Solar cell, preparation method of solar cell and photovoltaic module

Abstract

The invention relates to the field of photovoltaic technology, and provides a solar cell, a preparation method of the solar cell and a photovoltaic module, and the solar cell comprises a substrate and a passivation layer. Wherein the substrate comprises a light facing surface and a backlight surface which are oppositely arranged in the thickness direction; the passivation layer is arranged on the backlight surface of the substrate and comprises at least two silicon nitride layers, a silicon oxynitride layer and a silicon oxide layer which are sequentially stacked in the direction away from the substrate; the refractive indexes of the silicon nitride layers are sequentially increased in the direction away from the substrate. The solar cell is good in passivation effect and high in photoelectric conversion efficiency.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a solar cell, a method for preparing a solar cell, and a photovoltaic module. Background Art

[0002] BC cells, which refer to back contact cells, are an advanced design used to improve the efficiency of solar cells. The core design concept is to place all the metal electrodes of the cell on the backlight side of the cell, thereby ensuring that the light-facing side of the cell is not blocked by any metal grid lines, thereby maximizing the area of ​​the cell absorbing sunlight, reducing optical losses, and improving photoelectric conversion efficiency. In traditional technology, high-purity silicon nitride laminated film is used as the passivation layer. Since the P-end and N-end of the back contact cell are both on the backlight side of the cell, it is necessary to further improve the back passivation performance. Summary of the invention

[0003] Based on this, an embodiment of the present application provides a solar cell with good passivation performance and high photoelectric conversion efficiency, a method for preparing a solar cell, and a photovoltaic module.

[0004] In a first aspect, the present application provides a solar cell, the solar cell comprising:

[0005] The substrate comprises a light-facing surface and a backlight surface which are arranged opposite to each other along a thickness direction.

[0006] A passivation layer is arranged on the backlight surface of the substrate, and the passivation layer includes at least two silicon nitride layers, a silicon nitride oxide layer and a silicon oxide layer stacked in sequence in a direction away from the substrate; the refractive index of each silicon nitride layer increases in sequence in a direction away from the substrate.

[0007] In some embodiments, the passivation layer includes a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer, and a fourth silicon nitride layer which are sequentially stacked in a direction away from the substrate.

[0008] Optionally, the thickness of the first silicon nitride layer is 15 nm to 25 nm, and the refractive index of the first silicon nitride layer is 1.90 to 1.95.

[0009] Optionally, the thickness of the second silicon nitride layer is 20 nm to 30 nm, and the refractive index of the second silicon nitride layer is 1.95 to 2.00.

[0010] Optionally, the thickness of the third silicon nitride layer is 25 nm to 35 nm, and the refractive index of the third silicon nitride layer is 2.00 to 2.05.

[0011] Optionally, the thickness of the fourth silicon nitride layer is 35 nm to 45 nm, and the refractive index of the fourth silicon nitride layer is 2.05 to 2.10.

[0012] In some embodiments, the refractive index of the silicon oxynitride layer is greater than the total refractive index of the silicon nitride layers.

[0013] Optionally, the total refractive index of each of the silicon nitride layers is 2.1-2.17.

[0014] In some embodiments, the passivation layer includes at least two silicon oxynitride layers; the refractive index of each silicon oxynitride layer increases sequentially in a direction away from the substrate.

[0015] Optionally, the passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer which are sequentially stacked in a direction away from the substrate.

[0016] Further optionally, the thickness of the first silicon oxynitride layer is 20 nm to 30 nm, and the refractive index of the first silicon oxynitride layer is 2.04 to 2.08.

[0017] Further optionally, the thickness of the second silicon oxynitride layer is 25 nm to 35 nm, and the refractive index of the second silicon oxynitride layer is 2.07 to 2.15.

[0018] In a second aspect, the present application provides a method for preparing a solar cell, the method for preparing a solar cell comprising:

[0019] Providing a substrate, wherein the substrate comprises a light-facing surface and a backlight surface that are arranged opposite to each other in a thickness direction;

[0020] At least two silicon nitride layers, at least one silicon oxynitride layer and a silicon oxide layer are sequentially formed on the backlight side of the substrate, and a passivation layer is obtained on the backlight side of the substrate, wherein the refractive index of the silicon nitride layer increases sequentially in a direction away from the substrate.

[0021] In some embodiments, after forming the silicon oxide layer, the substrate is annealed.

[0022] Optionally, the annealing temperature is 550° C. to 600° C., and the annealing time is 200 s to 300 s.

[0023] In some embodiments, the passivation layer includes a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer, and a fourth silicon nitride layer sequentially formed in a direction away from the substrate.

[0024] Optionally, the first silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600sccm~2800sccm, the flow rate of the nitrogen source is 9000sccm~11000sccm, the temperature is 430℃~480℃, the pressure is 1500mtorr~1700mtorr, the time is 50s~180s, the power is 11000W~13000W, and the duty cycle is 0.03~0.07.

[0025] Optionally, the second silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600sccm~2800sccm, the flow rate of the nitrogen source is 9000sccm~11000sccm, the temperature is 430℃~480℃, the pressure is 1500mtorr~1700mtorr, the time is 100s~200s, the power is 12000W~15000W, and the duty cycle is 0.03~0.07.

[0026] Optionally, the third silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1800sccm~2000sccm, the flow rate of the nitrogen source is 11000sccm~13000sccm, the temperature is 430℃~480℃, the pressure is 1600mtorr~1700mtorr, the time is 180s~220s, the power is 13000W~15000W, and the duty cycle is 0.03~0.07.

[0027] Optionally, the fourth silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1200sccm~1400sccm, the flow rate of the nitrogen source is 12000sccm~14000sccm, the temperature is 430℃~480℃, the pressure is 1600mtorr~1800mtorr, the time is 300s~400s, the power is 14000W~16000W, and the duty cycle is 0.03~0.07.

[0028] In some embodiments, the passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer sequentially formed in a direction away from the substrate.

[0029] Optionally, the first silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 900sccm~1100sccm, the flow rate of the nitrogen source is 2000sccm~4000sccm, the flow rate of the oxygen source is 6000sccm~8000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1800mtorr, the time is 110s~160s, the power is 14000W~16000W, and the duty cycle is 0.03~0.05.

[0030] Optionally, the second silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 800sccm~1000sccm, the flow rate of the nitrogen source is 2000sccm~4000sccm, the flow rate of the oxygen source is 8500sccm~9000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1800mtorr, the time is 130s~230s, the power is 14000W~16000W, and the duty cycle is 0.03~0.05.

