Passivated contact cell, photovoltaic module and system
By using a self-limiting film layer and nickel/copper/tin composite electrode design in TOPCon batteries, the problems of high silver consumption and high contact resistivity are solved, and cost reduction and efficiency improvement are achieved.
Patent Information
- Application Number
- CN202421732779.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-19
- Publication Date
- 2025-07-22
- Estimated Expiration
- 2034-07-19
AI Technical Summary
The front and rear electrodes of existing TOPCon batteries are made of highly conductive silver materials, resulting in high material cost. The copper plating process cannot form a uniform and dense nickel seed layer, which cannot reduce the contact resistivity, and affects the photoelectric conversion efficiency.
The back structural layer is adopted, which includes a phosphorus-doped polysilicon layer, a carbon/phosphorus-doped polysilicon layer and a hydrogen/phosphorus-doped polysilicon layer, and a self-limiting film layer, combined with a nickel/copper/tin composite electrode, and a uniform and dense back metal electrode is formed by electroplating to replace the silver electrode and reduce silver consumption.
Reduces material costs, improves photoelectric conversion efficiency, forms better ohmic contact, reduces resistivity, and improves battery performance.
Smart Images
Figure CN223142403U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of solar cells, and particularly relates to a passivated contact cell, and also relates to a photovoltaic module and a photovoltaic system. Background Art
[0002] At present, efficient c-Si cell technologies include silicon heterojunction (HJT), tunnel oxide passivated contact (TOPCon), and back contact (BC). Among them, the TOPCon cell consists of a boron-doped emitter and a tunnel oxide layer / doped polysilicon layer. The tunnel oxide layer / doped polysilicon layer belongs to a passivated contact structure, which can selectively allow majority carriers to pass through the tunnel oxide layer and block minority carriers, realizing the spatial separation of minority carriers and majority carriers on the back side, greatly reducing recombination, and enabling the cell to have excellent open-circuit voltage and fill factor performance; moreover, TOPCon is widely regarded as one of the most promising c-Si technologies in the next-generation photovoltaic industry due to its high compatibility with traditional passivated emitter rear contact (PERC) technology on the production line and relatively low production line upgrade cost.
[0003] However, high-conductivity silver materials are used for both the front and back electrodes of TOPCon cells, resulting in a large amount of silver consumption, thereby increasing the material cost. Therefore, developing a metallization scheme with low silver consumption is particularly important for reducing the material cost and accelerating the market expansion of TOPCon. At the same time, in the electroplated copper process adopted, a uniform, dense, and void-free nickel seed layer cannot be formed in the metal area, and hydrogen bubble retention cannot be formed in the non-metal area, resulting in nickel seed layer deposition, which not only causes the electroplated phosphorus-doped polysilicon layer and the metal electrode to be unable to form a better ohmic contact and unable to reduce the contact resistivity; but also increases the processing cost, and the lower the photoelectric conversion efficiency. Summary of the Utility Model
[0004] The technical problem to be solved by the utility model is to overcome the deficiencies of the prior art and provide an improved passivated contact cell.
[0005] At the same time, the utility model also relates to a photovoltaic module and a photovoltaic system.
[0006] To solve the above technical problems, the technical solutions adopted by the utility model are as follows:
[0007] A passivated contact cell, which includes a silicon wafer body, a front structure layer, a back structure layer, a front metal electrode, and a back metal electrode. In particular,
[0008] The back structure layer includes a tunneling oxide layer formed on the back of the silicon wafer body and a self-limiting film layer. The self-limiting film layer includes a phosphorus-doped polysilicon layer, a carbon / phosphorus-doped polysilicon layer, and a hydrogen / phosphorus-doped polysilicon layer that form internal and external doping layers. The thickness of the internal doping layer is greater than that of the external doping layer. The carbon / phosphorus-doped polysilicon layer corresponds to the metal region, and the hydrogen / phosphorus-doped polysilicon layer corresponds to the non-metal region and is located in the external doping layer. The back metal electrode is a nickel / copper / tin composite electrode and is electroplated on the carbon / phosphorus-doped polysilicon layer.
