Patent Description:
A solar cell can be used widely due to a good photoelectric conversion capacity. The solar cell generally has a passivation structure on a surface of the solar cell in order to inhibit a recombination of carriers on the surface. The passivation structure on the surface of the solar cell has a relatively high refractive index and relatively good passivation effect, so that as much incident light as possible can be absorbed by the solar cell, and a carrier concentration of the solar cell can be increased.

However, the existing solar cell with the passivation layer still has relatively high reflectivity for the incident light, so that the existing solar cell has a relatively low open circuit voltage, a low short-circuit current and a low filling factor, resulting in a relatively low photoelectric conversion rate of the solar cell. <CIT> relates to a TBC solar cell structure and preparation method thereof, which includes a front surface of the silicon wafer substrate is sequentially provided with a front surface field and a front surface passivation anti-reflection layer, the backside of the silicon wafer substrate is sequentially provided with a tunnel oxide layer and a backside passivation layer, the tunnel oxide layer and the backside N+ doped polysilicon/amorphous silicon, intrinsic polysilicon/amorphous silicon and P+ doped polysilicon/amorphous silicon are arranged between the passivation layers, and the backside of the backside passivation layer is respectively provided with a positive electrode sub-gate line and negative electrode sub-gate line.

The invention is set out in the appended set of claims and provides a solar cell, including: a substrate having a front surface and a back surface opposite to the front surface; a first passivation layer, a second passivation layer and a third passivation layer sequentially formed on the front surface of the substrate and in a direction away from the substrate; the first passivation layer includes a dielectric material; the second passivation layer includes a first SiuNv material, and a value of v/u is in a range of <NUM> to <NUM>; and the third passivation layer includes a SirOs material, and a value of s/r is in a range of <NUM> to <NUM>; and a tunneling oxide layer and a doped conductive layer sequentially formed on the back surface of the substrate and in a direction away from the back surface, the doped conductive layer and the substrate are doped to have a same conductivity type.

In some examples, a refractive index of the third passivation layer is smaller than a refractive index of the second passivation layer.

In some examples, the third passivation layer has a refractive index in a range of <NUM> to <NUM>, and the second passivation layer has a refractive index in a range of <NUM> to <NUM>.

In some examples not part of the invention, the third passivation layer includes a first silicon oxide sub-layer and a second silicon oxide sub-layer stacked in the direction away from the substrate, the value of s/r of the SirOs material of the first silicon oxide sub-layer is in a range of <NUM> to <NUM>; the value of s/r of the SirOs material of the second silicon oxide sub-layer is in a range of <NUM> to <NUM>, and a refractive index of the first silicon oxide sub-layer is greater than a refractive index of the second silicon oxide sub-layer.

In some examples, the dielectric material includes at least one of aluminum oxide, titanium oxide, gallium oxide and hafnium oxide.

In some examples, the dielectric material is an AlxOy material, and a value of y/x is in a range of <NUM> to <NUM>.

In some examples, the third passivation layer has a thickness in a range of <NUM> to <NUM> in a direction perpendicular to the front surface.

In some examples, the second passivation layer has a thickness in a range of <NUM> to <NUM> in a direction perpendicular to the front surface.

In some examples, the first passivation layer has a thickness in a range of <NUM> to <NUM> in a direction perpendicular to the front surface.

In some examples, the first passivation layer has a refractive index in a range of <NUM> to <NUM>.

In some examples, the solar cell further includes: a fourth passivation layer formed on a side of the doped conductive layer facing away from the substrate; the fourth passivation layer includes a second SimNn material, and a value of n/m is in a range of <NUM> to <NUM>.

In some examples, the fourth passivation layer has a refractive index in a range of <NUM> to <NUM>, and the fourth passivation layer has a thickness in a range of <NUM> to <NUM> in a direction perpendicular to the back surface.

In some examples, the substrate is an N-type semiconductor substrate; the doped conductive layer 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.

As a second aspect, some embodiments of the present disclosure further provide a solar cell module, including: at least one cell string formed by connecting a plurality of the above solar cells; a packaging layer configured to cover a surface of the at least one cell string; and a cover plate configured to cover a surface of the packaging layer away from the at least one cell string.

The invention further provides a method for preparing a solar cell according to claim <NUM>, including: providing a substrate having a front surface and a back surface opposite to the front surface; forming a tunneling oxide layer and a doped conductive layer sequentially on the back surface of the substrate in a direction away from the back surface, the doped conductive layer and the substrate are doped to have a same conductivity type; and forming a first passivation layer, a second passivation layer and a third passivation layer sequentially on the front surface of the substrate and in a direction away from the substrate; the first passivation layer includes a dielectric material; the second passivation layer includes a first SiuNv material, and a value of v/u is in a range of <NUM> to <NUM>; and the third passivation layer includes a SirOs material, and a value of s/r is in a range of <NUM> to <NUM>.

In some examples, the forming the third passivation layer is performed by a plasma-enhanced chemical vapor deposition process, and includes: introducing silane and nitrous oxide into a reaction chamber; and ionizing the silane and the nitrous oxide; a pulse power per unit area is in a range of 140mW/cm<NUM> to 170mW/cm<NUM>, a pressure of the reaction chamber is in a range of <NUM> mTorr to <NUM> mTorr, a flow ratio of the silane to the nitrous oxide is in a range of <NUM>:<NUM> to <NUM>:<NUM>; and a reaction time is in a range of <NUM> to <NUM>.

In some examples, the forming the second passivation layer is performed by a plasma-enhanced chemical vapor deposition process, and includes: introducing silane and ammonia gas into a reaction chamber; and ionizing the silane and the ammonia gas; a pulse power per unit area is in a range of 140mW/cm<NUM> to 180mW/cm<NUM>; a pressure of the reaction chamber is in a range of <NUM> mTorr to <NUM> mTorr; a flow ratio of the silane to the ammonia gas is in a range of <NUM>:<NUM> to <NUM>: <NUM>; and a reaction time is in a range of <NUM> to <NUM>.

In some examples, the forming the first passivation layer is performed by an atomic layer deposition process, and includes: introducing trimethyl aluminum and water into a reaction chamber, a ratio of the trimethyl aluminum to the water is in a range of <NUM>:<NUM> to <NUM>:<NUM>, and a temperature is in a range of <NUM> to <NUM>.

In some examples, after the first passivation layer is formed, the method further includes: performing an annealing process on the first passivation layer in a nitrogen atmosphere, an annealing temperature is in a range of <NUM> to <NUM>, and an annealing duration is in a range of <NUM> to <NUM>.

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

It can be known from the background technology that there exists a problem that a reflectivity of a solar cell to incident light is relatively high.

It is found that one reason for the relatively high reflectivity of the solar cell to the incident light may be that: a silicon nitride material is generally used for a passivation layer on a surface of the solar cell; the silicon nitride material has a good passivation effect, but a relatively high refractive index, which results in certain light absorption loss. That is, a silicon nitride passivation layer may have a relatively low anti-reflectivity, resulting in a relatively weak light absorption capacity of the solar cell to the incident light.

Some embodiments of the present disclosure provide a solar cell, including: a first passivation layer, a second passivation layer and a third passivation layer sequentially formed on a front surface of a substrate and in a direction away from the substrate. The first passivation layer includes a dielectric material. The second passivation layer includes a first SiuNv material, and a value of v/u is <NUM>≤v/u≤<NUM>. The second passivation layer has a relatively high refractive index by adjusting an atomic ratio in the first SiuNv material, so that the second passivation layer has relatively strong light absorption capacity for long-wave light (e.g., an infrared light or near infrared light). The third passivation layer includes a SirOs material, and a value of s/r is <NUM>≤s/r≤<NUM>. The SirOs material has relatively strong light absorption capacity for short-wave light by adjusting an atomic ratio in the SirOs material. In this way, the third passivation layer having relatively strong light absorption capacity for short-wave light, together with the second passivation layer having relatively strong light absorption capacity for short-wave light, allows the whole solar cell have relatively strong light absorption capacity for incident light, and thus the solar cell surface can have a relatively large anti-reflectivity. Further, the first SiuNv material and the SirOs material have a good passivation effect, thereby improving an open-circuit voltage, a short-circuit current and a filling factor of the solar cell and increasing a photoelectric conversion rate of the solar cell.

