A method for laser opening film on the back of a tbc cell and a back contact cell

Abstract

The application discloses a kind of TBC battery back laser film opening method and back contact battery, belong to solar cell field, be provided with the first area and a plurality of second areas of alternately spaced arrangement on the back of silicon substrate, third area is formed between the first area and the second area;Square spot is used to laser film opening treatment to the first area, form laser scanning path along longitudinal continuous scanning, adjacent spot on laser scanning path has first overlap area, second overlap area between adjacent two laser scanning paths, and the spot between adjacent two laser scanning paths is staggered scanning.By limiting the size of laser spot, and design adjacent two laser scanning paths are staggered scanning, so that the battery piece will not be more damaged due to transition scanning, avoid the passivation layer to be destroyed after battery piece after subsequent cleaning due to multiple laser scanning, and the probability of forming perforated pit is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar cells, in particular, to a method for laser opening film on the back of a TBC cell and a back contact cell. BACKGROUND

[0002] The back contact solar cell is one of the crystalline silicon solar cells with high photoelectric conversion efficiency in the market, and its biggest feature is that the positive and negative metal electrodes are all placed on the back of the cell, so that there is no metal electrode on the front surface to block the sunlight, which can maximize the absorption of sunlight. The design of the metal electrode on the back can improve the series resistance and fill factor of the cell as much as possible without considering the shading effect, and a higher photoelectric conversion efficiency can be obtained. However, the back contact cell is limited by metal recombination and passivation film layer, and cannot obtain higher photoelectric conversion efficiency.

[0003] TOPCon solar cell is a kind of high-efficiency cell based on carrier selective collection passivation contact structure, and its feature is to prepare a passivation contact structure composed of a tunneling silicon oxide layer (SiO x ) and a heavily doped silicon thin film layer (poly-Si) on the back of the cell, which effectively reduces surface recombination and metal contact recombination, thereby improving the open circuit voltage and energy conversion efficiency of the cell. Although the conversion efficiency of TOPCon cell is already high, due to the parasitic absorption of polysilicon layer to light, the front passivation contact structure cannot be made on the front surface of the cell, and only the passivation contact structure can be made at the grid line position, which limits the potential of further improving the efficiency of TOPCon cell.

[0004] Tunneling oxide passivation back contact (TBC) solar cell combines the passivation contact technology of back contact solar cell and TOPCon cell, which can further improve the solar conversion efficiency. However, in the production process of preparing polysilicon layer on the back of TBC solar cell, a large amount of loose silicon powder is indirectly aggregated into silicon powder particles distributed on the surface of the doped polysilicon layer due to the process reasons. Under the action of subsequent laser and cleaning process, the silicon powder particles are washed away, but the holes are left on the surface of the polysilicon layer, which causes damage to the polysilicon layer, and the area with holes makes the passivation invalid, affecting the photoelectric conversion efficiency. Moreover, due to the large particle size of the silicon powder particles, it also causes the pit to be too large and too deep, and in serious cases, the pit even penetrates the polysilicon layer, causing electric leakage.

[0005] In addition, the conventional laser film opening process usually adopts the way of partially overlapping laser spot path, at least there are two overlapping areas of laser path, and the spot is repeatedly acted on the cell for 4 times at most, which brings more damage to the silicon substrate of the cell than once laser scanning, so that the energy density of the overlapping area is too high to cause the silicon powder particles to remain in the pit after laser and cleaning, and the cell Voc electrical performance is also reduced. SUMMARY

[0006] To address the shortcomings and deficiencies of existing technologies, the present invention provides a method for laser ablation of the back surface of a TBC cell and a back-contact cell. By limiting the size of the laser spot and designing two adjacent laser scanning paths for staggered scanning, the laser spot between the two laser scanning paths can be repeatedly applied to the cell up to three times. This prevents excessive scanning from causing further damage to the cell and also alleviates the problem of pitting of silicon powder particles after laser ablation. The technical solution is as follows:

[0007] A method for laser film opening on the back side of a TBC battery comprises the following steps:

