Solar cells and photovoltaic modules

Abstract

Embodiments of the present application relate to the field of photovoltaics, and particularly to a solar cell and a photovoltaic module, which include a substrate, a tunneling layer, a field passivation layer, a first passivation film sequentially disposed on the back surface of the substrate, and a first electrode that penetrates the first passivation film to form a contact with the field passivation layer; the doping concentration of the first doping element in the tunneling layer is less than the doping concentration of the first doping element in the field passivation layer, and the doping concentration of the first doping element in the tunneling layer is greater than the doping concentration of the first doping element in the substrate; the field passivation layer includes a first doping region and a second doping region, and the doping curve slope of the first doping region is greater than the doping curve slope of the second doping region. In the embodiments of the present application, the doping concentration of the first doping element in the field passivation layer is higher than that in the tunneling layer and the substrate, and a relatively high activation rate of the first doping element is achieved on the surface layer of the field passivation layer, which is beneficial to improving the passivation effect of the solar cell and enhancing the conversion efficiency of the solar cell.

Description

Technical Field

[0001] Embodiments of the present application relate to the field of photovoltaics, and in particular to a solar cell and a photovoltaic module. Background Art

[0002] Conventional fossil fuels for photovoltaic modules are being depleted day by day. Among all sustainable energy sources, solar energy is undoubtedly one of the cleanest, most common, and most promising alternative energy sources. Currently, among all solar cells, crystalline silicon solar cells are one of the solar cells that have been widely commercially promoted. This is because silicon materials have extremely rich reserves in the earth's crust. At the same time, crystalline silicon solar cells have excellent electrical and mechanical properties compared with other types of solar cells. Therefore, crystalline silicon solar cells occupy an important position in the field of photovoltaics.

[0003] With the continuous development of solar cell technology, the recombination loss in the metal contact region has become one of the important factors restricting the further improvement of the conversion efficiency of solar cells. In order to improve the conversion rate of solar cells, the solar cells are often passivated by passivated contacts to reduce the recombination inside and on the surface of the solar cells. Commonly used passivated contact cells include heterojunction with intrinsic thin-layer (HIT) cells and tunnel oxide passivated contact (TOPCon) cells. However, the conversion efficiency of existing passivated contact cells needs to be improved. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a solar cell and a photovoltaic module, so as to improve the passivation effect of the solar cell and increase the conversion efficiency of the solar cell.

[0005] To solve the above problems, an embodiment of the present application provides a solar cell, including: a substrate, a tunneling layer, a field passivation layer, a first passivation film, and a first electrode that are sequentially disposed on the back surface of the substrate, wherein the first electrode penetrates the first passivation film and forms a contact with the field passivation layer; wherein, the substrate, the tunneling layer, and the field passivation layer all include the same first doping element, and the doping concentration of the first doping element in the tunneling layer is less than the doping concentration of the first doping element in the field passivation layer, and the doping concentration of the first doping element in the tunneling layer is greater than the doping concentration of the first doping element in the substrate; the field passivation layer includes a first doping region and a second doping region, and the second doping region is closer to the tunneling layer than the first doping region; wherein, the slope of the doping curve of the first doping region is greater than the slope of the doping curve of the second doping region; the first doping element is activated by annealing to obtain an activated first doping element; the slope of the doping curve is the slope of the curve of the doping concentration of the activated first doping element changing with the doping depth; in the direction from the upper surface of the substrate to the back surface of the substrate, the substrate includes a first region, a second region, and a third region; wherein, the second region is located between the first region and the third region; the first region is closer to the upper surface of the substrate than the second region, and the third region is closer to the back surface of the substrate than the second region; the doping concentration of the second doping element in the second region and the doping concentration of the second doping element in the third region are both less than the doping concentration of the second doping element in the first region.

[0006] In addition, during the process of the back surface of the substrate facing the inside of the substrate, the slope of the doping curve of the substrate gradually increases and tends to be stable.

[0007] In addition, the slope of the doping curve of the substrate is less than or equal to the average value of the slope of the doping curve of the second doping region.

[0008] In addition, the doping concentration of the activated first doping element in the field passivation layer is 1×10 20 atom / cm 3 ~5×10 20 atom / cm 3 ; the activation rate of the first doping element in the field passivation layer is 50% - 70%; the activation rate is the ratio of the doping concentration of the activated first doping element to the concentration of the total implanted first doping element.

[0009] In addition, in the direction of the tunneling layer facing the substrate, the slope of the doping curve of the tunneling layer gradually decreases.

[0010] In addition, the slope of the doping curve of the first doping region is 5×10 18 ~1×10 19 ; the slope of the doping curve of the second doping region is -5×10 18 ~5×10 18 .

[0011] In addition, the slope of the doping curve of the tunneling layer is -2.5×10 19~ -2.5×10 18 ; The doping curve slope of the substrate is -2.5×10 19 ~0.

[0012] In addition, in the direction perpendicular to the surface of the substrate, the thickness of the field passivation layer is 60 nm to 130 nm, and the thickness of the tunneling layer is 0.5 nm to 3 nm.

[0013] In addition, the above solar cell further includes: a second passivation film disposed on the upper surface of the substrate in sequence and a second electrode penetrating the second passivation film.

[0014] In addition, after the second doping element is annealed and activated, an activated second doping element is obtained; the doping concentration of the activated second doping element on the upper surface of the substrate is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3 ; The concentration of the total implanted doping elements of the second doping element on the upper surface of the substrate is 1.5×10 19 atom / cm 3 ~1×10 20 atom / cm 3 .