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.

<FIG> shows a schematic structural diagram of a 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 and a back surface opposite to the front surface; a first passivation layer <NUM>, a second passivation layer <NUM> and a third passivation layer <NUM> sequentially formed on the front surface of the substrate <NUM> and in a direction away from the substrate <NUM>; and a tunneling oxide layer <NUM> and a doped conductive layer <NUM> sequentially formed on the back surface of the substrate <NUM> and in a direction away from the back surface. The first passivation layer <NUM> includes a dielectric material. The second passivation layer <NUM> includes a first SiuNv material, and a value of v/u is <NUM>≤v/u≤<NUM>. The third passivation layer <NUM> includes a SirOs material, and a value of s/r is <NUM>≤s/r≤<NUM>. The doped conductive layer <NUM> and the substrate <NUM> are doped to have a same conductivity type.

The substrate <NUM> is used to receive incident light and generate photo-generated carriers. In some examples, the substrate <NUM> may be a silicon substrate <NUM>, and the material of the silicon substrate <NUM> may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon and microcrystalline silicon. In some examples, the material of the substrate <NUM> may be a carbon simple substance, an organic material or a multi-component compound, and the multi-component compound includes gallium arsenide, cadmium telluride, copper indium selenium, etc. In some examples, the solar cell is configured as a tunnel oxide passivated contact (TOPCON) solar cell. In some embodiments, the front surface and/or back surface of the substrate <NUM> can be used to receive the incident light. Generally, the front surface of the solar call may be designated as a main light-receiving surface that faces a light source (e.g., the sun). In some examples, the front surface of the substrate <NUM> may be set as a pyramid textured surface, so that the front surface of the substrate <NUM> can have a relatively small reflectivity to the incident light, as well as a relatively large light absorption and utilization rate. The back surface of the substrate <NUM> may be set as a non-pyramid textured surface, such as a stacked and stepped morphology, to ensure that the tunneling oxide layer <NUM> on the back surface has relatively high density and uniformity, and accordingly the tunneling oxide layer <NUM> can have a good passivation effect on the back surface of the substrate <NUM>.

In some examples, the substrate <NUM> is an N-type semiconductor substrate <NUM>, that is, the substrate <NUM> is doped with N-type dopants (or doping elements), and the N-type dopants may include at least one of phosphorus, arsenic or antimony. The front surface of the substrate <NUM> is provided with an emitter <NUM>. The emitter <NUM> may be a P-type doped layer doped with P-type dopants. The substrate <NUM> and the emitter <NUM> form a PN junction. In some examples, the emitter <NUM> may be formed by doping and diffusing P-type dopants at a surface layer of the substrate <NUM>, and a doped part of the substrate <NUM> severs as the emitter <NUM>. In some examples, the P-type dopants may be boron.

For the SirOs material of the third passivation layer <NUM>, a value of s/r is <NUM>≤s/r≤<NUM>, where s represents the number of oxygen atoms (i.e., O atoms) and r represents the number of silicon atoms (i.e., Si atoms). By adjusting the atomic ratio of the O atoms to the Si atoms in the SirOs material, a refractive index of the SirOs material may be adjusted. In this way, the refractive index of the third passivation layer <NUM> is adjusted to match a refractive index of the second passivation layer <NUM>, so that light reflection loss caused by poor refractive index matching between the third passivation layer <NUM> and the second passivation layer <NUM> can be reduced. On the other hand, a thickness of the third passivation layer <NUM> is adjusted to match with a wavelength of the incident light and the refractive index. The thickness of the passivation layer, the refractive index of the passivation layer and the wavelength of the incident light shall satisfy a following formula: a wavelength of incident light = <NUM>× thickness × refractive index. In this way, the passivation layer can have better light transmission capacity, relatively strong light absorption capacity for the incident light, as well as better passivation effect. In some examples, the wavelength of the incident light may be set to <NUM>.

In addition, by adjusting the atomic ratio of the O atoms to the Si atoms in the SirOs material, the third passivation layer <NUM> has relatively strong light absorption capacity for short-wave light. The third passivation layer <NUM>, together with the second passivation layer <NUM> having the relatively strong light absorption capacity for long-wave light, allows the whole solar cell to have relatively strong light absorption capacity for the incident light (including short-wave light and long-wave light). In this way, a carrier concentration of the front surface of the substrate <NUM> of the solar cell can be increased, thus increasing an open-circuit voltage, a short-circuit current, and a filling factor of the solar cell, and improving the photoelectric conversion rate of the solar cell. It is worth noting that the existing solar cells are generally blue, due to that the reflectivity of the passivation layer to the short-wave light is relatively high in the existing solar cells. However, in the present embodiments, since the third passivation layer <NUM> has relatively strong light absorption capacity for the short-wave light, a solar cell module including the solar cells may be grayish blue or even black, which is beneficial for preparing dark-colored solar cell modules.

In some examples, the refractive index of the third passivation layer <NUM> is lower than the refractive index of the second passivation layer <NUM>. This may be achieved by adjusting the atomic ratio of the O atoms to the Si atoms in the SirOs material of the third passivation layer <NUM>. In this case, the third passivation layer <NUM> is an optically thinner medium, and the second passivation layer <NUM> is an optically denser medium. In a case that the incident light enters the optically denser medium from the optically thinner medium, an angle between the incident light and a normal line of the optically denser medium is relatively small because the refractive index of the optically denser medium is relatively large, so that the incident light may enter the substrate <NUM> at an angle close to vertical incidence. In this way, more light may enter the substrate <NUM>, and the reflectivity of the solar cell to the incident light may be relatively small. It is worth noting that although a refractive index of the SirOs material in the third passivation layer <NUM> is lower than a refractive index of the first SiuNv material in the second passivation layer <NUM> intrinsically, the refractive index of the SirOs material may be further decreased as compared with the refractive index of the first SiuNv material, by further adjusting the atomic ratio of the O atoms to the Si atoms in SirOs material. As such, the incident light may enter the second passivation layer <NUM> from the third passivation layer <NUM> at a more vertical angle, thereby further reducing the reflectivity of the solar cell to the incident light, increasing the carrier concentration on the front surface of the substrate <NUM> and improving the photoelectric conversion rate of the solar cell.

In some examples, the refractive index of the third passivation layer <NUM> is <NUM>-<NUM>. Within this range, the refractive index of the SirOs material is smaller than the refractive index of the first SiuNv material, and thus the refractive index of the third passivation layer <NUM> is smaller than the refractive index of the second passivation layer <NUM>, thereby the solar cell can have relatively high light absorption and utilization rate for the incident light. Moreover, since the refractive index of the third passivation layer <NUM> is <NUM>-<NUM>, the problem that the refractive index of the SirOs material being too small may be avoided, so that the third passivation layer <NUM> can have a relatively strong anti-reflection effect on the incident light, and further improve the utilization rate of the incident light.

It can be understood that when the wavelength of the incident light and the refractive index of the third passivation layer <NUM> are provided, the thickness of the third passivation layer <NUM> may be determined according to the incident light and the refractive index, by adjusting the atomic ratio of the O atoms to the Si atoms in the SirOs material, so as to achieve better passivation effect and light transmission capacity of the solar cell. In addition, the thickness of the third passivation layer <NUM> is enabled to match the thickness of the second passivation layer <NUM>, so that the front surface of the substrate <NUM> of the solar cell can have a relatively good overall passivation effect.

