Solar cell and preparation method therefor, and photovoltaic module

Abstract

A solar cell and a preparation method therefor, and a photovoltaic module, which relate to the technical field of solar cells. The solar cell comprises: an N-type silicon substrate, a P-type doped layer arranged on the front surface of the N-type silicon substrate, and a tunnel oxide layer, an N-type doped layer and a transparent conductive oxide film which are sequentially arranged on the back surface of the N-type silicon substrate from inside to outside, wherein the front surface of the N-type silicon substrate is a light incident surface. By means of additionally providing a transparent conductive oxide film for the solar cell, the transverse resistance can be reduced, the consumption of the transverse resistance is reduced, and the collection rate of charge carriers is improved; in addition, the transparent conductive oxide film has the capability of reflecting infrared light, and can perform secondary absorption and utilization on infrared light transmitted to the back surface. The front-surface efficiency of the solar cell increases by 0.23%-0.38% compared with that of a solar cell without a transparent conductive oxide film, and the back-surface efficiency of the solar cell increases by 4.22%-4.43%.

Description

A solar cell and its preparation method, and photovoltaic module

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 25, 2023, with application number 2023112438425 and invention name “A solar cell, its preparation method, and photovoltaic module”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of solar cells, and in particular to a solar cell and a preparation method thereof, and a photovoltaic module. Background Art

[0003] TOPCon cells are tunnel oxide passivated contact solar cells based on the principle of selective carriers. The structural difference between TOPCon cells and Perc cells lies in the tunnel oxide layer and the poly layer. The tunnel oxide layer is a SiO2 layer with a thickness of 1nm to 2nm. x The poly layer can protect the ultra-thin tunneling oxide layer from being damaged.

[0004] The backside of existing TOPCon solar cells features a poly layer. The resistivity of this poly layer, determined by the phosphorus doping concentration, is typically between 0.1Ω·cm and 0.3Ω·cm, making it difficult to further reduce. Furthermore, the existing poly layer suffers from low infrared light utilization. These two factors contribute to high short-circuit current losses in current TOPCon solar cells, limiting improvements in cell conversion efficiency.

[0005] Summary of the Invention

[0006] In order to solve the above technical problems, the present application discloses a solar cell and its preparation method, and a photovoltaic module to solve the current problems of difficulty in further reducing the resistivity of TOPCon solar cells and low infrared light utilization, thereby solving the problem of limited battery conversion efficiency.

[0007] In a first aspect, an embodiment of the present application provides a solar cell, comprising an N-type silicon substrate, a P-type doped layer disposed on a front surface of the N-type silicon substrate, and a tunneling oxide layer, an N-type doped layer, and a transparent conductive oxide film disposed sequentially from the inside out on a back surface of the N-type silicon substrate;

[0008] The front surface of the N-type silicon substrate is the light incident surface.

[0009] Optionally, the transparent conductive oxide film is made of at least one selected from aluminum-doped zinc oxide, tin-doped indium oxide, cadmium oxide, indium oxide, tin oxide or zinc oxide.

[0010] Optionally, the transparent conductive oxide film has a thickness of 10 nm to 50 nm.

[0011] Optionally, the solar cell further includes a front passivation layer and an anti-reflection layer sequentially stacked on the P-type doped layer from the inside to the outside.

[0012] Optionally, the back surface of the N-type silicon substrate is a suede structure.

[0013] Optionally, the solar cell further comprises a back protection layer, wherein the back protection layer is provided on a side of the transparent conductive oxide film away from the N-type doping layer;

[0014] And / or, the solar cell further includes a front electrode and a back electrode, the front electrode forms an ohmic contact with the P-type doped layer, and the back electrode forms an ohmic contact with the N-type doped layer.

[0015] In a second aspect, an embodiment of the present application provides a method for preparing a solar cell as described in the first aspect, comprising:

[0016] Providing an N-type silicon substrate;

[0017] Prepare a P-type doped layer on the front surface of the N-type silicon substrate;

[0018] Sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate;

[0019] A transparent conductive oxide film is formed on a side of the N-type doped layer facing away from the tunneling oxide layer.

[0020] Furthermore, the method for preparing the solar cell further comprises:

[0021] A back protection layer is deposited on a side of the transparent conductive oxide film away from the N-type doping layer, and the transparent conductive oxide film is annealed at the same time.

[0022] Furthermore, the deposition temperature of the transparent conductive oxide film is 300°C to 500°C.

[0023] Furthermore, forming a transparent conductive oxide film on a side of the N-type doped layer away from the tunneling oxide layer includes:

[0024] A transparent conductive oxide film is formed on the N-type doped layer by radio frequency magnetron sputtering using a zinc oxide aluminum target; wherein the zinc oxide aluminum target comprises 97.8wt% to 98.2wt% of zinc oxide and 1.8wt% to 2.2wt% of aluminum oxide.

[0025] Furthermore, the step of sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate comprises:

[0026] In the same furnace tube, depositing the tunneling oxide layer, the phosphorus-doped amorphous silicon thin film and the silicon dioxide mask layer in sequence on the back side of the N-type silicon substrate;

[0027] Annealing is performed on the N-type silicon substrate so that the crystal structure of the phosphorus-doped amorphous silicon thin film is transformed into a polycrystalline silicon thin film, thereby obtaining the N-type doped layer.

