Patent Application
20240363773
This application claims priority to Chinese patent application No. 202310996038.8, filed on Aug. 9, 2023, and titled “SOLAR CELL, PREPARATION METHOD THEREOF AND PHOTOVOLTAIC MODULE”, the content of which is hereby incorporated herein in its entirety by reference.
The present application relates to the technical field of solar cells, and in particular to a solar cell, a preparation method thereof, and a photovoltaic module.
With the development of solar cell technology, tunnel oxide passivated contact (TOPCon) technology has emerged, which involves forming an ultra-thin tunnel oxide layer on a surface of a crystalline silicon wafer and stacking a doped polysilicon layer on the tunnel oxide layer, thereby obtaining a passivating contact structure. The passivating contact structure can significantly reduce charge carrier recombination in the metal contact area while achieving desirable contact performance, thereby effectively enhancing the efficiency of the solar cell. However, the polysilicon layer in the passivating contact structure exhibits severe parasitic absorption of light. A thick polysilicon layer formed across the entire surface of the silicon wafer will greatly reduce the utilization rate of light, decreasing the short-circuit current, which leads to current loss, limiting further improvements of the open-circuit voltage and conversion efficiency of the solar cell.
In view of the above, there is a need to provide a solar cell, a preparation method thereof, and a photovoltaic module.
According to a first aspect, a solar cell includes:
In an embodiment, the tunnel oxide layer includes a silicon dioxide layer; and/or a thickness of the tunnel oxide layer is smaller than 3 nm.
In an embodiment, the laser-absorption layer includes a titanium oxide layer or an aluminum oxide layer; and/or a thickness of the laser-absorption layer is in a range from 1 nm to 5 nm.
In an embodiment, a thickness of the second doped polysilicon layer is greater than a thickness of the first doped polysilicon layer.
In an embodiment, the first doped polysilicon layer includes a phosphorus-doped polysilicon film or a boron-doped polysilicon film; and/or a thickness of the first doped polysilicon layer is in a range from 5 nm to 100 nm.
In an embodiment, the second doped polysilicon layer includes a phosphorus-doped polysilicon film or a boron-doped polysilicon film; and/or a thickness of the second doped polysilicon layer is in a range from 70 nm to 200 nm.
In an embodiment, the solar cell further includes a passivation and anti-reflection layer and a metal electrode, wherein the passivation and anti-reflection layer is disposed on the non-metal contact region of the surface of the first doped polysilicon layer and a surface of the second doped polysilicon layer, and the metal electrode is fixedly connected to the second doped polysilicon layer.
In an embodiment, the passivation and anti-reflection layer includes a silicon nitride layer or a stack of an aluminum oxide layer and a silicon nitride layer; and/or a thickness of the passivation and anti-reflection layer is in a range from 70 nm to 80 nm.
According to a second aspect, a method for preparing a solar cell is provided. The method is configured to prepare the solar cell in any one of the embodiments in the first aspect.
The method includes:
In an embodiment, the laser is an ultraviolet picosecond laser, and the predetermined wavelength is in a range from 355 nm to 532 nm.
In an embodiment, the method further includes:
According to a third aspect, a photovoltaic module includes the solar cell in any one of the embodiments in the first aspect.
In the above-described embodiments of the solar cell and the preparation method thereof, the second doped polysilicon layer is only disposed in the metal contact region, thereby achieving passivating contact while reducing blocking and/or absorption of light on the non-metal contact region. Accordingly, on the one hand, the light utilization rate can be improved, and the current loss of the solar cell can be reduced; on the other hand, the charge carrier recombination in the metal contact region and the non-metal contact region can be effectively reduced while desirable contact performance can be achieved, thereby effectively improving the efficiency of the solar cell. Moreover, the laser-absorption layer is disposed between the first doped polysilicon layer and the second doped polysilicon layer, and thus the portion of the laser-absorption layer and the portion of the second doped polysilicon layer located on the non-metal contact region can be removed through laser-induced vaporization due to the intense laser absorption of the laser-absorption layer, obviating the need for masking and chemical etching to remove the portion of the second doped polysilicon layer on the non-metal contact region. Thus, the preparation process of the solar cell is simplified. This method is compatible with the existing mass production process for crystalline silicon solar cells, and only requires to add a laser-etching apparatus, which reduces preparation cost, and facilitates industrialization and mass production. Consequently, the complexity and high cost issues associated with the preparation method of a passivating contact structure employing a selective polysilicon layer can be effectively addressed.
