Patent Description:
With the continuous development of solar cell technology, light absorption efficiency of a solar cell has become an important factor that restricts the further improvement of conversion efficiency of the solar cell. The light absorption efficiency of the solar cell is related to parameters of a passivation structure of the solar cell, which include but are not limited to type of passivation layer(s), material composition(s) and thickness of the passivation layer(s). Therefore, it is desired to optimize the parameters of the passivation structure to improve the conversion efficiency of the solar cell.

<CIT> disclosed a solar cell, a method for producing a solar cell, and a solar module in related art. In this document, the emitter of the solar cell is covered by a passivation stack comprising a first SiOxNy passivation layer, a second SimNn passivation layer with a ratio n/m = <NUM> - <NUM> and a third SiOiNj passivation layer with a ratio j/i = <NUM> - <NUM>. Some disadvantages of using aluminum oxide for the material of the first passivation layer are mentioned in the disclosure of said document.

One or more embodiments are described as examples with reference to the corresponding figures in the accompanying drawings. The figures in the accompanying drawings do not constitute a proportion limitation unless otherwise stated.

In order to make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. However, those skilled in the art may appreciate that, in the 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.

Some embodiments of the present disclosure provide a solar cell, a method for producing a solar cell and a solar cell module. The solar cell provided by embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. <FIG> shows a schematic diagram of a cross-sectional structure of a solar cell according to some embodiments of the present disclosure. <FIG> shows a wavelength-reflectivity comparison diagram according to some embodiments of the present disclosure. <FIG> shows a schematic diagram of a surface of the solar cell according to some embodiments of the present disclosure.

As shown in <FIG>, the solar cell includes: a substrate <NUM> having a front surface 10a and a rear surface 10b opposite to the front surface 10a; a first passivation layer <NUM>, a second passivation layer <NUM> and a third passivation layer <NUM> sequentially formed on the front surface 10a and in a direction away from the front surface 10a; and a tunneling oxide layer <NUM> and a doped conductive layer <NUM> sequentially formed on the rear surface 10b and in a direction away from the rear surface 10b. The first passivation layer <NUM> includes a dielectric material. The second passivation layer <NUM> includes a first silicon nitride SimNn material, and a ratio of n/m is <NUM>~<NUM>. The third passivation layer <NUM> includes a silicon oxynitride SiOiNj material, and a ratio of j/i is <NUM>~<NUM>. The doped conductive layer <NUM> and the substrate <NUM> have a doping element of a same conductivity type.

It can be understood that the y/x, n/m and j/i refer to atomic ratios.

In some examples, the atomic ratio in each film layer may be obtained by an X-ray energy dispersive spectroscopy (EDS) process or an electron energy loss spectroscopy (EELS) process. In some examples, the second passivation layer <NUM> is a silicon-rich layer. That is, the proportion of silicon atoms in the first silicon nitride SimNn material is greater than the proportion of nitrogen atoms in the first silicon nitride SimNn material. The third passivation layer <NUM> may also be a silicon-rich layer, that is, the proportion of silicon atoms in the silicon oxynitride SiOiNj material is greater than both the proportion of nitrogen atoms and the proportion of oxygen atoms in the silicon oxynitride SiOiNj material.

Herein, the third passivation layer <NUM> including the silicon oxynitride SiOiNj material is formed on a side of the second passivation layer <NUM> facing away from the substrate <NUM>, which is beneficial to make the solar cell have a relatively good absorption efficiency for short-wave light. Moreover, an atomic ratio of the silicon oxynitride SiOiNj material is defined, which is beneficial to make the third passivation layer <NUM> have a relatively high refractive index, so that external light can enter the substrate <NUM> at a relative smaller incident angle.

In addition, an atomic ratio of the first silicon nitride SimNn material of the second passivation layer <NUM> is defined, so that the second passivation layer <NUM> may have a higher refractive index than the third passivation layer <NUM>, which is beneficial to reduce internal reflection and emission of light. Besides, the second passivation layer <NUM> may have a relatively weak electropositivity, which is beneficial to avoid an effect of the second passivation layer <NUM> on a field passivation effect of the first passivation layer <NUM> and a photoelectric effect of the substrate <NUM>. Further, the second passivation layer <NUM> may have an appropriate amount of hydrogen ions, which may not only effectively saturate dangling bonds of the front surface 10a through migration, but also inhibit recombination with carriers, thereby ensuring that the carriers can effectively converge to a corresponding electrode of the solar cell.

The solar cell shown in <FIG> will be described in more detail below with reference to the accompanying drawings.

In some examples, the substrate <NUM> is a silicon-based material, such as at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon and microcrystalline silicon. In other examples, the material of the substrate may be a carbon simple substance, an organic material or a multi-component compound, and the multi-component compound may include but is not limited to: perovskite, gallium arsenide, cadmium telluride, copper indium selenium, etc. In addition, the front surface 10a is a light-receiving surface, and the rear surface 10b is a back surface opposite to the light-receiving surface. The front surface 10a is set as a pyramid textured surface, so as to reduce light reflection of the front surface 10a, increase the light absorption and utilization rate, and improve the conversion efficiency of the solar cell. The rear surface 10b is set as a non-pyramid textured surface, such as a stacked and stepped morphology, to ensure that the tunneling oxide layer covering the rear surface 10b has relatively high density and uniformity, and accordingly the tunneling oxide layer can have a good passivation effect on the rear surface 10b.