[0008] A silicon substrate is provided, having a front side and a back side opposite to each other, with a plurality of first regions and a plurality of second regions alternately arranged on the back side, and a third region formed between the first and second regions; the first region includes a first passivation layer and a P-type doping layer stacked on the back side of the silicon substrate, and the second region includes a second passivation layer and an N-type doping layer stacked in sequence on the back side of the silicon substrate; the first region is laser-opened using a square light spot, and a laser scanning path is formed by continuous scanning along the longitudinal direction, wherein adjacent light spots on the laser scanning path have a first overlapping region, and a second overlapping region is formed between two adjacent laser scanning paths, and the light spot between the two adjacent laser scanning paths is staggered scanning; when the first region has a main gate, the fine gate width of the first region is set to A, the main gate width is set to C, the width of the third region is set to B, and the side length of the square light spot is set to L, where L=min(A, C)+2B.

[0009] Preferably, the side length L of the light spot accounts for 55% to 60% of the total width of the wider area [max(A, C) + 2B]. This range is limited to the wider main gate area or fine gate area, that is, max(A, C), so that two laser scanning paths can scan side by side to achieve full coverage.

[0010] Preferably, the fine gate width A and the main gate width C of the first region have the following relationship:

[0011] [min(A,C)+2B]∈55%×[max(A,C)+2B]~60%×[max(A,C)+2B].

[0012] Preferably, the distance between the staggered scanning of the light spots of two adjacent laser scanning paths is S1, then

[0013] S1∈ηL~(1-2η)L,

[0014] The overlap rate η=(LV / f) / L, and η≤33%, L=min(A,C)+2B is the side length of the light spot, V is the laser scanning speed, and f is the laser scanning frequency.

[0015] Preferably, the overlapping width of the first overlapping area in the longitudinal direction is S2=LV / f, and the overlapping width of the second overlapping area in the transverse direction is S3=2L-[max(A,C)+2B].

[0016] Preferably, the laser device for laser film opening treatment of the first area adopts a pulsed laser with a laser wavelength of 532 nm, a pulse width of 10 ps, ​​a spot side length L of 100-300 μm, a scanning frequency f and a scanning speed V satisfying the relationship of overlap rate η=(LV / f) / L≤33%, a scanning speed V of 10000 mm / s-900000 m / s, and an energy density of 1×10 3 ~9×10 3 J / m 2 .

[0017] The present invention also provides a method for laser film opening on the back side of a TBC battery, comprising the following steps:

[0018] A silicon substrate is provided, having opposite front and back surfaces. The back surface is provided with a plurality of first regions and a plurality of second regions arranged alternately and spaced apart, with a third region formed between the first and second regions. The first region comprises a first passivation layer and a P-type doped layer stacked on the back surface of the silicon substrate, while the second region comprises a second passivation layer and an N-type doped layer stacked in sequence on the back surface of the silicon substrate. When the first region lacks a main gate, the fine gate width of the first region is set to A, the width of the third region is set to B, and the side length of the square laser spot is set to L, where L = A + 2B. The laser spot side length L in this design fully covers the fine gate width and the spacers in the first region, improving laser processing efficiency.

[0019] Preferably, the fine gate width A is 300-500 μm, and the third region width B is 50-150 μm.

[0020] Preferably, the laser film opening further includes cleaning, specifically using 1% alkaline solution at 70-90° C. for 500-800 seconds.

[0021] The present invention also provides a back contact battery, which is manufactured by the above-mentioned laser film opening method.

[0022] The beneficial effects produced by the technical solution of the present invention are as follows:

[0023] The present invention limits the size of the laser spot and designs two adjacent laser scanning paths for staggered scanning, thereby improving the laser scanning efficiency and achieving a maximum of three repeated effects of the spot on the battery cell between the laser scanning paths, so that the battery cell will not be further damaged due to excessive scanning, reducing the perforation rate of the battery cell, avoiding the damage of the passivation layer of the battery cell after multiple laser scanning and subsequent cleaning, and reducing the probability of forming perforation pits, thereby avoiding the reduction of the passivation effect directly caused by the damage to the passivation layer, improving the Voc of the battery cell and significantly reducing the efficiency of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces 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 invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the laser scanning path without a main grid in the first area of ​​Example 1;

[0026] Figure 2 Schematic diagram of the laser scanning path with a main grid in the first region of Example 2;

[0027] Figure 3 This is a schematic diagram of the back side of the cell after laser scanning in Example 2;

[0028] Figure 4 Schematic diagram of the laser scanning path without misalignment in comparative example 1;

[0029] Figure 5 This is a schematic diagram of the back side of the cell after laser scanning in comparative example 1.

