Solar cell cleaning method, solar cell and preparation method thereof

Abstract

The invention discloses a cleaning method for a back contact solar cell substrate, the cleaning method comprises at least two cleaning periods, and the cleaning periods comprise the following steps: carrying out oxidation cleaning on the back contact solar cell substrate by using a first cleaning solution, the first cleaning solution being an alkaline cleaning solution with oxidability; the back contact solar cell substrate subjected to oxidation cleaning is subjected to secondary cleaning through second cleaning liquid, the second cleaning liquid is aqueous alkali, and the aqueous alkali is suitable for dissolving silicon oxide. The invention further provides a preparation method of the solar cell and the solar cell.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a method for cleaning a back-contact solar cell substrate, a method for preparing a solar cell, and a solar cell. Background Art

[0002] Compared with traditional front-electrode solar cells, the biggest difference of back-contact solar cells is that the PN junction and metal electrode are moved to the back of the cell, so that there is no electrode blocking the front, which improves the light absorption and conversion efficiency.

[0003] like Figure 4 As shown, the back-contact solar cell includes a silicon substrate 100, and an N-type conductive region 31 and a P-type conductive region 32 alternately arranged on the back of the silicon substrate. In order to realize the alternating arrangement of the N-type conductive region 31 and the P-type conductive region 32 to form a PN junction, when preparing the back-contact solar cell, it is necessary to perform patterning etching on the intrinsic passivation layer and the doping layer of the N-type conductive region or the P-type conductive region to obtain a back-contact solar cell substrate, and then supplementally plate an intrinsic passivation layer and a doping layer of another conductive type on the back-contact solar cell substrate.

[0004] However, oil stains and semiconductor material particles generated in the graphic etching process will adhere to the surface of the back contact solar cell substrate, and form traps and carrier recombination on the surface of the back contact solar cell substrate, reducing the open circuit voltage of the solar cell being released, and ultimately reducing the photoelectric conversion efficiency of the back contact solar cell.

[0005] For non-back contact solar cells, cleaning is performed after the texturing process. In order to remove organic residues such as oil stains, a cleaning solution containing an oxidant is required to clean the surface of the substrate.

[0006] When the back contact solar cell substrate is cleaned with an oxidant, the oxidant will react with the surface of the back contact solar cell substrate during the cleaning process, resulting in the formation of an oxide layer on the surface of the back contact solar cell substrate. In order to perform the deposition passivation of amorphous silicon in the subsequent process, the conventional method is to use hydrofluoric acid to remove the oxide layer. Hydrofluoric acid easily reacts with the oxide layer, and the dangling bonds on the surface of the silicon substrate are saturated with hydrogen, thereby enabling the silicon substrate to obtain good passivation performance. However, hydrofluoric acid will also react with the insulating layer of the back contact solar cell substrate, resulting in damage to the insulating layer.

[0007] Therefore, how to effectively clean the back-contact solar cell substrate without causing damage to the back-contact solar cell substrate has become a technical problem to be solved in the field. Summary of the invention

[0008] The present application aims to solve one of the technical problems in the related art to a certain extent. To this end, the present application provides a cleaning method for a back-contact solar cell, which can effectively maintain the cleanliness of the silicon substrate surface to obtain a higher photoelectric conversion efficiency.

[0009] In order to achieve the above object, the present application provides a method for cleaning a back contact solar cell substrate, wherein the cleaning method comprises at least two cleaning cycles, and the cleaning cycle comprises:

[0010] The back-contact solar cell substrate is oxidatively cleaned by using a first cleaning liquid, wherein the first cleaning liquid is an oxidative alkaline cleaning liquid, and is used to remove dirt particles on the surface of the back-contact solar cell substrate; wherein the back-contact solar cell substrate comprises a silicon substrate, and a first functional graphic layer disposed on the back side of the silicon substrate, wherein the first functional graphic layer comprises an insulating graphic layer;

[0011] The back contact solar cell substrate after oxidation cleaning is secondarily cleaned by using a second cleaning liquid, wherein the second cleaning liquid is an alkaline solution, and the alkaline solution is suitable for dissolving silicon oxide.