The substrate <NUM> is an N-type semiconductor substrate. Herein, the substrate <NUM> includes a base <NUM> and an emitter <NUM>. The base <NUM> includes an N-type doping element (such as phosphorus, arsenic, antimony, etc.), and the emitter <NUM> includes a P-type doping element. The emitter <NUM> and the base <NUM> form a PN junction. In some examples, the first passivation layer <NUM> covers the emitter <NUM>. The emitter <NUM> may be formed by doping and diffusing P-type ions (e.g., boron ions) at a surface layer of the base <NUM>, and the doped layer of the base <NUM> may be referred as the emitter <NUM>. The doped conductive layer <NUM> and the substrate <NUM> have a doping element of a same conductivity type refers to that a doping ion type of the doped conductive layer <NUM> is the same as a doping ion type of a main body of the substrate <NUM>, that is, the doping ion type of the doping conductive layer <NUM> is the same as a doping ion type of the base <NUM>.

The material of the first passivation layer <NUM> may be an interface passivation material or a field passivation material depending on a main passivation effect (i.e., an interface passivation effect or a field passivation effect) to be achieved by the first passivation layer <NUM>. The interface passivation material includes at least one of silicon oxide and silicon oxynitride. The field passivation material includes at least one of aluminum oxide, titanium oxide, gallium oxide and hafnium oxide. In the present invention, the material of the first passivation layer <NUM> is the field passivation material, with said field passivation material being an aluminum oxide AlxOy material.

With regard to material characteristics of the first passivation layer <NUM>, from the perspective of enhancing the field passivation effect of the first passivation layer <NUM> and achieving a selective transmission of the carriers, it is required to set the first passivation layer <NUM> to have a relatively strong electronegativity; from the perspective of inhabiting the migration and permeation of external positive ions toward the substrate <NUM>, it is required to set the first passivation layer <NUM> to have a relatively weak electronegativity; from the perspective of reducing a stress between the first passivation layer <NUM> and an adjacent film layer, it is required to set the first passivation layer <NUM> to have a relatively low hardness; in addition, an absorption effect of the first passivation layer <NUM> on the short-wave light needs to be considered, so as to improve the absorption efficiency of the solar cell for the short-wave light. Based on the above considerations, the ratio of y/x of the aluminum oxide AlxOy material of the first passivation layer <NUM> is set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>, and optionally, the ratio of y/x is greater than or equal to <NUM> and less than <NUM>.

With regard to a thickness of the first passivation layer <NUM> in a direction perpendicular to the front surface 10a, it can be understood that the thicker the thickness of the first passivation layer <NUM>, the stronger the field passivation effect. Moreover, due to the great difference in material characteristics between the aluminum oxide and silicon, the thicker the first passivation layer <NUM>, the greater the stress exerted by the first passivation layer <NUM> on the substrate <NUM>. Further, since any film layer may have a barrier effect per se, the thicker the thickness of the first passivation layer <NUM>, the less likely it is for the hydrogen ions in the second passivation layer <NUM> to pass through the first passivation layer <NUM> to saturate the dangling bonds of the front surface 10a. Based on the above considerations, the thickness of the first passivation layer <NUM> is <NUM>~<NUM>, for example, <NUM>, <NUM>, or <NUM>.

In some examples, the first passivation layer <NUM> further includes a silicon oxide material, which covers the front surface 10a. In other words, the silicon oxide material is embedded between the N-type substrate <NUM> and the dielectric material, and the dielectric material includes the aluminum oxide AlxOy material. The silicon oxide material may be formed by a natural oxidation process or a thermal oxygen process, to passivate the front surface. In the direction perpendicular to the front surface 10a, a thickness of a film layer including the silicon oxide material may be set to <NUM>~<NUM>, for example, <NUM>, <NUM>, <NUM> or <NUM>. If the thickness of the film layer is too thick, the carriers may be unable to pass through the film layer due to the tunneling effect; and if the thickness of the film layer is too thin, the passivation effect thereof is relatively poor.

In some examples, when the atomic ratio of the first silicon nitride SimNn material of the second passivation layer <NUM> is set, a refractive index range of the second passivation layer <NUM> is also roughly determined (the refractive index is also affected by other impurity elements in the second passivation layer <NUM>). In order to ensure that the light incident through the second passivation layer <NUM> is closer to the center of the substrate <NUM>, and to inhibit the emission of the light, the thickness of the second passivation layer <NUM> in the direction perpendicular to the front surface 10a may be set to <NUM>~<NUM>, for example, <NUM>, <NUM>, or <NUM>. If the thickness of the second passivation layer <NUM> is too thin, the refraction effect of the second passivation layer <NUM> on light is poor, and the incident light may be emitted out of other passivation layers or emitted out of the substrate <NUM> before being absorbed by the substrate <NUM>, which is not conducive to improving the incident efficiency of the light on the solar cell. In addition, since the second passivation layer <NUM> has a relatively weak electropositivity, the hydrogen ions in the second passivation layer <NUM> may be unable to saturate the dangling bonds in the front surface 10a, which needs to be supplemented by the hydrogen ions in the third passivation layer <NUM>. Therefore, if the second passivation layer <NUM> is too thick, the transmission of the hydrogen ions may be blocked, resulting in more interface defects in the front surface 10a, which is not conducive to inhibiting the carrier recombination in the front surface 10a and reducing a contact resistance of the front surface 10a.

In addition, it can be understood that a thickness selection of the second passivation layer <NUM> is also affected by the atomic ratio of material of the second passivation layer <NUM>. The two factors, i.e., the thickness and the atomic ratio, are coordinated, so as to enable the second passivation layer <NUM> to mainly absorb light in a specific wavelength band, for example, mainly absorb a long-wave light. Further, the thickness of the second passivation layer <NUM> is also limited by a overall thickness requirement of the solar cell. If the overall thickness of the solar cell is too thin, the solar cell is easy to damage under the influence of an external stress; and if the overall thickness of the solar cell is too thick, it is not conducive to overall packaging and the process cost is relatively high.

