Back contact solar cell and method of manufacturing the same, solar cell module

Abstract

The present disclosure relates to the technical field of solar cells, and discloses a back contact solar cell, a preparation method thereof and a battery assembly. The back contact solar cell comprises a substrate layer, a first polarity structure, a second polarity structure and an isolation groove. The substrate layer comprises a light-receiving surface and a back surface arranged oppositely. The first polarity structure and the second polarity structure are alternately formed on the back surface side of the substrate layer. The isolation groove is formed between the first polarity structure and the second polarity structure and extends into the substrate layer. The bottom of the isolation groove is formed with a chamfer structure at the end close to the first polarity structure and / or the second polarity structure. The chamfer structure is recessed from the bottom surface of the isolation groove towards the light-receiving surface side. The chamfer structure of the present disclosure is deeper than the depth of the isolation groove, effectively blocking the conduction between the diffusion atoms of different polarities, and can further narrow the width of the bottom of the isolation groove, while enhancing the effective internal reflection of the back surface side to the incident sunlight, improving the optical performance of the cell.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of solar cells, in particular to a back contact solar cell and a preparation method and a cell module thereof. BACKGROUND

[0002] A back contact solar cell (BC cell for short) is a new type of solar cell technology in which the positive and negative electrodes are both moved to the back surface of the cell, which can eliminate the shading loss of the grid lines on the front surface of the traditional solar cell, significantly improve the light absorption efficiency and appearance consistency of the cell, and become an important technical direction in the photovoltaic field.

[0003] In order to effectively prevent short circuit conduction between different polarity regions on the back side of the existing back contact solar cell, an isolation region is often formed between the n region structure and the p region structure when the n region structure and the p region structure are constructed, and the size of the isolation region is relatively wide and the depth is relatively deep, so that the different polarity doping atoms on the two sides cannot be interconnected through the isolation region. However, in this structure, on the one hand, the excessively wide isolation region will reduce the effective passivation area on the back surface of the cell, thereby reducing the overall surface passivation performance, and on the other hand, the excessively deep isolation region will also induce the generation of leakage, thereby affecting the performance of the back contact solar cell. SUMMARY

[0004] Therefore, the present disclosure provides a back contact solar cell and a preparation method and a cell module thereof to solve the problem that the isolation region structure of the existing back contact solar cell affects the performance of the cell.

[0005] In a first aspect, the present disclosure provides a back contact solar cell, comprising: a substrate layer, a first polarity structure, a second polarity structure and an isolation groove, the substrate layer comprising a light-receiving surface and a back surface arranged oppositely; the first polarity structure and the second polarity structure are alternately formed on the back surface side of the substrate layer; the isolation groove is formed between the first polarity structure and the second polarity structure and extends into the substrate layer; a chamfer structure is formed at the end of the bottom of the isolation groove close to the first polarity structure and / or close to the second polarity structure, and the chamfer structure is recessed from the bottom surface of the isolation groove towards the light-receiving surface side.

[0006] In an optional embodiment, the cross-sectional size of the chamfer structure gradually decreases in the direction from the bottom of the isolation groove towards the light-receiving surface side.

[0007] In an optional embodiment, the maximum width size of the chamfer structure is greater than zero and less than or equal to 50 μm, and the depth size of the chamfer structure is greater than zero and less than or equal to 50 μm.

[0008] In an alternative embodiment, the side wall surface of the isolation groove close to the first polarity structure presents a first slope, and the side wall surface of the isolation groove close to the second polarity structure presents a second slope.

[0009] In an alternative embodiment, the first polarity structure comprises a first tunneling oxide layer and a first doped layer which are sequentially stacked, and the first tunneling oxide layer is relatively close to the back surface; and the second polarity structure comprises a second tunneling oxide layer and a second doped layer which are sequentially stacked, and the second tunneling oxide layer is relatively close to the back surface, and the second doped layer is opposite to the first doped layer in the conductive type.

[0010] In an alternative embodiment, when the conductive type of the first polarity structure is p-type and the conductive type of the second polarity structure is n-type, the second polarity structure extends into the back surface of the base layer, and the surface of the first polarity structure is higher than the surface of the second polarity structure.

[0011] In an alternative embodiment, the first polarity structure further comprises a first inner extension layer formed in the back surface of the base layer, the first inner extension layer is in contact with the first tunneling oxide layer and has the same conductive type as the first doped layer; and the second polarity structure further comprises a second inner extension layer formed in the back surface of the base layer, the second inner extension layer is in contact with the second tunneling oxide layer and has the same conductive type as the second doped layer.

[0012] In an alternative embodiment, the doping depth of the first polarity structure is greater than the doping depth of the second polarity structure.

[0013] In an alternative embodiment, the bottom surface of the isolation groove is further provided with a textured structure.

[0014] In a second aspect, the present disclosure further provides a preparation method of the back contact solar cell, for preparing the above-mentioned back contact solar cell, comprising:

[0015] providing a base layer, the base layer comprising a light receiving surface and a back surface which are oppositely arranged;

[0016] forming a first polarity structure and a second polarity structure on the back surface side of the base layer, the first polarity structure and the second polarity structure being alternately arranged;

[0017] forming an isolation groove between the first polarity structure and the second polarity structure, the isolation groove extending into the base layer, and a chamfer structure being formed at the end of the bottom of the isolation groove close to the first polarity structure and / or close to the second polarity structure, the chamfer structure being recessed from the bottom surface of the isolation groove towards the light receiving surface side.

[0018] In an alternative embodiment, the chamfer structure is formed in the isolation groove by a wet process or a laser process.

