Patent Description:
A typical passivated emitter and rear cell (PERC) uses stacked aluminum oxide/silicon nitride as a rear passivation layer. An aluminum oxide layer has a relatively high fixed negative charge density, and a large number of the fixed negative charges may shield electrons on a silicon substrate surface, thus reducing the electrons usable for recombination and achieving suppression of carrier recombination on the surface. The PERC has become a mainstream technology in the photovoltaic cell. However, for a PERC based photovoltaic module, a potential induced degradation (PID) effect may negatively affect the performance of the cell, thus resulting in lowered conversion efficiency. An important cause of the PID effect may be that a potential difference between the cells and other structures (such as a packaging material) of the photovoltaic module disturbs a normal current path in the cells during the power generation, then the photovoltaic cell presents undesirable situations such as power attenuation and lower power generation. For example, <CIT> discloses a method for fabricating a passivation layer stack for photovoltaic devices. Therefore, it is desirable to improve an anti-PID effect of the PERC and maintain high efficiency of the PERC.

One or more embodiments are described as examples with reference to the corresponding figures in the accompanying drawings, and the examples do not constitute a limitation to the embodiments. Elements with the same reference numerals in the accompanying drawings represent similar elements. The figures in the accompanying drawings do not constitute a proportion limitation unless otherwise stated.

The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings in order to make the objectives, technical solutions and advantages of the present disclosure clearer. However, it will be appreciated by those of ordinary skill in the art that, in various embodiments of the present disclosure, numerous technical details are set forth in order to provide the reader with a better understanding of the present disclosure. However, the technical solutions claimed in the present disclosure may be implemented without these technical details and various changes and modifications based on the following embodiments.

The present disclosure provides a photovoltaic cell, which includes a substrate; a first passivation layer and a first anti-reflection layer that are sequentially disposed on a front surface of the substrate in a direction away from the substrate; and a second passivation layer, a polarization phenomenon weakening (PPW) layer and at least one silicon nitride layer SiuNv that are sequentially disposed on a rear surface of the substrate in a direction away from the substrate, where <NUM><u/v<<NUM>. The second passivation layer includes at least one aluminum oxide layer AlxOy, where <NUM><y/x<<NUM> and a refractive index of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>, and a thickness of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>. The PPW layer includes at least one silicon oxynitride layer SirOsNt, where r>s>t and a refractive index of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>, and a thickness of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>. A refractive index of the at least one silicon nitride layer is in a range of <NUM> to <NUM>, and a thickness of the at least one silicon nitride layer is in a range of <NUM> to <NUM>.

By disposing the PPW layer including the at least one silicon oxynitride layer between the at least one aluminum oxide layer and the at least one silicon nitride layer, a potential difference between the at least one aluminum oxide layer and the at least one silicon nitride layer may be reduced, and the anti-PID performance of the photovoltaic cell may be improved, thus ensuring the high conversion efficiency of the photovoltaic cell. Furthermore, a refractive index of each layer on the rear surface of the photovoltaic cell is within a reasonable refractive index range by defining a relationship between the atom number of each kind of atoms in the silicon nitride layer, the aluminum oxide layer and the silicon oxynitride layer. When the refractive index of all the layers on the rear surface of the photovoltaic cell is within the reasonable refractive index range and each layer has a suitable thickness, the light utilization rate of the photovoltaic cell can be increased and the light conversion efficiency of the photovoltaic cell can be improved.

Some embodiments of the photovoltaic cell of the present disclosure will be described in detail below. The following contents are merely provided for convenience of understanding the implementation details, and are not necessary for the implementation of the technical solution of the present disclosure.

<FIG> is a schematic structural diagram of a photovoltaic cell according to some embodiments of the present disclosure.

As shown in <FIG>, the photovoltaic cell includes a substrate <NUM>. The substrate <NUM> includes an intrinsic silicon substrate <NUM> and an emitter <NUM>. The intrinsic silicon substrate <NUM> and the emitter <NUM> form a PN junction of the photovoltaic cell. For example, the intrinsic silicon substrate <NUM> may be a P-type substrate, the emitter <NUM> may be anN-type doped layer, that is, the P-type substrate and the N-type doped layer form a PN junction. In some embodiments, the intrinsic silicon substrate <NUM> includes, but is not limited to, a monocrystalline silicon substrate, a polycrystalline silicon substrate, a monocrystalline silicon-like substrate, etc. It should be noted that a front surface of the substrate <NUM> is designated as a light-receiving surface, and a rear surface of the substrate <NUM> refers to a surface opposite to the front surface. In some embodiments, a surface close to the emitter <NUM> is referred to as the front surface, and a surface close to the intrinsic silicon substrate <NUM> is referred to as the rear surface.