[0030] Among them: 1. Laser spot; 2. First overlapping area; 3. Second overlapping area. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] The present invention provides a method for laser debonding the backside of a TBC cell and a back-contact cell. By limiting the size of the laser spot and designing two adjacent laser scanning paths for staggered scanning, the laser scanning efficiency is improved while also achieving a maximum of three repetitive effects on the cell between the laser scanning paths. This prevents further damage to the cell due to excessive scanning, reduces the cell perforation rate to below 5%, avoids burning through the silicon wafer due to multiple laser scans, and improves the problem of pits left by silicon powder particles after laser ablation. The technical solution is as follows:

[0033] A method for laser film opening on the back side of a TBC battery comprises the following steps:

[0034] A silicon substrate is provided, having a front side and a back side opposite to each other, with a plurality of first regions and a plurality of second regions alternately arranged on the back side, and a third region formed between the first and second regions; the first region includes a first passivation layer and a P-type doping layer stacked on the back side of the silicon substrate, and the second region includes a second passivation layer and an N-type doping layer stacked in sequence on the back side of the silicon substrate; the first region is laser-opened using a square light spot, and a laser scanning path is formed by continuous scanning along the longitudinal direction, wherein adjacent light spots on the laser scanning path have a first overlapping region, and a second overlapping region is formed between two adjacent laser scanning paths, and the light spot between the two adjacent laser scanning paths is staggered scanning; when the first region has a main gate, the fine gate width of the first region is set to A, the main gate width is set to C, the width of the third region is set to B, and the side length of the square light spot is set to L, where L=min(A, C)+2B.

[0035] As a preferred embodiment, the spot side length L accounts for 55% to 60% of the total width of the wider region [max(A, C) + 2B]. This range is limited to the wider main gate region or fine gate region, i.e., max(A, C), to achieve full coverage by scanning two laser scanning paths side by side.

[0036] As a preferred embodiment, the fine gate width A and the main gate width C of the first region have the following relationship:

[0037] [min(A,C)+2B]∈55%×[max(A,C)+2B]~60%×[max(A,C)+2B].

[0038] As a preferred embodiment, the distance between the staggered scanning of the light spots of two adjacent laser scanning paths is S1, then

[0039] S1∈ηL~(1-2η)L,

[0040] The overlap rate η=(LV / f) / L, and η≤33%, L=min(A,C)+2B is the side length of the light spot, V is the laser scanning speed, and f is the laser scanning frequency.

[0041] As a preferred embodiment, the overlapping width of the first overlapping area in the longitudinal direction is S2=LV / f, and the overlapping width of the second overlapping area in the transverse direction is S3=2L-[max(A,C)+2B].

[0042] As a preferred embodiment, the laser device for laser film opening treatment of the first area adopts a pulsed laser with a laser wavelength of 532 nm, a pulse width of 10 ps, ​​a spot side length L of 100-300 μm, a scanning frequency f and a scanning speed V satisfying the relationship of overlap rate η=(LV / f) / L≤33%, a scanning speed V of 10000 mm / s-900000 m / s, and an energy density of 1×10 3 ~9×10 3 J / m 2 .

[0043] The present invention also provides a method for laser film opening on the back side of a TBC battery, comprising the following steps:

[0044] A silicon substrate is provided, having opposite front and back surfaces. The back surface is provided with a plurality of first regions and a plurality of second regions arranged alternately and spaced apart, with a third region formed between the first and second regions. The first region comprises a first passivation layer and a P-type doped layer stacked on the back surface of the silicon substrate, while the second region comprises a second passivation layer and an N-type doped layer stacked in sequence on the back surface of the silicon substrate. When the first region lacks a main gate, the fine gate width of the first region is set to A, the width of the third region is set to B, and the side length of the square laser spot is set to L, where L = A + 2B. The laser spot side length L in this design fully covers the fine gate width and the spacers in the first region, improving laser processing efficiency.