[0019] In a third aspect, the present disclosure further provides a back contact solar cell module comprising the back contact solar cell described above.

[0020] Beneficial effects: The present disclosure forms a downwardly recessed chamfer structure at the bottom of the isolation groove close to the end of the first polarity structure and / or the second polarity structure. On the one hand, the chamfer structure is deeper than the isolation groove, effectively blocking the conduction between the diffusion atoms of different polarities, reducing the risk of conduction between the different polarity structures on the back of the cell, and ensuring the power generation performance of the cell. On the other hand, the setting of the chamfer structure also narrows the width of the bottom of the isolation groove, so correspondingly, the width of the region where the doped first polarity structure and the second polarity structure on both sides are located will increase, which enhances the effective internal reflection of the incident sunlight on the back side, and improves the optical performance of the cell. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments of the present disclosure or the prior art, the drawings needed to be used in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is a structural schematic diagram of a back contact solar cell of an embodiment of the present disclosure;

[0023] Figure 2 is an electron microscope scanning schematic diagram of the isolation groove of the back contact solar cell of the embodiment of the present disclosure;

[0024] Figure 3 is an optical microscope scanning schematic diagram of the isolation groove of the back contact solar cell of the embodiment of the present disclosure;

[0025] Figure 4 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure when the cross-sectional shape of the chamfer structure is a rectangle;

[0026] Figure 5 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure when the cross-sectional shape of the chamfer structure is an inverted normal trapezoid;

[0027] Figure 6 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure when the cross-sectional shape of the chamfer structure is an inverted right-angle trapezoid;

[0028] Figure 7 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure when the cross-sectional shape of the chamfer structure is an inverted triangle;

[0029] Figure 8 is a flowchart of a preparation method of a back contact solar cell according to an embodiment of the present disclosure;

[0030] Figure 9 is an electrochemical-capacitance voltage curve of a back contact solar cell according to an embodiment of the present disclosure and a conventional back contact solar cell with respect to the atomic concentration of phosphorus doping on the n-poly surface varying with depth.

[0031] Explanation of reference signs:

[0032] 1, substrate layer; 11, light-receiving surface; 12, back surface;

[0033] 2, first polarity structure; 21, first tunneling oxide layer; 22, first doped layer; 23, first inner extension layer;

[0034] 3, second polarity structure; 31, second tunneling oxide layer; 32, second doped layer; 33, second inner extension layer;

[0035] 4, isolation groove; 41, first slope; 42, second slope;

[0036] 5, chamfer structure; 51, extension surface; 52, chamfer surface;

[0037] 6, textured structure. DETAILED DESCRIPTION

[0038] The present disclosure will be further described below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are intended to be illustrative only and not limiting of the present disclosure. In addition, it is to be understood that not all of the features described herein are necessarily included in every embodiment of the present disclosure. In the following description, descriptions of well-known functions and constructions are omitted for clarity and conciseness. Various structural diagrams according to embodiments of the present disclosure are shown in the accompanying drawings. These diagrams are not drawn to scale, in which certain details are shown in a somewhat exaggerated manner for the purpose of clarity and conciseness, and certain details can be omitted. The shapes of various regions, layers, and the relative sizes and positional relationships between them shown in the diagrams are merely exemplary, and in actuality, they can be deviated due to manufacturing tolerances or technical limitations, and a person skilled in the art can additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present disclosure, when a layer / element is referred to as being located “on” another layer / element, the layer / element can be directly located on the other layer / element, or there can be an intermediate layer / element therebetween. In addition, if a layer / element is located “on” another layer / element in one orientation, it can be located “under” the other layer / element when the orientation is reversed.

[0039] In the related art, an isolation region is arranged between the p-region structure and the n-region structure on the back surface of the back contact solar cell, which is generally a structure of a groove. In order to effectively prevent conduction of different polarity regions, the isolation region tends to be wide and deep, but the isolation region that is too wide will reduce the area of the structure region on both sides and weaken the passivation contact performance. Since the p-type material is generally deposited first in the cell preparation process, then a laser slotting and wet cleaning are performed to form a space for forming the n-region structure, then the n-type material is deposited, and finally a laser treatment and wet cleaning are performed again to remove the n-type material on the p-region structure and the isolation region, so as to finally form the p-region structure, the n-region structure and the isolation region. In this process, since the p-region material will be laterally etched in the wet cleaning process, there is a gap at the bottom of the p-region material, so that in the process of depositing the n-type material, the n-type material will partially enter the gap, and it is also difficult to remove subsequently, thereby forming a short circuit and leakage. The deeper the isolation region structure is, the longer the wet cleaning time is, and the larger the corresponding gap is, which will aggravate the leakage phenomenon.

[0040] Based on this, the present disclosure provides a back contact solar cell and a preparation method thereof, and a back contact solar cell module, to solve the problem of affecting the performance of the cell caused by improper design of the isolation region in the related solution.

[0041] Embodiment 1

[0042] Reference Figures 1 to 6 The present embodiment provides a back contact solar cell, which comprises a substrate layer 1, a first polarity structure 2, a second polarity structure 3 and an isolation groove 4. The substrate layer 1 comprises a light-receiving surface 11 and a back surface 12 arranged oppositely. The first polarity structure 2 and the second polarity structure 3 are alternately formed on the back surface 12 of the substrate layer 1. The isolation groove 4 is formed between the first polarity structure 2 and the second polarity structure 3 and extends into the substrate layer 1. A chamfer structure 5 is formed at the end of the bottom of the isolation groove 4 close to the second polarity structure 3, and the chamfer structure 5 is recessed from the bottom surface of the isolation groove 4 towards the light-receiving surface 11.