[0028] Furthermore, before preparing the P-type doping layer on the front surface of the N-type silicon substrate, the method for preparing the solar cell further includes:

[0029] Texturing is performed on the front and back sides of the N-type silicon substrate.

[0030] Furthermore, the step of preparing a P-type doped layer on the front surface of the N-type silicon substrate includes:

[0031] Single-side diffusion is performed on the front surface of the N-type silicon substrate to form a P-type doping layer.

[0032] Furthermore, after preparing the P-type doped layer on the front surface of the N-type silicon substrate and before sequentially preparing the tunneling oxide layer and the N-type doped layer on the back surface of the N-type silicon substrate, the solar cell manufacturing method further includes:

[0033] The N-type silicon substrate is alkali-etched to remove the PN junction on the back side and the edge of the N-type silicon substrate, and to form a textured surface on the back side.

[0034] Furthermore, after sequentially forming a tunneling oxide layer and an N-type doping layer on the back surface of the N-type silicon substrate, and before forming a transparent conductive oxide film on a side of the N-type doping layer facing away from the tunneling oxide layer, the solar cell manufacturing method further includes:

[0035] Performing RCA cleaning on the solar cell to remove a first wrap-around layer that is wrap-around plated onto the front surface of the N-type silicon substrate when depositing the silicon dioxide mask layer and a phosphosilicate glass layer generated during annealing of the N-type silicon substrate, then removing a second wrap-around layer that is wrap-around plated onto the front surface of the N-type silicon substrate when depositing the N-type doped layer, and finally removing the silicon dioxide mask layer and the borosilicate glass layer on the front surface of the N-type silicon substrate;

[0036] A front passivation layer and an anti-reflection layer are sequentially deposited on the front surface of the N-type silicon substrate.

[0037] Furthermore, after depositing a back protective layer on a side of the transparent conductive oxide film away from the N-type doped layer and annealing the transparent conductive oxide film, the preparation method further comprises:

[0038] Printing slurry on the front and back sides of the N-type silicon substrate to form a front electrode and a back electrode, respectively;

[0039] The solar cell is manufactured after the N-type silicon substrate is sintered, light injected and tested.

[0040] In a third aspect, an embodiment of the present application provides a photovoltaic module comprising the solar cell as described in the first aspect.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention provides a solar cell and its preparation method. By adding a layer of transparent conductive oxide film, the solar cell can reduce lateral resistance, reduce lateral resistance consumption, and improve carrier collection efficiency. Furthermore, the transparent conductive oxide film has the ability to reflect infrared light, allowing for secondary absorption and utilization of infrared light transmitted to the back surface. This eliminates the need for the back surface of the solar cell to be polished to enhance infrared light reflection. Furthermore, the back surface of the solar cell can have a velvet structure, thereby improving the backside efficiency of the cell. The fill factor (FF) of the solar cell of the present invention is improved by 0.13% to 0.26% compared to a solar cell without the transparent conductive oxide film. The front side efficiency of the solar cell of the present invention is improved by 0.23% to 0.38%, while the backside efficiency is improved by 4.22% to 4.43%. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] FIG1 is a schematic structural diagram of a solar cell provided in an embodiment of the present application;

[0045] FIG2 is a flow chart of a method for preparing a solar cell according to an embodiment of the present application;

[0046] FIG3 is another flow chart of the method for preparing a solar cell provided in an embodiment of the present application;

[0047] FIG4 is another flow chart of the method for preparing a solar cell provided in an embodiment of the present application.

[0048] Explanation of main reference numerals: 100, solar cell; 101, N-type silicon substrate; 102, tunneling oxide layer; 103, N-type doping layer; 104, transparent conductive oxide film; 105, back protective layer; 106, P-type doping layer; 107, front passivation layer; 108, anti-reflection layer; 110, front electrode; 111, back electrode. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] In the present invention, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe the present invention and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0051] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0052] Furthermore, the terms "installed," "disposed," "provided with," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integral structures; mechanical connections or electrical connections; direct connections or indirect connections through an intermediary; or internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0053] Furthermore, the terms "first," "second," and the like are primarily used to distinguish between different devices, elements, or components (which may or may not be of the same type and configuration), and are not intended to indicate or imply the relative importance or quantity of the devices, elements, or components indicated. Unless otherwise specified, "plurality" means two or more.

[0054] In addition, the reagents such as hydrofluoric acid, sodium hydroxide solution and various types of additives used in the solar cell preparation method in the embodiments of the present application can be obtained through commercial purchase and are not limited here.

[0055] The backside of the existing N-type TOPCon cell structure features a poly layer. The resistivity of the poly layer is determined by the phosphorus doping concentration, typically ranging from 0.1Ω·cm to 0.3Ω·cm. Due to the saturation of phosphorus doping, further increasing the doping concentration to reduce the resistivity is impossible. This results in high lateral resistance and significant carrier transport losses. Furthermore, the poly layer cannot effectively reflect transmitted long-wavelength infrared light back to the silicon wafer for secondary use, resulting in low infrared light utilization. These two factors result in significant short-circuit current losses, limiting improvements in cell conversion efficiency.

