Solar cell and solar cell module

Embodiments of the present disclosure provide a solar cell and a solar cell module. The solar cell includes a first region and a second region, and further includes a substrate having a first surface and a second surface; a tunneling layer covering the second surface; a first emitter disposed on part of the tunneling layer in the first region; and a second emitter disposed on part of the tunneling layer in the second region and on the first emitter, a conductivity type of the second emitter being different from a conductivity type of the first emitter. The solar cell further includes a first electrode disposed in the first region and configured to electrically connect with the first emitter by penetrating through the second emitter; and a second electrode disposed in the second region and configured to electrically connect with the second emitter.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority to Chinese Patent Application No. 202110738433.7 filed on Jun. 30, 2021, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a photovoltaic technique, in particular to a solar cell and a solar cell module.

BACKGROUND

A solar cell is a photovoltaic device for converting solar radiation energy to electric energy. The solar cell includes a light receiving surface facing the sun to collect the solar radiation energy during normal operation, and a rear surface opposite to the light receiving surface. In an interdigitated back-contact (IBC) solar cell, electrodes and emitters corresponding to the electrodes are formed on the rear surface of the solar cell. An external circuit, such as a load, may be connected to the electrodes of the solar cell for power supply.

In order to enhance the commercial value of the IBC solar cell, it is desired to improve electrical performance of the solar cell and reduce preparation cost of the IBC solar cell.

SUMMARY

Some embodiments of the present disclosure provide a solar cell and a solar cell module, which are beneficial to improving the electrical performance of the solar cell and reducing the preparation cost of the solar cell.

Some embodiments of the present disclosure provide a solar cell, which includes a first region and a second region, and includes a substrate having a first surface and a second surface; a tunneling layer covering the second surface; a first emitter disposed on the tunneling layer of the first region; a second emitter disposed on the tunneling layer of the second region and on the first emitter, a conductivity type of the second emitter being different from a conductivity type of the first emitter; a first electrode disposed in the first region and configured to electrically connect with the first emitter by penetrating through the second emitter; and a second electrode disposed in the second region and configured to electrically connect with the second emitter.

In some embodiments, a sidewall surface of the first emitter is in contact with a sidewall surface of the second emitter.

In some embodiments, the second emitter has a thickness of 30 nm to 200 nm in a direction perpendicular to the second surface.

In some embodiments, a substrate of the second region is convex relative to a substrate of the first region at the second surface of the substrate, the first emitter has a third surface facing away from the tunneling layer, the second emitter has a fourth surface in contact with the tunneling layer, and the third surface is flush with or lower than the fourth surface in a direction away from the second surface of the substrate.

In some embodiments, the tunneling layer includes a first dielectric layer and a second dielectric layer, where the first dielectric layer is disposed between the first emitter and the substrate, the second dielectric layer is configured to cover the second surface of the substrate of the second region and cover a third surface and a sidewall of the first emitter, the third surface is a surface of the first emitter facing away from the first dielectric layer, the second emitter is disposed on the second dielectric layer, and the first electrode is further configured to electrically connect with the first emitter by penetrating through the second dielectric layer.

In some embodiments, a material of the second dielectric layer is different from a material of the first dielectric layer.

In some embodiments, a material of the first dielectric layer includes at least one of oxygen silicide, nitrogen silicide and carbon silicide.

In some embodiments, the second emitter includes a first doped portion and a second doped portion, at least part of the second doped portion is disposed between the first doped portion and the first electrode, a doping concentration of the first doped portion is greater than or equal to a doping concentration of the second doped portion, and doping concentrations of different regions of the second doped portion decreases in a direction of the first doped portion towards the first electrode.

In some embodiments, a concentration gradient of the second doped portion is in a range of 5E16 atoms×cm−3/cm to 2E22 atoms×cm−3/cm.

In some embodiments, a width of the second doped portion is greater than 20 μm in the direction of the first doped portion towards the first electrode.

In some embodiments, the conductivity type of the first emitter is P type, and the conductivity type of the second emitter is N type.

Some embodiment of the present disclosure further provide a solar cell module, which includes: a cell string formed by connecting any one of the above-described solar cells; an encapsulation film configured to cover a surface of the cell string; and a cover plate configured to cover a surface of the encapsulation film facing away from the cell string.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings in order to make the objectives, technical solutions and advantages of the present disclosure clearer. However, it will be apparent to those skilled in the art 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.