[0031] In some embodiments, the silicon oxide layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1100sccm~1300sccm, the flow rate of the oxygen source is 10000sccm~13000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1900mtorr, the time is 80s~280s, the power is 15000W~16000W, and the duty cycle is 0.03~0.04.

[0032] In a third aspect, the present application provides a photovoltaic module, wherein the photovoltaic module comprises the solar cell as described in the first aspect and / or the solar cell prepared by the method for preparing the solar cell as described in the second aspect.

[0033] Compared with the traditional technology, this application has at least the following beneficial effects:

[0034] The passivation layer on the back of the solar cell of the present application adopts a combination of a silicon nitride layer, a silicon oxynitride layer and a silicon oxide layer, and adopts a multi-layer silicon nitride layer with a refractive index increasing in sequence, which can increase the thickness of the passivation layer, improve the long-wave response, and effectively reduce light loss. In addition, it can also increase the hydrogen ion concentration in the silicon nitride layer, improve the hydrogen passivation effect, and cooperate to improve the passivation performance of the back of the solar cell, thereby improving the photoelectric conversion efficiency of the back contact cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the structure of a solar cell provided in a specific embodiment of the present application;

[0036] Figure 2 A schematic structural diagram of a substrate provided in a specific embodiment of the present application.

[0037] Among them, 100-substrate; 101-silicon substrate; 102-first tunneling oxide layer; 103-second tunneling oxide layer; 104-first doping layer; 105-second doping layer; 106-intrinsic amorphous silicon layer; 110-passivation layer; 111-first silicon nitride layer; 112-second silicon nitride layer; 113-third silicon nitride layer; 114-fourth silicon nitride layer; 115-first silicon oxynitride layer; 116-second silicon oxynitride layer; 117-silicon oxide layer; 120-passivation anti-reflection layer. DETAILED DESCRIPTION

[0038] Below in conjunction with the embodiments and examples, the present application is further described in detail. These embodiments and examples are only used to illustrate the present application and are not used to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the understanding of the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms, and is not limited to the embodiments and examples described herein. Those skilled in the art can make various changes or modifications without violating the connotation of the present application, and the equivalent form obtained also falls within the protection scope of the present application. In addition, in the description below, a large number of specific details are given in order to provide a more comprehensive understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0040] In this application, "optionally", "optional", and "optional" mean optional or dispensable, that is, any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0041] In this application, the terms "first", "second", etc. in "the first aspect", "the second aspect", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0042] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0043] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for a broad range of quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0044] All documents mentioned in this application are cited as references in this application, just as each document is cited as reference separately. Unless they conflict with the application purpose and / or technical solution of this application, the cited documents involved in this application are cited with all contents and all purposes. When the cited documents are involved in this application, the definitions of relevant technical features, terms, nouns, phrases, etc. in the cited documents are also cited. When the cited documents are involved in this application, the examples and preferred methods of the cited relevant technical features can also be incorporated into this application as references, but are limited to the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, the present application shall prevail or be modified adaptively according to the description of this application.

[0045] In traditional technology, a multilayer high-refractive-index silicon nitride layer is used as the back passivation layer of the back-contact battery. However, the silicon nitride layer as a passivation layer has the following problems: 1. Lattice matching problem: The lattice matching of the silicon nitride layer (SiNx) and silicon is poor, which leads to a high defect density at the SiNx / Si interface, affecting the passivation effect. 2. The influence of fixed charge: The SiNx film carries a fixed positive charge and has a good passivation effect only on the N-type silicon surface. When applied to a highly doped p+ surface, it does not show effective passivation. 3. The passivation effect decays after high-temperature treatment: After the SiNx film is metallized at 450°C, the surface passivation will decay, affecting the battery efficiency. 4. Stress problem: SiNx has strong tensile stress on the Si surface. Although hydrogen can diffuse to the Si-SiNx interface and effectively passivate the interface state, its interface quality is not as good as Si-SiO2. 5. Increased interface state density caused by hydrogen escape: During rapid thermal processing, the Si-H bonds and NH bonds in the SiNx film are easily broken, resulting in the escape of hydrogen atoms, which increases the interface state density and reduces the minority carrier lifetime. 6. Adhesion problem: The loss of hydrogen during rapid thermal processing may cause cracks or bubbles in the film, reducing the adhesion between the film and the substrate. 7. Photoinduced degradation effect (SW effect): Hydrogenated amorphous silicon (a-Si:H) thin film solar cells are affected by the photoinduced degradation effect (SW effect). Although the introduction of hydrogen fills the redundant dangling bonds in amorphous silicon and improves the performance of a-Si:H, hydrogen may play an important role in the SW effect.

[0046] In a first aspect, the present application provides a solar cell, the solar cell comprising:

[0047] The substrate comprises a light-facing surface and a backlight surface which are arranged opposite to each other along a thickness direction.

[0048] A passivation layer is arranged on the backlight surface of the substrate, and the passivation layer includes at least two silicon nitride layers, a silicon nitride oxide layer and a silicon oxide layer stacked in sequence in a direction away from the substrate; the refractive index of each silicon nitride layer increases in sequence in a direction away from the substrate.

[0049] The passivation layer on the back of the solar cell of the present application adopts a combination of a silicon nitride layer, a silicon oxynitride layer and a silicon oxide layer, and adopts a multi-layer silicon nitride layer with a refractive index increasing in sequence, which can increase the thickness of the passivation layer, improve the long-wave response, and effectively reduce light loss. In addition, it can also increase the hydrogen ion concentration in the silicon nitride layer, improve the hydrogen passivation effect, and cooperate to improve the passivation performance of the back of the solar cell, thereby improving the photoelectric conversion efficiency of the back contact cell.

[0050] In some embodiments, the passivation layer includes a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer, and a fourth silicon nitride layer which are sequentially stacked in a direction away from the substrate.

[0051] In some embodiments, the thickness of the first silicon nitride layer is 15 nm to 25 nm, for example, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm or 25 nm.

[0052] Optionally, the refractive index of the first silicon nitride layer is 1.90-1.95, for example, 1.90, 1.91, 1.92, 1.93, 1.94 or 1.95.

[0053] In some embodiments, the thickness of the second silicon nitride layer is 20 nm to 30 nm, for example, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or 30 nm.

[0054] Optionally, the refractive index of the second silicon nitride layer is 1.95-2.00, for example, 1.95, 1.96, 1.97, 1.98, 1.99 or 2.00.

[0055] In some embodiments, the thickness of the third silicon nitride layer is 25 nm to 35 nm, for example, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm or 35 nm.

[0056] Optionally, the refractive index of the third silicon nitride layer is 2.00-2.05, for example, may be 2.00, 2.01, 2.02, 2.03, 2.04 or 2.05.