[0056] In a first aspect, an embodiment of the present application provides a solar cell 100. Referring to FIG1 , the solar cell 100 includes an N-type silicon substrate 101, a P-type doped layer 106 disposed on the front surface of the N-type silicon substrate 101, and a tunneling oxide layer 102, an N-type doped layer 103, and a transparent conductive oxide film 104 disposed sequentially from the inside to the outside on the back surface of the N-type silicon substrate 101.

[0057] Among them, the P-type doped layer and the N-type silicon substrate 101 form a PN junction. The N-type doped layer 103 and the transparent conductive oxide film 104 jointly play the role of transporting carriers. The tunneling oxide layer 102 can enable majority carriers to tunnel into the phosphorus-doped polysilicon thin layer while blocking the recombination of minority carriers, thereby allowing majority carriers to be transported laterally in the polysilicon layer and collected by the metal, thereby greatly reducing the metal contact recombination current density, improving the open circuit voltage and short circuit current of the battery, and improving the photoelectric conversion efficiency of the battery. Exemplarily, the above-mentioned tunneling oxide layer 102 is a layer of silicon dioxide. In order to achieve tunneling conduction of majority carriers, the tunneling oxide layer 102 needs to be set to a thinner thickness, for example, set to 0.8nm to 1.4nm. In addition, the N-type doped layer 103 (n + -poly-Si) can be a layer of doped polysilicon.

[0058] Transparent conductive oxide film 104 has excellent optoelectronic properties, including a wide bandgap, low resistivity, high visible light transmittance, and high infrared light reflectivity. For example, transparent conductive oxide film 104 may be an oxide of In, Sb, Zn, and Cd, or a composite multi-element oxide thin film material thereof.

[0059] It can be seen that the solar cell 100 can reduce the lateral resistance, reduce the consumption of lateral resistance, and improve the carrier collection rate by adding a layer of transparent conductive oxide film 104. On the other hand, the transparent conductive oxide film 104 has the ability to reflect infrared light. Since the front side of the N-type silicon substrate 101 is the light incident side, the transparent conductive oxide film 104 can absorb and utilize the infrared light transmitted to the back side for a second time. In contrast, in order to enhance the reflection of infrared light on the back side of current solar cells, the back side needs to be prepared into a polished structure, but the polished structure is not conducive to the utilization of light on the back side. In actual use, the back side of the solar cell also has a certain amount of light. Increasing the light utilization rate on the back side will also be beneficial to the power generation of the solar cell. However, the back side of the solar cell of the present application is no longer required to be prepared into a polished surface; further, the back side of the N-type silicon substrate of the solar cell is a velvet structure, thereby improving the back side efficiency of the cell.

[0060] The filling factor (FF) of the solar cell 100 provided in the embodiment of the present application is improved by 0.13% to 0.26% compared to the solar cell without the transparent conductive oxide film 104. The conversion efficiency (Eta) of the solar cell 100 provided in the embodiment of the present application is improved by 0.23% to 0.38% compared to the solar cell without the transparent conductive oxide film 104.

[0061] Optionally, the material of the transparent conductive oxide film 104 is selected from at least one of aluminum-doped zinc oxide, tin-doped indium oxide, cadmium oxide, indium oxide, tin oxide or zinc oxide; more preferably, indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO), whose far-infrared reflectivity can reach 90%.

[0062] As an example, in the embodiment of the present application, the material of the transparent conductive oxide film 104 is aluminum-doped zinc oxide (AZO). The band gap width of AZO (3.37eV) is greater than the energy of visible photons (1.59eV~3.27eV), so it cannot cause intrinsic excitation under the irradiation of visible light, so it is transparent to the entire visible light. The AZO film deposited using a low-resistivity AZO target has a high carrier concentration for enhanced absorption of short waves and exhibits excellent conductivity; at the same time, it has a large reflection for long waves, and the reflectivity increases with the increase of film thickness and the decrease of sheet resistance. In short, the AZO film formed using a low-resistivity AZO target exhibits excellent conductivity and increased reflection of long-wave infrared light, so that the infrared light transmitted from the front of the battery to the back is reflected to the silicon wafer for secondary absorption and utilization, thereby increasing the short-circuit current.

[0063] A low resistivity AZO film is formed on the N-type doped layer 103 on the back of the N-type silicon substrate, which can effectively reduce the resistivity (up to 4×10 -4Ω·cm), thereby reducing the lateral resistance of the N-type doped layer 103 and improving the carrier collection rate; on the other hand, the low-resistivity AZO has a good reflective effect on infrared light, so that the infrared light transmitted to the back of the silicon wafer is reflected back to the N-type silicon substrate 101, so that the infrared light can be reused and the utilization rate of the long-wave band can be improved.