[0015] In addition, the doping concentration of the activated second doping element in the first region is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3 .

[0016] In addition, the distance between the bottom surface of the first region and the upper surface of the substrate is 350 nm to 450 nm; the distance between the bottom surface of the second region and the upper surface of the substrate is 1000 nm to 1200 nm; the distance between the bottom surface of the third region and the upper surface of the substrate is 1200 nm to 1600 nm.

[0017] In addition, the activation probability of the second doping element in the first region is 20% to 40%; the activation probability of the second doping element in the second region is 60% to 90%; the activation probability of the second doping element in the third region is 5% to 90%; the activation probability is the ratio of the doping concentration of the annealed and activated second doping element to the concentration of the total implanted second doping element.

[0018] The embodiment of the present application further provides a photovoltaic module, including: a battery string, a packaging layer, and a cover plate, the battery string is formed by connecting the above solar cells; the packaging layer is used to cover the surface of the battery string; the cover plate is used to cover the surface of the packaging layer away from the battery string.

[0019] Compared with the prior art, the technical solution provided by the embodiment of the present application has the following advantages:

[0020] Embodiments of the present application provide a solar cell and a photovoltaic module, including a substrate, a tunneling layer, a field passivation layer, a first passivation film, and a first electrode; wherein, the substrate, the tunneling layer, and the field passivation layer are all doped with a first doping element, and the doping concentration of the first doping element in the field passivation layer is greater than that in the tunneling layer and the substrate, and as the doping depth increases, the doping concentration of the first doping element gradually decreases. The slope of the doping curve of the first doping element shows a gradient distribution as the doping depth increases; in the first doping region of the field passivation layer, the slope of the doping curve first decreases, and then stabilizes near 0 in the second doping region, indicating that the change in the doping concentration of the first doping element is relatively large at the surface layer of the field passivation layer and then tends to be stable; in the tunneling layer, the slope of the doping curve of the first doping element is negative and decreases significantly, indicating that the doping concentration of the first doping element gradually decreases and the decrease amplitude is large; in the substrate, the slope of the doping curve of the first doping element gradually increases and tends to be stable. The doping concentration of the first doping element in the field passivation layer in the embodiments of the present application is higher than that in the tunneling layer and the substrate, and the first doping element achieves a high activation rate in the surface layer of the field passivation layer, which is beneficial to improving the passivation effect of the solar cell and the conversion efficiency of the solar cell. Description of the Drawings

[0021] Figure 1 Schematic structural diagram of a solar cell provided by an embodiment of the present application;

[0022] Figure 2 Curve graph showing the change of the doping concentration of the first doping element with the doping depth in the solar cell provided by an embodiment of the present application;

[0023] Figure 3 Distribution graph showing the change of the slope of the doping curve of the first doping element with the doping depth in the solar cell provided by an embodiment of the present application;

[0024] Figure 4 Curve graph showing the change of the doping concentration of the second doping element with the doping depth in the solar cell provided by an embodiment of the present application;

[0025] Figure 5 Distribution graph showing the change of the activation probability of the second doping element with the doping depth in the solar cell provided by an embodiment of the present application;

[0026] Figure 6 Schematic structural diagram of a photovoltaic module provided by an embodiment of the present application. Detailed Embodiments

[0027] As known from the background art: Currently, the tunnel oxide passivated contact (TOPCon) cell has received continuous attention due to its excellent surface passivation effect, high theoretical efficiency, and good compatibility with traditional production lines. The most significant feature of the TOPCon technology is its laminated structure of high-quality ultra-thin silicon oxide and heavily doped polycrystalline silicon (poly-Si). Therefore, phosphorus diffusion doping is an important part of it. The excellent passivated contact on the back of TOPCon needs to form a field effect through phosphorus diffusion doping to achieve.

[0028] Currently, the research on doping phosphorus mainly focuses on the distribution of phosphorus in Poly-Si. The research on the concentration change and distribution of phosphorus in Poly-Si-SiO x -Si is not perfect yet, and it is impossible to optimize the field effect and passivated contact essentially, so as to further improve the efficiency of solar cells.

[0029] In order to improve the conversion efficiency of solar cells and optimize the field effect and passivated contact essentially, the embodiments of this application propose a solar cell. The doping concentration of the first doping element in the field passivation layer is higher than that in the tunneling layer and the substrate, and a relatively high activation rate of the first doping element is achieved on the surface layer of the field passivation layer, which is beneficial to improving the passivation effect of the solar cell and the conversion efficiency of the solar cell. The embodiments of this application also analyze the doping concentration distribution of phosphorus in Poly-Si-SiO x -Si of the solar cell, so as to provide a basis for the improvement of the phosphorus doping process and the efficiency increase of the cell.

[0030] Referring to Figure 1 , the embodiments of this application provide a solar cell, including: a substrate 10, a tunneling layer 121, a field passivation layer 122, a first passivation film 123, and a first electrode 124 that are sequentially arranged on the back surface of the substrate 10. The first electrode 124 penetrates the first passivation film 123 and forms a contact with the field passivation layer 122. Among them, the substrate 10, the tunneling layer 121, and the field passivation layer 122 all include the same first doping element, and the doping concentration of the first doping element in the tunneling layer 121 is less than that in the field passivation layer 122, and the doping concentration of the first doping element in the tunneling layer 121 is greater than that in the substrate 10. The field passivation layer 122 includes a first doping region and a second doping region, and the second doping region is closer to the tunneling layer 121 than the first doping region. Among them, the doping curve slope of the first doping region is greater than that of the second doping region. The first doping element is activated after annealing to obtain an activated first doping element. The doping curve slope is the slope of the curve of the doping concentration of the activated first doping element changing with the doping depth. In the direction of the tunneling layer 121 facing the substrate 10, the doping curve slope of the tunneling layer 121 gradually decreases.