[0043] Specifically, the aforementioned substrate 1 is a silicon substrate, specifically an n-type substrate in this embodiment. The first polar structure 2 and the second polar structure 3 are structural layers of different polarities diffused on the backlight side of the substrate 1. For example, in this embodiment, the first polar structure 2 can be a p-type conductive layer, and the second polar structure 3 can be an n-type conductive layer. This is the case used for illustration in this embodiment. Of course, it is also possible that the first polar structure 2 is an n-type structural layer and the second polar structure 3 is a p-type structural layer. The aforementioned isolation groove 4 can be a trench structure that is relatively recessed in the surfaces of the first polar structure 2 and the second polar structure 3, obtained by laser etching and wet cleaning. In this embodiment, the isolation trench extends a certain distance into the substrate 1. For example, the height difference between the bottom surface of the isolation groove 4 and the backlight surface 12 of the substrate 1 can be greater than or equal to 2 μm. Based on this, in this embodiment, the bottom of the isolation groove 4 forms a locally recessed chamfered structure 5 at the end near the n-type conductive second polar structure 3, as shown in the reference. Figure 2 and Figure 3 The chamfered structure 5 shown is... Figure 1 and Figure 2 Both can be seen as along Figure 3 A schematic diagram of the cross-section cut by aa.

[0044] Furthermore, the chamfer structure 5 may include at least an extending surface 51 and a chamfer surface 52. The extending surface 51 extends from the intersection line of the second polar structure 3 and the bottom of the isolation groove 4 toward the base layer 1. The chamfer surface 52 extends from the bottom of the isolation groove 4 at a position with a small gap from the intersection line toward the base layer 1. An open chamfer structure 5 is formed between the extending surface 51 and the chamfer surface 52. (Refer to...) Figures 4 to 7 As shown, the cross-sectional shape of the chamfer structure 5 can be an inverted triangle, an inverted trapezoid, or a rectangle. For example, when both the extension surface 51 and the chamfer surface 52 are vertical surfaces, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfer structure 5 is rectangular. (Refer to...) Figure 4 As shown; when both the extension surface 51 and the chamfered surface 52 are inclined surfaces, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfered structure 5 is an inverted ordinary trapezoid or an inverted isosceles trapezoid, as shown in the reference. Figure 5 As shown; when one of the extension surface 51 and the chamfered surface 52 is a vertical surface and the other is an inclined surface, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfered structure 5 is a chamfered right trapezoid, as shown in the reference. Figure 6 As shown; when both the extension surface 51 and the chamfered surface 52 are inclined surfaces, and one end located inside the base layer 1 is directly connected, the cross-sectional shape of the chamfered structure 5 is an inverted triangle, as shown in the reference. Figure 7 As shown.

[0045] To sum up, in the back contact solar cell with the chamfer structure 5 formed at the bottom of the isolation groove 4, on the one hand, the chamfer structure 5 is deeper than the isolation groove 4, effectively blocking the conduction between the diffusion atoms of different polarities, reducing the risk of conduction between the structures of different polarities on the back of the cell, and ensuring the power generation performance of the cell; on the other hand, the chamfer structure 5 further narrows the width of the bottom of the isolation groove 4, so that the width of the regions where the first polarity structure 2 and the second polarity structure 3 are located on the two sides increases accordingly, which enhances the effective internal reflection of the sunlight entering the cell on the side of the back, and improves the optical performance of the cell.

[0046] Further, referring to the flowchart of the preparation method of the back contact solar cell shown in FIG. 8, the preparation method of the back contact solar cell specifically includes the following steps: Figure 8

[0047] In step S801, a substrate layer 1 is provided, which includes a light-receiving surface 11 and a back surface 12 arranged oppositely.

[0048] For example, a suitable silicon wafer is selected and polished on both sides to remove the cutting damage on the surface of the silicon wafer, so as to obtain a double-sided flat and clean substrate layer 1. In this embodiment, the substrate layer 1 is an n-type silicon wafer.

[0049] In step S802, a first polarity structure 2 and a second polarity structure 3 are formed on the back surface 12 side of the substrate layer 1, and the first polarity structure 2 and the second polarity structure 3 are arranged alternately.

[0050] Specifically, an initial first polarity layer can be first deposited on the substrate layer 1 by LPCVD technology; then the initial first polarity layer is processed by slotting on the back surface 12 side by means such as laser etching, which removes part of the substrate layer 1, and then alkali cleaning is performed to remove impurities; then the initial second polarity layer is deposited on the substrate layer 1 after slotting by LPCVD technology, which covers the remaining initial first polarity layer and the sidewall and bottom substrate layer 1 of the slotting area; then the initial second polarity layer on the initial first polarity layer is removed by means such as laser etching in the region adjacent to the initial second polarity layer deposited in the slotting area, to form the first polarity structure 2 and the second polarity structure 3 arranged alternately.

[0051] It can be known that the deposition of the initial first polarity layer and the initial second polarity layer is formed on the light-receiving surface 11, the back surface 12 and the sidewall of the substrate layer 1, which simplifies the processing technology. Based on this, after removing the initial second polarity layer on the initial first polarity layer, the deposited material on the light-receiving surface 11 side and the sidewall surface of the cell is removed by a chain method.

