A preparation method of a back contact solar cell and a back contact solar cell

Abstract

The application discloses a preparation method of a back junction solar cell and the back junction solar cell. The preparation method comprises the following steps: forming a plurality of holes in an array arrangement on a front surface passivation anti-reflection layer of a P-type silicon substrate; arranging aluminum paste in the holes; performing first sintering on the P-type silicon substrate with the aluminum paste in the holes at 700 DEG C-950 DEG C, so as to form a P+ heavy-doped local front surface field, an aluminum electrode and an oxide layer covering the aluminum electrode; stripping the oxide layer covering the aluminum electrode; printing a plurality of silver paste lines on the front surface passivation anti-reflection layer, the silver paste lines being in contact with the front surfaces of the aluminum electrodes with the oxide layer stripped, and the silver paste lines being connected with the aluminum electrodes with the oxide layer stripped; and performing second sintering on the P-type silicon substrate with the silver paste lines, so that the sintering temperature of the second sintering is lower than the melting point of aluminum, and a silver electrode and the aluminum electrodes connected with the silver electrode form a front surface fine grid line of the back junction solar cell. The light-electricity conversion efficiency of the back junction solar cell is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a back junction solar cell and the back junction solar cell. BACKGROUND

[0002] At present, in order to overcome the influence of the electron-hole pairs generated by the doped silicon layer arranged on the light-receiving surface of the P-type passivated contact solar cell on the absorption of incident light by the solar cell, and to overcome the influence of the high temperature or laser grooving preparation of the back surface field on the performance of the solar cell, the P-type back junction solar cell (the PN junction is located on the back surface of the cell) with the front surface field has begun to attract widespread attention.

[0003] The existing setting of the front electrode of the P-type back junction solar cell mainly covers the aluminum paste on the grooving area of the front passivation anti-reflection layer to form the sub-grid lines of the front metal electrode, then prints the silver paste on the front passivation anti-reflection layer to form the main grid lines of the front metal electrode, and finally, through sintering, the aluminum paste and the P-type silicon matrix are doped to form a local front surface field. The high temperature in the sintering process of the existing back junction solar cell makes the aluminum sub-grid lines and the silver main grid lines of the front metal electrode both in a molten state, and the silver and aluminum in the molten state interpenetrate. Therefore, in the high-temperature sintering process, the impurity silver interpenetrated in the aluminum sub-grid lines contacts the P-type silicon matrix, forms a recombination center on the surface of the P-type silicon matrix, causes the carrier recombination on the surface of the P-type silicon matrix, and increases the contact resistance between the surface of the P-type silicon matrix and the front fine grid lines, thereby reducing the photoelectric conversion efficiency of the back junction solar cell. SUMMARY

[0004] Therefore, the present application provides a preparation method of a back junction solar cell and the back junction solar cell. The preparation method can ensure the electrical contact between the aluminum electrode and the silver electrode in the fine grid lines of the back junction solar cell by combining two sintering processes and introducing a stripping process between the two sintering processes, and can effectively prevent the silver in the silver electrode from entering the aluminum electrode and the silver from contacting the surface of the P-type silicon matrix, thereby reducing the carrier recombination on the surface of the P-type silicon matrix and the contact resistance between the surface of the P-type silicon matrix and the front fine grid lines, and effectively improving the photoelectric conversion efficiency of the prepared back junction solar cell.

[0005] In order to solve the above technical problems, the present application provides the following technical solutions:

[0006] In a first aspect, the present application provides a preparation method of a back junction solar cell, comprising:

[0007] Step a, forming a plurality of holes in an array arrangement on the front passivation anti-reflection layer formed on the P-type silicon matrix;

[0008] b. disposing aluminum paste in the plurality of holes, wherein the aluminum paste is in contact with the P-type silicon substrate in the region corresponding to the holes;

[0009] c. performing first sintering on the P-type silicon substrate with aluminum paste disposed in the holes to form P+ heavily doped local front surface field in the contact region of the aluminum paste and the P-type silicon substrate, and to form aluminum electrode and oxide layer covering the aluminum electrode, wherein the sintering temperature is 700-950℃;

[0010] d. stripping the oxide layer covering the front surface of the aluminum electrode;

[0011] e. printing a plurality of silver paste lines on the front surface passivation anti-reflection layer, wherein each of the silver paste lines is in contact with the front surface of a plurality of aluminum electrodes with the oxide layer stripped, so that each of the silver paste lines is connected with the plurality of aluminum electrodes with the oxide layer stripped;

[0012] f. performing second sintering on the P-type silicon substrate with the silver paste lines printed to form silver electrode, wherein the sintering temperature of the second sintering is lower than the melting point of aluminum, and the silver electrode and the aluminum electrodes connected therewith constitute the front surface fine grid lines of the back junction solar cell.