[0031] The substrate 10 is used to receive incident light and generate photo-generated carriers. In some embodiments, the back surface of the substrate 10 is disposed opposite to the upper surface, and both the back surface and the upper surface of the substrate 10 can be used to receive incident light or reflect light.

[0032] In some embodiments, the substrate 10 can be a silicon substrate, and the material of the silicon substrate can include at least one of single-crystalline silicon, polycrystalline silicon, amorphous silicon, or microcrystalline silicon. The substrate 10 can be an N-type semiconductor substrate, that is, the substrate 10 is doped with an N-type first doping element. The first doping element can be any one of phosphorus, arsenic, or antimony. Specifically, when the first doping element is phosphorus, phosphorus diffusion can be performed on the back surface of the substrate 10 through a doping process (for example, thermal diffusion, ion implantation, etc.), so that the tunneling layer 121, the field passivation layer 122, and the substrate 10 are all doped with phosphorus, and the phosphorus is activated by annealing treatment to obtain activated phosphorus.

[0033] The tunneling layer 121 is used to achieve interface passivation of the back surface of the substrate 10 and facilitate the migration of carriers through the tunneling effect; in some embodiments, the tunneling layer 121 can be formed by a deposition process, for example, a chemical vapor deposition process can be used. In some other embodiments, the tunneling layer 121 can also be formed by an in-situ generation process. Specifically, the tunneling layer 121 can include a dielectric material that provides passivation and tunneling effects, such as oxides, nitrides, semiconductors, conductive polymers, etc. For example, the material of the tunneling layer 121 can include silicon oxide, silicon nitride, silicon oxynitride, intrinsic amorphous silicon, intrinsic polycrystalline silicon, etc. In some instances, the tunneling layer 121 may not actually be a perfect tunnel barrier because it can contain defects such as pinholes, which can cause other charge carrier transport mechanisms (such as drift, diffusion) to dominate over the tunneling effect.

[0034] The field passivation layer 122 is used to form field passivation. In some embodiments, the material of the field passivation layer 122 can be doped silicon. Specifically, in some embodiments, the field passivation layer 122 and the substrate 10 have doping elements of the same conductivity type. The doped silicon can include one or more of N-type doped polycrystalline silicon, N-type doped microcrystalline silicon, or N-type doped amorphous silicon. Preferably, the material of the field passivation layer 122 is a phosphorus-doped polycrystalline silicon layer. In some embodiments, the field passivation layer 122 can be formed by a deposition process. Specifically, intrinsic polycrystalline silicon can be deposited on the back surface of the tunneling layer 121 away from the substrate 10 to form a polycrystalline silicon layer, and the first doping element is doped by ion implantation and source diffusion to form an N-type doped polycrystalline silicon layer, and the N-type doped polycrystalline silicon layer is used as the field passivation layer 122. In some embodiments, N-type doped amorphous silicon can be first formed on the back surface of the tunneling layer 121 away from the substrate 10, and then an N-type doped polycrystalline silicon layer is formed after high-temperature treatment.

[0035] See Figure 1 The first passivation film 123 is a back passivation film, which is formed on the side of the field passivation layer 122 away from the back surface of the substrate 10. In some embodiments, the material of the first passivation film 123 may be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, or silicon carbon oxynitride. Specifically, in some embodiments, the first passivation film 123 may be a single-layer structure. In other embodiments, the first passivation film 123 may also be a multi-layer structure. In some embodiments, the first passivation film 123 may be formed by a plasma enhanced chemical vapor deposition (PECVD) method.

[0036] The first passivation film 123 passivates the defects in the field passivation layer 122 existing on the back surface of the substrate 10, removes the recombination sites of minority carriers, thereby increasing the open-circuit voltage of the solar cell. In addition, a first antireflection film may be provided on the side of the first passivation film 123 away from the back surface of the substrate 10. The first antireflection film reduces the reflectivity of the light incident on the back surface of the substrate 10, thereby increasing the amount of light reaching the tunnel junction formed by the substrate 10 and the through layer 121, thereby increasing the short-circuit current (Isc) of the solar cell. Therefore, the first passivation film 123 and the first antireflection film can increase the open-circuit voltage and short-circuit current of the solar cell, thereby improving the conversion efficiency of the solar cell.

[0037] In some embodiments, the first antireflection film may be formed of various materials capable of preventing surface reflection. For example, the material of the first antireflection film may be one or more of silicon nitride, hydrogen-containing silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, MgF2, ZnS, TiO2, or CeO2. Specifically, in some embodiments, the first antireflection film may be a single-layer structure. In other embodiments, the first antireflection film may also be a multi-layer structure. In some embodiments, the first antireflection film may be formed by a PECVD method.

[0038] In some embodiments, the first electrode 124 penetrates the first passivation film 123 to form an electrical connection with the field passivation layer 122. Specifically, the first electrode 124 is electrically connected to the field passivation layer 122 via an opening formed in the first passivation film 123 (i.e., while the first electrode 124 penetrates the first passivation film 123).