Referring toFIGS.1and2, a solar cell includes a first region101and a second region102. In other words, the first region101corresponds to a first portion of the solar cell, and the second region102corresponds to a second portion of the solar cell. In some embodiments, the solar cell includes a substrate10, a tunneling layer11, a first emitter12, a second emitter13, a first electrode15and a second electrode16. The substrate10has a first surface10aand a second surface10b. The tunneling layer11covers the second surface10b. The first emitter12is disposed on the tunneling layer11of the first region101. The second emitter13is disposed on the tunneling layer11of the second region102and on the first emitter12. The first emitter12and the second emitter13have different conductivity types. The first electrode15is disposed in the first region101, and is configured to electrically connect with the first emitter12by penetrating through the second emitter13. Herein, the first electrode15penetrates through the second emitter13means that the first electrode15may be in contact with the second emitter13. The second electrode16is disposed in the second region102and is configured to electrically connect with the second emitter13.

In some embodiments, a material of the substrate10is a silicon material, which may include one or more of monocrystalline silicon, polycrystalline silicon, amorphous silicon and microcrystalline silicon. In other embodiments, the material of the substrate may also be a carbon simple substance, an organic material or a multinary compound. The multicomponent compound may include, but is not limited to, perovskite, gallium arsenide, cadmium telluride, copper indium selenium, etc.

In some embodiments, the first surface10ais designated as a light receiving surface, the second surface10bis a rear surface opposite to the light receiving surface. The first surface10amay be set as a pyramid textured surface to reduce the reflection of light on the first surface10a, thus increasing an absorption and utilization rate of the light and improving the conversion efficiency of the solar cell. The solar cell may further include a first passivation layer14covering surfaces of the first emitter12and the second emitter13facing away from the substrate10. A material of the first passivation layer14may include one or more of silicon nitride, silicon oxynitride, silicon carbonitride oxide, titanium oxide, hafnium oxide, aluminum oxide and the like. Accordingly, the solar cell may further include a second passivation layer17covering the first surface10a. A material of the second passivation layer17may be silicon nitride, or silicon oxide, etc.

In some embodiments, the substrate10includes an N-type doping element (such as phosphorus, arsenic, etc.) and the substrate10is N-type substrate; the first emitter12includes a P-type doping element; the second emitter13includes an N-type doping element. The first emitter12and the substrate10form a PN junction. The first electrode15connected with the first emitter12serves as a positive electrode of the solar cell, and the second electrode16connected with the second emitter13serves as a negative electrode of the solar cell. In other embodiments, the first emitter12includes an N-type doping element, the second emitter13includes a P-type doping element; the second emitter13and the substrate10form a PN junction.

It should be noted that although the first emitter12and the second emitter13are in direct contact in the structure shown inFIG.1, it does not mean that the positive electrode and the negative electrode of the solar cell are short-circuited. This is because the first emitter12and the second emitter13contain different types of doped ions, and the same typed carriers in the first emitter12and the second emitter13have greatly different transmission efficiencies. That is, under the condition of a same transmission path length, a transmission path resistance of the same typed carriers in different emitters is greatly different, which makes the carriers in the first emitter12always tend to flow out through the first electrode15. Besides, since the second emitter13generally has a relatively thin thickness and a relatively small cross-sectional area in a direction perpendicular to the second surface10b, a resistance that the carriers in the second emitter13needs to be resisted for a transverse transmission is much greater than a resistance that needs to be resisted for a direct convergence toward the second electrode16. Therefore, carriers flowing through the tunneling layer11to the second emitter13always tend to converge toward the second electrode16. That is to say, even if the first emitter12and the second emitter13with different conductivity types are in contact with each other, due to a restriction of the transmission path resistance, the solar cell has obviously discrete positive electrode and negative electrode, and the positive electrode and negative electrode of the solar cell may not have obvious short-circuit problem. The present structure overcomes the prejudice of the existing technologies.