[0052] ​Step S803, a separation groove 4 is formed between the first polarity structure 2 and the second polarity structure 3, the separation groove 4 is deep into the base layer 1, and a chamfer structure 5 is formed at the end of the bottom of the separation groove 4 close to the second polarity structure 3, the chamfer structure 5 is recessed from the bottom surface of the separation groove 4 to the light receiving surface 11 side.

[0053] After the first polarity structure 2 and the second polarity structure 3 are formed as described above, the separation groove 4 can also be formed between the first polarity structure 2 and the second polarity structure 3 by means such as laser etching or wet etching, and at the same time, a chamfer structure 5 with a deeper depth is formed at the bottom edge of the formed separation groove 4. The chamfer structure 5 of the present embodiment can be formed only on the side close to the n-type second polarity structure 3. On the one hand, the chamfer structure 5 formed is deeper than the separation groove 4, effectively blocking the conduction between the diffusion atoms of different polarities, reducing the risk of conduction between different polarity structures on the back of the battery, and effectively ensuring the power generation performance of the battery; on the other hand, the chamfer structure 5 further narrows the width of the bottom of the separation groove 4, so correspondingly, the width of the region where the first polarity structure 2 and the second polarity structure 3 doped on both sides are located will increase, which enhances the effective internal reflection of the solar light entering the battery on the back side, and improves the optical performance of the battery.

[0054] In another embodiment, the chamfer structure 5 can also be arranged only at the end of the bottom of the separation groove 4 close to the first polarity structure 2 of the p-type conduction type; or arranged at both ends of the bottom of the separation groove 4.

[0055] It can be known that when the chamfer structure 5 is formed only on the side close to the n-type second polarity structure 3, or only on the side close to the p-type first polarity structure 2, or on both sides, the laser etching laser process can be adopted to complete, and a laser with a suitable wavelength is selected according to different depth requirements, for example, when a long-wavelength laser such as infrared light is selected, the penetration depth is deep; when a short-wavelength laser such as ultraviolet light is selected, the penetration depth is shallow. However, in the present embodiment, when the chamfer structure 5 is formed only on the side close to the n-type second polarity structure 3, the wet etching wet process method can also be preferably adopted. Specifically, on the one hand, when the initial second polarity layer is deposited, the side surface of the initial first polarity layer will also be deposited with the initial second polarity layer, and the subsequent laser is difficult to completely remove the initial second polarity structure 3 layer on the side surface of the first polarity structure 2, so that in the process of forming the isolation groove 4 by wet etching, the etching rate of the side surface of the first polarity structure 2 is slower than that of the second polarity structure 3; on the other hand, the diffusion layer with a higher doping atom concentration and an electron conduction type is more likely to react in the reaction process of wet etching, so the part close to the n-type second polarity structure 3 has a higher phosphorus atom doping concentration and an electron conduction type, and thus the chamfer structure 5 is formed faster. Such a wet etching method for forming the chamfer structure 5 is compatible with the subsequent wet cleaning step, and the process is simpler than laser etching.

[0056] Embodiment 2

[0057] On the basis of embodiment 1, in the back contact solar cell of the present embodiment 2, the cross-sectional size of the chamfer structure 5 gradually decreases in the direction from the bottom of the isolation groove 4 to the light-receiving surface 11, that is, in the direction from top to bottom as indicated by the arrow in the middle. Figure 1 Specifically, the cross-sectional size includes the size of the pattern obtained by cutting the chamfer structure 5 in the horizontal direction, which can include a length size and a width size. The length size is the extension size of the chamfer structure 5 in the second direction, and the width size is the size in the first direction. Since the length size changes little, the change in the cross-sectional size of the chamfer structure 5 can be considered as the change in the width size. Figure 3 Figure 1 , Figures 5 to 7 That is, at least one of the extension surface 51 and the chamfer surface 52 of the chamfer structure 5 is provided as an inclined surface, and as the depth size gradually increases, the cross-sectional size of the chamfer structure 5 gradually decreases, which helps to reduce the area of the recessed part and ensure uniform stress distribution of the whole cell to improve the strength of the cell.

[0058] Embodiment 3

[0059] ​In the back contact solar cell of this embodiment 3, the maximum width dimension of the chamfer structure 5 is greater than zero and less than or equal to 50 μm, and the depth dimension of the chamfer structure 5 is greater than zero and less than or equal to 50 μm, based on embodiment 2.

[0060] That is, when the chamfer structure 5 as a whole presents a structure whose cross-sectional dimension gradually decreases from top to bottom, the maximum cross-sectional dimension is at the bottom of the isolation groove 4, i.e., the plane where the uppermost portion is located. Figure 1 The maximum cross-sectional dimension in the horizontal direction under the viewing angle shown is within 50 μm, and the depth of the chamfer structure 5 in the vertical direction is within 50 μm. Within such a range, the chamfer structure 5 can achieve the optimal performance for the trench structure, the first polarity structure 2, and the second polarity structure 3, thereby achieving high power generation of the back contact solar cell. It can be understood that the width of the isolation trench is set to be 50-100 μm. Therefore, compared with setting the chamfer structure 5 at one end of the bottom of the isolation groove 4, setting the chamfer structure 5 at both ends of the bottom of the isolation groove 4 can appropriately reduce the width of the chamfer structure 5.

[0061] Embodiment 4

[0062] In the back contact solar cell of this embodiment 4, as shown in Figure 1 and Figure 2 The side wall surface of the isolation groove 4 close to the first polarity structure 2 presents a first slope 41, and the side wall surface of the isolation groove 4 close to the second polarity structure 3 presents a second slope 42.

