Patent Description:
Solar cells have good photoelectric conversion capabilities. In solar cells, a diffusion process is required on the surface of silicon wafers to produce p-n junctions. In existing solar cells, boron diffusion processes are usually performed on the surface of silicon wafers to form an emitter on the surface of silicon wafers. On one hand, the emitter forms a p-n junction with the silicon wafer, and on the other hand, the emitter is also electrically connected with a metal electrode, so that the carriers transporting in the emitter can be collected by the metal electrode. Therefore, the emitter has a great influence on the photoelectric conversion performance of the solar cells.

The photoelectric conversion performance of the existing solar cells is poor.

<CIT> discloses a solar cell including a substrate, an emitter region, an anti-reflection layer positioned on the emitter region, a first electrode, and a second electrode. The substrate contains impurities of a first conductive type. The emitter region is positioned at a first surface of the substrate and contains impurities of a second conductive type opposite the first conductive type to form a p-n junction along with the substrate. The first electrode is positioned on the anti-reflection layer and is coupled to the emitter region. The second electrode is positioned on a second surface of the substrate and is coupled to the substrate.

Embodiments of the present disclosure provide a solar cell and a photovoltaic module, which is at least conducive to the improvement of photoelectric conversion performance of a solar cell.

The present invention relates to a solar cell, comprising a N-type substrate; a P-type emitter provided on a first surface of the N-type substrate, wherein the P-type emitter comprises a first portion and a second portion, a top surface of the first portion comprises a first pyramid structure, and at least a part of at least one inclined surface of the first pyramid structure is concave or convex relative to a center of the first pyramid structure, wherein a top surface of the second portion comprises a second pyramid structure, and inclined surfaces of the second pyramid structure are planes, and wherein in a direction perpendicular to the first surface of the N-type substrate, a junction depth of the first portion is greater than a junction depth of the second portion; and a tunnel layer and a doped conductive layer, wherein the tunnel layer and the doped conductive layer are located on a second surface of the N-type substrate and are arranged in sequence in a direction away from the N-type substrate;wherein at least part of the first pyramid structure comprises a first substructure located at a top of the first pyramid structure, wherein the first substructure is a sphere or a spheroid.

Some embodiments of the present disclosure provide a solar cell, including: a N-type substrate; a P-type emitter provided on a first surface of the N-type substrate, the P-type emitter includes a first portion and a second portion, a top surface of the first portion includes a first pyramid structure, and at least a part of at least one inclined surface of the first pyramid structure is concave or convex relative to a center of the first pyramid structure, a top surface of the second portion includes a second pyramid structure, and inclined surfaces of the second pyramid structure are planes, and in a direction perpendicular to the first surface of the N-type substrate, a junction depth of the first portion is greater than a junction depth of the second portion; and a tunnel layer and a doped conductive layer, the tunnel layer and the doped conductive layer are located on a second surface of the N-type substrate and are arranged in sequence in a direction away from the N-type substrate.

In an example, a crystal structure of the first portion of the P-type emitter has dislocations.

In an example, a sheet resistance of the first portion of the P-type emitter is lower than a sheet resistance of the second portion of the P-type emitter.

In an example, the sheet resistance of the first portion of the P-type emitter ranges from 20ohm/sq to 300ohm/sq, and the sheet resistance of the second portion of the P-type emitter ranges from 100ohm/sq to 1000ohm/sq.

In an example, a height of the first pyramid structure ranges from <NUM> to <NUM>, and an one-dimensional size of a bottom of the first pyramid structure ranges from <NUM> to <NUM>.

In accordance with the invention, at least part of the first pyramid structure further includes a first substructure located at a top of the first pyramid structure, where the first substructure is a sphere or a spheroid.

In an example, a ratio of the junction depth of the first portion to the junction depth of the second portion is not less than <NUM>.

In an example, the junction depth of the first portion ranges from <NUM> to <NUM>, and the junction depth of the second portion ranges from <NUM> to <NUM>.

In an example, a doping concentration at the top surface of the first portion of the P-type emitter is greater than or equal to a doping concentration at the top surface of the second portion of the P-type emitter.

In an example, the doping concentration at the top surface of the first portion of the P-type emitter ranges from 1E<NUM>atoms/cm<NUM> to 5E<NUM>atoms/cm<NUM>.

In an example, a difference between the doping concentration at the top surface of the first portion and a doping concentration at a bottom surface of the first portion ranges from 1E<NUM>atoms/cm<NUM> to 5E<NUM>atoms/cm<NUM>.

In an example, a difference between the doping concentration at the top surface of the second portion and a doping concentration at a bottom surface of the second portion ranges from 1E<NUM>atoms/cm<NUM> to 1E<NUM>atoms/cm<NUM>.

In an example, a ratio of a width of the second portion to a width of the first portion is not less than <NUM>.

In an example, the solar cell further includes a first metal electrode, where the first metal electrode is provided on the first surface of the N-type substrate, and is electrically connected to the first portion of the P-type emitter.

In an example, the P-type emitter further includes a transition region located between the first portion and the second portion, a doping concentration at a top surface of the transition region is greater than or equal to the doping concentration at the top surface of the second portion, and is less than or equal to the doping concentration at the top surface of the first portion.

Some embodiments of the present disclosure provide a production method for a solar cell, including: providing a N-type substrate; forming a P-type emitter on a first surface of the N-type substrate, where the P-type emitter includes a first portion and a second portion, a top surface of the first portion includes a first pyramid structure, and at least a part of at least one inclined surface of the first pyramid structure is concave or convex relative to a center of the first pyramid structure, a top surface of the second portion includes a second pyramid structure, and inclined surfaces of the second pyramid structure are planes, and in a direction perpendicular to the first surface of the N-type substrate, a junction depth of the first portion is greater than a junction depth of the second portion; and forming a tunnel layer and a doped conductive layer, where the tunnel layer and the doped conductive layer are located on a second surface of the N-type substrate and are arranged in sequence in a direction away from the N-type substrate.

In an example, forming the P-type emitter includes: providing a N-type initial substrate; depositing a trivalent doping source on a top surface of the N-type initial substrate; treating, by using a process of external energy source treatment, a preset region of the top surface of the N-type initial substrate, to diffuse the trivalent doping source treated by the process of external energy source treatment into an interior of the N-type initial substrate; performing a high temperature treatment on the N-type initial substrate to form the P-type emitter in the interior of the N-type initial substrate, a top surface of the P-type emitter is exposed from the N-type initial substrate; forming the N-type substrate in a region of the N-type initial substrate excluding the P-type emitter; and forming the first portion of the P-type emitter in the preset region of the N-type initial substrate, and forming the second portion of the P-type emitter in a region of the P-type emitter excluding the preset region.

In an example, depositing the trivalent doping source on the top surface of the N-type initial substrate includes forming a first thin film layer, where the first thin film layer includes the trivalent doping source, and further includes at least one of boron element, oxygen element, silicon element, chlorine element, nitrogen element or carbon element, a deposition time ranges from <NUM> to <NUM>, and a temperature ranges from <NUM> to <NUM>; and performing the high temperature treatment on the N-type initial substrate includes introducing, for a duration ranged from <NUM> to <NUM> and under a temperature ranged from <NUM> to <NUM>, oxygen of a first flow rate to form a second thin film layer, a thickness of the second thin film layer is smaller than a thickness of the first thin film layer.

In an example, the first flow rate ranges from 200sccm to 80000sccm.

In an example, the process of external energy source treatment includes any one of laser doping process, plasma irradiation process or directional ion implantation process.

In an example, the production method further includes forming a first metal electrode, where the first metal electrode is electrically connected to the first portion of the P-type emitter.

In an example, a width of the first metal electrode is less than or equal to a width of the first portion of the P-type emitter.

Some embodiments of the present disclosure provide a photovoltaic module, including: a cell string formed by connecting a plurality of solar cells as described in any one of the above embodiments; an encapsulation layer used for covering a surface of the cell string; and a cover plate used for covering a surface of the encapsulation layer facing away from the cell string.

One or more embodiments are exemplarily illustrated in reference to corresponding accompanying drawing(s), and these exemplary illustrations do not constitute limitations on the embodiments. Unless otherwise stated, the accompanying drawings do not constitute scale limitations.