In some embodiments, a sidewall surface of the first emitter12is in contact with a sidewall surface of the second emitter13. Further, in the direction perpendicular to the second surface10b, the second emitter13has a thickness of 30 nm to 200 nm, such as 40 nm, 70 nm, 90 nm, 120 nm, 150 nm, 160 nm or the like. If the thickness of the second emitter13is less than the above threshold, the field passivation effect of the second emitter13of the second region102may be relatively weak, and the second region102may have a relatively serious carrier recombination problem. If the thickness of the second emitter13is greater than the above threshold, then the resistance of the carriers in the second emitter13for the transverse transmission is relatively small, and the carriers in the second emitter13of the second region102is more likely to undergo the transverse transmission to move into the first electrode15, which is not conducive to suppressing the short circuit problem between the first emitter12and the second emitter13.

Further, by configuring the first electrode15away from the second region102, a path resistance of the carriers in the second emitter13of the second region102to the first electrode15may be increased, and thus a short-circuit current between the first electrode15and the second electrode16may be suppressed. Similarly, by configuring the second electrode16to extend into the second emitter13, a path resistance of the carriers in the second region102to the second electrode16may be decreased, and the carriers may be promoted to converge toward the second electrode16.

In some embodiments, the substrate10has a substantially flat second surface10b. In some embodiments, the flat second surface10bcan be formed by a polishing process. A surface of the first emitter12facing the substrate10is flush with a surface of the second emitter13of the second region102facing the substrate10. The second emitter13covers the sidewall surface of the first emitter12. A specific process for forming the above structure includes: providing the substrate10with the second surface10band the tunneling layer11with a uniform film thickness; sequentially performing a maskless deposition process and a patterned etching process to form the patterned first emitter12; and performing a second maskless deposition process to form the second emitter13. That is to say, the above structure may be formed by performing the patterned etching process once. Compared with a traditional process of performing patterned etching processes twice, which respectively configures the positions of the first emitter12and the second emitter13, it is beneficial to reducing the accuracy alignment requirements and the number of masks required, thus improving the electrical performance of the solar cell and reducing the preparation cost of the solar cell.

In some embodiments, compared with a textured surface, configuring the flat second surface10bis also beneficial to preventing a sunlight incident on the first surface10afrom being transmitted out of the second surface10b, thereby reducing the light transmission loss of the solar cell and improving the light absorption efficiency of the solar cell.

In some embodiments, referring toFIG.3, the substrate20of the second region202is convex relative to the substrate20of the first region201, e.g., at the second surface20bof the substrate20. Herein, the substrate20of the second region202refers to a first portion of the substrate20corresponding to the second region, and the substrate20of the first region201refers to a second portion of the substrate20corresponding to the first region. The first emitter22has a third surface (not labeled) facing away from the tunneling layer21. The second emitter23has a fourth surface (not labeled) in contact with the tunneling layer21. The third surface is flush with or lower than the fourth surface, e.g., in a direction away from the second surface20bof the substrate20. The specific process for forming the above structure includes: patterning and etching the substrate20to form a relatively concave-convex second surface20b; covering the second surface20bwith a tunnel layer21having a uniform film thickness; sequentially performing a deposition process and a planarization process to form the first emitter22disposed at the first region201, where the third surface of the first emitter22is lower than or flush with a surface of the tunneling layer21of the second region away from the substrate; performing a maskless deposition process to form the second emitter23. That is to say, the above structure may be formed by performing the patterned etching process once, and the second emitter23in the structure has a flat surface facing away from the substrate20, which is beneficial to reducing the complexity of subsequent coating of conductive paste and ensuring that the first electrode25and the second electrode26have good alignment accuracy.

Herein, when the third surface is lower than the fourth surface, a vertical distance between the third surface and the fourth surface in a direction perpendicular to the second surface20bmay be set to 0.1 μm to 5 μm, such as 1 μm, 2 μm or 3 μm.

In some embodiments, referring toFIG.4, the tunneling layer31includes a first dielectric layer311and a second dielectric layer312. The first dielectric layer311is disposed between the first emitter32and the substrate30, that is, the first dielectric layer311is only disposed in the first region301. The second dielectric layer312covers the second surface30bof the second region302as well as a third surface and a sidewall of the first emitter32. Herein, the second surface30bof the substrate30of the second region302refers to the surface of the second portion of the substrate30corresponding to the second portion302. The third surface is a surface of the first emitter32facing away from the first dielectric layer311. The second emitter33is disposed on the second dielectric layer312. The first electrode35is in electrical contact with the first emitter32by penetrating through the first passivation layer34, the second emitter33and the second dielectric layer312sequentially.

