface arranged opposite to each other;

[0009] A front surface passivation layer provided on the front surface of the silicon substrate;

[0010] The first region and the second region are alternately arranged on the back surface of the silicon substrate; the first region sequentially includes a first tunneling oxide layer, a first doped polysilicon layer, a back passivation layer, and a first metal electrode along the direction away from the silicon substrate, and the first doped polysilicon layer is in ohmic contact with the first metal electrode; the second region sequentially includes a second tunneling oxide layer, a second doped polysilicon layer, a back passivation layer, and a second metal electrode along the direction away from the silicon substrate, and the second doped polysilicon layer is in ohmic contact with the second metal electrode;

[0011] An isolation region located between the first region and the second region, the isolation region is recessed inward and is closer to the silicon substrate relative to the first region and the second region;

[0012] A first identification point and a second identification point for realizing alignment printing are arranged on the back surface of the silicon substrate, the second identification point wraps the first identification point or the first identification point wraps the second identification point, and the height difference D between the first identification point and the second identification point satisfies 0 < D ≤ 3, with the unit of μm.

[0013] Further, the height difference between the first identification point and the second identification point is 0.5 μm to 2.5 μm.

[0014] Further, the first identification point is a polished surface, and the second identification point is a matte surface.

[0015] Further, the reflectivity of the first identification point is 30% to 40%, and the reflectivity of the second identification point is less than 15%.

[0016] Further, when the second identification point wraps the first identification point, the area of the first identification point is 20% to 85% of the area of the second identification point;

[0017] When the first identification point wraps the second identification point, the area of the second identification point is 20% to 85% of the area of the first identification point.

[0018] Further, the shapes of the first identification point and the second identification point are any one of a cross shape, a circular shape, a triangular shape, a quadrilateral shape, and a hexagonal shape.

[0019] The present invention also provides a preparation method of the back contact battery, including the following steps:

[0020] (1) Polishing the silicon substrate;

[0021] (2) Sequentially forming a first tunneling oxide layer and a first polysilicon layer on the back surface of the silicon substrate, doping the first polysilicon layer to form a first doped polysilicon layer, and forming a first mask layer on the surface of the first doped polysilicon layer;

[0022] (3) Perform first laser treatment on the second region and the first identification point to remove or thin the first mask layer, and then use a single wet etching process to thin the first laser treatment region. There is a height difference between the first identification point, the first region, and the second region;

[0023] (4) Sequentially form a second tunneling oxide layer and a second polysilicon layer on the back of the silicon substrate, dope the second polysilicon layer to form a second doped polysilicon layer, and form a second mask layer on the surface of the second doped polysilicon layer;

[0024] (5) Perform second laser treatment on the first region, the second identification point, and the isolation region to remove or thin the second mask layer, and then use a double wet etching process to thin the second laser treatment region. There is a height difference between the first identification point and the second identification point;

[0025] (6) Remove the remaining first mask layer and second mask layer;

[0026] (7) Texture the front surface of the silicon substrate and the isolation region to form a pyramid texture surface;

[0027] (8) Deposit a passivation layer on the front and back surfaces of the silicon substrate to form a front passivation layer and a back passivation layer;

[0028] (9) Print a first metal electrode on the first region on the back of the silicon substrate and a second metal electrode on the second region. After sintering, the first metal electrode forms an ohmic contact with the first doped polysilicon layer, and the second metal electrode forms an ohmic contact with the second doped polysilicon layer.

[0029] Further, step (7) further includes texturing the second identification point to form a pyramid texture surface.

[0030] Further, in step (3), the laser spot size of the first laser treatment process is 50 μm to 550 μm, and the single-pulse energy density of the laser is 80 mJ / cm 2 ~ 500 mJ / cm 2 , and the single-pulse energy density of the laser at the first identification point is less than the single-pulse energy density of the laser in the second region.

[0031] Further, in step (3), the height difference between the first identification point and the first region surrounding the first identification point is 0 to 3 μm.

[0032] Further, in step (5), the second laser treatment process has a laser spot size of 50 μm to 550 μm, and the single-pulse energy density of the laser is 80 mJ / cm 2 ~ 500 mJ / cm 2 , and the single-pulse energy density of the laser at the second identification point is less than the single-pulse energy density of the laser in the isolation region.

[0033] Furthermore, the first wet etching process uses an alkali solution with a concentration of 5% - 10% and a protective additive of 0.5% - 1% to react at 80°C - 88°C for 100s - 320s;

[0034] The second wet etching process uses an alkali solution with a concentration of 1% - 5% and a protective additive of 0.5% - 1% to react at 70°C - 80°C for 500s - 700s.