[0063] The side wall surface of the isolation groove 4 close to the first polarity structure 2 and the second polarity structure 3 in this embodiment 4 is shaped as a slope, and the overall isolation groove 4 presents a "inverted trapezoidal" shape. Compared with the vertical side wall surface of the isolation groove 4, the side wall surface of the isolation groove 4 in this embodiment is shaped as a slope, which, on the one hand, makes the distance between the first polarity structure 2 and the second polarity structure 3 remain unchanged at the bottom region of the isolation groove 4, and the distance between the two increases at the top region, which can more effectively prevent the first polarity structure 2 and the second polarity structure 3 from short-circuiting and conducting, and reduce the risk of electric leakage; on the other hand, this design with a larger port opening size is more conducive to the uniform deposition of the passivation film on the back surface 12.

[0064] Embodiment 5

[0065] Based on embodiment 1, referring to Figure 1In the back contact solar cell of the present embodiment 5, the first polarity structure 2 comprises: a first tunneling oxide layer 21 and a first doped layer 22 which are sequentially stacked, the first tunneling oxide layer 21 is relatively close to the back light surface 12; the second polarity structure 3 comprises: a second tunneling oxide layer 31 and a second doped layer 32 which are sequentially stacked, the second tunneling oxide layer 31 is relatively close to the back light surface 12, and the second doped layer 32 is opposite to the first doped layer 22 in the conductive type.

[0066] Exemplarily, the first tunneling oxide layer 21 is an ultra-thin silicon oxide, and the first doped layer 22 is a p-type boron-doped polysilicon; the second tunneling oxide layer 31 is also an ultra-thin silicon oxide, and the second doped layer 32 is an n-type phosphorus-doped polysilicon, that is, the passivation contact structure of the back light surface 12 of the back contact cell of the present disclosure adopts the combination of the tunneling oxide layer and the polysilicon layer, the first polarity structure 2 and the second polarity structure 3 of different polarities are alternately arranged, the carrier recombination is effectively reduced, and the cell performance is improved.

[0067] Embodiment 6

[0068] On the basis of the embodiment 5, as shown in Figure 1 and Figure 2 In the back contact solar cell of the present embodiment 6, when the conductive type of the first polarity structure 2 is p-type and the conductive type of the second polarity structure 3 is n-type, the second polarity structure 3 extends into the back light surface 12 of the base layer 1, and the surface of the first polarity structure 2 is higher than the surface of the second polarity structure 3.

[0069] The first polar structure 2 of p-type is higher than the first polar structure 2 of n-type based on the preparation process. That is, the first polar structure 2 of p-type is prepared first and then the second polar structure 3 of n-type is prepared. After the first polar structure 2 of p-type is prepared, the second polar structure 3 of n-type is initially formed after the laser slotting removes part of the thickness of the substrate layer 1. The thickness of the first polar structure 2 and the second polar structure 3 is usually the same, so the first polar structure 2 is higher than the second polar structure 3, which helps to improve the passivation performance of the entire film of the first polar structure 2 of p-type and the second polar structure 3 of n-type. Specifically, the first polar structure 2 of p-type, especially the first doped layer 22 of p-type (also referred to as p-poly), has a higher preparation process temperature, usually between 950-1050 ℃, while the second polar structure 3 of n-type, especially the second doped layer 32 of n-type (also referred to as n-poly), has a lower preparation process temperature, usually between 850-950 ℃. If the n-poly is prepared first and then the p-poly is prepared, the high temperature in the preparation process of the p-poly will have a secondary effect on the n-poly, which will seriously damage the initial passivation performance of the n-poly. If the p-poly is prepared first and then the n-poly is prepared, the temperature of the n-poly is relatively lower than that of the p-poly, so the secondary effect is smaller, and the passivation performance of the entire p-poly and n-poly film is better.

[0070] As a preferred embodiment, the process of forming the second polar structure 3 later can specifically include the following steps:

[0071] Step P1, using a low-pressure chemical vapor deposition (LPCVD) device to deposit a first sub-layer of the second tunneling oxide layer 31 at a low temperature, wherein the flow rate of the oxygen introduced is 2000-10000 sccm, the flow rate of the nitrogen introduced is 5000-20000 sccm, the temperature of the deposition process is 300-500 ℃, the time is 50-200 s, and the thickness of the first sub-layer formed is 0.1-1 nm.

[0072] Specifically, since the tunneling oxide layer is thin, it is necessary to ensure the uniformity of the oxide layer grown on the silicon wafer between different regions in the tube during deposition. The process temperature for conventional deposition of the tunneling oxide layer is between 500 and 700 DEG C, and only oxygen is introduced, which can cause the oxide layer grown on the surface of the silicon wafer between different regions to be seriously uneven, because: first, the tube in the LPCVD device is relatively long (usually 2-3 meters) and has a large diameter (usually 0.4-0.5 meters), and when the tunneling oxide layer is deposited, the oxygen introduced cannot be uniformly diffused to all parts of the LPCVD tube in a short time, and the oxygen concentration in different regions will be high and low, thereby causing the oxide layer grown between different regions of the silicon wafer to be uneven. Secondly, a higher process temperature can also accelerate the reaction of oxygen with the surface of the silicon wafer, and under the premise that the oxygen concentration in different regions of the tube is inconsistent, the uneven growth of the oxide layer between different regions of the silicon wafer will be further aggravated. In addition, if oxygen is directly introduced into the tube, the oxygen concentration near the oxygen inlet will be generally higher, which will directly cause the oxide layer on the surface of the silicon wafer near the inlet to be thicker, and if the flow of oxygen introduced is reduced, the diffusion speed of oxygen will also be slower, and it is difficult to uniformly diffuse into the entire tube in a short time.

