Back contact solar cell and preparation method thereof

Abstract

The invention relates to the technical field of photovoltaic cells, and discloses a back contact solar cell and a preparation method thereof. The preparation method comprises the following steps: providing a substrate layer of a first conductive type having a first surface and a second surface opposite to each other; a first groove is formed in the first surface, and a bulge is formed beside the first groove; performing doping treatment on the inner wall surface of the first groove to form a first doping layer; the first doped layer is of a second conductive type; forming a passivation layer on the surface of the first doping layer; a second groove isolated from the first groove is formed in the protrusion; forming a first tunneling oxide layer on the second groove; forming a second doping layer of the first conduction type in the second groove and on the first tunneling oxide layer; a first electrode and a second electrode are formed, the first electrode penetrates through the passivation layer to be connected with the first doping layer, and the second electrode is connected with the second doping layer. The first groove and the second groove which are relatively isolated are formed by grooving at different positions of the substrate layer, so that efficient current collection is facilitated, short circuit is prevented, and the photoelectric conversion efficiency and the power generation efficiency are improved.

Description

Technical Field

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

[0002] Traditional crystalline silicon photovoltaic cells usually have metal electrodes on the front and back of the cell. However, with this design, the metal electrode on the front of the cell will block some light, thereby reducing the cell's photoelectric conversion efficiency. In addition, the metal electrode on the front will also increase the series resistance of the cell, thereby affecting the cell's fill factor and overall photoelectric conversion performance.

[0003] As a result, the back contact (BC) battery, which has both the PN junction and the metal contact on the back of the battery, came into being. As an innovative solar technology, the back contact battery has no obstruction on the front, which increases the effective power generation area of ​​the battery, thereby improving the photoelectric conversion efficiency of the battery. However, since the positive electrode and the negative electrode of the back contact battery exist on the same side of the battery, carriers such as electrons and holes are easily contacted and recombined during the transmission process, which affects the current output, reduces the photoelectric conversion efficiency of the battery, and reduces the power generation efficiency of the battery. Summary of the invention

[0004] In view of this, the present invention provides a back-contact solar cell and a method for preparing the same, in order to solve the problem that electrons and holes in existing back-contact batteries are easily contacted and recombined during the transmission process, thus affecting the current output, causing the photoelectric conversion efficiency of the battery to decrease, thereby reducing the power generation efficiency of the battery.

[0005] In a first aspect, the present invention provides a method for preparing a back-contact solar cell, comprising:

[0006] Providing a base layer, the base layer having a first surface and a second surface opposite to each other, and the base layer is of a first conductivity type;

[0007] A first groove is formed on the first surface of the base layer, and a protrusion is formed beside the first groove;

[0008] Doping the inner wall surface of the first groove to form a first doped layer; the first doped layer is a second conductive type opposite to the first conductive type;

[0009] forming a passivation layer on a surface of the first doped layer facing away from the substrate layer;

[0010] A second groove is formed on the protrusion, and the second groove is isolated from the first groove;

[0011] forming a first tunneling oxide layer on an inner wall surface of the second groove;

[0012] forming a second doped layer in the second groove and on a side of the first tunnel oxide layer facing away from the base layer, wherein the second doped layer is of the first conductivity type;

[0013] A first electrode and a second electrode are formed, wherein the first electrode penetrates the passivation layer to connect to the first doped layer, and the second electrode connects to the second doped layer.

[0014] Beneficial effects: The present invention precisely grooves the base layer to form a special structure on the base layer itself: by grooves at different positions on the base layer, relatively isolated first and second grooves are formed, the first groove is provided with a first doping layer and a passivation layer, the second groove is provided with a first tunneling oxide layer and a second doping layer, the first doping layer and the second doping layer have opposite conductivity types, this structural design is conducive to the effective collection of current, and the protrusions can effectively prevent the short circuit between the positive and negative electrodes, carriers of different conductivity types can be accurately and efficiently diverted to flow to doping layers of different conductivity types, and then efficiently extracted through electrodes, reducing carrier contact recombination, and improving the photoelectric conversion efficiency and power generation efficiency of the battery.

[0015] In an optional embodiment, the first groove is formed on the first surface of the base layer, including: using laser grooving to form a plurality of first grooves at intervals on one side of the first surface of the base layer, and forming a protrusion between any adjacent first grooves.

[0016] Beneficial effect: Through laser-assisted precision grooving, multiple first grooves and corresponding multiple protrusions are precisely formed on the lower surface of the substrate layer, which facilitates the precise formation of the first doping layer and the passivation layer in the recessed first grooves, improves the forming quality of the first doping layer and the passivation layer, and thus improves the battery performance.

[0017] In an optional implementation, the inner wall surface of the first groove is doped to form a first doping layer, including:

[0018] Performing boron diffusion treatment on one side of the first surface of the substrate layer to form an initial first doping layer, wherein the initial first doping layer completely covers one side of the first surface of the substrate layer;

[0019] The initial first doping layer on the protrusion is removed to form a first doping layer covering the inner wall surface of the first groove.

[0020] Beneficial effect: By forming a continuous initial first doping layer on the entire side of the first surface of the substrate layer, and then grinding the initial first doping layer on the raised area, a relatively isolated first doping layer is formed in a plurality of first grooves. The plurality of first doping layers formed are uniform and consistent, and the preparation is efficient and quick, thereby improving the processing efficiency while improving the battery conversion efficiency.

[0021] In an optional embodiment, after performing boron diffusion treatment on one side of the first surface of the base layer to form an initial first doping layer and before removing the initial first doping layer located on the protrusion, it also includes: forming an initial passivation layer on a surface of the initial first doping layer facing away from the base layer, wherein the initial passivation layer conformally covers the initial first doping layer;

[0022] Removing the first doped layer on the protrusion also includes: simultaneously removing the initial passivation layer on the protrusion to form a passivation layer located in the first groove and on a side of the first doped layer away from the base layer.