[0057] In some embodiments, the thickness of the fourth silicon nitride layer is 35 nm to 45 nm, for example, 35 nm, 36 nm, 37 nm, 38 nm, 39 nm, 40 nm, 41 nm, 42 nm, 43 nm, 44 nm or 45 nm.

[0058] Optionally, the refractive index of the fourth silicon nitride layer is 2.05-2.10, for example, may be 2.05, 2.06, 2.07, 2.08, 2.09 or 2.10.

[0059] The present application selects the thickness and refractive index of the first silicon nitride layer, the second silicon nitride layer, the third silicon nitride layer and the fourth silicon nitride layer as above, and uses the interference effect of light to reduce reflection. In the multilayer film structure, light waves are reflected and transmitted between interfaces with different refractive indices. When the destructive interference condition is met, the reflected light can be significantly reduced, thereby increasing the transmitted light and improving the photoelectric conversion efficiency of the battery. Further, in the present application, the refractive index of the silicon nitride layer increases in the direction away from the surface of the silicon wafer, which can cause the incident sunlight to be reflected and interfered multiple times inside, thereby increasing the absorption of the incident light to a greater extent and achieving a better anti-reflection effect. Furthermore, the present application selects the refractive index of the silicon nitride layer to avoid the problem of enhanced light absorption caused by the high extinction coefficient, and effectively takes into account the passivation effect and anti-reflection effect of the silicon nitride stacking; and by controlling the thickness and refractive index of the silicon nitride layer, it is possible not only to optimize the optical performance and reduce the reflection of light, but also to improve the electrical performance of the battery by passivating the defects on the surface and in the body of the silicon wafer, such as improving the open circuit voltage and short circuit current, thereby improving the photoelectric conversion efficiency. In addition, the present application uses four silicon nitride layers, which can have better anti-reflection effects in the entire wavelength range, especially in the short-wave part, compared with a single-layer or double-layer structure, which helps to improve the utilization of the spectrum by solar cells.

[0060] In some embodiments, the refractive index of the silicon oxynitride layer is greater than the total refractive index of the silicon nitride layers.

[0061] Optionally, the total refractive index of each silicon nitride layer is 2.1-2.17, for example, may be 2.10, 2.11, 2.12, 2.13, 2.14, 2.15, 2.16 or 2.17.

[0062] In some embodiments, the passivation layer includes at least two silicon oxynitride layers; the refractive index of each silicon oxynitride layer increases sequentially in a direction away from the substrate.

[0063] In the present application, the refractive index of the silicon oxynitride layer is greater than the total refractive index of the multi-layer silicon nitride layer, which can reflect light passing through the silicon substrate back to the silicon substrate, thereby improving the multiple utilization of long-wave light and improving the photoelectric conversion efficiency.

[0064] In some embodiments, the passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer sequentially stacked in a direction away from the substrate.

[0065] In some embodiments, the thickness of the first silicon oxynitride layer is 20 nm to 30 nm, for example, 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm or 30 nm.

[0066] Optionally, the refractive index of the first silicon oxynitride layer is 2.04-2.08, for example, may be 2.04, 2.05, 2.06, 2.07 or 2.08.

[0067] In some embodiments, the thickness of the second silicon oxynitride layer is 25 nm to 35 nm, for example, 25 nm, 26 nm, 27 nm, 28 nm, 29 nm, 30 nm, 31 nm, 32 nm, 33 nm, 34 nm or 35 nm.

[0068] Optionally, the refractive index of the second silicon oxynitride layer is 2.07-2.15, for example, may be 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14 or 2.15.

[0069] As mentioned above, the thickness and refractive index of the first silicon oxynitride layer and the second silicon oxynitride layer are selected in this application to utilize the interference effect of light to reduce reflection, so that light of a specific wavelength can be reflected and transmitted between interfaces of different refractive indices. When the destructive interference condition is met, the reflected light can be significantly reduced, thereby increasing the transmitted light and improving the photoelectric conversion efficiency of the battery. Furthermore, in this application, the silicon oxynitride layer is designed with a refractive index that gradually increases from the surface of the silicon wafer to the outside, which can cause the incident sunlight to be reflected and interfered multiple times inside, thereby increasing the absorption of the incident light to a greater extent and achieving a better anti-reflection effect. Moreover, the silicon oxynitride layer has a higher refractive index than the silicon nitride layer, which means a higher silicon content and more Si-H bonds, thereby providing a better passivation effect. The passivation layer of this application can reduce the recombination of carriers on the surface and increase the open circuit voltage and short circuit current of the battery.

[0070] Therefore, the present application can utilize the principle of optical interference to reduce light reflection by designing silicon nitride layers and silicon nitride oxide layers with different thicknesses and refractive indices, and at the same time improve the passivation effect and stability of the film layer through gradient refractive index design and stress control, thereby improving the performance of the back contact battery.

[0071] In some embodiments, the thickness of the silicon oxide layer is 20 nm to 35 nm, for example, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 32 nm, 34 nm or 35 nm.

[0072] In some embodiments, a passivation anti-reflection layer is further disposed on the light-facing surface of the substrate. Optionally, the passivation anti-reflection layer may be a silicon nitride layer.

[0073] In some embodiments, Figure 1As shown, the solar cell includes a substrate 100, a passivation layer 110 and a passivation anti-reflection layer 120. The passivation layer 110 is disposed on the backlight side and comprises a first silicon nitride layer 111, a second silicon nitride layer 112, a third silicon nitride layer 113, a fourth silicon nitride layer 114, a first silicon oxynitride layer 115, a second silicon oxynitride layer 116 and a silicon oxide layer 117 stacked in sequence in a direction away from the substrate 100. The passivation anti-reflection layer 120 is disposed on the light-facing side of the substrate 100.

[0074] It is understandable that the solar cell in the present application may be a back contact solar cell, which can be divided into an N-type back contact solar cell or a P-type back contact solar cell according to the type of substrate. The back contact solar cell includes a substrate, and a passivation anti-reflection layer is sequentially stacked on the light-facing surface of the substrate in a direction away from the substrate; a first doping layer, a second doping layer, a back passivation layer and an electrode are arranged on the backlight surface of the substrate, and the back passivation layer adopts the structure of the passivation layer described above in the present application.

[0075] Furthermore, if Figure 2 As shown, the base 100 includes a silicon substrate 101, a tunneling oxide layer is arranged on the backlight side, the tunneling oxide layer includes a first tunneling oxide layer 102 and a second tunneling oxide layer 103, a first doping layer 104 is arranged on the surface of the first tunneling oxide layer 102, a second doping layer 105 is arranged on the surface of the second tunneling oxide layer 103, and an intrinsic amorphous silicon layer 106 is arranged between the first doping layer 104 and the second doping layer 105. The passivation anti-reflection layer 120 is arranged on the light-facing surface of the silicon substrate 101. In addition, the solar cell also includes an electrode arranged on the backlight side (not shown in the figure). The structural arrangement of the electrode, the first doping layer 104 and the second doping layer 105 can be adjusted according to actual needs.