[0035] The present invention has the following beneficial effects:

[0036] (1) For the back contact battery of the present invention, by setting the first identification point and the second identification point with a height difference on the back of the silicon substrate, it is convenient for effective and accurate identification, provides guarantee for the printing accuracy of subsequent overprinting, can improve the yield rate of solar cell production, and reduce production costs.

[0037] (2) For the back contact battery of the present invention, on the basis of the height difference between the first identification point and the second identification point, their morphologies are further set as a matte surface and a polished surface respectively, so as to form a significant morphological difference, further improve the identification accuracy, and improve the printing yield rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 It is a schematic cross-sectional view of the structure of the back contact battery of the present invention;

[0040] Figure 2 It is a top view of the structures of the first identification point and the second identification point in an embodiment of the back contact battery of the present invention;

[0041] Figure 3 It is a cross-sectional view of the structures of the first identification point and the second identification point in an embodiment of the back contact battery of the present invention;

[0042] Figure 4 It is a top view of the structures of the first identification point and the second identification point in another embodiment of the back contact battery of the present invention;

[0043] Figure 5 It is a cross-sectional view of the structures of the first identification point and the second identification point in another embodiment of the back contact battery of the present invention;

[0044] Figure 6 It is a scanning electron microscope image of the polished surface in the back contact battery of the present invention;

[0045] Figure 7 This is the SEM image of the textured surface in the back-contact battery of the present invention;

[0046] In the figure: 1 - silicon substrate, 2 - front passivation layer, 3 - first region, 4 - second region, 5 - first tunneling oxide layer, 6 - first doped polysilicon layer, 7 - back passivation layer, 8 - first metal electrode, 9 - second tunneling oxide layer, 10 - second doped polysilicon layer, 11 - second metal electrode, 12 - isolation region, 13 - first identification point, 14 - second identification point. Detailed implementation manners

[0047] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0048] The identification point referred to in the present invention, also called a marking point or a Mark point, refers to a closed area with certain characteristics within a certain range.

[0049] In the first aspect, the present invention provides a back-contact battery, as Figure 1-7 shown, including:

[0050] A silicon substrate 1 having a front surface and a back surface disposed opposite to each other;

[0051] A front passivation layer 2 disposed on the front surface of the silicon substrate;

[0052] A first region 3 and a second region 4 alternately disposed on the back surface of the silicon substrate; the first region 3 sequentially includes a first tunneling oxide layer 5, a first doped polysilicon layer 6, a back passivation layer 7, and a first metal electrode 8 along the direction away from the silicon substrate, and the first doped polysilicon layer 6 is in ohmic contact with the first metal electrode 8; the second region 4 sequentially includes a second tunneling oxide layer 9, a second doped polysilicon layer 10, a back passivation layer 7, and a second metal electrode 11 along the direction away from the silicon substrate, and the second doped polysilicon layer 10 is in ohmic contact with the second metal electrode 11;

[0053] An isolation region 12 located between the first region 3 and the second region 4, the isolation region 12 is recessed inward and is closer to the silicon substrate 1 relative to the first region 3 and the second region 4;

[0054] On the back surface of the silicon substrate, a first identification point 13 and a second identification point 14 for achieving alignment printing are provided. The second identification point 14 wraps the first identification point 13 or the first identification point 13 wraps the second identification point 14. The height difference D between the first identification point 13 and the second identification point 14 satisfies 0 < D ≤ 3, with the unit being μm.

[0055] For the back-contact battery of the present invention, on the one hand, thinning the isolation region can reduce problems such as parasitic absorption caused by too thick a polysilicon layer; on the other hand, by setting a first identification point and a second identification point with a height difference, there is an obvious brightness difference between the two, which helps to accurately align during the printing process, provides guarantee for the printing accuracy of subsequent overprinting, can improve the yield rate of solar cell production, and reduce production costs. The setting of the height difference makes the identification points have a significant contrast difference at a 3D stereoscopic angle, which is more conducive to grasping and has better printing accuracy compared to the identification points only set on a plane.

[0056] The first identification point and the second identification point of the present invention can achieve accurate alignment printing of electrodes in the front process of battery preparation, which helps to improve the yield rate of the battery. At the same time, different from the identification points formed in the prior art for tracking finished battery wafers, in the battery finished product prepared by the present invention, the identification points can be completely covered after accurate alignment printing, and will not affect the appearance and application of subsequent battery finished products.

[0057] Specifically, in some embodiments of the present invention, the height difference between the first identification point and the second identification point is 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.5μm, 2.6μm, 2.8μm, 3μm or the range value between any two of them; preferably, the height difference between the first identification point and the second identification point is 0.5μm to 2.5μm. If the height difference is too large, it will increase the difficulty of subsequent processes and production costs, and have an adverse impact on the performance of the finished battery. In the present invention, the size of the height difference between the first identification point and the second identification point is obtained by testing with an Olympus semiconductor microscope or other microtopography instruments.