[0039] In some embodiments, the method of forming the first electrode 124 may include: printing a conductive paste on the surface of the first passivation film 123 in a preset area, and the conductive material in the conductive paste may be at least one of silver, aluminum, copper, tin, gold, lead, or nickel; sintering the conductive paste, for example, sintering may be performed at a peak temperature of 750°C to 850°C to form the first electrode 124.

[0040] In some embodiments, for Figure 1 the solar cell described above, when the first doping element is phosphorus, the concentration of activated phosphorus atoms and the total implanted phosphorus atoms in the phosphorus diffusion doping process can be measured by Electrochemical Capacitance Voltage (ECV) and Secondary Ion Mass Spectrometry (SIMS), and the distribution curves of the concentration of activated phosphorus atoms and the total implanted phosphorus atoms with the doping depth can be obtained, as Figure 2 shown. As can be seen from Figure 2 , the distribution trend of the total implanted phosphorus element concentration in the field passivation layer 122, the tunneling layer 121, and the substrate 10 is that the doping concentration gradually decreases. In the field passivation layer 122 (Poly-Si thin film), the concentration of activated phosphorus element is about 3×10 20 atom / cm 3 , and the total implanted phosphorus element concentration is about 5×10 20 atom / cm 3 , and the activation rate of phosphorus element is 50%-70%, achieving a high probability of phosphorus element activation.

[0041] Referring to Figure 2 , the field passivation layer 122 includes a first doping region with a high doping concentration and a second doping region with a doping concentration lower than that of the first doping region. Therefore, the passivation effect when light is incident on the field passivation layer 122 is improved. At the same time, the contact resistance between the field passivation layer 122 and the first electrode 124 can also be reduced, thereby improving the conversion efficiency of the solar cell.

[0042] As Figure 2 shown, there is an obvious doping concentration peak in the total implanted phosphorus element concentration spectrum obtained by SIMS testing. This is mainly because the chemical environment of phosphorus element changes on both sides of the interface between the field passivation layer 122 and the tunneling layer 121 (Poly-Si-SiO x thin film), which affects the ionization rate of phosphorus element. Especially in the SiO x thin layer of the tunneling layer 121, there is a rich oxygen element, which will increase the signal intensity of phosphorus element in the SIMS positive ion test mode, resulting in a higher measured doping concentration. When the test depth reaches the single crystal silicon layer where the substrate 10 is located, the signal intensity will gradually stabilize and become stable.

[0043] As an example, by combining ECV and SIMS testing, it can be found that the interface depth positions of Poly-Si-SiO x and SiO x -Si are approximately 94 nm and 101 nm respectively. AsFigure 2 As shown, at the position from the surface layer of the in-situ passivation layer 122 to the tunneling layer 121 (interface depth 0 nm to 94 nm), the total implanted phosphorus element concentration is about 5×10 20 atom / cm 3 , and the change trend is stable; at the position with an interface depth of about 94 nm, the total implanted phosphorus element concentration begins to fluctuate, and there is a doping concentration peak in the range of the interface depth approximately between 94 nm and 101 nm; after the interface depth is greater than 101 nm, the total implanted phosphorus element concentration gradually decreases and reaches stability at an interface depth of about 310 nm. Between the interface depths of 310 nm and 500 nm, the total implanted phosphorus element concentration is between 5×10 18 atom / cm 3 ~5×10 19 atom / cm 3 . And the activated phosphorus element concentration is about 3×10 20 atom / cm 3 at the position from the surface layer of the in-situ passivation layer 122 to the tunneling layer 121 (interface depth 0 nm to 94 nm), and the change trend is stable; at the position with an interface depth of about 94 nm, the activated phosphorus element concentration drops significantly; after the interface depth is greater than 101 nm, the change trend of the activated phosphorus element concentration is a slow decrease, and it reaches the lowest value near the position with an interface depth of 160 nm.

[0044] It should be noted that the doping curve is the relationship between the phosphorus doping concentration (unit: atom / cm 3 ) and the doping depth (unit: nm). The slope of the doping curve is the slope of the curve of the doping concentration of the annealed-activated phosphorus element changing with the doping depth.

[0045] Figure 3 shows the gradient distribution of the slope of the phosphorus element doping curve with the doping depth, which can more clearly analyze the change of the phosphorus element doping concentration in the TOPCon structure. As Figure 3 shown, the dividing line between the first doping region and the second doping region is the dotted line D, the dividing line between the tunneling layer 121 (SiO x thin film) and the second doping region is the dotted line E, and the dividing line between the tunneling layer 121 and the substrate 10 is the dotted line C. In the first doping region of the in-situ passivation layer 122 (Poly-Si thin film), the slope of the phosphorus element doping curve decreases significantly. In the second doping region, the decreasing amplitude of the slope of the phosphorus element doping curve slows down and then stabilizes near 0, indicating that the change amplitude of the phosphorus doping concentration is large in the first doping region of the in-situ passivation layer 122 (which can also be called the Poly-Si surface layer), and then the change of the phosphorus doping concentration in the first doping region of the in-situ passivation layer 122 tends to be stable; in the tunneling layer 121 (SiO xIn the thin film), the slope of the phosphorus doping curve is negative and decreases significantly, indicating that the phosphorus doping concentration gradually decreases and the decreasing amplitude gradually becomes larger.

[0046] In some embodiments, during the process of the back surface of the substrate 10 facing the inside of the substrate 10, the slope of the doping curve of the substrate 10 gradually increases and tends to be stable. As Figure 3 shown, in the substrate 10, as the interface depth increases, the slope of the doping curve of phosphorus in the substrate 10 gradually increases and tends to be stable, indicating that the decreasing amplitude of the doping concentration of phosphorus in the substrate 10 slows down and gradually tends to be stable.

