Back contact cell, back contact cell string and photovoltaic module

Abstract

Disclosed in the present invention are a back contact cell, a back contact cell string and a photovoltaic module. The back contact cell comprises: first doped layers, second doped layers and isolation trenches which are disposed on a back surface of a silicon substrate, the first doped layers and the second doped layers being alternately arranged, the isolation trenches being provided between the first doped layers and the second doped layers, and the doping types of the first doped layers and the second doped layers being different; and a passivation layer, the passivation layer being provided on the first doped layers, the second doped layers and the isolation trenches, the passivation layer on the first doped layers and the second doped layers being provided with through holes for depositing electrodes, and sidewalls of the through holes at the first doped layers and / or the second doped layers being provided with a raised-and-recessed structure. Implementing the present invention can increase the lateral contact area between the electrodes and the doped layer regions and thus reduce the resistivity while ensuring the passivation performance of the passivation layer, thereby improving the efficiency of the back contact cell.

Description

Back contact cell, back contact cell string and photovoltaic module

[0001] The present disclosure claims priority to the Chinese patent application No. 202411386466.X, filed on September 30, 2024, and entitled "Back contact cell, back contact cell string and photovoltaic module", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of solar cells, in particular to a back contact cell, a back contact cell string and a photovoltaic module. BACKGROUND

[0003] The positive electrode and the negative electrode of the back contact solar cell are both arranged on the back surface of the cell, and the front surface is not blocked by the metal electrode, so that the entire area can be used for absorbing sunlight, which can minimize the short-circuit current loss caused by the front surface of the cell, and has the advantages of high conversion efficiency, large short-circuit current and high fill factor, which has attracted widespread attention from the academic and industrial circles. The positive and negative electrodes of the back contact solar cell are connected to different doped layer domains through through holes on the passivation layer. The contact area between the electrode and the doped layer domain determines the resistivity of the cell. However, the increase of the contact area will correspondingly lead to the decrease of the passivation performance of the passivation layer, and finally lead to the decrease of the efficiency of the back contact solar cell. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a back contact cell, a back contact cell string and a photovoltaic module, which can increase the contact area between the electrode and the doped layer, reduce the resistivity and improve the efficiency of the back contact cell while ensuring the passivation performance of the passivation layer.

[0005] In order to solve the above problems, the present application discloses a back contact cell, comprising a first doped layer, a second doped layer and a separation groove arranged on the back surface of a silicon substrate, the first doped layer and the second doped layer are arranged alternately, the separation groove is arranged between the first doped layer and the second doped layer, and the first doped layer and the second doped layer have different doping types.

[0006] A passivation layer is arranged on the first doped layer, the second doped layer and the separation groove.

[0007] Through holes for depositing electrodes are arranged on the passivation layer of the first doped layer and the second doped layer, and the side wall of the through hole on the first doped layer and / or the second doped layer has a concave-convex structure.

[0008] As an improvement of the above technical solution, the concave-convex structure comprises a concave part and a convex part arranged in a first direction, and the concave part and the convex part are connected in sequence.

[0009] As an improvement of the above technical solution, the concave-convex structure comprises periodically repeated concave parts and convex parts arranged along the first direction, and the concave parts and convex parts are connected in sequence.

[0010] As an improvement of the above technical solution, the repeating period of the concave parts and convex parts is 2-6.

[0011] As an improvement of the above technical solution, both sides of the through hole are provided with a concave-convex structure.

[0012] Along the second direction, the distance between the concave parts on both sides of the through hole is D1, and the distance between the convex parts on both sides of the through hole is D2, and D1 and D2 satisfy: D1=(1.5-2.5)D2.

[0013] As an improvement of the above technical solution, D1 is 60-120 μm, and D2 is 30-50 μm.

[0014] As an improvement of the above technical solution, the depth of the concave part is H1, and the height of the convex part is H2, and H1 and H2 satisfy: H2=(0.8-1.5)H1.

[0015] As an improvement of the above technical solution, H1 is 2-5 μm, and H2 is 2-5 μm.

[0016] As an improvement of the above technical solution, the shape of the concave part and the convex part is one or more of rectangular, triangular, trapezoidal, and arc.

[0017] As an improvement of the above technical solution, the passivation layer comprises periodically and alternately stacked first passivation layers and second passivation layers; the concave parts are formed on the first passivation layers, and the convex parts are formed on the second passivation layers.

[0018] As an improvement of the above technical solution, the materials of the first passivation layer and the second passivation layer are different.