It can be known from the background art that the existing solar cells have a poor photoelectric conversion performance.

By analysis, it is found that one of the reasons for the poor photoelectric conversion performance of the existing solar cells is that the emitter is usually electrically connected to a metal electrode, so that the metal electrode can collect carriers in the emitter. In order to reduce the contact resistance between the metal electrode and the emitter, the sheet resistance of the emitter should be reduced. At present, in order to reduce the sheet resistance of the emitter, the doping concentration of the emitter is usually increased. However, when the doping concentration of the emitter increases, the doping element in the emitter becomes too much, so that the doping element in the emitter becomes a strong recombination center, causing the increase of Auger recombination. Thus, the passivation performance of the emitter deteriorates, which in turn makes the photoelectric conversion performance of the solar cell to be poor.

Embodiments of the present disclosure provide a solar cell, provided with a P-type emitter located on a first surface of a N-type substrate, a top surface of a first portion of the P-type emitter includes a first pyramid structure, and at least a part of at least one inclined surface of the first pyramid structure is concave or convex relative to a center of the first pyramid structure. In other words, a crystal structure of the surface of the first portion of the P-type emitter is an irregular tetrahedral structure, which causes the first portion of the P-type emitter to have a deep energy level in interior, thereby reducing the sheet resistance of the first portion of the P-type emitter. Thus, the resistance of the first portion of the P-type emitter can be reduced without greatly increasing the doping concentration of the first portion of the P-type emitter. In this way, not only a good passivation performance of the first portion of the P-type emitter can be maintained, but also the ohmic contact can be improved, thereby improving the photoelectric conversion performance of the solar cell. Moreover, the second portion of the P-type emitter has a shallower junction depth, and inclined surfaces of the second pyramid structure of the top surface of the second portion are planes, that is, the second portion of the P-type emitter is a regular tetrahedral structure. Thus, no dislocation is formed in the second portion of the P-type emitter, thereby making the second portion of the P-type emitter maintain a high sheet resistance, and maintaining a good passivation performance of the second portion. In this way, the overall photoelectric conversion efficiency of the solar cell can be improved.

Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Those skilled in the art should understand that, in the embodiments of the present disclosure, many technical details are provided for the reader to better understand the present disclosure. However, even without these technical details and various modifications and variants based on the following embodiments, the technical solutions claimed in the present disclosure can be realized.

<FIG> is a structural schematic diagram of a solar cell according to an embodiment of the present disclosure. <FIG> is a partial enlarged view of the part marked with the dotted frame in <FIG>.

Referring to <FIG>, the solar cell includes: a N-type substrate <NUM>; a P-type emitter <NUM> provided on a first surface of the N-type substrate <NUM>, the P-type emitter <NUM> includes a first portion <NUM> and a second portion <NUM>, a top surface of the first portion <NUM> includes a first pyramid structure <NUM>, and at least a part of at least one inclined surface of the first pyramid structure <NUM> is concave or convex relative to a center of the first pyramid structure <NUM>, a top surface of the second portion <NUM> includes a second pyramid structure <NUM>, and inclined surfaces of the second pyramid structure <NUM> are planes, and in a direction perpendicular to the first surface of the N-type substrate <NUM>, a junction depth of the first portion <NUM> is greater than a junction depth of the second portion <NUM>; and a tunnel layer <NUM> and a doped conductive layer <NUM>, the tunnel layer and the doped conductive layer are located on a second surface of the N-type substrate <NUM> and are arranged in sequence in a direction away from the N-type substrate <NUM>.

The N-type substrate <NUM> is used to receive incident light and generate photo-generated carriers. In some embodiments, the N-type substrate <NUM> may be a N-type silicon substrate <NUM>, and the material of the N-type silicon substrate may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or microcrystalline silicon. The N-type substrate <NUM> is a N-type semiconductor substrate <NUM>, that is, the N-type substrate <NUM> is doped with N-type dopant ions, and the N-type dopant ions may be any one of phosphorus ions, arsenic ions, or antimony ions.

In some embodiments, the solar cell is a tunnel oxide passivated contact (TOPCON) cell. The first surface and the second surface of the N-type substrate <NUM> are arranged opposite to each other, and both the first surface and the second surface of the N-type substrate <NUM> can be used to receive incident light or reflected light. In some embodiments, the first surface may be the back surface of the N-type substrate <NUM>, and the second surface may be the front surface of the N-type substrate <NUM>. In some other embodiments, the first surface may be the front surface of the N-type substrate <NUM>, and the second surface may be the back surface of the N-type substrate <NUM>.

In some embodiments, the second surface of the N-type substrate <NUM> may be designed as a pyramid textured surface, so that the reflectivity of the second surface of the N-type substrate <NUM> to incident light is low, therefore the absorption and utilization rate of light is high. The first surface of the N-type substrate <NUM> may be designed as a non-pyramid textured surface, such as a stacked step form, so that the first thin film layer <NUM> located on the first surface of the N-type substrate <NUM> has high density and uniformity, therefore the first thin film layer <NUM> has a good passivation effect on the first surface of the N-type substrate <NUM>. In some embodiments, the first surface may be the back surface of the N-type substrate <NUM>, and the second surface may be the front surface of the N-type substrate <NUM>. In some other embodiments, the first surface may be the front surface of the N-type substrate <NUM>, and the second surface may be the back surface of the N-type substrate <NUM>.

Referring to <FIG>, the first pyramid structure <NUM> includes a bottom surface and three inclined surfaces connected to the bottom surface, and the three inclined surfaces connect to each other to form a tetrahedral structure. At least a part of at least one inclined surface of the first pyramid structure <NUM> is concave or convex relative to the center of the first pyramid structure <NUM>, that is, at least one inclined surface of the first pyramid structure <NUM> has irregular deformation. For example, one of the inclined surfaces of the pyramid structure <NUM> may be only concave relative to the center of the first pyramid structure <NUM>, or only convex relative to the center of the first pyramid structure <NUM>, or a part of the inclined surface is concave relative to the center of the first pyramid structure <NUM> and another part is convex relative to the center of the first pyramid structure <NUM>. In some embodiments, in the first pyramid structure <NUM>, only one inclined surface has irregular deformation; in some other embodiments, there may be two inclined surfaces having irregular deformation; in still some other embodiments, all of the three inclined surfaces have irregular deformation. In addition, in yet some other embodiments, at least a part of the bottom surface of the first pyramid structure <NUM> is concave or convex relative to the center of the first pyramid structure <NUM>, that is, the bottom surface of the first pyramid structure <NUM> also has irregular deformation.

It should be understood that the first pyramid structure <NUM> and the second pyramid structure <NUM> here are different from the textured structure, and the first pyramid structure <NUM> and the second pyramid structure <NUM> in the embodiments of the present application refer to the crystal structure morphologies of the P-type emitter <NUM>. By changing the morphology of the crystal structure of the P-type emitter <NUM>, the performance of the first portion <NUM> of the P-type emitter <NUM> is changed.

As an example, at least one inclined surface in the first pyramid structure <NUM> is designed to have irregular deformation, so that the crystal structure of the first pyramid structure <NUM> becomes from a regular tetrahedral structure to an irregular tetrahedral structure, thereby making the first portion <NUM> of the P-type emitter <NUM> have a deep energy level in interior, and reducing the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>. In this way, the resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced without greatly increasing the doping concentration of the first portion <NUM> of the P-type emitter <NUM>. It should be understood that the regular tetrahedral structure here refers to that the inclined surfaces and the bottom surface of the tetrahedral structure have no irregularly deformation, for example, the inclined surfaces and the bottom surface of the tetrahedral structure may be planes.

Continuing to refer to <FIG>, in some embodiments, the crystal structure of the first portion <NUM> of the P-type emitter <NUM> has dislocations. In some embodiments, the dislocations are formed by a series of dangling bonds, and thus, when there are dislocations in the crystal structure of the first portion <NUM> of the P-type emitter <NUM>, dangling bonds are correspondingly generated. Dislocations and dangling bonds can form deep energy levels in interior of the first portion <NUM> of the P-type emitter <NUM>, and the formed deep energy levels reduce the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>. That is to say, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced without greatly increasing the doping concentration of the first portion <NUM> of the P-type emitter <NUM>, so that both a low sheet resistance of the first portion <NUM> of the P-type emitter <NUM> and a reduced doping concentration of the first portion <NUM> of the P-type emitter <NUM> can be obtained. In this way, not only the passivation performance of the first portion <NUM> of the P-type emitter <NUM> can be good, but also the ohmic contact of P-type emitter <NUM> can be improved.