In some examples, in order to make the solar cell have better absorption efficiency for both the long-wave light and the short-wave light, the second passivation layer <NUM> is mainly used to absorb the long-wave light and the third passivation layer <NUM> is mainly used to absorb the short-wave light. Moreover, since a refractive index of the silicon oxynitride material of the third passivation layer <NUM> which mainly absorbs the short-wave light is relatively low, in order to make the solar cell have a relatively high refractive index for lights in different wave bands, the refractive index of the second passivation layer <NUM> may be set to be greater than that of the third passivation layer <NUM>, so as to improve the absorption efficiency of the solar cell for the light.

In some examples, when the atomic ratio of the silicon oxynitride SiOiNj material of the third passivation layer <NUM> is set, in order to make the solar cell have a relatively high absorption efficiency for the short-wave light and enable the hydrogen ions in the third passivation layer <NUM> to supplement the hydrogen ions in the second passivation layer <NUM>, the thickness of the third passivation layer <NUM> in a direction perpendicular to the front surface 10a may be set to be <NUM>~<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. In some cases, the existing solar cells are usually light blue, which is mainly due to the high reflectivity of the short-wave light (such as an ultraviolet light wave band). However, in the case that the thickness of the third passivation layer <NUM> is within a specific range (e.g., <NUM>~<NUM>) to mainly absorb the short-wave light, the solar cell may be dark blue or even black. The solar cell module formed by packaging the solar cells is black, which can have high power generation efficiency and prospect of being suitable for multi-application scenarios (e.g., BIPV, building integrated solar cell).

In some examples, the solar cell may be light blue if the thickness of the third passivation layer <NUM> is less than <NUM>; and the solar cell may be green if the thickness of the third passivation layer <NUM> is greater than <NUM>.

It should be noted that both the second passivation layer <NUM> and the third passivation layer <NUM> may have a multi-layer structure, and the refractive indices of different sub-layers in the multi-layer structure gradually decrease in the direction away from the front surface 10a of the substrate <NUM>. In this way, it is conducive to reducing an internal reflection and emission caused by an excessive difference in the refractive indices of adjacent film layers. The adjacent film layers may include the film layers in the solar cell, or may include a packaging film and a cover plate in a solar cell module.

In some examples, a second refractive index of the second passivation layer <NUM> is greater than both a first refractive index of the first passivation layer <NUM> and a third refractive index of the third passivation layer <NUM>. Herein, the second refractive index is greater than the third refractive index, which is beneficial to reducing reflection and emission of light incident through the third passivation layer <NUM>. Further, in some examples, the first refractive index is greater than the third refractive index, which is beneficial to further reduce the reflection and emission of the light incident through the third passivation layer <NUM> and improve the light absorption efficiency of the solar cell. It can be understood that when the above-mentioned film layer includes a plurality of sub-film layers, the refractive index of the film layer is an average refractive index of the plurality of sub-film layers.

With regard to the third passivation layer <NUM>, from the perspective of reducing the incident angle of the external light, it is required to set the third passivation layer <NUM> to have a relatively high refractive index; from the perspective of suppressing the internal reflection and the emission, it is required to set the third passivation layer <NUM> to have a relatively small refractive index, and make a difference between the refractive index of the third passivation layer <NUM> and the refractive index of the second passivation layer <NUM> be relatively small; from the perspective of mainly absorbing the short-wave light, it is required to set an oxygen atomic ratio of the third passivation layer <NUM> to be relatively large, but the refractive index of the third passivation layer <NUM> gradually decreases with the increase of the oxygen atomic ratio of the third passivation layer <NUM>. In order to make the solar cell have relatively high absorption efficiency for the short-wave light, the atomic ratio j/i of the third passivation layer <NUM> including the silicon oxynitride SiOiNj material may be set to <NUM>~<NUM>, for example, <NUM> or <NUM>, and the refractive index of the third passivation layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

In addition, the atomic ratio n/m of the second passivation layer <NUM> including the first silicon nitride SimNn material may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>, and the refractive index of the second passivation layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>. The refractive index of the first passivation layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>.

As shown in <FIG>, in the short-wave (e.g., the ultraviolet light wave band) range, the solar cell provided by the embodiments of the present disclosure has a lower reflectivity than a conventional TOPCON solar cell (N-type TOPCON solar cell) and a PERC solar cell (P-type PERC solar cell). The conventional TOPCON solar cell usually uses an aluminum oxide/silicon nitride stacked layer as a front passivation layer, and the conventional PERC solar cell usually uses a silicon nitride layer as the front passivation layer. Taking light at a wavelength of <NUM> as an example, a reflectivity of the conventional PERC solar cell is about <NUM>%, a reflectivity of the conventional TOPCON solar cell is about <NUM>%, and a reflectivity of the solar cell provided by the embodiments of the present disclosure is about <NUM>%, which is reduced by nearly half. Taking light at a wavelength of <NUM> as an example, the reflectivity of the conventional PERC solar cell is about <NUM>%, the reflectivity of the conventional TOPCON solar cell is about <NUM>%, and the reflectivity of the solar cell provided by the embodiments of the present disclosure is about <NUM>%, which is also reduced by nearly half. Due to the relatively low reflectivity of light in the short-wave range, compared with the conventional solar cell or a conventional solar cell module, the solar cell provided in the embodiments may be dark blue or even black, thus facilitate forming a black solar cell module. As shown in <FIG>, the solar cell based on the structure shown in <FIG> is dark blue and near black.