[0064] Optionally, the thickness of transparent conductive oxide film 104 is between 10 nm and 50 nm, including any value within this thickness range. For example, the thickness of transparent conductive oxide film 104 is 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, 22 nm, 26 nm, 27 nm, 30 nm, 31 nm, 33 nm, 35 nm, 38 nm, 40 nm, 42 nm, 45 nm, 48 nm, or 50 nm. More preferably, the thickness of transparent conductive oxide film 104 is between 20 nm and 40 nm. Further, the thickness of transparent conductive oxide film 104 is between 25 nm and 35 nm. The Eta (%) of solar cell 100 in an IV test increases with increasing thickness of transparent conductive oxide film 104, then reaches a maximum value and then decreases.

[0065] Furthermore, the solar cell 100 further includes a front passivation layer 107 and an anti-reflection layer 108 sequentially stacked on the P-type doped layer 106 from the inside to the outside.

[0066] Optionally, the front passivation layer 107 is a front aluminum oxide passivation layer. Aluminum oxide has a negative fixed charge and is suitable for passivating a P-type emitter; and / or,

[0067] The anti-reflection layer 108 is a silicon nitride anti-reflection layer 108 , which is deposited on the front aluminum oxide passivation layer to provide optical anti-reflection.

[0068] In this embodiment, in order to achieve electrical connection, the solar cell 100 further includes a front electrode 110 and a back electrode 111 . The front electrode 110 forms an ohmic contact with the P-type doped layer 106 , and the back electrode 111 forms an ohmic contact with the N-type doped layer 103 .

[0069] In some embodiments, the solar cell 100 further includes a back protection layer 105, which is disposed on a side of the transparent conductive oxide film 104 facing away from the N-type doped layer 103. For example, the back protection layer 105 is silicon nitride (SiN x ) protective layer, which plays a role in back protection.

[0070] In a second aspect, referring to FIG. 2 , an embodiment of the present application further provides a method for preparing a solar cell as described in the first aspect, comprising:

[0071] Providing an N-type silicon substrate;

[0072] A P-type doped layer is prepared on the front surface of the N-type silicon substrate;

[0073] A tunneling oxide layer and an N-type doping layer are sequentially formed on the back side of an N-type silicon substrate;

[0074] A transparent conductive oxide film is formed on a side of the N-type doped layer away from the tunneling oxide layer.

[0075] In the steps of sequentially depositing a tunneling oxide layer and an N-type doping layer on the back side of an N-type silicon substrate, each layer is generally sequentially deposited using a plasma enhanced chemical vapor deposition (PECVD) method.

[0076] Furthermore, the steps of sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate include:

[0077] In the same furnace tube, a tunneling oxide layer, a phosphorus-doped amorphous silicon film and a silicon dioxide mask layer are sequentially deposited on the back side of an N-type silicon substrate;

[0078] Annealing is performed on the N-type silicon substrate to transform the crystal structure of the phosphorus-doped amorphous silicon film into a polycrystalline silicon film, thereby obtaining an N-type doped layer.

[0079] This step simplifies the process steps by sequentially depositing a tunnel oxide layer, a phosphorus-doped amorphous silicon film, and a silicon dioxide mask layer in the same furnace tube, thereby improving production efficiency and equipment utilization.

[0080] Exemplarily, the tunnel oxide layer is deposited by PECVD, an oxygen source (oxygen or nitrous oxide) is introduced, and a tunnel oxide layer with a thickness of 0.5 nm to 2 nm is deposited. A thin layer of silicon oxide is deposited on the surface of the silicon wafer under the action of a radio frequency electric field, with a deposition pressure of 100 Pa to 150 Pa and a deposition temperature of 200° C. to 300° C.

[0081] The phosphorus-doped amorphous silicon film is deposited by PECVD, wherein SiH4, PH3, and carrier gas (H2 and / or Ar) are introduced to deposit the phosphorus-doped amorphous silicon film with a thickness of 80 nm to 150 nm. The flow ratio of SiH4, PH3 to carrier gas is 1:(2-3):(4-6), and the deposition temperature is 350° C. to 400° C.

[0082] The silicon dioxide mask layer is deposited by PECVD, with SiH4 and N2O introduced to deposit a SiO2 wet mask layer with a thickness of 10nm to 40nm. It is used to protect the N-type doped layer from being damaged during de-plating and cleaning. The ratio of SiH4 to N2O is 1:(6-10), and the deposition temperature is 350℃ to 400℃.

[0083] Furthermore, the step of forming a transparent conductive oxide film on a side of the N-type doped layer facing away from the tunneling oxide layer includes:

[0084] A transparent conductive oxide film is formed on the N-type doped layer via radio frequency magnetron sputtering using a zinc oxide aluminum target. The zinc oxide aluminum target comprises 97.8-98.2% zinc oxide and 1.8-2.2% aluminum oxide. The AZO film, formed using the low-resistivity AZO target, exhibits excellent conductivity and enhanced reflection of long-wavelength infrared light.

[0085] For example, a PVD method is used, and a zinc aluminum oxide (AZO, 98% ZnO + 2% Al2O3) target is used. Under the action of an electromagnetic field, Ar ions are used to bombard the AZO target and deposit it on the N-type doped layer.

[0086] Preferably, the transparent conductive oxide film has a thickness of 10 nm to 50 nm. The deposition temperature is 300°C to 500°C, including any value within this temperature range, such as 300°C, 350°C, 380°C, 400°C, 450°C, 480°C, or 500°C. Within a certain temperature range, the Eta (%) and FF (%) of the solar cell in an IV test increase with increasing deposition temperature of the transparent conductive oxide film. More preferably, the deposition temperature is 400°C to 500°C; further, the deposition temperature is 450°C to 500°C.