It should be understood that the larger the height and the one-dimensional size of the bottom of the first pyramid structure <NUM> in the first portion <NUM> of the P-type emitter <NUM> are, the larger the overall size of the first pyramid structure <NUM> is, so that in a unit area, the number of the first pyramid structures <NUM> in the first portion <NUM> of the P-type emitter <NUM> is smaller. Since the dislocations in the first portion <NUM> of the P-type emitter <NUM> are formed by the first pyramid structures <NUM>, the smaller the number of the first pyramid structures <NUM> in the first portion <NUM> of the P-type emitter <NUM> in a unit area, the less dislocations are formed, that is, the lower the dislocation density is. Correspondingly, the smaller the size of the first pyramid structure <NUM> is, the greater the number of the first pyramid structures <NUM> in the first portion <NUM> of the P-type emitter <NUM> per unit area, and the greater the dislocation density. Based on this, in some embodiments, the height of the first pyramid structure <NUM> is set to be <NUM>-<NUM>, and the one-dimensional size of the bottom of the first pyramid structure <NUM> is set to be <NUM>-<NUM>. Within this range, on one hand, the dislocation density in the first portion <NUM> of the P-type emitter <NUM> can be made higher, so that the deep energy level formed based on dislocations can be higher, thereby leading to a lower sheet resistance of the first portion <NUM> of the P-type emitter <NUM>, and improving ohmic contact. On the other hand, within this range, excessive dislocation density in the first part <NUM> of the P-type emitter <NUM> can be avoided, which can prevent the problem of occurring an excessive deep energy level in the first portion <NUM> of the P-type emitter <NUM> due to excessive dislocation density, thereby forming a strong recombination center in the P-type emitter <NUM>. In this way, the passivation performance of the first portion <NUM> of the P-type emitter <NUM> can be improved.

Referring to <FIG>, in accordance with the present invention, at least part of the first pyramid structure <NUM> further includes a first substructure <NUM> located at a top of the first pyramid structure <NUM>, and the first substructure <NUM> is a sphere or a spheroid. The first substructure <NUM> is also one of the irregular deformations of the first pyramid structure <NUM>. The existence of the first substructure <NUM> makes the deformation degree of the first pyramid structure <NUM> greater, correspondingly, larger dislocations can be generated, so that the formed deep energy level is higher, and the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> can be further reduced.

Referring <FIG> and <FIG>, the inclined surfaces of the second pyramid structure <NUM> on the top surface of the second portion <NUM> are designed to be planes, that is, the second pyramid structure <NUM> is not irregularly deformed, so that the second pyramid structure <NUM> is a regular tetrahedron structure. Thus, dislocations and dangling bonds will not be caused in the second portion <NUM> of the P-type emitter <NUM>, and thus no deep energy levels will be formed in the second portion <NUM> of the P-type emitter <NUM>, thereby leading to a relatively high sheet resistance of the second portion <NUM> of the P-type emitter <NUM>, and maintaining a good passivation performance of the second portion <NUM> of the P-type emitter <NUM>. In this way, the open-circuit voltage and short-circuit current of the solar cell can be relatively high, and photoelectric conversion performance of the solar cell can be improved. In some examples, it may be designed that the top surface of the second portion <NUM> of the P-type emitter <NUM> includes the second pyramid structure <NUM>, and at least a part of at least one inclined surface of the second pyramid structure <NUM> is concave or convex relative to a center of the second pyramid structure <NUM>. That is to say, the top surface of the entire P-type emitter <NUM> has an irregular tetrahedral structure, so that the entire P-type emitter <NUM> has dislocations and dangling bonds, thereby reducing the sheet resistance of the entire P-type emitter <NUM>.

In some embodiments, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is lower than the sheet resistance of the second portion <NUM> of the P-type emitter <NUM>. That is to say, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is relatively low, so that a transport rate of carriers in the first portion <NUM> of the P-type emitter <NUM> can be increased, which is conducive to the transport of carriers from the first portion <NUM> of the P-type emitter <NUM> to the metal electrode when an electrical connection is formed between the first portion <NUM> of the P-type emitter <NUM> and the metal electrode, thereby improving a collection rate of carriers by the metal electrode, and improving the photovoltaic performance of the solar cell. By setting the sheet resistance of the second portion <NUM> of the P-type emitter <NUM> to be low, a good passivation performance of the second portion <NUM> of the P-type emitter <NUM> can be maintained, the recombination of carriers can be suppressed, and the number of carriers can be increased, thereby increasing the open-circuit voltage and short-circuit current of the solar cell. By setting the sheet resistance of the first portion <NUM> to be lower than that of the second portion <NUM>, the ohmic contact can be improved while maintaining a good passivation effect of the P-type emitter <NUM>, thereby improving the overall photoelectric conversion performance of the solar cell.

As an example, in some embodiments, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> may be 20ohm/sq~300ohm/sq, for example may be 20ohm/sq~50ohm/sq, 50ohm/sq~100ohm/sq, 100ohm/sq~150ohm/sq, 150ohm/sq~200ohm/sq, 200ohm/sq~250ohm/sq or 250ohm/sq~300ohm/sq, the sheet resistance of the second portion <NUM> of the P-type emitter <NUM> may be 100ohm/sq~1000ohm/sq, for example may be 100ohm/sq~200ohm/sq, 200ohm/sq~300ohm/sq, 300ohm/sq~500ohm/sq, 500ohm/sq~700ohm/sq, 700ohm/sq~800ohm/sq or 800ohm/sq~1000ohm/sq. The sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is designed to be in the range of 20ohm/sq~300ohm/sq, so that the sheet resistance of the first portion <NUM> is much lower than that of the second portion <NUM>, thus an improved ohmic contact of the first portion <NUM> of the P-type emitter <NUM> can be obtained, which can reduce the contact resistance between the first portion <NUM> of the P-type emitter <NUM> and the metal electrode when the metal electrode is arranged to be in an electrical contact with the first portion <NUM> of the P-type emitter <NUM>, thereby improving the transport efficiency of carriers in the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM>. On the other hand, within this range, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is not too low, so that the first portion <NUM> of the P-type emitter <NUM> can be prevented from becoming a strong recombination center. In addition, by setting the resistance of the second portion <NUM> of the P-type emitter <NUM> to 100ohm/sq~1000ohm/sq, the recombination of carriers in the second portion <NUM> of the P-type emitter <NUM> can be suppressed, thereby improving the passivation effect of the emitter. In this way, the open-circuit voltage, the short-circuit current and the photoelectric conversion efficiency of the solar cell can be improved.

The junction depth of the first portion <NUM> is greater than that of the second portion <NUM>, that is, the junction depth of the first portion <NUM> of the P-type emitter <NUM> is deeper, and the junction depth of the second portion <NUM> of the P-type emitter <NUM> is shallower. That is to say, the thickness of the first portion <NUM> is relatively large, on one hand, more doping elements, such as boron, can exist in the first portion <NUM> of the P-type emitter <NUM>, so that the doping concentration of the first portion <NUM> the P-type emitter <NUM> is higher, thereby further reducing the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>, which is conducive to the improvement of the ohmic contact. On the other hand, since the junction depth of the first portion <NUM> of the P-type emitter <NUM> is deep, an electrical connection can be provided between the metal electrode and the first portion <NUM> of the P-type emitter <NUM>, so that the problem that the paste for forming the metal electrode penetrates the P-type emitter <NUM> and directly contacts with the N-type initial substrate during the sintering of the paste can be prevented. In addition, the junction depth of the second portion <NUM> is designed to be shallower, that is, the thickness of the second portion <NUM> of the P-type emitter <NUM> is smaller, so that the number of doping elements of the second portion <NUM> is smaller than that of the first portion <NUM>, that is, the doping concentration of the second portion <NUM> of the P-type emitter <NUM> is lower. Therefore, compared with the first portion <NUM> of the P-type emitter <NUM>, the second portion <NUM> of the P-type emitter <NUM> has a better passivation effect, which is conducive to reduction of the recombination of carriers and improvement of the open-circuit voltage and short-circuit current of the solar cell.

