Solar cell and preparation method thereof

Abstract

The invention relates to the field of batteries, particularly provides a solar battery and a preparation method of the solar battery, and aims to solve the problem of serious minority carrier lifetime attenuation of the solar battery with a transparent conductive passivation layer under low injection concentration. To this end, the solar cell of the present invention comprises a first layer having a first conductivity type, a second layer having a second conductivity type, and a transparent conductive passivation layer; the second layer is arranged on the first surface of the first layer and has a second conduction type opposite to the first conduction type, so that a PN junction is formed between the first layer and the second layer; the transparent conductive passivation layer is arranged on a second surface, opposite to the first surface, of the first layer, and the transparent conductive passivation layer has a doping concentration capable of promoting majority carriers in the first layer to flow to the second surface. When the doping concentration is appropriate, the motion direction of the majority carriers can be influenced, so that the bending direction and degree of the energy band can promote the majority carriers to flow to the second surface of the first layer, and the service life of the minority carriers is prolonged.

Description

Technical Field

[0001] The invention relates to the field of solar cells, and specifically provides a solar cell and a method for preparing the solar cell. Background Art

[0002] Improving the passivation properties of crystalline silicon surface is an important means to improve the efficiency of crystalline silicon solar cells. With the advancement of technology, higher requirements are placed on the passivation dielectric film used on the surface of crystalline silicon solar cells. It is required to have excellent passivation properties, as well as the lowest possible optical parasitic absorption loss, and excellent conductive properties to prevent direct contact damage between the electrode and the crystalline silicon substrate.

[0003] The transparent conductive passivation layer is expected to become a new generation of passivation dielectric film for crystalline silicon solar cells. First, it has both field effect and chemical passivation characteristics, and its passivation structure can achieve excellent passivation performance with an implicit open circuit voltage (iVoc) > 736mV; in addition, the band gap of zinc oxide is greater than 3.2eV, which has the characteristics of high transmittance to visible light; and it can also serve as a good conductive layer. However, although the new transparent conductive passivation structure exhibits excellent passivation performance with high implicit open circuit voltage (iVoc) and low reverse saturation current density (J0), its minority carrier lifetime measured at low injection concentration is severely attenuated.

[0004] Therefore, the art needs a new solar cell and a method for preparing a solar cell to solve the problem of severe minority carrier lifetime decay under low injection concentration in a solar cell with a transparent conductive passivation layer. Summary of the invention

[0005] The present invention aims to solve the above technical problem, namely, to solve the problem that the minority carrier lifetime is seriously attenuated under low injection concentration in a solar cell having a transparent conductive passivation layer.

[0006] In a first aspect, the present invention provides a solar cell, comprising a first layer, the first layer having a first conductivity type; a second layer, the second layer being arranged on a first surface of the first layer, the second layer having a second conductivity type opposite to the first conductivity type, so that a PN junction is formed between the first layer and the second layer; and a transparent conductive passivation layer, wherein the transparent conductive passivation layer is arranged on a second surface of the first layer opposite to the first surface, the transparent conductive passivation layer having a doping concentration capable of causing majority carriers in the first layer to flow to the second surface.

[0007] When the above scheme is adopted, when the doping concentration is appropriate, the transparent conductive passivation layer can make its own work function match the work function of the first layer, thereby affecting the movement direction of the majority carriers, that is, the direction and degree of band bending at the doping concentration can prompt the majority carriers to flow to the second surface of the first layer, thereby improving the minority carrier lifetime and helping to improve the fill factor.

[0008] In an optional technical solution of the above solar cell, the first layer is a p-type substrate and the second layer is an n-type doped layer; or the first layer is a p-type doped layer and the second layer is an n-type substrate; the transparent conductive passivation layer includes an intrinsic transparent conductive passivation layer, and the intrinsic transparent conductive passivation layer is arranged on the second surface.

[0009] When the above technical solution is adopted, due to the use of an intrinsic transparent conductive passivation layer with extremely low doping concentration, it can have a higher work function, thereby forming a better work function match with the p-type substrate or p-type doped layer, preventing the reduction of minority carrier lifetime caused by electron enrichment on the surface of the p-type substrate or p-type doped layer.

[0010] In an optional technical solution of the above-mentioned solar cell, the transparent conductive passivation layer also includes a first doped transparent conductive passivation layer, and the first doped transparent conductive passivation layer is arranged on a side of the intrinsic transparent conductive passivation layer away from the first layer, wherein gradient doping is formed in the first doped transparent conductive passivation layer, and the doping concentration on the side close to the intrinsic transparent conductive passivation layer is less than the doping concentration on the side away from the intrinsic transparent conductive passivation layer.

[0011] When the above technical solution is adopted, it is beneficial to improve the field effect passivation performance on the side with low doping concentration, while the high doping concentration on the other side ensures the high transmittance and high lateral conductivity of the transparent conductive passivation layer.

[0012] In an optional technical solution of the above solar cell, the solar cell further includes a first passivation layer, the first passivation layer is arranged between the second surface and the intrinsic transparent conductive passivation layer, and the first passivation layer carries a fixed negative charge.