[0023] Beneficial effect: After the initial first doping layer is formed on the entire surface, the initial passivation layer is formed by thermal oxidation on the initial first doping layer to conformally cover the initial first doping layer; similarly, the formation of the initial passivation layer on the entire surface also helps to form a uniform passivation layer in multiple first grooves. Afterwards, the initial passivation layer and the initial first doping layer on the protrusion are removed at one time by grinding, and the initial passivation layer and the initial first doping layer in the first groove are retained, thereby forming relatively isolated passivation layers and first doping layers in different first grooves. The passivation layer and the first doping layer have excellent structural performance, and the one-time molding is simple and efficient, which helps to improve the photovoltaic conversion efficiency and processing efficiency of the battery.

[0024] In an optional implementation, forming a first tunneling oxide layer on the inner wall surface of the second groove includes:

[0025] Depositing an initial tunneling oxide layer on one side of the first surface of the base layer, wherein the initial tunneling oxide layer completely covers one side of the first surface of the base layer;

[0026] The initial tunnel oxide layer on the protruding surface is removed to form a first tunnel oxide layer in the second groove and a second tunnel oxide layer in the first groove.

[0027] Beneficial effect: After forming a continuous initial tunneling oxide layer on the entire side of the first surface of the base layer, and then polishing the initial tunneling oxide layer on the raised area, a relatively isolated tunneling oxide layer structure is achieved between the first groove and the second groove, and between multiple second grooves. The multiple tunneling oxide layer structures formed are uniform and consistent, and the preparation is efficient and quick. They can also play an isolation role to prevent unnecessary recombination, thereby improving the processing efficiency while improving the battery conversion efficiency.

[0028] In an optional embodiment, after depositing and forming an initial tunneling oxide layer on one side of the first surface of the base layer and before removing the initial tunneling oxide layer on the protruding surface, the method further includes: forming an initial second doping material layer on one side of the first surface of the base layer, wherein the initial second doping material layer completely covers the initial tunneling oxide layer; performing phosphorus diffusion treatment on the initial second doping material layer; and performing annealing treatment on the initial second doping material layer after the phosphorus diffusion treatment to form an initial second doping layer;

[0029] Removing the initial tunneling oxide layer on the protruding surface also includes: simultaneously removing the initial second doping layer on the protruding surface to flatten the side of the first surface of the base layer to form a second doping layer in the second groove and a third doping layer in the first groove.

[0030] Beneficial effect: After the initial tunneling oxide layer is formed on the entire surface, the initial second doping material is deposited on the initial tunneling oxide layer on the entire surface, and then the initial second doping material is diffused with phosphorus to form an initial second doping material layer, and finally the initial second doping layer is formed by annealing. At this time, the initial second doping layer fills and smoothes the concave areas in the first groove and the second groove, and other areas form convex parts; similarly, forming the initial second doping layer on the entire surface also helps to form a uniform and consistent second doping layer in multiple second grooves.

[0031] In addition, the protruding initial tunneling oxide layer and the initial second doping layer are removed at one time by grinding, and the initial tunneling oxide layer and the initial second doping layer in the first groove and the second groove are retained, thereby forming the first tunneling oxide layer and the second doping layer relatively isolated in different second grooves, and the second tunneling oxide layer and the third doping layer relatively isolated in different first grooves. The above-mentioned structural layer has excellent performance, and the one-time molding is simple and efficient, which helps to reduce the mutual influence between different conductive types, thereby improving the photoelectric conversion efficiency and processing efficiency of the battery, and finally re-forms a flat plane on the second surface side of the substrate layer, which is helpful for subsequent process processing.

[0032] In an optional embodiment, in the second groove, after forming the second doping layer on the side of the first tunneling oxide layer away from the base layer, and before forming the first electrode and the second electrode, the method further includes:

[0033] A first anti-reflection layer is formed on the first surface side of the base layer, and a second anti-reflection layer is formed on the second surface side of the base layer.

[0034] Beneficial effect: A first anti-reflection layer is formed on one side of the first surface, the first anti-reflection layer encapsulates the structures in the first groove and the second groove respectively, and a second anti-reflection layer is formed on one side of the second surface. The anti-reflection layer helps to reduce the reflection of photons after reaching the battery surface, thereby improving the absorption efficiency of photons and ultimately improving the power generation efficiency of the battery.

[0035] In an optional embodiment, after forming a first anti-reflection layer on one side of the first surface of the substrate layer and forming a second anti-reflection layer on one side of the second surface of the substrate layer, and before forming the first electrode and the second electrode, the method further includes:

[0036] Etching the first groove and the second groove to form a first channel penetrating the third doping layer, the second tunneling oxide layer and the passivation layer until penetrating a portion of the first doping layer, and a second channel penetrating a portion of the second doping layer;

[0037] A metal contact layer is formed on the inner wall surface of the first channel and the inner wall surface of the second channel, and the metal contact layer is suitable for being fixedly connected to the electrode structure.

[0038] Beneficial effect: By setting a metal contact layer in the channel, it helps to improve the electrical connection performance of the inner wall of the channel and reduce the contact resistance, thereby ensuring that the current can be effectively transmitted from the active layer inside the battery (such as the PN junction) to the external circuit, facilitating subsequent connection and fixation with the electrode structure.

[0039] In the second aspect, the present invention also provides a back-contact solar cell, which is prepared by the above-mentioned back-contact battery preparation method, including: a substrate layer, a first groove, a first doped layer, a passivation layer, a second groove, a first tunneling oxide layer, a second doped layer, a first electrode and a second electrode, the substrate layer includes a first surface and a second surface relative to each other, and the substrate layer is of a first conductive type; the first groove is formed on one side of the first surface of the substrate layer, and correspondingly, a protrusion is formed on the side of the first groove; the first doped layer is formed in the first groove, and the first doped layer is of a second conductive type opposite to the first conductive type; the passivation layer is arranged on a side surface of the first doped layer away from the substrate layer; the second groove is formed on the protrusion, and the second groove is isolated from the first groove; the first tunneling oxide layer is arranged on the inner wall surface of the second groove; the second doped layer is formed in the second groove and is located on the side of the first tunneling oxide layer away from the substrate layer, and the second doped layer is of the first conductive type; the first electrode passes through the passivation layer and is connected to the first doped layer, and the second electrode is connected to the second doped layer.