[0087] 3 , an embodiment of the present application provides a method for preparing a solar cell according to the first aspect, comprising:

[0088] Providing an N-type silicon substrate;

[0089] A P-type doped layer is prepared on the front surface of the N-type silicon substrate;

[0090] A tunneling oxide layer and an N-type doping layer are sequentially formed on the back side of an N-type silicon substrate;

[0091] forming a transparent conductive oxide film on a side of the N-type doped layer facing away from the tunneling oxide layer;

[0092] A back protection layer is deposited on a side of the transparent conductive oxide film away from the N-type doping layer, and the transparent conductive oxide film is annealed at the same time.

[0093] For example, in the step of depositing a back protective layer on the transparent conductive oxide film, the back protective layer is deposited by PECVD, and the material of the back protective layer is preferably SiN x .

[0094] This preparation method further simplifies the production process, eliminating the need for a separate annealing step for the transparent conductive oxide film. Furthermore, annealing the transparent conductive oxide film under the same process conditions as the backside protective layer deposition can improve the electrical properties of the transparent conductive oxide film.

[0095] 4 , an embodiment of the present application provides a method for preparing a solar cell according to the first aspect, comprising:

[0096] Providing an N-type silicon substrate;

[0097] Texturing on the front and back sides of an N-type silicon substrate;

[0098] A P-type doped layer is prepared on the front surface of the N-type silicon substrate;

[0099] Performing alkaline polishing on the N-type silicon substrate to remove the PN junction on the back and edge of the N-type silicon substrate;

[0100] A tunneling oxide layer and an N-type doping layer are sequentially formed on the back side of an N-type silicon substrate;

[0101] Perform RCA cleaning on solar cells;

[0102] A front passivation layer and an anti-reflection layer are sequentially deposited on the front surface of the N-type silicon substrate;

[0103] forming a transparent conductive oxide film on a side of the N-type doped layer facing away from the tunneling oxide layer;

[0104] depositing a back protective layer on a side of the transparent conductive oxide film facing away from the N-type doped layer, and annealing the transparent conductive oxide film at the same time;

[0105] Printing paste on the front and back sides of an N-type silicon substrate to form a front electrode and a back electrode, respectively;

[0106] After sintering, light injection and testing, the N-type silicon substrate is used to produce a solar cell.

[0107] Exemplarily, in the steps of texturing the front and back sides of an N-type silicon substrate, a mixed solution of hydrogen peroxide with a volume fraction of 1.5% to 2.5% and an alkali with a mass concentration of 0.2% to 0.4% is first used for cleaning to remove oil stains on the surface of the silicon wafer, and then an alkali solution with a mass concentration of 0.8% to 1.2% is used for texturing, and an auxiliary texturing additive is provided to slow down the reaction rate and form a pyramidal velvet structure on the surface of the silicon wafer, which plays a role in reducing reflection and limiting light.

[0108] Optionally, in the step of performing single-sided diffusion on the front side of the N-type silicon substrate to form a P-type doped layer, the cleaned and dried silicon wafer enters a boron diffusion furnace, and BCl3 and oxygen are diffused at 800°C to 1050°C to form a pn junction. The ratio of BCl3 to oxygen is 1:(14 to 16), and the volume proportion of BCl3 in the furnace tube atmosphere is 1.2% to 1.6%. Through high-temperature diffusion, a 100nm to 120nm borosilicate glass layer (BSG) is generated on the surface of the N-type silicon substrate, and the square resistance range is 80Ω / sq to 150Ω / sq.

[0109] Exemplarily, an N-type silicon substrate is subjected to alkali polishing to remove the PN junction on the back and edge of the N-type silicon substrate. The boron-expanded silicon wafer is first subjected to a chain HF machine to remove the BSG of the boron-expanded winding on the back, with the volume percentage of HF being 30% to 80%. The wafer is then transferred to a slot-type alkali polishing machine by a robot, and an alkali solution with a mass concentration of 1.5% to 2.5% and an alkali polishing additive are used to remove the PN junction on the back and edge of the silicon wafer, while a small velvet structure of 0.3μm to 1μm is formed on the back of the silicon wafer.

[0110] Exemplarily, in the step of annealing the N-type silicon substrate to convert the amorphous silicon structure into polycrystalline silicon, the annealing gas atmosphere is nitrogen (N2) or oxygen (O2), the temperature is 600°C to 1000°C, and the time is 10 minutes to 60 minutes, so that the crystal structure of the deposited amorphous silicon film is transformed to form a polycrystalline silicon film poly-Si.

[0111] More specifically, the solar cell is subjected to an RCA cleaning step to remove the first coating layer that is coated on the front surface of the N-type silicon substrate when depositing the silicon dioxide mask layer and the phosphosilicate glass layer generated during the annealing of the N-type silicon substrate, and then the second coating layer that is coated on the front surface of the N-type silicon substrate when depositing the N-type doped layer is removed, and finally the silicon dioxide mask layer and the borosilicate glass layer on the front surface of the N-type silicon substrate are removed.