[0013] When the above technical solution is adopted, for the p-type substrate or p-type doped layer, the majority carriers are holes. Since the first passivation layer itself carries a fixed negative charge, the holes can be enriched on the surface of the p-type substrate or the p-type doped layer. In other words, the majority carriers are enriched on the surface of the p-type substrate or the p-type doped layer, thereby increasing the minority carrier lifetime, preventing inversion, and improving the field effect passivation capability.

[0014] In an optional technical solution of the above solar cell, the first passivation layer is doped with a first conductive doping source.

[0015] When the above technical solution is adopted, the conductivity of the passivation structure can be improved and the contact resistance can be reduced.

[0016] In an optional technical solution of the above solar cell, the first layer is an n-type substrate and the second layer is a p-type doped layer; or the first layer is an n-type doped layer and the second layer is a p-type substrate; a second doped transparent conductive passivation layer is provided on the second surface.

[0017] When the above technical solution is adopted, the energy band of the silicon at the contact interface is further bent downward, which is beneficial to the formation of electron enrichment on the surface of the n-type substrate or the n-type doped layer and improves the minority carrier lifetime.

[0018] In the optional technical solution of the above solar cell, the doping concentration range of the second doped transparent conductive passivation layer is 3E20cm -3 -8E20cm -3 .

[0019] In the case of adopting the above technical solution, three values ​​within the doping concentration range are selected as embodiments, wherein the doping concentration of embodiment 1 is 8E20cm -3 , the doping concentration of Example 2 is 5E20cm -3 , the doping concentration of Example 3 is 3E20cm -3 Two comparative examples were selected, where the doping concentration of comparative example 1 was 5E19cm -3 , Comparative Example 2 is intrinsic and undoped. Figure 5 The experimental results of Examples 1-3 and Comparative Examples 1-2 show that the doping concentration ranges from 3E20cm -3 -8E20cm -3 Compared with comparative examples 1-2, the minority carrier lifetime is significantly improved; and within this doping concentration range, it has excellent passivation performance with low reverse saturation current density and high implicit open circuit voltage. The above experimental results show that the present invention can improve the minority carrier lifetime while ensuring the excellent passivation performance of the transparent conductive passivation structure.

[0020] In an optional technical solution of the above solar cell, the solar cell further includes a second passivation layer disposed between the second surface and the second doped transparent conductive passivation layer, and the second passivation layer carries a fixed positive charge.

[0021] When the above technical solution is adopted, since the second passivation layer carries a fixed positive charge, the negative charge of the n-type substrate or the n-type doped layer can be derived, so that the surface of the n-type substrate or the n-type doped layer is in a negative charge-enriched state, thereby increasing the minority carrier lifetime and optimizing the field effect passivation.

[0022] In an optional technical solution of the above solar cell, the second passivation layer includes a first sublayer and a second sublayer stacked in sequence in a direction away from the second surface, wherein the second sublayer is a doped layer, and the first sublayer and the second sublayer as a whole carry a fixed positive charge.

[0023] When the above technical solution is adopted, the first sublayer is used to adjust the overall charge amount of the second passivation layer so that the second passivation layer is positively charged as a whole. Specifically, the first sublayer itself can carry a fixed positive charge to prevent the doping layer with a fixed negative charge from causing the surface of the silicon substrate to form an inversion. By arranging a doping layer on the side of the first sublayer away from the substrate, the doping can be increased, such as doping silicon oxide with aluminum, which is equivalent to a high doping concentration at the contact interface of the silicon substrate, thereby performing a high doping, thereby appropriately reducing the work function, adjusting the band bending of the crystalline silicon interface, and preventing the occurrence of charge transfer caused by work function mismatch.

[0024] In an optional technical solution of the above solar cell, the doping layer is doped with a second conductive doping source.

[0025] When the above technical solution is adopted, the conductivity of the passivation structure can be improved and the contact resistance can be reduced.

[0026] In an optional technical solution of the solar cell described above, a second doped transparent conductive passivation layer is provided on a surface of the second layer away from the first layer.

[0027] In the optional technical solution of the above solar cell, the doping concentration range of the second doped transparent conductive passivation layer is 3E20cm -3 -8E20cm -3 .

[0028] In an optional technical solution of the above solar cell, the solar cell further comprises a second passivation layer provided between a surface of the second layer away from the first layer and the second doped transparent conductive passivation layer, and the second passivation layer carries a fixed positive charge.

[0029] In an optional technical solution of the above solar cell, the second passivation layer includes a first sublayer and a second sublayer stacked in sequence in a direction away from the second layer, wherein the second sublayer is a doped layer, and the first sublayer and the second sublayer as a whole carry a fixed positive charge.

[0030] In an optional technical solution of the above solar cell, the doping layer is doped with a second conductive doping source.

[0031] On the other hand, the present invention also provides a method for preparing a solar cell, characterized in that it includes: forming a second layer on a first surface of a first layer of a first conductive type, the second layer having a second conductive type opposite to the first conductive type, so that a PN junction is formed between the first layer and the second layer; forming a transparent conductive passivation layer, wherein the transparent conductive passivation layer is formed on a second surface of the first layer opposite to the first surface, the transparent conductive passivation layer having a doping concentration that can cause majority carriers in the first layer to flow to the second surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

[0033] Figure 1 It is a schematic structural diagram of a first possible implementation mode of a solar cell of the present invention;

[0034] Figure 2 is a schematic structural diagram of a second possible implementation mode of a solar cell of the present invention;

[0035] Figure 3 is a schematic structural diagram of a third possible implementation mode of a solar cell of the present invention;

[0036] Figure 4 is a schematic structural diagram of a fourth possible implementation mode of a solar cell of the present invention;

[0037] Figure 5 This is an experimental data table of different doping concentrations of the second doped transparent conductive passivation layer.