The photovoltaic cell further includes a first passivation layer <NUM> and a first anti-reflection layer <NUM> that are sequentially disposed on the front surface of the substrate <NUM> in a direction away from the substrate <NUM>. In some embodiments, the photovoltaic cell further includes a first electrode <NUM> penetrating through the first passivation layer <NUM> and the first anti-reflection layer <NUM> and forming an ohmic contact with the emitter <NUM> of the substrate <NUM>.

Herein, the first passivation layer <NUM> includes, but is not limited to, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, etc. The first passivation layer <NUM> is configured to reduce the recombination of carriers, thereby increasing an open circuit voltage and a short circuit current of the photovoltaic cell. The first anti-reflection layer <NUM> may be provided with a layer similar to or substantially the same as the first passivation layer <NUM>, for example, including but not limited to the aluminum oxide layer, the silicon nitride layer, the silicon oxynitride layer, etc. The first anti-reflection layer <NUM> may not only reduce the reflectivity of lights incident on a surface of the photovoltaic cell, but also passivate the surface of the photovoltaic cell.

The photovoltaic cell further includes a second passivation layer <NUM>, a polarization phenomenon weakening (PPW) layer <NUM> and a silicon nitride layer <NUM> that are sequentially disposed on the rear surface of the substrate <NUM> in a direction away from the substrate <NUM>. In some embodiments, the photovoltaic cell further includes a second electrode <NUM> penetrating through the second passivation layer <NUM>, the polarization phenomenon weakening layer <NUM> and the silicon nitride layer <NUM> and forming an ohmic contact with the substrate <NUM>.

The second passivation layer <NUM> includes at least one aluminum oxide layer AlxOy, where <NUM><y/x<<NUM>. Particularly, <NUM><y/x≤<NUM>, <NUM><y/x<<NUM>, or <NUM>≤y/x<<NUM>. When the at least one aluminum oxide layer is provided with a single layer (i.e., an aluminum oxide layer <NUM> shown in <FIG>), a thickness of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the aluminum oxide layer <NUM> is <NUM>, <NUM>, <NUM> or <NUM>. When forming the aluminum oxide layer <NUM> with a particular thickness, a ratio of y and x in the aluminum oxide layer <NUM> is controlled in a range of <NUM> to <NUM>, and a refractive index of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the refractive index of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. It should be noted that, when the at least one aluminum oxide layer is provided with a plurality of layers (not shown), the refractive index mentioned here should be a refractive index of all the aluminum oxide layers, that is, the refractive index of all of the plurality of aluminum oxide layers is in a range of <NUM> to <NUM>. Particularly, the refractive index of all of the plurality of aluminum oxide layers is in a range of <NUM> to <NUM>.

As shown in <FIG>, the second passivation layer <NUM> further includes a silicon oxide layer <NUM>. The silicon oxide layer <NUM> is disposed between the substrate <NUM> and the aluminum oxide layer <NUM> to isolate the aluminum oxide layer <NUM> from the substrate <NUM>, thereby avoiding a direct contact between the aluminum oxide layer <NUM> and the substrate <NUM>. A dense silicon oxide layer <NUM> is chemically stable, which may chemically passivate a dangling bond on the surface of the substrate <NUM>. Herein, a thickness of the silicon oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the silicon oxide layer <NUM> is <NUM>, <NUM> or <NUM>.

It is found through an experimental verification that the PID may be improved by <NUM>% to <NUM>% via providing the silicon oxide layer <NUM> with a special design (for example, the thickness of the silicon oxide layer <NUM> is in a range of <NUM> to <NUM>) compared with providing a passivation layer without silicon oxide.