[0040] Beneficial effects: The base layer itself forms a special structure: a plurality of first grooves and protrusions are opened on the back side of the base layer, which is conducive to the effective collection of current, and the protrusions can effectively prevent the short circuit between the positive and negative electrodes. Carriers of different conductivity types can be accurately and efficiently diverted to flow to doping layers of different conductivity types, and then efficiently exported through electrodes, reducing carrier contact and recombination, and improving the photoelectric conversion efficiency and power generation efficiency of the battery; the use of laser grooving technology can accurately groove the lower end of the N-type silicon wafer, which helps to achieve highly precise structural control. The laser can also be used in subsequent secondary grooving to form a second groove. The second groove is not connected to the first groove to ensure the independence of each battery cell.

[0041] In an optional embodiment, it also includes: a second tunneling oxide layer, a third doping layer, a first anti-reflection layer and a second anti-reflection layer, the second tunneling oxide layer is formed in the first groove and conformally covers the passivation layer; the third doping layer is formed in the first groove and contacts the second tunneling oxide layer; the first anti-reflection layer is formed on one side of the first surface of the substrate layer; the second anti-reflection layer is formed on one side of the second surface of the substrate layer.

[0042] Beneficial effects: The second tunneling oxide layer and the third doping layer at the first groove can reduce surface carrier recombination and improve the battery conversion efficiency. At the same time, it can also make the first surface side of the substrate layer become a flat plane again, which is convenient for the preparation of subsequent structural layers and improves the stability and reliability of the battery. The first anti-reflection layer and the second anti-reflection layer help reduce the reflection of photons after reaching the battery surface, thereby improving the absorption efficiency of photons and ultimately improving the power generation efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related technologies, the drawings required for use in the specific embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 is a schematic flow chart of a method for preparing a back-contact solar cell according to an embodiment of the present invention;

[0045] Figure 2 is a schematic structural diagram of a base layer according to an embodiment of the present invention;

[0046] Figure 3 is a schematic structural diagram of an embodiment of the present invention after a first groove is formed on the first surface of the base layer;

[0047] Figure 4 is a schematic structural diagram of an embodiment of the present invention in which an initial first doping layer is arranged on a substrate layer;

[0048] Figure 5 is a schematic structural diagram of an initial passivation layer provided on an initial first doping layer according to an embodiment of the present invention;

[0049] Figure 6 It is a schematic structural diagram of forming a first doping layer and a passivation layer after polishing an initial first doping layer and an initial passivation layer according to an embodiment of the present invention;

[0050] Figure 7 is a schematic structural diagram of an embodiment of the present invention after a second groove is formed on the protrusion of the base layer;

[0051] Figure 8 is a schematic structural diagram of an embodiment of the present invention after an initial tunneling oxide layer is provided on a base layer;

[0052] Fig. 9 is a schematic structural diagram of an embodiment of the present invention after an initial second doping layer is provided on the tunneling oxide layer;

[0053] Fig.10 is a schematic diagram of the structure after polishing the initial tunneling oxide layer and the initial second doping layer in an embodiment of the present invention;

[0054] Fig.11 is a schematic diagram of the structure after the first anti-reflection layer and the second anti-reflection layer are provided in an embodiment of the present invention;

[0055] Fig.12 is a schematic diagram of the structure after the first channel and the second channel are opened in an embodiment of the present invention;

[0056] Fig.13 It is a schematic structural diagram of a back-contact solar cell formed after disposing a first electrode and a second electrode according to an embodiment of the present invention.

[0057] Description of reference numerals:

[0058] 1. base layer; 101. first surface; 102. second surface; 2. first groove; 3. protrusion; 400. initial first doping layer; 4. first doping layer; 500. initial passivation layer; 5. passivation layer; 6. second groove; 700. initial tunneling oxide layer; 7a. first tunneling oxide layer; 7b. second tunneling oxide layer; 800. initial second doping layer; 8. second doping layer; 9. first electrode; 10. second electrode; 11. third doping layer; 12. first anti-reflection layer; 13. second anti-reflection layer; 14. first channel; 15. second channel. DETAILED DESCRIPTION

[0059] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only some structures related to the present invention are shown in the accompanying drawings, rather than all structures. In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. In addition, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0060] In the related art, the back contact battery sets the PN junction and the metal contact on the back of the battery, and the front is unobstructed, so the effective power generation area of ​​the battery is increased, and the photoelectric conversion efficiency of the battery is improved. However, since the positive electrode and the negative electrode exist on the same side of the battery, the carriers such as electrons and holes are easily at risk of contact recombination when they are transmitted in the PN junction. At present, in order to solve this problem, the P region and the N region are usually physically isolated in the process of forming them on the back of the battery, that is, when the mask partitions to form the P region and the N region, a gap is controlled to be formed between the two. However, if the gap is too large, it is easy to affect the actual carrier transmission area and reduce the power generation efficiency. If the gap is too small, it is difficult to form and has high process requirements, and it is easy to be incompletely isolated, which affects the carrier transportation, and affects the photoelectric conversion efficiency and power generation efficiency of the battery.

[0061] refer to Figures 1 to 13 This embodiment provides a method for preparing a back-contact solar cell. Figure 1 is a flow chart of a method for preparing a back contact solar cell according to an embodiment of the present invention, Figure 1 As shown, the process includes the following steps:

[0062] Step S101 , providing a base layer 1 , wherein the base layer 1 has a first surface 101 and a second surface 102 opposite to each other, and the base layer 1 is of a first conductivity type.