Similarly, the above structure may be formed by performing the patterned etching process once, which is used to sequentially etch a first emitter film and a first dielectric film stacked to form the first emitter32and the first dielectric layer311. In addition, the second dielectric layer312and the second emitter33may be formed by a maskless deposition process. The design of the above structure may provide the second dielectric layer312which isolates the first emitter32from the second emitter33without increasing the patterned etching process, so as to inhibit the possible carrier recombination and interpenetration of doped ions between the first emitter32and the second emitter33, and ensure the solar cell to have a relatively high photoelectric conversion efficiency.

In some embodiments, a material of the second dielectric layer312is different from a material of the first dielectric layer311. For example, a dielectric constant of the material of the second dielectric layer312is smaller than a dielectric constant of the material of the first dielectric layer311, so that the first dielectric layer311has a better tunneling effect and the second dielectric layer312has a better isolation effect. In other embodiments, a film thickness of the first dielectric layer311is different from a film thickness of the second dielectric layer312. For example, under a condition that the dielectric constant of the material of the second dielectric layer312is smaller than the dielectric constant of the material of the first dielectric layer311, and the tunneling effect of the material of the second dielectric layer312is weaker than the tunneling effect of the material of the first dielectric layer311, the film thickness of the second dielectric layer312may be set to be smaller than the film thickness of the first dielectric layer311, so that the second dielectric layer312has a good tunneling effect while meeting the isolation requirements.

The material of the second dielectric layer312is different from that of the first dielectric layer311. In a first case, the first dielectric layer311and the second dielectric layer312are respectively composed of different single materials. In a second case, the first dielectric layer311is composed of a single material, while the second dielectric layer312includes a plurality of sub-film layers, and different sub-film layers have different materials. For example, the second dielectric layer312includes a first sub-film layer (not shown) and a second sub-film layer (not shown). The first sub-film layer covers the second surface30band the surface of the first emitter32, while the second sub-film layer covers a surface of the first sub-film. In this way, a material of the first sub-film layer may be selected to make the first sub-film layer have a good passivation effect, reduce a surface defect and carrier recombination on the second surface30bof the substrate30, and a material of the second sub-film layer may be selected so that there is a good electrical isolation effect between the first emitter32and the second emitter33.

Herein, the material of the first dielectric layer311includes at least one of oxygen silicide, nitrogen silicide and carbon silicide.

In some embodiments, referring toFIG.5, the second emitter43includes a first doped portion431and a second doped portion432. At least part of the second doped portion432is disposed between the first doped portion431and the first electrode45. A doping concentration of the first doped portion431is greater than or equal to a doping concentration of the second doped portion432. Doping concentrations of different regions of the second doped portion432decreases in a direction of the first doped portion431towards the first electrode45. Compared with providing an intrinsic polysilicon between the second emitter43and the first electrode45for isolation, providing the second doped portion432with a concentration gradient is beneficial to reducing a concentration difference between different interfaces, weakening a diffusive force of doped ions in the second emitter43, preventing the intrinsic polysilicon from being uniformly doped due to a strong diffusive force, and ensuring that a contact surface between the first electrode45and the second doped portion432has a relatively large contact resistance, thereby suppressing a short-circuit current between the first electrode45and the second emitter43.

In a case that a doping concentration of a surface layer of the second doped portion432facing the first doped portion431may be regarded as equal to the doping concentration of the first doped portion431, it can be understood that the smaller the concentration gradient of the second doped portion432, the smaller diffusive force of doped ions in the first doped portion431due to the concentration difference, and the better the barrier effect of the second doped portion432. Under the condition that a doping concentration range of different regions of the second doped portion432remains unchanged, the smaller the concentration gradient of the second doped portion432, the wider a width of the second doped portion432in the direction of the first doped portion431towards the first electrode45. In other words, when the width of the second doped portion432and a minimum doping concentration of the second doped portion432are unchanged, the smaller the concentration gradient of the second doped portion432, the lower the doping concentration of the first doped portion431, and the weaker a conductivity of the first doped portion431.