The polarization phenomenon weakening layer <NUM> includes at least one silicon oxynitride layer SirOsNt, where r>s>t. A concentration of silicon atoms in the at least one silicon oxynitride layer is in a range of <NUM>×<NUM><NUM>/cm<NUM> to <NUM>×<NUM><NUM>/cm<NUM>. The PPW layer <NUM> is configured to reduce a cell difference between layers on two sides of the PPW layer <NUM>, so as to improve the anti-PID effect. In some embodiments, a thickness of the at least one silicon oxynitride layer in the PPW layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the at least one silicon oxynitride layer is <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. When forming the at least one silicon oxynitride layer SirOsNt with a particular thickness, where r>s>t, a refractive index of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>. It should be noted that when the at least one silicon oxynitride layer is provided with a plurality of layers (not shown), the refractive index mentioned here should be a refractive index of all the silicon oxynitride layers, that is, the refractive index of all of the plurality of silicon oxynitride layers is in a range of <NUM> to <NUM>.

It is found through an experimental verification that the PID may be improved by <NUM>% to <NUM>% via providing the PPW layer <NUM> with a specific design (for example, a thickness of the PPW layer is in a range of <NUM> to <NUM>) compared with providing a passivation layer without the PPW layer.

It is found through an experimental verification that, in some embodiments, the PID may be improved by up to <NUM>% to <NUM>% when the rear surface of the photovoltaic cell is provided with both the silicon oxide layer <NUM> and the PPW layer <NUM> for isolation.

In an embodiment, the at least one silicon nitride layer SiuNv is provided with a single layer (i.e., the silicon nitride layer <NUM> shown in <FIG>), where <NUM><u/v<<NUM>. Particularly, <NUM><u/v≤<NUM> or <NUM><u/v<<NUM>. A thickness of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the silicon nitride layer <NUM> is <NUM>, <NUM> or <NUM>. When forming the silicon nitride layer <NUM> with a particular thickness, the ratio of u and v in the silicon nitride layer <NUM> may be controlled in a range of <NUM> to <NUM>, and a refractive index of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. In some embodiments, the at least one silicon nitride layer is provided with a plurality of layers (shown in <FIG> and <FIG>), for example, <NUM> to <NUM> layers. Refractive indexes of the plurality of silicon nitride layers decrease layer by layer in the direction away from the substrate <NUM>, but a refractive index of all the silicon nitride layers should be controlled in a range of <NUM> to <NUM>. It should be noted that the number of the plurality of silicon nitride layers may be configured according to requirements on the thickness and refractive index of the deposited silicon nitride layer, which is not limited in the present disclosure.

In order to achieve a photovoltaic cell with high anti-PID effect and high efficiency, for example, the thicknesses of the second passivation layer <NUM>, the PPW layer <NUM> and the silicon nitride layer <NUM> on the rear surface of the photovoltaic cell and their corresponding refractive indexes are designed to be matched. The refractive index of all the layers on the rear surface of the photovoltaic cell is within a reasonable refractive index range by defining a relationship of the atom number of each kind of atoms in the aluminum oxide layer <NUM> included in the second passivation layer <NUM>, the polarization phenomenon weakening layer <NUM> and the silicon nitride layer <NUM>. When the refractive index of all the layers on the rear surface of the photovoltaic cell is within the reasonable refractive index range and each layer has a suitable thickness, which result in a relatively high anti-reflective property, the light utilization rate of the photovoltaic cell can be increased and the light conversion efficiency of the photovoltaic cell can be improved.