[0045] As a preferred embodiment, the fine gate width A is 300-500 μm, and the third region width B is 50-150 μm.

[0046] As a preferred embodiment, the laser film opening further includes cleaning, specifically using 1% alkaline solution at 70-90° C. for 500-800 seconds.

[0047] The present invention also provides a back contact battery, which is manufactured by the above-mentioned laser film opening method.

[0048] The following further reviews the beneficial effects of the TBC battery back laser film opening method and back contact battery provided by the present invention in combination with several groups of embodiments.

[0049] Example 1:

[0050] This embodiment 1 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0051] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and clean both the front and back surfaces.

[0052] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is composed of a first passivation layer, a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is composed of a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0053] Step 3: Set the first area to have no main grid, its fine grid width is A = 300μm, and the width of the third area is B = 50μm. Perform laser film opening treatment on the first area, using a square spot with a spot size of L = A + 2B = 300 + 2 × 50 = 400μm, a laser wavelength of 532nm, a frequency f of 250kHz, a scanning speed V of 60000mm / s, an overlap ratio η = (LV / f) / L = 40%, and an overlap width S2 of the first overlapping portion in the longitudinal direction = 160μm.

[0054] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0055] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0056] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0057] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0058] Example 2:

[0059] This embodiment 2 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0060] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatment in sequence;

[0061] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is composed of a first passivation layer, a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is composed of a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0062] Step 3: Set the first area to have no main grid, its fine grid width is A = 300μm, and the width of the third area is B = 50μm. Perform laser film opening treatment on the first area, using a square spot with a spot size of L = A + 2B = 300 + 2 × 50 = 400μm, a laser wavelength of 532nm, a frequency f of 250kHz, a scanning speed V of 70000mm / s, an overlap ratio η = (LV / f) / L = 30%, and an overlap width S2 of 120μm in the longitudinal direction of the first overlapping area.

[0063] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0064] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0065] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0066] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0067] Example 3:

[0068] This embodiment 3 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0069] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatment in sequence;

[0070] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0071] Step 3: Set the first area to have a main grid, whose fine grid width is A=300μm, and the width of the third area is B=50μm, then C∈120~140μm, taking 130μm, and perform laser film opening treatment on the first area and the third area, using a square spot and the size of the square spot is L=min(A,C)+2B=130+2×50=230μm, the laser wavelength is 532nm, the frequency f is 300kHz, the scanning speed V is 62100mm / s, the overlap rate η=(LV / f) / L=10%, the offset distance S1∈23~184μm, taking 50μm, the longitudinal overlap width S2 of the first overlapping area is 23μm, and the transverse overlap width S3 of the second overlapping area is 2L-[max(A,C)+2B]=60μm;

[0072] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0073] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0074] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0075] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0076] Example 4:

[0077] This embodiment 4 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0078] Step 1: Select a single-crystal silicon wafer with a resistivity of 30 Ω·cm and clean both the front and back surfaces. Step 2: Prepare alternating first and second regions on the back surface of the silicon wafer, with a third region formed between the first and second regions. The first region comprises a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back surface of the silicon wafer, while the second region comprises a stacked layer.

[0079] Step 3: Set the first area to have a main grid, whose fine grid width is A=300μm, and the width of the third area is B=50μm, then C∈120~140μm, taking 130μm, and perform laser film opening treatment on the first area and the third area, using a square spot and the size of the square spot is L=min(A,C)+2B=130+2×50=230μm, the laser wavelength is 532nm, the frequency f is 337.5kHz, the scanning speed V is 62100mm / s, the overlap rate η=(LV / f) / L=20%, the offset distance S1∈46~138μm, taking 50μm, the longitudinal overlap width S2 of the first overlapping part is 46μm, and the transverse overlap width S3 of the second overlapping part is 2L-[max(A,C)+2B]=60μm;