[0009] Preferably, the thickness of the internal doping layer is 4 to 8 times that of the external doping layer. The self-limiting film layer structure includes thick phosphorus-doped polysilicon, thin locally carbon / phosphorus-doped polysilicon, and thin locally hydrogen / phosphorus-doped polysilicon. Since the carbon-doped polysilicon has highly polar C-Si bonds, it greatly improves the hydrophilicity of the polysilicon film and reduces the retention of hydrogen bubbles during electroplating, enabling the electroplated nickel solution to better contact the carbon / phosphorus-doped polysilicon film to obtain a uniform, dense, and void-free nickel seed layer. The surface tension of the hydrogen-doped polysilicon increases and the corresponding water contact angle increases, enhancing the hydrophobicity of the polysilicon surface. The electroplated nickel solution is difficult to adhere to the hydrogen / phosphorus-doped polysilicon film layer, and there is excessive hydrogen bubble retention on the surface of the hydrogen / phosphorus-doped polysilicon during electroplating, further reducing the possibility of nickel seed layer deposition.
[0010] Furthermore, the phosphorus-doped polysilicon layer is formed by activating phosphorus atoms in an in-situ phosphorus-doped polysilicon layer with a thickness of 80 to 200 nm to form substitutional doping.
[0011] According to a specific implementation and preferred aspect of the present invention, both the carbon / phosphorus-doped polysilicon layer and the hydrogen / phosphorus-doped polysilicon layer are located in the external doping layer, and their thicknesses are both 10 to 50 nm. Here, by forming C-H chemical bonds to inhibit the escape of H, it is beneficial to promote surface passivation. In addition, doping carbon elements in the polysilicon layer can reduce the activity of phosphorus atoms, reduce Auger recombination and SRH recombination. Therefore, during the phosphorus diffusion process, the advancement of phosphorus atoms in the non-metallized region is inhibited. In the metallized region, due to the absence of carbon-doped polysilicon, phosphorus atoms can be doped to the maximum extent. A higher doping concentration will form a better ohmic contact because the resistivity of the high-concentration doping region is greatly reduced, reducing the resistance at the contact interface between the semiconductor and the metal electrode. The parasitic absorption in the low-concentration region doped with carbon in the non-metallized part will also decrease compared to traditional solar cells.
[0012] Preferably, the carbon / phosphorus-doped polysilicon layer and the hydrogen / phosphorus-doped polysilicon layer have equal thicknesses, both being 10 to 20 nm.
[0013] According to another specific implementation and preferred aspect of the present invention, the width of the nickel / copper / tin composite electrode is less than or equal to the width of the carbon / phosphorus-doped polysilicon layer, and the width is 10 to 20 μm, and the height is 15 to 25 μm.
[0014] Preferably, the nickel / copper / tin composite electrode includes a nickel seed layer, a copper electrode layer, and a tin electrode layer. The electroplated nickel / copper / tin composite electrode replaces the silver electrode prepared by screen printing, saving the cost of silver paste; at the same time, the nickel / copper / tin composite electrode has advantages such as better morphology, lower bulk resistivity, stronger conductivity, and stronger ability to collect photo-generated carriers compared with the silver electrode, which can further improve the absolute conversion efficiency of the battery.
[0015] In some specific embodiments, the silicon wafer body is an N-type silicon wafer with a thickness of 100 - 180 μm; the thickness of the tunneling oxide layer is 0.5 - 2.5 nm.
[0016] According to another specific implementation and preferred aspect of the present invention, the front structure layer includes a boron-doped emitter and a passivation and antireflection layer arranged in sequence from inside to outside.
[0017] Preferably, the boron-doped emitter, the passivation and antireflection layer, and the front surface of the silicon wafer body have the same shape and the surfaces are all in a pyramid-shaped matte surface.
[0018] Furthermore, the passivation and antireflection layer is a combination of two or three layers among an alumina layer, a silicon nitride layer, a silicon oxynitride layer, a silicon dioxide layer, and a magnesium fluoride layer. Preferably, the passivation and antireflection layer is a three-layer film system composed of an alumina layer, a silicon nitride layer, and a silicon oxynitride layer, etc., where the thickness of the alumina layer is 2 - 8 nm, the refractive index of the silicon nitride layer is 2.0 - 2.1, and the thickness is 20 - 40 nm, and the refractive index of the silicon oxynitride layer is 1.5 - 1.6, and the thickness is 60 - 100 nm.