[0063] The first conductivity type mentioned above can be N-type or P-type, such as Figure 2As shown, in this embodiment, the first conductivity type is N-type for example. The base layer 1 in this embodiment is an N-type silicon wafer, which is obtained by cutting a silicon rod into a plurality of silicon wafers, and then doping the silicon wafers with pentavalent elements such as phosphorus and arsenic to form an N-type silicon wafer, so as to obtain the base layer 1. Exemplarily, in this embodiment, the first surface 101 of the base layer 1 is the back surface, and the second surface 102 is the front surface.

[0064] Step S102 , a first groove 2 is formed on the first surface 101 of the base layer 1 , and a protrusion 3 is formed beside the first groove 2 .

[0065] like Figure 2 As shown, a first groove 2 is formed on the back side, i.e., the lower surface, of the base layer 1, and a protrusion 3 is correspondingly formed beside the first groove 2; grooves are directly formed on the base layer 1 body to form different areas of the groove and the protrusion 3, so as to prepare different structural layers in areas of different shapes.

[0066] Step S103 , performing doping treatment on the inner wall surface of the first groove 2 to form a first doped layer 4 ; the first doped layer 4 is of a second conductivity type opposite to the first conductivity type.

[0067] The second conductivity type in this embodiment is P type, that is, a trivalent element is diffused on the entire inner wall surface of the first groove 2 including the bottom surface and the side wall surface to form a P type first doping layer 4, where the P type first doping layer 4 forms a PN junction with the original N type base layer 1, and at this time, the P type region is the first doping layer 4 doped with a large amount of trivalent elements, and the N type region includes a silicon region that is not doped or doped with a small amount of trivalent elements.

[0068] Step S104 , forming a passivation layer 5 on a surface of the first doping layer 4 facing away from the substrate layer 1 .

[0069] Exemplarily, by heating the silicon wafer to between 600°C and 1200°C and exposing it to an oxygen atmosphere, a layer of hot silicon dioxide is formed on the first doped layer 4 on the lower surface of the silicon wafer to serve as a passivation layer 5 to achieve a passivation effect, reduce surface recombination, and improve the overall efficiency of the battery by reducing the surface defect density. In addition, it can also serve as an isolation layer in subsequent processes.

[0070] Step S105 , a second groove 6 is formed on the protrusion 3 , and the second groove 6 and the first groove 2 are isolated from each other.

[0071] like Figure 7 As shown, a second groove 6 is formed by cutting a groove on the protrusion 3. The second groove 6 is not connected to the first groove 2, and the depth of the second groove 6 is set to be slightly smaller than the depth of the first groove 2, so as to distinguish the first groove 2 from the second groove 6, and to accurately prepare structural layers of different conductive types in different groove areas.

[0072] Step S106 , forming a first tunneling oxide layer 7 a on the inner wall surface of the second groove 6 .

[0073] Exemplarily, a first ultra-thin tunneling oxide layer 7a is formed on the inner wall surface of the second groove 6, including the bottom and the side wall surface, by a wet chemical growth method or a thermal oxidation method. Specifically, the first tunneling oxide layer 7a can be silicon dioxide. The first tunneling oxide layer 7a allows electrons to tunnel while preventing holes from penetrating, thereby achieving effective separation of carriers.

[0074] Step S107 , forming a second doped layer 8 in the second groove 6 and on a side of the first tunnel oxide layer 7 a away from the base layer 1 , wherein the second doped layer 8 is of the first conductivity type.

[0075] Exemplarily, a second doping layer 8 is formed on the lower surface of the first tunneling oxide layer 7a by chemical vapor deposition (CVD) technology. The second doping layer 8 is an N+ polysilicon layer. The high doping concentration of the N+ second doping layer 8 helps to provide a sufficiently high energy level so that electrons can tunnel into the second doping layer 8, while holes are blocked by the first tunneling oxide layer 7a and the second doping layer 8; at the same time, the second doping layer 8 with a high doping concentration helps to reduce carrier recombination losses and improve battery conversion efficiency.

[0076] Step S108 , forming a first electrode 9 and a second electrode 10 , wherein the first electrode 9 penetrates the passivation layer 5 to connect to the first doping layer 4 , and the second electrode 10 connects to the second doping layer 8 .

[0077] In this embodiment, the first electrode 9 is fixedly connected to the first doped layer 4 of P-type conductivity in the first groove 2, and the second electrode 10 is fixedly connected to the second doped layer 8 of N-type conductivity in the second groove 6. The first electrode 9 serves as the positive electrode of the back-contact solar cell, and the second electrode 10 serves as the negative electrode of the back-contact solar cell, so that carriers such as holes and electrons are respectively transmitted and exported to the external circuit via the positive electrode and the negative electrode. The first electrode 9 and the second electrode 10 are connected to the doped layer on the battery cell by laser sintering. The use of laser sintering can locally destroy the structural layer in a very precise manner, and promote the electron transmission between the metal and the silicon wafer, ensuring the reliable connection between the negative electrode and the positive electrode and the internal components of the battery, while protecting other parts from damage.

[0078] The preparation method of the back-contact battery of this embodiment is as follows: first, a first groove 2 is opened on the back side of the substrate layer 1, and a first doping layer 4 of the second conductivity type is arranged in the first groove 2, and a passivation layer 5 is arranged to reduce surface recombination; then, a second groove 6 is opened on the protrusion 3 adjacent to the first groove 2, the second groove 6 is not connected to the first groove 2, and a second doping layer 8 of the first conductivity type with a high doping concentration is arranged in the second groove 6, and a first tunneling oxide layer 7a is arranged between the substrate layer 1 and the second doping layer 8 to achieve separation of different carriers, so that electrons flow to the second doping layer 8 and holes flow to the first doping layer 4, and at the same time, the first tunneling oxide layer 7a can also reduce surface recombination of carriers. In this embodiment, grooves are opened at different positions on the base layer 1 to form relatively isolated first grooves 2 and second grooves 6. The first groove 2 is provided with a first doping layer 4 and a passivation layer 5, and the second groove 6 is provided with a first tunneling oxide layer 7a and a second doping layer 8. The first doping layer 4 and the second doping layer 8 have opposite conductivity types. Carriers of different conductivity types can be accurately and efficiently diverted to flow to doping layers of different conductivity types, and then efficiently extracted through electrodes, thereby reducing carrier contact recombination and improving the photoelectric conversion efficiency and power generation efficiency of the battery.