[0073] Based on this, the embodiment first adopts a low-temperature deposition method to pre-grow an oxide layer to form a first sub-layer of the second tunneling oxide layer 31. Since the reaction temperature is low, the oxidation reaction rate on the surface of the silicon wafer is also slow, which helps to reduce the thickness difference between the oxide layers in different regions on the surface of the silicon wafer. Secondly, nitrogen and oxygen are introduced together in the embodiment, which can reduce the concentration of oxygen introduced into the tube, so that the difference in oxygen concentration between different regions is not too large, and on the other hand, nitrogen can carry oxygen into the tube at the same time, and the flow rate is large, which can diffuse into all regions of the tube in a shorter time. Therefore, the low-temperature pre-deposition of part of the second tunneling oxide layer can help to grow a more uniform oxide layer between the silicon wafers in different regions of the tube.

[0074] In step P2, the temperature in the tube is raised without changing the flow rate of the introduced gas, and the second sub-layer of the second tunneling oxide layer 31 is formed at a higher temperature to accelerate the formation. The temperature range of the deposition process is 500-700 DEG C, the time range is 20-300 s, and the thickness range of the formed second sub-layer is 1-3 nm.

[0075] Since the oxygen concentration in different regions of the tube has become consistent after step P1, the rate of the oxide layer grown on the surface of the silicon wafer can be increased, the process time can be shortened, and the thickness of the oxide layer between different regions of the silicon wafer can also be ensured to have no obvious difference.

[0076] Step P3, then immediately after low-temperature deposition of the second intrinsic polysilicon layer, wherein the LPCVD method is used, the flow range of the silane (SiH4) is 300-2000 sccm, the deposition temperature range is 350-550 ℃ (the conventional process temperature is 550-600 ℃), the time range is 2-6 h, the working pressure range is 100-500 mTorr, and the thickness range of the second intrinsic polysilicon layer is 100-300 nm.

[0077] First, low-temperature deposition can reduce the thermal stress impact on the substrate layer 1 and other functional layers, and avoid lattice defects or interface degradation caused by high temperature. Second, under low-temperature process, the decomposition of silane and the deposition rate on the silicon wafer surface are slow, the stress concentration between silicon atoms can be relieved, and the hydrogen bond breakage is reduced, thereby significantly reducing the probability of film explosion, and the quality of the formed second intrinsic polysilicon layer is higher.

[0078] Step P4, in-pipe heating for one-time high-temperature pre-annealing crystallization treatment. The pre-annealing crystallization treatment first helps to increase the initial thin film grain size of the second intrinsic polysilicon layer, improve the crystallization rate, reduce the grain boundary density, improve the thin film quality, and improve the subsequent metal / semiconductor contact performance; second, it can also adjust the stoichiometric ratio and valence state of silicon atoms and oxygen atoms in the second tunnel oxide layer 31, to obtain higher quality of the second tunnel oxide layer 31; in addition, it can also increase the phosphorus atom doping concentration of the second intrinsic polysilicon layer in the subsequent phosphorus diffusion process (most of the atoms in the initial second intrinsic polysilicon layer exist in amorphous disordered form, and it is difficult for the doping atoms to replace or embed into or between silicon atoms, resulting in a decrease in the doping amount), and the increase in phosphorus doping concentration also means an increase in the number of electrons, which can improve the concentration difference between the n-type doped layer and the substrate layer 1 (n→n+→n++), improve the field passivation performance, and is also conducive to the subsequent metal / semiconductor contact; on the other hand, the increase in electron concentration and reaction rate is also conducive to the formation of the chamfer structure 5 near the second polarity structure 3 in the laser treatment + wet cleaning process, and finally improves the isolation performance of the isolation groove 4.

[0079] Since step P3 is a low-temperature deposition process, the corresponding second intrinsic polysilicon layer has small grain size and many grain boundaries. If high-temperature annealing treatment is directly performed in step P5, the crystallization rate of the initial intrinsic polysilicon layer will be too fast, the internal stress will not be fully released, the crystal lattice will be distorted, and the thin film quality will be affected. Therefore, after the deposition of the second intrinsic polysilicon layer, a higher-temperature pre-annealing treatment is simultaneously performed in-pipe integration, wherein the temperature range is 550-700 ℃, the time range is 1-3 h, and an inert gas atmosphere such as nitrogen, argon, etc. is simultaneously introduced.

[0080] Step P5, the silicon wafer with the second intrinsic polysilicon layer after the high-temperature pre-annealing crystallization treatment is moved to a phosphorus diffusion tube, and before phosphorus diffusion, a high-temperature annealing treatment is performed again to further increase the grain size and crystallization rate of the second intrinsic polysilicon layer. The two gradient annealing pre-crystallization treatments can sufficiently reduce the risk of insufficient stress release between lattices caused by high temperature, and improve the film quality. The temperature range of this high-temperature annealing treatment is 900-1050°C, and the time range is 2-6h, and an inert gas atmosphere is also introduced.

[0081] Step P6, phosphorus diffusion treatment is performed in the phosphorus diffusion tube to convert the surface layer and the inner layer of the second intrinsic polysilicon layer into a PSG layer and a phosphorus diffusion layer, respectively, and the phosphorus diffusion layer is the second doped layer 32. The diffusion temperature range is 750-850°C, the diffusion time range is 5-30min, the flow range of phosphorus oxychloride (POCl3) carried by nitrogen is 500-1200sccm, and the flow range of oxygen is 500-1000sccm; then oxygen is introduced for oxidation promotion, the temperature range is 850-950°C, the promotion time range is 20-60min, the flow range of oxygen is 1000-10000sccm, and a PSG layer with a thickness range of 30-70nm is generated.