[0038] Description of reference numerals:

[0039] 11-n-type substrate; 12-p-type doped layer; 13-p-type substrate; 14-n-type doped layer; 2-first passivation layer; 3-intrinsic transparent conductive passivation layer; 4-first doped transparent conductive passivation layer; 5-third passivation layer; 6-first electrode; 7-second passivation layer; 71-first sublayer; 72-second sublayer; 8-second doped transparent conductive passivation layer; 9-fourth passivation layer; 10-second electrode. DETAILED DESCRIPTION

[0040] First of all, it should be noted that the following embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. In order to better illustrate the present invention, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present invention can also be implemented without certain specific details.

[0041] It should be noted that in the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. In addition, it should be understood that the first feature may be disposed, connected or formed on the second feature in direct contact or in contact with the first feature and the second feature through an intermediate medium.

[0042] After research, it was found that when a transparent conductive passivation layer is used to passivate doped single-crystal silicon, charge transfer will occur due to work function mismatch, causing the silicon at the contact interface to undergo band bending and form an inversion (i.e., the majority carrier concentration on the silicon side is reduced and the minority carriers are enriched). The direct result of this mechanism is a reduction in the field effect passivation performance, which is manifested in the severe attenuation of the minority carrier lifetime measured for the passivation structure at low injection concentrations. The adverse effect when applied to the battery end is a reduction in the fill factor.

[0043] Based on this, the present invention provides a solar cell, the solar cell comprising a first layer having a first conductivity type and a second layer having a second conductivity type, the first conductivity type being opposite to the second conductivity type, and the second layer being arranged on a first surface of the first layer so that a PN junction is formed between the first layer and the second layer. Specifically, the first layer may be a substrate, and the second layer may be a doped layer; or the first layer may be a doped layer, and the second layer may be a substrate.

[0044] The substrate of the present invention can be a crystalline silicon substrate, and the resistivity of the substrate is preferably 5Ω·cm-20Ω·cm. The substrate can be an n-type substrate or a p-type substrate. When the substrate is an n-type substrate, it is formed by doping pentavalent elements (such as phosphorus, arsenic, and antimony) into the semiconductor. These pentavalent elements provide additional electrons in the silicon lattice. Therefore, the n-type substrate uses free electrons as the majority carriers; then the n-type substrate is p-type doped, for example, by diffusion or ion implantation, trivalent elements (such as boron) are infiltrated or injected into the surface of the n-type substrate to form a p-type doped layer. The p-type substrate is a region formed by doping trivalent elements (such as boron, indium, and gallium) into semiconductor materials; the trivalent elements introduce holes in the silicon lattice, and these holes become majority carriers, thereby giving the region p-type conductivity; then the p-type substrate is n-doped, for example, pentavalent elements (such as phosphorus, arsenic, and antimony) are introduced into the surface of the p-type substrate by diffusion or ion implantation to form an n-type doped layer, so as to construct a pn junction.

[0045] When the first conductivity type of the first layer is p-type, the first layer can be a p-type substrate, in which case the second layer is an n-type doped layer; of course, the first layer can also be a p-type doped layer on an n-type substrate, in which case the second layer is an n-type substrate. When the first conductivity type of the first layer is n-type, the first layer can be an n-type substrate, in which case the second layer is a p-type doped layer; of course, the first layer can also be an n-type doped layer on a p-type substrate, in which case the second layer is a p-type substrate.

[0046] The solar cell of the present invention further comprises a transparent conductive passivation layer, which is arranged on a second surface of the first layer opposite to the first surface and has a doping concentration capable of causing the majority carriers in the first layer to flow to the second surface.

[0047] Among them, the transparent conductive passivation layer has a doping concentration that can cause the majority carriers in the first layer to flow to its second surface, that is, when the doping concentration is appropriate, the transparent conductive passivation layer can make its own work function match the work function of the first layer, thereby being able to affect the movement direction of the majority carriers, that is, the direction and degree of band bending under the doping concentration can cause the majority carriers to flow to the second surface of the first layer, thereby increasing the minority carrier lifetime, which is beneficial to improving the fill factor.