The solar cell provided by the embodiments of the present disclosure also has a greatly lower average reflectivity for the light at wavelength range of <NUM>~<NUM>. Generally, the average reflectivity of the conventional PERC solar cell and the conventional TOPCON solar cell for the light at wavelength range of <NUM>~<NUM> is <NUM>-<NUM>%. For example, the average reflectivity of the conventional PERC solar cell is about <NUM>%, and the average reflectivity of the conventional TOPCON solar cell is about <NUM>%, while the average reflectivity of the solar cell provided by the embodiments of the present disclosure is <NUM>%~<NUM>%, e.g., about <NUM>%, which is reduced by nearly <NUM>/<NUM>. Further, the average reflectivity for the light at the wavelength range of <NUM>~<NUM> of the solar cell provided by the embodiments of the present disclosure is also less than <NUM>%. Accordingly, in the case that the passivation stacked structure (the first passivation layer <NUM>, the second passivation layer <NUM> and the third passivation layer <NUM>) is applied to a TOPCON solar cell, a short-circuit current of the TOPCON solar cell may be increased by more than 30mA.

In some examples, a first intermediate layer may be provided between the first passivation layer <NUM> and the second passivation layer <NUM>. In this case, the first passivation layer <NUM> serves as a field effect passivation layer, the second passivation layer <NUM> serves as a chemical effect passivation layer, and the first intermediate layer may be used to optimize an electrical conductivity or light absorption performance between the first passivation layer <NUM> and the second passivation layer <NUM>. For example, the first intermediate layer may affect the reflection performance (such as reflectivity) of a short-wavelength-band incident light (such as ultraviolet light) in the overall passivation structure on the front surface. The material of the first intermediate layer may be a silicon oxide material, and a thickness of the first intermediate layer may be <NUM>~<NUM>.

In some examples, a second intermediate layer may be provided between the second passivation layer <NUM> and the third passivation layer <NUM>. The second intermediate layer may be used to affect the reflection performance of the overall passivation structure on the front surface. For example, the second intermediate layer may affect the reflection performance (e.g., reflectivity) of the short-wavelength-band incident light (e.g., ultraviolet light) in the overall passivation structure on the front surface. The material of the second intermediate layer may be a silicon carbon oxynitride material, and a thickness of the second intermediate layer may be less than <NUM>. Further, a passivation contact structure is provided on the rear surface 10b. The passivation contact structure at least includes the tunneling oxide layer <NUM> and the doped conductive layer <NUM> sequentially formed in a direction away from the substrate <NUM>. Herein, the material of the tunneling oxide layer <NUM> is a dielectric material, such as a silicon oxide, which is used to achieve an interface passivation of the rear surface 10b. The material of the doped conductive layer <NUM> is used to achieve the field passivation, and the material of the doped conductive layer <NUM> may be doped silicon. The doped conductive layer <NUM> and the substrate <NUM> have a doping element of a same conductivity type. The doped silicon may be at least one of N-type doped polycrystalline silicon, N-type doped microcrystalline silicon and N-type doped amorphous silicon, and the doped conductive layer <NUM> includes N-type doped ions. Herein, in some examples, the doped conductive layer <NUM> is a doped polycrystalline silicon layer. In the direction perpendicular to the rear surface 10b, a thickness of the doped conductive layer <NUM> ranges from <NUM> to <NUM>, for example, <NUM>, <NUM> or <NUM>, and a refractive index of the doped conductive layer <NUM> ranges from <NUM> to <NUM>, for example, <NUM>, <NUM> or <NUM>.

In some examples, a fourth passivation layer <NUM> is further provided on the doped conductive layer <NUM>, and the fourth passivation layer <NUM> is used to enhance the reflection effect of the incident light on a back of the solar cell. Herein, the fourth passivation layer <NUM> may include a plurality of sub-layers, and the refractive indices of different sub-layers gradually decrease in a direction from the rear surface 10b toward the doped conductive layer <NUM>, which is beneficial to enhance the reflection effect of the incident light on the back of the solar cell by the internal reflection. If a material of the fourth passivation layer <NUM> is silicon nitride, a silicon nitride sublayer with a relatively high refractive index has more hydrogen ions, and the hydrogen ions may migrate to the rear surface 10b under a diffusion power formed by a concentration difference or a thermal power due to a heat treatment process, so as to passivate interface defects between the substrate <NUM> and the passivation contact structure, inhibit the carrier recombination and improve the photoelectric conversion efficiency of the solar cell.

The fourth passivation layer <NUM> may include a bottom passivation layer, an intermediate passivation layer and a top passivation layer sequentially formed, and the bottom passivation layer covers a surface of the doped conductive layer <NUM>. A refractive index of the bottom passivation layer may be set to <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, and a thickness of the bottom passivation layer in the direction perpendicular to the rear surface 10b is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. A refractive index of the intermediate passivation layer may be set to <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, and a thickness of the intermediate passivation layer is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. A refractive index of the top passivation layer may be set to <NUM>~<NUM>, and a thickness of the top passivation layer is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. In general, the fourth passivation layer <NUM> includes a second silicon nitride SiaNb material, and a ratio of a/b is <NUM>~<NUM>, for example, <NUM>, <NUM>, <NUM> or <NUM>. An overall refractive index of the fourth passivation layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>. The thickness of the fourth passivation layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM> in the direction perpendicular to the rear surface 10b.