[0080] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0081] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0082] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0083] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0084] Example 5:

[0085] This embodiment 5 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0086] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatment in sequence;

[0087] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer, and the second region is a stacked layer;

[0088] Step 3: Set the first area to have a main grid, whose fine grid width is A=300μm, and the width of the third area is B=50μm, then C∈120~140μm, taking 130μm, and perform laser film opening treatment on the first area and the third area, using a square spot and the size of the square spot is L=min(A,C)+2B=130+2×50=230μm, the laser wavelength is 532nm, the frequency f is 337.5kHz, the scanning speed V is 62100mm / s, the overlap rate η=(LV / f) / L=20%, the offset distance S1∈46~138μm, taking 70μm, the longitudinal overlap width S2 of the first overlapping area is 46μm, and the transverse overlap width S3 of the second overlapping area is 2L-[max(A,C)+2B]=60μm;

[0089] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0090] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0091] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0092] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0093] Comparative Example 1:

[0094] This comparative example 1 provides a method for laser debonding the back surface of a TBC battery, comprising the following steps:

[0095] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and perform cleaning and texturing, front-side boron diffusion, and etching and alkaline polishing treatment in sequence;

[0096] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0097] Step three, set the first region without main grid, the fine grid width of which is A=300 μm, the width of the third region is B=50 μm, laser opening film processing is performed on the first region, a square spot is adopted and the spot size is L=150 μm, the laser wavelength is 532 nm, the frequency f is 250 kHz, the scanning speed V is 22550 mm / s, the overlap rate η=(L-V / f) / L=40%, the first overlap region has an overlap width S2=60 µm along the longitudinal direction, and the second overlap region has an overlap width S3=25 µm along the transverse direction;

[0098] Step four, cleaning the silicon wafer by using a NaOH solution with a concentration of 1% at 70°C for 500 s to remove the second passivation layer, the N-type doped layer and the PSG mask of the first region;

[0099] Step five, depositing a front passivation layer and a back passivation layer on the front and back surfaces of the silicon wafer respectively;

[0100] Step six, depositing a front anti-reflection layer and a back anti-reflection layer on the front and back surfaces of the silicon wafer respectively;

[0101] Step seven, slurry printing and metal sintering are performed on the silicon wafer to obtain a back contact cell.

[0102] Comparative Example 2

[0103] The present comparative example 2 provides a method for laser opening film on the back of a TBC cell, comprising the following steps:

[0104] Step one, a single crystal silicon wafer with a resistivity of 30 Ω·cm is selected, and cleaning, texturing, front boron diffusion and etching alkaline polishing are sequentially performed;

[0105] Step two, first and second regions alternately arranged on the back of the silicon wafer are prepared, and the first region and the second region form a third region; the first region is a stack of a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer and a PSG mask on the back of the silicon wafer, and the second region is a stack;

[0106] Step three, set the first region with main grid, the fine grid width of which is A=300 μm, the width of the third region is B=50 μm, and C is 250 µm, laser opening film processing is performed on the first region and the third region, a square spot is adopted and the size of the square spot is L=150 μm, the fine grid region of the first region adopts a laser wavelength of 532 nm, a frequency f of 860 kHz, a scanning speed V of 64500 mm / s, and an overlap rate η=(L-V / f) / L=50%, without staggered design; the main grid region of the first region does not adopt staggered design; the first overlap region has an overlap width S2=75 µm along the longitudinal direction, and the second overlap region has an overlap width S3=25 µm along the transverse direction;

[0107] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0108] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0109] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0110] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0111] Comparative Example 3:

[0112] This comparative example 3 provides a method for laser opening the back surface of a TBC battery, comprising the following steps:

[0113] Step 1: Select a single crystal silicon wafer with a resistivity of 30Ω·cm and clean both the front and back surfaces.