In some embodiments, the concentration gradient of the second doped portion432is in a range of 5E16 atoms/cm−3/cm to 2E22 atoms cm−3/cm, such as 1E21 atoms×cm−3/cm, 1E20 atoms/cm−3/cm, 1E19 atoms×cm−3/cm, 1E18 atoms×cm−3/cm or 1E17 atoms×cm−3/cm. If the concentration gradient is less than the above threshold, the width of the second doped portion432may be relatively wide to cover the second surface40bof the second region402, or the doping concentration of the first doped portion431may be relatively low, which is unfavorable for carriers in the substrate40to converge toward the second electrode46through the second emitter43. If the concentration gradient is greater than the above threshold, it is unfavorable to block the diffusion of the doped ions in the first doped portion431to the first electrode45.

In some embodiments, the width of the second doped portion432is greater than 20 μm in the direction of the first doped portion431towards the first electrode45. Under the condition that the concentration gradient of the second doped portion432and the doping concentration of the first doped portion431are unchanged, if the width of the second doped portion432is smaller than 20 μm, a doping concentration of the contact surface between the second doped portion432and the first electrode45may be relatively high, and electrical isolation effect of the second doped portion432may be relatively weak. Under the condition that the concentration gradient and the minimum doping concentration of the second doped portion432are unchanged, if the width of the second doped portion432is smaller than 20 μm, the doping concentration of the first doped portion431may be relatively small, and the carrier transmission capability of the second emitter43may be relatively weak.

It should be noted that in some embodiments, the second emitter43in contact with the tunneling layer41is only disposed on a side of the first emitter42, that is, the second region402is disposed at a side of the first region401. In this case, the second doped portion432is arranged at two sides of the first electrode45, which is used to block carriers passing through the tunneling layer41and entering the second emitter43. In other embodiments, the second region402and the first region401are alternately arranged. The second region402is disposed at two sides of part of the first region401, and the second emitter43in contact with the tunneling layer41is disposed at two sides of the first emitter42. The second doped portion432is disposed at two sides of the first electrode45.

In this embodiment, the second emitter is configured based on the first emitter. In the process for forming the first emitter and the second emitter, only one patterning process is required to form the first emitter, while the second emitter does not need a patterned etching to adjust the position accuracy after a maskless deposition process. In this way, only a position accuracy of the first emitter needs to be controlled, which is beneficial to reducing the alignment accuracy requirements in the preparation process of the solar cell; moreover, only one mask and one dry etching process are needed, which is beneficial to reducing the preparation cost of the solar cell.

An embodiment of the present disclosure further provides a solar cell, which is different from the solar structure shown inFIG.1in that the second emitter of the second region is electrically isolated from the second emitter of the first region, and there is a gap between the first emitter and the second emitter of the second region. The second emitter of the first region and the second emitter of the second region may be formed by the same process step.

An embodiment of the present disclosure further provides a solar cell module, which is configured to convert received light energy into electric energy. Referring toFIG.6, the solar cell module includes a cell string61, an encapsulation film62and a cover plate63. The cell string61is formed by connecting a plurality of solar cells, and the solar cell may be any one of the above-described solar cell (including but not limited to the solar cells shown inFIGS.1-5). The encapsulation film62may be an organic encapsulation film such as EVA or POE or PET, and the encapsulation film62covers a surface of the cell string61for sealing. The cover plate63may be a glass cover plate, a plastic cover plate or the like. The cover plate63covers a surface of the encapsulation film62facing away from the cell string61. In some embodiments, the cover plate63is provided with a light trapping structure to increase the utilization rate of an incident light. The solar cell module has a relatively high current collection capacity and a relatively low carrier recombination rate, and may realize relatively high photoelectric conversion efficiency.

Those skilled in the art should appreciate that the aforementioned embodiments are specific embodiments for implementing the present disclosure. In practice, however, various changes may be made in the forms and details of the specific embodiments without departing from the scope of the present disclosure. Any person skilled in the art may make their own changes and modifications without departing from the scope of the present disclosure, so the protection scope of the present disclosure shall be subject to the scope defined by the claims.