In some embodiments, a ratio of the junction depth of the first portion <NUM> to the junction depth of the second portion <NUM> is not less than <NUM>. Preferably, the ratio of the junction depth of the first portion <NUM> to the junction depth of the second portion <NUM> ranges from <NUM> to <NUM>. For example, the ratio can be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The junction depth of the first portion <NUM> is much deeper than that of the second portion <NUM>, so that the junction depth of the first portion <NUM> of the P-type emitter <NUM> is deeper. In this way, when the metal electrode is electrically connected with the first portion <NUM> of the P-type emitter <NUM>, it can be ensured that the paste will not burn through the first portion <NUM> of the p-type emitter <NUM> during the sintering, so as to prevent the problem of damaging the p-n junction due to the contact between the metal electrode and the substrate <NUM>, thereby ensuring better photoelectric conversion performance of the solar cell.

Considering that it is necessary to keep the junction depth of the first portion <NUM> not too deep, so as to avoid too many doping elements in the first portion <NUM> of the P-type emitter <NUM> to form a strong recombination center, in some embodiments, the junction depth of the first portion <NUM> is set to be <NUM>~<NUM>, for example, the junction depth can be <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM> or <NUM>~<NUM>. The junction depth of the second portion <NUM> is set to be <NUM>~<NUM>, for example, the junction depth can be <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM>, <NUM>~<NUM> or <NUM>~<NUM>. Within this range, there are fewer doping elements in the second portion <NUM> of the P-type emitter <NUM>, so that a better passivation effect can be obtained.

In some embodiments, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is greater than or equal to the doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM>. As an example, in some embodiments, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is greater than the doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM>. The doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is relatively high, which is conducive to further reduction of the sheet resistance of the first portion <NUM>. The doping concentration at the top surface at the second portion <NUM> of the P-type emitter <NUM> is relatively low, so that the sheet resistance of the second portion <NUM> is relatively high, which is conducive to maintenance of a good passivation effect of the second portion <NUM> of the P-type emitter <NUM>.

In some other embodiments, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is equal to the doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM>, that is, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is relatively low. The crystal structure of the surface of the first portion <NUM> of the P-type emitter <NUM> is an irregular tetrahedral structure, which will cause dislocations in the first portion <NUM> of the P-type emitter <NUM>, so that the first portion <NUM> of the P-type emitter <NUM> has deep energy levels in interior. In this way, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced, thereby improving the ohmic contact. At the same time, since the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> is relatively low, the passivation effect of the first portion <NUM> of the P-type emitter <NUM> can be kept good. As an example, in some embodiments, the doping element in the P-type emitter <NUM> may be a P-type trivalent doping source, such as boron.

As an example, in some embodiments, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> may be 1E<NUM>-5E<NUM>atoms/cm<NUM>, for example, may be 1E<NUM>. 1E<NUM>atoms/cm<NUM>, 1E<NUM>-1E<NUM>atoms/cm<NUM>, 1E<NUM>-1E<NUM>atoms/cm<NUM>, 1E<NUM>-IE<NUM>atoms/cm<NUM> or 1E<NUM>-5E<NUM>atoms/cm<NUM>. Within this range, on one hand, the doping concentration of the formed first portion <NUM> of the P-type emitter <NUM> is relatively high, so that the first portion <NUM> of the P-type emitter <NUM> has a relatively low sheet resistance, which can increase the transport efficiency of carriers. On the other hand, within this range, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> will not be too high, that is, the content of the doping element in the first portion <NUM> of the P-type emitter <NUM> It will not be too much, so that the problem that many doping elements become strong recombination centers due to excessive doping elements in the first portion <NUM> of the P-type emitter <NUM>, leading to poor passivation capability of the first portion <NUM> of the P-type emitter <NUM> can be avoided.

In some embodiments, concentration of the top surface of the second portion <NUM> of the P-type emitter <NUM> may be 1E<NUM>-1E<NUM>atoms/cm<NUM>, for example, may be 1E<NUM>-1E<NUM>atoms/cm<NUM>, 1E<NUM>-1E<NUM>atoms/cm<NUM>, 1E<NUM>-1E<NUM>atoms/cm<NUM>, 1E<NUM>-1E<NUM>atoms/cm<NUM> or 1E<NUM>-1E<NUM>atoms/cm<NUM>. The doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM> can be set to be 1E<NUM>-9E<NUM> atoms/cm<NUM>, so that the doping elements in the second portion <NUM> of the P-type emitter <NUM> are relatively few. In this way, a good passivation performance of the second portion <NUM> of the P-type emitter <NUM> can be maintained, and the open-circuit voltage and short-circuit current of the formed solar cell can be effectively improved.

In some embodiments, in a direction from the top surface of the P-type emitter <NUM> to the bottom surface of the P-type emitter <NUM>, the doping concentration in the interior of the first portion <NUM> of the P-type emitter <NUM> gradually decreases, and the doping concentration in the interior of the second portion <NUM> of the P-type emitter <NUM> gradually decreases. That is to say, each of the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM> has a descending doping concentration gradient, which is conducive to the transport of carriers in the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM> from the area with a relatively high concentration to the area with a relatively low concentration, until to the substrate <NUM>. In this way, the transport speed of carriers can be increased and the open-circuit voltage of the solar cell can be improved.

As an example, in some embodiments, the difference between the doping concentration at the top surface of the first portion <NUM> and the doping concentration at the bottom surface of the first portion <NUM> is 1E<NUM> atoms/cm<NUM> to 5E<NUM> atoms/cm<NUM>. Within this range, on one hand, the difference in doping concentration in the interior of the first portion <NUM> of the P-type emitter <NUM> is relatively high, thereby facilitating the transport of carriers. On the other hand, within this range, the overall doping concentration in the interior of the first portion <NUM> of the P-type emitter <NUM> is relatively high, so that the sheet resistance can be kept low.

In some embodiments, the difference between the doping concentration at the top surface of the second portion <NUM> and the doping concentration at the bottom surface of the second portion <NUM> is 1E<NUM> atoms/cm<NUM>-1E<NUM> atoms/cm<NUM>. Within this range, the doping concentration in the interior of the second portion <NUM> of the P-type emitter <NUM> will not be too low, so that the normal transport of carriers in the second portion <NUM> of the P-type emitter <NUM> can be ensured. In addition, within this range, the overall doping concentration of the second portion <NUM> of the P-type emitter <NUM> can be kept low, thus Auger recombination can be prevented from occurring in the second portion <NUM> of the P-type emitter <NUM>.

In some embodiments, the ratio of the width of the second portion <NUM> to the width of the first portion <NUM> is not less than <NUM>. As an example, the ratio of the width of the second portion <NUM> to the width of the first portion <NUM> may be <NUM> to <NUM>, for example, the ratio may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. The width of the second portion <NUM> is designed to be much larger than the width of the first portion <NUM>, that is to say, the second portion <NUM> of the P-type emitter <NUM> with relatively low sheet resistance accounts for a higher proportion, since the second portion <NUM> of the P-type emitter <NUM> has better passivation performance and can suppress the recombination of carriers, the overall passivation performance of the P-type emitter <NUM> is good. Furthermore, since the first portion <NUM> of the P-type emitter <NUM> only needs to be electrically connected to the metal electrode to improve the ohmic contact with the metal electrode, the width of the first portion <NUM> of the P-type emitter <NUM> can be set to be small, so as to improve the ohmic contact and maintain relatively good passivation performance of the emitter.