[0013] In the second aspect, the embodiments of the present application provide a back junction solar cell prepared by the embodiments of the first aspect, comprising:

[0014] a P-type silicon substrate;

[0015] a front surface passivation anti-reflection layer formed on one main surface of the P-type silicon substrate;

[0016] a plurality of holes arranged in an array on the front surface passivation anti-reflection layer;

[0017] a P+ heavily doped local front surface field formed in the region of the P-type silicon substrate corresponding to the holes;

[0018] an aluminum electrode in contact with the P+ heavily doped local front surface field and extending outward from the holes, wherein the surface of the aluminum electrode is formed with an oxide layer;

[0019] and a silver electrode connected with a plurality of the aluminum electrodes, wherein the silver electrode is in contact with the region of the aluminum electrode with the oxide layer stripped, and the silver electrode and the aluminum electrodes connected therewith constitute the front surface fine grid lines of the back junction solar cell.

[0020] The technical solution of the first aspect of the above-mentioned application has the following advantages or beneficial effects:

[0021] The method for fabricating a back-junction solar cell provided by this invention involves creating an array of holes in the front passivation and antireflection layer, placing aluminum paste within the holes, and then performing a first sintering at 700℃~950℃ to prepare a dotted aluminum electrode. Simultaneously, a P+ heavily doped local front surface field is formed, effectively reducing the area of ​​the aluminum electrode covering the front of the solar cell. Then, by removing the oxide layer on the front surface of the aluminum electrode, the silver paste lines printed on the front passivation and antireflection layer directly contact the oxide-removed area of ​​the aluminum electrode. This ensures direct contact between the silver paste lines and the aluminum electrode, reducing the contact resistance between them, while also enabling the silver paste lines to be connected in series with multiple... An aluminum electrode is further sintered a second time to form a silver electrode that is in electrical contact with the aluminum electrode. The silver electrode and the aluminum electrode connected in series form the fine grid lines on the front side of the back junction solar cell. Since the sintering temperature of the second sintering after printing the silver paste lines is lower than the melting point of aluminum (for example, the melting point of aluminum at normal pressure is 660°C), and the melting point of aluminum is much lower than that of silver, the interpenetration between the aluminum and silver electrodes is effectively avoided, thereby preventing the silver from contacting the P-type silicon substrate. This effectively reduces the carrier recombination on the surface of the P-type silicon substrate and the contact resistance between the surface of the P-type silicon substrate and the fine grid lines on the front side, thereby effectively improving the photoelectric conversion efficiency of the fabricated back junction solar cell.

[0022] In addition, compared with aluminum electrodes, silver electrodes have a stronger current conduction capability. By forming the front fine grid lines of the back junction solar cell with silver electrodes and aluminum electrodes connected in series, the current conduction capability of the front fine grid lines can be guaranteed by reducing the width of the silver electrodes, while further reducing the light-shielding area on the front of the back junction solar cell and reducing the silver paste consumption. This can further effectively improve the photoelectric conversion efficiency and cost of the fabricated back junction solar cell. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the main process of the fabrication method of a back junction solar cell provided in an embodiment of the present invention;

[0024] Figure 2 This is a partial structural cross-sectional schematic diagram of the fabrication process of a back-junction solar cell according to an embodiment of the present invention;

[0025] Figure 3 This is a partial cross-sectional structural schematic diagram obtained after step S101 according to an embodiment of the present invention;

[0026] Figure 4 It is provided according to the embodiments of the present invention. Figure 3 A top view of the structure;

[0027] Figure 5 This is a cross-sectional structural schematic diagram showing the relative positional relationship between the aluminum paste, the P-type silicon substrate 1, and the hole 3 according to an embodiment of the present invention.

[0028] Figure 6 is a schematic diagram of a structure cross section obtained by the first sintering of step S103 according to an embodiment of the present application;

[0029] Figure 7 is a schematic diagram of a structure cross section obtained by the first sintering of step S103 according to an embodiment of the present application, including a back silver electrode;

[0030] Figure 8 is a schematic diagram of a structure cross section obtained by the first sintering of step S104 according to an embodiment of the present application, including a back silver electrode;

[0031] Figure 9 is a schematic diagram of a structure cross section obtained by the first sintering of step S104 according to an embodiment of the present application, including a back silver electrode;

[0032] Figure 10 is a schematic diagram of a structure cross section obtained by the first sintering of step S106 according to an embodiment of the present application, including a back silver electrode;

[0033] Figure 11 is a schematic diagram of a structure cross section obtained by the first sintering of step S106 according to an embodiment of the present application, including a back silver electrode; Figure 10 is a top view of the back junction solar cell of the present application;

[0034] Figure 12 is a schematic diagram of a structure cross section obtained by the first sintering of step S106 according to an embodiment of the present application, including a back silver electrode.

[0035] The reference signs are as follows:

[0036] 1-P type silicon substrate; 2-front passivation anti-reflection layer; 3-hole; 4-P+ heavily doped local front surface field; 5-aluminum electrode; 6-oxidation layer covering the aluminum electrode; 7-silver electrode; 8-tunneling oxidation layer; 9-N type doped polysilicon layer; 10-back passivation anti-reflection layer; 11-back silver electrode. DETAILED DESCRIPTION

[0037] The inner-to-outer layer stack according to the embodiments of the present application means that a plurality of other structures are stacked in a direction away from a structure taken as a starting point. For example, Figure 2 , Figure 3 , Figure 5 , Figure 8The tunneling oxide layer 8, the N-type doped silicon layer 9 and the back passivation anti-reflection layer 10 shown in the schematic diagram are sequentially stacked on the first main surface of the P-type silicon substrate 1 from the first main surface of the P-type silicon substrate 1 to the direction away from the first main surface of the P-type silicon substrate 1, wherein the tunneling oxide layer 8 is in direct contact with the P-type silicon substrate 1, that is, the tunneling oxide layer 8 is closest to the first main surface of the P-type silicon substrate 1, the N-type doped silicon layer 9 is stacked on the tunneling oxide layer 2, and the back passivation anti-reflection layer 10 is stacked on the N-type doped silicon layer 9.