[0076] A second aspect of the present application provides a method for preparing a solar cell, the method comprising:

[0077] Providing a substrate, wherein the substrate comprises a light-facing surface and a backlight surface that are arranged opposite to each other in a thickness direction;

[0078] At least two silicon nitride layers, at least one silicon oxynitride layer and a silicon oxide layer are sequentially formed on the backlight side of the substrate, and a passivation layer is obtained on the backlight side of the substrate, wherein the refractive index of the silicon nitride layer increases sequentially in a direction away from the substrate.

[0079] The present application prepares solar cells as described above, and the preparation method is simple. Among them, the passivation layer on the back of the solar cell adopts a combination of a silicon nitride layer, a silicon oxynitride layer and a silicon oxide layer, and adopts a multilayer silicon nitride layer with a refractive index increasing in sequence, which can increase the thickness of the passivation layer, improve the long-wave response, and effectively reduce light loss. In addition, it can also increase the hydrogen ion concentration in the silicon nitride layer, improve the hydrogen passivation effect, and cooperate to improve the passivation performance of the back of the solar cell, thereby improving the photoelectric conversion efficiency of the back contact cell.

[0080] In some embodiments, after the silicon oxide layer is formed, the substrate is annealed. The present application performs annealing on the formed silicon nitride layer, silicon oxynitride layer and silicon oxide layer, which can excite hydrogen ions in the silicon nitride layer, improve the hydrogen passivation effect, and help improve the silicon surface passivation effect, effectively improving the electrical performance of the back contact battery, thereby improving the photoelectric conversion efficiency of the back contact battery.

[0081] In some embodiments, the annealing temperature is 550°C to 600°C, for example, 550°C, 555°C, 560°C, 565°C, 570°C, 575°C, 580°C, 585°C, 590°C, 595°C or 600°C.

[0082] The present application selects the annealing temperature as above, and during the annealing process, the lattice damage caused by ion implantation is repaired, the atoms are rearranged, and the order of the lattice is restored. Moreover, the annealing treatment can effectively improve the low-frequency direct passivation characteristics, help to improve the minority carrier lifetime and photoelectric conversion efficiency, and can reduce the surface recombination rate, increase the open circuit voltage and short circuit current of the battery, thereby improving the electrical performance and photoelectric conversion efficiency of the battery.

[0083] In addition, annealing can promote the initial activation and migration of the injected impurity atoms, so that the impurity atoms migrate from the lattice gap to the lattice position, forming effective doping. Moreover, annealing can improve the conductivity of the material, making it a better conductor. Furthermore, annealing can increase the density of the film layer and improve the rate of dry etching or wet etching.

[0084] Therefore, the annealing treatment performed in the present application as described above can effectively repair lattice damage, activate dopants, improve film properties, eliminate stress, improve electrical properties and optimize passivation effects, thereby avoiding problems such as reduced luminous intensity, changes in residual stress and decreased electrical properties.

[0085] Optionally, the annealing time is 200s to 300s, for example, it can be 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, 290s or 300s.

[0086] In some embodiments, the passivation layer includes a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer, and a fourth silicon nitride layer sequentially formed in a direction away from the substrate.

[0087] Optionally, the first silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600sccm~2800sccm, the flow rate of the nitrogen source is 9000sccm~11000sccm, the temperature is 430℃~480℃, the pressure is 1500mtorr~1700mtorr, the time is 50s~180s, the power is 11000W~13000W, and the duty cycle is 0.03~0.07.

[0088] Optionally, the second silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600sccm~2800sccm, the flow rate of the nitrogen source is 9000sccm~11000sccm, the temperature is 430℃~480℃, the pressure is 1500mtorr~1700mtorr, the time is 100s~200s, the power is 12000W~15000W, and the duty cycle is 0.03~0.07.

[0089] Optionally, the third silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1800sccm~2000sccm, the flow rate of the nitrogen source is 11000sccm~13000sccm, the temperature is 430℃~480℃, the pressure is 1600mtorr~1700mtorr, the time is 180s~220s, the power is 13000W~15000W, and the duty cycle is 0.03~0.07.

[0090] Optionally, the fourth silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1200sccm~1400sccm, the flow rate of the nitrogen source is 12000sccm~14000sccm, the temperature is 430℃~480℃, the pressure is 1600mtorr~1800mtorr, the time is 300s~400s, the power is 14000W~16000W, and the duty cycle is 0.03~0.07.

[0091] The present application selects the preparation process parameters of each silicon nitride layer as above, which effectively reduces the internal stress of the film layer and improves the stability and durability of the film layer.

[0092] In some embodiments, the passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer sequentially formed in a direction away from the substrate.

[0093] Optionally, the first silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 900sccm~1100sccm, the flow rate of the nitrogen source is 2000sccm~4000sccm, the flow rate of the oxygen source is 6000sccm~8000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1800mtorr, the time is 110s~160s, the power is 14000W~16000W, and the duty cycle is 0.03~0.05.

[0094] Optionally, the second silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 800sccm~1000sccm, the flow rate of the nitrogen source is 2000sccm~4000sccm, the flow rate of the oxygen source is 8500sccm~9000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1800mtorr, the time is 130s~230s, the power is 14000W~16000W, and the duty cycle is 0.03~0.05.

[0095] The present application selects the preparation process parameters of each silicon oxynitride layer as above, which can reduce the internal stress of the film and improve the stability and durability of the film layer.

[0096] In some embodiments, the silicon oxide layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1100sccm~1300sccm, the flow rate of the oxygen source is 10000sccm~13000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1900mtorr, the time is 80s~280s, the power is 15000W~16000W, and the duty cycle is 0.03~0.04.

[0097] It is to be understood that the present application does not make any specific requirements or special restrictions on the above silicon source, nitrogen source and oxygen source. It is sufficient that a silicon nitride layer, a silicon oxynitride layer and a silicon oxide layer can be formed. For example, the silicon source can be silane, the nitrogen source can be ammonia, and the oxygen source can be laughing gas.