[0114] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0115] Step 3: Set the first area with a main grid, whose fine grid width is A=300μm, the width of the third area is B=50μm, and C=250μm. Perform laser film opening treatment on the first and third areas, using a square spot with a size of L=150μm, a laser wavelength of 532nm, a frequency f of 500kHz, a scanning speed V of 67500mm / s, an overlap ratio η=(150-67500 / 500) / 150=10%, and no staggered design is used. The longitudinal overlap width S2 of the first overlapping part is 15μm, and the transverse overlap width S3 of the second overlapping part is 25μm.

[0116] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0117] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0118] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0119] Step seven, slurry printing and metal sintering are performed on the silicon wafer to obtain a back contact cell.

[0120] Comparative Example 4:

[0121] Comparative Example 4 provides a method for laser opening a film on the back of a TBC cell, comprising the following steps:

[0122] Step one, a single crystal silicon wafer with a resistivity of 30 Ω·cm is selected, and the front and back surfaces are cleaned;

[0123] Step two, first and second regions are prepared on the back surface of the silicon wafer in an alternating and spaced manner, and a third region is formed between the first and second regions; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back surface of the silicon wafer, and the second region is a second passivation layer and an N-type doped layer stacked on the back surface of the silicon wafer;

[0124] Step three, the first region is provided with a main grid, the width of the fine grid is A=300 μm, the width of the third region is B=50 μm, C ∈ 120~140 µm, and 130 µm is taken, the first region and the third region are subjected to laser film opening treatment, a square spot is used, the size of the square spot is L=150 μm, the laser wavelength is 532 nm, the frequency f is 500 kHz, the scanning speed V is 67500 mm / s, the overlap rate η=(L-V / f) / L=10%, there is no misregistration design, the first overlap part has a longitudinal overlap width S2=15 µm, and the second overlap part has a transverse overlap width S3=25 µm;

[0125] Step four, the silicon wafer is cleaned by using a 1% NaOH solution at 70°C for 500 s to remove the second passivation layer, the N-type doped layer, and the PSG mask of the first region;

[0126] Step five, a front passivation layer and a back passivation layer are respectively deposited on the front and back surfaces of the silicon wafer;

[0127] Step six, a front anti-reflection layer and a back anti-reflection layer are respectively deposited on the front and back surfaces of the silicon wafer;

[0128] Step seven, slurry printing and metal sintering are performed on the silicon wafer to obtain a back contact cell.

[0129] Comparative Example 5:

[0130] Comparative Example 5 provides a method for laser opening a film on the back of a TBC cell, comprising the following steps:

[0131] Step one, a single crystal silicon wafer with a resistivity of 30 Ω·cm is selected, and the front and back surfaces are cleaned;

[0132] Step 2: preparing a first region and a second region alternately arranged on the back side of the silicon wafer, with a third region formed between the first region and the second region; the first region is a first passivation layer and a P-type doped layer, a second passivation layer, an N-type doped layer, and a PSG mask stacked on the back side of the silicon wafer; and the second region is a second passivation layer and an N-type doped layer stacked on the back side of the silicon wafer;

[0133] Step 3: Set the first area to have a main grid, whose fine grid width is A=300μm, and the width of the third area is B=50μm, then C∈120~140μm, take 130μm, and perform laser film opening treatment on the first area and the third area, using a square spot and the size of the square spot is L=min(A,C)+2B=130+2×50=230μm, the laser wavelength is 532nm, the frequency f is 300kHz, the scanning speed V is 62100mm / s, the overlap rate η=(LV / f) / L=10%, and no staggered design is used. The longitudinal overlap width S2 of the first overlapping part is 23μm, and the transverse overlap width S3 of the second overlapping part is 2L-[max(A,C)+2B]=60μm;

[0134] Step 4: Clean the silicon wafer using a 1% NaOH solution at 70°C for 500 seconds to remove the second passivation layer, N-type doping layer, and PSG mask from the first region.

[0135] Step 5: depositing a front passivation layer and a back passivation layer on the front and back sides of the silicon wafer respectively;

[0136] Step 6: depositing a front anti-reflection layer and a back anti-reflection layer on the front and back sides of the silicon wafer respectively;

[0137] Step seven: perform slurry printing and metal sintering on the silicon wafer to obtain a back-contact battery.