[0058] Specifically, in some embodiments of the present invention, as Figure 2-5 shown, the first identification point 13 is a polished surface, and the second identification point 14 is a textured surface; the smooth polished surface and the pyramid textured surface structure form a significant difference in topography. Combining with the height difference, it can further improve the alignment accuracy and achieve accurate printing.

[0059] The doping types of the first doped polysilicon layer and the second doped polysilicon layer are opposite.

[0060] Specifically, in some embodiments of the present invention, the first doped polysilicon layer is a P-type doped polysilicon layer, and the second doped polysilicon layer is an N-type doped polysilicon layer; the first metal electrode is a metal positive electrode, and the second metal electrode is a metal negative electrode; the P-type doped polysilicon layer forms an ohmic contact with the metal positive electrode, and the N-type doped polysilicon layer forms an ohmic contact with the metal negative electrode.

[0061] As another embodiment of the present invention, the first doped polysilicon layer is an N-type doped polysilicon layer, and the second doped polysilicon layer is a P-type doped polysilicon layer; the first metal electrode is a metal negative electrode, and the second metal electrode is a metal positive electrode; the P-type doped polysilicon layer forms an ohmic contact with the metal positive electrode, and the N-type doped polysilicon layer forms an ohmic contact with the metal negative electrode.

[0062] Specifically, in some embodiments of the present invention, the reflectivity of the first identification point is 30% - 40%, and the reflectivity of the second identification point is less than 15%. By making the first identification point and the second identification point have a significant contrast difference, precise alignment is achieved.

[0063] Specifically, as some embodiments of the present invention, when the second identification point wraps the first identification point, the area of the first identification point is 20% - 85% of the area of the second identification point; when the first identification point wraps the second identification point, the area of the second identification point is 20% - 85% of the area of the first identification point. By defining the area ratio of the first identification point and the second identification point, it is prevented that the difference between the first identification point and the second identification point is not obvious due to the first identification point being too large or too small. The area of the identification point referred to in the present invention, as Figure 3 and Figure 5 shown, are respectively the areas of the closed figures enclosed by two quadrilaterals.

[0064] Specifically, as some embodiments of the present invention, the shapes of the first identification point and the second identification point are any one of a cross, a circle, a triangle, a quadrilateral, and a hexagon. More specifically, the shapes of the first identification point and the second identification point are the same.

[0065] The present invention also provides a method for preparing the above-mentioned back-contact battery, including the following steps:

[0066] (1) Polishing the silicon substrate;

[0067] (2) Sequentially forming a first tunneling oxide layer and a first polysilicon layer on the back surface of the silicon substrate, doping the first polysilicon layer to form a first doped polysilicon layer, and forming a first mask layer on the surface of the first doped polysilicon layer;

[0068] (3) Perform first laser treatment on the second region and the first identification point to remove or thin the first mask layer, and then use a single wet etching process to thin the first laser treatment region. There is a height difference between the first identification point and the first region and the second region;

[0069] (4) Sequentially form a second tunneling oxide layer and a second polysilicon layer on the back surface of the silicon substrate, dope the second polysilicon layer to form a second doped polysilicon layer, and form a second mask layer on the surface of the second doped polysilicon layer;

[0070] (5) Perform second laser treatment on the first region, the second identification point, and the isolation region to remove or thin the second mask layer, and then use a double wet etching process to thin the second laser treatment region. There is a height difference between the first identification point and the second identification point;

[0071] (6) Remove the remaining first mask layer and second mask layer;

[0072] (7) Texture the front surface of the silicon substrate and the isolation region to form a pyramid texture surface;

[0073] (8) Deposit a passivation layer on the front and back surfaces of the silicon substrate to form a front passivation layer and a back passivation layer;

[0074] (9) Print a first metal electrode on the first region on the back surface of the silicon substrate, and print a second metal electrode on the second region. After sintering, the first metal electrode forms an ohmic contact with the first doped polysilicon layer, and the second metal electrode forms an ohmic contact with the second doped polysilicon layer.

[0075] In the preparation method of the back contact battery of the present invention, during the preparation process of the first region and the second region, a first identification point and a second identification point with a height are formed on the back surface of the silicon substrate; specifically, in some embodiments of the present invention, the first identification point is located in the first region, and in step (3), the first identification point is thinned to form a height difference between the first identification point and other positions in the first region, which is convenient for grabbing points during the second laser treatment in the subsequent step (5), and helps to form a second identification point around the first identification point; at the same time, in step (5), after grabbing the position of the second identification point, it is thinned to form a height difference between the first identification point and the second identification point. Through the height difference, it helps to achieve precise alignment during the process of printing the metal electrode in step (9), and improves the yield of the back contact battery product.