[0048] The first possible implementation:

[0049] Reference Figure 1 The substrate of the solar cell is a p-type substrate 13, and an n-type doped layer 14 is formed on the front side of the p-type substrate 13. The solar cell includes a first passivation structure, and the first passivation structure includes a p-type doped layer 12 and a first passivation layer 2. The p-type doped layer 12 and the first passivation layer 2 are sequentially arranged on the back side of the p-type substrate 13, and the first passivation layer 2 carries a fixed negative charge. Among them, the function of the p-type doped layer 12 is to form a back field, which is beneficial to the selective transmission of holes. The p-type doped layer 12 includes but is not limited to one or more combinations of single crystal silicon, polycrystalline silicon, microcrystalline silicon, nanocrystalline silicon, and amorphous silicon, and the thickness is preferably 0-2um, and it is possible that its doping concentration is 5E18cm -3 -5E20cm -3. Preferably, the first passivation layer 2 is an aluminum oxide layer. For the p-type substrate 13, the majority carriers are holes. Since the aluminum oxide layer itself carries a fixed negative charge, the holes can be enriched on the back side of the p-type substrate 13, that is, the majority carriers are enriched on the back side of the p-type substrate 13, thereby increasing the minority carrier lifetime, preventing inversion, and improving the field effect passivation capability. It should be noted that although the above-mentioned first passivation layer 2 is described using the aluminum oxide layer as an example, this is not intended to limit the scope of protection of the present invention, as long as it can carry a fixed negative charge, such as aluminum nitride (AlN), etc., these adjustments do not deviate from the principles of the present invention and are within the scope of protection of the present invention.

[0050] Possibly, the first passivation layer 2 is doped with a first conductive doping source to improve its conductivity and reduce contact resistance. Preferably, the first conductive doping source is preferably titanium tetrachloride, and the ratio of aluminum oxide / titanium oxide formed after doping is preferably 1:1-3:1. It should be noted that the above-mentioned first conductive doping source is only exemplary, and as long as it can improve conductivity and reduce contact resistance, the adjustment of its specific form does not deviate from the principle of the present invention and is within the protection scope of the present invention.

[0051] Possibly, the first passivation structure includes a transparent conductive passivation layer, which includes an intrinsic transparent conductive passivation layer 3 arranged on the side of the first passivation layer 2 away from the p-type substrate 13, and also includes a first doped transparent conductive passivation layer 4, which is arranged on the side of the intrinsic transparent conductive passivation layer 3 away from the p-type substrate 13; gradient doping is formed in the first doped transparent conductive passivation layer 4, and the doping concentration on the side close to the intrinsic transparent conductive passivation layer 3 is less than the doping concentration on the side away from the intrinsic transparent conductive passivation layer 3.

[0052] The intrinsic transparent conductive passivation layer 3 includes but is not limited to zinc oxide, tin oxide, titanium oxide, etc. The intrinsic transparent conductive passivation layer 3 doped with extremely low concentration can have a higher work function, so that it can form a better work function match with the p-type substrate 13, weaken the bending degree of the silicon energy band, and promote the p-type substrate 13 holes to enrich to the back of the p-type substrate 13, and prevent the reduction of minority carrier lifetime caused by electron enrichment on the surface of the p-type substrate 13. The first doped transparent conductive passivation layer 4 includes but is not limited to zinc oxide, tin oxide, titanium oxide, etc., wherein the majority carrier concentration after doping on the side close to the intrinsic transparent conductive passivation layer 3 is preferably 0.8E20cm -3 -2E20cm -3 The peak majority carrier concentration on the side away from the intrinsic passivation dielectric film is preferably 5E20cm -3 -8E20cm -3The above-mentioned gradient doping is conducive to improving the field effect passivation performance on the side with low doping concentration, while the high doping concentration on the other side ensures the high transmittance and high lateral conductivity of the transparent conductive passivation layer.

[0053] Possibly, the first passivation structure further includes a third passivation layer 5 , which is disposed on a side of the first doped transparent conductive passivation layer 4 away from the p-type substrate 13 , and is used to provide chemical passivation for dangling bonds on the surface of the p-type substrate 13 .

[0054] Possibly, the third passivation layer 5 includes but is not limited to one or more combinations of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, indium tin oxide, and titanium oxide, and its function is to provide free hydrogen to chemically passivate the dangling bonds on the surface of the crystalline silicon p-type substrate 13 .

[0055] Possibly, the first electrode 6 of the solar cell penetrates the third passivation layer 5 and contacts the first doped transparent conductive passivation layer 4. A hole can be opened in the third passivation layer 5 by photolithography and etching processes, so that the first electrode 6 directly contacts the first doped transparent conductive passivation layer 4 below through the hole. After the hole is opened, a metal material can be deposited on the electrode area by physical vapor deposition or electroplating process to form the first electrode 6. After the first electrode 6 is deposited, a post-processing process, such as annealing, can be performed to optimize the contact interface between the first electrode 6 and the transparent conductive passivation layer, reduce the contact resistance, and improve the overall performance of the battery. Of course, the above introduction is not restrictive, and the first electrode 6 can also be formed by screen printing. These adjustments do not deviate from the principles of the present invention and are within the scope of protection of the present invention. In the above-mentioned setting, the first electrode 6 can penetrate the third passivation layer 5 and contact the transparent conductive passivation layer, avoiding damage caused by direct contact with the substrate, and can effectively protect the substrate; it also avoids the formation of a high load in the contact area caused by direct contact between the first electrode 6 and the crystalline silicon substrate, thereby improving efficiency.

[0056] Possibly, the method for preparing the solar cell mentioned above comprises:

[0057] Step S101: forming an n-type doping layer on the front surface of a p-type substrate.

[0058] Step S102: forming a p-type doping layer on the back side of the p-type substrate.

[0059] Step S103: forming a first passivation layer with fixed negative charge on a side of the p-type doped layer away from the substrate.