[0079] In addition, before the grooving process is performed on the base layer 1, the present embodiment also performs surface treatment on the base layer 1, including: texturing and cleaning the N-type silicon wafer. Texturing is to form a rough texture on the surface of the N-type silicon wafer by chemical or mechanical methods, remove the mechanical damage layer on the surface of the N-type silicon wafer, and reduce the surface recombination center; cleaning is to use detergents such as deionized water and ultrasonic waves to remove particles and pollutants generated during the texturing process, thereby ensuring the cleanliness of the surface of the base layer 1 and improving the battery conversion efficiency.

[0080] In one embodiment, the above step S102 of opening the first groove 2 on the first surface 101 of the base layer 1 includes: using laser grooving to form a plurality of first grooves 2 at intervals on one side of the first surface 101 of the base layer 1, and forming a protrusion 3 between any adjacent first grooves 2.

[0081] Specifically, Figure 3 As shown, a plurality of first grooves 2 and corresponding plurality of protrusions 3 are precisely formed on the lower surface of the substrate layer 1 by laser grooving, so as to facilitate the precise formation of the first doping layer 4 and the passivation layer 5 in the recessed first grooves 2, thereby improving the forming quality of the first doping layer 4 and the passivation layer 5 and further improving the battery performance.

[0082] In one embodiment, the above step S103, performing doping treatment on the inner wall surface of the first groove 2 to form the first doping layer 4, includes:

[0083] Step S1031 , performing boron diffusion treatment on one side of the first surface 101 of the base layer 1 to form an initial first doping layer 400 , wherein the initial first doping layer 400 completely covers one side of the first surface 101 of the base layer 1 .

[0084] like Figure 4 As shown, a boron diffusion treatment is performed on the first surface 101 of the base layer 1 as a whole, and a P-type initial first doping layer 400 is formed on the entire lower end of the N-type base layer 1. The initial first doping layer 400 is formed on the bottom and side walls of the first groove 2 and the surface of the protrusion 3, which helps to form a consistent and uniform first doping layer 4 on the inner wall surfaces of the multiple first grooves 2 themselves.

[0085] Step S1032 , removing the initial first doping layer 400 on the protrusion 3 to form a first doping layer 4 covering the inner wall surface of the first groove 2 .

[0086] As an implementation method, the initial first doping layer 400 on the surface of the protrusion 3 is conveniently removed by grinding to form a first doping layer 4 located at the bottom and sidewall of the first groove 2, and multiple first doping layers 4 are respectively located in multiple relatively isolated first grooves 2.

[0087] In the present embodiment, after forming a continuous initial first doping layer 400 on one side of the first surface 101 of the substrate layer 1, the initial first doping layer 400 on the protrusion 3 area is polished to form relatively isolated first doping layers 4 in the plurality of first grooves 2. The plurality of first doping layers 4 formed are uniform and consistent, and the preparation is efficient and quick, thereby improving the processing efficiency while improving the battery conversion efficiency.

[0088] As a preferred embodiment, after boron diffusion treatment is performed on one side of the first surface 101 of the substrate layer 1 to form an initial first doping layer 400 in step S1031, and before removing the initial first doping layer 400 located on the protrusion 3 in step S1032, it also includes: forming an initial passivation layer 500 on the surface of the initial first doping layer 400 facing away from the substrate layer 1, and the initial passivation layer 500 conformally covers the initial first doping layer 400.

[0089] That is, after the initial first doping layer 400 is formed on the entire surface, the initial passivation layer 500 is formed on the initial first doping layer 400 by thermal oxidation to conformally cover the initial first doping layer 400. Figure 5 As shown; similarly, forming the initial passivation layer 500 on the entire surface also helps to form a uniform passivation layer 5 in the plurality of first grooves 2.

[0090] Based on the above scheme, step S1032 of removing the first doped layer 4 on the protrusion 3 also includes: simultaneously removing the initial passivation layer 500 on the protrusion 3 to form a passivation layer 5 located in the first groove 2 and on the side of the first doped layer 4 away from the base layer 1.

[0091] Specifically, Figure 6 As shown, the initial passivation layer 500 and the initial first doping layer 400 on the protrusion 3 are removed at one time by grinding, and the initial passivation layer 500 and the initial first doping layer 400 in the first groove 2 are retained, thereby forming relatively isolated passivation layers 5 and first doping layers 4 in different first grooves 2. The passivation layer 5 and the first doping layer 4 have excellent structural performance, and the one-time molding is simple and efficient, which helps to improve the photoelectric conversion efficiency and processing efficiency of the battery.

[0092] In this embodiment, the passivation layer 5 includes silicon oxide, silicon nitride or other passivation materials, which are not specifically limited.

[0093] In one embodiment, the step S106 of forming the first tunnel oxide layer 7a on the inner wall surface of the second groove 6 includes:

[0094] Step S1061 , depositing an initial tunneling oxide layer 700 on one side of the first surface 101 of the base layer 1 , wherein the initial tunneling oxide layer 700 completely covers one side of the first surface 101 of the base layer 1 .

[0095] like Figure 8 As shown, a continuous initial tunneling oxide layer 700 is deposited on the first surface 101 side of the base layer 1, that is, the back side, and the initial tunneling oxide layer 700 covers the passivation layer 5 in the first groove 2, the lower surface of the protrusion 3 and the inner wall surface of the second groove 6.