[0076] The formation of the first identification point and the second identification point of the present invention is carried out before depositing the passivation layer, which will not damage the passivation layer and does not affect the passivation performance of the battery. At the same time, the first identification point and the second identification point are obtained by generating a height difference during the thinning process in the first region, the second region, or the isolation region, and will not damage the silicon substrate.

[0077] Specifically, in some embodiments of the present invention, step (7) further includes texturing the second identification points to form a pyramidal textured surface. In order to further improve the contrast between the first identification points and the second identification points, in step (7), the second identification points are textured, so that the pyramidal textured surface structure of the second identification points forms a significant topographical difference from the planar polished structure of the first identification points; the first identification points and the second identification points produce a significant contrast difference through the height difference and topographical difference, further improving the alignment accuracy during the printing process.

[0078] Specifically, in some embodiments of the present invention, in step (3), the laser spot size of the first laser treatment process is 50 μm to 550 μm, and the single-pulse energy density of the laser is 80 mJ / cm 2 ~500 mJ / cm 2 , and the single-pulse energy density of the laser for the first identification points is less than the single-pulse energy density of the laser in the second region.

[0079] In step (5), the laser spot size of the second laser treatment process is 50 μm to 550 μm, and the single-pulse energy density of the laser is 80 mJ / cm 2 ~500 mJ / cm 2 , and the single-pulse energy density of the laser for the second identification points is less than the single-pulse energy density of the laser in the isolation region outside the second identification points.

[0080] More specifically, the laser spot size is 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, 320 μm, 350 μm, 380 μm, 400 μm, 420 μm, 450 μm, 480 μm, 500 μm, 520 μm, 550 μm or a range value composed of any two of them; the single-pulse energy density of the laser is 80 mJ / cm 2 、100 mJ / cm 2 、120 mJ / cm 2 、150 mJ / cm 2 、180 mJ / cm 2 、200 mJ / cm 2 、240 mJ / cm 2 、270 mJ / cm 2 、300 mJ / cm 2 、320 mJ / cm 2 、350 mJ / cm 2 、380 mJ / cm 2 、400 mJ / cm 2 、420 mJ / cm 2 、450 mJ / cm2 、 480 mJ / cm 2 、 500 mJ / cm 2 or a range value composed of any two of them.

[0081] Specifically, in some embodiments of the present invention, the first wet etching process is to react with an alkali solution with a concentration of 5% - 10% and a protective additive with a concentration of 0.5% - 1% at 80°C - 88°C for 100 s - 320 s;

[0082] The second wet etching process is to react with an alkali solution with a concentration of 1% - 5% and a protective additive with a concentration of 0.5% - 1% at 70°C - 80°C for 500 s - 700 s.

[0083] More specifically, in the first wet etching process, NaOH or KOH is used for the reaction; the concentration of the alkali solution is 5%, 6%, 7%, 8%, 9%, 10% or a range value between any two of them; the concentration of the protective additive is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or a range value between any two of them; the reaction temperature is 80°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C or a range value between any two of them; the reaction time is 100 s, 120 s, 150 s, 180 s, 200 s, 240 s, 270 s, 300 s, 320 s or a range value between any two of them.

[0084] In the second wet etching process, NaOH or KOH is used for the reaction; the concentration of the alkali solution is 1%, 2%, 3%, 4%, 5% or a range value between any two of them; the concentration of the protective additive is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% or a range value between any two of them; the reaction temperature is 70°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 80°C or a range value between any two of them; the reaction time is 500 s, 520 s, 550 s, 580 s, 600 s, 620 s, 640 s, 650 s, 670 s, 680 s, 700 s or a range value between any two of them.

[0085] The present invention controls the thinning amplitude through a mask + laser treatment + wet etching process to achieve the control of the height difference of different structures. By controlling the single-pulse energy density of the laser at the first identification point to be less than that of the second region, and then performing wet etching, the thinning amplitude of the second region in step (3) is made larger, that is, the height of the first identification point is less than the height of the first region and greater than the height of the second region; at the same time, the thinning degree of the first identification point is controlled so that there is a height difference of 0-3 μm between the first identification point and the first region surrounding the first identification point, which is convenient for grabbing points during the second laser treatment in subsequent step (5) and helps the formation of the second identification point. By controlling the single-pulse energy density of the laser at the second identification point to be less than that of the isolation region, and further controlling the alkali concentration, time, etc. in the secondary wet etching, the thinning amplitude of the isolation region is made larger, and the height of the second identification point is made greater than the height of the isolation region. Finally, the height of the first identification point > the height of the second identification point > the height of the isolation region is obtained.