[0098] Exemplarily, a method for preparing the above solar cell is provided, comprising the following steps:

[0099] S1, placing the substrate in a reaction chamber of a deposition device;

[0100] S2, introducing 2600sccm~2800sccm of silane and 9000sccm~11000sccm of ammonia into the reaction chamber, the temperature is 430℃~480℃, the pressure is 1500mtorr~1700mtorr, the deposition time is 50s~100s, the power is 11000W~13000W, the duty cycle is (3~7):100, and the first silicon nitride layer is deposited on the surface of the substrate, and the residual gas is purged and constant pressure preparation is performed;

[0101] S3, introducing 2600sccm~2800sccm of silane and 9000sccm~11000sccm of ammonia into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1500mtorr~1700mtorr, a deposition time of 100s~150s, a power of 12000W~14000W, a duty cycle of (3~7):100, depositing a second silicon nitride layer on the surface of the first silicon nitride layer, and preparing constant pressure after purging the residual gas;

[0102] S4, introducing 1800sccm~2000sccm of silane and 11000sccm~13000sccm of ammonia into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1600mtorr~1700mtorr, a deposition time of 180s~220s, a power of 13000W~15000W, a duty cycle of (3~7):100, depositing a third silicon nitride layer on the surface of the second silicon nitride layer, and preparing constant pressure after purging the residual gas;

[0103] S5, introducing 1200sccm~1400sccm of silane and 12000sccm~14000sccm of ammonia into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1600mtorr~1800mtorr, a deposition time of 300s~400s, a power of 14000W~16000W, a duty cycle of (3~7):100, depositing a fourth silicon nitride layer on the surface of the third silicon nitride layer, and preparing constant pressure after purging the residual gas;

[0104] S6, introducing 900sccm~1100sccm of silane, 2000sccm~4000sccm of ammonia, and 6000sccm~8000sccm of nitrous oxide into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1700mtorr~1800mtorr, a deposition time of 110s~130s, a power of 14000W~16000W, a duty cycle of (3~7):125, depositing a first silicon oxynitride layer on the surface of the fourth silicon nitride layer, and preparing constant pressure after purging the residual gas;

[0105] S7, introducing 800sccm~1000sccm of silane, 2000sccm~4000sccm of ammonia, and 8500sccm~9000sccm of nitrous oxide into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1700mtorr~1800mtorr, a deposition time of 130s~150s, a power of 14000W~16000W, a duty cycle of (3~7):125, depositing a second silicon oxynitride layer on the surface of the first silicon oxynitride layer, and preparing constant pressure after purging the residual gas;

[0106] S8, introducing 1100sccm~1300sccm of silane and 10000sccm~13000sccm of nitrous oxide into the reaction chamber, with a temperature of 430℃~480℃, a pressure of 1700mtorr~1900mtorr, a deposition time of 80s~120s, a power of 15000W~16000W, a duty cycle of (3~5):125, depositing a silicon oxide layer on the surface of the second silicon oxynitride layer, and then evacuating the chamber after completion;

[0107] S9. After the deposition is completed, the temperature is raised for 100s~150s to 550℃~600℃, and constant temperature annealing is performed for 200s~300s. The cavity is evacuated and purged, and nitrogen is introduced to break the vacuum. The process is completed after the pressure returns to normal and the boat is taken out to form a passivation layer on the substrate.

[0108] A third aspect of the present application provides a photovoltaic module, which includes the solar cell as described in the first aspect and / or a solar cell prepared by the method for preparing the solar cell as described in the second aspect.

[0109] The embodiments of the present application will be described in detail below in conjunction with examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are preferably referred to the guidance provided in the present application, and can also be based on the experimental manual or normal conditions in this area, can also be based on the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0110] The substrates used in the following examples and comparative examples are as follows: Figure 2 As shown, the silicon substrate 101 is an N-type crystalline silicon substrate, the first doped layer 104 is a phosphorus-doped polysilicon layer, and the second doped layer 105 is a boron-doped polysilicon layer.

[0111] Example 1

[0112] S1, placing the substrate in a reaction chamber of a deposition device;

[0113] S2, introducing 2700sccm of silane and 10000sccm of ammonia into the reaction chamber, the temperature is 450°C, the pressure is 1600mtorr, the deposition time is 80s, the power is 12000W, the duty cycle is 5:100, and a first silicon nitride layer is deposited on the surface of the substrate. The thickness of the first silicon nitride layer is 20nm and the refractive index is 1.92. After the residual gas is purged, constant pressure preparation is performed;

[0114] S3, introducing 2700sccm of silane and 10000sccm of ammonia into the reaction chamber, with a temperature of 450°C, a pressure of 1600mtorr, a deposition time of 120s, a power of 13000W, a duty cycle of 5:100, and depositing a second silicon nitride layer on the surface of the first silicon nitride layer. The second silicon nitride layer has a thickness of 25nm and a refractive index of 1.96. After the residual gas is purged, constant pressure preparation is performed;

[0115] S4, introducing 1900 sccm of silane and 12000 sccm of ammonia into the reaction chamber, with a temperature of 450°C, a pressure of 1650 mtorr, a deposition time of 200 s, a power of 14000 W, a duty cycle of 5:100, and depositing a third silicon nitride layer on the surface of the second silicon nitride layer. The third silicon nitride layer has a thickness of 30 nm and a refractive index of 2.03. After the residual gas is purged, constant pressure preparation is performed;

[0116] S5, introducing 1300 sccm of silane and 13000 sccm of ammonia into the reaction chamber, with a temperature of 450°C, a pressure of 1700 mtorr, a deposition time of 380 s, a power of 15000 W, a duty cycle of 5:100, and depositing a fourth silicon nitride layer on the surface of the third silicon nitride layer. The fourth silicon nitride layer has a thickness of 40 nm and a refractive index of 2.06. After purging the residual gas, constant pressure preparation is performed;

[0117] S6, introducing 1000 sccm of silane, 3000 sccm of ammonia, and 7000 sccm of nitrous oxide into the reaction chamber, with a temperature of 450°C, a pressure of 1750 mtorr, a deposition time of 120 s, a power of 15000 W, a duty cycle of 5:125, and depositing a first silicon oxynitride layer on the surface of the fourth silicon nitride layer. The first silicon oxynitride layer has a thickness of 25 nm and a refractive index of 2.06. After purging the residual gas, constant pressure preparation is performed;

[0118] S7, introducing 900 sccm of silane, 3000 sccm of ammonia, and 8700 sccm of nitrous oxide into the reaction chamber, with a temperature of 450°C, a pressure of 1750 mtorr, a deposition time of 140 s, a power of 15000 W, a duty cycle of 5:125, and depositing a second silicon oxynitride layer on the surface of the first silicon oxynitride layer. The second silicon oxynitride layer has a thickness of 30 nm and a refractive index of 2.09. After purging the residual gas, constant pressure preparation is performed;

[0119] S8, introducing 1200 sccm of silane and 12000 sccm of nitrous oxide into the reaction chamber, with a temperature of 450° C., a pressure of 1800 mtorr, a deposition time of 100 s, a power of 15500 W, a duty cycle of 4:125, and depositing a silicon oxide layer on the surface of the second silicon oxynitride layer. The thickness of the silicon oxide layer is 22 nm, and then evacuating the chamber after completion;

[0120] S9, after the deposition is completed, the temperature is raised for 120s to 580°C, and constant temperature annealing is performed for 250s. The cavity is evacuated and purged, and nitrogen is introduced to break the vacuum. The process is completed after the pressure is returned to normal and the boat is taken out to form a passivation layer on the substrate.