[0082] Reference Figure 9 Compared with the traditional scheme of directly diffusing the intrinsic polysilicon layer, the second doped layer 32 has a relatively larger doping concentration, and the chamfer structure 5 can be formed synchronously by using the above two steps to form the second tunnel oxide layer 31 and the two pre-annealing treatments before diffusion to finally form the second polarity structure 3.

[0083] Embodiment 7

[0084] Based on Embodiment 6, referring to Figure 1 In the back contact solar cell of Embodiment 7, the first polarity structure 2 further includes a first inner diffusion layer 23 formed in the back light surface 12 of the base layer 1, the first inner diffusion layer 23 is in contact with the first tunnel oxide layer 21 and has the same conductivity type as the first doped layer 22; and the second polarity structure 3 further includes a second inner diffusion layer 33 formed in the back light surface 12 of the base layer 1, the second inner diffusion layer 33 is in contact with the second tunnel oxide layer 31 and has the same conductivity type as the second doped layer 32.

[0085] Specifically, when boron diffusion or phosphorus diffusion is performed on the intrinsic polysilicon, part of the diffusion atoms will enter the base layer 1 to form an inner diffusion layer, thereby forming a p-type first inner diffusion layer 23 of the p-type first polarity structure 2 and an n-type second inner diffusion layer 33 of the n-type second polarity structure 3, thereby enhancing the carrier collection capability and transmission performance, improving the contact performance of the base layer 1 and the passivation contact structure, reducing the recombination rate of the surface of the base layer 1, and improving the open-circuit voltage and conversion efficiency of the cell.

[0086] On this basis, the step S802 of forming the first polarity structure 2 and the second polarity structure 3 can include the following steps:

[0087] Step S8021, depositing an ultra-thin silicon oxide on the base layer 1 to form an initial first tunnel oxide layer;

[0088] Step S8022, depositing to form a first intrinsic polysilicon layer on the initial first tunnel oxide layer;

[0089] Step S8023, performing boron diffusion treatment on the first intrinsic polysilicon layer to form a boron-doped initial first doped layer, a boron-silicon glass layer (BSG layer) located on the outer surface of the initial first doped layer, and an initial first inner diffusion layer on the surface of the base layer 1;

[0090] Step S8024, first laser treatment, sequentially removing part of the boron-silicon glass layer, part of the initial first doped layer, part of the initial first tunnel oxide layer, and at least part of the initial first inner diffusion layer 23 to form a notch;

[0091] Step S8025, depositing an ultra-thin silicon oxide again to form an initial second tunnel oxide layer, the initial second tunnel oxide layer covering the boron-silicon glass layer and the notch;

[0092] Step S8026, forming a second intrinsic polysilicon layer on the initial second tunnel oxide layer;

[0093] Step S8027, performing phosphorus diffusion treatment on the second intrinsic polysilicon layer to form a phosphorus-doped initial second doped layer, a phosphorus-silicon glass layer (PSG layer) located on the outer surface of the initial second doped layer, and an initial second inner diffusion layer on the surface of the base layer 1;

[0094] Step S8028, second laser treatment, removing the phosphorus-silicon glass layer, the initial second doped layer, and the initial second tunnel oxide layer at the position of the preset first polarity structure 2 to expose the first polarity structure 2, and the notch is the second polarity structure 3, thereby forming the first polarity structure 2 and the second polarity structure 3 arranged alternately. Of course, the first polarity structure 2 and the second polarity structure 3 of this step are connected to each other, and need to be isolated by subsequent de-winding, forming an isolation groove 4 through a wet process, etc.

[0095] Embodiment 8

[0096] In the back contact solar cell of this embodiment 8 based on embodiment 7, the doping depth of the first polarity structure 2 is greater than the doping depth of the second polarity structure 3.

[0097] That is, the depth of boron diffusion in the above step S8023 is greater than the depth of phosphorus diffusion in step S8027, and specifically, the depth of boron diffusion is set to 1-2 μm in this embodiment, and the depth of phosphorus diffusion is set to 0.2-0.6 μm. In this way, on the premise that the surface of the first polarity structure 2 is higher than the surface of the second polarity structure 3, the different settings of the doping depths make the horizontal height difference of the diffused boron / phosphorus atoms smaller, which helps to balance the separation and migration rate of the electron-hole pairs generated by the base layer 1 to the p region and the n region, and improves the carrier transport and collection performance. Moreover, the diffusion depth of each doping atom is also an effective control means for cleaning intensity in the wet process. The doped region is often more easily etched by wet etching than the non-doped region. The higher surface of the first polarity structure 2 and the deeper doping depth of boron atoms can make the etching of the first polarity structure 2 and the second polarity structure 3 after the wet cleaning process be approximately at the same level, so that no obvious step structure is formed between them, which is beneficial to the uniform coverage of the subsequent passivation film.

[0098] Embodiment 9

[0099] Based on any one of the above embodiments 1-8, in the back contact solar cell of this embodiment 9, the bottom surface of the isolation groove 4 is further provided with a textured structure 6.