In some embodiments of the present disclosure, the aluminum oxide layer <NUM> is provided on the rear surface of the photovoltaic cell. Since the growth and annealing temperature of the aluminum oxide layer <NUM> is relatively low, octahedral structures of aluminum atoms in the aluminum oxide layer <NUM> will be transformed into tetrahedral structures after a high temperature heat treatment to generate interstitial oxygen atoms. The interstitial oxygen atoms capture valence electrons in the substrate <NUM> to form fixed negative charges, so that the aluminum oxide layer <NUM> shows an electronegativity and an interface electric field directed to the inside of the substrate <NUM> is generated at the interface, thus causing carriers to escape from the interface quickly, reducing an interface recombination rate and increasing a minority carrier lifetime of the substrate <NUM>. The PPW layer <NUM> disposed on the aluminum oxide layer <NUM> may effectively prevent subsequent products of sodium ions, ~OH and ~CH3 groups from migrating into the photovoltaic cell, block the movement and migration of mobile ions under an external electric field, temperature and humidity, and reduce the potential difference between layers and enhance the anti-PID effect, thus having better anti-PID performance and anti-aging/attenuation performance. The silicon nitride layer <NUM> disposed on the PPW layer <NUM> achieves the optimal anti-reflection effect by combining optical path matching, and protects the adjacent aluminum oxide layer <NUM> and polarization phenomenon weakening layer <NUM> from corrosion caused by the excessive paste. After annealing, an H passivation effect of the silicon nitride layer <NUM> is significant, which further improves the minority carrier lifetime of a silicon wafer and also prevents subsequent products of Na+, ~OH and ~CH3 groups from migrating into the photovoltaic cell to a certain extent, thus avoiding power attenuation caused by electric leakage of cell components. The combination of the aluminum oxide layer <NUM> and the polarization phenomenon weakening layer <NUM> reduces the power loss of the cell components, and improves light attenuation performance, heat-assisted light attenuation performance and anti-PID performance of the photovoltaic cell.

In an embodiment, as shown in <FIG>, the at least one silicon nitride layer is provided with three silicon nitride layers, i.e., a first silicon nitride layer <NUM>, a second silicon nitride layer <NUM> and a third silicon nitride layer <NUM> that are stacked in the direction away from the substrate <NUM>. In this embodiment, a refractive index of the three and silicon nitride layers is in a range of <NUM> to <NUM>. A thickness of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, a thickness of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a thickness of the third silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. A refractive index of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, a refractive index of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a refractive index of the third silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. It should be noted that although there are the same values in the refractive index ranges of every two silicon nitride layers in the above three silicon nitride layers, the refractive indexes of the three silicon nitride layers need to satisfy the condition that "the refractive indexes of the plurality of silicon nitride layers decrease layer by layer in the direction away from the substrate <NUM>" in practical applications. Therefore, a situation that every two silicon nitride layers in the three silicon nitride layers have the same refractive indexes may not happen.

In an embodiment, as shown in <FIG>, the at least one silicon nitride layer is provided with two silicon nitride layers, i.e., a first silicon nitride layer <NUM> and a second silicon nitride layer <NUM> that are stacked in the direction away from the substrate <NUM>. In this embodiment, a refractive index of the two silicon nitride layers is in a range of <NUM> to <NUM>. A thickness of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a thickness of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. A refractive index of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a refractive index of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>.

Some embodiments of the present disclosure provide a photovoltaic module, which includes at least one photovoltaic cell string. The photovoltaic cell string is composed of the above photovoltaic cells electrically connected, for example, the photovoltaic cells illustrated in <FIG>. The photovoltaic cells are electrically connected in series and/or parallel in the photovoltaic cell string. The photovoltaic module includes, but is not limited to, a laminate module, a double-sided module, a multi-main grid module, etc. For example, the photovoltaic cells (e.g., <FIG>) described above can be obtained, and the cells can be electrically connected with adjacent ones via conductive materials to form the cell string. A back plate, an ethylene-vinyl acetate (EVA) copolymer and the cell string are stacked in a certain order through a lamination process. Then the stacked structure is installed with a frame to form the photovoltaic module. The photovoltaic cells may convert absorbed light energy into electric energy. The module may transfer the electric energy obtained by the cells to a load.

Some embodiments of the present disclosure provide a method for manufacturing the photovoltaic cell described in the above embodiments. A schematic flow chart of the method for manufacturing the photovoltaic cell is shown in <FIG>, which includes the following steps.

Specifically, the substrate includes an intrinsic silicon substrate and an emitter. The intrinsic silicon substrate and the emitter form a PN junction of the photovoltaic cell. As shown in <FIG>, the substrate <NUM> includes an intrinsic silicon substrate <NUM> and an emitter <NUM>. The intrinsic silicon substrate <NUM> and the emitter <NUM> form a PN junction. For example, the intrinsic silicon substrate <NUM> may be a P-type substrate, the emitter <NUM> may be an N-type doped layer, that is, the P-type substrate and the N-type doped layer form a PN junction. In some embodiments, the intrinsic silicon substrate <NUM> includes, but is not limited to, a monocrystalline silicon substrate, a polycrystalline silicon substrate, a monocrystalline silicon-like substrate, etc. It should be noted that a front surface of the substrate <NUM> is designated as a light-receiving surface, and a rear surface of the substrate <NUM> refers to a surface opposite to the front surface. In some embodiments, a surface close to the emitter <NUM> is referred to as the front surface, and a surface close to the intrinsic silicon substrate <NUM> is referred to as the rear surface.