[0112] For example, in the step of sequentially depositing a front passivation layer and an anti-reflection layer on the front surface of an N-type silicon substrate, the front passivation layer is deposited by atomic layer deposition (ALD), and the material of the front passivation layer is preferably aluminum oxide (Al2O3). The anti-reflection layer is deposited by PECVD, and the material of the anti-reflection layer is preferably silicon nitride (SiN x ).

[0113] In summary, this preparation method, by depositing a transparent conductive oxide film on the N-type doped layer, can, on the one hand, reduce lateral resistance, reduce lateral resistance consumption, and improve carrier collection efficiency; on the other hand, the transparent conductive oxide film can reflect infrared light and can secondary absorb and utilize infrared light transmitted to the back side of the N-type silicon substrate. The fill factor (FF) of the solar cell produced using the preparation method of the present application embodiment is improved by 0.13% to 0.26% compared to the solar cell without the addition of the transparent conductive oxide film 104. The cell conversion efficiency of the solar cell produced using the preparation method of the present application embodiment is improved by 0.23% to 0.38% compared to the solar cell without the transparent conductive oxide film deposited on the N-type doped layer.

[0114] In a third aspect, an embodiment of the present application provides a photovoltaic module, comprising the aforementioned solar cell 100 .

[0115] The technical solution of the present invention will be described below with reference to embodiments and drawings.

[0116] Example 1

[0117] The method for preparing a solar cell provided in this embodiment comprises the following steps:

[0118] (1) Texturing: Using an N-type silicon substrate, the oil stains on the surface of the silicon wafer are first cleaned with a mixed solution of 2% by volume hydrogen peroxide and 0.3% by mass alkali, and then a 1% by mass alkali solution is used for texturing. Auxiliary texturing additives are used to slow down the reaction rate, forming a pyramidal velvet structure on the surface of the silicon wafer, which plays a role in anti-reflection and light limiting.

[0119] (2) Boron diffusion: After cleaning and drying, the N-type silicon substrate enters the boron diffusion furnace, and is deposited at 840°C using BCl3 and oxygen. The temperature is then gradually raised to 1050°C, and oxygen is introduced to diffuse to form a pn junction. The ratio of BCl3 to oxygen during deposition at 840°C is 1:15, and the volume proportion of BCl3 in the furnace atmosphere is 1.4%. The temperature is raised to 1050°C, and 100% oxygen is introduced. High-temperature diffusion is promoted to form a 100nm to 120nm borosilicate glass (BSG) layer on the surface of the N-type silicon substrate, with an average square resistance of 110Ω / sq.

[0120] (3) Alkali texturing: After the boron expansion, the silicon wafer is firstly removed from the back of the boron-expanded borosilicate glass layer by a chain HF machine. The volume percentage of HF is 30%. Then the wafer is transferred to the texturing equipment by a robot. The pn junction on the back and edge of the silicon wafer is removed by using an alkali solution with a mass concentration of 2% and a texturing additive. At the same time, a 0.3μm to 3μm velvet structure is formed on the back of the silicon wafer.

[0121] (4) Fabrication of tunnel oxide layer and polysilicon passivation film: Tubular PECVD is used to deposit tunnel oxide layer, phosphorus-doped amorphous silicon film and silicon dioxide mask layer. The above three layers are deposited in one furnace tube without breaking the vacuum.

[0122] Layer 1: PECVD deposition is used, with nitrous oxide (N2O) introduced as an oxygen source to deposit a tunneling oxide layer with a thickness of 0.5-2 nm. A thin layer of silicon oxide is deposited on the surface of the silicon wafer under the action of an RF electric field at a deposition pressure of 100 Pa and a deposition temperature of 300°C.

[0123] Film layer 2: PECVD deposition is used to deposit a phosphorus-doped amorphous silicon film with a thickness of 80nm to 150nm by introducing SiH4, PH3, and H2. The ratio of SiH4, PH3, and H2 is 1:3:6, and the deposition temperature is 400°C.

[0124] Layer 3: PECVD deposition, with SiH4 and N2O introduced, deposits a SiO2 wet mask layer with a thickness of 10nm to 40nm. This protects the N-type doped layer from being damaged during de-coating and cleaning. The ratio of SiH4 to N2O is 1:6, and the deposition temperature is 400°C.

[0125] (5) Annealing: The battery is annealed in a tubular annealing furnace with a nitrogen (N2) or oxygen (O2) atmosphere at a temperature of 920°C for 30 minutes to transform the crystal structure of the deposited amorphous silicon film into a polycrystalline silicon film (poly-Si).

[0126] (6) RCA cleaning: first, the mask layer on the front is removed by chain HF, with the volume percentage of HF being 8%, and the oxide layer plated on the front of the N-type silicon substrate when the silicon dioxide mask layer is deposited in step (4), as well as the phosphorus silicon glass layer (PSG) generated during the annealing process are removed. Then, the substrate is transferred to an alkaline tank to remove the poly coating on the front of the N-type silicon substrate. At this time, the N-type doped layer on the back is not damaged under the protection of the SiO2 mask layer (silicon dioxide mask layer). The mass concentration of the alkaline solution in the alkaline tank is 3%. After the poly coating on the front of the N-type silicon substrate is completely removed, the substrate is transferred to a tank HF, with the volume percentage of HF being 10%, to remove the borosilicate glass layer (BSG) and silicon dioxide mask layer on the front.