[0100] Specifically, in the process of forming the isolation groove 4 by wet process, the textured structure 6 is also formed at the bottom of the isolation groove 4, which facilitates the formation of the chamfer structure 5. It can be known that a larger textured structure 6 can also be formed on the light-receiving surface 11 of the base layer 1 to enhance the light trapping ability of the light-receiving surface 11.

[0101] Embodiment 10

[0102] This embodiment provides a back contact solar cell module, which comprises the back contact solar cell described in embodiments 1-9.

[0103] The back contact solar cell module of the embodiment includes several back contact solar cells, each of which has a chamfer structure 5 formed in the isolation groove 4 on the back surface 12, and the bottom of the isolation groove 4 forms a downwardly recessed chamfer structure 5 near one end of the second polarity structure 3 of the n-type conductive type. On the one hand, the chamfer structure 5 is deeper than the depth of the isolation groove 4, effectively blocking the conduction between the diffusion atoms of different polarities, reducing the risk of conduction between different polarity structures on the back of the cell, and ensuring the power generation performance of the cell. On the other hand, the setting of the chamfer structure 5 also further narrows the width of the bottom of the isolation groove 4, so correspondingly, the width of the region where the first polarity structure 2 and the second polarity structure 3 on both sides are doped will increase. This enhances the effective internal reflection of the solar light entering the cell on the back side, improves the optical performance of the cell, and ultimately improves the performance of the back contact solar cell module.

[0104] Further functional descriptions of the above structures are the same as those of the corresponding embodiments described above, and will not be described here.

[0105] In the above description, the patterning, etching and other technical details of each layer are not described in detail. However, those skilled in the art should understand that the layers, regions and the like with the required shape can be formed by various technical means. In addition, those skilled in the art can also design methods that are not exactly the same as the methods described above in order to form the same structure. In addition, although each embodiment is described above, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0106] Although the embodiments of the present disclosure are described in conjunction with the drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present disclosure, and such modifications and changes fall within the scope defined by the appended claims.

Claims

1. A back-contact solar cell, characterized in that, include: The base layer includes a light-receiving surface and a backlighting surface that are positioned opposite to each other; A first polar structure and a second polar structure are alternately formed on one side of the backlight surface of the substrate layer; An isolation groove is formed between the first polar structure and the second polar structure and extends into the base layer; The bottom of the isolation groove has a chamfered structure at the end near the first polar structure and / or near the second polar structure. The chamfered structure is recessed from the bottom surface of the isolation groove toward the light-receiving surface. The distance between the bottom of the chamfered structure and the backlight surface is greater than the distance between the bottom of the isolation groove and the backlight surface.

2. The back-contact solar cell according to claim 1, characterized in that, The cross-sectional dimensions of the chamfered structure gradually decrease from the bottom of the isolation groove toward the light-receiving surface.

3. The back-contact solar cell according to claim 2, characterized in that, The maximum width dimension of the chamfered structure is greater than zero and less than or equal to 50 μm, and the depth dimension of the chamfered structure is greater than zero and less than or equal to 50 μm.

4. The back-contact solar cell according to claim 1, characterized in that, The isolation groove forms a first slope near the side wall of the first polar structure, and the isolation groove forms a second slope near the side wall of the second polar structure.

5. The back-contact solar cell according to claim 1, characterized in that, The first polar structure includes: a first tunneling oxide layer and a first doped layer stacked sequentially, wherein the first tunneling oxide layer is relatively close to the backlight surface; The second polar structure includes: a second tunneling oxide layer and a second doped layer stacked sequentially, the second tunneling oxide layer being relatively close to the backlight surface, and the second doped layer having the opposite conductivity type to the first doped layer.

6. The back-contact solar cell according to claim 5, characterized in that, When the conductivity type of the first polar structure is p-type and the conductivity type of the second polar structure is n-type, the second polar structure extends into the back surface of the substrate layer, and the surface of the first polar structure is higher than the surface of the second polar structure.

7. The back-contact solar cell according to claim 6, characterized in that, The first polar structure further includes a first inner expansion layer formed in the backlight surface of the substrate layer, the first inner expansion layer being in contact with the first tunneling oxide layer and having the same conductivity type as the first doped layer; The second polar structure further includes a second inner expansion layer formed within the back surface of the substrate layer, the second inner expansion layer being in contact with the second tunneling oxide layer and having the same conductivity type as the second doped layer.

8. The back-contact solar cell according to claim 7, characterized in that, The doping depth of the first polar structure is greater than that of the second polar structure.

9. The back-contact solar cell according to any one of claims 1-8, characterized in that, The bottom surface of the isolation groove is also provided with a velvety structure.

10. A method for preparing a back-contact solar cell, used to prepare the back-contact solar cell according to any one of claims 1-9, characterized in that, include: A substrate layer is provided, the substrate layer comprising a light-receiving surface and a backlight surface disposed opposite to each other; A first polar structure and a second polar structure are formed on one side of the backlight surface of the substrate layer, and the first polar structure and the second polar structure are alternately arranged. An isolation groove is formed between the first polar structure and the second polar structure, the isolation groove extending into the substrate layer. The bottom of the isolation groove has a chamfered structure at the end near the first polar structure and / or near the second polar structure. The chamfered structure is recessed from the bottom surface of the isolation groove toward the light-receiving surface. The distance between the bottom of the chamfered structure and the backlight surface is greater than the distance between the bottom of the isolation groove and the backlight surface.

11. The method for fabricating a back-contact solar cell according to claim 10, characterized in that, The chamfered structure is formed in the isolation groove by a wet process or a laser process.

12. A back-contact solar cell module, characterized in that, include: The back-contact solar cell according to any one of claims 1-9.

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