[0121] S10. Forming an electrode on the passivation layer.

[0122] Example 2

[0123] A solar cell is prepared according to the method of Example 1, except that the preparation steps of the passivation layer include:

[0124] S1, placing the substrate in a reaction chamber of a deposition device;

[0125] S2, introducing 2600sccm of silane and 9000sccm of ammonia into the reaction chamber, the temperature is 430°C, the pressure is 1500mtorr, the deposition time is 100s, the power is 11000W, the duty cycle is 5:100, and a first silicon nitride layer is deposited on the surface of the substrate. The thickness of the first silicon nitride layer is 16nm and the refractive index is 1.93. After the residual gas is purged, constant pressure preparation is performed;

[0126] S3, introducing 2600 sccm of silane and 9000 sccm of ammonia into the reaction chamber, with a temperature of 430°C, a pressure of 1500 mtorr, a deposition time of 150 s, a power of 12000 W, a duty cycle of 5:100, and depositing a second silicon nitride layer on the surface of the first silicon nitride layer. The second silicon nitride layer has a thickness of 26 nm and a refractive index of 1.96. After purging the residual gas, constant pressure preparation is performed;

[0127] S4, introducing 1800 sccm of silane and 11000 sccm of ammonia into the reaction chamber, with a temperature of 430°C, a pressure of 1600 mtorr, a deposition time of 180 s, a power of 13000 W, a duty cycle of 5:100, and depositing a third silicon nitride layer on the surface of the second silicon nitride layer. The third silicon nitride layer has a thickness of 28 nm and a refractive index of 1.98. After the residual gas is purged, constant pressure preparation is performed;

[0128] S5, introducing 1200 sccm of silane and 12000 sccm of ammonia into the reaction chamber, with a temperature of 430°C, a pressure of 1600 mtorr, a deposition time of 400 s, a power of 14000 W, a duty cycle of 5:100, and depositing a fourth silicon nitride layer on the surface of the third silicon nitride layer. The fourth silicon nitride layer has a thickness of 43 nm and a refractive index of 2.07. After purging the residual gas, constant pressure preparation is performed;

[0129] S6, introducing 900 sccm of silane, 2000 sccm of ammonia, and 6000 sccm of nitrous oxide into the reaction chamber, with a temperature of 430°C, a pressure of 1700 mtorr, a deposition time of 130 s, a power of 14000 W, a duty cycle of 5:125, and depositing a first silicon oxynitride layer on the surface of the fourth silicon nitride layer. The first silicon oxynitride layer has a thickness of 25 nm and a refractive index of 2.08. After purging the residual gas, constant pressure preparation is performed;

[0130] S7, introducing 800 sccm of silane, 2000 sccm of ammonia, and 8500 sccm of nitrous oxide into the reaction chamber, with a temperature of 430°C, a pressure of 1700 mtorr, a deposition time of 150 s, a power of 14000 W, a duty cycle of 5:125, and depositing a second silicon oxynitride layer on the surface of the first silicon oxynitride layer. The second silicon oxynitride layer has a thickness of 28 nm and a refractive index of 2.11. After purging the residual gas, constant pressure preparation is performed;

[0131] S8, introducing 1100 sccm of silane and 10000 sccm of nitrous oxide into the reaction chamber, with a temperature of 430°C, a pressure of 1700 mtorr, a deposition time of 120 s, a power of 15000 W, a duty cycle of 4:125, and depositing a silicon oxide layer on the surface of the second silicon oxynitride layer. The thickness of the silicon oxide layer is 25 nm, and then evacuating the chamber after completion;

[0132] S9. After the deposition is completed, the temperature is raised for 100s to 550°C, and constant temperature annealing is performed for 300s. The cavity is evacuated and purged, and nitrogen is introduced to break the vacuum. The process is completed by returning to normal pressure and exiting the boat, and a passivation layer with a thickness of 175±10nm is formed on the substrate.

[0133] Example 3

[0134] A solar cell is prepared according to the method of Example 1, except that the preparation steps of the passivation layer include:

[0135] S1, placing the substrate in a reaction chamber of a deposition device;

[0136] S2, introducing 2800sccm of silane and 11000sccm of ammonia into the reaction chamber, the temperature is 480°C, the pressure is 1700mtorr, the deposition time is 180s, the power is 13000W, the duty cycle is 5:100, and a first silicon nitride layer is deposited on the surface of the substrate. The thickness of the first silicon nitride layer is 20nm and the refractive index is 1.91. After the residual gas is purged, constant pressure preparation is performed;

[0137] S3, introducing 2800sccm of silane and 11000sccm of ammonia into the reaction chamber, with a temperature of 480°C, a pressure of 1700mtorr, a deposition time of 200s, a power of 15000W, a duty cycle of 5:100, and depositing a second silicon nitride layer on the surface of the first silicon nitride layer. The second silicon nitride layer has a thickness of 23nm and a refractive index of 1.98. After the residual gas is purged, constant pressure preparation is performed;

[0138] S4, introducing 2000 sccm of silane and 13000 sccm of ammonia into the reaction chamber, with a temperature of 480°C, a pressure of 1700 mtorr, a deposition time of 220 s, a power of 15000 W, a duty cycle of 5:100, and depositing a third silicon nitride layer on the surface of the second silicon nitride layer. The third silicon nitride layer has a thickness of 27 nm and a refractive index of 2.03. After purging the residual gas, constant pressure preparation is performed;

[0139] S5, introducing 1400 sccm of silane and 14000 sccm of ammonia into the reaction chamber, with a temperature of 480°C, a pressure of 1800 mtorr, a deposition time of 300 s, a power of 16000 W, a duty cycle of 5:100, and depositing a fourth silicon nitride layer on the surface of the third silicon nitride layer. The fourth silicon nitride layer has a thickness of 37 nm and a refractive index of 2.07. After purging the residual gas, constant pressure preparation is performed;