[0047] In some embodiments, the slope of the doping curve of the substrate 10 is less than or equal to the average value of the slope of the doping curve of the second doping region. Continuing to refer to Figure 3 , the slope of the doping curve of the substrate 10 gradually increases and tends to a stable value, and this stable value is approximately equal to the average value of the slope of the doping curve of the second doping region.

[0048] In some embodiments, the doping concentration of the activated first doping element in the field passivation layer 122 is 1×10 20 atom / cm 3 ~5×10 20 atom / cm 3 ; the activation rate of the first doping element in the field passivation layer 122 is 50% - 70%; the activation rate is the ratio of the doping concentration of the activated first doping element to the concentration of the total implanted first doping element.

[0049] As Figure 2 shown, when the first doping element is phosphorus, the doping concentration of the activated phosphorus in the field passivation layer 122 can be 1×10 20 atom / cm 3 、2×10 20 atom / cm 3 、3×10 20 atom / cm 3 、4×10 20 atom / cm 3 or 5×10 20 atom / cm 3 ; preferably, the doping concentration of the activated phosphorus in the field passivation layer 122 can be 3×10 20 atom / cm 3 , the concentration of the total implanted phosphorus element is about 5×10 20 atom / cm 3 , and the activation rate of the first doping element in the field passivation layer 122 is 50% - 70%, achieving a relatively high probability of phosphorus element activation.

[0050] In some embodiments, the doping curve slope of the first doping region is 5×10 18 ~1×10 19 ; the doping curve slope of the second doping region is -5×10 18 ~5×10 18 .

[0051] As Figure 3 shown, at the position where the depth from the surface layer to the interface of the field passivation layer 122 is about 10 mn, it is the first doping region, and the doping curve slope of the first doping region decreases significantly; in the second doping region, the doping curve slope first decreases gently (the interface depth is about 10 nm - 20 mn), the doping curve slope is stable in the region where the interface depth is about 20 nm, and remains stable and continues until the interface position of the Poly-Si-SiO x film (the interface depth is about 94 mn).

[0052] In some embodiments, the doping curve slope of the tunneling layer 121 is -2.5×10 19 ~-2.5×10 18 ; the doping curve slope of the substrate 10 is -2.5×10 19 ~0.

[0053] Please continue to refer to Figure 3 , within the interface depth range from the tunneling layer 121 to the substrate 10, that is, Figure 3 within the interface depth range from the SiO x film to the crystalline silicon layer, the doping curve slope begins to decrease significantly (as shown at point A in Figure 3 ), from 2.5×10 18 decreasing significantly to -2.5×10 19 . This is mainly because phosphorus elements enter the SiO x film from the Poly-Si film, and the chemical environment where the phosphorus elements are located changes, affecting the ionization rate of the phosphorus elements, resulting in a significant decrease in the doping concentration of the phosphorus elements. Within the interface depth range from the back surface of the substrate 10 (Si) to the upper surface of the substrate 10, the doping curve slope begins to increase significantly (as shown at point B in 19 Figure 3 ), until 2.5×10 18 x , and then the phosphorus doping curve slope tends to be stable. As can be seen from Figure 3 , the doping curve slope curves on the left and right sides of the interface position of the SiO x -Si are approximately symmetric about the dashed line C in Figure 3 , and the phosphorus doping curve slope after stabilization in the substrate 10 is approximately equal to the average value of the doping curve slopes of the second doping region. From Figure 3It can be seen that the center line of the slope of the phosphorus doping curve in the second doping region is approximately flush with the center line of the slope of the phosphorus doping curve stabilized in the substrate 10.

[0054] In some embodiments, in the direction perpendicular to the surface of the substrate 10, the thickness of the field passivation layer 122 is 60 nm to 130 nm, and the thickness of the tunneling layer 121 is 0.5 nm to 3 nm.

[0055] In some embodiments, in order to provide sufficient passivation and tunneling effects, the thickness of the tunneling layer 121 can be 0.5 nm to 3 nm. When the thickness of the tunneling layer 121 exceeds 3 nm, tunneling cannot be effectively performed, and the solar cell may not work. When the thickness of the tunneling layer 121 is less than 0.5 nm, the passivation performance may deteriorate. In order to further improve the tunneling effect, the thickness of the tunneling layer 121 can also be 0.5 nm to 2 nm, or the thickness of the tunneling layer 121 can also be 0.5 nm to 1 nm.

[0056] In some embodiments, the thickness of the substrate 10 is 130 μm to 250 μm.

[0057] The embodiments of the present application provide a solar cell and a photovoltaic module, which provide a theoretical basis for optimizing the field effect, passivation contact, and cell efficiency improvement by analyzing the activation rate and doping curve slope of phosphorus atoms in the phosphorus diffusion doping process of the solar cell. Through the above analysis, it is known that the activation rate of phosphorus atoms in the field passivation layer 122 is 50%-70%; in the Poly-Si thin film, the slope of the phosphorus atom doping curve first decreases and then stabilizes at 5×10 18 to -5×10 18 range. In the SiO x thin film, the slope of the phosphorus atom doping curve decreases from about -1×10 18 to about -3×10 19 . In the crystalline silicon, the slope of the phosphorus atom doping curve gradually increases and stabilizes at -1×10 17 to -1×10 18 range.