[0019] Another technical solution of the present invention is: a photovoltaic module, which includes a front encapsulation layer, a photovoltaic cell, and a back encapsulation layer, wherein the photovoltaic cell is the above-mentioned passivated contact cell.
[0020] Another technical solution of the present invention is: a photovoltaic system, which includes the above-mentioned photovoltaic module, wherein there is one or more photovoltaic modules, and when there are multiple photovoltaic modules, the multiple photovoltaic modules are connected in communication. In short, the multiple photovoltaic modules are connected in communication (in series).
[0021] According to another specific implementation and preferred aspect of the present invention, the front structure layer includes a boron-doped emitter, a front passivation layer, and a front antireflection layer arranged in sequence from inside to outside.
[0022] Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:
[0023] In existing passivated contact cells with polysilicon layers, high-conductivity silver materials are used for both the front and back electrodes of TOPCon cells, resulting in a large amount of silver consumption, thus increasing the material cost. Therefore, developing a metallization scheme with low silver consumption is particularly important for reducing material costs and accelerating the market expansion of TOPCon cells. At the same time, in the electroplated copper process adopted, a uniform, dense, and void-free nickel seed layer cannot be formed in the metal region, and hydrogen bubble retention cannot be formed in the non-metal region, resulting in nickel seed layer deposition. This not only fails to form a better ohmic contact between the electroplated phosphorus-doped polysilicon layer and the metal electrode, unable to reduce the contact resistivity, but also increases the processing cost. Moreover, free carrier absorption (FCA) is an ineffective absorption. The greater the thickness or the higher the doping concentration of the doped polysilicon, the more serious the FCA absorption and the lower the photoelectric conversion efficiency, etc. The overall design of the passivated contact cell of the present utility model ingeniously solves various deficiencies of the existing structure.After adopting the passivated contact battery, first select a single-crystalline silicon wafer to remove the damaged layer on the surface of the silicon wafer, and then fabricate a textured surface; then, perform a double-sided boron diffusion process on the textured silicon wafer to form a boron-doped emitter; then remove the back layer of the silicon wafer after boron diffusion and perform a polishing treatment, and then grow a tunneling oxide layer and a phosphorus in-situ doped polysilicon layer on the polished back surface of the single-crystalline silicon wafer, and then perform an annealing treatment. The microcrystalline silicon phase in the polysilicon layer will transform into a polysilicon phase to complete crystallization, and at the same time, the in-situ doped phosphorus atoms are activated to form a substitutionally doped phosphorus-doped polysilicon layer; then inject carbon atoms and hydrogen atoms in sequence to form a carbon / phosphorus doped polysilicon layer and a hydrogen / phosphorus doped polysilicon layer in the metal region and the non-metal region. Then, deposit a passivation antireflection film layer and a front metal electrode on the front of the boron-doped emitter. Finally, electroplate a nickel / copper / tin composite electrode on the back of the carbon / phosphorus doped polysilicon layer. Therefore, on the one hand, the carbon-doped polysilicon in the present invention has highly polar C-Si bonds, which greatly improves the hydrophilicity of the polysilicon film and reduces the retention of hydrogen bubbles during electroplating, enabling the electroplated nickel solution to better contact the carbon / phosphorus doped polysilicon film to obtain a uniform, dense, and void-free back metal electrode. At the same time, the surface tension of the hydrogen-doped polysilicon increases and the corresponding water contact angle increases, enhancing the hydrophobicity of the polysilicon surface, making it difficult for the electroplating solution to adhere to the hydrogen / phosphorus doped polysilicon film layer, and there is excessive hydrogen bubble retention on the surface of the hydrogen / phosphorus doped polysilicon during electroplating, further reducing the possibility of depositing the back metal electrode; on the other hand, the back metallization of this TOPCon battery uses an electroplating method, electroplating nickel, copper, and tin electrodes on the carbon / phosphorus doped polysilicon layer in sequence. The electroplated