[0140] S6, introducing 1100 sccm of silane, 4000 sccm of ammonia, and 8000 sccm of nitrous oxide into the reaction chamber, with a temperature of 480°C, a pressure of 1800 mtorr, a deposition time of 160 s, a power of 16000 W, a duty cycle of 5:125, and depositing a first silicon oxynitride layer on the surface of the fourth silicon nitride layer. The first silicon oxynitride layer has a thickness of 23 nm and a refractive index of 2.05. After purging the residual gas, constant pressure preparation is performed;

[0141] S7, introducing 1000 sccm of silane, 4000 sccm of ammonia, and 9000 sccm of nitrous oxide into the reaction chamber, with a temperature of 480°C, a pressure of 1800 mtorr, a deposition time of 230 s, a power of 16000 W, a duty cycle of 5:125, and depositing a second silicon oxynitride layer on the surface of the first silicon oxynitride layer. The second silicon oxynitride layer has a thickness of 27 nm and a refractive index of 2.13. After purging the residual gas, constant pressure preparation is performed;

[0142] S8, introducing 1300 sccm of silane and 13000 sccm of nitrous oxide into the reaction chamber, with a temperature of 480°C, a pressure of 1900 mtorr, a deposition time of 280 s, a power of 16000 W, a duty cycle of 4:125, and depositing a silicon oxide layer on the surface of the second silicon oxynitride layer. The thickness of the silicon oxide layer is 30 nm, and then evacuating the chamber after completion;

[0143] S9. After the deposition is completed, the temperature is raised for 150s to 600°C, and constant temperature annealing is performed for 200s. The cavity is evacuated and purged, and nitrogen is introduced to break the vacuum. The pressure is returned to normal and the boat is taken out to end the process, forming a passivation layer with a thickness of 130±10nm on the substrate.

[0144] Example 4

[0145] A solar cell is prepared according to the method of Example 1, except that step S5 is not performed, that is, the passivation layer does not contain the fourth silicon nitride layer, and the first silicon oxynitride layer is directly formed on the surface of the third silicon nitride layer.

[0146] Example 5

[0147] A solar cell is prepared according to the method of Example 1, the difference being that a fifth silicon nitride layer is deposited on the surface of the fourth silicon nitride layer, and then a first silicon oxynitride layer is formed on the fifth silicon nitride layer.

[0148] The preparation method of the fifth silicon nitride layer comprises:

[0149] 1400 sccm of silane and 13500 sccm of ammonia were introduced into the reaction chamber. The temperature was 450°C, the pressure was 1800 mtorr, the deposition time was 250 s, the power was 15000 W, the duty cycle was 5:100, and a fifth silicon nitride layer was deposited on the surface of the fourth silicon nitride layer. The thickness of the fifth silicon nitride layer was 25 nm, and the refractive index was 2.06.

[0150] Example 6

[0151] A solar cell is prepared according to the method of Example 1, except that the preparation method of step S2 is adjusted so that the thickness of the first silicon nitride layer is 25 nm and the refractive index is 2.13, so that the total refractive index of the first silicon nitride layer, the second silicon nitride layer, the third silicon nitride layer and the fourth silicon nitride layer is the same as the total refractive index of the first silicon oxynitride layer and the second silicon oxynitride layer.

[0152] Example 7

[0153] A solar cell was prepared according to the method of Example 1, except that the annealing in step S9 was not performed.

[0154] Example 8

[0155] A solar cell is prepared according to the method of Example 1, except that the annealing temperature in step S9 is 500° C.

[0156] Example 9

[0157] A solar cell was prepared according to the method of Example 1, except that the annealing temperature in step S9 was 650°C.

[0158] Comparative Example 1

[0159] A solar cell was prepared according to the method of Example 1, except that the first silicon nitride layer, the second silicon nitride layer, the third silicon nitride layer and the fourth silicon nitride layer were replaced by a silicon nitride layer with a thickness of 115 nm and a refractive index of 2.10.

[0160] Comparative Example 2

[0161] A solar cell was prepared according to the method of Example 1, except that the passivation layer was replaced by a silicon nitride layer of equal thickness, and the refractive index of the silicon nitride layer was 2.15.

[0162] Comparative Example 3

[0163] A solar cell is prepared according to the method of Example 1, except that the deposition sequence is adjusted to sequentially form a fourth silicon nitride layer, a third silicon nitride layer, a second silicon nitride layer and a first silicon nitride layer on the surface of the substrate, thereby forming a first silicon nitride oxide layer on the surface of the first silicon nitride layer.

[0164] The solar cells prepared in the above examples and comparative examples were tested for performance, and the testing method included:

[0165] (1) Preparation before the test:

[0166] Before testing the battery cell, it must be placed in the test room for more than 24 hours before testing. Test environment temperature and humidity requirements: temperature is (25±3)℃, humidity is 20%~60%, and doors and windows must be closed and dust-free during testing.

[0167] (2) Open circuit voltage (Uoc), short circuit current (Isc) and efficiency (Eff) tests:

[0168] Use a 500W halogen tungsten lamp and a 0~250V AC transformer. Set the light intensity to 38,000 LUX~40,000 LUX. The distance between the lamp and the test platform is approximately 15cm~20cm. Direct test values ​​are open-circuit voltage, short-circuit current and efficiency.

[0169] (3) Maximum power point (Pmax) test:

[0170] By changing the size of the load resistance, the output power of the solar cell under different loads is measured, and the operating point with the maximum output power is found.

[0171] (4) Fill factor (FF) test:

[0172] The fill factor FF is Pmax / (UOC×ISC), which reflects the variation of the battery's output power with load.

[0173] (5) Equivalent series resistance (Rs) and equivalent parallel resistance (Rsh) test:

[0174] By measuring the current-voltage (IV) curve of the solar cell, the series resistance (Rs) and parallel resistance (Rsh) are measured. The equivalent series resistance inside the solar cell will affect its forward volt-ampere characteristics and short-circuit current. In addition, the increase in series resistance will reduce the fill factor and photoelectric conversion efficiency of the solar cell.

[0175] The test results are shown in Table 1.

[0176] Table 1

[0177]

[0178] From the above table we can see that:

[0179] (1) Compared with Examples 4-5, Example 1 shows that the present application uses four silicon nitride layers, which improves the short-circuit current and open-circuit voltage compared with three or five layers, thereby improving the photoelectric conversion efficiency.

[0180] (2) Compared with Example 6, the present application controls the refractive index of the multi-layer silicon nitride layer and the multi-layer silicon oxynitride layer, and can reflect the light passing through the silicon substrate back to the silicon substrate, thereby improving the multiple utilization of long-wave light and improving the photoelectric conversion efficiency.

[0181] (3) Compared with Examples 7-9, it can be seen that the present application can effectively repair lattice damage, activate dopants, improve film properties, eliminate stress, improve electrical properties and optimize passivation effects through annealing treatment, thereby avoiding problems such as weakened luminous intensity, changes in residual stress and decreased electrical properties.