[0060] For example, a first passivation layer, preferably an aluminum oxide layer, is formed on the side of the p-type doped layer away from the substrate by atomic deposition. When forming the aluminum oxide layer, the source is a combination of trimethylaluminum and water, the flow ratio of trimethylaluminum and water can be controlled at 1:1-3:1, the reaction temperature can be controlled at 100°C-250°C, and aluminum oxide is deposited layer by layer through multiple cycles of reaction, preferably with a thickness controlled at 0.5nm-2nm. During the above deposition process, the aluminum oxide passivation layer will spontaneously carry a fixed negative charge when it is formed, which is related to the intrinsic properties of the aluminum oxide material. Specifically, the aluminum oxide surface will generate a fixed negative charge during the formation process due to the formation of chemical bonds and inherent defect states in the material (such as oxygen vacancies), thereby effectively passivating the surface of the p-type substrate.

[0061] When depositing the first passivation layer, appropriate doping may be performed to improve the conductivity of the entire passivation structure and reduce the contact resistance. The doping source is preferably titanium tetrachloride, and the ratio of aluminum oxide to titanium oxide is preferably 1-3:1.

[0062] Step S103: forming an intrinsic transparent conductive passivation layer on a side of the first passivation layer away from the substrate.

[0063] Preferably, an intrinsic transparent conductive passivation layer may be formed on the side of the first passivation layer away from the substrate by atomic deposition, and the film thickness is preferably 5 nm-10 nm.

[0064] Step S104: forming a gradient-doped first doped transparent conductive passivation layer on a side of the intrinsic transparent conductive passivation layer away from the substrate.

[0065] The doping concentration on the side close to the intrinsic transparent conductive passivation layer is less than the doping concentration on the side away from the intrinsic transparent conductive passivation layer. The first doped transparent conductive passivation layer can be prepared by atomic deposition to achieve n-type gradient doping, preferably with a film thickness of 20nm-40nm.

[0066] Step S105: forming a third passivation layer on a side of the first doped transparent conductive passivation layer away from the substrate.

[0067] The third passivation layer includes, but is not limited to, one or more combinations of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, indium tin oxide, and titanium oxide, preferably with a film thickness of 10nm-150nm. After preparation, annealing is performed to activate the passivation performance, and the annealing temperature is preferably 400-550°C. For example, when the third passivation layer includes silicon nitride, a plasma enhanced chemical vapor deposition (PECVD) method can be used for deposition. During the deposition process, since the reaction gas usually contains hydrogen (such as ammonia, NH3), hydrogen will be introduced, which helps to passivate the dangling bonds on the surface of the crystalline silicon. When the third passivation layer 5 includes aluminum oxide, it can be prepared by atomic layer deposition. The precursors used in this process are usually trimethylaluminum and water, wherein trimethylaluminum contains hydrogen elements, and hydrogen can also be introduced during the deposition process to further enhance the surface passivation effect.

[0068] It should be noted that the specific method for forming at least one of the first passivation layer 2, the intrinsic transparent conductive passivation layer 3, the first doped transparent conductive passivation layer 4, and the third passivation layer 5 is not fixed. For example, it can also be replaced by chemical vapor deposition, physical vapor deposition, etc. These adjustments do not deviate from the principles of the present invention and are within the scope of protection of the present invention.

[0069] Reference Figure 1 Possibly, the solar cell includes a second passivation structure, the second passivation structure includes a second passivation layer 7, the second passivation layer 7 is disposed on the surface of the n-type doped layer 14 away from the p-type substrate 13, and the second passivation layer 7 carries a fixed positive charge. Since the second passivation layer 7 carries a fixed positive charge, the negative charge of the n-type doped layer 14 can be derived, so that the surface of the n-type doped layer 14 is in a state of negative charge enrichment, thereby improving the minority carrier lifetime, thereby optimizing the field effect passivation.

[0070] Possibly, the second passivation layer 7 includes a first sublayer 71 and a second sublayer 72, the second sublayer 72 is a doped layer, and the first sublayer 71 and the second sublayer 72 are stacked in sequence in a direction away from the front of the p-type substrate 13. The first sublayer 71 is preferably a silicon oxide layer, and the second sublayer 72 is preferably an aluminum oxide layer, but this is not restrictive, the first sublayer 71 can also be a silicon nitride layer, etc., and the second sublayer 72 can also be an aluminum nitride layer, etc.; the first sublayer 71 is used to adjust the charge amount of the second passivation layer 7 as a whole, so that the second passivation layer 7 as a whole carries a positive charge, specifically, the first sublayer 71 itself can carry a fixed positive charge to prevent the fixed negative charge of aluminum oxide from causing the silicon substrate surface to form an inversion; by arranging a doped layer on the side of the first sublayer 71 away from the substrate, doping can be increased, such as aluminum doping of silicon oxide, which is equivalent to a high doping concentration at the silicon substrate contact interface, so that a high doping is performed, so that the work function can be appropriately reduced, the band bending of the crystalline silicon interface is adjusted, and the occurrence of charge transfer caused by work function mismatch is prevented.