In some examples, the third passivation layer <NUM> has a thickness of <NUM>~<NUM> in a direction perpendicular to the front surface. In this way, the third passivation layer <NUM> has good light transmission capacity and is capable for absorbing more short-wave light. In addition, the third passivation layer <NUM> within this thickness range also has a good passivation effect, which not only allows a relatively high carrier concentration on the front surface of the substrate <NUM> of the solar cell, but also inhibits the recombination of carriers on the front surface of the substrate <NUM>, thereby increasing the open-circuit voltage and short-circuit current of the solar cell and further increasing the photoelectric conversion rate of the solar cell.

In some examples, for the SirOs material of the third passivation layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>. The third passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the SirOs material of the third passivation layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>. The third passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the SirOs material of the third passivation layer <NUM>, the atomic ratio of the O atoms to the Si atoms may also be <NUM>≤s/r≤<NUM>. The third passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the SirOs material of the third passivation layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>. The third passivation layer <NUM> may have a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>.

As shown in <FIG>, in some examples, the third passivation layer <NUM> may have a double-layer structure, including a first silicon oxide sub-layer <NUM> and a second silicon oxide sub-layer <NUM> stacked in the direction away from the substrate <NUM>. Both the first silicon oxide sub-layer <NUM> and the second silicon oxide sub-layer <NUM> include the SirOs material. Herein, the value of s/r of the SirOs material in the first silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>; the value of s/r of SirOs material in the second silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>, and a refractive index of the first silicon oxide sub-layer <NUM> is greater than a refractive index of the second silicon oxide sub-layer <NUM>.

Compared with the third passivation layer <NUM> having a single-layer structure, in the exemplary solar cell as show in <FIG>, the first silicon oxide sub-layer <NUM> and the second silicon oxide sub-layer <NUM> are provided, and the refractive index of the first silicon oxide sub-layer <NUM> is greater than the refractive index of the second silicon oxide sub-layer <NUM>, so that reflection times and interference times of the incident light in the third passivation layer <NUM> may be increased, and absorption of the incident light by the third passivation layer <NUM> may be increased to a greater extent, thus achieving a good anti-reflection effect of the third passivation layer <NUM>.

Both the first silicon oxide sub-layer <NUM> and the second silicon oxide sub-layer <NUM> include the SirOs material. The refractive indices of the first silicon oxide sub-layer <NUM> and the second silicon oxide sub-layer <NUM> are adjusted by adjusting the atomic ratio of the O atoms to the Si atoms in the SirOs material, so that the refractive index of the first silicon oxide sub-layer <NUM> is larger than the refractive index of the second silicon oxide sub-layer <NUM>. The thickness of the first silicon oxide sub-layer <NUM> is set to match the refractive index of the first silicon oxide sub-layer <NUM>, and the thickness of the second silicon oxide sub-layer <NUM> is set to match the refractive index of the second silicon oxide sub-layer <NUM>; so that both the first silicon oxide sub-layer <NUM> and the second silicon oxide sub-layer <NUM> can have good passivation effect.

In some examples, the first silicon oxide sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>. Accordingly, for the SirOs material of the first silicon oxide sub-layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r<<NUM>, and the thickness of the first silicon oxide sub-layer <NUM> may be <NUM>~<NUM>. The second silicon oxide sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>. Accordingly, for the SirOs material of the second silicon oxide sub-layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>, and the thickness of the second silicon oxide sub-layer <NUM> may be <NUM>~<NUM>.

As shown in <FIG>, in other examples, the third passivation layer <NUM> may have a three-layer structure, including a first silicon oxide sub-layer <NUM>, a second silicon oxide sub-layer <NUM> and a third silicon oxide sub-layer <NUM> stacked in the direction away from the substrate <NUM>. The first silicon oxide sub-layer <NUM>, the second silicon oxide sub-layer <NUM> and the third silicon oxide sub-layer <NUM> all include the SirOs material. Refractive indices of the first silicon oxide sub-layer <NUM>, the second silicon oxide sub-layer <NUM>, and the third silicon oxide sub-layer <NUM> gradually decrease. In some examples, for the SirOs material of the first silicon oxide sub-layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>, such as <NUM>≤s/r≤M. The first silicon oxide sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. For the SirOs material of the second silicon oxide sub-layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>, such as <NUM>≤s/r≤<NUM>. The second silicon oxide sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. For the SirOs material of the third silicon oxide sub-layer <NUM>, the atomic ratio of the O atoms to the Si atoms may be <NUM>≤s/r≤<NUM>, such as <NUM>≤s/r≤<NUM>. The third silicon oxide sub-layer <NUM> may have a refractive index of <NUM>~<NUM>, such as <NUM>-<NUM>, and a thickness of <NUM>~<NUM>.

It is worth noting that the overall refractive index of the third passivation layer <NUM> is in the range of <NUM>-<NUM>, regardless of whether the third passivation layer <NUM> is a single-layer structure or a multi-layer structure, so that the refractive index of the third passivation layer <NUM> matches the refractive index of the second passivation layer <NUM>, and thus the substrate <NUM> can have relatively strong light absorption capacity for the incident light. It can be understood that under the condition that the overall refractive index of the third passivation layer <NUM> is in the range of <NUM>-<NUM>, the overall thickness of the third passivation layer <NUM> is in the range of <NUM>~<NUM> regardless of whether the third passivation layer <NUM> is the single-layer structure or the multi-layer structure.

With continued reference to <FIG>, the first SiuNv material of the second passivation layer <NUM> has a relatively high refractive index, so a Si-H bond density in the first SiuNv material is relatively high, which makes the first SiuNv material have a good passivation effect. However, the second passivation layer <NUM> may bring certain light absorption loss due to the relatively high refractive index of the first SiuNv material, that is, the second passivation layer <NUM> may have poor anti-reflection capacity to the incident light. In the present embodiments, the third passivation layer <NUM> is provided on a side of the second passivation layer <NUM> away from the substrate <NUM>, and the SirOs material of the third passivation layer <NUM> has a relatively small refractive index. As such, the relatively high refractive index of the second passivation layer <NUM> optically matches the relatively low refractive index of the third passivation layer <NUM>, so as to improve the light absorption capacity of the substrate <NUM> to the incident light. In addition, the second passivation layer <NUM> mainly absorbs long-wave light, and the third passivation layer <NUM> mainly absorbs short-wave light, so that the solar cell can have good light absorption capacity for the incident light in different wave bands.

For the first SiuNv material of the second passivation layer <NUM>, a value of v/u is <NUM>≤v/u≤<NUM>, where the v represents the number of nitrogen atoms (i.e., N atoms) and the u represents the number of Si atoms. By adjusting the atomic ratio of the N atoms to the Si atoms, the refractive index of the second passivation layer <NUM> is adjusted to be greater than the refractive index of the third passivation layer <NUM>. In this way, the incident light may be incident from the third passivation layer <NUM> to the second passivation layer <NUM> at a nearly vertical angle, so as to improve the utilization of the incident light.

In some examples, the second passivation layer <NUM> may have a single-layer structure, and the second passivation layer <NUM> may have a refractive index of <NUM>-<NUM>. An optical matching performance between the refractive index of the second passivation layer <NUM> and the refractive index of the third passivation layer <NUM> is good within this refractive index range, so that the substrate <NUM> can have relatively strong light absorption capacity for the incident light, thereby reducing the reflectivity of the solar cell for the incident light. In addition, the refractive index of the second passivation layer <NUM> may not be too low within this refractive index range, so that reflected light or emitting light from the first passivation layer <NUM> may re-enter the substrate <NUM> due to the second passivation layer <NUM>. In addition, the second passivation layer <NUM> within this refractive index range may have good passivation effect, and decreased interface state defects on the front surface of the substrate <NUM>, thereby inhibiting the recombination of carriers on the front surface of the substrate <NUM> and improving the photoelectric conversion rate of the solar cell.