In step <NUM>, a first passivation layer, a first anti-reflection layer and a first electrode are sequentially disposed on a front surface of the substrate in a direction away from the substrate.

As shown in <FIG>, a first passivation layer <NUM> and a first anti-reflection layer <NUM> are sequentially stacked on the front surface of the substrate <NUM> in the direction away from the substrate <NUM>. Herein, the first passivation layer <NUM> includes, but is not limited to, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, etc. The first passivation layer <NUM> is used to reduce the recombination of carriers, thereby increasing an open circuit voltage and a short circuit current of the photovoltaic cell. The first anti-reflection layer <NUM> may be provided with a layer similar to or substantially the same as the passivation layer <NUM>, for example, including but not limited to, the aluminum oxide layer, the silicon nitride layer, the silicon oxynitride layer, etc. The first anti-reflection layer <NUM> may not only reduce the reflectivity of lights incident on a surface of the photovoltaic cell, but also passivate the surface of the photovoltaic cell.

The first passivation layer <NUM> or the first anti-reflection layer <NUM> may be formed by, including but not limited to, plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapour deposition (PVD), etc..

In an embodiment, a first electrode <NUM> is further formed on the front surface of the substrate <NUM>. The first electrode <NUM> penetrates through the first passivation layer <NUM> and the first anti-reflection layer <NUM>, and forms an ohmic contact with the emitter <NUM> of the substrate <NUM>. The first electrode <NUM> may be formed by a metallization process, for example, by screen printing the conductive paste.

In step <NUM>, a second passivation layer is formed on a rear surface of the substrate in the direction away from the substrate.

As shown in <FIG>, a second passivation layer <NUM> is formed on the rear surface of the substrate <NUM>. The second passivation layer <NUM> includes at least one aluminum oxide layer AlxOy, where <NUM><y/x<<NUM>. Particularly, <NUM><y/x≤<NUM>, <NUM><y/x<<NUM> or <NUM>≤y/x<<NUM>. When the at least one aluminum oxide layer is provided with a single layer (i.e., an aluminum oxide layer <NUM>), a thickness of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the aluminum oxide layer <NUM> is <NUM>, <NUM>, <NUM> or <NUM>. When forming the aluminum oxide layer <NUM> with a particular thickness, a ratio of y and x in the aluminum oxide layer <NUM> is controlled in a range of <NUM> to <NUM>, and a refractive index of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the refractive index of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. It should be noted that when the at least one aluminum oxide layer is provided with a plurality of layers (not shown), the refractive index mentioned here should be a refractive index of all the aluminum oxide layers, that is, the refractive index of all of the plurality of aluminum oxide layers is in a range of <NUM> to <NUM>. Particularly, the refractive index of all of the plurality of aluminum oxide layers is in a range of <NUM> to <NUM>.

In an embodiment, the aluminum oxide layer <NUM> in the second passivation layer <NUM> is prepared by the PECVD. Argon, trimethylaluminium and nitrous oxide may be used as precursors of the aluminum oxide layer <NUM>. Herein, a gas flow ratio of the argon, the trimethylaluminium and the nitrous oxide is in a range of <NUM>:<NUM>:<NUM> to <NUM>. <NUM>:<NUM>:<NUM>. Particularly, the gas flow ratio is in a range of <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>, and the pressure in a PECVD reaction chamber is <NUM> mbar. A thickness of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>. A ratio of y and x in the aluminum oxide layer <NUM> may be controlled in a range of <NUM> to <NUM>. A refractive index of the aluminum oxide layer <NUM> is in a range of <NUM> to <NUM>.