[0096] Step S1062 , removing the initial tunneling oxide layer 700 on the surface of the protrusion 3 to form a first tunneling oxide layer 7 a in the second groove 6 and a second tunneling oxide layer 7 b in the first groove 2 .

[0097] As an embodiment, this part of the initial tunneling oxide layer 700 on the surface of the protrusion 3 is conveniently removed by grinding, so that the continuous initial tunneling oxide layer 700 is separated into a second tunneling oxide layer 7b located in the first groove 2, and a first tunneling oxide layer 7a located in the second groove. The first tunneling oxide layer 7a allows electrons to tunnel while preventing holes from penetrating, thereby achieving effective separation of carriers at the second groove 6; the second tunneling oxide layer 7b is arranged at the first groove 2, which helps to reduce surface recombination of carriers.

[0098] In the present embodiment, after forming a continuous initial tunneling oxide layer 700 on the entire side of the first surface 101 of the base layer 1, the initial tunneling oxide layer 700 on the protrusion 3 area is polished to achieve a relatively isolated tunneling oxide layer structure between the first groove 2 and the second groove 6, and between the multiple second grooves 6. The multiple tunneling oxide layer structures formed are uniform and consistent, and the preparation is efficient and quick. They can also play an isolation role to prevent unnecessary recombination, thereby improving the processing efficiency while improving the battery conversion efficiency.

[0099] As a preferred embodiment, in step S1061, after the initial tunneling oxide layer 700 is deposited on one side of the first surface 101 of the base layer 1, and before the initial tunneling oxide layer 700 located on the surface of the protrusion 3 is removed in step S1062, it also includes: forming an initial second doping material layer on one side of the first surface 101 of the base layer 1, the initial second doping material layer completely covering the initial tunneling oxide layer 700; performing phosphorus diffusion treatment on the initial second doping material layer; and annealing the initial second doping material layer after the phosphorus diffusion treatment to form an initial second doping layer 800.

[0100] That is, after the initial tunneling oxide layer 700 is formed on the entire surface, the initial second doping material is deposited on the initial tunneling oxide layer 700, and then the initial second doping material is phosphorus diffused to form an initial second doping material layer, and finally the initial second doping layer 800 is formed by annealing. At this time, the initial second initial doping layer fills and flattens the concave areas in the first groove 2 and the second groove 6, and other areas form convex parts, such as Fig. 9 As shown; similarly, forming the initial second doping layer 800 on the entire surface also helps to form a uniform second doping layer 8 in the plurality of second grooves 6.

[0101] In this embodiment, the initial second doped layer 800 is an N+ doped polysilicon layer.

[0102] Based on the above scheme, step S1062 of removing the initial tunneling oxide layer 700 located on the surface of the protrusion 3 also includes: synchronously removing the initial second doping layer 800 located on the surface of the protrusion 3 to flatten the side where the first surface 101 of the base layer 1 is located, forming a second doping layer 8 located in the second groove 6 and a third doping layer 11 located in the first groove 2.

[0103] Specifically, Fig.10As shown, the protruding initial tunneling oxide layer 700 and the initial second doping layer 800 are removed at one time by grinding, and the initial tunneling oxide layer 700 and the initial second doping layer 800 in the first groove 2 and the second groove 6 are retained, thereby forming a relatively isolated first tunneling oxide layer 7a and a second doping layer 8 in different second grooves 6, and a relatively isolated second tunneling oxide layer 7b and a third doping layer 11 in different first grooves 2. The above-mentioned structural layer has excellent performance, and the one-time molding is simple and efficient, which helps to reduce the mutual influence between different conductive types, thereby improving the photoelectric conversion efficiency and processing efficiency of the battery, and finally re-forms a flat plane on the side of the second surface 102 of the substrate layer 1, which is helpful for subsequent process processing.

[0104] In this embodiment, a double polishing technique is used to remove unnecessary material layers to ensure that the various components do not interfere with each other and to ensure the independence of the battery cells.

[0105] In one embodiment, in step S107, after forming the second doping layer 8 in the second groove 6 and on the side of the first tunneling oxide layer 7a facing away from the substrate layer 1, and before forming the first electrode 9 and the second electrode 10 in step S108, it also includes: forming a first anti-reflection layer 12 on the side of the first surface 101 of the substrate layer 1, and forming a second anti-reflection layer 13 on the side of the second surface 102 of the substrate layer 1.

[0106] like Fig.11 As shown, after a flat plane is re-formed on one side of the first surface 101 of the substrate layer 1, a first anti-reflection layer 12 is formed on the first surface 101 side by coating the anti-reflection layer material on the upper and lower surfaces of the substrate layer 1 respectively. The first anti-reflection layer 12 encapsulates the structures in the first groove 2 and the second groove 6 respectively, and a second anti-reflection layer 13 is formed on the second surface 102 side. The anti-reflection layer helps to reduce the reflection of photons after reaching the battery surface, thereby improving the absorption efficiency of photons and ultimately improving the power generation efficiency of the battery.

[0107] On the basis of the above scheme, after forming the first anti-reflection layer 12 on the first surface 101 side of the substrate layer 1, forming the second anti-reflection layer 13 on the second surface 102 side of the substrate layer 1, and before forming the first electrode 9 and the second electrode 10, it also includes: etching the first groove 2 and the second groove 6 to form a first channel 14 penetrating the third doping layer 11, the second tunneling oxide layer 7b and the passivation layer 5 to the deep part of the first doping layer 4, and a second channel 15 penetrating the deep part of the second doping layer 8; forming a metal contact layer on the inner wall surface of the first channel 14 and the inner wall surface of the second channel 15, and the metal contact layer is suitable for being fixedly connected to the electrode structure.