According to the wavelength of the incident light and the refractive index of the second passivation layer <NUM>, the thickness of the second passivation layer <NUM> is set to match the refractive index of the second passivation layer <NUM>, so that the second passivation layer <NUM> can have good light absorption capacity of incident light and good passivation effect. In addition, the thickness of the second passivation layer <NUM> is also set to adapt to the overall thickness of the solar cell. The overall thickness of the solar cell is prevented from being too thin, which may lead to breakage. The overall thickness of the solar cell is also prevented from being too thick, which may lead to difficulty in packaging. The thickness of the second passivation layer <NUM> may be adjusted by adjusting the atomic ratio of the Si atoms to the N atoms of the first SiuNv material of the second passivation layer <NUM>.

In some examples, the second passivation layer <NUM> has a thickness of <NUM>~<NUM> in a direction perpendicular to the front surface. Within this thickness range, the thickness of the second passivation layer <NUM> is not too thin, so that the second passivation layer <NUM> can have a good refraction effect on the incident light, thus avoiding the problem that the incident light may be emitted through other passivation layers or emitted out of the substrate <NUM> before being absorbed by the substrate <NUM> due to the second passivation layer <NUM> being too thin. On the other hand, the number of positive charges in the second passivation layer <NUM> can achieve the hydrogen passivation effect within this thickness range, thereby further inhibiting the recombination of carriers on the front surface of the substrate <NUM>.

In some examples, for the first SiuNv material of the second passivation layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>. The second passivation layer <NUM> may have a refractive index of <NUM>∼<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the first SiuNv material of the second passivation layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>. The second passivation layer <NUM> may have a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the first SiuNv material of the second passivation layer <NUM>, the atomic ratio of the N atoms to the Si atoms is <NUM>≤v/u≤<NUM>. The second passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the first SiuNv material of the second passivation layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>. The second passivation layer <NUM> may have a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>.

As shown in <FIG>, in some examples, the second passivation layer <NUM> may have a three-layer structure, including a first silicon nitride sub-layer <NUM>, a second silicon nitride sub-layer <NUM> and a third silicon nitride sub-layer <NUM> stacked in the direction away from the substrate <NUM>. The refractive indices of the first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM> and the third silicon nitride sub-layer <NUM> gradually decrease. The first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM> and the third silicon nitride sub-layer <NUM> all include the first SiuNv material. In this way, long-wave photons in the long-wave light may be reflected and interfered many times in the second passivation layer <NUM>. Compared with a single-layered silicon nitride layer, the utilization ratio of the long-wave photons can be increased to a greater extent, and the long-wave response can be improved, so that more long-wave light can be absorbed in the solar cell.

The refractive indices and thicknesses of the first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM> and the third silicon nitride sub-layer <NUM> are adjusted by adjusting the atomic ratio of the N atoms to the Si atoms in the first SiuNv material of the first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM> and the third silicon nitride sub-layer <NUM> respectively. In some examples, the atomic ratio of the N atoms to the Si atoms of the first SiuNy material of the first silicon nitride sub-layer <NUM> may be adjusted to be <NUM>≤v/u≤<NUM>. The atomic ratio of the N atoms to the Si atoms in the first SiuNv material of the second silicon nitride sub-layer <NUM> may be adjusted to be <NUM>≤v/u≤<NUM>. The atomic ratio of the N atoms to the Si atoms of the first SiuNy material of the third silicon nitride sub-layer <NUM> may be adjusted to be <NUM>≤v/u≤<NUM>.

Accordingly, the first silicon nitride sub-layer <NUM> may have a refractive index of <NUM>-<NUM> and a thickness of <NUM>~<NUM>. The second silicon nitride sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>~<NUM>. Accordingly, for the second silicon nitride layer <NUM>, the atomic ratio of the N atoms to the Si atoms of the first SiuNv material may be <NUM>≤v/u≤<NUM>, and the thickness may be <NUM>~<NUM>. The third silicon nitride sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>. Accordingly, for the third silicon nitride layer <NUM>, the atomic ratio of the N atoms to the Si atoms of the first SiuNv material may be <NUM>≤v/u≤<NUM>, and the thickness may be <NUM>~<NUM>.

In some examples, the second passivation layer <NUM> may have a four-layer structure, including a first silicon nitride sub-layer <NUM>, a second silicon nitride sub-layer <NUM>, a third silicon nitride sub-layer <NUM> and a fourth silicon nitride sub-layer stacked in the direction away from the substrate <NUM>. The first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM>, the third silicon nitride sub-layer <NUM> and the fourth silicon nitride sub-layer all include the first SiuNv material. The refractive indices of the first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM>, the third silicon nitride sub-layer <NUM>, and the fourth silicon nitride sub-layer gradually decrease. In some examples, for the first SiuNv material of the first silicon nitride sub-layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>, such as <NUM>≤v/u≤<NUM>. The first silicon nitride sub-layer <NUM> may have a refractive index of <NUM>∼<NUM>, such as <NUM>∼<NUM>, and a thickness of <NUM>~<NUM>. For the first SiuNv material of the second silicon nitride sub-layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>, such as <NUM>≤v/u≤<NUM>. The second silicon nitride sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. For the first SiuNv material of the third silicon nitride sub-layer <NUM>, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>, such as <NUM>≤v/u≤<NUM>. The third silicon nitride sub-layer <NUM> may have a refractive index of <NUM>-<NUM>, such as <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. For the first SiuNv material of the fourth silicon nitride sub-layer, the atomic ratio of the N atoms to the Si atoms may be <NUM>≤v/u≤<NUM>, such as <NUM>≤v/u≤<NUM>. The fourth silicon nitride sub-layer may have a refractive index of <NUM>-<NUM>, such as <NUM>~<NUM>, and a thickness of <NUM>~<NUM>.

It is worth noting that the refractive index of the second passivation layer <NUM> is in the range of <NUM>∼<NUM>, regardless of whether the second passivation layer <NUM> has the single-layer structure or the multi-layer structure. In this way, the refractive index of the second passivation layer <NUM> optically matches the refractive index of the third passivation layer <NUM>, so that the reflectivity of the front surface of the substrate <NUM> to the incident light is relatively low, and the light absorption capacity of the substrate to the incident light is relatively strong. It can be understood that under the condition that the overall refractive index of the second passivation layer <NUM> is in the range of <NUM>~<NUM>, the overall thickness of the second passivation layer <NUM> is in the range of <NUM>~<NUM> regardless of whether the second passivation layer <NUM> has the single-layer structure or the multi-layer structure.

As shown in <FIG>, the solar cell provided by the embodiments of the present disclosure has a lower reflectivity in the short-wave range (e.g., an ultraviolet light or near ultraviolet light) than a conventional TOPCON solar cell. The conventional TOPCON solar cell generally uses an aluminum oxide/silicon nitride stacked layer as a front passivation layer. Taking light at a wavelength of <NUM> as an example, 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 about <NUM>%. In addition, compared with the conventional solar cell which is blue, the solar cell provided by the embodiments of the present disclosure may be grayish blue, since the reflectivity of light is relatively low in the short-wave range, which is beneficial for preparing a dark-colored solar cell module.

The solar cell provided by the embodiments of the present disclosure also has a greatly lower average reflectivity for the light at a wavelength range of <NUM>~<NUM>. Generally, the average reflectivity of the conventional TOPCON solar cell for the light at the wavelength range of <NUM>~<NUM> is <NUM>%, while the average reflectivity of the solar cell provided by the embodiments of the present disclosure is <NUM>%, which is reduced by about <NUM>%. In addition, a TOPCON solar cell including the first passivation layer <NUM>, the second passivation layer <NUM>, and the third passivation layer <NUM> in the present embodiments, has a short-circuit current increased by more than 70mA.

As a passivation layer disposed close to the substrate <NUM>, the first passivation layer <NUM> is required to have a good passivation effect. In some examples, the dielectric material of the first passivation layer <NUM> may include at least one of aluminum oxide, titanium oxide, gallium oxide and hafnium oxide. It is worth noting that the aluminum oxide, the titanium oxide, the gallium oxide and the hafnium oxide are field passivation materials, which have a field passivation effect on the front surface of the substrate <NUM>. A field passivation refers to forming a built-in electric field at an interface of the substrate <NUM> to reduce the concentration of electrons or holes at the interface of the substrate <NUM>, thus achieving the surface passivation effect. This built-in electric field may generally be obtained by providing fixed electrical charges at the interface of the substrate <NUM>.