In addition, the solar cell further includes at least one first electrode <NUM> and at least one second electrode <NUM>. The at least one first electrode <NUM> is electrically connected with the emitter <NUM>, and the least one second electrode <NUM> is electrically connected with the doped conductive layer <NUM> by penetrating through the fourth passivation layer <NUM>. In some examples, the least one first electrode <NUM> and/or the least one second electrode <NUM> may be sintered and printed by a conductive paste (a silver paste, an aluminum paste or a silver-aluminum paste).

In the present disclosure, the solar cell is provided with the third passivation layer including the silicon oxynitride material on the side of the second passivation layer away from the substrate; thereby the solar cell can have relatively good absorption efficiency for the short-wave light. Moreover, the atomic ratio of the silicon oxynitride material is defined, which is beneficial to make the third passivation layer have relatively high refractive index, so that the external light can enter the substrate at a smaller incident angle. In addition, the atomic ratio of the first silicon nitride material of the second passivation layer is defined, so that the second passivation layer can have higher refractive index than the third passivation layer, which is beneficial to reduce the internal reflection and the emission of the light, and moreover, the second passivation layer can have relatively weak electropositivity, which is beneficial to avoid the effect of the second passivation layer on the field passivation effect of the first passivation layer and the photoelectric effect of the substrate.

Some embodiments of the present disclosure further provide a solar cell module, which is used to convert received light energy into electric energy. As shown in <FIG>, the solar cell module includes at least one solar cell string, a packaging film <NUM> and a cover plate <NUM>. Each solar cell string is formed by connecting a plurality of solar cells <NUM>. The solar cell <NUM> may be any of the aforementioned solar cells (including but not limited to the solar cell shown in <FIG>). Adjacent solar cells <NUM> are electrically connected by a conductive strip. The adjacent solar cells <NUM> may be either partially stacked or spliced with each other. The packaging film <NUM> may be an organic packaging film such as an ethylene-vinyl acetate copolymer (EVA) film, a polyethylene octene co-elastomer (POE) film or a polyethylene terephthalate (PET) film. The packaging film <NUM> covers a surface of each of the at least one solar cell string for sealing. The cover plate <NUM> may be a transparent or translucent cover plate such as a glass cover plate or a plastic cover plate, and the cover plate <NUM> covers a surface of the packaging film <NUM> away from the at least one solar cell string. In some examples, a light trapping structure is provided for the cover plate <NUM> to increase utilization rate of incident light, and the cover plate may have different light trapping structures. The solar cell module has relatively high current collection ability and relatively low carrier recombination rate, which may realize the relatively high photoelectric conversion efficiency of the solar cell module. Moreover, a front of the solar cell module is dark blue or even black, which may be suitable for more scenarios.

In some examples, the packaging film <NUM> and the cover plate <NUM> are just formed on a front surface of the solar cell <NUM>, because that the packaging film <NUM> and the cover plate <NUM> formed on a rear surface of the solar cell <NUM> may block and weaken relatively weak light. Further, the solar cell module may be packaged in a side edge fully enclosed manner, that is, the side edges of the solar cell module are completely covered by the packaging film <NUM>, so as to prevent the solar cell module from lamination offset during lamination and avoid the external environment from affecting the performance of the solar cell through the side edges of the solar cell module, such as water vapor intrusion.

In some examples, as shown in <FIG>, the solar cell module further includes an edge sealing member <NUM>, which at least fixedly packages the side edges of the solar cell module. Further, the edge sealing member <NUM> at least fixedly packages a portion of the side edges close to corners of the solar cell module. The edge sealing member <NUM> may be a high-temperature resistant adhesive tape. Since the edge sealing member <NUM> has high-temperature resistant characteristic, the solar cells may not be damaged or fall off during the lamination and use, which is beneficial to ensuring reliable packaging of the solar cell module. In some examples, the high-temperature resistant adhesive tape is adhered not only to side surfaces of the solar cell module, but also to a front surface and rear surface of the solar cell module, so that it is beneficial to inhibit the lamination offset of the solar cell module during the lamination and stress deformation of the solar cell module under stress.

Some embodiments of the present disclosure further provide a method for producing a solar cell. <FIG> and <FIG> shows schematic structural diagrams corresponding to each step of the method for producing the solar cell according to the embodiments of the present disclosure.

As shown in <FIG>, a base <NUM> is provided and is double-sided textured.

In some examples, the base <NUM> is cleaned, and a pyramid textured surface is prepared by a wet chemical etching process. The pyramid textured surface may reduce the light reflection at the surface of the base <NUM>, thereby increasing the absorption and utilization rate of light by the base <NUM> and improving the conversion efficiency of the solar cell. In some examples, a material of the base <NUM> is monocrystalline silicon, a thickness of the base <NUM> is <NUM>~<NUM>, such as, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, etc., and a resistivity of the base <NUM> ranges from <NUM> to <NUM> ohm. In addition, the base <NUM> may be an N-type semiconductor or a P-type semiconductor, and hereinafter, the base <NUM> is the N-type semiconductor is taken as an example.

For example, the texturing of the base <NUM> may be performed by but not limited to a wet texturing process. If the base <NUM> is the N-type monocrystalline silicon, alkaline solution such as potassium hydroxide solution may be used for texturing the base <NUM>. NaOH solution has anisotropic corrosivity, and is beneficial to prepare pyramid-shaped microstructures. The pyramid-shaped microstructures may be tetrahedron shape, approximate tetrahedron shape, pentahedron shape, approximate pentahedron shape or other structures. In addition, the texturing process may also be a chemical etching process, a laser etching process, a mechanical process, or a plasma etching process, etc. The pyramid-shaped microstructures enable a screen printing metal paste to better fill the microstructures when forming electrodes, thus achieving a more excellent electrode contact, effectively reducing a series resistance of the solar cell and improving a filling factor. The overall refractive index of the solar cell may be less than <NUM>% by controlling the morphology of the pyramid-shaped microstructures.