[0127] (7) Deposition of aluminum oxide film and silicon nitride film on the front: Atomic layer deposition (ALD) is used to deposit aluminum oxide (Al2O3) film for passivation to form a front passivation layer; PECVD is used to deposit silicon nitride (SiN x ) The film is used for anti-reflection, forming an anti-reflection layer;

[0128] (8) Back AZO film (transparent conductive oxide film) and silicon nitride deposition (back protective layer):

[0129] Radio frequency magnetron sputtering (PVD) was used, with aluminum zinc oxide (AZO, 98% ZnO + 2% Al2O3) as the target. Under the action of an electromagnetic field, Ar ions bombarded the AZO target to deposit an AZO film on the N-type doped layer. The deposition temperature of the AZO film was 300°C, and the thickness of the AZO film was 10nm.

[0130] SiN deposition using PECVD x The film is used for back side protection. The AZO film is annealed while the back side silicon nitride is deposited, eliminating the need for a separate annealing step.

[0131] (9) Screen printing the front and back slurries to make electrodes, i.e., the front electrode and the back electrode;

[0132] (10) Light injection, test efficiency and sorting.

[0133] Example 2

[0134] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the AZO film is 20 nm.

[0135] Example 3

[0136] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the AZO film is 30 nm.

[0137] Example 4

[0138] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the AZO film is 40 nm.

[0139] Example 5

[0140] The difference between this embodiment and embodiment 1 is that in step (8), the thickness of the AZO film is 50 nm.

[0141] Example 6

[0142] The difference between this embodiment and embodiment 1 is that in step (8), the AZO film deposition temperature is 500° C. and the thickness of the AZO film is 20 nm.

[0143] Comparative Example 1

[0144] The difference between this comparative example and Example 1 is that in step (8), only back silicon nitride is deposited, and no AZO film is deposited.

[0145] The photovoltaic current-voltage characteristic test (IV test) was performed on the solar cells of Examples 1-6 and Comparative Example 1, and the obtained data are shown in Table 1.

[0146] Table 1. Solar cell IV test data

[0147] As shown in Table 1, the front-side efficiency of the solar cells in Examples 1-6, as measured by IV testing, increased by 0.23% to 0.38% compared to Comparative Example 1, while the back-side efficiency increased by 4.22% to 4.43%. The fill factor (FF) of the solar cells in Examples 1-6, as measured by IV testing, also increased by 0.13% to 0.26% compared to Comparative Example 1. This indicates that depositing a transparent conductive oxide film on the N-type doped layer can, on the one hand, reduce lateral resistance, reduce lateral resistance consumption, and improve carrier collection efficiency. On the other hand, the transparent conductive oxide film can reflect infrared light and reabsorb and utilize infrared light transmitted to the back side. Due to the improved infrared light reflection and excellent light transmittance, the back side of the solar cells in Examples 1-6 was fabricated into a suede structure to improve back-side conversion efficiency and enhance back-side light utilization. In summary, adding a transparent conductive oxide film is beneficial for improving the front-side conversion efficiency and fill factor, front-side current, and back-side conversion efficiency of the solar cell, ultimately enhancing the solar cell's power generation capacity.

[0148] By comparing the test data of Examples 1-5, it can be seen that when the thickness of the AZO film is less than 30 nm, as the thickness of the AZO film increases, the front efficiency and back efficiency in the solar cell IV test results increase accordingly, and reach a maximum value when the AZO film is 30 nm; when the thickness of the AZO film is greater than 30 nm, as the thickness of the AZO film increases, the front efficiency and back efficiency in the solar cell IV test results decrease.

[0149] By comparing the test data of Examples 1-5, it can be seen that as the thickness of the AZO film increases, the fill factor in the solar cell IV test results increases accordingly; and after the thickness reaches more than 30nm, the thickness of the AZO film increases, but the fill factor does not change much; in addition, as the thickness of the AZO film increases, the open circuit voltage (V OC )decline.

[0150] As can be seen from the above, by changing the thickness of the AZO film, the performance of the solar cell can be changed. Preferably, the thickness of the AZO film is 20nm to 30nm.

[0151] By comparing the test data of Example 2 and Example 6, it can be seen that increasing the deposition temperature of the AZO thin film is helpful to improve the conversion efficiency of the solar cell.

[0152] The solar cells, preparation methods and photovoltaic modules disclosed in the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the solar cells, preparation methods, photovoltaic modules and their core concepts of the present invention. At the same time, for those skilled in the art, according to the concepts of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A solar cell, characterized in that: The solar cell comprises an N-type silicon substrate, a P-type doping layer arranged on the front side of the N-type silicon substrate, and a tunneling oxide layer, an N-type doping layer and a transparent conductive oxide film arranged in sequence from the inside to the outside on the back side of the N-type silicon substrate; The front side of the N-type silicon substrate is the light incident side.