In some examples, the dielectric material may be AlxOy material, and a value of y/x is <NUM>≤y/x≤<NUM>, where y represents the number of O atoms and x represents the number of aluminum atoms (i.e., Al atoms). The AlxOy material has a good field passivation effect, because the AlxOy material may provide a sufficient number of fixed negative electrical charges. As such, the built-in electric field may be formed at the front surface of the substrate <NUM>, so as to reduce a minority carrier concentration at the front surface of the substrate <NUM> and inhibit the recombination of carriers, thereby improving the open-circuit voltage and short-circuit current of the solar cell. In addition, the AlxOy material further has a certain chemical passivation effect, that is, the recombination rate of carriers can be suppressed by reducing the number of defects on the front surface of the substrate <NUM>. The refractive index and thickness of the first passivation layer <NUM> are adjusted by adjusting the atomic ratio of the O atoms to the Al atoms, so that the refractive index and thickness of the first passivation layer <NUM> are optimized and the first passivation layer <NUM> has a good passivation effect.

In some examples, the first passivation layer <NUM> has a refractive index of <NUM>-<NUM>. In this refractive index range, the refractive index of the first passivation layer <NUM> matches the refractive index of the second passivation layer <NUM>, thus reducing the light reflection loss caused by poor refractive index matching between the first passivation layer <NUM> and the second passivation layer <NUM>, so that the first passivation layer <NUM> can have good light absorption capacity for the incident light.

Under the condition that the wavelength of the incident light and the refractive index of the first passivation layer <NUM> are determined, a thickness of the first passivation layer <NUM> may be determined to enable the thickness of the first passivation layer <NUM> to match the refractive index, so that the first passivation layer <NUM> can have good passivation effect. In some examples, the first passivation layer <NUM> has a thickness of <NUM>~<NUM> in the direction perpendicular to the front surface. In this case, the first passivation layer <NUM> has relatively strong electronegativity, so that a selective transmission of carriers can be realized. In addition, the thickness of the first passivation layer <NUM> is related to the field passivation effect. The greater the thickness of the first passivation layer <NUM>, the better the field passivation effect of the first passivation layer <NUM>. The thickness of the first passivation layer <NUM> is adjusted within this ratio range, which can not only make the first passivation layer <NUM> have good field passivation effect, but also avoid the problem that the substrate <NUM> is damaged by stress due to excessive thickness.

In some examples, for the AlxOy material of the first passivation layer <NUM>, the atomic ratio of the O atoms to the Al atoms may be <NUM>≤y/x≤<NUM>. The first passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the AlxOy material of the first passivation layer <NUM>, the atomic ratio of the O atoms to the Al atoms may be <NUM>≤y/x≤<NUM>. The first passivation layer <NUM> may have a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the AlxOy material of the first passivation layer <NUM>, the atomic ratio of the O atoms to the Al atoms may be <NUM>≤y/x≤<NUM>. The first passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, for the AlxOy material of the first passivation layer <NUM>, the atomic ratio of the O atoms to the Al atoms may be <NUM>≤y/x≤<NUM>. The first passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>.

The tunneling oxide layer <NUM> and the doped conductive layer <NUM> are formed on the back surface of the substrate <NUM> as a passivation contact structure, and the tunneling oxide layer <NUM> is used to achieve interface passivation on the back surface. In some examples, the material of the tunneling oxide layer <NUM> may be a dielectric material, such as silicon oxide. The doped conductive layer <NUM> is used to achieve field passivation. The doped conductive layer <NUM> and the substrate <NUM> are doped to have a same conductivity type. The doped conductive layer <NUM> and the substrate <NUM> may be doped with same dopants (or doping elements) or different dopants. In some examples, the doped conductive layer <NUM> may be 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. The doped conductive layer <NUM> includes N-type dopants, such as at least one of phosphorus, arsenic or antimony.

In some examples, the doped conductive layer <NUM> is a doped polycrystalline silicon layer. The doped conductive layer <NUM> has a thickness of <NUM>~<NUM> in the direction perpendicular to the back surface, such as <NUM>, <NUM> or <NUM>.

In some examples, the solar cell includes a fourth passivation layer <NUM>, which is disposed on a side of the doped conductive layer <NUM> facing away from the substrate <NUM>. The fourth passivation layer <NUM> includes a second SimNn material, and a value of n/m is <NUM>≤y/x≤<NUM>. The fourth passivation layer <NUM> is used to enhance the reflection effect of the incident light on the back of the solar cell, and further to enhance the passivation effect of the passivation contact structure on the back surface of the substrate <NUM>. In the second SimNn material, n represents the number of N atoms and m represents the number of Si atoms. A refractive index and thickness of the fourth passivation layer <NUM> may be adjusted by adjusting the value of n/m. In some examples, the fourth passivation layer <NUM> has a single-layer structure. The fourth passivation layer <NUM> may have a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. In some examples, the fourth passivation layer <NUM> may have a multi-layer structure. The refractive index of each sub-layer of the fourth passivation layer <NUM> gradually decreases in a direction from the back surface of the substrate <NUM> toward the doped conductive layer <NUM>, so that it is beneficial to enhance the reflection effect of the incident light on a back of the solar cell by internal reflection.

The solar cell further includes a first electrode <NUM> and a second electrode <NUM>. The first electrode <NUM> is disposed on the front surface of the substrate <NUM> and is electrically connected with the emitter <NUM> by penetrating through the third passivation layer <NUM>, the second passivation layer <NUM> and the first passivation layer <NUM>. The second electrode <NUM> is disposed on the back surface of the substrate <NUM> and is electrically connected with the doped conductive layer by penetrating through the fourth passivation layer <NUM>.

In the above embodiments, the solar cell includes the first passivation layer <NUM>, the second passivation layer <NUM> and the third passivation layer <NUM> sequentially formed on the front surface of the substrate <NUM> and in the direction away from the substrate <NUM>. The first passivation layer <NUM> includes the dielectric material. The second passivation layer <NUM> includes the first SiuNv material, and the value of v/u is <NUM>≤v/u≤<NUM>. The second passivation layer has relatively high refractive index by adjusting the atomic ratio in the first SiuNv material, so that the second passivation layer can have relatively strong light absorption capacity for long-wave light. The third passivation layer <NUM> includes the SirOs material, and the value of s/r is <NUM>≤s/r≤<NUM>. The SirOs material can have relatively strong light absorption capacity for short-wave light by adjusting the atomic ratio in the SirOs material. In this way, the third passivation layer <NUM>, together with the second passivation layer, allows the whole solar cell have relatively strong light absorption capacity for the incident light (including short-wave light and long-wave light), and thus the anti-reflectivity of the solar cell surface can be relatively large. Moreover, the first SiuNv material and the SirOs material have a good passivation effect, thereby increasing improving the open-circuit voltage, the short-circuit current and the filling factor of the solar cell and improving the photoelectric conversion rate of the solar cell.