[0019] As an improvement of the above technical solution, the number of stacking periods of the passivation layer is 1-6.

[0020] As an improvement of the above technical solution, the thickness of the passivation layer is 50-150 μm, and the thickness ratio of the first passivation layer to the second passivation layer is 1:(0.8-1.5).

[0021] As an improvement of the above technical solution, the passivation layer is one or more of intrinsic amorphous silicon layer, intrinsic polycrystalline silicon layer, intrinsic nanocrystalline silicon layer, intrinsic mixed-crystal silicon layer, silicon oxide layer, aluminum oxide layer, silicon oxynitride layer, silicon nitride layer, and silicon oxycarbonitride layer.

[0022] As an improvement of the above technical solution, the passivation layer comprises a silicon nitride layer and a silicon oxide layer stacked in sequence.

[0023] As an improvement of the above technical solution, the first doped layer comprises a first tunneling layer and a first polarity doped layer stacked on the first tunneling layer, and the second doped layer comprises a second tunneling layer and a second polarity doped layer stacked on the second tunneling layer.

[0024] The first tunneling layer and the second tunneling layer are one or more of a silicon oxide layer, an aluminum oxide layer, a titanium oxide layer, a zinc oxide layer, an intrinsic amorphous silicon layer, an intrinsic polycrystalline silicon layer, an intrinsic nanocrystalline silicon layer, and an intrinsic mixed-crystal silicon layer.

[0025] The first polarity doped layer and the second polarity doped layer are one or more of a doped polycrystalline silicon layer, a doped amorphous silicon layer, and a doped microcrystalline silicon layer, and the polarity of the first polarity doped layer is opposite to that of the second polarity doped layer.

[0026] Correspondingly, the application also discloses a back contact cell string comprising the back contact cell.

[0027] Correspondingly, the application also discloses a photovoltaic module comprising the back contact cell string.

[0028] The application has the following beneficial effects: the first doped layer and the second doped layer of the application are provided with through holes for electrode deposition on the passivation layer, the side wall of the through hole on the first doped layer and / or the second doped layer has a concave-convex structure, the concave part increases the lateral area of the electrode, which is conducive to reducing the resistivity, and the convex part can reduce the amount of electrode metal paste while ensuring the passivation performance of the passivation layer, thereby finally improving the efficiency of the back contact cell. BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a structural schematic diagram of a back contact cell provided by an embodiment of the application;

[0030] FIG. 2 is a structural schematic diagram of a back contact cell provided by an embodiment of the application;

[0031] FIG. 3 is a structural schematic diagram of a back contact cell provided by an embodiment of the application;

[0032] FIG. 4 is a size schematic diagram of a passivation layer on the side wall of a through hole of a back contact cell provided by an embodiment of the application;

[0033] FIG. 5 is a structural schematic diagram of a back contact cell after a passivation layer is deposited in the back contact cell provided by an embodiment of the application;

[0034] FIG. 6 is a structural schematic diagram of a back contact cell after a through hole for electrode deposition is formed in the back contact cell provided by an embodiment of the application;

[0035] Figure 7 is a schematic diagram of the structure of the back contact cell provided by the embodiment 2 of the present application after forming the concave-convex structure on the side wall of the through hole;

[0036] Figure 8 is a schematic diagram of the structure of the back contact cell provided by the embodiment 2 of the present application after depositing the electrode. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is described in further detail as follows.

[0038] Referring to Figure 1, the present application provides a back contact cell, which comprises a first doped layer 11, a second doped layer 12 and an isolation groove 13 arranged on the back surface of a semiconductor substrate 1. A plurality of the first doped layer 11 and the second doped layer 12 are arranged alternately, and the isolation groove 13 is arranged between the adjacent first doped layer 11 and second doped layer 12. Specifically, the doping type of the first doped layer 11 can be different from or the same as the doping type of the semiconductor substrate 1. The second doped layer 12 and the first doped layer 11 have different conductive types, so that the back surface side of the back contact cell has the first doped layer 11 and the second doped layer 12 with different conductive types, and the isolation groove 13 is arranged between the first doped layer 11 and the second doped layer 12 with different conductive types. The first doped layer 11 and the second doped layer 12 arranged at intervals can prevent the first doped layer 11 and the second doped layer 12 from contacting and causing short circuit. The first doped layer 11, the second doped layer 12 and the isolation groove 13 are all provided with a passivation layer 2, which is used for chemically passivating the back surface side of the semiconductor substrate 1 and reducing the carrier recombination rate of the back surface side. The passivation layer 2 on the first doped layer 11 and the second doped layer 12 is provided with a through hole 3 for depositing an electrode, and the side wall of the through hole 3 of the first doped layer 11 and / or the second doped layer 12 has a concave-convex structure.