Referring to <FIG>, in some embodiments, the solar cell further includes: a first metal electrode <NUM>, the first metal electrode is provided on the first surface of the N-type substrate <NUM> and is electrically connected to the first portion <NUM> of the P-type emitter <NUM>. Since the carriers in the P-type emitter <NUM> will transport to the first metal electrode <NUM> electrically connected to the first portion <NUM> of the P-type emitter <NUM>, and the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is low, so that the contact resistance between the first portion <NUM> of the P-type emitter <NUM> and the first metal electrode <NUM> is low, thereby increasing the transport rate of carriers to the first metal electrode <NUM>. In addition, since the first portion <NUM> of the P-type emitter <NUM> has a relatively deep junction depth, it is difficult for the formed first metal electrode <NUM> to penetrate the first portion <NUM> of the P-type emitter <NUM> during the preparation of the first metal electrode <NUM>. In this way, the structure of the formed p-n junction will not be damaged, which is conducive to maintenance of the integrity of the solar cell, thereby maintaining the good photoelectric conversion performance of the solar cell.

Referring to <FIG>, in some embodiments, the P-type emitter <NUM> further includes a transition region <NUM> located between the first portion <NUM> and the second portion <NUM>, a doping concentration at a top surface of the transition region <NUM> is greater than or equal to the doping concentration at the top surface of the second portion <NUM>, and is less than or equal to the doping concentration at the top surface of the first portion <NUM>. As an example, in some embodiments, when the doping concentration at the top surface of the first portion <NUM> is greater than the doping concentration at the top surface of the second portion <NUM>, the doping concentration at the top surface of the transition region <NUM> is set to be greater than the doping concentration at the top surface of the second portion <NUM>, and is lower than the doping concentration at the top surface of the first portion <NUM>, that is, the doping concentration of the transition region <NUM> gradually decreases in a direction from the first portion <NUM> to the second portion <NUM>. In this way, more gradation space can be provided for the concentration of the doping element in the P-type emitter <NUM>, so that a sudden change of potential energy difference between the first portion <NUM> and the second portion <NUM> can be avoided, so as to reduce the probability of recombination of the carrier in the transition region <NUM>. Furthermore, the provision of the transition region <NUM> further leads to a gradient trend of the sheet resistance in the transition region <NUM>, thereby reducing the transport resistance of the transition region <NUM> to carriers, which is conducive to the transport of the carriers in the second portion <NUM> of the P-type emitter <NUM> to the first portion <NUM> of the P-type emitter <NUM>, and further to the first metal electrode <NUM>. In this way, the transport efficiency of the carriers can be improved, thereby improving the photoelectric conversion efficiency of the solar cell.

It should be understood that in some other embodiments, the doping concentration at the top surface of the transition region <NUM> may be equal to the doping concentration at the top surface of the first portion <NUM>, or be equal to the doping concentration at the top surface of the second portion <NUM>. In still some other embodiments, the doping concentration at the top surface of the transition region <NUM> may be equal to the doping concentration at the top surface of the first portion <NUM> and the doping concentration at the top surface of the second portion <NUM>.

Referring to <FIG>, in some embodiments, the solar cell further includes an anti-reflection layer <NUM> located on the top surface of the first portion <NUM> of the P-type emitter <NUM> and the top surface of the second portion <NUM> of the P-type emitter <NUM>, the anti-reflection layer is used for reducing reflection of incident light by the substrate. In some embodiments, the anti-reflection layer may be a silicon nitride layer including a silicon nitride material.

The tunnel layer <NUM> is used to achieve interface passivation of the second surface of the substrate. As an example, in some embodiments, the material of the tunnel layer <NUM> may be a dielectric material, such as silicon oxide.

The doped conductive layer <NUM> is used to form field passivation. In some embodiments, the material of the doped conductive layer <NUM> may be doped silicon. As an example, in some embodiments, the doped conductive layer <NUM> and the substrate include doping elements of the same conductivity type. The doped silicon may include one or more of N-type doped polysilicon, N-type doped microcrystalline silicon and N-type doped amorphous silicon.

In some embodiments, the solar cell further includes a first passivation layer <NUM> located on the surface of the doped conductive layer <NUM> away from the substrate. In some embodiments, the material of the first passivation layer <NUM> may be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride and silicon oxycarbonitride. As an example, in some embodiments, the first passivation layer <NUM> may be a single-layer structure. In some other embodiments, the first passivation layer <NUM> may be a multi-layer structure.

In some embodiments, the solar cell further includes a second metal electrode <NUM> penetrating the first passivation layer <NUM> to form an electrical connection with the doped conductive layer <NUM>.

In the solar cell as described in the above embodiments, at least one inclined surface in the first pyramid structure <NUM> is designed to have irregular deformation, so that the crystal structure of the first pyramid structure <NUM> becomes from a regular tetrahedral structure to an irregular tetrahedral structure, thereby making the first portion <NUM> of the P-type emitter <NUM> have a deep energy level in interior, and reducing the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>. In this way, the resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced without greatly increasing the doping concentration of the first portion <NUM> of the P-type emitter <NUM>. Furthermore, the inclined surfaces of the second pyramid structure <NUM> on the top surface of the second portion <NUM> are designed to be planes, that is, the second pyramid structure <NUM> is not irregularly deformed, so that the second pyramid structure <NUM> is a regular tetrahedron structure. Thus, dislocations and dangling bonds will not be caused in the second portion <NUM> of the P-type emitter <NUM>, and thus no deep energy levels will be formed in the second portion <NUM> of the P-type emitter <NUM>, thereby leading to a relatively high sheet resistance of the second portion <NUM> of the P-type emitter <NUM>, and maintaining a good passivation performance of the second portion <NUM> of the P-type emitter <NUM>. In this way, the open-circuit voltage and short-circuit current of the solar cell can be relatively high, and photoelectric conversion performance of the solar cell can be improved.

Embodiments of the present disclosure further provide a photovoltaic module, referring to <FIG>, the photovoltaic module includes: a cell string formed by connecting a plurality of solar cells <NUM> as provided in the above embodiments; an encapsulation layer <NUM> used for covering a surface of the cell string; and a cover plate <NUM> used for covering a surface of the encapsulation layer <NUM> facing away from the cell string. The solar cells <NUM> are electrically connected in a form of a single piece or multiple pieces to form a plurality of cell strings, and the plurality of cell strings are electrically connected in series and/or parallel.

As an example, in some embodiments, the plurality of cell strings may be electrically connected by conductive strips <NUM>. The encapsulation layer <NUM> covers the front and back surfaces of the solar cell <NUM>. As an example, the encapsulation layer <NUM> may be an organic encapsulation adhesive film, such as an adhesive film of ethylene-vinyl acetate copolymer (EVA), an adhesive film of polyethylene octene co-elastomer (POE) or an adhesive film of polyethylene terephthalate (PET) and the like. In some embodiments, the cover plate <NUM> may be a cover plate <NUM> with a light-transmitting function, such as a glass cover plate, a plastic cover plate, or the like. As an example, the surface of the cover plate <NUM> facing the encapsulation layer <NUM> may be a concave-convex surface, thereby increasing the utilization rate of incident light.

Another embodiment of the present disclosure further provides a production method for a solar cell, the solar cell as provided in the above embodiments can be obtained by implementing the method. The production method for a semiconductor structure provided by this embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings.

<FIG> are structural schematic diagrams corresponding to the operations of the production method for the solar cell provided by this embodiment of the present disclosure.

The N-type substrate is used to receive incident light and generate photo-generated carriers. In some embodiments, the N-type substrate may be a N-type silicon substrate <NUM>, and the material of the N-type silicon substrate may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or microcrystalline silicon. The N-type substrate is a N-type semiconductor substrate, that is, the N-type substrate is doped with N-type dopant ions, and the N-type dopant ions may be any one of phosphorus ions, arsenic ions, or antimony ions.

Referring to <FIG>, a P-type emitter <NUM> is formed on a first surface of the N-type substrate, the P-type emitter <NUM> includes a first portion <NUM> and a second portion <NUM>, a top surface of the first portion <NUM> includes a first pyramid structure <NUM> (referring to <FIG>), and at least a part of at least one inclined surface of the first pyramid structure <NUM> is concave or convex relative to a center of the first pyramid structure <NUM>, a top surface of the second portion <NUM> includes a second pyramid structure <NUM> (referring to <FIG>), and inclined surfaces of the second pyramid structure are planes, and in a direction perpendicular to the first surface of the N-type substrate <NUM>, a junction depth of the first portion <NUM> is greater than a junction depth of the second portion <NUM>.