[0071] It is understandable that the first sublayer 71 may have a fixed positive charge due to an intrinsic property of the material, or may be induced to form a fixed positive charge on the surface by introducing a specific defect state or doping during the deposition process. For example, nitrogen vacancies in silicon nitride may form a positive charge center inside the material, stably maintaining the positive charge distribution. Alternatively, the first sublayer 71 may have a fixed positive charge due to the influence of the deposition process, the post-processing process, etc.

[0072] Possibly, the second sublayer 72 is doped with a second conductive doping source, such as appropriately doping aluminum oxide to improve conductivity and reduce contact resistance. The second conductive doping source is preferably titanium tetrachloride, and the ratio of aluminum oxide to titanium oxide formed after doping is preferably 1:1-3:1. It should be noted that the above-mentioned second conductive doping source is only exemplary, and as long as it can improve conductivity and reduce contact resistance, the adjustment of its specific form does not deviate from the principle of the present invention and is within the scope of protection of the present invention.

[0073] Possibly, the second passivation structure includes a transparent conductive passivation layer, which includes a second doped transparent conductive passivation layer 8, and the second doped transparent conductive passivation layer 8 is arranged on the side of the second sublayer 72 away from the substrate. The second doped transparent conductive passivation layer 8 includes but is not limited to zinc oxide, tin oxide, titanium oxide, etc., and the doping type is n-type doping. Preferably, the doping concentration range of the second doped transparent conductive passivation layer 8 is 3E20cm -3 -8E20cm -3 At this doping concentration, the work function is low, so that the energy band of the silicon at the contact interface is further bent downward, which promotes the formation of electron enrichment on the surface of the n-type doped layer 14 and improves the minority carrier lifetime. The present invention selects a 5Ωcm n-type silicon substrate and adds a symmetrical second passivation structure on its front and back surfaces. Three values ​​within the doping concentration range of the second doped transparent conductive passivation layer 8 are selected as embodiments, wherein the doping concentration of embodiment 1 is 8E20cm -3 , the doping concentration of Example 2 is 5E20cm -3 , the doping concentration of Example 3 is 3E20cm -3 Two comparative examples were selected, where the doping concentration of comparative example 1 was 5E19cm -3 , Comparative Example 2 is intrinsic and undoped. Figure 5 The experimental results of Examples 1-3 and Comparative Examples 1-2 show that the doping concentration ranges from 3E20cm -3 -8E20cm -3 Compared with comparative examples 1-2, the minority carrier lifetime is significantly improved; and within this doping concentration range, it has excellent passivation performance with low reverse saturation current density and high implicit open circuit voltage. The above experimental results can reflect that the present invention can improve the minority carrier lifetime while ensuring the excellent passivation performance of the transparent conductive passivation structure.

[0074] Possibly, the second passivation structure further includes a fourth passivation layer 9, which is disposed on a side of the second doped transparent conductive passivation layer 8 away from the substrate, and the fourth passivation layer 9 is used to provide chemical passivation for dangling bonds on the surface of the substrate. Possibly, the fourth passivation layer 9 includes, but is not limited to, one or more combinations of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, indium tin oxide, and titanium oxide, and its function is to provide free hydrogen to chemically passivate dangling bonds on the surface of the crystalline silicon substrate.

[0075] Possibly, the second electrode 10 of the solar cell penetrates the fourth passivation layer 9 and contacts the second doped transparent conductive passivation layer 8. A hole can be opened in the fourth passivation layer 9 by photolithography and etching processes, so that the second electrode 10 directly contacts the second doped transparent conductive passivation layer 8 below through the hole. After the hole is opened, a metal material can be deposited on the electrode area by physical vapor deposition or electroplating process to form the second electrode 10. After the second electrode 10 is deposited, a post-processing process, such as annealing, can be performed to optimize the contact interface between the second electrode 10 and the transparent conductive passivation layer, reduce the contact resistance, and improve the overall performance of the battery. Of course, the above introduction is not restrictive, and the second electrode 10 can also be formed by screen printing. These adjustments do not deviate from the principles of the present invention and are within the scope of protection of the present invention. Since the second electrode 10 can penetrate the fourth passivation layer 9 and contact the transparent conductive passivation layer, damage caused by direct contact with the substrate is avoided, and the substrate can be effectively protected; it also avoids the formation of a high load in the contact area caused by direct contact between the second electrode 10 and the crystalline silicon substrate, thereby improving efficiency.

[0076] Possibly, the method for preparing the solar cell comprises:

[0077] Step S201: forming an n-type doping layer on the front surface of a p-type substrate.

[0078] Step S202: forming a first sub-layer on a surface of the n-type doped layer away from the substrate.

[0079] For example, a silicon oxide layer may be formed on the surface of the n-type doped layer by thermal oxidation or atomic deposition, preferably with a thickness of 0.5 nm to 1 nm.

[0080] Step S203: forming a second sub-layer on a side of the first sub-layer away from the substrate.

[0081] The second sublayer is a doped layer. For example, an aluminum oxide layer is formed on the side of the silicon oxide layer away from the substrate by atomic layer deposition. The source is a combination of trimethylaluminum and water, the flow ratio of trimethylaluminum and water can be controlled at 1:1-3:1, the reaction temperature can be controlled at 100°C-250°C, and aluminum oxide is deposited layer by layer through multiple cycles of reaction, preferably with a thickness of 0.5nm-2nm.