[0039] Compared with the existing regular-shaped through hole, the present application further provides a concave-convex structure 4 on the side wall of the through hole 3 of the first doped layer 11. The concave-convex structure 4 comprises a recessed part 41 and a protruding part 42. The recessed part 41 increases the lateral contact area of the electrode and the doped layer, which is beneficial to reducing the resistivity and ultimately improving the efficiency of the back contact cell. The setting of the protruding part 42 can reduce the overall amount of electrode paste and save costs.

[0040] Specifically, the first via hole for depositing the first electrode 51 is formed on the passivation layer 2 of the first doped layer 11, and the side wall of the first via hole has the concave-convex structure 4. It can be understood that the first doped layer 11 can be an emitter or a back surface field, preferably an emitter. For example, the semiconductor substrate 1 is an N-type silicon substrate, the first doped layer 11 is a P-type doped layer, collects holes and transmits them to the first electrode 51, the side wall of the first via hole for depositing the first electrode 51 is set as a non-flat surface with the concave-convex structure, which increases the lateral area of the first electrode 51, reduces the resistivity, and more holes can be transmitted to the first electrode 51. The concave-convex structure 4 includes concave portions 41 and convex portions 42 arranged along a first direction, and the concave portions 41 and the convex portions 42 are connected in sequence. Along a second direction, the distance between the concave portion 41 on one side wall of the first via hole and the other side wall is 60 μm to 120 μm, for example, 70 μm, 80 μm, 90 μm, 100 μm or 110 μm, but not limited to this, and the distance between the convex portion 42 on one side wall of the first via hole and the other side wall is 30 μm to 50 μm, for example, 32 μm, 35 μm, 38 μm, 42 μm or 48 μm, but not limited to this. Preferably, the ratio between the two satisfies 1.5 to 2.5. It can be understood that the distance between the concave portion 41 on one side wall and the other side wall, and the distance between the convex portion 42 on one side wall and the other side wall are the minimum distances between the concave portion 41 or the convex portion 42 and the other side wall.

[0041] In a preferred embodiment, the concave-convex structure 4 includes periodically repeated concave portions 41 and convex portions 42 arranged along a first direction, and the concave portions 41 and the convex portions 42 are connected in sequence, and the repetition period of the concave portions 41 and the convex portions 42 is 2 to 6, for example, 3, 4, 5. The periodically repeated concave-convex structure 4 can further increase the surface area of the passivation layer 2, thereby improving the passivation effect. If the repetition period of the concave portions 41 and the convex portions 42 is greater than 6, it will increase the complexity of the preparation process, and also cause the thickness of the passivation layer 2 to be too large, thereby increasing the overall thickness of the battery. The first direction can be perpendicular to the front surface and / or the back surface of the solar cell, and the second direction can be parallel to the direction in which the first doped layer 11 and the second doped layer 12 are arranged alternately, and the two are perpendicular to each other.

[0042] In a preferred embodiment, the two side walls of the first through hole are provided with the concave-convex structure 4, further increasing the lateral area of the first electrode 11. As shown in FIG. 2 and FIG. 4, along the second direction, the distance between the concave portions 41 on the two side walls of the first through hole is D1, and the distance between the convex portions 42 on the two side walls of the first through hole is D2, and D1 and D2 satisfy: D1 = (1.5-2.5)D2. It can be understood that the distance D1 between the concave portions 41 on the two side walls of the through hole and the distance D2 between the convex portions 42 on the two side walls of the through hole are both the minimum distance between two concave portions 41 or two convex portions 42 on the two side walls. If the ratio of D1 and D2 is less than 1.5, the concave-convex amplitude of the concave-convex structure 4 formed by the concave portions 41 and the convex portions 42 is not large, and the performance improvement compared with the flat surface of the passivation layer 2 structure is not large; if the ratio of D2 and D1 is greater than 2.5, the concave-convex amplitude of the concave-convex structure 4 formed by the concave portions 41 and the convex portions 42 is too large, increasing the complexity of the preparation process. Specifically, the D1 is 60-120 μm, and is exemplarily 70 μm, 80 μm, 90 μm, 100 μm or 110 μm, but is not limited thereto. The D2 is 30-50 μm, and is exemplarily 32 μm, 35 μm, 38 μm, 42 μm or 48 μm, but is not limited thereto. If D1 is too large, the width of the first through hole needs to be increased accordingly, which increases the consumption of electrode metal and also increases the contact recombination loss between the electrode and the doped layer.