[0038] The structure of one structure penetrating another structure refers to that a part of the one structure penetrates from one side of the other structure to the other side in the thickness direction of the other structure, for example, a hole or an aluminum electrode in the hole penetrating the front passivation anti-reflection layer refers to that the hole or the aluminum electrode in the hole penetrates from one side of the front passivation anti-reflection layer to the other side of the front passivation anti-reflection layer.

[0039] In addition, the first main surface and the second main surface of the P-type silicon substrate refer to two surfaces of the P-type silicon substrate which are oppositely arranged, have a large area and are used as a light-receiving surface (a surface facing the sunlight) or a back surface (a surface facing away from the sunlight) of a solar cell. Among them, the "first" and "second" in the first main surface and the second main surface are only to distinguish the two surfaces of the P-type silicon substrate which are used as the back surface of the solar cell and the light-receiving surface of the solar cell, respectively, and are not a limitation on the number or order of the main surfaces.

[0040] The one structure stringing the other structure can refer to that the one structure is in contact with a plurality of other structures to connect the plurality of other structures in series, for example, the silver paste line or the silver electrode stringing a plurality of aluminum electrodes, that is, the silver paste line or the silver electrode is in direct contact with the plurality of aluminum electrodes to connect the plurality of aluminum electrodes in series.

[0041] In order to solve the problem that the aluminum electrode prepared by the preparation method of the existing back junction solar cell is seriously shaded and the high-temperature sintering in the preparation process causes the silver to form a recombination center on the surface of the P-type silicon substrate, causing the carrier recombination on the surface of the P-type silicon substrate and the contact resistance between the surface of the P-type silicon substrate and the front fine grid line to increase, resulting in low photoelectric conversion efficiency, the embodiment of the present application provides a preparation method of a back junction solar cell. Figure 1 The main flowchart of the preparation method of the back junction solar cell is shown; Figures 2 to 12 The structure diagram of the part structure relied on by each process or the part structure obtained by each process included in the preparation method is shown. As Figure 1 The preparation method of the back junction solar cell can include the following steps:

[0042] Step S101: forming a plurality of holes in array on the front surface passivation anti-reflective layer formed on the P-type silicon substrate;

[0043] Step S102: disposing aluminum paste in the plurality of holes, wherein the aluminum paste is in contact with the region of the P-type silicon substrate corresponding to the holes;

[0044] Step S103: performing first sintering on the P-type silicon substrate with the aluminum paste disposed in the holes, so that the contact region of the aluminum paste and the P-type silicon substrate forms a P+ heavily doped local front surface field, and forms an aluminum electrode and an oxide layer covering the aluminum electrode, wherein the sintering temperature is 700-950°C;

[0045] Step S104: peeling off the oxide layer covering the front surface of the aluminum electrode;

[0046] Step S105: printing a plurality of silver paste lines on the front surface passivation anti-reflective layer, wherein each silver paste line is in contact with the front surface of a plurality of aluminum electrodes with the oxide layer peeled off, so that each silver paste line is connected in series with the plurality of aluminum electrodes with the oxide layer peeled off;

[0047] Step S106: performing second sintering on the P-type silicon substrate with the silver paste lines printed, so as to form a silver electrode, wherein the sintering temperature of the second sintering is lower than the melting point of aluminum, and the silver electrode and the aluminum electrodes connected in series form the front surface fine grid lines of the back junction solar cell.

[0048] It can be understood that the front surface passivation anti-reflective layer or the front surface passivation layer or the front surface anti-reflective layer is completed before the step S101, which can be obtained by the existing process based on the P-type silicon substrate for preparing the back junction solar cell, and will not be described here.

[0049] In addition, in order to obtain the front surface anti-reflective layer formed on the P-type silicon substrate, the embodiment of the present application further comprises the following process steps before the step S101:

[0050] The first main surface of the P-type silicon substrate 1 is formed from inside to outside by a tunneling oxide layer 8 and an N-type doped polysilicon layer 9; and the second main surface of the P-type silicon substrate 1 is formed with a front surface passivation anti-reflective layer 2 and a back surface passivation anti-reflective layer 10 formed on the back surface of the N-type doped polysilicon layer 9, wherein the front surface passivation anti-reflective layer 2 and the back surface passivation anti-reflective layer 10 can be formed synchronously, and the cross-sectional structure variation diagram obtained by this step can be shown as Figure 2 Figure 2 ​The structural changes observed in this process are as follows: First, a tunneling oxide layer 8 is formed on the first main surface of the P-type silicon substrate 1. Then, an N-type doped polycrystalline silicon layer 9 is formed on the tunneling oxide layer 8. Simultaneously, a back passivation antireflection layer 10 is formed on the N-type doped polycrystalline silicon layer 9, and a front passivation antireflection layer 2 is formed on the second main surface of the P-type silicon substrate 1. The tunneling oxide layer 8 and the N-type doped polycrystalline silicon layer 9 are prepared by one or more deposition methods selected from low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). The resulting tunneling oxide layer 8 is typically silicon oxide, with a thickness ranging from 0.5 to 3.0 nm.