[0182] (4) Compared with Comparative Examples 1-3, it can be seen that the passivation layer on the back of the solar cell of the present application adopts a combination of a silicon nitride layer, a silicon oxynitride layer and a silicon oxide layer, and adopts a multi-layer silicon nitride layer with a refractive index increasing in sequence, which can increase the thickness of the passivation layer, improve the long-wave response, and effectively reduce light loss. In addition, it can also increase the hydrogen ion concentration in the silicon nitride layer, improve the hydrogen passivation effect, and cooperate to improve the passivation performance of the back of the solar cell, thereby improving the photoelectric conversion efficiency of the back contact cell.

[0183] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0184] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the application. It should be noted that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A solar cell, characterized in that: The solar cell comprises: A substrate, the substrate comprising a light-facing surface and a backlight surface that are arranged opposite to each other in a thickness direction; A passivation layer is arranged on the backlight surface of the substrate, and the passivation layer includes at least two silicon nitride layers, a silicon nitride oxide layer and a silicon oxide layer stacked in sequence in a direction away from the substrate; the refractive index of each silicon nitride layer increases in sequence in a direction away from the substrate.

2. The solar cell according to claim 1, characterized in that The passivation layer comprises a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer and a fourth silicon nitride layer which are sequentially stacked in a direction away from the substrate; Optionally, the thickness of the first silicon nitride layer is 15 nm to 25 nm, and the refractive index of the first silicon nitride layer is 1.90 to 1.95; Optionally, the thickness of the second silicon nitride layer is 20 nm to 30 nm, and the refractive index of the second silicon nitride layer is 1.95 to 2.00; Optionally, the thickness of the third silicon nitride layer is 25 nm to 35 nm, and the refractive index of the third silicon nitride layer is 2.00 to 2.05; Optionally, the thickness of the fourth silicon nitride layer is 35 nm to 45 nm, and the refractive index of the fourth silicon nitride layer is 2.05 to 2.

10.

3. The solar cell according to claim 1, characterized in that The refractive index of the silicon oxynitride layer is greater than the total refractive index of the silicon nitride layers; Optionally, the total refractive index of each of the silicon nitride layers is 2.1-2.

17.

4. The solar cell according to any one of claims 1 to 3, characterized in that: The passivation layer comprises at least two silicon oxynitride layers; the refractive index of each silicon oxynitride layer increases in sequence in a direction away from the substrate; Optionally, the passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer stacked in sequence in a direction away from the substrate; Further optionally, the thickness of the first silicon oxynitride layer is 20 nm to 30 nm, and the refractive index of the first silicon oxynitride layer is 2.04 to 2.08; Further optionally, the thickness of the second silicon oxynitride layer is 25 nm to 35 nm, and the refractive index of the second silicon oxynitride layer is 2.07 to 2.

15.

5. A method for preparing a solar cell, characterized in that: The preparation method of the solar cell comprises: Providing a substrate, wherein the substrate comprises a light-facing surface and a backlight surface that are arranged opposite to each other in a thickness direction; At least two silicon nitride layers, at least one silicon oxynitride layer and a silicon oxide layer are sequentially formed on the backlight side of the substrate, and a passivation layer is obtained on the backlight side of the substrate, wherein the refractive index of the silicon nitride layer increases sequentially in a direction away from the substrate.

6. The method for preparing a solar cell according to claim 5, characterized in that: After forming the silicon oxide layer, annealing the substrate; Optionally, the annealing temperature is 550° C. to 600° C., and the annealing time is 200 s to 300 s.

7. The method for preparing a solar cell according to claim 5, characterized in that: The passivation layer comprises a first silicon nitride layer, a second silicon nitride layer, a third silicon nitride layer and a fourth silicon nitride layer which are sequentially formed in a direction away from the substrate; Optionally, the first silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600 sccm~2800 sccm, the flow rate of the nitrogen source is 9000 sccm~11000 sccm, the temperature is 430°C~480°C, the pressure is 1500mtorr~1700mtorr, the time is 50s~180s, the power is 11000W~13000W, and the duty cycle is 0.03~0.07; Optionally, the second silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 2600 sccm~2800 sccm, the flow rate of the nitrogen source is 9000 sccm~11000 sccm, the temperature is 430°C~480°C, the pressure is 1500mtorr~1700mtorr, the time is 100s~200s, the power is 12000W~15000W, and the duty cycle is 0.03~0.07; Optionally, the third silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1800 sccm~2000 sccm, the flow rate of the nitrogen source is 11000 sccm~13000 sccm, the temperature is 430°C~480°C, the pressure is 1600mtorr~1700mtorr, the time is 180s~220s, the power is 13000W~15000W, and the duty cycle is 0.03~0.07; Optionally, the fourth silicon nitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1200sccm~1400sccm, the flow rate of the nitrogen source is 12000sccm~14000sccm, the temperature is 430℃~480℃, the pressure is 1600mtorr~1800mtorr, the time is 300s~400s, the power is 14000W~16000W, and the duty cycle is 0.03~0.

07.

8. The method for preparing a solar cell according to claim 5, characterized in that: The passivation layer includes a first silicon oxynitride layer and a second silicon oxynitride layer sequentially formed in a direction away from the substrate; Optionally, the first silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 900 sccm~1100 sccm, the flow rate of the nitrogen source is 2000 sccm~4000 sccm, the flow rate of the oxygen source is 6000 sccm~8000 sccm, the temperature is 430°C~480°C, the pressure is 1700mtorr~1800mtorr, the time is 110s~160s, the power is 14000W~16000W, and the duty cycle is 0.03~0.05; Optionally, the second silicon oxynitride layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 800sccm~1000sccm, the flow rate of the nitrogen source is 2000sccm~4000sccm, the flow rate of the oxygen source is 8500sccm~9000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1800mtorr, the time is 130s~230s, the power is 14000W~16000W, and the duty cycle is 0.03~0.

05.

9. The method for preparing a solar cell according to any one of claims 5 to 7, characterized in that: The silicon oxide layer is formed by chemical vapor deposition, wherein the flow rate of the silicon source is 1100sccm~1300sccm, the flow rate of the oxygen source is 10000sccm~13000sccm, the temperature is 430℃~480℃, the pressure is 1700mtorr~1900mtorr, the time is 80s~280s, the power is 15000W~16000W, and the duty cycle is 0.03~0.

04.

10. A photovoltaic module, characterized in that: The photovoltaic module comprises the solar cell according to any one of claims 1 to 4 and / or a solar cell prepared by the method for preparing a solar cell according to any one of claims 5 to 7.

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