100. solar cell; 1. silicon substrate; 2. tunnel oxide layer; 3. first doped polysilicon layer; 4. laser-absorption layer; 5. second doped polysilicon layer; 6. passivation and anti-reflection layer; 7. metal electrode.
To make the objectives, features, and advantages of the present application more understandable, detailed description of specific embodiments are provided below, along with accompanying drawings. Many specific details are disclosed in the following description to facilitate a comprehensive understanding of the present application. However, it should be noted that the present application can be implemented in various ways different from those described herein, and those skilled in the art may make improvements without departing from the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.
In the description of the present application, it should be understood that the terms “central”, “longitudinal”, “transverse”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc. indicate the orientations or positional relationships on the basis of the drawings. These terms are only for describing the present application and simplifying the description, rather than indicating or implying that the related devices or elements must have the specific orientations, or be constructed or operated in the specific orientations, and therefore cannot be understood as limitations of the present application.
The drawings provided herein are for the purpose of illustration, and the drawings are not necessarily drawn to scale. In addition, the terms “first” and “second” are used merely as labels to distinguish one element having a certain name from another element having the same name, and cannot be understood as indicating or implying any priority, precedence, or order of one element over another, or indicating the quantity of the element. Therefore, the element modified by “first” or “second” may explicitly or implicitly includes at least one of the elements. In the description of the present application, “a plurality of” means at least two, such as two, three, etc., unless otherwise specifically defined.
In the present application, unless otherwise clearly specified and defined, the terms “installed”, “connected”, “coupled”, “fixed” and the like should be interpreted broadly. For example, an element, when being referred to as being “installed”, “connected”, “coupled”, “fixed” to another element, unless otherwise specifically defined, may be fixedly connected, detachably connected, or integrated to the other element, may be mechanically connected or electrically connected to the other element, and may be directly connected to the other element or connected to the other element via an intermediate element. For those of ordinary skill in the art, the specific meaning of the above-mentioned terms in the present application can be understood according to specific circumstances.
In the present application, unless otherwise specifically defined, an element, when being referred to as being located “on” or “under” another element, may be in direct contact with the other element or contact the other element via an intermediate element. Moreover, the element, when being referred to as being located “on”, “above”, “over” another element, may be located right above or obliquely above the other element, or merely located at a horizontal level higher than the other element; the element, when being referred to as being located “under”, “below”, “beneath” another element, may be located right below or obliquely below the other element, or merely located at a horizontal level lower than the other element.
It should be noted that an element, when being referred to as being “fixed” or “mounted” to another element, may be directly fixed or mounted to the other element or via an intermediate element. Such terms as “vertical”, “horizontal”, “up”, “down”, “left”, “right” and the like used herein are for illustrative purposes only and are not meant to be the only ways for implementing the present application.
In a crystalline silicon solar cell, serious charge carrier recombination may exist in a contact region between a metal electrode and a surface of a crystalline silicon wafer (i.e., a metal contact region), leading to an increased recombination current, which significantly hinders the efficiency of the crystalline silicon solar cell from being improved. A tunnel oxide passivating contact structure composed of an ultra-thin tunnel oxide layer and a doped polysilicon layer can significantly reduce the charge carrier recombination in the metal contact region while achieving desirable contact performance, thereby greatly improve the efficiency of the solar cell.
However, in the passivating contact structure of the solar cell, the polysilicon layer exhibits severe parasitic absorption of light, and a thick polysilicon layer formed across the entire surface of the silicon wafer will greatly reduce the utilization rate of light for the solar cell, which decreases the short-circuit current of the solar cell and leads to current loss. Thus, an issue to be promptly addressed is how to effectively reduce the charge carrier recombination both in the metal contact region and in a non-metal contact region, which is the region beyond the metal contact region, while ensuring light utilization rate of the solar cell.