[0051] The simultaneously formed front passivation antireflection layer 2 and back passivation antireflection layer 10 can also be fabricated using one or more deposition methods selected from LPCVD, PECVD, PVD, and ALD. Both the front passivation antireflection layer 2 and the back passivation antireflection layer 10 can include at least one of aluminum oxide, silicon oxide, gallium oxide, silicon nitride, aluminum nitride, and silicon oxynitride. The simultaneous formation of the front passivation antireflection layer 2 and the back passivation antireflection layer 10 effectively simplifies the fabrication process of back-junction solar cells.

[0052] The following is based on Figure 2 Taking the structure shown as an example, which includes a tunneling oxide layer 8, an N-type doped polysilicon layer 9, a front passivation antireflection layer 2, and a back passivation antireflection layer, the structure obtained after each step in steps S101 to S105 is explained in detail. Figure 3 It shows Figure 2 A schematic cross-sectional view of the structure obtained after the above step S101 is obtained.

[0053] Figure 4 It shows Figure 2 A top view of the structure obtained after the above step S101 is obtained;

[0054] Figure 5 It shows Figure 3 The diagram shows a cross-sectional view of the structure obtained after step S102.

[0055] Figure 6 and Figure 7 They are shown respectively Figure 5The diagram shows a cross-sectional view of the structure obtained after step S103. Figure 8 It shows Figure 7 The diagram shows a cross-sectional view of the structure obtained after step S104. Figure 10 It shows Figure 8 The diagram shows a cross-sectional view of the structure obtained after steps S105 and S106. Figure 11 It shows Figure 8 The structure shown is a top view obtained after steps S105 and S106.

[0056] Among them, such as Figure 3 As shown, the multiple holes 3 arranged in the array in step S101 are generally holes that penetrate the front passivation antireflection layer 2. That is, the area on the P-type silicon substrate 1 corresponding to the holes 3 is exposed. The relationship between the multiple holes arranged in the array can be as follows: Figure 4 As shown. From Figure 4 It can be seen that the array of multiple holes forms a multi-row, multi-column distribution. The width of the hole 3 created in step S101 (the width of hole 3 is generally the maximum distance between two points on the edge of the hole along a certain direction, such as parallel to the edge of the P-type silicon substrate) is generally controlled between 50 and 60 μm to ensure electrical contact of the aluminum electrode and the effective current conduction to the silver electrode connected to it. Furthermore, the shape of the hole is not limited here. For example, the cross-section of the hole can be circular, rectangular, elliptical, etc. If the cross-section of the hole is circular, the width of the hole generally refers to the diameter of the circle.

[0057] It is worth noting that the spacing between any two adjacent holes in each row is generally the same, and the spacing between any two adjacent holes in each column is also generally the same. This makes the hole-making process easier to control, and it also allows the entire back junction solar cell to collect current more evenly through the front electrode. However, the correlation between the spacing between any two adjacent holes in each row and the spacing between any two adjacent holes in each column is not specified here.

[0058] In step S102, the aluminum paste can be applied by extrusion into the hole 3 or by printing the aluminum paste onto the hole, so that the aluminum paste contacts the area of ​​the P-type silicon substrate 1 corresponding to the hole 3. The relative positions of the aluminum paste, the P-type silicon substrate 1, and the hole 3 are as follows: Figure 5 As shown. It is worth noting that the aluminum paste generally completely fills hole 3. In a preferred embodiment, the aluminum paste extends beyond hole 3 (this extended portion can be the part of the aluminum paste exposed outside hole 3 covering the edge of hole 3 in a "cap" shape, or the height of the aluminum paste can be greater than the depth of hole 3) to facilitate subsequent contact between the aluminum electrode and the silver electrode. Additionally, as... Figure 5As shown, after this step, silver paste can be printed on the back passivation antireflection layer for subsequent fabrication of the back silver electrode.

[0059] Furthermore, the partial structure obtained through the first sintering in step S103 above is as follows: Figure 6 As shown. Figure 6 As shown, after the first sintering, a P+ heavily doped local front surface field 4 is formed at the contact area between the aluminum paste and the P-type silicon substrate 1, and an aluminum electrode 5 and an oxide layer 6 covering the aluminum electrode are formed. The width of the aluminum electrode is generally 50–60 μm. Furthermore, the width of the P+ heavily doped local front surface field 4 formed in step S103 is generally greater than or equal to the width of the aluminum electrode 5. In a preferred embodiment, the width of the P+ heavily doped local front surface field 4 is equal to the width of the aluminum electrode 5. This achieves a front surface field while reducing the shading of the P+ heavily doped local front surface field 4 on the light-absorbing area of ​​the back junction solar cell, which is beneficial for improving the photoelectric conversion efficiency of the back junction solar cell.