nickel / copper / tin composite electrode replaces the silver electrode prepared by screen printing, saving the cost of silver paste. At the same time, the nickel / copper / tin composite electrode has advantages such as better morphology, lower bulk resistivity, stronger conductivity, and stronger ability to collect photo-generated carriers compared with the silver electrode, and can form a better ohmic contact, reducing the contact resistivity and improving the photoelectric conversion efficiency of the battery. In addition, the hydrogen / phosphorus doped polysilicon also has good passivation performance, that is, it cannot passivate the back structure, optimize the structure, and reduce the cost. Description of the Drawings
[0024] Figure 1 It is a schematic structural diagram of a passivated contact battery with a selective polysilicon layer in Example 1;
[0025] Figure 2 It is a schematic structural diagram of a passivated contact battery in Comparative Example 1;
[0026] Wherein: 1. Silicon wafer body;
[0027] 2. Front structure layer; 20. Boron-doped emitter; 21. Passivation antireflection layer;
[0028] 3. Back structure layer; 30. Tunneling oxide layer; 31. Self-limiting film layer; 310. Phosphorus-doped polysilicon layer; 311. Carbon / phosphorus-doped polysilicon layer; 312. Hydrogen / phosphorus-doped polysilicon layer; 32. Single-layer polysilicon doping layer; 33. Back passivation and antireflection layer;
[0029] 4. Front metal electrode;
[0030] 5. Back metal electrode; 50. Nickel seed layer; 51. Copper electrode layer; 52. Tin electrode layer. Detailed implementation manners
[0031] To make the above objects, features, and advantages of the present utility model more obvious and understandable, the present utility model will be described in detail below in conjunction with the accompanying drawings and specific implementation manners. Many specific details are set forth in the following description to facilitate a thorough understanding of the present utility model. However, the present utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present utility model. Therefore, the present utility model is not limited by the specific embodiments disclosed below.
[0032] In the description of the present utility model, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present utility model and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present utility model.
[0033] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present utility model, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.
[0034] In the present utility model, unless otherwise clearly defined and limited, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.
[0035] In a utility model, unless otherwise clearly specified or limited, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.
[0036] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time. The terms "vertical", "horizontal", "above", "below", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation.
[0037] Embodiment 1
[0038] As Figure 1 shown, the passivated contact battery provided in this embodiment includes a silicon wafer body 1, a front structure layer 2, a back structure layer 3, a front metal electrode 4 and a back metal electrode 5.
[0039] Specifically, the silicon wafer body 1 is an N-type silicon wafer with a thickness of 100 - 180 μm.
[0040] The front structure layer 2 includes a boron-doped emitter 20 and a passivation and antireflection layer 21 arranged in sequence from the inside out. Among them, the boron-doped emitter 20, the passivation and antireflection layer 21 and the front surface of the silicon wafer body 1 have the same shape and their surfaces are all in a pyramid-shaped matte surface. The passivation and antireflection layer 21 is a combination of two or three layers among an alumina layer, a silicon nitride layer, a silicon oxynitride layer, a silicon dioxide layer, a magnesium fluoride layer. In some specific embodiments, the passivation and antireflection layer is a three-layer film system composed of an alumina layer, a silicon nitride layer, a silicon oxynitride layer, etc. Among them, the thickness of the alumina is 2 - 8 nm, the refractive index of the silicon nitride is 2.0 - 2.1, and the thickness is 20 - 40 nm, the refractive index of the silicon oxynitride is 1.5 - 1.6, and the thickness is 60 - 100 nm. In this example, screen printing and sintering are performed on the front to form the front metal electrode 4. Among them, the screen printing pattern on the front is a non-main grid pattern, the front metal fine grid lines are made of silver-aluminum material, the interval between the front fine grid lines is 0.9 - 1.6 mm, the width of the front fine grid lines is 25 - 35 μm, the height is 8 - 12 μm, and the peak temperature of sintering is 700 - 760 °C.