[0086] The following will further describe the present invention with specific embodiments.

[0087] Embodiment 1

[0088] This embodiment provides a back-contact battery, including:

[0089] A silicon substrate having a front surface and a back surface disposed opposite to each other;

[0090] A front passivation layer disposed on the front surface of the silicon substrate;

[0091] A first region and a second region alternately disposed on the back surface of the silicon substrate; the first region sequentially includes a first tunneling oxide layer, a P-type doped polysilicon layer, a back passivation layer, and a metal positive electrode from the direction away from the silicon substrate, and the P-type doped polysilicon layer is in ohmic contact with the metal positive electrode; the second region sequentially includes a second tunneling oxide layer, an N-type doped polysilicon layer, a back passivation layer, and a metal negative electrode from the direction away from the silicon substrate, and the N-type doped polysilicon layer is in ohmic contact with the metal negative electrode;

[0092] An isolation region located between the first region and the second region, the isolation region is recessed inward and is closer to the silicon substrate relative to the first region and the second region;

[0093] A first identification point and a second identification point wrapping the first identification point are disposed on the back surface of the silicon substrate, and the height difference between the first identification point and the second identification point is 2 μm.

[0094] The area of the first identification point is 50% of the area of the second identification point.

[0095] The preparation method of the back-contact battery of this embodiment includes the following steps:

[0096] (1)The silicon substrate is polished;

[0097] (2)A first tunneling oxide layer and a first polysilicon layer are sequentially formed on the back surface of the silicon substrate. The first polysilicon layer is doped to form a P-type doped polysilicon layer, and a first mask layer is formed on the surface of the P-type doped polysilicon layer;

[0098] (3)Perform a first laser treatment on the second region and the first identification point to remove or thin the first mask layer, and then use a single wet etching process to thin the first laser treatment region. There is a height difference between the first identification point and the second region; during the first laser treatment, the spot size of the laser is 300 μm, the single-pulse energy density of the laser for the second region is 200 mJ / cm 2 , and the single-pulse energy density of the laser for the first identification point is 150 mJ / cm 2 ; in the single wet etching process, sodium hydroxide with a concentration of 5% and a protective additive with a concentration of 0.5% are used to react at 85 °C for 200 s;

[0099] (4)A second tunneling oxide layer and a second polysilicon layer are sequentially formed on the back surface of the silicon substrate. The second polysilicon layer is doped to form an N-type doped polysilicon layer, and a second mask layer is formed on the surface of the N-type doped polysilicon layer;

[0100] (5)Perform a second laser treatment on the first region, the second identification point, and the isolation region to remove or thin the second mask layer, and then use a double wet etching process to thin the second laser treatment region. There is a height difference between the first identification point and the second identification point; during the second laser treatment, the spot size of the laser is 300 μm, the single-pulse energy density of the laser for the first region is 200 mJ / cm 2 , the single-pulse energy density of the laser for the second identification point is 300 mJ / cm 2 , and the single-pulse energy density of the laser for the isolation region outside the second identification point is 350 mJ / cm 2 ; in the double wet etching process, sodium hydroxide with a concentration of 2.5% and a protective additive with a concentration of 0.5% are used to react at 75 °C for 600 s;

[0101] (6)Remove the remaining first mask layer and second mask layer;

[0102] (7)Texturize the front surface of the silicon substrate and the isolation region to form a pyramid-shaped textured surface;

[0103] (8)Deposit a passivation layer on the front and back surfaces of the silicon substrate to form a front passivation layer and a back passivation layer;

[0104] (9) Print a positive metal electrode on the first area of the back side of the silicon substrate, and print a negative metal electrode on the second area. After sintering, the positive metal electrode forms an ohmic contact with the P-type doped polysilicon layer, and the negative metal electrode forms an ohmic contact with the N-type doped polysilicon layer.

[0105] Example 2

[0106] The back-contact battery structure and preparation method of this example are basically the same as those of Example 1, except that: the height difference between the first identification point and the second identification point is 3 μm.

[0107] The main difference in its preparation method is in step (5), specifically:

[0108] In the secondary wet etching process, sodium hydroxide with a concentration of 2.5% and ADD2 with a concentration of 0.5% are used to react at 75 °C for 700 s.

[0109] Example 3

[0110] The back-contact battery structure and preparation method of this example are basically the same as those of Example 1, except that: the height difference between the first identification point and the second identification point is 0.5 μm.

[0111] The main difference in its preparation method is in step (5), specifically:

[0112] In the secondary wet etching process, sodium hydroxide with a concentration of 3% and ADD2 with a concentration of 0.5% are used to react at 75 °C for 500 s.