[0060] In addition, step S103 can ensure that the P+ heavily doped local front surface field 4 is formed synchronously with the aluminum electrode by controlling the sintering temperature between 700℃ and 950℃, thus omitting the process of forming the front surface field separately.

[0061] Furthermore, to further reduce the fabrication steps of the back junction solar cell, after step S102 and before step S103, the process may further include: printing silver paste onto the back passivation antireflection layer 10 formed on the P-type silicon substrate 1; correspondingly, step S103 may further include: simultaneously sintering the silver paste printed on the back passivation antireflection layer 10 during the first sintering process, so that the silver paste penetrates the back passivation antireflection layer 10 to form contact with the N-type doped polycrystalline silicon layer 9, and simultaneously forming the back silver electrode 11, resulting in... Figure 7 The structure shown.

[0062] Furthermore, the specific implementation of step S104, which involves peeling off the oxide layer covering the front side of the aluminum electrode 5, may include: in a peeling chamber filled with a protective gas, peeling off the oxide layer 6 on the front side of the aluminum electrode 5 by laser peeling or plasma peeling. The protective gas is generally a gas that does not react with aluminum, such as nitrogen, or an inert gas such as argon. Figure 7 Taking the structure shown as an example, after step S104, the following is obtained: Figure 8 The structure shown is such that by stripping the oxide layer covering the front side of the aluminum electrode 5, the silver electrode formed in subsequent steps can directly contact the aluminum electrode, thereby effectively improving the ohmic contact of the electrodes.

[0063] In step S104, the front side of the aluminum electrode 5 generally refers to the side of the aluminum electrode 5 facing sunlight during the use of the back junction solar cell. The width W2 of the stripped oxide layer can be less than or equal to the width of the front side of the aluminum electrode 5. In a preferred embodiment, as... Figure 9 As shown, the width W2 of the stripped oxide layer is smaller than the width W1 of the aluminum electrode 5, so as to better control the width of the subsequently formed narrower silver electrode.

[0064] Furthermore, in step S105 above, each silver paste line connecting multiple aluminum electrodes with stripped oxide layers generally means that aluminum electrodes in each row or column are connected in series by a single silver paste line, with aluminum electrodes in different rows or columns connected to different silver paste lines. In this step, the width of each silver paste line is generally greater than or equal to 20 μm and smaller than the width of the aluminum electrode. This effectively increases the light-receiving area on the front side of the back-junction solar cell, thereby further improving the photoelectric conversion efficiency of the back-junction solar cell, while simultaneously reducing aluminum paste consumption and the production cost of the back-junction solar cell.

[0065] Furthermore, based on Figure 8 The structure shown, after step S106 described above, forms a cross-sectional structure as follows: Figure 10 As shown, the Figure 10 The corresponding top view can be seen as follows Figure 11 As shown. From Figure 10 It can be seen that the area of ​​aluminum electrode 5 where the oxide layer has been peeled off is in contact with silver electrode 7. Additionally, as... Figure 11 As shown, the silver electrode 7 is connected in series with multiple aluminum electrodes located in the same row or column to form the front fine grid lines of the back junction solar cell. The second sintering in step S106, by controlling the sintering temperature below the melting point of aluminum, can form the silver electrode while simultaneously establishing a stable electrical contact between the silver electrode and the contacting aluminum electrode. This also prevents silver from penetrating into the aluminum electrode and avoids contact between the silver and the P-type silicon substrate, effectively preventing metal recombination between the P-type silicon substrate surface and the silver. This effectively reduces carrier recombination on the P-type silicon substrate surface and the contact resistance between the P-type silicon substrate surface and the front fine grid lines.

[0066] Furthermore, the width W3 of the silver electrode 7 obtained through the above step S106 is generally less than or equal to the width W2 of the stripped oxide layer 6. In a preferred embodiment, as... Figure 12 As shown, the width W3 of the silver electrode 7 is smaller than the width W2 of the stripped oxide layer 6, and the width W2 of the stripped oxide layer 6 is smaller than the width W1 of the aluminum electrode 5, so that the areas where the silver electrode 7 and the aluminum electrode 5 are in contact can be as close as possible, thus ensuring the current collection capability without increasing the light-shielding area.

[0067] In a preferred embodiment, the sintering temperature of the second sintering of step S106 can be 300-550°C. For example, the sintering temperature of the second sintering can be any one of 300°C, 320°C, 330°C, 350°C, 380°C, 400°C, 420°C, 450°C, 480°C, 500°C, 510°C, 530°C, 540°C, 550°C, etc. By controlling the sintering temperature of the second sintering within the range of 300-550°C, good electrical contact between the silver electrode and the aluminum electrode can be achieved, while reducing energy consumption, reducing the occurrence of silver-aluminum inter-diffusion and the formation of a composite center where the silver penetrates the aluminum electrode and contacts the surface of the P-type silicon substrate, thereby improving the efficiency of the battery and reducing the production cost of the back junction solar cell.