[0043] In a preferred embodiment, along the first direction, the height of the concave portion 41 is H1, and the depth of the convex portion 42 is H2, and H1 and H2 satisfy: H2 = (0.8-1.5)H1. The ratio between the height H1 of the concave portion 41 and the depth H2 of the convex portion 42 is too large or too small, which is not conducive to the improvement of the passivation performance of the passivation layer 2. More preferably, the height H1 of the concave portion 41 and the depth H2 of the convex portion 42 are the same. Specifically, the H1 is 2-5 μm, and is exemplarily 2.5 μm, 3 μm, 3.5 μm, 4 μm or 4.5 μm, but is not limited thereto. The H2 is 2-5 μm, and is exemplarily 2.5 μm, 3 μm, 3.5 μm, 4 μm or 4.5 μm, but is not limited thereto.

[0044] It can be understood that the shapes of the recessed portions 41 and the protruding portions 42 can be the same or different, and specifically, the shapes of the recessed portions 41 and the protruding portions 42 can be one or more of a rectangle, a triangle, a trapezoid, and an arc, but are not limited thereto. Preferably, the shapes of the recessed portions 41 and the protruding portions 42 are arcs, the edges of the passivation layer 2 formed by the recessed portions 41 and the protruding portions 42 form a wavy structure, the wavy structure has a lower requirement for process precision, and is conducive to reducing process difficulty. It should be noted that in actual production, the structural sizes of the recessed portions in different periods and the protruding portions in different periods are difficult to be completely consistent, but overall, the size deviation can be controlled within 5%.

[0045] In a preferred embodiment, as shown in FIG. 3, the passivation layer 2 of the second doped layer 12 is provided with a second through hole for depositing a second electrode 52, the sidewall of the second through hole has a concave-convex structure 4, the concave-convex structure 4 includes recessed portions 41 and protruding portions 42 arranged along a first direction, and the recessed portions 41 and the protruding portions 42 are sequentially connected. The sidewall of the electrode through hole on the second doped layer 12 is also provided with a concave-convex structure, which can increase the lateral area of the second electrode 52, improve the carrier collection efficiency, and further improve the conversion efficiency of the battery. Optionally, the concave-convex structure 4 of the first through hole can be the same as or different from the concave-convex structure 4 of the second through hole, and preferably, the concave-convex structures 4 on the first through hole and the second through hole are the same, which can simplify the preparation process and improve the preparation efficiency.

[0046] It can be understood that the first doped layer 11 and the second doped layer 12 are arranged on the semiconductor substrate 1. Optionally, the semiconductor substrate is an N-type silicon substrate, the first doped layer 11 is an N-type doped layer, and the second doped layer 12 is a P-type doped layer, or the semiconductor substrate is an N-type silicon substrate, the first doped layer 11 is a P-type doped layer, and the second doped layer 12 is an N-type doped layer, which is not specifically limited herein. Optionally, the first doped layer 11 can be located in the semiconductor substrate 1 or on a part of the back surface of the semiconductor substrate 1, and the second doped layer 12 can be located in the semiconductor substrate 1 or on a part of the back surface of the semiconductor substrate 1. The first doped layer 11 and the second doped layer 12 can be rectangular strip regions, wavy strip regions, or the like, which are matched with the electrode structure topography printed thereon, which is not specifically limited herein. In addition, for the first doped layer 11 and the second doped layer 12, the range of the first doped layer 11 and the second doped layer 12 affects the junction area range of the PN junction in the back contact battery, and further affects the strength of the built-in electric field in the back contact battery, so the area ratio between the first doped layer 11 and the second doped layer 12 can be determined according to the requirement for the junction area range of the PN junction in the actual application scenario, which is not specifically limited herein.

[0047] Specifically, the material of the semiconductor substrate 1 can be a semiconductor material such as silicon, silicon-germanium, germanium or gallium arsenide. When the first doped layer 11 is formed on a part of the back surface of the semiconductor substrate 1, the first doped layer 11 comprises a first doped semiconductor layer 111, and the material of the first doped semiconductor layer 111 can be a semiconductor material such as silicon, silicon-germanium, germanium or gallium arsenide; the crystal orientation of the first doped semiconductor layer 111 can be amorphous, nanocrystalline, microcrystalline, single crystal or polycrystalline, etc. When the second doped layer 12 is formed on a part of the back surface of the semiconductor substrate 1, the second doped layer 12 comprises a second doped semiconductor layer 122, and the material of the second doped semiconductor layer 122 can be a semiconductor material such as silicon, silicon-germanium, germanium or gallium arsenide; the crystal orientation of the second doped semiconductor layer 122 can be amorphous, nanocrystalline, microcrystalline, single crystal or polycrystalline, etc. The materials of the first doped semiconductor layer 111 and the second doped semiconductor layer 122 can be the same or different, which is not specifically limited herein.