[0108] Specifically, Fig.12As shown, after anti-reflection layers are respectively provided on both sides of the substrate layer 1, the first anti-reflection layer 12, the third doping layer 11, the second tunneling oxide layer 7b, the passivation layer 5 and part of the first doping layer 4 are first etched at the position of the first groove 2 on the back side to form a first channel 14; the first anti-reflection layer 12 and part of the second doping layer 8 are etched at the position of the second groove 6 to form a second channel 15. Secondly, metallization contact and gate line formation are performed on the inner walls of the first channel 14 and the second channel 15. Metallization contact refers to depositing a thin layer of metal on the inner wall of the channel including the bottom and the sidewall to improve the electrical connection performance on the contact surface and reduce the contact resistance, thereby ensuring that the current can be effectively transmitted from the active layer (such as PN junction) inside the battery to the external circuit; the gate line is a metal line formed on the basis of metallization contact, which is used to collect current and lead it to the external circuit. The gate line is usually a thicker metal layer deposited on the metallization contact layer, and it is patterned by photolithography and etching processes to form a conductive path. The thin metal formed by the metallization contact and the gate line together constitute a metal contact layer, which is convenient for the connection and fixation of the electrode structure.

[0109] The first electrode 9 penetrates the multi-layer structure and is connected to the first doped layer 4, while the side wall is connected to the multiple structural layers penetrated, which helps to improve the contact quality, carrier selective transmission and passivation effect. The third doped layer 11 with a high doping concentration helps to form a good ohmic contact and reduce the contact resistance. At the same time, the selective contact formed by the third doped layer 11 and the second tunneling oxide layer 7b helps to reduce surface recombination.

[0110] like Fig.13 As shown, this embodiment also provides a back-contact solar cell, which is prepared by the above-mentioned back-contact cell preparation method, including: a substrate layer 1, a first groove 2, a first doping layer 4, a passivation layer 5, a second groove 6, a first tunneling oxide layer 7a, a second doping layer 8, a first electrode 9 and a second electrode 10, wherein the substrate layer 1 includes a first surface 101 and a second surface 102 opposite to each other, and the substrate layer 1 is of a first conductive type; the first groove 2 is formed on one side of the first surface 101 of the substrate layer 1, and correspondingly, a protrusion 3 is formed on the side of the first groove 2; the first doping layer 4 is formed on the first surface 101 of the substrate layer 1 In the groove 2, the first doped layer 4 is a second conductive type opposite to the first conductive type; the passivation layer 5 is arranged on the surface of the first doped layer 4 on the side facing away from the substrate layer 1; the second groove 6 is formed on the protrusion 3, and the second groove 6 is isolated from the first groove 2; the first tunneling oxide layer 7a is arranged on the inner wall surface of the second groove 6; the second doped layer 8 is formed in the second groove 6 and is located on the side of the first tunneling oxide layer 7a facing away from the substrate layer 1, and the second doped layer 8 is of the first conductive type; the first electrode 9 penetrates the passivation layer 5 and is connected to the first doped layer 4, and the second electrode 10 is connected to the second doped layer 8.

[0111] The back-contact solar cell of the present embodiment is manufactured by the above-mentioned method for preparing a back-contact solar cell. The substrate layer 1 is precisely grooved with the assistance of laser to form a special structure on the substrate layer 1 itself: a plurality of first grooves 2 and protrusions 3 are opened on the back side of the N-type silicon wafer. This structural design is conducive to the effective collection of current, and the protrusions 3 can effectively prevent the short circuit between the positive and negative electrodes. Carriers of different conductivity types can be accurately and efficiently diverted to flow to doping layers of different conductivity types, and then efficiently extracted through electrodes, thereby reducing carrier contact and recombination, and improving the photoelectric conversion efficiency and power generation efficiency of the battery. The use of laser grooving technology can accurately groove the lower end of the N-type silicon wafer, which helps to achieve highly precise structural control. The laser can also be used in subsequent secondary grooving to form a second groove 6. The second groove 6 is not connected to the first groove 2 to ensure the independence of each battery cell.

[0112] In one embodiment, the back-contact solar cell further includes: a second tunneling oxide layer 7b, a third doping layer 11, a first anti-reflection layer 12 and a second anti-reflection layer 13, wherein the second tunneling oxide layer 7b is formed in the first groove 2 and conformally covers the passivation layer 5; the third doping layer 11 is formed in the first groove 2 and contacts the second tunneling oxide layer 7b; the first anti-reflection layer 12 is formed on one side of the first surface 101 of the substrate layer 1; and the second anti-reflection layer 13 is formed on one side of the second surface 102 of the substrate layer 1.

[0113] In this embodiment, while forming the first tunneling oxide layer 7a and the second doping layer 8 at the second groove 6, the second tunneling oxide layer 7b and the third doping layer 11 are simultaneously formed at the first groove 2, so as to further reduce the surface carrier recombination at the first groove 2, improve the battery conversion efficiency, and also enable the first surface 101 side of the substrate layer 1 to become a flat plane again, which is convenient for the preparation of subsequent structural layers, and improves the stability and reliability of the battery. The first anti-reflection layer 12 and the second anti-reflection layer 13 help to reduce the reflection of photons after reaching the battery surface, thereby improving the absorption efficiency of photons and ultimately improving the power generation efficiency of the battery.

[0114] The further functional description of each of the above structures is the same as that of the above corresponding embodiments and will not be repeated here.

[0115] The battery of this embodiment was sampled and tested three times, and the battery performance was compared with that of the conventional back contact battery of the comparative example, and the test results shown in the following table were obtained:

[0116] Battery samples Uoc(v) Jsc(A) FF(%) Efficiency(%) Sample 1 0.723 13.399 86.11 26.21 Sample 2 0.726 13.45 86.15 26.26 Sample 3 0.731 13.48 86.21 26.50 Comparative Example 0.705 13.121 83.47 23.98

[0117] It can be seen from the above table that the back-contact solar cell in this embodiment has increased open circuit voltage (Uoc), short circuit current (Jsc), fill factor (FF) and power generation efficiency (Efficiency) compared with the control battery, that is, the photoelectric conversion performance of the back-contact solar cell in this embodiment is significantly improved.