[0041] The back structure layer 3 includes a tunneling oxide layer 30 formed on the back of the silicon wafer body and a self-limiting film layer 31. The self-limiting film layer 31 includes a phosphorus-doped polysilicon layer 310, a carbon / phosphorus-doped polysilicon layer 311, and a hydrogen / phosphorus-doped polysilicon layer 312 that form inner and outer doped layers. The thickness of the inner doped layer is greater than that of the outer doped layer. The carbon / phosphorus-doped polysilicon layer 311 corresponds to the metal region, and the hydrogen / phosphorus-doped polysilicon layer 312 corresponds to the non-metal region and is in the outer doped layer. The back metal electrode 5 is a nickel / copper / tin composite electrode and is electroplated on the carbon / phosphorus-doped polysilicon layer 312. The self-limiting film layer structure includes thick phosphorus-doped polysilicon, thin locally carbon / phosphorus-doped polysilicon, and thin locally hydrogen / phosphorus-doped polysilicon. Since the carbon-doped polysilicon has highly polar C-Si bonds, it greatly improves the hydrophilicity of the polysilicon film and reduces the retention of hydrogen bubbles during electroplating, enabling the electroplated nickel solution to better contact the carbon / phosphorus-doped polysilicon film to obtain a uniform, dense, and void-free nickel seed layer. The surface tension of the hydrogen-doped polysilicon increases and the corresponding water contact angle increases, enhancing the hydrophobicity of the polysilicon surface. The electroplated nickel solution is difficult to adhere to the hydrogen / phosphorus-doped polysilicon film layer, and there is excessive retention of hydrogen bubbles on the surface of the hydrogen / phosphorus-doped polysilicon during electroplating, further reducing the possibility of nickel seed layer deposition.
[0042] In some specific embodiments, a plasma-enhanced chemical vapor deposition (PECVD) device is used to grow an ultra-thin tunneling oxide layer 30 and an in-situ phosphorus-doped polysilicon layer on the entire back surface of the silicon wafer. The material of the tunneling oxide layer 30 is silicon dioxide, and its thickness is 1.0 - 1.5 nm. The deposition temperature of the in-situ phosphorus-doped polysilicon is 500 - 650 °C, and its thickness is 80 - 200 nm (the phosphorus-doped polysilicon layer 310 on the back of the tunneling oxide layer 30 is formed by substitution doping with phosphorus atoms activated based on the in-situ phosphorus-doped polysilicon layer with a thickness of 80 - 200 nm, and the phosphorus-doped polysilicon layer 310 forms the inner doped layer). The carbon / phosphorus-doped polysilicon layer 311 and the hydrogen / phosphorus-doped polysilicon layer 312 form the outer doped layer, and the carbon / phosphorus-doped polysilicon layer 311 and the hydrogen / phosphorus-doped polysilicon layer 312 correspond to the metal region and the non-metal region respectively. Here, by forming C-H chemical bonds to inhibit the escape of H, it is beneficial to promote surface passivation. In addition, doping carbon elements in the polysilicon layer can reduce the activity of phosphorus atoms, reduce Auger recombination and SRH recombination. Thus, during the phosphorus diffusion process, the advancement of phosphorus atoms in the non-metallized region is inhibited. In the metallized region, due to the absence of carbon-doped polysilicon, phosphorus atoms can be doped to the maximum extent. A higher doping concentration will form a better ohmic contact because the resistivity of the high-concentration doping region is greatly reduced, reducing the resistance at the contact interface between the semiconductor and the metal electrode. The parasitic absorption in the low-concentration region with carbon doping in the non-metallized part also decreases compared to traditional solar cells.
[0043] In this example, the thickness of the inner doped layer is 70 - 180 nm, and the thickness of the outer doped layer is 10 - 20 nm. The thicknesses of the carbon / phosphorus doped polysilicon layer 311 and the hydrogen / phosphorus doped polysilicon layer 312 in the outer doped layer are equal. The width of the nickel / copper / tin composite electrode is less than or equal to the width of the carbon / phosphorus doped polysilicon layer, and the width is 10 - 20 μm, and the height is 15 - 25 μm.
[0044] In some specific embodiments, the nickel / copper / tin composite electrode 5 includes a nickel seed layer 50, a copper electrode layer 51, and a tin electrode layer 52. In this example, the electroplating current density of the nickel seed layer 50 is 30 mA / cm 2 , the electroplating duration is 2 min, and the height is 0.5 μm; the electroplating current density of the copper electrode layer 51 is 20 mA / cm 2 , the electroplating duration is 10 min; the electroplating current density of the tin electrode layer 52 is 20 mA / cm 2 , the electroplating duration is 15 min, and the temperature of the tin electroless plating solution is 40 °C. The electroplated nickel / copper / tin composite electrode replaces the silver electrode prepared by screen printing, saving the cost of silver paste; at the same time, the nickel / copper / tin composite electrode has advantages such as better morphology, lower bulk resistivity, stronger conductivity, and stronger ability to collect photo-generated carriers compared with the silver electrode, which can further improve the absolute conversion efficiency of the battery.