[0058] In some embodiments, the above solar cell further includes: an emitter 111, a second passivation film 112, and a second electrode 114 that are sequentially disposed on the upper surface of the substrate 10 and penetrate the second passivation film 112 to form a contact with the emitter 111; wherein, the substrate 10 further includes a second doping element.

[0059] Specifically, the manufacturing process of the above solar cell includes: First, deposit a P-type doping source on the upper surface of the substrate 10 to form a thin film layer. Then, diffuse the P-type doping source in the thin film layer in a preset area into the substrate 10 through a doping process to form an emitter 111 inside the substrate 10 in the preset area.

[0060] In some embodiments, the P-type doping source is an element or compound containing trivalent elements such as boron tribromide or boron trichloride. In some embodiments, when the P-type doping source is a boron source, the second doping element is boron; an element or compound containing trivalent elements such as boron tribromide or boron trichloride can be used as the doping source. Specifically, the second doping element in a preset region can be diffused into the upper surface of the substrate 10 through a doping process (for example: laser doping process, plasma positioning doping process or ion implantation process).

[0061] In some embodiments, before forming the thin film layer on the upper surface of the substrate 10, the upper surface of the substrate 10 is pre-treated, including cleaning the substrate 10 and texturing the upper surface of the substrate 10; specifically, a pyramidal texture structure can be formed on the upper surface of the substrate 10 by processes such as chemical etching, laser etching, mechanical method or plasma etching. On the one hand, it can increase the roughness of the upper surface of the substrate 10, so that the reflectivity of the upper surface of the substrate 10 to incident light is small, thereby increasing the absorption and utilization rate of incident light. On the other hand, compared with the upper surface of the substrate 1 being a flat surface, the presence of the pyramidal texture structure increases the surface area of the upper surface of the substrate 10. Therefore, more second doping elements can be stored on the upper surface of the substrate 10, which is beneficial to forming an emitter 111 with a higher concentration. In some embodiments, the emitter 111 is a doped layer diffused to a certain depth on the upper surface of the substrate 10, forming a PN junction structure in the substrate 10.

[0062] See Figure 1 , the second passivation film 112 is a front passivation film, formed on the side of the emitter 111 away from the upper surface of the substrate 10. The material of the second passivation film 112 can be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride or carbon oxynitride. Specifically, in some embodiments, the second passivation film 112 can be a single-layer structure. In other embodiments, the second passivation film 112 can also be a multi-layer structure. In some embodiments, the second passivation film 112 can be formed by the PECVD method.

[0063] In addition, a second antireflection film can be provided on the side of the second passivation film 112 away from the upper surface of the substrate 10. The second antireflection film reduces the reflectivity of light incident on the upper surface of the substrate 10, thereby increasing the amount of light reaching the tunnel junction formed by the substrate 10 and the emitter 111, thereby increasing the short-circuit current (Isc) of the solar cell. Therefore, the second passivation film 112 and the second antireflection film can increase the open-circuit voltage and short-circuit current of the solar cell, thereby improving the conversion efficiency of the solar cell.

[0064] In some embodiments, the material of the second anti-reflection film is the same as that of the first anti-reflection film. For example, the material of the second anti-reflection film can be one or more of silicon nitride, hydrogenated silicon nitride, silicon oxide, silicon oxynitride, aluminum oxide, MgF2, ZnS, TiO2 or CeO2. Specifically, in some embodiments, the second anti-reflection film can be a single-layer structure. In other embodiments, the second anti-reflection film can also be a multi-layer structure. In some embodiments, the second anti-reflection film can be formed by a PECVD method.

[0065] In some embodiments, the second electrode 114 penetrates the second passivation film 112 to form an electrical connection with the emitter 111. Specifically, the second electrode 114 is electrically connected to the emitter 111 via an opening formed in the second passivation film 112 (that is, the second electrode 114 penetrates the second passivation film 112). Specifically, the method of forming the second electrode 114 can be the same as the method of forming the first electrode 124, and the material of the second electrode 114 can also be the same as the material of the first electrode 124.

[0066] In some embodiments, for Figure 1 In the solar cell, the second doping element is activated by annealing to obtain an activated second doping element; the doping concentration of the activated second doping element on the upper surface of the substrate 10 is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3 The total implanted doping element concentration of the second doping element on the upper surface of the substrate 10 is 1.5×10 19 atom / cm 3 ~1×10 20 atom / cm 3 .

[0067] In some embodiments, the doping concentration of the activated second doping element on the upper surface of the substrate 10 may be, for example, 5×10 18 atom / cm 3 ,9×10 18 atom / cm 3 , 1×10 19 atom / cm 3 , 1.2×10 19 atom / cm 3 or 1.5 × 10 19 atom / cm 3 The total implanted doping element concentration of the second doping element on the upper surface of the substrate 10 may be, for example, 1.5×10 19 atom / cm 3 , 3×10 19 atom / cm3 , 6×10 19 atom / cm 3 , 8×10 19 atom / cm 3 , 1×10 20 atom / cm 3 .

[0068] Preferably, the doping concentration of the activated second doping element on the upper surface of the substrate 10 is 1×10 19 atom / cm 3 ; the concentration of the total implanted doping element of the second doping element on the upper surface of the substrate 10 is 3×10 19 atom / cm 3 ~5×10 19 atom / cm 3 .