[0113] Example 4

[0114] The back-contact battery structure of this example is basically the same as that of Example 1, except that:

[0115] The first identification point wraps the second identification point.

[0116] Example 5

[0117] The back-contact battery structure of this example is different from that of Example 1 only in that: the first identification point is a polished surface, and the second identification point is a textured surface, as Figure 2-3 shown. Specifically:

[0118] This example provides a back-contact battery, including:

[0119] A silicon substrate having a front side and a back side disposed opposite to each other;

[0120] A front passivation layer disposed on the front side of the silicon substrate;

[0121] The first region and the second region are alternately arranged on the back surface of the silicon substrate; the first region sequentially includes a first tunneling oxide layer, a P-type doped polysilicon layer, a back passivation layer, and a metal positive electrode along the direction away from the silicon substrate, and the P-type doped polysilicon layer is in ohmic contact with the metal positive electrode; the second region sequentially includes a second tunneling oxide layer, an N-type doped polysilicon layer, a back passivation layer, and a metal negative electrode along the direction away from the silicon substrate, and the N-type doped polysilicon layer is in ohmic contact with the metal negative electrode;

[0122] An isolation region located between the first region and the second region, the isolation region is recessed inward and is closer to the silicon substrate relative to the first region and the second region;

[0123] A first identification point and a second identification point wrapping the first identification point are arranged on the back surface of the silicon substrate, the first identification point is a polished surface, the second identification point is a matte surface, and the height difference between the first identification point and the second identification point is 2 μm.

[0124] The reflectivity of the first identification point is 30-40%, and the reflectivity of the second identification point is less than 15%. The width of the second identification point is less than the width of the isolation region, and the area of the first identification point is 50% of the area of the second identification point.

[0125] The preparation method of the back-contact battery in this embodiment includes the following steps:

[0126] (1) Polish the silicon substrate;

[0127] (2) Sequentially form a first tunneling oxide layer and a first polysilicon layer on the back surface of the silicon substrate, dope the first polysilicon layer to form a P-type doped polysilicon layer, and form a first mask layer on the surface of the P-type doped polysilicon layer;

[0128] (3) Perform a first laser treatment on the second region and the first identification point to remove or thin the first mask layer, and then use a single wet etching process to thin the first laser treatment region. There is a height difference between the first identification point and the second region; in the first laser treatment, the spot size of the laser is 300 μm, and the single-pulse energy density of the laser for the second region is 200 mJ / cm 2 2, and the single-pulse energy density of the laser for the first identification point is 150 mJ / cm 2 2; in the single wet etching process, use sodium hydroxide with a concentration of 5% and a protective additive with a concentration of 0.5% to react at 85 °C for 200 s;

[0129] (4) Sequentially form a second tunneling oxide layer and a second polysilicon layer on the back surface of the silicon substrate, dope the second polysilicon layer to form an N-type doped polysilicon layer, and form a second mask layer on the surface of the N-type doped polysilicon layer;

[0130] (5) Perform second laser treatment on the first region, the second identification point, and the isolation region to remove or thin the second mask layer, and then use a secondary wet etching process to thin the second laser treatment region. There is a height difference between the first identification point and the second identification point. During the second laser treatment, the spot size of the laser is 300 μm, and the single-pulse energy density of the laser for the first region is 200 mJ / cm 2 , and the single-pulse energy density of the laser for the second identification point is 300 mJ / cm 2 , and the single-pulse energy density of the laser for the isolation region outside the second identification point is 350 mJ / cm 2 ; In the secondary wet etching process, use sodium hydroxide with a concentration of 2.5% and a protective additive with a concentration of 0.5% to react at 75°C for 600 s;

[0131] (6) Remove the remaining first mask layer and second mask layer;

[0132] (7) Texture the front surface of the silicon substrate, the second identification point, and the isolation region to form a pyramid-shaped textured surface, and the first identification point is a polished surface;

[0133] (8) Deposit a passivation layer on the front and back surfaces of the silicon substrate to form a front passivation layer and a back passivation layer;

[0134] (9) Print a positive metal electrode on the first region on the back surface of the silicon substrate and a negative metal electrode on the second region. After sintering, the positive metal electrode forms an ohmic contact with the P-type doped polysilicon layer, and the negative metal electrode forms an ohmic contact with the N-type doped polysilicon layer.

[0135] Example 6

[0136] The back-contact battery structure and preparation method of this example are basically the same as those of Example 5, except that: the height difference between the first identification point and the second identification point is 1.5 μm.

[0137] The main difference in its preparation method is in step (5), specifically:

[0138] In the secondary wet etching process, use sodium hydroxide with a concentration of 1% and ADD2 with a concentration of 0.5% to react at 75°C for 700 s.