[0068] It should be noted that although the schematic diagram of each embodiment of the present application does not show the main grid of the back junction solar cell, a front main grid intersecting the front fine grid line formed by the silver electrode 7 and the aluminum electrode 5 connected in series can be further prepared by printing. The front main grid can be printed synchronously with the silver electrode 7, so that the fine grid and the main grid can be formed synchronously in step S106. It should be noted that the front main grid generally directly contacts the silver electrode 7 without directly contacting the aluminum electrode, so as to effectively improve the electrical conductivity of the electrode of the back junction solar cell and better collect the current.

[0069] The preparation method described above forms the aluminum electrode in a dot-like distribution and forms the P+ heavily doped local front surface field by opening an array of holes in the front passivation anti-reflection layer and disposing aluminum paste in the holes, and then performing first sintering at 700-950°C. The area of the aluminum electrode covering the front surface of the solar cell is effectively reduced. Then, by removing the oxide layer on the front surface of the aluminum electrode, the silver paste line printed on the front passivation anti-reflection layer contacts the area where the oxide layer of the aluminum electrode is removed. While ensuring direct contact between the silver paste line and the aluminum electrode, the silver paste line can be connected in series with multiple aluminum electrodes. The silver electrode in electrical contact with the aluminum electrode is further formed by second sintering. The silver electrode and the aluminum electrode connected in series form the front fine grid line of the back junction solar cell. Since the sintering temperature of the second sintering after printing the silver paste line is lower than the melting point of aluminum (for example, the melting point of aluminum under normal pressure is 660°C), which is much lower than the melting point of silver, the occurrence of silver-aluminum inter-diffusion and the formation of a composite center where the silver penetrates the aluminum electrode and contacts the P-type silicon substrate is effectively avoided, i.e., the metal recombination between silver and the P-type silicon substrate is effectively avoided, thereby reducing the carrier recombination of the P-type silicon substrate and the contact resistance between the surface of the P-type silicon substrate and the front fine grid line, and effectively improving the photoelectric conversion efficiency of the prepared back junction solar cell.

[0070] In addition, compared with the aluminum electrode, the silver electrode has a stronger current leading capacity. By forming the front fine grid line of the back junction solar cell through the silver electrode and the aluminum electrode connected in series, the width of the silver electrode can be reduced to ensure the current leading capacity of the front fine grid line, further reduce the shading area of the front of the back junction solar cell, reduce the consumption of silver paste, and effectively improve the photoelectric conversion efficiency and cost of the prepared back junction solar cell.

[0071] The cross-sectional structure and top view of the back junction solar cell prepared by the preparation method provided in each of the above embodiments can be shown in Figure 10 and Figure 11 .

[0072] As shown in Figure 10 and Figure 11 , the back junction solar cell can include:

[0073] a P-type silicon substrate 1;

[0074] a front passivation anti-reflection layer 2 formed on one main surface of the P-type silicon substrate 1;

[0075] a plurality of holes 3 arranged in an array on the front passivation anti-reflection layer 2;

[0076] a P+ heavily doped local front surface field 4 formed on the P-type silicon substrate 1 corresponding to the region of the hole 3;

[0077] an aluminum electrode 5 in contact with the P+ heavily doped local front surface field 4 and extending outward from the hole 3, wherein an oxide layer 6 is formed on the surface of the aluminum electrode 5;

[0078] and a silver electrode 7 connected in series with a plurality of aluminum electrodes 5, wherein the silver electrode 7 is in contact with the region of the aluminum electrode 5 from which the oxide layer 6 is stripped, and the silver electrode 7 and the aluminum electrode 5 connected in series form the front fine grid line of the back junction solar cell.

[0079] The P+ heavily doped local front surface field 4 is formed by the aluminum paste forming the aluminum electrode 5 and the P-type silicon substrate, and the P+ heavily doped local front surface field 4 corresponds to the aluminum electrode 5, that is, the aluminum electrode 5 is in contact with the P+ heavily doped local front surface field 4, and the projection of the aluminum electrode 5 on the second main surface of the P-type silicon substrate 1 falls on one P+ heavily doped local front surface field 4. The width of the P+ heavily doped local front surface field 4 is generally greater than or equal to the width of the aluminum electrode 5. In a preferred embodiment, the width of the P+ heavily doped local front surface field 4 is equal to the width of the aluminum electrode 5, so as to realize the front surface field while reducing the shading of the light absorption area of the back junction solar cell by the local front surface field 4, which is conducive to improving the photoelectric conversion efficiency of the back junction solar cell.

[0080] In addition, as shown in Figure 10As shown in the drawings, the back junction solar cell further comprises a tunneling oxide layer 8, an N-type doped polysilicon layer 9 and a back passivation anti-reflection layer 10 formed on the other main surface (first main surface) of the P-type silicon substrate 1. The front metal-semiconductor recombination can be reduced, the front metal-semiconductor contact resistance can be lowered, the influence of the doped silicon layer on the absorption of incident light can be avoided, and the current collection efficiency of the solar cell is improved.