[0069] In some embodiments, for Figure 1 the solar cell described above, the distribution curves of the activated boron element concentration and the total implanted boron element concentration with the doping depth are obtained through ECV testing and SIMS testing, as Figure 4 shown. As can be seen from Figure 4 , the total implanted boron element concentration on the surface layer of crystalline silicon is about 3×10 19 atom / cm 3 , and as the doping depth increases, the total implanted boron concentration shows a trend of first increasing and then decreasing, reaching the peak concentration at a depth of about 300 nm, which is about 5×10 19 atom / cm 3 . The activated boron element concentration shows the same change trend as the total implanted boron element concentration, and the activated boron concentration on the surface layer is about 1×10 19 atom / cm 3 , and also reaches the peak at a depth of 300 nm.

[0070] In some embodiments, in the direction from the upper surface of the substrate 10 to the back surface of the substrate 10, the substrate 10 includes a first region, a second region, and a third region; wherein, the second region is located between the first region and the third region; the first region is closer to the upper surface of the substrate 10 than the second region, and the third region is closer to the back surface of the substrate 10 than the second region; the doping concentration of the second doping element in the second region and the doping concentration of the second doping element in the third region are both less than the doping concentration of the second doping element in the first region.

[0071] In some embodiments, the doping concentration of the activated second doping element in the first region is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3。

[0072] In some embodiments, the distance between the bottom surface of the first region and the upper surface of the substrate 10 is 350 nm to 450 nm; the distance between the bottom surface of the second region and the upper surface of the substrate 10 is 1000 nm to 1200 nm; the distance between the bottom surface of the third region and the upper surface of the substrate 10 is 1200 nm to 1600 nm.

[0073] As Figure 4 shown, the interface depth of the first region is approximately at a position near 400 nm, and the doping concentration of the activated boron element in the surface layer of the first region is 1×10 19 atom / cm 3 . As the doping depth increases, the doping concentration of the activated boron element in the first region first increases slowly, reaching the highest point (the doping concentration is about 1.5×10 19 atom / cm 3 ), and then decreases slowly (the doping concentration is about 1.1×10 19 atom / cm 3 ); the doping concentration of the activated boron element in the second region continues to decrease until it reaches around 1×10 18 atom / cm 3 ; the doping concentration of the activated boron element in the third region continues to decrease to reach the lowest value, approximately around 1×10 17 atom / cm 3 .

[0074] In some embodiments, the activation probability of the second doping element in the first region is 20% to 40%; the activation probability of the second doping element in the second region is 60% to 90%; the activation probability of the second doping element in the third region is 5% to 90%; the activation probability is the ratio of the doping concentration of the annealed-activated second doping element to the concentration of the total implanted second doping element.

[0075] When at the surface layer of the substrate 10, due to the high concentration of the total implanted boron element and the low surface layer doping concentration, the activation probability of the doping element in the first region is 20% to 40%; when in the second region and the third region, as the doping depth increases, the concentration of the total implanted boron element decreases, and the activation probability increases. When the doping depth is greater than 1100 nm, the activation probability of the boron element during diffusion reaches the limit at a doping depth of 1100 nm. When the doping depth continues to increase, the activation probability drops sharply.

[0076] Figure 5The gradient distribution curve of the activation probability of boron atoms with doping depth in the boron diffusion doping process is shown. By measuring the activation probability data of boron atoms at different doping depths and performing data fitting, a fitting curve is obtained. From the fitting curve, it can be known that the activation probability of boron atoms in the silicon crystal surface layer and the shallow junction region (doping depth less than 400 nm) is relatively low, about 33% or so, indicating that the dead layer problem is mainly concentrated in this part of the region, and targeted adjustment can be carried out through the diffusion process. When the doping depth exceeds 400 nm, the activation probability of boron atoms gradually increases and reaches a peak at about 1100 nm, and the peak activation probability is in the range of 60%-90%. When the doping depth further increases, the activation probability of boron atoms drops sharply. Thus, it can be seen that the activation probability of boron atoms in the surface layer of the substrate 10 (doping depth from 0 nm to 400 nm) is relatively stable, in the range of 20%-40%; when the doping depth increases from 400 nm to 1400 nm, the activation probability of boron atoms first increases and then decreases, and the peak position is at a doping depth of 1000 nm to 1200 nm, and the peak activation probability is in the range of 60%-90%.

[0077] See Figure 6 , an embodiment of the present application further provides a photovoltaic module, including: a battery string 101, a packaging layer 102, and a cover plate 103. The battery string 101 is formed by connecting the solar cells provided in the above embodiment; the packaging layer 102 is used to cover the surface of the battery string 101; the cover plate 103 is used to cover the surface of the packaging layer 102 away from the battery string 101.

[0078] In some embodiments, the solar cells can be electrically connected in the form of a whole piece or multiple segments to form multiple battery strings 101, and the multiple battery strings 101 are electrically connected in series and / or in parallel.

[0079] Specifically, in some embodiments, the multiple battery strings 101 can be electrically connected through a conductive strip 104. The packaging layer 102 covers the front and back of the solar cells. Specifically, the packaging layer 102 can be an organic packaging film such as an ethylene-vinyl acetate copolymer (EVA) film, a polyethylene octene copolymer (POE) film, or a polyethylene terephthalate (PET) film. In some embodiments, the cover plate 103 can be a glass cover plate, a plastic cover plate, or other cover plates 103 with a light-transmitting function. Specifically, the surface of the cover plate 103 facing the packaging layer 102 can be a concave-convex surface, so as to increase the utilization rate of incident light.