[0138] The solar cells obtained in the above examples and comparative examples were subjected to performance tests, and the results are as follows:

[0139] Table 1 Performance test results of back contact cells prepared in Examples and Comparative Examples

[0140] Group Conversion efficiency EFF (%) Current density Jsc (A) Open circuit voltage Voc (mV) Fill factor FF (%) Parallel resistance Rsh (ohm) Passivation layer perforation rate Example 1 26.75 16.065 747.3 85.47 2834 0.7% Example 2 26.77 16.071 747.5 85.48 2493 0.5% Comparative Example 1 26.66 16.062 746.1 85.35 2764 5.2% Example 3 26.60 16.055 745.3 85.29 1756 0.2% Example 4 26.57 16.045 745.0 85.28 1836 0.6% Example 5 26.58 16.044 745.1 85.3 1687 0.6% Comparative Example 2 26.48 16.057 743.2 85.02 1864 6.5% Comparative Example 3 26.52 16.052 744.3 85.15 1864 3.8% Comparative Example 4 26.51 16.048 744.1 85.16 1925 3.9% Comparative Example 5 26.55 16.053 744.8 85.2 2153 1.5%

[0141] The above-mentioned Examples 1 and 2 are back-contact cells designed with spot sizes in the absence of a main grid in the first region according to the present invention. Compared with Comparative Example 1, Example 1 maintains the same overlap width in the longitudinal direction, and only changes the spot size, that is, eliminates the lateral overlap. Furthermore, compared with Example 1, Example 2 maintains the same spot size, that is, there is no lateral overlap, and the longitudinal overlap area is reduced. Comparative Example 1 is a back-contact cell with a conventional spot size and no misalignment between laser scanning paths in the absence of a main grid in the first region, and the width of the second lateral overlap region is 25µm. As can be seen from Table 1, the cell conversion efficiency, current density, open circuit voltage, and fill factor of Examples 1 and 2 of the present application are all better than those of Comparative Example 1, and the perforation rate of the passivation layer is also reduced. Therefore, the spot size designed by the present application is more suitable for the laser scanning process of the back-contact cell. By comparing the electrical properties of Example 1 and Example 2, it can be seen that further reducing the longitudinal overlapping area can further reduce the perforation rate and improve the battery efficiency; by comparing the electrical properties of Example 1 and Comparative Example 1, it can be seen that in the absence of a second overlapping area, although the overlap rate η between the two is the same, in Comparative Example 1, there is a situation in which the laser spot scans and covers the second overlapping area 4 times, and the perforation rate is greatly increased, while the perforation rate of Example 1 of the present application is significantly lower than that of Comparative Example 1. This shows that by setting the side length of the light spot to directly scan the grid line width without extending the horizontal overlap, there is less negative effect on the back of the battery.

[0142] Examples 3 to 5 are back-contact cells obtained by using the spot size and staggered distance designed by the present invention when there is a main grid in the first area. Comparative Example 2 is a back-contact cell using a conventional spot size and no staggered distance between the two laser scanning paths when there is a main grid in the first area. Comparative Example 3 only changes the longitudinal overlap rate compared to Comparative Example 2; Comparative Example 4 only changes the main grid width compared to Comparative Example 3; Comparative Example 5 only changes the spot size compared to Comparative Example 4; Example 3 adds a staggered design compared to Comparative Example 5, so that the second overlapping area is covered by the laser spot scan at most 3 times, which significantly reduces the perforation rate; Example 4 only changes the longitudinal overlapping area compared to Example 3; Example 5 only has a staggered spacing compared to Example 4; It can be seen from Table 1 that the cell conversion efficiency of Examples 3 to 5 of the present application is better than that of Comparative Example 5, and the perforation rate of the passivation layer is also reduced, so the spot size obtained by the design of the present application is more suitable for the laser scanning process of the back-contact cell. At the same time, through the comparison of electrical performance between Examples 3 to 5, it can be seen that when the misalignment spacing is within the set formula, the perforation rate and electrical performance of the battery are the same; by comparing the electrical performance of Example 3 and Example 4, it can be seen that further reducing the longitudinal overlap area can also further reduce the perforation rate and improve battery efficiency.