As shown in <FIG>, a P-type emitter <NUM> is formed.

After the double-sided texturing of the base <NUM>, a boron diffusion treatment is performed for a front surface 10a of the base <NUM> to form the P-type emitter <NUM>. The P-type emitter <NUM> occupies a portion of a surface layer of a sun-facing side of the base <NUM>. The P-type emitter <NUM> and the N-type base <NUM> constitute the substrate <NUM>. Herein, a diffusion square resistance of the P-type emitter <NUM> ranges from <NUM> to <NUM>Ω, and a surface diffusion concentration of the P-type emitter <NUM> ranges from E18 to E19.

It should be noted that the boron diffusion treatment may also generate unwanted borosilicate glass at the front surface (i.e., the front surface 10a), a rear surface and a side surface of the base <NUM>. The borosilicate glass has a certain protective effect on the base <NUM>, thus avoiding damage to the surface of the base <NUM> caused by some further processes. In other words, the unwanted borosilicate glass may be used as a mask layer for the base <NUM>. Herein, a boron source used in the boron diffusion treatment includes liquid boron tribromide, and a microcrystalline silicon phase may convert into a polycrystalline silicon phase during the boron diffusion treatment.

As shown in <FIG>, a planarization process (e.g., alkali polishing) is performed on the rear surface of the base <NUM>.

The rear surface is a surface of the solar cell facing away from sunlight, and the rear surface may turn to a flat surface (i.e., the rear surface 10b) by the planarization process. The flat surface is required for depositing a further film layer thereon. During the planarization process, the borosilicate glass at the rear surface is removed at the same time.

In some examples, before the polishing process, the following steps are further included: removing the borosilicate glass at the rear surface 10b of the base <NUM> with a prepared mixed acid. The mixed acid includes hydrofluoric acid solution with a mass fraction of <NUM>%~<NUM>%, sulfuric acid solution with a mass fraction of <NUM>%~<NUM>% and nitric acid solution with a mass fraction of <NUM>%~<NUM>%. An acid washing time is <NUM>~<NUM>, an acid washing temperature is <NUM>~<NUM>. The acid-washed rear surface 10b of the substrate <NUM> is further washed with water and is further performed with a drying treatment. It should be noted that the acid-washed rear surface 10b of the substrate 10a may be porous structure.

In some examples, the rear surface 10b of the substrate 10a may be polished with the alkaline solution. In an example, the rear surface 10b is firstly washed by alkaline solution with a mass fraction of <NUM>%~<NUM>% to remove porous silicon. A micro-droplet of the alkaline solution is dropped onto the rear surface 10b by spraying for a roughening treatment, and the hydrofluoric acid with a mass fraction of <NUM>%~<NUM>% is used for pre-cleaning. The rear surface 10b is further polished with a polishing liquid at a polishing temperature of <NUM>~<NUM>°Cwith a polishing time less than <NUM>; the polishing liquid includes NaOH with a mass fraction of <NUM>%~<NUM>%, KOH with a mass fraction of <NUM>%~<NUM>% and an additive with a mass fraction of <NUM>%~<NUM>%. A mixed solution of potassium hydroxide with a mass fraction of <NUM>%~<NUM>% and hydrogen peroxide with a mass fraction of <NUM>%~<NUM>% is used to remove organic component in an etching liquid. The polished substrate <NUM> is washed with water and dried later.

In some examples, since the boron concentration of the rear surface 10b is relatively low, etching the rear surface 10b with the alkaline solution can effectively improve the etching efficiency. The alkaline solution includes an organic base and/or an inorganic base. The inorganic base may be NaOH, KOH, Ga(OH)<NUM>, or NH<NUM>. The organic base may be triethylamine, nitrophenol, pyridine, quinine, or colchicine, etc. The additive in the polishing liquid may be a buffer solution composed of sodium sulfonate, maleic anhydride, alkyl glycoside, etc. In some examples, a polishing weight loss of the substrate <NUM> is less than <NUM>. The rear surface 10b of the substrate <NUM> may have a desired structure by controlling the polishing time and polishing temperature during the polishing treatment.

The structural morphology of the rear surface 10b is different from that of the front surface 10a, so as to enhance the absorption of light through the different morphologies of the surfaces. The front surface 10a has a pyramid-shaped structure, focusing on improving the anti-reflection ability. The rear surface 10b may have a stacked and stepped morphology to ensure that the tunneling oxide layer covering the rear surface 10b has relatively high density and uniformity, thus ensuring that the tunneling oxide layer has a good passivation effect on the rear surface 10b.

As shown in <FIG>, a tunneling oxide layer <NUM> and a doped conductive layer <NUM> are formed.

In some examples, the tunneling oxide layer <NUM> is formed by a deposition process. In an example, the material of the tunneling oxide layer <NUM> includes silicon oxide, and the deposition process includes a chemical vapor deposition process. In a direction perpendicular to the rear surface 10b, the tunneling oxide layer <NUM> has a thickness of <NUM>~<NUM>, such as <NUM>, <NUM>, <NUM> or <NUM>. In other embodiments, the tunneling oxide layer may be formed by an in-situ generation process. In an example, the tunneling oxide layer may be formed in-situ by a thermal oxidation process and a nitric acid passivation process on a silicon substrate.