In an embodiment, the second passivation layer <NUM> further includes a silicon oxide layer <NUM>. The silicon oxide layer <NUM> is disposed between the substrate <NUM> and the aluminum oxide layer <NUM>. The silicon oxide layer <NUM> is formed between the substrate <NUM> and the aluminum oxide layer <NUM> to isolate the aluminum oxide layer <NUM> from the substrate <NUM>. The silicon oxide layer <NUM> is formed by applying an ozone (O<NUM>) process in a process of etching the substrate <NUM>. The dense silicon oxide layer <NUM> is chemically stable, which may chemically passivate a dangling bond on the surface of the substrate <NUM>. A thickness of the silicon oxide layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the silicon oxide layer <NUM> is <NUM>, <NUM> or <NUM>.

In step <NUM>, a polarization phenomenon weakening (PPW) layer is formed on a surface of the second passivation layer away from the substrate.

The PPW layer may be configured as an intermediate layer to reduce a potential difference between its upper and lower layers, thus improving the anti-PID performance of the photovoltaic cell and further ensuring the high conversion efficiency of the photovoltaic cell. In some embodiments, as shown in <FIG>, the PPW layer <NUM> includes at least one silicon oxynitride layer SirOsNt, where r>s>t. A concentration of silicon atoms in the at least one silicon oxynitride layer is in a range of <NUM>×<NUM><NUM>/cm<NUM> to <NUM>×<NUM><NUM>/cm<NUM>.

In an embodiment, when depositing the at least one silicon oxynitride layer on the surface of the aluminum oxide layer <NUM>, silanes, ammonia and nitrous oxide are simultaneously introduced into a reaction chamber, where a gas flow ratio of the silanes, the ammonia and the nitrous oxide is in a range of <NUM>:<NUM>:<NUM> to <NUM>:<NUM>:<NUM>, and the pressure in the reaction chamber is <NUM> mbar. A thickness of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>, and a refractive index of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>. It should be noted that when the at least one silicon oxynitride layer is provided with a plurality of layers, the refractive index mentioned here should be a refractive index of all the silicon oxynitride layers, that is, the refractive index of all of the plurality of silicon oxynitride layers is in a range of <NUM> to <NUM>.

In an embodiment, an intermediate silicon oxide layer is deposited on the surface of the aluminum oxide layer <NUM>, and precursors of the intermediate silicon oxide layer are the silanes and the nitrous oxide, where a gas flow ratio of the silanes and the nitrous oxide is in a range of <NUM>:<NUM> to <NUM>:<NUM>, and the pressure in the reaction chamber is <NUM> mbar. After the intermediate silicon oxide layer is formed, nitrogen source gas is introduced to produce nitrogen plasmas to react with the intermediate silicon oxide layer, so as to form the at least one silicon oxynitride layer. That is to say, an intermediate silicon dioxide layer is formed first by the reaction on the surface of the aluminum oxide layer <NUM>, and then the nitrogen source gas is introduced to produce nitrogen plasmas to react with the silicon dioxide layer, so as to form the at least one silicon oxynitride layer. A thickness of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>, and the refractive index of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>.

In step <NUM>, at least one silicon nitride layer is formed on a surface of the polarization phenomenon weakening layer away from the substrate.

As shown in <FIG>, the at least one silicon nitride layer SiuNv is provided with a single layer (i.e., the silicon nitride layer <NUM>), where <NUM><u/v<<NUM>, and the silicon nitride layer <NUM> is formed on the surface of the PPW layer <NUM>. A thickness of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>.

In an embodiment, the silicon nitride layer <NUM> is prepared by the PECVD, the silanes and the ammonia may be used as precursors of the silicon nitride layer <NUM>. The pressure in the reaction chamber is <NUM> mbar, and a gas flow ratio of the silanes and the ammonia is in a range of <NUM>:<NUM> to <NUM>:<NUM>. A thickness of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a refractive index of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. Particularly, the thickness of the silicon nitride layer <NUM> is <NUM>, <NUM> or <NUM>.