[0143] In summary, the main factor leading to the increase in perforation rate is the number of times the light spot repeatedly acts on the battery cell. The overlapping parts of the first overlapping area and the second overlapping area have both horizontal and vertical overlaps. Therefore, by maximizing the reduction of the second overlapping area or even avoiding the second overlapping area, it is beneficial to reduce the perforation rate. Similarly, reducing the first overlapping area or performing a staggered design to improve the number of laser actions in the overlapping area can also achieve a reduction in the perforation rate, thereby avoiding the reduction in passivation effect directly caused by the damage to the passivation layer, and improving the Voc of the battery cell to have a significant decrease, thereby improving the efficiency of the battery cell.

[0144] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for laser film opening on the back side of a TBC battery, characterized in that: The following steps are involved: A silicon substrate is provided, having a front side and a back side opposite to each other, wherein a plurality of first regions and a plurality of second regions are alternately arranged on the back side, and a third region is formed between the first regions and the second regions; the first regions include a first passivation layer and a P-type doped layer stacked on the back side of the silicon substrate, and the second regions include a second passivation layer and an N-type doped layer stacked in sequence on the back side of the silicon substrate; A square light spot is used to perform laser film opening treatment on the first area, and a laser scanning path is formed by continuous scanning along the longitudinal direction. Adjacent light spots on the laser scanning path have a first overlapping area, and there is a second overlapping area between two adjacent laser scanning paths. The light spot between the two adjacent laser scanning paths is staggered scanning; when there is a main grid in the first area, the fine grid width of the first area is set to A, the main grid width is set to C, the width of the third area is set to B, the side length of the square light spot is L, and L=min(A,C)+2B.

2. The laser film opening method according to claim 1, characterized in that: The side length L of the light spot accounts for 55% to 60% of the total width of the wider area [max(A, C)+2B].

3. The laser film opening method according to claim 2, characterized in that: The fine gate width A and the main gate width C of the first region have the following relationship: [min(A,C)+2B]∈55%×[max(A,C)+2B]~60%×[max(A,C)+2B].

4. The laser film opening method according to claim 3, characterized in that: The distance between the staggered scanning of the light spots of two adjacent laser scanning paths is S1, then S1∈ηL~(1-2η)L, The overlap rate η=(LV / f) / L, and η≤33%, L=min(A,C)+2B is the side length of the light spot, V is the laser scanning speed, and f is the laser scanning frequency.

5. The laser film opening method according to claim 4, characterized in that: The overlapping width of the first overlapping area along the longitudinal direction is S2=LV / f, and the overlapping width of the second overlapping area along the transverse direction is S3=2L-[max(A,C)+2B].

6. The laser film opening method according to claim 5, characterized in that: The laser equipment for laser film opening treatment of the first area adopts a pulsed laser with a laser wavelength of 532 nm, a pulse width of 10 ps, ​​a spot side length L of 100-300 μm, a scanning frequency f and a scanning speed V satisfying the relationship of overlap rate η=(LV / f) / L≤33%, a scanning speed V of 10000 mm / s-900000 m / s, and an energy density of 1×10 3 ~9×10 3 J / m 2 .

7. A method for laser film opening on the back of a TBC battery, characterized in that: The following steps are involved: A silicon substrate is provided, having a front side and a back side opposite to each other, wherein a plurality of first regions and a plurality of second regions are alternately arranged on the back side, and a third region is formed between the first regions and the second regions; the first regions include a first passivation layer and a P-type doped layer stacked on the back side of the silicon substrate, and the second regions include a second passivation layer and an N-type doped layer stacked in sequence on the back side of the silicon substrate; When there is no main gate in the first region, the width of the fine gate in the first region is set to A, the width of the third region is set to B, the side length of the square light spot is set to L, and L=A+2B.

8. The laser film opening method according to any one of claims 1 to 3 or 7, characterized in that: The fine gate width A is 300-500 μm, and the third region width B is 50-150 μm.

9. A back contact battery, characterized in that: The film is prepared by the laser film opening method according to any one of claims 1 to 8.

Images