[0139] Example 7

[0140] The back-contact battery structure and preparation method of this example are basically the same as those of Example 5, except that: the height difference between the first identification point and the second identification point is 2.5 μm.

[0141] The main difference in its preparation method is in step (5), specifically:

[0142] In the secondary wet etching process, sodium hydroxide with a concentration of 5% and ADD2 with a concentration of 0.5% are used to react at 75°C for 500 s.

[0143] Example 8

[0144] The back-contact battery structure and preparation method of this example are basically the same as those of Example 5, except that: the height difference between the first marking point and the second marking point is 2 μm.

[0145] The difference in its preparation method is mainly in step (5), specifically:

[0146] In the secondary wet etching process, sodium hydroxide with a concentration of 3.5% and ADD2 with a concentration of 0.5% are used to react at 75°C for 550 s.

[0147] Example 9

[0148] The back-contact battery structure of this example is basically the same as that of Example 5, except that: the area of the first marking point is 20% of the area of the second marking point.

[0149] Example 10

[0150] The back-contact battery structure of this example is basically the same as that of Example 5, except that: the area of the first marking point is 85% of the area of the second marking point.

[0151] Example 11

[0152] The back-contact battery structure of this example is basically the same as that of Example 5, except that: the area of the first marking point is 5% of the area of the second marking point.

[0153] Example 12

[0154] The back-contact battery structure of this example is basically the same as that of Example 5, except that: the area of the first marking point is 90% of the area of the second marking point.

[0155] Example 13

[0156] The back-contact battery structure of this example is basically the same as that of Example 5, except that:

[0157] As Figure 4-5 shown, a second marking point and a first marking point wrapping the second marking point are provided on the back of the silicon substrate, and the area of the second marking point is 50% of the area of the first marking point.

[0158] Comparative Example 1

[0159] The back-contact battery structure and preparation method of this comparative example are basically the same as those of Example 1, except that:

[0160] The height difference between the first identification point and the second identification point is 0.

[0161] The main difference in its preparation method lies in step (5), specifically:

[0162] In the secondary wet etching process, the reaction time is less than 500 s.

[0163] Comparative Example 2

[0164] The back-contact battery structure and preparation method of this comparative example are basically the same as those of Example 1, and the only difference is that:

[0165] The height difference between the first identification point and the second identification point is 4 μm.

[0166] The main difference in its preparation method lies in step (5), specifically:

[0167] In the secondary wet etching process, sodium hydroxide with a concentration of 2.5% and ADD2 with a concentration of 0.5% are used to react at 75 °C for 700 s.

[0168] Comparative Example 3

[0169] The back-contact battery structure and preparation method of this comparative example are basically the same as those of Example 1, and the only difference is that:

[0170] The height difference between the first identification point and the second identification point is 5 μm.

[0171] The main difference in its preparation method lies in step (5), specifically:

[0172] In the secondary wet etching process, sodium hydroxide with a concentration of 2.5% and ADD2 with a concentration of 0.5% are used to react at 75 °C for 800 s.

[0173] Comparative Example 4

[0174] The back-contact battery structure and preparation method of this comparative example are basically the same as those of Comparative Example 1, and the only difference is that: the first identification point is a polished surface and the second identification point is a matte surface.

[0175] The performance of the solar cells prepared in each example and comparative example was tested, and the results are shown in Table 1.

[0176] Table 1

[0177]

[0178] It can be seen from the test results of Examples 1-13 and Comparative Examples 1-4 in Table 1 that by setting the first identification point and the second identification point with a height difference in the isolation area, the present invention is convenient for effective and accurate identification, provides guarantee for the printing accuracy of subsequent overprinting, can improve the yield rate of solar cell production, and reduce the production cost. It can be seen from the test results of Examples 1-3 and Comparative Examples 5-8 that on the premise of meeting the height difference, further making the morphologies of the two into a matte surface and a polished surface respectively to form a significant morphological difference is more conducive to alignment and grasping, and further improves the printing yield rate. It can be seen from the test results of Example 5 and Examples 9-12 that when the first identification point and the second identification point meet the corresponding height difference and morphological difference, and their area relationship further meets that the area of the first identification point is 20-85% of the area of the second identification point, a better discrimination effect can be obtained, which is more conducive to improving the printing accuracy. It can be seen from the test results of Example 1, Example 4, Example 5, and Example 13 that whether the first identification point wraps the second identification point or the second identification point wraps the first identification point, accurate printing can be achieved under the condition of meeting the corresponding morphological or height difference requirements. It can be seen from the test results of Example 1 and Comparative Examples 1-4 that when the height difference is too small, point grasping cannot be performed, resulting in process abnormalities; when the height difference is too large, the battery performance will deteriorate; if there is only a morphological difference without a height difference, the alignment printing accuracy will be worse, and the product yield rate will be reduced.