[0082] Step S304: forming a second doped transparent conductive passivation layer on a side of the second sub-layer away from the substrate.

[0083] For example, the second doped transparent conductive passivation layer is formed by atomic deposition, preferably with a film thickness of 10nm-50nm, and the doping type is n-type doping. The majority carrier concentration after doping is preferably 3E20cm -3 -8E20cm -3 .

[0084] Step S305: forming a fourth passivation layer on a side of the second doped transparent conductive passivation layer away from the substrate.

[0085] The fourth passivation layer includes, but is not limited to, one or more combinations of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, indium tin oxide, and titanium oxide, preferably with a film thickness of 10nm-150nm. After preparation, annealing is performed to activate the passivation performance, and the annealing temperature is preferably 400℃-550℃. For example, when the fourth passivation layer includes silicon nitride, a plasma enhanced chemical vapor deposition (PECVD) method can be used for deposition. During the deposition process, since the reaction gas usually contains hydrogen (such as ammonia, NH3), hydrogen will be introduced, which helps to passivate the dangling bonds on the surface of the crystalline silicon. When the fourth passivation layer includes aluminum oxide, atomic layer deposition can be used for preparation. The precursors used in this process are usually trimethylaluminum and water, wherein trimethylaluminum contains hydrogen elements, and hydrogen can also be introduced during the deposition process to further enhance the surface passivation effect.

[0086] It should be noted that the specific method for forming at least one of the first sublayer 71, the second sublayer 72, the second doped transparent conductive passivation layer 8, and the fourth passivation layer 9 is not fixed. For example, it can also be replaced by chemical vapor deposition, physical vapor deposition, etc. These adjustments do not deviate from the principles of the present invention and are within the protection scope of the present invention.

[0087] It should be noted that although the present invention is introduced by taking the example that the above-mentioned first passivation structure is formed on the back side of the p-type substrate 13 and the above-mentioned second passivation structure is formed on the side of the n-type doping layer 14 away from the substrate, this is not intended to limit the scope of protection of the present invention. For example, one of the first passivation structure and the second passivation structure can be omitted.

[0088] The second possible implementation is:

[0089] Reference Figure 2The substrate of the solar cell of this embodiment is a p-type substrate 13, and the n-type doping layer 14 is formed on the back of the p-type substrate 13. In this case, the p-type doping layer 12, the first passivation layer 2, the intrinsic transparent conductive passivation layer 3, the first doped transparent conductive passivation layer 4 and the third passivation layer 5 are sequentially formed on the front of the p-type substrate 13. The p-type doping layer 12 of this embodiment acts on the front field, which is conducive to the selective transmission of holes. It can be made of single crystal silicon, the doping layer thickness can be 0um-2um, and the doping concentration can be 5E18cm -3 -5E20cm -3 . And / or a first sublayer 71, a second sublayer 72, a second doped transparent conductive passivation layer 8 and a fourth passivation layer 9 are sequentially formed on the side of the n-type doped layer 14 away from the substrate. Among them, the specific structures and functions of the first passivation layer 2, the intrinsic transparent conductive passivation layer 3, the first doped transparent conductive passivation layer 4, the third passivation layer 5, the first sublayer 71, the second sublayer 72, the second doped transparent conductive passivation layer 8 and the fourth passivation layer 9 are similar to those in the first possible implementation manner, and are not described in detail.

[0090] A third possible implementation:

[0091] like Figure 3 As shown, the substrate of the solar cell is an n-type silicon substrate 11, and a p-type doped layer 12 is formed on the front side of the n-type silicon substrate 11. In this case, an n-type doped layer 14, a first sublayer 71, a second sublayer 72, a second doped transparent conductive passivation layer 8 and a fourth passivation layer 9 are sequentially formed on the back side of the n-type silicon substrate 11. The n-type doped layer 14 of this embodiment acts on the back field, which is beneficial to the selective transmission of electrons. Among them, the n-type doped layer 14 includes but is not limited to one or more combinations of single crystal silicon, polycrystalline silicon, nanocrystalline silicon, and amorphous silicon, with a thickness of 0um-2um and a doping concentration of 1E19cm -3 -5E20cm -3 . And / or a first passivation layer 2, an intrinsic transparent conductive passivation layer 3, a first doped transparent conductive passivation layer 4 and a third passivation layer 5 are sequentially formed on the side of the p-type doped layer 12 away from the substrate. Among them, the specific structures and functions of the first passivation layer 2, the intrinsic transparent conductive passivation layer 3, the first doped transparent conductive passivation layer 4, the third passivation layer 5, the first sublayer 71, the second sublayer 72, the second doped transparent conductive passivation layer 8 and the fourth passivation layer 9 are similar to those in the first possible implementation manner, and are not described in detail.