In order to further improve the efficiency of the solar cell, the portion of the polysilicon layer and the portion of the tunnel oxide layer corresponding to the metal electrode can be retained while portions of layers where passivating contact is not achieved can be removed. This structure not only achieves passivating contact but also reduces absorption of light on the non-metal region, and thus is referred to as a passivating contact structure employing a selective polysilicon layer.
In related art, the preparation method of the passivating contact structure employing the selective polysilicon layer may involve chemical etching to remove the portion of the polysilicon layer located on the non-metal contact region or depositing the polysilicon layer only on the metal contact region by using a mask. These methods are complex and will increase the cost, which limit their application in mass production and hinder their popularization in the photovoltaic industry.
In the present embodiment, the silicon substrate 1 is adapted to be used in preparing the solar cell 100. The silicon substrate 1 can be a silicon wafer, which can be a monocrystalline silicon wafer or a polysilicon wafer. The silicon substrate 1 includes a front side and a back side. The front side is configured to face the sun (also referred to as a light-receiving side); the back side is configured to be back from the sun (also referred to as a back side). The front side or back side of the silicon substrate 1 can be doped to form a doped surface. The doping type of the doped surface can be either the p-type or the n-type, which is not limited herein.
The doped surface of the silicon substrate 1, the surface of the tunnel oxide layer 2, the surface of the first doped polysilicon layer 3, the surface of the laser-absorption layer 4, and the surface of the second doped polysilicon layer 5 are not adjacent to each other.
The tunnel oxide layer 2 and the first doped polysilicon layer 3 are sequentially formed on one side (i.e., the back side or the front side) of the silicon substrate 1, entirely covering the surface which is opposite to the doped surface. The tunnel oxide layer 2 and the first doped polysilicon layer 3 together form a passivating contact structure, thereby sufficiently passivating the surface of the silicon substrate 1, and reducing the surface recombination. Since the tunnel oxide layer 2 is very thin and the first doped polysilicon layer 3 includes dopant, majority carriers can penetrate these two passivation layers while minority carriers are blocked. The surface of the first doped polysilicon layer 3 can be metallized, such as covered with a metal electrode 7, to achieve passivating contact, while the metal electrode does not have to be in direct contact with the silicon substrate 1 through an opening in the two layers. The surface of the first doped polysilicon layer 3 includes the metal contact region and the non-metal contact region. The metal contact region is the region configured to realize the passivating contact, e.g., the region corresponding to the metal electrode 7, and the non-metal contact region is the region where no passivating contact is required, e.g., the region beyond the metal contact region.
The laser-absorption layer 4 and the second doped polysilicon layer 5 are sequentially stacked on the metal contact region of the surface of the first doped polysilicon layer 3. Therefore, the metal contact region is provided with two doped polysilicon layers, i.e., the first doped polysilicon layer 3 and the second doped polysilicon layer 5 simultaneously, thus forming a relatively thick passivating contact structure, which can effectively enhance the passivation in the metal contact region, and prevent the passivating contact structure from being damaged during the metallization, i.e., the forming of the metal electrode 7. The thick passivating contact structure can significantly reduce the charge carrier recombination in the metal contact region while providing desirable contact performance.
Moreover, the second doped polysilicon layer 5 is disposed only on the metal contact region, which requires the passivating contact, and only the first doped polysilicon layer 3 is formed in the non-metal contact region, which requires no passivating contact. Thus, the polysilicon layer in the non-metal contact region can be relatively thin, so as to form the passivating contact structure employing the selective polysilicon layer, which can reduce blocking and/or absorption of light on the non-metal contact region to improve the light utilization rate, reduce the current loss of the solar cell 100, and thus improve the efficiency of the solar cell 100.
Further, the laser-absorption layer 4 is disposed between the two doped polysilicon layers in the metal contact region. The laser-absorption layer 4 can be an oxide layer having a tunneling effect to ensure the passivating contact effect. Moreover, the laser-absorption layer 4 is adapted to be vaporized by absorbing a laser having a predetermined wavelength, and thus in preparation of the solar cell 100, the portion of the laser-absorption layer 4 located on the non-metal contact region and the portion of the second doped polysilicon layer 5 stacked on the portion of the laser-absorption layer 4 can be removed through laser-induced vaporization due to the intense laser absorption of the laser-absorption layer 4.