Correspondingly, as shown in <FIG>, some embodiments of the present disclosure further provide a solar cell module, including: at least one cell string formed by connecting a plurality of the solar cells <NUM> provided by the above embodiments; a packaging layer <NUM> configured to cover a surface of the at least one cell string; and a cover plate <NUM> configured to cover a surface of the packaging layer <NUM> away from the at least one cell string. The solar cells are electrically connected in a form of a whole piece or multiple pieces (for example, <NUM>/<NUM> equal pieces, <NUM>/<NUM> equal pieces, <NUM>/<NUM> equal pieces and other multiple pieces) to form a plurality of cell strings, and the plurality of cell strings are electrically connected in series and/or parallel. In some examples, the plurality of cell strings may be electrically connected through conductive ribbons. The packaging layer <NUM> covers the front surface and the back surface of the solar cell. In some examples, the packaging layer <NUM> on the back surface of the solar cell may be white. In this way, in a case that incident light incident from the front surface of the solar cell is irradiated to the back of the solar cell from a gap between two adjacent solar cell, the incident light may be reflected to the cover plate <NUM> on the front surface of the solar cells through the white packaging layer <NUM>, and then reflected to the front surface of the solar cell once again, thus increasing the light absorption capacity of the incident light. In some examples, the packaging layer <NUM> may be made of organic materials such as ethylene-vinyl acetate copolymer (EVA), polyolefin thermoplastic elastomer (POE) or polyethylene glycol terephthalate (PET). In some examples, the cover plate <NUM> may be a cover plate with a light-transmitting function, such as a glass cover plate, a plastic cover plate, and the like. A surface of the cover plate facing the packaging layer <NUM> may be a concave-convex surface, thereby increasing the utilization rate of the incident light. The solar cell of the present solar cell module includes a first passivation layer <NUM>, a second passivation layer <NUM> and a third passivation layer <NUM> sequentially formed on the front surface. The second passivation layer <NUM> mainly absorbs long-wave light and the third passivation layer <NUM> mainly absorbs short-wave light, so that the solar cell has relatively strong light absorption capacity for incident light of different wave bands, thereby reducing a reflectivity of a front surface of a substrate <NUM> of the solar cell to light. Therefore, after the solar cells are packaged to form the solar cell module, the solar cell module is grayish blue or even black, which is beneficial for preparing a dark-colored solar cell module.

Correspondingly, some embodiments of the present disclosure further provide a method for preparing a solar cell, to prepare the solar cell provided in the above embodiments. The method will be described in detail with reference to the accompanying drawings.

<FIG> show schematic structural diagrams corresponding to each step of the method for preparing the solar cell according to some embodiments of the present disclosure.

As shown in <FIG>, a substrate <NUM> having a front surface and a back surface opposite to the front surface is provided.

The substrate <NUM> is used to receive incident light and generate photo-generated carriers. In some examples, the substrate <NUM> may be a silicon substrate <NUM>, and the materials of the silicon substrate <NUM> may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon and microcrystalline silicon. In some examples, the material of the substrate <NUM> may be a carbon simple substance, an organic material or a multi-component compound. The multi-component compound includes gallium arsenide, cadmium telluride, copper indium selenium, etc. In some examples, the solar cell is a tunnel oxide passivated contact (TOPCON) solar cell, and both the front surface and back surface of the substrate <NUM> are used to receive the incident light. In some examples, the front surface of the substrate <NUM> may be set as a pyramid textured surface, so that a reflectivity of the front surface of the substrate <NUM> to the incident light is relatively small, and thus the light absorption and utilization rate of the front surface of the substrate <NUM> is relatively large. In some examples, the substrate <NUM> is an N-type semiconductor substrate, that is, the substrate <NUM> is doped with N-type dopants, and the N-type dopants may be any one of phosphorus, arsenic, or antimony.

As shown in <FIG>, an emitter <NUM> is formed.

In some examples, the substrate <NUM> is the N-type semiconductor substrate, and the emitter <NUM> is a P-type emitter. A specific process method for forming the emitter <NUM> may be as follows. The front surface of the substrate <NUM> is subjected to a boron diffusion treatment to form the emitter <NUM>. The emitter <NUM> and the N-type substrate <NUM> form a PN junction. It is worth noting that after the emitter <NUM> is formed, borosilicate glass formed by the boron diffusion treatment is required to be removed, so that when a first passivation layer <NUM> is subsequently formed on the emitter <NUM>, the first passivation layer <NUM> has a uniform thickness, which is beneficial to improving the light absorption capacity of the front surface of the substrate <NUM> to the incident light. In some examples, a boron source used in the boron diffusion treatment includes liquid boron tribromide.

As shown in <FIG>, a tunneling oxide layer <NUM> and a doped conductive layer <NUM> are sequentially formed on the back surface of a substrate <NUM> in a direction away from the back surface. The doped conductive layer <NUM> and the substrate <NUM> are doped to have a same conductivity type.

In some examples, the tunneling oxide layer <NUM> is deposited on the back surface of the substrate <NUM> 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>, such as <NUM>, <NUM> or <NUM>, etc. In some examples, the tunneling oxide layer <NUM> may be formed by an in-situ generation process, such as a thermal oxidation process or a nitric acid passivation process.

In some examples, the tunneling oxide layer <NUM> may have a thickness of <NUM>~<NUM>, such as <NUM>, <NUM>, <NUM> or <NUM>.

In some examples, after forming the tunneling oxide layer <NUM>, a deposition process may be adopted to form the doped conductive layer <NUM> on a surface of the tunneling oxide layer <NUM>. The deposition process may be adopted to deposit intrinsic polycrystalline silicon on the surface of the tunneling oxide layer <NUM> to form a polycrystalline silicon layer. Then, phosphorus is doped to the polycrystalline silicon layer by an ion implantation and a source diffusion process to form an N-type doped polycrystalline silicon layer. The doped polycrystalline silicon layer serves as the doped conductive layer <NUM>.

In some examples, the doped conductive layer <NUM> may have a thickness of <NUM>~<NUM>, such as <NUM>, <NUM> or <NUM>, in a direction perpendicular to the back surface of the substrate <NUM>.

As shown in <FIG>, the first passivation layer <NUM>, a second passivation layer <NUM> and a third passivation layer <NUM> are sequentially formed on the front surface of a substrate <NUM> in a direction away from the substrate <NUM>. The first passivation layer <NUM> includes a dielectric material. The second passivation layer <NUM> includes a first SiuNv material, and a value of v/u is <NUM>≤v/u≤<NUM>. The third passivation layer <NUM> includes a SirOs material, and a value of s/r is <NUM>≤s/r≤<NUM>.

As shown in <FIG>, the first passivation layer <NUM> is formed on the surface of the emitter <NUM>. The first passivation layer <NUM> includes an AlxOy material. In some examples, the first passivation layer <NUM> may be formed by an atomic layer deposition process. A method for forming the first passivation layer <NUM> includes introducing trimethyl aluminum and water into a reaction chamber, where a ratio of the trimethyl aluminum to the water is <NUM>: <NUM>~<NUM>: <NUM>, and a temperature is <NUM> ~<NUM>. In the first passivation layer <NUM>, the atomic ratio of O atoms to Al atoms of the AlxOy material is <NUM>≤y/x≤<NUM>. The first passivation layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>.

In some examples, after the first passivation layer <NUM> is formed, the method further includes: performing an annealing process on the first passivation layer <NUM> in a nitrogen atmosphere, where an annealing temperature is <NUM>~<NUM>, and an annealing duration is <NUM> mim~<NUM>. In this way, residual water molecules and organic functional groups can be removed.

As shown in <FIG>, the second passivation layer <NUM> is formed on a surface of the first passivation layer <NUM>, and the second passivation layer <NUM> includes the first SiuNv material. In some examples, the second passivation layer <NUM> may be formed by a plasma-enhanced chemical vapor deposition process. A method for forming the second passivation layer includes: introducing silane and ammonia gas into a reaction chamber and ionizing the silane and the ammonia gas. A pulse power per unit area is 140mW/cm<NUM>~180mW/cm<NUM>. A pressure of the reaction chamber is <NUM> mTorr~<NUM> mTorr. A flow ratio of the silane to the ammonia gas is <NUM>:<NUM>-<NUM>:<NUM>, and a reaction time is <NUM>~<NUM>.