In some examples, the tunneling oxide layer <NUM> is deposited on the rear surface 10b by using a temperature-variable process and a chemical vapor deposition process. During the deposition, the heating rate is controlled to be <NUM>/min~<NUM>/min, such as <NUM>/min, <NUM>/min, <NUM>/min or <NUM>/min, etc.; the deposition temperature is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, etc.; and the deposition time is <NUM>~<NUM>, for example <NUM>, <NUM> or <NUM>, etc..

In some examples, after forming the tunneling oxide layer <NUM>, intrinsic polycrystalline silicon is deposited on the tunneling oxide layer <NUM> to form a polycrystalline silicon layer, and phosphorus ions are doped by an ion implantation and source diffusion process to form an N-type doped polycrystalline silicon layer, and the doped polycrystalline silicon layer serves as the doped conductive layer <NUM>. In the direction perpendicular to the rear surface 10b, the thickness of the doped conductive layer <NUM> may be set to <NUM>~<NUM>, for example, <NUM>, <NUM> or <NUM>. In other embodiments, the doped conductive layer <NUM> and the substrate <NUM> has a doping element of a same conductivity type. If the substrate <NUM> is an N-type semiconductor, the doped conductive layer <NUM> is at least one of an N-type doped polycrystalline silicon layer, an N-type doped microcrystalline silicon layer and an N-type doped amorphous silicon layer.

During forming the tunneling oxide layer <NUM> and the doped conductive layer <NUM> by the deposition process, since the front surface has the borosilicate glass as a mask layer to protect the front surface 10a of the base <NUM>, there is no need to limit the deposition area to the rear surface by a mask during the deposition process, and further the boric acid glass on the front surface as well as the silicon oxide and polycrystalline silicon deposited on the front surface can be removed at the same time by using a same process. In this way, no additional mask is required, which is conducive to reducing process steps, shortening process flow, and reducing process cost. In other examples, if the interface passivation layer is formed by the in-situ generation process, only polycrystalline silicon is deposited on the borosilicate glass on the front surface of the substrate.

In some examples, the deposition of the tunneling oxide layer <NUM> and the polycrystalline silicon layer as well as the doping of the polycrystalline silicon layer are performed in a low pressure chemical vapor deposition device. The specific steps include: first, placing the substrate <NUM> after the alkali polishing in the deposition device, introducing an oxygen source (for example, oxygen, nitrous oxide, ozone) of <NUM> to <NUM>, heating the temperature in the deposition device to <NUM>~<NUM> at a heating rate of <NUM>/min~<NUM>/min, and the deposition time being <NUM>~<NUM> to form the tunneling oxide layer <NUM>; entering a constant temperature stage after the oxygen introduction is finished, and then introducing a proper amount of silane to form the polycrystalline silicon layer; and finally, doping the polycrystalline silicon layer in situ to form the doped conductive layer <NUM>.

As shown in <FIG>, a first passivation layer <NUM>, a second passivation layer <NUM>, and a third passivation layer <NUM> are formed on the front surface 10a.

In some examples, before forming the first passivation layer, it is required to remove the unwanted borosilicate glass, silicon oxide, and polycrystalline silicon plated on the front surface 10a of the substrate <NUM>. In other embodiments, before forming the first passivation layer, it is required to remove the unwanted borosilicate glass and polycrystalline silicon plated on the front surface 10a of the substrate <NUM>.

Further, in some examples, after removing the unwanted material, a thin silicon oxide layer is grown on the front surface of the substrate. The formation process for the thin silicon oxide layer includes a natural oxidation process, a thermal oxidation process, a wet oxidation process, an atomic layer deposition process, or a plasma enhanced chemical vapor deposition process, etc. The thin silicon oxide layer has a thickness of <NUM>~<NUM> in the direction perpendicular to the substrate surface, such as <NUM>, <NUM> or <NUM>.

In some examples, the first passivation layer <NUM>, the second passivation layer <NUM>, and the third passivation layer <NUM> may be formed by, but not limited to such as a chemical vapor deposition process, a low pressure chemical vapor deposition process, a plasma-enhanced chemical vapor deposition process (e.g., a direct plasma deposition process or an indirect plasma deposition process), and a magnetron sputtering process. Herein, the first passivation layer <NUM> includes a dielectric material; the second passivation layer <NUM> includes a first silicon nitride SimNn material, and a ratio of n/m is <NUM>~<NUM>; and the third passivation layer <NUM> includes a silicon oxynitride SiOiNj material, and a ratio of j/i is <NUM>~<NUM>. Hereinafter, an atomic layer deposition process combined with a tubular plasma-enhanced chemical vapor deposition process is taken as an example of the preparation process for description.

The material of the first passivation layer <NUM> may be an interface passivation material or a field passivation material depending on whether the main passivation effect to be achieved is a field passivation or an interface passivation. The interface passivation material includes at least one of silicon oxide and silicon oxynitride, and the field passivation material includes at least one of aluminum oxide, titanium oxide, gallium oxide and hafnium oxide. In the present invention, the material of the first passivation layer <NUM> is mainly the field passivation material, said field passivation material being an aluminum oxide AlxOy material.

In some examples, the first passivation layer <NUM> is formed by the atomic layer deposition process. During the process, reactants include trimethyl aluminum and water, and the deposition temperature is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. A refractive index of the first passivation layer <NUM> at a wavelength of <NUM> is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. The first passivation layer <NUM> has a thickness of <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, in the direction perpendicular to the front surface 10a.