In an embodiment, the at least one silicon nitride layer is provided with a plurality of silicon nitride layers. Particularly, the at least one silicon nitride layer is provided with <NUM> to <NUM> silicon nitride layers, such as <NUM> layers, <NUM> layers, etc. As shown in <FIG>, the at least one silicon nitride layer includes a first silicon nitride layer <NUM>, a second silicon nitride layer <NUM> and a third silicon nitride layer <NUM>. Specifically, precursors of the three silicon nitride layers are introduced into a first reaction chamber of a PECVD equipment, and the precursors are the silanes and the ammonia. A gas flow ratio of the silanes and the ammonia is in a range of <NUM>:<NUM> to <NUM>:<NUM>, the pressure in the first reaction chamber is <NUM> mbar, and the first silicon nitride layer <NUM> is formed by the PECVD process. The same kind of precursors are continuously introduced into the first reaction chamber, a gas flow ratio of the silanes and the ammonia is in a range of <NUM>:<NUM>. <NUM> to <NUM> :<NUM>, the pressure in the first reaction chamber is <NUM> mbar, and the second silicon nitride layer <NUM> is formed by the PECVD process. The same kind of precursors are introduced into a second reaction chamber of the PECVD equipment, a gas flow ratio of the silanes and the ammonia is in a range of <NUM>:<NUM> to <NUM>:<NUM>, the pressure in the reaction chamber is <NUM> mbar, and the third silicon nitride layer <NUM> is formed by the PECVD process.

Based on the preparation processes, a thickness of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, a thickness of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a thickness of the third silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. A refractive index of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, a refractive index of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a refractive index of the third silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. A refractive index of the three silicon nitride layers is in a range of <NUM> to <NUM>. It should be noted that although there are the same values in the refractive index ranges of every two silicon nitride layers in the above three silicon nitride layers, the refractive indexes of the three silicon nitride layers need to satisfy the condition that "the refractive indexes of the plurality of silicon nitride layers decrease layer by layer in the direction away from the substrate <NUM>" in practical applications. Therefore, a situation that every two silicon nitride layers in the three silicon nitride layers have the same refractive indexes may not happen.

In an embodiment, as shown in <FIG>, the at least one silicon nitride layer is provided with two silicon nitride layers, i.e., a first silicon nitride layer <NUM> and a second silicon nitride layer <NUM>. Specifically, precursors of the two silicon nitride layers are introduced into a first reaction chamber of a PECVD equipment, and the reactants are the silanes and the ammonia. A gas flow ratio of the silanes and the ammonia is <NUM>:<NUM>, a reaction chamber pressure is <NUM> mbar, and the first silicon nitride layer <NUM> is formed by the PECVD process. The same kind of precursors are continuously introduced into the first reaction chamber, a gas flow ratio of the silanes and the ammonia is <NUM>:<NUM>, a reaction chamber pressure is <NUM> mbar, and the second silicon nitride layer <NUM> is formed by the PECVD process.

Based on the above preparation processes, a thickness of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a thickness of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. A refractive index of the first silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a refractive index of the second silicon nitride layer <NUM> is in a range of <NUM> to <NUM>.

In step <NUM>, a conductive paste is printed on the surface of the at least one silicon nitride layer and sintered to form a second electrode. The second electrode penetrates through the second passivation layer, the PPW layer and the at least one silicon nitride layer, and forms an ohmic contact with the substrate.

In order to achieve a photovoltaic cell with high anti-PID effect and high efficiency, for example, the thicknesses of the second passivation layer <NUM>, the PPW layer <NUM> and the silicon nitride layer <NUM> on the rear surface of the photovoltaic cell and their corresponding refractive indexes are designed to be matched. A relationship of the atom number of each kind of atoms in the aluminum oxide layer <NUM> included in the second passivation layer <NUM>, the PPW layer <NUM> and the silicon nitride layer <NUM> is specified through a proper process, so that the refractive index of all the layers on the rear surface of the photovoltaic cell is within a reasonable refractive index range. When the refractive index of all the layers on the rear surface of the photovoltaic cell is within the reasonable refractive index range and each layer has a suitable thickness, which result in a relatively high anti-reflective property, the light utilization rate of the photovoltaic cell can be increased and the light conversion efficiency of the photovoltaic cell can be improved.