[0048] In a preferred embodiment, a first tunneling layer 111 is formed between the first doped semiconductor layer 111 and the semiconductor substrate 1, and / or a second tunneling layer 121 is formed between the second doped semiconductor layer 122 and the semiconductor substrate 1. The material of the first tunneling layer 111 and / or the second tunneling layer 121 can be silicon oxide, aluminum oxide, titanium oxide, etc.

[0049] In addition to the above structure, the back contact cell further comprises a first electrode 51 and a second electrode 52, the first electrode 51 is arranged at least in the first through hole on the first doped layer 11, and the first electrode 51 is electrically connected with the first doped layer 11; the second electrode 52 is arranged at least in the second through hole on the second doped layer 12, and the second electrode 52 is electrically connected with the second doped layer 12. The first electrode 51 and the second electrode 52 are fine grids (secondary grids) of the solar cell, which are used to collect and aggregate the current of the solar cell. The first electrode 51 and the second electrode 52 can be sintered from a burn-through type paste or a non-burn-through type paste. The material of the first electrode 51 and the second electrode 52 can be one or more of aluminum, silver, gold, nickel, molybdenum or copper.

[0050] In order to form the concave-convex structure 4 of the passivation layer 2, the passivation layer 2 comprises a first passivation layer 21 and a second passivation layer 22 which are stacked in sequence, wherein the materials of the first passivation layer 21 and the second passivation layer 22 are different, specifically, the etching rates of the first passivation layer 21 and the second passivation layer 22 under the same etching condition are different, the passivation layer structure is formed by alternately using the materials with different etching rates, and the first passivation layer and the second passivation layer are selectively etched under the same etching condition to form different etching surfaces, and finally the passivation layer 2 with the concave-convex structure is obtained. Specifically, the thickness of the passivation layer 2 is 5 μm to 50 μm, and is exemplarily 10 μm, 15 μm, 20 μm, 30 μm or 40 μm, but is not limited thereto. If the thickness of the passivation layer 2 is less than 5 μm, sufficient passivation effect cannot be provided, a higher surface recombination rate is caused, the open circuit voltage is affected, and the passivation layer 2 is easily damaged in subsequent preparation processes, thereby affecting the stability and reliability. If the thickness of the passivation layer 2 is greater than 50 μm, unnecessary parasitic absorption is caused, the short-circuit current density of the battery is reduced, the series resistance of the battery is increased, and the fill factor of the battery is affected. In a preferred embodiment, the thickness ratio of the first passivation layer 21 to the second passivation layer 22 is 1:(0.8-1.5), and is exemplarily 1:0.9, 1:1, 1:1.2, 1:1.3 or 1:1.4, but is not limited thereto. Specifically, the first passivation layer 21 is formed with a recess, which can be referred to as a passivation recess 211, and the second passivation layer 22 is formed with a protrusion, which can be referred to as a passivation protrusion 221. In a preferred embodiment, the passivation layer 2 comprises the first passivation layer 21 and the second passivation layer 22 which are periodically and alternately stacked, and the number of stacking periods of the first passivation layer 21 and the second passivation layer 22 is 1-6, and is exemplarily 2, 3, 4 or 5. In addition, different passivation layer materials can be used to form the first passivation layer, the second passivation layer, the third passivation layer and the like, and the concave-convex structure is formed by selectively etching the passivation layer materials.

[0051] Optionally, the passivation layer 2 is one or more of intrinsic amorphous silicon layer, intrinsic polycrystalline silicon layer, intrinsic nanocrystalline silicon layer, intrinsic mixed-crystal silicon layer, silicon oxide layer, aluminum oxide layer, silicon oxynitride layer, silicon nitride layer, silicon oxycarbonitride layer. Regarding the formation of the passivation layer 2, the aluminum oxide layer can be prepared by chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma-assisted ALD, molecular beam epitaxy, etc., which are not specifically limited herein; the silicon nitride layer, silicon oxide layer, silicon oxynitride layer, etc. can be prepared by chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), magnetron sputtering technology, etc., which are not specifically limited herein. The silicon nitride and aluminum oxide will generate a large amount of hydrogen during thin film deposition, which can form good hydrogen passivation. In a preferred embodiment, the passivation layer 2 comprises a silicon nitride layer and a silicon oxide layer stacked in sequence.