[0179] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A back-contact battery, characterized in that, Comprising: A silicon substrate having a front side and a back side which are oppositely arranged; A front passivation layer provided on the front side of the silicon substrate; A first region and a second region alternately provided on the back side of the silicon substrate; the first region sequentially includes a first tunneling oxide layer, a first doped polysilicon layer, a back passivation layer, and a first metal electrode along the direction away from the silicon substrate, and the first doped polysilicon layer is in ohmic contact with the first metal electrode; the second region sequentially includes a second tunneling oxide layer, a second doped polysilicon layer, a back passivation layer, and a second metal electrode along the direction away from the silicon substrate, and the second doped polysilicon layer is in ohmic contact with the second metal electrode; An isolation region located between the first region and the second region, the isolation region is recessed inward and is closer to the silicon substrate relative to the first region and the second region; A first identification point and a second identification point for achieving alignment printing are provided on the back side of the silicon substrate, the second identification point wraps the first identification point or the first identification point wraps the second identification point, and the height difference D between the first identification point and the second identification point satisfies 0 < D ≤ 3, with the unit being μm.

2. The back-contact battery according to claim 1, wherein The height difference between the first identification point and the second identification point is 0.5 μm to 2.5 μm.

3. The back contact battery according to claim 1, characterized in that, The first identification point is a polished surface, and the second identification point is a textured surface.

4. The back contact battery according to claim 3, characterized in that, The reflectivity of the first identification point is 30% to 40%, and the reflectivity of the second identification point is less than 15%.

5. The back contact battery according to claim 1, wherein When the second identification point wraps the first identification point, the area of the first identification point is 20% to 85% of the area of the second identification point; When the first identification point wraps the second identification point, the area of the second identification point is 20% to 85% of the area of the first identification point.

6. The preparation method of the back contact battery according to any one of claims 1-5, characterized in that, Including the following steps: (1) Polishing the silicon substrate; (2) Sequentially forming a first tunneling oxide layer and a first polysilicon layer on the back side of the silicon substrate, doping the first polysilicon layer to form a first doped polysilicon layer, and forming a first mask layer on the surface of the first doped polysilicon layer; (3) Performing a first laser treatment on the second region and the first identification point to remove or thin the first mask layer, and then using a single wet etching process to thin the first laser treatment region, and the first identification point has a height difference from the first region and the second region; (4) Sequentially forming a second tunneling oxide layer and a second polysilicon layer on the back side of the silicon substrate, doping the second polysilicon layer to form a second doped polysilicon layer, and forming a second mask layer on the surface of the second doped polysilicon layer; (5) Performing a second laser treatment on the first region, the second identification point, and the isolation region to remove or thin the second mask layer, and then using a second wet etching process to thin the second laser treatment region, and the first identification point and the second identification point have a height difference; (6) Removing the remaining first mask layer and second mask layer; (7) Texturing the front side of the silicon substrate and the isolation region to form a pyramid textured surface; (8) Depositing a passivation layer on the front side and the back side of the silicon substrate to form a front passivation layer and a back passivation layer; (9) Print a first metal electrode on the back surface first region of the silicon substrate, and print a second metal electrode on the second region. After sintering, the first metal electrode forms an ohmic contact with the first doped polysilicon layer, and the second metal electrode forms an ohmic contact with the second doped polysilicon layer.

7. The preparation method of the back contact battery according to claim 6, characterized in that, The step (7) further includes texturing the second identification point to form a pyramid texture surface.

8. The manufacturing method of the back contact battery according to claim 6, characterized in that, In step (3), the laser spot size of the first laser processing process is 50 μm to 550 μm, and the single-pulse energy density of the laser is 80 mJ / cm 2 ~500 mJ / cm 2 , and the single-pulse energy density of the laser for the first marking point is less than the single-pulse energy density of the second region; The primary wet etching process is to react with an alkali solution with a concentration of 5% - 10% and a protective additive of 0.5% - 1% at 80°C - 88°C for 100s - 320s.

9. The preparation method of the back-contact battery according to claim 6, characterized in that, In step (3), the height difference between the first identification point and the first region surrounding the first identification point is 0 - 3μm.

10. The method for preparing a back-contact battery according to claim 6, characterized in that, In step (5), the laser spot size of the second laser treatment process is 50 μm to 550 μm, and the single pulse energy density of the laser is 80 mJ / cm 2 ~500 mJ / cm 2 , and the single pulse energy density of the laser for the second marking point is less than that of the isolation area; The secondary wet etching process is to react with an alkali solution with a concentration of 1 - 5% and a protective additive of 0.5 - 1% at 70 - 80°C for 500s - 700s.

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