2. The solar cell according to claim 1, characterized in that: The material of the transparent conductive oxide film is selected from at least one of aluminum-doped zinc oxide, tin-doped indium oxide, cadmium oxide, indium oxide, tin oxide or zinc oxide.

3. The solar cell according to claim 1 or 2, characterized in that: The thickness of the transparent conductive oxide film is 10nm-50nm.

4. The solar cell according to any one of claims 1 to 3, characterized in that The solar cell further comprises a front passivation layer and an anti-reflection layer which are sequentially stacked on the P-type doping layer from the inside to the outside.

5. The solar cell according to any one of claims 1 to 4, characterized in that: The back side of the N-type silicon substrate is a suede structure.

6. The solar cell according to any one of claims 1 to 5, characterized in that The solar cell further comprises a back side protection layer, and the back side protection layer is arranged on a side of the transparent conductive oxide film away from the N-type doping layer.

7. The solar cell according to any one of claims 1 to 6, characterized in that The solar cell further comprises a front electrode and a back electrode, wherein the front electrode forms an ohmic contact with the P-type doping layer, and the back electrode forms an ohmic contact with the N-type doping layer.

8. A method for preparing a solar cell according to any one of claims 1 to 7, characterized in that: include: Providing an N-type silicon substrate; Preparing a P-type doped layer on the front side of the N-type silicon substrate; Sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate; A transparent conductive oxide film is formed on a side of the N-type doped layer away from the tunneling oxide layer.

9. The method for preparing a solar cell according to claim 8, characterized in that: The method for preparing the solar cell further comprises: A back protection layer is deposited on a side of the transparent conductive oxide film away from the N-type doping layer, and the transparent conductive oxide film is annealed at the same time.

10. The method for preparing a solar cell according to claim 8 or 9, characterized in that: The deposition temperature of the transparent conductive oxide film is 300° C. to 500° C.

11. The method for preparing a solar cell according to any one of claims 8 to 10, characterized in that: The step of forming a transparent conductive oxide film on a side of the N-type doped layer away from the tunneling oxide layer comprises: A transparent conductive oxide film is formed on the N-type doped layer by radio frequency magnetron sputtering using a zinc oxide aluminum target; wherein the zinc oxide aluminum target comprises 97.8wt% to 98.2wt% of zinc oxide and 1.8wt% to 2.2wt% of aluminum oxide.

12. The method for preparing a solar cell according to any one of claims 8 to 11, characterized in that: The step of sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate comprises: In the same furnace tube, sequentially depositing the tunneling oxide layer, the phosphorus-doped amorphous silicon film and the silicon dioxide mask layer on the back side of the N-type silicon substrate; The N-type silicon substrate is annealed so that the crystal structure of the phosphorus-doped amorphous silicon film is transformed into a polycrystalline silicon film to obtain the N-type doped layer.

13. The method for preparing a solar cell according to claim 12, characterized in that: Before preparing the P-type doping layer on the front surface of the N-type silicon substrate, the method for preparing the solar cell further includes: Texturing is performed on the front and back sides of the N-type silicon substrate.

14. The method for preparing a solar cell according to claim 12 or 13, characterized in that: The step of preparing a P-type doped layer on the front surface of the N-type silicon substrate comprises: Single-side diffusion is performed on the front side of the N-type silicon substrate to form a P-type doping layer.

15. The method for preparing a solar cell according to any one of claims 12 to 14, characterized in that: After preparing the P-type doping layer on the front side of the N-type silicon substrate, and before sequentially preparing the tunneling oxide layer and the N-type doping layer on the back side of the N-type silicon substrate, the method for preparing the solar cell further includes: The N-type silicon substrate is alkali-etched to remove the PN junction on the back side and the edge of the N-type silicon substrate and to form a textured surface on the back side.

16. The method for preparing a solar cell according to any one of claims 12 to 15, characterized in that: After sequentially preparing a tunneling oxide layer and an N-type doping layer on the back side of the N-type silicon substrate, and before forming a transparent conductive oxide film on a side of the N-type doping layer away from the tunneling oxide layer, the method for preparing a solar cell further includes: Performing RCA cleaning on the solar cell to remove the first coating layer coated on the front side of the N-type silicon substrate when depositing the silicon dioxide mask layer and the phosphorus silicon glass layer generated during the annealing of the N-type silicon substrate, then removing the second coating layer coated on the front side of the N-type silicon substrate when depositing the N-type doping layer, and finally removing the silicon dioxide mask layer and the borosilicate glass layer on the front side of the N-type silicon substrate; A front passivation layer and an anti-reflection layer are sequentially deposited on the front surface of the N-type silicon substrate.

17. The method for preparing a solar cell according to any one of claims 12 to 16, characterized in that: After depositing a back protective layer on a side of the transparent conductive oxide film away from the N-type doping layer and annealing the transparent conductive oxide film, the preparation method further comprises: Printing slurry on the front and back sides of the N-type silicon substrate to respectively form a front electrode and a back electrode; The solar cell is manufactured after the N-type silicon substrate is sintered, light injected and tested.

18. A photovoltaic module, characterized in that: Comprising the solar cell according to any one of claims 1 to 7.

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