[0052] Specifically, the method for forming the passivation layer 2 comprises the following steps:

[0053] S1. Forming a first passivation layer and a second passivation layer stacked in sequence on the first doped layer and the second doped layer, as shown in FIG. 5;

[0054] In a preferred embodiment, a periodic first passivation layer and a second passivation layer are formed on the first doped layer and the second doped layer of the back contact cell, and the stacking period is 2-6;

[0055] S2. Forming a through hole penetrating the passivation layer of the first doped layer, as shown in FIG. 6, specifically, the through hole can be formed by laser;

[0056] S3. Selectively etching the side wall of the through hole to obtain a concave-convex structure, as shown in FIG. 7;

[0057] In a preferred embodiment, the method further comprises:

[0058] S4. Forming a through hole penetrating the passivation layer of the second doped layer;

[0059] S5. Selectively etching the side wall of the through hole to obtain a concave-convex structure.

[0060] The specific selective etching method can be dry etching or wet etching. In one embodiment, the first and second passivation layers are selectively etched by remote plasma dry etching. For example, when the first passivation layer is a silicon nitride layer and the second passivation layer is a silicon oxide layer, the etching rate ratio of the silicon nitride layer to the silicon oxide layer is greater than 30:1, and the silicon oxide layer or the silicon substrate is not etched during the etching of the silicon nitride layer. Specifically, the dry etching gas is O2 and N2, the flow rate of O2 is 700-900 sccm, the flow rate of N2 is 100-120 sccm, preferably, the flow rate of O2 is 800 sccm, and the flow rate of N2 is 110 sccm; the etching gas for the silicon nitride is NF3, and the flow rate is 30-50 sccm, preferably, the flow rate of NF3 is 40 sccm.

[0061] In one embodiment, the first and second passivation layers are selectively etched by wet etching. For example, when the first passivation layer is a silicon nitride layer and the second passivation layer is a silicon oxide layer, the selective etching is performed by using an HF solution diluted by NH4F, and the etching rate of the HF solution on SiO2 and SiNx:H is different. The etching of the HF solution on SiO2 is based on the action of HF 2- on SiOH 2+ , and the etching of the HF solution on SiNx:H is based on the action of F- on SiNH 3+ . By properly adjusting the pH value of the solution, the relative content of HF 2- and F - is changed, the etching rate of SiO2 is ensured, the etching of HF on SiNx:H is reduced, and the selectivity of etching SiO2 / SiNx:H is improved. Preferably, the pH value of the etching solution is 4-7, and better SiO2 / SiNx:H selectivity can be obtained, more preferably, the pH value of the etching solution is 5.

[0062] S6, as shown in FIG. 8, at least depositing metal in the through hole to form an electrode; specifically, the metal can be deposited by physical vapor deposition, thermal evaporation, magnetron sputtering, etc.

[0063] It can be understood that the structure of the passivation layer on the isolation groove 13 can be the same as or different from the structure of the passivation layer on the first doped layer 11 and / or the second doped layer 12, and is selected according to specific conditions.

[0064] Correspondingly, the embodiment of the present application also provides a solar cell string comprising the above solar cell, each solar cell string comprises a plurality of solar cells connected in series, the plurality of solar cells can be arranged in partial overlap to form the solar cell string, the contact area between the overlap is not electrically connected, that is, the overlap area does not need to be provided with conductive glue or other adhesive glue, and the solar cells are only overlapped together. Optionally, the solar cell can be a whole back contact cell or a split back contact cell (such as a half split back contact cell or a third split back contact cell, etc.). The whole back contact cell can be a whole cell without splitting; or the whole back contact cell can also comprise at least two slice units with a symmetrical electrode design; or the whole back contact cell can also comprise at least two slice units with an asymmetrical electrode design. The overlap area of adjacent solar cells in the solar cell string is provided with a series welding strip to fixedly connect the adjacent solar cells, and the series welding strip connects the adjacent solar cells in series. Different solar cell strings are connected in series and / or parallel.