[0045] Example 2
[0046] The passivated contact battery provided in this embodiment has exactly the same structure as that in Example 1, and the differences are as follows.
[0047] The formation processes of the tunneling oxide layer 30 and the self-limiting film layer 31 are different. That is, the graphite carrier plate with the silicon wafer is transported into the plate chamber of the physical vapor deposition (PVD) equipment. First, oxygen or nitrous oxide (N2O) is introduced, and plasma oxidation is used to generate an ultra-thin tunneling oxide layer 30 on the back of the silicon wafer. The power of the plasma oxidation is 100 - 300 W, the growth temperature is 250 - 300 °C, the thickness is 0.5 - 2.0 nm, and the preferred thickness is 1.0 - 1.5 nm; then, by magnetron sputtering a heavily phosphorus-doped silicon target, the phosphorus-doped silicon target is located below the graphite carrier plate. During the magnetron sputtering process, silicon atoms are desorbed from the target and move upward to deposit on the back of the silicon wafer to form an in-situ phosphorus-doped polysilicon layer. The power of the magnetron sputtering is 28000 - 30000 W, the temperature is 200 - 250 °C, and the thickness is 80 - 200 nm.
[0048] Comparative Example 1
[0049] The passivated contact cell involved in this Comparative Example 1 includes an N-type monocrystalline silicon wafer 1, a front-side structure layer formed on the front side of the N-type monocrystalline silicon wafer, and a back-side structure layer formed on the back side of the N-type monocrystalline silicon wafer. The back-side structure layer includes a tunneling oxide layer 30, a single-layer polycrystalline silicon doping layer 32, and a back-side passivation and antireflection layer 33 arranged in sequence from inside to outside. The single-layer polycrystalline silicon doping layer 32 covers the entire area of the back side of the cell. The front-side structure layer is the same as that in Examples 1 and 2, and the back-side passivation and antireflection layer 33 is a single-layer silicon nitride layer.
[0050] Performance test: The cells obtained in the above Examples 1 and 2 and Comparative Example 1 were subjected to the following performance tests. The test method was as follows: Using an IV tester, the photovoltaic conversion efficiency and related electrical performance parameters of the cells under standard illumination power were tested under a simulated solar light source (and the electrical performance data were the average values of 100 Pcs cells of various samples). The specific test results are shown in Table 1 (Eta: conversion efficiency, Voc: open-circuit voltage, Jsc: short-circuit current density, FF: fill factor).
[0051] Table 1
[0052] Sample Eta(%) Voc(mV) <![CDATA[Jsc (mA / cm 2 )]]> FF(%) Example 1 25.00 723 40.81 84.73 Example 2 25.04 723 40.85 84.77 Comparative Example 1 24.86 722 40.75 84.50
[0053] Based on the data in Table 1, it can be seen that Examples 1 and 2 of the present invention have at least the following advantages compared with Comparative Example 1:
[0054] 1) In the metal contact area on the back side of the cell, due to the doping of carbon elements, it is beneficial to inhibit the escape of H by forming C-H chemical bonds, which is more conducive to promoting surface passivation, and the open-circuit voltage Voc has a certain increase compared with the comparative example;
[0055] 2) The morphology of the nickel / copper / tin composite electrode grid is better than that of the silver electrode, and its aspect ratio can reach 1.3. Compared with the screen-printed silver electrode with an aspect ratio of 0.3, it has a stronger ability to collect photo-generated carriers, so the short-circuit current density Jsc will have an advantage of about 0.1+ mA / cm2;
[0056] 3) The nickel / copper / tin composite electrode has advantages such as lower bulk resistivity and stronger conductivity. The fill factor FF of this structure will have a significant increase compared with the comparative example;
[0057] 4) The photovoltaic conversion efficiency Eta formed by this structure also has an increase of 0.14 to 0.18%.