After forming the first passivation layer <NUM>, the first passivation layer <NUM> is placed in a protective gas atmosphere for a high-temperature annealing treatment to remove residual water molecules and organic functional groups. During the high-temperature annealing treatment, an annealing temperature is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, and an annealing time is longer than <NUM>, such as <NUM>, <NUM> or <NUM>. It should be noted that the "protective gas" may be any gas that does not participate in the reaction, such as inert gas. In some examples, nitrogen gas may be used as the protective gas.

In some examples, the second passivation layer <NUM> is formed by the plasma-enhanced chemical vapor deposition process. During the deposition process, reactants are silane and ammonia gas. A flow ratio of the silane to the ammonia gas is <NUM>/<NUM>~<NUM>/<NUM>, such as <NUM>/<NUM>, <NUM>/<NUM> or <NUM>/<NUM>, and a pulse power per unit area is <NUM>~40mW/cm<NUM>, such as 33mW/cm<NUM>, 35mW/cm<NUM> or 37mW/cm<NUM>. The atomic ratio of the first silicon nitride SimNn material of the second passivation layer <NUM> may be set to a preset range, by controlling the flow ratio and the pulse power per unit area in the deposition process, so that the second passivation layer <NUM> may have a desired refractive index. Exemplarily, an overall refractive index of the second passivation layer <NUM> including the first silicon nitride SimNn material at a wavelength of <NUM> is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. In addition, the second passivation layer <NUM> has a thickness of <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, in the direction perpendicular to the front surface 10a.

In some examples, the third passivation layer <NUM> is formed by using the plasma-enhanced chemical vapor deposition process. During the deposition process, reactants are silane, nitrous oxide and ammonia gas. A flow ratio of the silane to the nitrous oxide is not less than <NUM>/<NUM>, for example, <NUM>/<NUM>, <NUM>/<NUM> or <NUM>/<NUM>, and a pulse power per unit area is <NUM>~40mW/cm<NUM>, for example, 28mW/cm<NUM>, 30mW/cm<NUM> 33mW/cm<NUM>, or 36mW/cm<NUM>. The atomic ratio of the silicon oxynitride SiOiNj material of the third passivation layer <NUM> may be set to a preset range, by controlling the flow ratio and the pulse power per unit area in the deposition process, so that the third passivation layer <NUM> may have a desired refractive index. Exemplarily, an overall refractive index of the third passivation layer <NUM> at a wavelength of <NUM> is <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>. In addition, the third passivation layer <NUM> has a thickness of <NUM>~<NUM>, such as <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, in the direction perpendicular to the front surface 10a.

As shown in <FIG>, a fourth passivation layer <NUM> is formed on the doped conductive layer <NUM>, as well as at least one first electrode <NUM> and at least one second electrode <NUM> are formed.

In a case that the fourth passivation layer <NUM> is a silicon nitride layer, the silicon nitride layer may include <NUM>~<NUM> multi-layers with gradient refractive indices according to actual requirements. That is, the refractive indices of different silicon nitride sub-layers gradually decrease in a direction away from the substrate <NUM>. In addition, reactants for forming the silicon nitride layer may be the silane and the ammonia gas, and a ratio of the number of silicon atoms to the number of nitrogen atoms in the fourth passivation layer <NUM> may be <NUM>~<NUM>, such as <NUM>, <NUM>, <NUM> or <NUM>. A refractive index range may be <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, and a thickness range may be <NUM>~<NUM>, such as <NUM>, <NUM>, or <NUM>.

After forming the fourth passivation layer <NUM>, the at least one first electrode <NUM> and the at least one second electrode <NUM> may be formed by such as a metallization process, a screen printing process, and a high-temperature sintering process. In addition, after the electrodes are formed, a light-annealing treatment is further required to be performed, that is, the solar cell is heated under a temperature of <NUM> to <NUM> (e.g., <NUM> or <NUM>) for <NUM> ~<NUM> (e.g., <NUM>, <NUM>, <NUM> or <NUM>), and then treated for <NUM>~<NUM> under a temperature of <NUM>~<NUM> (e.g., <NUM>, <NUM>, <NUM>) and <NUM>~<NUM> times (e.g., <NUM>, <NUM>, <NUM>, or <NUM> times) of sunlight intensity.

Claim 1:
A solar cell, comprising:
a substrate (<NUM>) having a front surface (10a) and a rear surface (10b) opposite to the front surface (10a), wherein the substrate (<NUM>) includes a base (<NUM>) and an emitter (<NUM>);
a first passivation layer (<NUM>), a second passivation layer (<NUM>) and a third passivation layer (<NUM>) formed on the front surface (10a); and
a tunneling oxide layer (<NUM>) and a doped conductive layer (<NUM>) formed on the rear surface (10b) and in a direction away from the rear surface (10b), wherein the rear surface (10b) is a non-pyramid textured surface, and wherein the doped conductive layer (<NUM>) and the substrate (<NUM>) have a doping element of a same conductivity type;
wherein the front surface (10a) is a pyramid textured surface, the first passivation layer (<NUM>) is configured to cover the emitter (<NUM>) and includes a dielectric material, the second passivation layer (<NUM>) is formed between the first passivation layer (<NUM>) and the third passivation layer (<NUM>) and includes a first silicon nitride SimNn material, a ratio of n/m ranges from <NUM> to <NUM>, the third passivation layer (<NUM>) includes a silicon oxynitride SiOiNj material, and a ratio of j/i ranges from <NUM> to <NUM>;
wherein the first passivation layer (<NUM>) has a thickness ranged from <NUM> to <NUM> in a direction perpendicular to the front surface (10a), the dielectric material is an aluminum oxide AlxOy material, and a ratio of y/x ranges from <NUM> to <NUM>; and
wherein the y/x, n/m, and j/i refer to atomic ratios.