[0065] Correspondingly, the embodiment of the present application also provides a battery assembly comprising the above solar cell string. The battery assembly can also comprise a metal frame, a back plate, photovoltaic glass and a glue film. The glue film can be filled between the front and back of the solar cell string, the photovoltaic glass, the back plate and the like, and the glue film can be selected from transparent glue with good light transmittance and aging resistance, such as EVA glue film or POE glue film, which can be selected according to actual conditions and is not specifically limited here.

[0066] The photovoltaic glass can cover the front of the solar cell string, and the photovoltaic glass can be super white glass, which has high light transmittance, high transparency, and superior physical, mechanical and optical properties. For example, the light transmittance of super white glass can reach more than 92%, which can protect the solar cell string as much as possible without affecting the efficiency of the solar cell string. At the same time, the glue film can bond the photovoltaic glass and the solar cell string together, and the presence of the glue film can seal and insulate the solar cell string to achieve waterproof and moisture-proof.

[0067] The back plate can be attached to the back of the solar cell string, and the back plate can protect and support the solar cell string, and the back plate has reliable insulation, water resistance and aging resistance. The back plate can be tempered glass, organic glass, aluminum alloy TPT composite glue film, etc., which can be selected according to actual conditions and is not specifically limited here. The whole composed of the back plate, the solar cell string, the glue film and the photovoltaic glass can be arranged on the metal frame, and the metal frame serves as the main external support structure of the whole battery assembly, providing stable support and installation for the battery assembly.

[0068] The present application will be further described in the following specific embodiments:

[0069] Embodiment 1

[0070] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through hole of the P-type doped layer are all provided with concave-convex structures.

[0071] The concave-convex structure comprises concave parts and convex parts arranged in the direction perpendicular to the back surface of the solar cell, the distance between the concave part on one side wall of the through hole and the other side wall is 100 μm, the distance between the convex part on one side wall of the through hole and the other side wall is 30 μm, the depth of the concave part is 2 μm, and the height of the convex part is 5 μm.

[0072] Embodiment 2

[0073] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through hole of the P-type doped layer are all provided with concave-convex structures.

[0074] The concave-convex structure comprises concave parts and convex parts arranged in the direction perpendicular to the back surface of the solar cell, the distance between the concave part on one side wall of the through hole and the other side wall is 100 μm, the distance between the convex part on one side wall of the through hole and the other side wall is 30 μm, the depth of the concave part is 2 μm, and the height of the convex part is 5 μm.

[0075] Embodiment 3

[0076] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through hole of the P-type doped layer are all provided with concave-convex structures.

[0077] The concave-convex structure comprises concave parts and convex parts arranged in the direction perpendicular to the back surface of the solar cell, the distance between the concave part on one side wall of the through hole and the other side wall is 100 μm, the distance between the convex part on one side wall of the through hole and the other side wall is 30 μm, the depth of the concave part is 2 μm, and the height of the convex part is 5 μm.

[0078] Embodiment 4

[0079] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, and the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through holes of the P-type doped layers have a concave-convex structure.

[0080] The concave-convex structure comprises periodically repeated concave parts and convex parts arranged in a direction perpendicular to the back surface of the solar cell, the distance between the concave parts on the two side walls of the through hole is 90 μm, the distance between the convex parts on the two side walls of the through hole is 40 μm, the depth of the concave part is 5 μm, and the height of the convex part is 2 μm.

[0081] Embodiment 5

[0082] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, and the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through holes of the P-type doped layers have a concave-convex structure.

[0083] The concave-convex structure comprises periodically repeated concave parts and convex parts arranged in a direction perpendicular to the back surface of the solar cell, the distance between the concave parts on the two side walls of the through hole is 90 μm, the distance between the convex parts on the two side walls of the through hole is 40 μm, the depth of the concave part is 4 μm, and the height of the convex part is 4 μm.

[0084] Embodiment 6

[0085] The embodiment provides a back contact cell, which comprises N-type doped layers, P-type doped layers and isolation grooves arranged on the back surface of an N-type silicon substrate, the N-type doped layers and the P-type doped layers are arranged alternately, and the isolation grooves are arranged between the N-type doped layers and the P-type doped layers. The N-type doped layers, the P-type doped layers and the isolation grooves are all provided with passivation layers, and the passivation layers of the P-type doped layers and the N-type doped layers are provided with through holes for depositing electrodes, and the two side walls of the through holes of the P-type doped layers and the N-type doped layers have a concave-convex structure.

[0086] The concave-convex structure comprises periodically repeated concave parts and convex parts arranged in a direction perpendicular to the back surface of the solar cell, the distance between the concave parts on the two side walls of the through hole is 90 μm, the distance between the convex parts on the two side walls of the through hole is 40 μm, the depth of the concave part is 4 μm, and the height of the convex part is 4 μm.