[0081] Further, the width of the region where the oxide layer 6 is peeled off in the aluminum electrode 5 of the back junction solar cell is generally less than the width of the aluminum electrode 5, so as to better control the width of the narrow silver electrode and reduce the consumption of silver paste.

[0082] Further, in the back junction solar cell, the width of the silver electrode 7 is less than or equal to the width of the region where the oxide layer 6 is peeled off in the aluminum electrode 5. The conductivity of the silver electrode is effectively utilized, and the performance of the silver electrode is not wasted.

[0083] The embodiment of the present application also provides a photovoltaic module, which can comprise the cell piece made of the back junction solar cell of the above-mentioned embodiment.

[0084] The embodiment of the present application also provides a power station, which can comprise the photovoltaic module provided by the above-mentioned embodiment.

[0085] The preparation method is described in detail below with two specific embodiments.

[0086] Embodiment 1:

[0087] Step A1, using atomic deposition technology, depositing a 1.4 nm thick silicon dioxide tunneling oxide layer on one main surface of a P-type silicon substrate at a deposition temperature of 100-500℃;

[0088] Step B1, using an LPCVD (Low Pressure Chemical Vapor Deposition) device, growing an intrinsic polysilicon layer or an intrinsic amorphous silicon layer on the tunneling oxide layer; then using an ion implantation device, implanting phosphorus ions into the intrinsic polysilicon layer or the intrinsic amorphous silicon layer, and performing high-temperature annealing, wherein the annealing temperature is 800-950℃, and the polysilicon layer or the amorphous silicon layer implanted with phosphorus ions forms an N-type doped silicon layer with a thickness of 100-200 nm after annealing;

[0089] Step C1, using silicon oxide and silicon oxynitride, forming a back passivation anti-reflection layer on the N-type doped silicon layer and a front passivation anti-reflection layer on the other main surface of the P-type silicon substrate;

[0090] Step D1, opening a plurality of holes in an array on the front passivation anti-reflection layer;

[0091] Step E1, printing aluminum paste on the hole position respectively, printing silver paste on the back passivation anti-reflection layer;

[0092] Step F1, first sintering at 900℃, so that the P-type silicon substrate and the aluminum paste doped to form P+ heavily doped local front surface field, at the same time, forming the front aluminum electrode and the back silver electrode, and the back silver electrode burns through the back passivation anti-reflection layer and the N-type doped silicon layer to form electrical connection;

[0093] Step G1, stripping the part of the oxide layer covering the front of the aluminum electrode;

[0094] Step H1, printing multiple silver paste lines on the front passivation anti-reflection layer, wherein each silver paste line is in contact with multiple aluminum electrodes whose oxide layer is stripped, so that each silver paste line is connected in series with the multiple aluminum electrodes whose oxide layer is stripped;

[0095] Step I1, second sintering at 500℃ for the P-type silicon substrate with printed silver paste lines to form silver electrodes, and the formed silver electrodes and the aluminum electrodes they are connected in series constitute the front fine grid lines of the back junction solar cell.

[0096] Example 2:

[0097] Step A2, using LPCVD equipment to deposit a 3nm thick silicon dioxide tunneling oxide layer on one main surface of the P-type silicon substrate;

[0098] Step B2, using PVD equipment to grow an intrinsic polysilicon layer or an intrinsic amorphous silicon layer on the tunneling oxide layer; then using ion implantation equipment to implant phosphorus ions into the intrinsic polysilicon layer or the intrinsic amorphous silicon layer, and performing high-temperature annealing, wherein the annealing temperature is 800-950℃, and the polysilicon layer or the amorphous silicon layer implanted with phosphorus ions forms a 100-200nm N-type doped silicon layer after annealing;

[0099] Step C2, using silicon oxide and silicon oxynitride to form a back passivation anti-reflection layer on the N-type doped silicon layer and a front passivation anti-reflection layer on the other main surface of the P-type silicon substrate;

[0100] Step D3, opening multiple holes arranged in an array on the front passivation anti-reflection layer;

[0101] Step E4, printing aluminum paste on the hole position respectively, printing silver paste on the back passivation anti-reflection layer;

[0102] Step F2, first sintering at 850℃, so that the P-type silicon substrate and the aluminum paste doped to form P+ heavily doped local front surface field, at the same time, forming the front aluminum electrode and the back silver electrode, and the back silver electrode burns through the back passivation anti-reflection layer and the N-type doped silicon layer to form electrical connection;

[0103] Step G2, stripping part of the oxide layer on the front side of the aluminum electrode;

[0104] Step H2, printing a plurality of silver paste lines on the front side passivation anti-reflection layer, wherein each silver paste line is in contact with a plurality of aluminum electrodes with the oxide layer stripped on the front side, so that each silver paste line is connected in series with the plurality of aluminum electrodes with the oxide layer stripped on the front side;

[0105] Step I2, second sintering at 450℃ of the P-type silicon substrate with the silver paste lines printed thereon to form silver electrodes, the silver electrodes and the aluminum electrodes connected in series with them constituting the front side fine grid lines of the back junction solar cell.

[0106] The above description is only used to help understand the method, structure and core idea of the present application. For those skilled in the art, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also belong to the scope of protection of the claims of the present application.