In some examples, the second passivation layer <NUM> may have a three-layer structure, and may include a first silicon nitride sub-layer <NUM> (refer to <FIG>), a second silicon nitride sub-layer <NUM> (refer to <FIG>), and a third silicon nitride sub-layer <NUM> (refer to <FIG>) stacked in the direction away from the substrate <NUM>. The process method for forming the second passivation layer <NUM> is as follows. The silane and the ammonia gas are introduced into a reaction chamber and ionized to form the first silicon nitride sub-layer <NUM> on the surface of the first passivation layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the ammonia gas are continuously introduced into the reaction chamber and ionized to form the second silicon nitride sub-layer <NUM> on a surface of the first silicon nitride sub-layer <NUM>. The pulse power per unit area is 150mW/cm<NUM>~180mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>~<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the ammonia gas are continuously introduced into the reaction chamber and ionized to form the third silicon nitride sub-layer <NUM> on a surface of the second silicon nitride sub-layer <NUM>. The pulse power per unit area is 150mW/cm<NUM>~180mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>.

Based on the preparation process, an atomic ratio of N atoms to Si atoms in the first silicon nitride sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The first silicon nitride sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. The atomic ratio of the N atoms to the Si atoms in the second silicon nitride sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The second silicon nitride sub-layer <NUM> has a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>. The atomic ratio of the N atoms to the Si atoms in the third silicon nitride sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The third silicon nitride sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>.

In some examples, the second passivation layer <NUM> may have a four-layer structure, including the first silicon nitride sub-layer <NUM>, the second silicon nitride sub-layer <NUM>, the third silicon nitride sub-layer <NUM> and a fourth silicon nitride sub-layer stacked in the direction away from the substrate <NUM>. The process method for forming the second passivation layer <NUM> is as follows. The silane and the ammonia gas are introduced into the reaction chamber and ionized to form the first silicon nitride sub-layer <NUM> on the surface of the first passivation layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the ammonia gas are continuously introduced into the reaction chamber and ionized to form the second silicon nitride sub-layer <NUM> on the surface of the first silicon nitride sub-layer <NUM>. The pulse power per unit area is 150mW/cm<NUM>~180mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the ammonia gas are continuously introduced into the reaction chamber and ionized to form the third silicon nitride sub-layer <NUM> on the surface of the second silicon nitride sub-layer <NUM>. The pulse power per unit area is 150mW/cm<NUM>~180mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the ammonia gas are continuously introduced into the reaction chamber and ionized to form the fourth silicon nitride sub-layer on a surface of the third silicon nitride sub-layer <NUM>. The pulse power per unit area is 150mW/cm<NUM>~180mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr-<NUM> mTorr. The gas flow ratio of the silane to the ammonia gas may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~ <NUM>.

As shown in <FIG>, the third passivation layer <NUM> is formed on the surface of the second passivation layer <NUM>, and the third passivation layer <NUM> includes the SirOs material. In some examples, the third passivation layer <NUM> may be formed by the plasma-enhanced chemical vapor deposition process. A method for forming the third passivation layer <NUM> includes: introducing the silane and nitrous oxide into the reaction chamber and ionizing the silane and the nitrous oxide. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorr∼<NUM> mTorr. A flow ratio of the silane to the nitrous oxide is <NUM>:<NUM>∼<NUM>:<NUM>, and the reaction time is <NUM>~<NUM>.

In some examples, the third passivation layer <NUM> may have a two-layer structure, and may include a first silicon oxide sub-layer <NUM> (refer to <FIG>) and a second silicon oxide sub-layer <NUM> (refer to <FIG>) stacked in the direction away from the substrate <NUM>. The process method for forming the third passivation layer <NUM> is as follows. The silane and the nitrous oxide are introduced into the reaction chamber and ionized to form the first silicon oxide sub-layer <NUM> on the surface of the second passivation layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the nitrous oxide may be <NUM>:<NUM>∼<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the nitrous oxide are continuously introduced into the reaction chamber and ionized to form the second silicon oxide sub-layer <NUM> on a surface of the first silicon oxide sub-layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the nitrous oxide may be <NUM>:<NUM>~<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>.

Based on the preparation process, an atomic ratio of O atoms to Si atoms in the first silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The first silicon oxide sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. The atomic ratio of the O atoms to the Si atoms in the second silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The second silicon oxide sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>.

In some examples, the third passivation layer <NUM> may have a three-layer structure, and may include the first silicon oxide sub-layer <NUM> (refer to <FIG>), the second silicon oxide sub-layer <NUM> (refer to <FIG>), and a third silicon oxide sub-layer <NUM> (refer to <FIG>) stacked in the direction away from the substrate <NUM>. The process method for forming the third passivation layer <NUM> is as follows. The silane and the nitrous oxide are introduced into the reaction chamber and ionized to form the first silicon oxide sub-layer <NUM> on the surface of the second passivation layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the nitrous oxide may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the nitrous oxide are continuously introduced into the reaction chamber and ionized to form the second silicon oxide sub-layer <NUM> on the surface of the first silicon oxide sub-layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the nitrous oxide may be <NUM>:<NUM>~<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>. The silane and the nitrous oxide are continuously introduced into the reaction chamber and ionized to form the third silicon oxide sub-layer <NUM> on a surface of the second silicon oxide sub-layer <NUM>. The pulse power per unit area is 140mW/cm<NUM>~170mW/cm<NUM>. The pressure of the reaction chamber is <NUM> mTorrr~<NUM> mTorr. The gas flow ratio of the silane to the nitrous oxide may be <NUM>:<NUM>-<NUM>:<NUM>, and the reaction time may be <NUM>~<NUM>.

Based on the preparation process, the atomic ratio of the O atoms to the Si atoms in the first silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The first silicon oxide sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. The atomic ratio of the O atoms to the Si atoms in the second silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The second silicon oxide sub-layer <NUM> has a refractive index of <NUM>-<NUM>, and a thickness of <NUM>~<NUM>. The atomic ratio of the O atoms to the Si atoms in the third silicon oxide sub-layer <NUM> is <NUM>≤s/r≤<NUM>. The third silicon oxide sub-layer <NUM> has a refractive index of <NUM>~<NUM>, and a thickness of <NUM>~<NUM>.

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

In some examples, the fourth passivation layer <NUM> includes a second SimNn material. The fourth passivation layer <NUM> may be formed on a surface of the doped conductive layer <NUM> by using the plasma-enhanced chemical vapor deposition process. In some examples, the fourth passivation layer <NUM> may have a single-layer structure. In some examples, the fourth passivation layer <NUM> may have a multi-layer structure, and the refractive index of each layer gradually decreases in a direction from the back surface of the substrate <NUM> toward the doped conductive layer <NUM>.

After the fourth passivation layer <NUM> is formed, a metallization treatment is performed on the surfaces of the third passivation layer <NUM> on the front surface of the substrate <NUM> and the fourth passivation layer <NUM> on the back surface of the substrate <NUM>,. The metallization treatment includes a screen printing process and a high-temperature sintering process, so as to form the first electrode <NUM> electrically connected with the emitter <NUM> on the front surface of the substrate <NUM> and the second electrode <NUM> electrically connected with the doped conductive layer <NUM> on the back surface of the substrate <NUM>. The first electrode <NUM> penetrates through the third passivation layer <NUM>, the second passivation layer <NUM> and the first passivation layer <NUM> on the front surface of the substrate <NUM>. The formed second electrode <NUM> penetrates through the fourth passivation layer <NUM>.

In the above method for preparing the solar cell, the first passivation layer <NUM>, the second passivation layer <NUM> and the third passivation layer <NUM> are formed sequentially on the front surface of the substrate <NUM> and in the direction away from the substrate <NUM>. The first passivation layer <NUM> includes the dielectric material. The second passivation layer <NUM> includes the first SiuNv material, and the value of v/u is <NUM>≤v/u≤<NUM>. The second passivation layer has relatively high refractive index by adjusting the atomic ratio in the first SiuNv material, so that the second passivation layer has relatively strong light absorption capacity for long-wave light. Besides, the first SiuNv material in the second passivation layer <NUM> has good hydrogen passivation effect. The third passivation layer <NUM> includes the SirOs material, and the value of s/r is <NUM>≤s/r≤<NUM>. The SirOs material can have relatively strong light absorption capacity for short-wave light by adjusting the atomic ratio in the SirOs material. In this way, the third passivation layer <NUM>, together with the relatively strong light, allows the whole solar cell have relatively strong light absorption capacity for the incident light (including short-wave light and long-wave light), and thus the anti-reflectivity of the solar cell surface can be relatively large. Moreover, the first SiuNv material and the SirOs material have a good passivation effect, thereby improving an open-circuit voltage, a short-circuit current and a filling factor of the solar cell and increasing the photoelectric conversion rate of the solar cell.