The solar cell 100 in the present embodiment can be formed as follows: first, the tunnel oxide layer 2, the first doped polysilicon layer 3, the laser-absorption layer 4, and the second doped polysilicon layer 5 can be sequentially formed on the entire surface of the front side or the back side the silicon substrate 1. Then, the portion of the laser-absorption layer 4 and the portion of the second doped polysilicon layer 5 on the non-metal contact region can be removed through laser etching due to the intense laser absorption and laser-induced vaporization of the laser-absorption layer 4, so as to achieve the solar cell 100 of the present embodiment.
In the present embodiment of the solar cell 100, the second doped polysilicon layer 5 is only disposed in the metal contact region, achieving passivating contact while reducing blocking and/or absorption of light on the non-metal contact region. Accordingly, on the one hand, the light utilization rate can be improved, and the current loss of the solar cell 100 can be reduced, and on the other hand, the charge carrier recombination in the metal contact region and the non-metal contact region can be effectively reduced while desirable contact performance can be achieved, thereby effectively improving the efficiency of the solar cell 100. Moreover, the laser-absorption layer 4 is disposed between the first doped polysilicon layer 3 and the second doped polysilicon layer 5, and thus the portion of the laser-absorption layer 3 and the portion of the second doped polysilicon layer 5 located on the non-metal contact region can be removed through laser-induced vaporization due to the intense laser absorption of the laser-absorption layer 4, obviating the need for masking and chemical etching. Thus, the preparation process of the solar cell 100 is simplified. This method is compatible with the existing mass production process for crystalline silicon solar cells, and only requires to add a laser-etching device, reducing preparation cost, and facilitates industrialization and mass production. Consequently, the complexity and high cost issues associated with the preparation method of a passivating contact structure employing a selective polysilicon layer can be effectively addressed.
In some embodiments, the tunnel oxide layer 2 can include a silicon dioxide layer.
In some embodiments, the tunnel oxide layer 2 has a thickness smaller than 3 nm, enabling a quantum tunneling effect. Optionally, the thickness of the tunnel oxide layer 2 can be in a range from 0.5 nm to 2.5 nm. Further, the thickness of the tunnel oxide layer 2 can be in a range from 1 nm to 2.5 nm. For example, the tunnel oxide layer 2 can have a thickness of 1.5 nm.
In some embodiments, the laser-absorption layer 4 includes a titanium oxide layer or an aluminum oxide layer. Titanium oxide and aluminum oxide can intensely absorb a laser of 355 nm and be vaporized under the action of the laser. Thus, scanning the non-metal contact region with an ultraviolet picosecond laser of 355 nm can quickly remove the portion of the laser-absorption layer 4 and the portion of the second doped polysilicon layer 5 on the non-metal contact region. This method is simple, cost effective, and adapted to be industrialized.
In some embodiments, the thickness of the laser-absorption layer 4 can be in a range from 1 nm to 5 nm, enabling the quantum tunneling effect. Further, the thickness of the laser-absorption layer 4 can be in a range from 1 nm to 3 nm. For example, the titanium oxide layer of the laser-absorption layer 4 can have a thickness of 3 nm.
In some embodiments, the thickness of the second doped polysilicon layer 5 can be greater than the thickness of the first doped polysilicon layer 3. By forming the second doped polysilicon layer 5 with a greater thickness on the metal contact region, the passivating contact structure can be prevented from being damaged during forming the metal electrode 7, and effectively reduce the charge carrier recombination in the metal contact region. On the other hand, in the non-metal contact region, the first doped polysilicon layer 3 has a smaller thickness, which is conducive to further reducing the blocking and/or absorption of light on the non-metal contact region, increasing the light utilization rate. Accordingly, the overall passivation by the passivating contact structure, the reduction of light parasitic absorption, and the protection from damage caused by forming the metal electrode can be simultaneously achieved, thereby further improving the efficiency of the solar cell 100.