Claims

1. A method for fabricating a back-junction solar cell, characterized in that, include: Step a: To create an array of holes (3) in the front passivation antireflection layer (2) formed on the P-type silicon substrate (1); Step b: Aluminum paste is placed in the plurality of holes (3), wherein the aluminum paste is in contact with the region of the P-type silicon substrate corresponding to the hole (3); Step c: The P-type silicon substrate (1) with aluminum paste in the hole (3) is sintered for the first time so that the contact area between the aluminum paste and the P-type silicon substrate (1) forms a P+ heavily doped local front surface field (4), and forms an aluminum electrode (5) and an oxide layer (6) covering the aluminum electrode. The sintering temperature is 700℃~950℃. Step d: Peel off the oxide layer (6) covering the front side of the aluminum electrode (5); Step e: Print multiple silver paste lines on the front passivation antireflection layer (2), wherein each silver paste line is in contact with the front of multiple aluminum electrodes (5) with oxide layers removed, so that each silver paste line is connected in series with the multiple aluminum electrodes (5) with oxide layers removed that it contacts. Step f: The P-type silicon substrate (1) on which the silver paste lines are printed is sintered a second time to form a silver electrode (7), wherein the sintering temperature of the second sintering is lower than the melting point of aluminum, and the formed silver electrode (7) and the aluminum electrode (5) connected in series thereto constitute the front fine grid lines of the back junction solar cell.

2. The method for preparing a back-junction solar cell according to claim 1, characterized in that, Also includes: Step a0: A tunneling oxide layer (8) and an N-type doped polysilicon layer (9) are stacked from the inside to the outside on the first main surface of the P-type silicon substrate (1); a front passivation antireflection layer (2) is formed on the second main surface of the P-type silicon substrate (1) and a back passivation antireflection layer (10) is formed on the back side of the N-type doped polysilicon layer (9), wherein the front passivation antireflection layer (2) and the back passivation antireflection layer (10) are formed simultaneously.

3. The method for preparing a back-junction solar cell according to claim 2, characterized in that, After step b and before step c, it also includes: Step b': Print silver paste onto the back passivation antireflection layer (10) formed on the P-type silicon substrate (1); Step c further includes: during the first sintering process, simultaneously sintering the silver paste printed on the back passivation antireflection layer (10) so that the silver paste penetrates the back passivation antireflection layer (10) and forms a contact with the N-type doped polycrystalline silicon layer (9) to form a back silver electrode (11).

4. The method for fabricating a back-junction solar cell according to claim 1, characterized in that, The width of the oxide layer (6) stripped in step d is smaller than the width of the aluminum electrode (5) formed in step c.

5. The method for preparing a back-junction solar cell according to claim 1 or 4, characterized in that, The width of the silver paste line printed in step e is less than or equal to the width of the oxide layer (6) stripped in step d.

6. The method for fabricating a back-junction solar cell according to claim 1, characterized in that, Step d includes: in a stripping chamber filled with protective gas, stripping the oxide layer (6) on the front side of the aluminum electrode (5) by laser stripping or plasma stripping; And / or, The sintering temperature for the second sintering is 300℃~550℃.

7. The method for preparing a back-junction solar cell according to claim 2, characterized in that, The back passivation antireflection layer (10) formed in step a0 includes at least one of aluminum oxide, silicon oxide, gallium oxide, silicon nitride, aluminum nitride, and silicon oxynitride; And / or, The front passivation antireflection layer (2) formed in step a0 includes at least one of aluminum oxide, silicon oxide, gallium oxide, silicon nitride, aluminum nitride, and silicon oxynitride.

8. A back-junction solar cell prepared according to any one of the preparation methods of claims 1 to 7, characterized in that, include: P-type silicon substrate (1); A front passivation antireflection layer (2) is formed on a main surface of the P-type silicon substrate (1); Multiple holes (3) arranged in an array on the front passivation antireflection layer (2); A P+ heavily doped local front surface field (4) is formed in the region corresponding to the hole (3) on the P-type silicon substrate (1); An aluminum electrode (5) is in contact with the P+ heavily doped local front surface field (4) and extends outward from the hole (3), wherein an oxide layer (6) is formed on the surface of the aluminum electrode; And a silver electrode (7) connected in series with multiple aluminum electrodes (5), wherein the silver electrode (7) is in contact with the area of ​​the aluminum electrode (5) where the oxide layer (6) has been stripped, and the silver electrode (7) and the aluminum electrode (5) connected in series thereto constitute the front fine grid lines of the back junction solar cell.

9. The back-junction solar cell according to claim 8, characterized in that, Also includes: A tunneling oxide layer (8), an N-type doped polysilicon layer (9), and a back passivation antireflection layer (10) are stacked on another main surface of the P-type silicon substrate (1).

10. The back-junction solar cell according to claim 8, characterized in that, The width of the region in the aluminum electrode (5) where the oxide layer (6) has been stripped is smaller than the width of the aluminum electrode (5); And / or, The width of the silver electrode (7) is less than or equal to the width of the region in the aluminum electrode (5) where the oxide layer (6) has been stripped.

Images