The first comparative example provides a solar cell, as shown in <FIG>, including: a substrate <NUM> having a front surface and a back surface opposite to the front surface; a front passivation layer <NUM> formed on a front surface of the substrate <NUM>. The front passivation layer includes a SiaNb material.

With reference to the structure of the solar cell according to some embodiments of the present disclosure shown in <FIG>, the first comparative example differs from the embodiments of the present disclosure in that: a single-layered front passivation layer <NUM> is formed on the front surface of the substrate <NUM> in the first comparative example, and the material of the front passivation layer <NUM> is the SiaNb material. In the embodiments of the present disclosure, the solar cell includes the first passivation layer <NUM>, the second passivation layer <NUM> and the third passivation layer <NUM> sequentially formed on the front surface of the substrate <NUM> in the direction away from the substrate <NUM>. Herein, the first passivation layer <NUM> includes the dielectric material, the second passivation layer <NUM> includes the first SiuNv material, and the third passivation layer <NUM> includes the SirOs material. It is found through comparative experiments that the parameter comparison between the embodiments of the present disclosure and the first comparative example is shown in Table <NUM>.

It can be seen from Table <NUM> that, compared with the first comparative example, the solar cell in the embodiments of the present disclosure has relatively lower reflectivity to incident light, and has relatively larger open-circuit voltage, short-circuit current and parallel resistance, so that the solar cell in the embodiments of the present disclosure has higher conversion efficiency. Herein, the reflectivity of the solar cell to the incident light is <NUM>% lower than the reflectivity of the solar cell in the first comparative example, and the conversion efficiency of the solar cell is <NUM>% higher than the conversion efficiency of the solar cell in the first comparative example. This is because in the first comparative example, the front passivation layer <NUM> is the SiaNb material and is in a single-layered structure. The SiaNb material has a relatively high refractive index, which may bring certain light absorption loss and poor light absorption capacity for the incident light. In the embodiments of the present disclosure, the second passivation layer <NUM> is the first SiuNv material, for mainly absorbing long-wave light, and the third passivation layer is the SirOs material, for mainly absorbing short-wave light, so that the solar cell has good light absorption capacity for the incident light in different wave bands, thus making the solar cell have relatively high utilization rate of the incident light, thereby increasing the carrier concentration on the front surface of the substrate <NUM> and improving the conversion efficiency of the solar cell.

The second comparative example provides a solar cell, as shown in <FIG>, including: a substrate <NUM> having a front surface and a back surface opposite to the front surface; a first passivation layer <NUM> and a second passivation layer <NUM> sequentially formed on the front surface of the substrate <NUM> and in a direction away from the substrate <NUM>. The first passivation layer <NUM> includes an AjOk material, and the second passivation layer <NUM> includes a SipNq material.

With reference to the structure of the solar cell according to some embodiments of the present disclosure shown in <FIG>, the second comparative example differs from the embodiments of the present disclosure in that: two passivation layers are formed on the front surface of the substrate <NUM> in the second comparative example. In the embodiments of the present disclosure, the solar cell includes the first passivation layer <NUM>, the second passivation layer <NUM> and the third passivation layer <NUM> sequentially formed on the front surface of the substrate <NUM> in the direction away from the substrate <NUM>. Herein, the first passivation layer <NUM> includes the dielectric material, the second passivation layer <NUM> includes the first SiuNv material, and the third passivation layer <NUM> includes the SirOs material. It is found through comparative experiments that the parameter comparison between the embodiments of the present disclosure and the second comparative example is shown in Table <NUM>.

It can be can be seen from Table <NUM> that, compared with the second comparative example, the solar cell in the embodiments of the present disclosure has relatively lower reflectivity to incident light, and has relatively larger open-circuit voltage, short-circuit current, filling factor and parallel resistance, so that the solar cell in the embodiments of the present disclosure has higher conversion efficiency. Herein, the reflectivity of the solar cell to the incident light is <NUM>% lower than the reflectivity of the solar cell in the second comparative example, and the conversion efficiency of the solar cell is <NUM>% higher than the conversion efficiency of the solar cell in the second comparative example. This is because in the second comparative example, the second passivation layer <NUM> is the SipNq material, so the solar cell in the second comparative example may merely have good absorption effect on long-wave light. In the embodiments of the present disclosure, the third passivation layer is the SirOs material, for mainly absorbing short-wave light. The SirOs material of the third passivation layer, together with the first SiuNv material of the second passivation layer <NUM>, allows the solar cell have good light absorption capacity for the incident light in different wave bands. Further, in the embodiments of the present disclosure, the refractive index of the third passivation layer <NUM> is set to be lower than the refractive index of the second passivation layer <NUM>, so that the incident light enters the optically denser medium from the optically thinner medium and enters the substrate <NUM> at a nearly vertical angle. Therefore, the utilization rate of the incident light is relatively high, thereby increasing the carrier concentration on the front surface of the substrate <NUM> and improving the conversion efficiency of the solar cell.

Although the present disclosure has been disclosed above in terms of preferred embodiments, the preferred embodiments are not intended to limit the claims. Any person skilled in the art may make some possible changes and modifications without departing from the scope of the claims.

Claim 1:
A solar cell, comprising:
a substrate (<NUM>) having a front surface and a back surface opposite to the front surface;
a first passivation layer (<NUM>), a second passivation layer (<NUM>) and a third passivation layer (<NUM>) sequentially formed on the front surface of the substrate (<NUM>) and in a direction away from the substrate (<NUM>); wherein the first passivation layer (<NUM>) includes a dielectric material; the second passivation layer (<NUM>) includes a first silicon nitride material, and a ratio of a number of nitrogen atoms to a number of silicon atoms in the first silicon nitride material is in a range of <NUM> to <NUM>; and the third passivation layer (<NUM>) includes a silicon oxide material, and a ratio of a number of oxygen atoms to a number of silicon atoms in the silicon oxide material is in a range of <NUM> to <NUM>; and
a tunneling oxide layer (<NUM>) and a doped conductive layer (<NUM>) sequentially formed on the back surface of the substrate (<NUM>) and in a direction away from the back surface, wherein the doped conductive layer (<NUM>) and the substrate (<NUM>) are doped to have a same conductivity type;
characterized in that
the third passivation layer (<NUM>) includes a first silicon oxide sub-layer (<NUM>), a second silicon oxide sub-layer (<NUM>), and a third silicon oxide sub-layer (<NUM>) stacked in the direction away from the substrate, wherein the first silicon oxide sub-layer (<NUM>), the second silicon oxide sub-layer (<NUM>), and the third silicon oxide sub-layer (<NUM>) each includes
a silicon oxide material, and refractive indices of the first silicon oxide sub-layer (<NUM>), the second silicon oxide sub-layer (<NUM>), and the third silicon oxide sub-layer (<NUM>) gradually decrease; and
wherein a ratio of a number of oxygen atoms to a number of silicon atoms of the silicon oxide material of the first silicon oxide sub-layer (<NUM>) is in a range of <NUM> to <NUM>, a ratio of a number of oxygen atoms to a number of silicon atoms of the silicon oxide material of the second silicon oxide sub-layer (<NUM>) is in a range of <NUM> to <NUM>, and a ratio of a number of oxygen atoms to a number of silicon atoms of the silicon oxide material of the third silicon oxide sub-layer is in a range of <NUM> to <NUM>.