In the formed first pyramid structure <NUM>, at least a part of at least one inclined surface is concave or convex relative to the center of the first pyramid structure <NUM>, that is, at least one inclined surface of the first pyramid structure <NUM> has irregular deformation, so that the crystal structure of the first pyramid structure <NUM> becomes from a regular tetrahedral structure to an irregular tetrahedral structure. The irregular tetrahedral structure leads to dislocations and dangling bonds in the emitter, thereby modifying the emitter. In particular, the generated dislocations and dangling bonds lead to a deep energy level in interior of the first portion <NUM> of the P-type emitter <NUM>, thereby reducing the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>. The first portion <NUM> of the P-type emitter <NUM> can have a relatively low sheet resistance by modifying the structure of the first portion <NUM> of the P-type emitter <NUM>. In this way, the resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced without greatly increasing the doping concentration of the first portion <NUM> of the P-type emitter <NUM>.

The inclined surfaces of the second pyramid structure <NUM> on the top surface of the second portion <NUM> are designed to be planes, that is, the second pyramid structure <NUM> is not irregularly deformed, so that the second pyramid structure <NUM> is a regular tetrahedron structure. Thus, dislocations and dangling bonds will not be caused in the second portion <NUM> of the P-type emitter <NUM>, and thus no deep energy levels will be formed in the second portion <NUM> of the P-type emitter <NUM>, thereby leading to a relatively high sheet resistance of the second portion <NUM> of the P-type emitter <NUM>, and maintaining a good passivation performance of the second portion <NUM> of the P-type emitter <NUM>. In this way, the open-circuit voltage and short-circuit current of the solar cell can be relatively high, and photoelectric conversion performance of the solar cell can be improved.

In some embodiments, a method for forming the P-type emitter <NUM> includes the following operations.

Referring to <FIG>, an N-type initial substrate <NUM> is provided, and the N-type initial substrate <NUM> is used as a basis for forming the N-type substrate <NUM> and the P-type emitter <NUM>. Therefore, the materials of the N-type initial substrate <NUM> and the N-type substrate <NUM> may be of the same.

In some embodiments, a first surface of the N-type initial substrate <NUM> may be designed as a pyramid textured surface, so that the reflectivity of the first surface of the N-type initial substrate <NUM> to incident light is low, and the absorption and utilization rate of light is high. In some embodiments, the N-type initial substrate <NUM> is a N-type initial semiconductor substrate, that is, the N-type initial substrate <NUM> is doped with N-type dopant ions, and the N-type dopant ions may be any one of phosphorus ions, arsenic ions, or antimony ions.

The method for forming the P-type emitter <NUM> further includes, referring to <FIG> and <FIG>, depositing a trivalent doping source on a top surface of the N-type initial substrate <NUM>, so as to subsequently diffuse the trivalent doping source into the N-type initial substrate <NUM> to form the P-type emitter <NUM>. In some embodiments, the trivalent doping source may be a boron source, and may for example be boron trichloride or boron tribromide.

Referring to <FIG>, in some embodiments, depositing the trivalent doping source on the top surface of the N-type initial substrate <NUM> includes forming a first thin film layer <NUM>, the first thin film layer <NUM> includes the trivalent dopant source and at least one of boron element, oxygen element, silicon element, chlorine element, nitrogen element or carbon element. A deposition time ranges from <NUM> to <NUM>, and a temperature ranges from <NUM> to <NUM>. As an example, in some embodiments, when the trivalent doping source is a boron source, the main components of the first thin film layer <NUM> may include silicon oxide and boron oxide, and the trivalent doping source may be stored in the first thin film layer <NUM> in a form of boron oxide. Since silicon oxide has high hardness, it can protect the N-type initial substrate <NUM> during the doping process. In addition, the first thin film layer <NUM> further includes a small amount of chlorine element, nitrogen element and carbon element, these elements provide the first thin film layer <NUM> with a higher refractive index than that of the existing borosilicate glass. In this way, during the subsequent treatment performed on a preset region of first thin film layer <NUM> by using a process of external energy source treatment, the first thin film layer <NUM> can absorb more external energy sources, such as laser, so that more laser can irradiate to the interior of the first thin film layer <NUM>. In this way, the loss of laser can be reduced, and the amount of the trivalent doping source diffused into the N-type initial substrate <NUM> can be increased.

In addition, since the thickness of the first thin film layer <NUM> is relatively small, when a relatively thin first thin film layer <NUM> includes relatively many trivalent doping sources, the trivalent doping sources aggregates in the first thin film layer <NUM>, thereby increasing the concentration of the trivalent doping source. In this way, when the trivalent doping source is subsequently diffused into the N-type initial substrate <NUM> by the doping process, the doping process is facilitated and it is easier to form the first portion of the P-type emitter with relatively high doping concentration, thereby reducing the sheet resistance of the first portion of the P-type emitter. In addition, since the thickness of the first thin film layer <NUM> is relatively small, the trivalent doping source that can be included in the first thin film layer <NUM> will not be too much, so that excessive trivalent doping source elements can prevented from being doped into the N-type initial substrate <NUM>. In this way, the problem that relatively many trivalent doping source elements become strong recombination centers due to too many trivalent doping source elements being contained in the N-type initial substrate <NUM>, which leads to poor passivation capability of the formed first portion <NUM> of the P-type emitter <NUM> can be prevented.

In some embodiments, a method for forming the first thin film layer <NUM> may include depositing a trivalent doping source on the first surface of the N-type initial substrate <NUM>, the trivalent doping source is a simple substance or compound containing a trivalent element. In some embodiments, when the trivalent doping source is a boron source, the simple substance or compound containing a trivalent element may be boron tribromide or boron trichloride. In some embodiments, boron trichloride can be deposited, as the trivalent doping source, on the first surface of the N-type initial substrate <NUM> by chemical vapor deposition or spin coating, and the concentration of the trivalent doping source can be 1E<NUM>-9E<NUM> atoms/cm<NUM>.

In some embodiments, a method of depositing the trivalent doping source may include: performing a boat feeding process on the N-type initial substrate <NUM>; then raising a temperature to a first preset temperature, the first preset temperature may be <NUM> to <NUM>; depositing a trivalent doping source on the first surface of the N-type initial substrate <NUM>; then raising the temperature to a second preset temperature, the second preset temperature is greater than the first preset temperature, for example, the second preset temperature may be <NUM> to <NUM>; and performing a junction pushing process in a nitrogen atmosphere, which can improve the density and uniformity of the formed first thin film layer <NUM>. In some embodiments, while depositing the trivalent doping source, a small amount of oxygen may be introduced, for example, <NUM> sccm to <NUM> sccm, which is conducive to the further formation of a first thin film layer <NUM> with relatively high density.

Referring to <FIG>, after depositing the trivalent dopant source, the preset region of the top surface of the N-type initial substrate <NUM> is treated using the process of external energy source treatment, and the trivalent dopant source treated by the process of external energy source treatment is diffused into an interior of the N-type initial substrate <NUM> to form the first portion <NUM> of the P-type emitter <NUM> in the preset region of the N-type initial substrate <NUM>, and a top surface of the first portion <NUM> of the P-type emitter <NUM> is exposed from the N-type initial substrate <NUM>. The process of external energy source treatment is performed on the preset region, so that the trivalent doping source in the preset region of the first thin film layer <NUM> is diffused into the interior of the N-type initial substrate <NUM>. At the same time, with the process of external energy source treatment, the crystal structure of the preset region of the N-type initial substrate <NUM> is deformed to form the first pyramid structure <NUM>. It is noted that the structure of the N-type initial substrate <NUM> is a regular tetrahedral structure before performing the process of external energy source treatment. After the process of external energy source treatment, at least part of the surfaces of the first pyramid structure <NUM> becomes concave or convex relative to the center of the first pyramid structure <NUM>, that is, the first pyramid structure <NUM> is transformed from the regular tetrahedral structure to an irregular tetrahedral structure. The first pyramid structure <NUM> causes dislocations and dangling bonds to appear in the preset region of the N-type initial substrate <NUM>. After the preset region of the N-type initial substrate <NUM> is doped with the trivalent doping source, the top surface of the formed first portion <NUM> of the P-type emitter <NUM> has the first pyramid structure <NUM>. In this way, the first portion <NUM> of the P-type emitter <NUM> can have a deep energy level, and the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced.