[0118] In the above description, the technical details of the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0119] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for preparing a back contact solar cell, characterized in that: include: Providing a base layer, the base layer having a first surface and a second surface opposite to each other, the base layer being of a first conductivity type; A first groove is formed on the first surface of the base layer, and a bulge is formed beside the first groove; Doping the inner wall surface of the first groove to form a first doping layer; the first doping layer is a second conductivity type opposite to the first conductivity type; forming a passivation layer on a surface of the first doped layer facing away from the base layer; A second groove is formed on the protrusion, and the second groove is isolated from the first groove; forming a first tunneling oxide layer on an inner wall surface of the second groove; forming a second doped layer in the second groove and on a side of the first tunneling oxide layer away from the base layer, wherein the second doped layer is of the first conductivity type; A first electrode and a second electrode are formed, wherein the first electrode penetrates the passivation layer to connect to the first doping layer, and the second electrode connects to the second doping layer.

2. The method for preparing a back contact solar cell according to claim 1, characterized in that: The step of opening a first groove on the first surface of the base layer comprises: A plurality of first grooves are formed at intervals on one side of the first surface of the base layer by laser grooving, and a bulge is formed between any adjacent first grooves.

3. The method for preparing a back contact solar cell according to claim 1 or 2, characterized in that: The step of doping the inner wall surface of the first groove to form a first doping layer includes: Performing boron diffusion treatment on one side of the first surface of the base layer to form an initial first doping layer, wherein the initial first doping layer completely covers one side of the first surface of the base layer; The initial first doping layer on the protrusion is removed to form a first doping layer covering the inner wall surface of the first groove.

4. The method for preparing a back contact solar cell according to claim 3, characterized in that: After performing boron diffusion treatment on one side of the first surface of the base layer to form an initial first doping layer and before removing the initial first doping layer located on the protrusion, the method further includes: forming an initial passivation layer on a surface of the initial first doping layer facing away from the base layer, wherein the initial passivation layer conformally covers the initial first doping layer; The removing of the first doping layer on the protrusion further comprises: simultaneously removing the initial passivation layer on the protrusion to form a passivation layer located in the first groove and on a side of the first doping layer away from the base layer.

5. The method for preparing a back contact solar cell according to claim 4, characterized in that: The forming of a first tunneling oxide layer on the inner wall surface of the second groove comprises: Depositing an initial tunneling oxide layer on one side of the first surface of the base layer, wherein the initial tunneling oxide layer completely covers one side of the first surface of the base layer; The initial tunnel oxide layer on the protruding surface is removed to form a first tunnel oxide layer in the second groove and a second tunnel oxide layer in the first groove.

6. The method for preparing a back contact solar cell according to claim 5, characterized in that: After depositing an initial tunneling oxide layer on one side of the first surface of the base layer and before removing the initial tunneling oxide layer on the convex surface, the method further includes: forming an initial second doping material layer on one side of the first surface of the base layer, wherein the initial second doping material layer completely covers the initial tunneling oxide layer; performing phosphorus diffusion treatment on the initial second doping material layer; and performing annealing treatment on the initial second doping material layer after the phosphorus diffusion treatment to form an initial second doping layer; The removing of the initial tunneling oxide layer on the raised surface also includes: simultaneously removing the initial second doping layer on the raised surface to flatten the side of the first surface of the base layer to form a second doping layer in the second groove and a third doping layer in the first groove.

7. The method for preparing a back contact solar cell according to claim 6, characterized in that: After forming the second doping layer in the second groove and on the side of the first tunneling oxide layer away from the base layer, and before forming the first electrode and the second electrode, the method further includes: A first anti-reflection layer is formed on one side of the first surface of the base layer, and a second anti-reflection layer is formed on one side of the second surface of the base layer.

8. The method for preparing a back contact solar cell according to claim 7, characterized in that: After forming a first anti-reflection layer on one side of the first surface of the substrate layer, and forming a second anti-reflection layer on one side of the second surface of the substrate layer, and before forming the first electrode and the second electrode, the method further includes: Performing etching on the first groove and the second groove to form a first channel penetrating the third doping layer, the second tunneling oxide layer and the passivation layer until penetrating a portion of the first doping layer, and a second channel penetrating a portion of the second doping layer; A metal contact layer is formed on the inner wall surface of the first channel and the inner wall surface of the second channel, and the metal contact layer is suitable for being fixedly connected to the electrode structure.

9. A back-contact solar cell, prepared by the method for preparing a back-contact solar cell according to any one of claims 1 to 8, characterized in that: include: A base layer, comprising a first surface and a second surface opposite to each other, wherein the base layer is of a first conductivity type; A first groove is formed on one side of the first surface of the base layer; correspondingly, a bulge is formed on the side of the first groove; A first doped layer is formed in the first groove; the first doped layer is a second conductivity type opposite to the first conductivity type; A passivation layer is disposed on a surface of the first doping layer facing away from the substrate layer; a second groove formed on the protrusion, wherein the second groove is isolated from the first groove; A first tunneling oxide layer is disposed on the inner wall surface of the second groove; A second doped layer is formed in the second groove and is located on a side of the first tunnel oxide layer away from the base layer, and the second doped layer is of a first conductivity type; A first electrode and a second electrode, wherein the first electrode penetrates the passivation layer and is connected to the first doping layer, and the second electrode is connected to the second doping layer.

10. The back contact solar cell according to claim 9, characterized in that: Also includes: A second tunneling oxide layer is formed in the first groove and conformally covers the passivation layer; a third doped layer formed in the first groove and contacting the second tunnel oxide layer; A first anti-reflection layer is formed on one side of the first surface of the base layer; The second anti-reflection layer is formed on the second surface side of the base layer.

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