In some embodiments, the first doped polysilicon layer 3 includes a phosphorus-doped polysilicon film or a boron-doped polysilicon film. In some embodiments, the silicon substrate 1 is an n-type silicon wafer, the first doped polysilicon layer 3 is disposed on an n-type surface of the silicon substrate 1, and for example is the phosphorus-doped polysilicon film. In some other embodiments, the silicon substrate 1 is a p-type silicon wafer, the first doped polysilicon layer 3 is disposed on a p-type surface of the silicon substrate 1, and for example is the boron-doped polysilicon film.
In some embodiments, the thickness of the first doped polysilicon layer 3 is in a range from 5 nm to 100 nm. Further, the thickness of the first doped polysilicon layer 3 is in a range from 10 nm to 50 nm. For example, the first doped polysilicon layer 3 has a thickness of 20 nm.
In some embodiments, the second doped polysilicon layer 5 includes a phosphorus-doped polysilicon film or a boron-doped polysilicon film. In some embodiments, the silicon substrate 1 is an n-type silicon wafer, the second doped polysilicon layer 5 is disposed on the n-type surface of the silicon substrate 1, and for example is the phosphorus-doped polysilicon film. In some other embodiments, the silicon substrate 1 is a p-type silicon wafer, the second doped polysilicon layer 5 is disposed on the p-type surface of the silicon substrate 1, and for example is the boron-doped polysilicon film. The first doped polysilicon layer 3 and the second doped polysilicon layer 5 are only different in thickness, but have the same doping type and/or made of the same material.
In some embodiments, the thickness of the second doped polysilicon layer 5 is in a range from 70 nm to 200 nm. Further, the thickness of the second doped polysilicon layer 5 is in a range from 100 nm to 150 nm. For example, the second doped polysilicon layer 5 has a thickness of 150 nm.
In some embodiments, as shown in
In some embodiments, the passivation and anti-reflection layer 6 can include a silicon nitride layer or a stack of an aluminum oxide layer and a silicon nitride layer. In some embodiments, the thickness of the passivation and anti-reflection layer 6 can be in a range from 70 nm to 80 nm.
In some embodiments, the metal electrode 7 can be a silver electrode or a silver-aluminum electrode.
In the present embodiment, the laser having the predetermined wavelength is adapted to be intensely absorbed by the laser-absorption layer and induce vaporization of the laser-absorption layer. In some embodiments, the laser is an ultraviolet picosecond laser or an ultraviolet nanosecond laser. In preparation of the solar cell, the tunnel oxide layer, the first doped polysilicon layer, the laser-absorption layer, and the second doped polysilicon layer can be sequentially formed on the entire surface of the front side or the back side the silicon substrate. Then, the portion of the laser-absorption layer and the portion of the second doped polysilicon layer on the non-metal contact region can be removed through the laser having the predetermined wavelength under the action of the intense laser absorption and laser-induced vaporization of the laser-absorption layer, thereby exposing the non-metal contact region of the surface of the first doped polysilicon layer, so as to achieve the solar cell of the present embodiment.
Removing the portion of the laser-absorption layer and the portion of the second doped polysilicon layer located on the non-metal contact region by using laser can simplify the preparation process of the selective passivation contact structure of the solar cell, obviating the need for masking and chemical etching. This method is compatible with the existing mass production process for crystalline silicon solar cells, and only requires to add a laser-etching device, reducing preparation cost, facilitating industrialization and mass production. Consequently, the complexity and high cost issues associated with the preparation method of a passivating contact structure employing a selective polysilicon layer can be effectively addressed.
Optionally, the step of providing the silicon substrate can include cleaning the silicon substrate to remove dirt from the surface of the silicon substrate, providing a clean and flat silicon substrate for subsequent use.
Optionally, the tunnel oxide layer can be formed on the surface of the silicon substrate through thermal oxidation. Silicon can be oxidized in air to form an oxide layer, which is referred to as thermal oxidation. Accordingly, a silicon dioxide layer having excellent performance can be formed on the surface of the silicon substrate.