In some embodiments, the process of external energy source treatment includes any one of a laser doping process, plasma irradiation, or a directional ion implantation process. Taking the laser doping process as an example, the laser doping process is simple to operate, and is conducive to large-scale utilization, and efficiency of the laser doping is high, thus the trivalent doping source can be efficiently doped into the N-type initial substrate <NUM>. The first thin film layer <NUM> can absorb a certain amount of laser energy, which can protect the N-type initial substrate <NUM> and reduce the damage to the N-type initial substrate <NUM> caused by laser doping, so that the formed first portion <NUM> of the P-type emitter <NUM> has high integrity, thereby obtaining good passivation performance of the first portion <NUM> of the P-type emitter <NUM>. In addition, since the concentration of the trivalent doping source in the first thin film layer <NUM> is high, when performing laser doping, the trivalent doping source is more easily doped into the N-type initial substrate <NUM>, so that the junction depth of the formed first portion <NUM> of the P-type emitter <NUM> is deep. That is to say, the deep junction depth of the formed first portion <NUM> of the P-type emitter <NUM> can be realized using little laser energy, thus the laser energy can be reduced when the junction depth of the first portion <NUM> of the P-type emitter <NUM> can be ensured to meet the expectations, thereby further reducing the damage of the laser to the N-type initial substrate <NUM>.

Moreover, after irradiate the preset region of the N-type initial substrate <NUM> using the laser process, it is easier to transform the crystal structure of the first portion <NUM> of the P-type emitter <NUM> into an irregular tetrahedral structure, so that the density of the dislocations formed in the interior of the first portion <NUM> of the P-type emitter <NUM> is relatively high, which is conducive to further reduction of the sheet resistance.

In some embodiments, after forming the first portion <NUM> of the P-type emitter <NUM>, the method further includes: performing a cleaning operation on the first surface of the N-type initial substrate <NUM> to remove the first thin film layer <NUM>. In this way, the remaining trivalent doping sources in the first thin film layer <NUM> and the adsorbed impurities on the surface of the N-type initial substrate <NUM> can be removed, which is conducive to prevention of leakage. Furthermore, the first thin film layer <NUM> contains a large number of trivalent doping sources, and these trivalent doping sources will be converted into non-activated trivalent doping sources, such as non-activated boron, in the subsequent high temperature process for forming the second thin film layer. The existence of the non-activated trivalent doping sources will increase the recombination of carriers on the surface of the N-type initial substrate <NUM>, thereby affecting the photoelectric conversion efficiency of the solar cell. Therefore, removing the first thin film layer <NUM> before the operation of forming the second thin film layer can also reduce the content of the non-activated trivalent doping sources on the surface of the N-type initial substrate <NUM> after subsequently forming the second thin film layer, thereby reducing the recombination of carriers on the surface of the N-type initial substrate <NUM> and improving the photoelectric conversion efficiency of the solar cell. As an example, the cleaning operation may include cleaning the surface of the N-type initial substrate <NUM> with alkali solution or acid solution, where the alkali solution may be at least one of KOH or H<NUM>O<NUM> aqueous solution, and the acid solution may be at least one of HF or HCl aqueous solution.

After forming the first portion <NUM> of the P-type emitter <NUM>, referring to <FIG>, a high temperature treatment is performed on the N-type initial substrate <NUM> to form the P-type emitter <NUM> in the N-type initial substrate <NUM>, and the top surface of the P-type emitter <NUM> is exposed from the N-type initial substrate <NUM>. As an example, the N-type substrate <NUM> is formed in a region of the N-type initial substrate <NUM> excluding the P-type emitter <NUM>, and the second portion <NUM> of the P-type emitter <NUM> is formed in a region of the P-type emitter <NUM> excluding the preset region. Since the process of external energy source treatment is only performed on the surface of the preset region of the N-type initial substrate <NUM>, the trivalent doping sources in the first thin film layer <NUM> corresponding to the preset region are diffused into the interior of the N-type initial substrate <NUM>. Thus, the junction depth of the formed first portion <NUM> of the P-type emitter <NUM> is greater than the junction depth of the second portion <NUM> of the P-type emitter <NUM>, and the metal electrode can be arranged to be in electrical connection with the first portion <NUM> of the P-type emitter <NUM>. In this way, the problem that the paste for forming the metal electrode penetrates the P-type emitter <NUM> and directly contacts with the N-type initial substrate <NUM> during the sintering process can be prevented. Moreover, the junction depth of the second portion <NUM> is designed to be shallow, that is, the thickness of the second portion <NUM> of the P-type emitter <NUM> is small, so that the number of doping elements of the second portion <NUM> is less than the number of doping elements of the first portion <NUM>, that is, the doping concentration of the second portion <NUM> of the P-type emitter <NUM> is lower. Therefore, compared with the first portion <NUM> of the P-type emitter <NUM>, the second portion <NUM> of the P-type emitter <NUM> has a better passivation effect, which is conducive to reduction of the recombination of carriers and to improvement of the open-circuit voltage and short-circuit current of the solar cell.

After performing the high temperature treatment on the N-type initial substrate <NUM>, part of the trivalent doping sources is doped into the N-type initial substrate <NUM>, so that part of the N-type initial substrate <NUM> is transformed into the second portion <NUM> of the P-type emitter <NUM>. That is to say, the portion of the N-type initial substrate <NUM> excluding the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM> corresponds to the N-type substrate <NUM>.

Referring to <FIG>, in some embodiments, in the operation of performing the high temperature treatment on the N-type initial substrate <NUM>, oxygen of a first flow rate is introduced for a duration ranged from <NUM> to <NUM> and under a temperature ranged from <NUM> to <NUM>, to form a second thin film layer <NUM>, a thickness of the second thin film layer <NUM> is smaller than a thickness of the first thin film layer <NUM>. The amount of the oxygen introduced in the process of forming the second thin film layer <NUM> is relatively large, so that the oxygen can react with more trivalent doping sources, thus the thickness of the formed second thin film layer <NUM> is larger than the thickness of the first thin film layer <NUM>. In this way, on one hand, when the thinner first thin film layer <NUM> includes more trivalent doping sources, the trivalent doping sources aggregate in the first thin film layer <NUM>, thereby increasing the concentration of the trivalent doping sources, which is conducive to the laser doping, and because the first thin film layer <NUM> is relatively thin, it is easy for the laser to penetrate into the N-type initial substrate <NUM>. On the other hand, the second thin film layer <NUM> is thicker, which can ensure that the amount of trivalent doping sources absorbed by the second thin film layer <NUM> in a region excluding the preset region of the first surface of the N-type initial substrate <NUM> is relatively large. In this way, the doping concentration at the top surface of the first portion <NUM> of the P-type emitter <NUM> and the doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM> can be reduced, and the passivation performance can be improved.

In some embodiments, the first flow rate ranges from <NUM> sccm to <NUM>,<NUM> sccm. For example, the first flow rate may be 200sccm to 1000sccm, 1000sccm to 5000sccm, 5000sccm to 10000sccm, 10000sccm to 20000sccm, 20000sccm to 30000sccm, 30000sccm to 50000sccm, 50000sccm to 70000sccm, or 70000sccm to 80000sccm. Setting the first flow rate within this range can ensure a high first flow rate, so that the formed second thin film layer <NUM> is thicker, and the second thin film layer <NUM> can absorb more trivalent doping sources. In this way, the doping concentration at the top surface of the second portion <NUM> of the P-type emitter <NUM> can be relatively low, which is conducive to obtaining a high sheet resistance of the second portion <NUM> of the P-type emitter <NUM>, thus the passivation performance of the second portion <NUM> of the P-type emitter <NUM> can be improved.