[0087] Performance detection:

[0088] The back contact solar cell pieces are obtained after printing electrodes, soldering and annealing of the back contact solar cell pieces prepared in Embodiments 1-5, and the photoelectric performance of the finished solar cell pieces is measured, and the results are shown in the following table.

[0089] The above is the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements are also considered to be within the scope of the present application.

Claims

1. A back contact cell, comprising a first doped layer, a second doped layer and an isolation groove arranged on the back of a silicon substrate, the first doped layer and the second doped layer are arranged alternately, the isolation groove is located between the first doped layer and the second doped layer, the first doped layer and the second doped layer are different in doping type; a passivation layer arranged on the first doped layer, the second doped layer and the isolation groove; a through hole for depositing an electrode is arranged on the passivation layer on the first doped layer and the second doped layer, the side wall of the through hole on the first doped layer and / or the second doped layer has a concave-convex structure.

2. The back contact cell of claim 1, wherein, The concave-convex structure comprises concave parts and convex parts arranged in a first direction, and the concave parts and the convex parts are connected in sequence.

3. The back contact cell of claim 1, wherein, The concave-convex structure comprises periodically repeated concave parts and convex parts arranged in a first direction, and the concave parts and the convex parts are connected in sequence.

4. The back contact cell of claim 3, wherein, The repetition period of the concave parts and the convex parts is 2-6.

5. The back contact cell of claim 2, wherein, Both side walls of the through hole are provided with the concave-convex structure; In a second direction, the distance between the concave parts on the two side walls of the through hole is D1, and the distance between the convex parts on the two side walls of the through hole is D2, and D1 and D2 satisfy: D1=(1.5-2.5)D2.

6. The back contact cell of claim 5, wherein, D1 is 60-120μm, and D2 is 30-50μm.

7. The back contact cell of claim 2, wherein, The depth of the concave part is H1, and the height of the convex part is H2, and H1 and H2 satisfy: H2=(0.8-1.5)H1.

8. The back contact cell of claim 7, wherein, H1 is 2-5μm, and H2 is 2-5μm.

9. The back contact cell of claim 1 wherein, The shape of the concave part and the convex part is one or more of rectangular, triangular, trapezoidal and arc.

10. The back contact cell of claim 1, wherein, The passivation layer comprises periodically and alternately stacked first passivation layers and second passivation layers; The first passivation layer is formed with a concave part, and the second passivation layer is formed with a convex part.

11. The back contact cell of claim 10, wherein, The materials of the first passivation layer and the second passivation layer are different.

12. The back contact cell of claim 10, wherein, The number of stacking periods of the passivation layer is 1-6.

13. The back contact cell of claim 10, wherein, The thickness of the passivation layer is 50-150μm, and the thickness ratio of the first passivation layer to the second passivation layer is 1:(0.8-1.5).

14. The back contact cell of claim 1 wherein, The passivation layer is one or more of intrinsic amorphous silicon layer, intrinsic polycrystalline silicon layer, intrinsic nanocrystalline silicon layer, intrinsic mixed crystal silicon layer, silicon oxide layer, aluminum oxide layer, silicon oxynitride layer, silicon nitride layer and silicon carbon nitride oxide layer.

15. The back contact cell of claim 14, wherein, The passivation layer comprises a silicon nitride layer and a silicon oxide layer stacked in sequence.

16. The back contact cell of claim 1 wherein, The first doped layer comprises a first tunneling layer and a first polarity doped layer stacked on the first tunneling layer, and the second doped layer comprises a second tunneling layer and a second polarity doped layer stacked on the second tunneling layer; The first tunneling layer and the second tunneling layer are one or more of silicon oxide layer, aluminum oxide layer, titanium oxide layer, zinc oxide layer, intrinsic amorphous silicon layer, intrinsic polycrystalline silicon layer, intrinsic nanocrystalline silicon layer and intrinsic mixed crystal silicon layer; The first polarity doped layer and the second polarity doped layer are one or more of doped polycrystalline silicon layer, doped amorphous silicon layer and doped microcrystalline silicon layer, and the polarity of the first polarity doped layer is opposite to that of the second polarity doped layer.

17. A back contact cell string characterized in that, A back contact cell comprising any of claims 1 to 16.

18. A photovoltaic module, characterized by, A string of back contact cells comprising the back contact cell of claim 17.

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