A comparative example provides a back structure of a PERC cell. The specific structure is shown in <FIG>, which includes: a substrate <NUM> having a PN junction; a first passivation layer <NUM>, a first anti-reflection layer <NUM> and a first electrode <NUM> that are sequentially disposed on a front surface of the substrate <NUM> in a direction away from the substrate <NUM>; a second passivation layer <NUM>, a silicon nitride layer <NUM> SiuNv and a second electrode <NUM> that are sequentially disposed on a rear surface of the substrate <NUM> in a direction away from the substrate <NUM>, where <NUM><u/v<<NUM>. The second passivation layer <NUM> includes at least one aluminum oxide layer AlxOy (shown as an aluminum oxide layer <NUM> in <FIG> when provided with a single layer), where <NUM><y/x<<NUM>. A refractive index of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>, and a thickness of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>. A refractive index of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>, and a thickness of the silicon nitride layer <NUM> is in a range of <NUM> to <NUM>. The second passivation layer <NUM> further includes a silicon oxide layer <NUM>. The silicon oxide layer <NUM> is disposed between the substrate <NUM> and the aluminum oxide layer <NUM> to isolate the aluminum oxide layer <NUM> from the substrate <NUM>, which may avoid a direct contact between the aluminum oxide layer <NUM> and the substrate <NUM>.

Compared with the photovoltaic cell in the present disclosure shown in <FIG>, the difference is that the back structure of the comparative example does not have the PPW layer <NUM>, and other structures and preparation method are the same. Through a comparative experiment, the results are shown in the following table.

Herein, the conversion efficiency of the photovoltaic cell = (open circuit voltage * short circuit current * fill factor) / (cell area * illumination amplitude) *<NUM>%. It can be seen that the open circuit voltage, the short circuit current and the fill factor are proportional to the conversion efficiency. The longer the minority carrier lifetime, the higher the conversion efficiency. It can be seen from the data in the table that a conversion efficiency of a photovoltaic cell with the SirOsNt on the rear surface is <NUM>% higher than that of a photovoltaic cell without the SirOsNt on the rear surface.

The steps in the above methods only aim to make the description clearer. In implementation, the steps may be combined into one or one step may be divided into multiple sub-steps, which, as long as the same logical relationship is included, all fall into the protection scope of the present disclosure. Such a trivial amendment or design added to an algorithm or procedure as not changing the algorithm or a core design of the procedure falls into the protection scope of the disclosure.

It is not difficult to find that this embodiment is a method embodiment related to the first embodiment, and this embodiment may be implemented in cooperation with the first embodiment. The relevant technical details mentioned in the first embodiment are still valid in this embodiment, thus not repeated herein in order to reduce repetition. Accordingly, the relevant technical details mentioned in this embodiment may also be applied in the first embodiment.

Claim 1:
A method for manufacturing a photovoltaic cell, comprising:
providing (<NUM>) a substrate;
forming (<NUM>) a first passivation layer (<NUM>), a first anti-reflection layer (<NUM>) and a first electrode (<NUM>) sequentially on a front surface of the substrate in a direction away from the substrate; and
forming (<NUM>) a second passivation layer (<NUM>) on a rear surface of the substrate in a direction away from the substrate;
forming (<NUM>) a silicon oxynitride layer (<NUM>) on a surface of the second passivation layer away from the substrate;
forming (<NUM>) at least one silicon nitride layer (<NUM>) on a surface of the silicon oxynitride layer away from the substrate, wherein a ratio of a number of silicon atoms to a number of nitrogen atoms in the at least one silicon nitride layer (<NUM>) is greater than <NUM> and less than <NUM>, and a refractive index of the at least one silicon nitride layer (<NUM>) is in a range of <NUM> to <NUM>; and,
printing (<NUM>) a conductive paste on the surface of the at least one silicon nitride layer and sintering the conductive paste to form a second electrode (<NUM>) wherein the second electrode penetrates through the second passivation layer, the silicon oxynitride layer and the at least one silicon nitride layer and forms an ohmic contact with the substrate; and
wherein the second passivation layer comprises at least one aluminum oxide layer, wherein a ratio of a number of oxygen atoms to a number of aluminum atoms in the at least one aluminum oxide layer is greater than <NUM> and less than <NUM>, a thickness of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>, and a refractive index of the at least one aluminum oxide layer is in a range of <NUM> to <NUM>; wherein a number of silicon atoms is greater than a number of oxygen atoms in the at least one silicon oxynitride layer and the number of oxygen atoms is greater than a number of nitrogen atoms in the at least one silicon oxynitride layer, a thickness of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>, and a refractive index of the at least one silicon oxynitride layer is in a range of <NUM> to <NUM>; wherein a thickness of the at least one silicon nitride layer is in a range of <NUM> to <NUM>.