Referring to <FIG>, in some embodiments, the method further includes: performing the cleaning operation on the N-type initial substrate <NUM> to remove the second thin film layer <NUM>; forming an anti-reflection layer <NUM> on the first surface of the N-type initial substrate <NUM>, the anti-reflection layer <NUM> is located on the top surface of the P-type emitter <NUM>, in some embodiments, the anti-reflection layer <NUM> may be a silicon nitride layer including silicon nitride material. In some embodiments, the anti-reflection layer <NUM> may be formed by a plasma enhanced chemical vapor deposition method (PECVD).

Referring to <FIG>, in some embodiments, the method further includes: forming a first metal electrode <NUM>, and the first metal electrode <NUM> is electrically connected to the first portion <NUM> of the P-type emitter <NUM>. The first metal electrode <NUM> is located on the first surface of the N-type initial substrate <NUM>. Since the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is low, the first metal electrode <NUM> is arranged to be electrically connected to the first portion <NUM> of the P-type emitter <NUM>. In this way, the contact resistance between the first metal electrode <NUM> and the first portion <NUM> of the P-type emitter <NUM> can be reduced, thereby facilitating the transport of carriers in the first metal electrode <NUM> penetrating the anti-reflection layer. The specific principles are as follows.

The incident light reaches the N-type initial substrate <NUM> through the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM>, and generates a plurality of electron-hole pairs in the N-type initial substrate <NUM>. The plurality of electron-hole pairs in the N-type initial substrate <NUM> are separated into electrons and holes, respectively, under the action of the photoelectric effect, the separated electrons transport to the N-type initial substrate <NUM>, and the separated holes transport to the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM>. The electrons transporting to the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM> are collected by the first metal electrode <NUM> in contact with the first portion <NUM> of the P-type emitter <NUM>, and transport in the first metal electrode <NUM> penetrating the anti-reflection layer. That is to say, the electrons in the first portion <NUM> and the second portion <NUM> are desired to transport to the first metal electrode <NUM> in contact with the first portion <NUM> of the P-type emitter <NUM>. Therefore, the transport of carrier can be greatly improved by the improvement of the contact resistance between the first metal electrode <NUM> and the first portion <NUM> of the P-type emitter <NUM>.

In some embodiments, a method for forming the first metal electrode <NUM> includes: printing conductive paste on a top surface of the anti-reflection layer <NUM> in the preset region, the conductive material in the conductive paste may be at least one of silver, aluminum, copper, tin, gold, lead or nickel; and sintering the conductive paste, for example, the sintering may be performed under a peak temperature of <NUM> to <NUM>, so as to penetrate the anti-reflection layer to form the first metal electrode <NUM>.

In some embodiments, a width of the first metal electrode <NUM> is less than or equal to the width of the first portion <NUM> of the P-type emitter <NUM>, so that the first metal electrode <NUM> can be surrounded by the first portion <NUM> of the P-type emitter <NUM>, and the side surfaces and the bottom surface of the first metal electrode <NUM> are in contact with the first portion <NUM> of the P-type emitter <NUM>. Compared with the case that a part of the side surfaces of the first metal electrode <NUM> is in contact with the second portion <NUM> of the P-type emitter <NUM> having higher sheet resistance, since the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> is lower, the contact resistance between the first metal electrode <NUM> and the first portion <NUM> of the P-type emitter <NUM> is lower, which is conducive to the further improvement of the transport of carriers in the first portion <NUM> of the P-type emitter <NUM> and the second portion <NUM> of the P-type emitter <NUM>.

Referring to <FIG>, a tunnel layer <NUM> and a doped conductive layer <NUM> are formed, the tunnel layer and the doped conductive layer are located on a second surface of the N-type substrate <NUM> and are arranged in sequence in a direction away from the N-type substrate <NUM>.

The tunnel layer <NUM> is used to realize the interface passivation of the second surface of the N-type substrate <NUM>. In some embodiments, the tunnel layer <NUM> may be formed using a deposition process, such as a chemical vapor deposition process. In some other embodiments, the tunnel layer <NUM> may be formed using an in-situ generation process. As an example, in some embodiments, the material of the tunnel layer <NUM> may be a dielectric material, such as silicon oxide.

The doped conductive layer <NUM> is used to form field passivation. In some embodiments, the material of the doped conductive layer <NUM> may be doped silicon. In some embodiments, the doped conductive layer <NUM> and the N-type substrate <NUM> include doping elements of the same conductivity type, the doped silicon may include one or more of N-type doped polysilicon, N-type doped microcrystalline silicon and N-type doped amorphous silicon. In some embodiments, the doped conductive layer <NUM> may be formed using a deposition process. As an example, intrinsic polysilicon may be deposited on the surface of the tunnel layer <NUM> away from the N-type substrate <NUM> to form a polysilicon layer, and phosphorus ions may be doped in manners of ion implantation and source diffusion to form an N-type doped polysilicon layer. The N-type doped polysilicon layer serves as the doped conductive layer <NUM>.

Referring to <FIG>, in some embodiments, the method further includes forming a first passivation layer <NUM> on a surface of the doped conductive layer <NUM> away from the N-type substrate <NUM>. In some embodiments, the material of the first passivation layer <NUM> may be one or more of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride and silicon oxycarbonitride. In some embodiments, the first passivation layer <NUM> may be a single-layer structure. In some other embodiments, the first passivation layer <NUM> may be a multi-layer structure. As an example, in some embodiments, the first passivation layer <NUM> may be formed using a PECVD method.

In some embodiments, the method further includes forming a second metal electrode <NUM> penetrating the first passivation layer <NUM> to form an electrical connection with the doped conductive layer <NUM>. As an example, the method for forming the second metal electrode <NUM> may be the same as the method for forming the first metal electrode <NUM>, and the material of the first metal electrode <NUM> may be the same as the material of the second metal electrode <NUM>.

In the production method for a solar cell as provided in the above embodiments, at least one inclined surface of the formed first pyramid structure <NUM> has irregular deformation, so that the crystal structure of the first pyramid structure <NUM> becomes from a regular tetrahedral structure to an irregular tetrahedral structure. The irregular tetrahedral structure leads to dislocations and dangling bonds in the emitter, thereby modifying the emitter. In particular, the generated dislocations and dangling bonds lead to a deep energy level in interior of the first portion <NUM> of the P-type emitter <NUM>, thereby reducing the sheet resistance of the first portion <NUM> of the P-type emitter <NUM>. The first portion <NUM> of the P-type emitter <NUM> can have a relatively low sheet resistance by modifying the structure of the first portion <NUM> of the P-type emitter <NUM>. In this way, the sheet resistance of the first portion <NUM> of the P-type emitter <NUM> can be reduced without greatly increasing the doping concentration of the first portion <NUM> of the P-type emitter <NUM>, which not only can improve the ohmic contact, but also is conducive to maintenance of a good passivation effect of the first portion <NUM> of the P-type emitter <NUM>, thus the overall photoelectric conversion performance of the formed solar cell can be improved.

Although the present disclosure is disclosed above with exemplary embodiments, they are not used to limit the claims. The scope of protection of the present disclosure shall be subject to the scope defined by the claims.

Claim 1:
A solar cell comprising:
a N-type substrate (<NUM>); and
a P-type emitter (<NUM>) provided on a first surface of the N-type substrate (<NUM>), wherein the P-type emitter (<NUM>) comprises a first portion (<NUM>) and a second portion (<NUM>), a top surface of the first portion (<NUM>) comprises a first pyramid structure (<NUM>), and at least a part of at least one inclined surface of the first pyramid structure (<NUM>) is concave or convex relative to a center of the first pyramid structure (<NUM>), wherein a top surface of the second portion (<NUM>) comprises a second pyramid structure (<NUM>), and inclined surfaces of the second pyramid structure (<NUM>) are planes, and wherein in a direction perpendicular to the first surface of the N-type substrate (<NUM>), a junction depth of the first portion (<NUM>) is greater than a junction depth of the second portion (<NUM>); characterised in that the solar cell further comprises
a tunnel layer (<NUM>) and a doped conductive layer (<NUM>), wherein the tunnel layer (<NUM>) and the doped conductive layer (<NUM>) are located on a second surface of the N-type substrate (<NUM>) and are arranged in sequence in a direction away from the N-type substrate (<NUM>);
wherein at least part of the first pyramid structure comprises a first substructure located at a top of the first pyramid structure, wherein the first substructure is a sphere or a spheroid.