[0058] Example 3
[0059] The photovoltaic module involved in this example includes a front-side encapsulation layer, a photovoltaic cell, and a back-side encapsulation layer, where the photovoltaic cell is the passivated contact cell in Example 1 or 2 above.
[0060] Example 4
[0061] The photovoltaic system involved in this embodiment includes the photovoltaic modules involved in Embodiment 3, where there are two, three, or more photovoltaic modules, and the multiple photovoltaic modules are connected in communication (generally in series).
[0062] Meanwhile, there can also be one photovoltaic module, that is, a photovoltaic system composed of a single photovoltaic module; or there are two, three, or more photovoltaic modules, and the multiple photovoltaic modules are connected in series and / or in parallel relative to each other.
[0063] In summary, for the passivated contact cell, after adopting the passivated contact cell, a single-crystalline silicon wafer is first selected to remove the damaged layer on the surface of the silicon wafer, and then a textured surface is formed; then, a double-sided boron diffusion process is performed on the textured silicon wafer to form a boron-doped emitter; then, the back layer of the silicon wafer after boron diffusion is removed and polished, and then a tunneling oxide layer and a phosphorus in-situ doped polysilicon layer are grown on the back of the polished single-crystalline silicon wafer, and then annealing treatment is performed. The microcrystalline silicon phase in the polysilicon layer will transform into a polysilicon phase to complete crystallization, and at the same time, the in-situ doped phosphorus atoms are activated to form a substitutionally doped phosphorus-doped polysilicon layer; then carbon atoms and hydrogen atoms are injected in sequence to form a carbon / phosphorus-doped polysilicon layer and a hydrogen / phosphorus-doped polysilicon layer in the metal region and the non-metal region. Then, a passivation antireflection film layer and a front metal electrode are deposited on the front of the boron-doped emitter. Finally, a nickel / copper / tin composite electrode is electroplated on the back of the carbon / phosphorus-doped polysilicon layer. Therefore, on the one hand, the carbon-doped polysilicon in the present invention has a highly polar C-Si bond, which greatly improves the hydrophilicity of the polysilicon film and reduces the retention of hydrogen bubbles during electroplating, enabling the electroplated nickel solution to better contact the carbon / phosphorus-doped polysilicon film, thereby obtaining a uniform, dense, and void-free back metal electrode. At the same time, the surface tension of the hydrogen-doped polysilicon increases and the corresponding water contact angle increases, enhancing the hydrophobicity of the polysilicon surface. It is difficult for the electroplating solution to adhere to the hydrogen / phosphorus-doped polysilicon film layer, and there is excessive hydrogen bubble retention on the surface of the hydrogen / phosphorus-doped polysilicon during electroplating, further reducing the possibility of depositing the back metal electrode; on the other hand, the back metallization of the TOPCon cell adopts an electroplating method, and nickel, copper, and tin electrodes are electroplated on the carbon / phosphorus-doped polysilicon layer in sequence. The electroplated nickel / copper / tin composite electrode replaces the silver electrode prepared by screen printing, saving the cost of silver paste. At the same time, the nickel / copper / tin composite electrode has advantages such as better morphology, lower bulk resistivity, stronger conductivity, and stronger ability to collect photo-generated carriers compared to the silver electrode, forming a better ohmic contact, reducing the contact resistivity, and further improving the photoelectric conversion efficiency of the cell. In addition, the hydrogen / phosphorus-doped polysilicon also has good passivation performance, that is, it cannot passivate the back structure, optimize the structure, and reduce the cost; on the third hand, the formation of C-H chemical bonds inhibits the escape of H, which is beneficial to promoting surface passivation; in addition, doping carbon elements in the polysilicon layer can reduce the activity of phosphorus atoms, reduce Auger recombination and SRH recombination, thereby inhibiting the advancement of phosphorus atoms in the non-metallized region during the phosphorus diffusion process. In the metallized region, due to the absence of carbon-doped polysilicon, phosphorus atoms can be doped to the maximum extent. A higher doping concentration will form a better ohmic contact because the resistivity of the high-concentration doping region is greatly reduced, reducing the resistance at the contact interface between the semiconductor and the metal electrode. The parasitic absorption in the low-concentration region doped with carbon in the non-metallized part will also decrease compared to traditional cell wafers.