[0092] A fourth possible implementation is:

[0093] like Figure 4As shown, the substrate of the solar cell is an n-type silicon substrate 11, and a p-type doped layer 12 is formed on the back of the n-type silicon substrate 11. In this case, an n-type doped layer 14, a first sublayer 71, a second sublayer 72, a second doped transparent conductive passivation layer 8 and a fourth passivation layer 9 are sequentially formed on the front of the n-type silicon substrate 11. The n-type doped layer 14 of this embodiment acts on the front field, which is beneficial to the selective transmission of electrons. Among them, the n-type doped layer 14 is preferably single crystal silicon, with a thickness of 0um-2um, and a doping concentration of 1E19cm -3 -5E20cm -3 . And / or a first passivation layer 2, an intrinsic transparent conductive passivation layer 3, a first doped transparent conductive passivation layer 4 and a third passivation layer 5 are sequentially formed on the side of the p-type doped layer 12 away from the substrate. Among them, the specific structures and functions of the first passivation layer 2, the intrinsic transparent conductive passivation layer 3, the first doped transparent conductive passivation layer 4, the third passivation layer 5, the first sublayer 71, the second sublayer 72, the second doped transparent conductive passivation layer 8 and the fourth passivation layer 9 are similar to those in the first possible implementation manner, and are not described in detail.

[0094] It should be noted that the above-mentioned specific forms are only exemplary and those skilled in the art can make adjustments as needed. For example, the substrate is an n-type silicon substrate 11, and a p-type doping layer 12 is formed on the front side of the n-type silicon substrate 11. The p-type doping layer 12 is provided with the above-mentioned first passivation structure, and a conventional passivation structure is formed on the back side, such as a tunneling oxide layer, etc. These adjustments do not deviate from the principles of the present invention and are within the protection scope of the present invention.

[0095] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A solar cell comprising: a first layer having a first conductivity type; a second layer, the second layer being disposed on a first surface of the first layer, the second layer having a second conductivity type opposite to the first conductivity type, so that a PN junction is formed between the first layer and the second layer; A transparent conductive passivation layer, wherein the transparent conductive passivation layer is disposed on a second surface of the first layer opposite to the first surface, and has a doping concentration capable of causing majority carriers in the first layer to flow to the second surface.

2. The solar cell according to claim 1, characterized in that The first layer is a p-type substrate, and the second layer is an n-type doped layer; or the first layer is a p-type doped layer, and the second layer is an n-type substrate; The transparent conductive passivation layer includes an intrinsic transparent conductive passivation layer, and the intrinsic transparent conductive passivation layer is disposed on the second surface.

3. The solar cell according to claim 2, characterized in that: The transparent conductive passivation layer also includes a first doped transparent conductive passivation layer, which is arranged on a side of the intrinsic transparent conductive passivation layer away from the first layer, wherein gradient doping is formed in the first doped transparent conductive passivation layer, and the doping concentration on the side close to the intrinsic transparent conductive passivation layer is less than the doping concentration on the side away from the intrinsic transparent conductive passivation layer.

4. The solar cell according to claim 2, characterized in that: The solar cell further comprises a first passivation layer, which is arranged between the second surface and the intrinsic transparent conductive passivation layer, and the first passivation layer carries a fixed negative charge.

5. The solar cell according to claim 4, characterized in that: The first passivation layer is doped with a first conductive doping source.

6. The solar cell according to claim 1, characterized in that The first layer is an n-type substrate, and the second layer is a p-type doped layer; or the first layer is an n-type doped layer, and the second layer is a p-type substrate; A second doped transparent conductive passivation layer is disposed on the second surface.

7. The solar cell according to claim 6, characterized in that: The doping concentration of the second doped transparent conductive passivation layer is in the range of 3E20cm -3 -8E20cm -3 .

8. The solar cell according to claim 6 or 7, characterized in that: The solar cell further comprises a second passivation layer disposed between the second surface and the second doped transparent conductive passivation layer, wherein the second passivation layer carries a fixed positive charge.

9. The solar cell according to claim 8, characterized in that The second passivation layer includes a first sublayer and a second sublayer which are sequentially stacked in a direction away from the second surface, wherein the second sublayer is a doped layer, and the first sublayer and the second sublayer as a whole carry a fixed positive charge.

10. The solar cell according to claim 9, characterized in that: The doping layer is doped with a second conductive doping source.

11. The solar cell according to any one of claims 2 to 5, characterized in that: A second doped transparent conductive passivation layer is disposed on a surface of the second layer away from the first layer.

12. The solar cell according to claim 11, characterized in that: The doping concentration of the second doped transparent conductive passivation layer is in the range of 3E20cm -3 -8E20cm -3 .

13. The solar cell according to claim 11, characterized in that: The solar cell further comprises a second passivation layer, which is arranged between a surface of the second layer away from the first layer and the second doped transparent conductive passivation layer, and the second passivation layer carries a fixed positive charge.

14. The solar cell according to claim 13, characterized in that: The second passivation layer includes a first sublayer and a second sublayer which are sequentially stacked in a direction away from the second layer, wherein the second sublayer is a doped layer, and the first sublayer and the second sublayer as a whole carry a fixed positive charge.

15. The solar cell according to claim 14, characterized in that: The doping layer is doped with a second conductive doping source.

16. A method for preparing a solar cell, characterized in that: include: forming a second layer on a first surface of the first layer of the first conductivity type, the second layer having a second conductivity type opposite to the first conductivity type, so that a PN junction is formed between the first layer and the second layer; A transparent conductive passivation layer is formed, wherein the transparent conductive passivation layer is formed on a second surface of the first layer opposite to the first surface, and has a doping concentration capable of causing majority carriers in the first layer to flow to the second surface.

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