Optionally, the first doped polysilicon layer can be formed through low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD). The PECVD is adapted to be used for forming a high quality film.
Optionally, the predetermined wavelength of the laser can be in a range from 355 nm to 532 nm.
In some embodiments, the laser is an ultraviolet picosecond laser, and the predetermined wavelength is 355 nm. The ultraviolet picosecond laser of 355 nm has a limited thermal effect, a fast speed, and a high processing accuracy.
In some embodiments, the power of the laser can be in a range from 1 W to 10 W, avoiding damage to the silicon substrate and reducing energy consumption.
In some embodiments, the method further includes:
Optionally, the passivation and anti-reflection layer can be formed through chemical vapor deposition or atomic layer deposition (ALD). The atomic layer deposition is a method configured to individually deposit atomic layers of material on a surface of a substrate, realizing a high film formation quality.
Optionally, the metal electrode can be formed on the passivation and anti-reflection layer through screen printing. The metal electrode is printed on the portion of the second doped polysilicon layer retained on the metal contact region.
The preparation method of the solar cell of the present application is further specifically described in a specific example as follows:
A silicon substrate is provided. The silicon substrate is a silicon wafer. The silicon wafer is cleaned.
A tunnel oxide layer is formed on a surface of the silicon substrate. Specifically, a silicon oxide layer having a thickness of 1.5 nm is formed on the surface of the silicon wafer through thermal oxidation.
A first doped polysilicon layer is formed on a surface of the tunnel oxide layer. Specifically, a phosphorus-doped polysilicon film or a boron-doped polysilicon film having a thickness of 20 nm is formed on the surface of the tunnel oxide layer through LPCVD or PECVD.
A laser-absorption layer is formed on a surface of the first doped polysilicon layer. Specifically, a titanium oxide layer having a thickness of 3 nm is formed on the surface of the first doped polysilicon layer through LPCVD or PECVD.
A second doped polysilicon layer is formed on a surface of the laser-absorption layer. Specifically, a phosphorus-doped polysilicon film or a boron-doped polysilicon film having a thickness of 150 nm is formed on the surface of the laser-absorption layer through LPCVD or PECVD.
The portion of the laser-absorption layer and the portion of the second doped polysilicon layer on the non-metal contact region of the surface of the first doped polysilicon layer are removed through a laser having a predetermined wavelength, thereby exposing the non-metal contact region of the surface of the first doped polysilicon layer. Specifically, the second doped polysilicon layer on the non-metal contact region is scanned with a picosecond laser having a wavelength of 355 nm. The titanium oxide layer can intensely absorb the laser of 355 nm and vaporized under the action of the laser. Thus, the laser-absorption layer and the second doped polysilicon layer on the non-metal contact region can be removed.
A passivation and anti-reflection layer is formed. Specifically, a stack of an aluminum oxide layer and a silicon nitride layer or a silicon nitride layer is deposited on the exposed non-metal contact region of the surface of the first doped polysilicon layer and the surface of the second doped polysilicon layer through chemical vapor deposition or atomic layer deposition.
A metal electrode is formed. Specifically, the metal electrode is formed on a surface of the passivation and anti-reflection layer through screen printing, corresponding to the second doped polysilicon layer remained on the metal contact region. The metal electrode is a silver electrode or a silver-aluminum electrode.
The photoelectric conversion efficiency of the solar cell prepared through the method in the present embodiment can be increased by 0.2%.
A photovoltaic module is provided according to an embodiment of the present application. The photovoltaic module includes the solar cell according to any one of the embodiments described above.
As including the solar cell according to any one of the embodiments described above, the photovoltaic module can provide the same effects, which will not be repeated herein.
The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features are described in the embodiments. However, as long as there is no contradiction in the combination of these technical features, the combinations should be considered as in the scope of the present application.
The above-described embodiments are only several implementations of the present application, and the descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present application. It should be understood that various modifications and improvements can be made by those of ordinary skill in the art without departing from the concept of the present application, and all fall within the protection scope of the present application. Therefore, the patent protection scope of the present application shall be defined by the appended claims, the description and drawings may be used to interpret the content of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202310996038.8 | Aug 2023 | CN | national |