[0080] The embodiments of the present application provide a solar cell and a photovoltaic module. By doping a first doping element on the back surface of the substrate 10 and a second doping element on the upper surface of the substrate 10, and the doping concentration of the first doping element in the field passivation layer is higher than that in the tunneling layer and the substrate, and a relatively high activation rate is achieved in the surface layer of the field passivation layer for the first doping element, which is beneficial to improving the passivation effect of the solar cell and enhancing the conversion efficiency of the solar cell. In addition, by increasing the activation probability of the second doping element in the surface layer of the upper surface of the substrate, the doping distribution of the second doping element in the surface layer of the substrate and the shallow junction region is improved, the influence of the dead layer is reduced, and the overall performance of the solar cell is improved, thereby enhancing the conversion efficiency of the solar cell.

[0081] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make respective changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A solar cell, characterized in that, Comprising: A substrate (10); A tunneling layer (121), a field passivation layer (122), a first passivation film (123) sequentially disposed on the back surface of the substrate (10), and a first electrode (124) that penetrates the first passivation film (123) and forms contact with the field passivation layer (122); Wherein, the substrate (10), the tunneling layer (121), and the field passivation layer (122) all include the same first doping element, and the doping concentration of the first doping element in the tunneling layer (121) is less than the doping concentration of the first doping element in the field passivation layer (122), and the doping concentration of the first doping element in the tunneling layer (121) is greater than the doping concentration of the first doping element in the substrate (10); The field passivation layer (122) includes a first doping region and a second doping region, and the second doping region is closer to the tunneling layer (121) than the first doping region; wherein, the doping curve slope of the first doping region is greater than the doping curve slope of the second doping region; the first doping element is activated after annealing to obtain an activated first doping element; the doping curve slope is the slope of the curve of the doping concentration of the activated first doping element varying with the doping depth; In the direction from the upper surface of the substrate (10) towards the back surface of the substrate (10), the substrate (10) includes a first region, a second region, and a third region; wherein, the second region is located between the first region and the third region; the first region is closer to the upper surface of the substrate (10) than the second region, and the third region is closer to the back surface of the substrate (10) than the second region; The doping concentration of the second doping element in the second region and the doping concentration of the second doping element in the third region are both less than the doping concentration of the second doping element in the first region; when the doping depth is 0 - 300 nm, the doping concentration of the activated second doping element in the substrate (10) increases with the increase of the doping depth.

2. The solar cell according to claim 1, characterized in that, During the process of the back surface of the substrate (10) facing towards the inside of the substrate (10), the doping curve slope of the substrate (10) gradually increases and tends to be stable.

3. The solar cell according to claim 2, wherein The doping curve slope of the substrate (10) is less than or equal to the average value of the doping curve slopes of the second doping region.

4. The solar cell according to claim 1, wherein The doping concentration of the activated first doping element in the field passivation layer (122) is 1×10 20 atom / cm 3 ~5×10 20 atom / cm 3 ; The activation rate of the first doping element in the field passivation layer (122) is 50% - 70%; the activation rate is the ratio of the doping concentration of the activated first doping element to the concentration of the total implanted first doping element.

5. The solar cell according to claim 1, characterized in that, In the direction of the tunneling layer (121) facing the substrate (10), the doping curve slope in the tunneling layer (121) gradually decreases.

6. The solar cell according to claim 1, characterized in that, The doping curve slope of the first doping region is 5×10 18 ~1×10 19 ; the doping curve slope of the second doping region is -5×10 18 ~5×10 18 .

7. The solar cell according to claim 6, characterized in that, The doping curve slope of the tunneling layer (121) is -2.5×10 19 ~ -2.5×10 18 ; the doping curve slope of the substrate (10) is -2.5×10 19 ~0.

8. The solar cell according to claim 1, characterized in that, In the direction perpendicular to the surface of the substrate (10), the thickness of the field passivation layer (122) is 60 nm - 130 nm, and the thickness of the tunneling layer (121) is 0.5 nm - 3 nm.

9. The solar cell according to claim 1, characterized in that, Further comprising: A second passivation film (112) and a second electrode (114) that penetrates the second passivation film (112) sequentially disposed on the upper surface of the substrate (10).

10. The solar cell according to claim 9, wherein, The second doping element is activated after annealing to obtain an activated second doping element; the doping concentration of the activated second doping element on the upper surface of the substrate (10) is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3 ; The concentration of the total implanted doping elements of the second doping element on the upper surface of the substrate (10) is 1.5×10 19 atom / cm 3 ~1×10 20 atom / cm 3 .

11. The solar cell according to claim 10, characterized in that, The doping concentration of the activated second doping element in the first region is 5×10 18 atom / cm 3 ~1.5×10 19 atom / cm 3 .

12. The solar cell according to claim 10, wherein, The distance between the bottom surface of the first region and the upper surface of the substrate (10) is 350 nm to 450 nm; The distance between the bottom surface of the second region and the upper surface of the substrate (10) is 1000 nm to 1200 nm; The distance between the bottom surface of the third region and the upper surface of the substrate (10) is 1200 nm to 1600 nm.

13. The solar cell according to claim 10, characterized in that, The activation probability of the second doping element in the first region is 20% to 40%; The activation probability of the second doping element in the second region is 60% to 90%; The activation probability of the second doping element in the third region is 5% to 90%; The activation probability is the ratio of the doping concentration of the activated second doping element to the concentration of the second doping element injected in total.

14. A photovoltaic module, characterized in that, Comprising: A battery string (101), which is formed by connecting a plurality of solar cells as described in any one of claims 1 to 13; An encapsulation layer (102), which is used to cover the surface of the battery string (101); A cover plate (103), which is used to cover the surface of the encapsulation layer (102) away from the battery string (101).

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