[0064] The above has made a detailed description of the present utility model, aiming to enable those skilled in the art to understand the content of the present utility model and implement it. However, this should not limit the protection scope of the present utility model. Any equivalent changes or modifications made according to the spirit of the present utility model should be covered within the protection scope of the present utility model.
Claims
1. A passivated contact cell, comprising a silicon wafer body (1), a front structure layer (2), a back structure layer (3), a front metal electrode (4), and a back metal electrode (5), characterized in that: The back structure layer (3) includes a tunneling oxide layer (30) and a self-limiting film layer (31) formed on the back of the silicon wafer body (1), wherein the self-limiting film layer (31) includes a phosphorus-doped polysilicon layer (310) forming an inner and outer doped layer, a carbon or phosphorus-doped polysilicon layer (311), and a hydrogen or phosphorus-doped polysilicon layer (312). The thickness of the inner doped layer is greater than that of the outer doped layer. The carbon or phosphorus-doped polysilicon layer (311) corresponds to the metal region, and the hydrogen or phosphorus-doped polysilicon layer (312) corresponds to the non-metal region and is located in the outer doped layer. The back metal electrode (5) is a nickel or copper or tin composite electrode and is electroplated on the carbon or phosphorus-doped polysilicon layer (311).
2. The passivated contact cell according to claim 1, wherein: The thickness of the inner doped layer is 4 to 8 times that of the outer doped layer.
3. The passivated contact cell according to claim 1, characterized in that: The thickness of the phosphorus-doped polysilicon layer (310) is 80 to 200 nm.
4. The passivated contact cell according to claim 1, wherein: Both the carbon or phosphorus-doped polysilicon layer (311) and the hydrogen or phosphorus-doped polysilicon layer (312) are located in the outer doped layer, and their thicknesses are both 10 to 50 nm.
5. The passivated contact cell according to claim 4, characterized in that: The carbon or phosphorus-doped polysilicon layer (311) and the hydrogen or phosphorus-doped polysilicon layer (312) have the same thickness, and are both 10 to 20 nm.
6. The passivated contact cell according to claim 1, wherein: The width of the nickel or copper or tin composite electrode is less than or equal to the width of the carbon or phosphorus-doped polysilicon layer (311), and the width is 10 to 20 μm, and the height is 15 to 25 μm.
7. The passivated contact cell according to claim 1, wherein: The nickel or copper or tin composite electrode includes a nickel seed layer, a copper electrode layer, and a tin electrode layer.
8. The passivated contact cell according to claim 1, wherein: The silicon wafer body (1) is an N-type silicon wafer, and the thickness is 100 to 180 μm; and / or, the thickness of the tunneling oxide layer (30) is 0.5 to 2.5 nm.
9. The passivated contact cell according to claim 1, characterized in that: The front structure layer (2) includes a boron-doped emitter (20) and a passivation and antireflection layer (21) arranged in sequence from the inside to the outside.
10. The passivated contact cell according to claim 9, wherein: The boron-doped emitter (20), the passivation and antireflection layer (21), and the front surface of the silicon wafer body (1) have the same shape and the surfaces are all in a pyramidal texture.
11. The passivated contact cell according to claim 10, characterized in that: The passivation and antireflection layer (21) is a combination of two or three layers of an alumina layer, a silicon nitride layer, a silicon oxynitride layer, a silicon dioxide layer, and a magnesium fluoride layer.
12. The passivated contact cell according to claim 11, characterized in that: The passivation and antireflection layer (21) is a three-layer film system composed of an alumina layer, a silicon nitride layer, and a silicon oxynitride layer, wherein the thickness of the alumina is 2 to 8 nm, the refractive index of the silicon nitride is 2.0 to 2.1, the thickness is 20 to 40 nm, and the refractive index of the silicon oxynitride is 1.5 to 1.6, the thickness is 60 to 100 nm.
13. A photovoltaic module, comprising a front encapsulation layer, a photovoltaic cell, and a back encapsulation layer, characterized in that: The photovoltaic cell is the passivated contact cell according to any one of claims 1 to 12.
14. A photovoltaic system, characterized in that: The photovoltaic system includes the photovoltaic module according to claim 13, wherein there is one or more photovoltaic modules, and when there are multiple photovoltaic modules, the multiple photovoltaic modules are connected in communication.