[0012] The cleaning method further comprises:

[0013] The back contact solar cell substrate cleaned by at least one cleaning cycle is acid-washed using a non-oxidizing acid.

[0014] Optionally, the cleaning cycle further includes the following steps performed between the oxidation cleaning step and the secondary cleaning step:

[0015] The back contact solar cell substrate after oxidation cleaning is washed with water.

[0016] Optionally, components of the first cleaning liquid include an oxidant and an alkali, the oxidant includes hydrogen peroxide, and the mass ratio of the alkali, hydrogen peroxide and water in the first cleaning liquid is (0.1~1):(0.1~1):(5~10); in each cleaning cycle, the cleaning temperature of the oxidative cleaning is 40℃~80℃, and the cleaning time is 120s~240s.

[0017] Optionally, the percentage concentration of the second cleaning solution is 0.1% to 30%; in each cleaning cycle, the cleaning temperature of the secondary cleaning is 40°C to 80°C, and the cleaning time is 10s to 240s. The solute of the secondary cleaning solution includes one or more of ammonia water, potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide, and the thickness of the insulating graphic layer is between 30nm and 70nm.

[0018] Optionally, the number of cleaning cycles is 2 to 5 times.

[0019] Optionally, the non-oxidizing acid is hydrochloric acid, and the percentage concentration of the hydrochloric acid is 1% to 15%.

[0020] As a second aspect of the present application, a method for preparing a solar cell is provided, wherein the preparation method comprises:

[0021] Providing a back-contact solar cell substrate, wherein the back-contact solar cell substrate comprises a silicon substrate, and a first functional pattern layer disposed on the back side of the silicon substrate, wherein the first functional pattern layer comprises an insulating pattern layer;

[0022] Using the cleaning method provided in the first aspect of the present application to clean the back contact solar cell substrate;

[0023] An electrode layer is formed on the back side of the cleaned back contact solar cell substrate.

[0024] Optionally, a plurality of notches are formed on the first functional pattern layer, wherein the first functional pattern layer comprises a first intrinsic pattern layer, a first doped pattern layer, and the insulating pattern layer which are sequentially stacked in a thickness direction, wherein the first intrinsic pattern layer is formed on the back side of the silicon substrate;

[0025] The method of forming an electrode layer on the back side of the cleaned back contact solar cell substrate comprises:

[0026] forming a second functional material layer, the second functional material layer comprising a second intrinsic material layer and a second doping material layer sequentially stacked in a thickness direction, wherein a material of the first doping pattern layer is selected from one of an N-type doping material and a P-type doping material, and a material of the second doping material layer is selected from the other of the N-type doping material and the P-type doping material;

[0027] The second functional material layer and the first functional pattern layer are patterned to form a plurality of electrode openings, and a second functional pattern layer is formed, wherein the electrode openings and the notches are alternately arranged, and the electrode openings penetrate the second doped material layer, the second intrinsic material layer, and the insulating pattern layer;

[0028] An electrode layer is formed on the back contact solar cell substrate having the second functional pattern layer formed thereon.

[0029] As a third aspect of the present application, a solar cell is provided, wherein the solar cell is a solar cell prepared by the preparation method provided in the second aspect of the present application.

[0030] Optionally, the solar cell further comprises a passivation layer and an anti-reflection layer, wherein the passivation layer is arranged on the front side of the silicon substrate, and the anti-reflection layer is located on a side of the passivation layer away from the silicon substrate.

[0031] After the etching process is completed, there will be oil residues. The residual oil residues and particles attached to the surface of the back contact solar cell substrate can be removed by using an oxidizing alkaline cleaning solution. At the same time, during the oxidation cleaning process, the oxidation of the first cleaning solution forms an oxide layer on the surface of the silicon substrate. The oxide layer formed by oxidation cleaning is silicon oxide. The back contact solar cell substrate after oxidation cleaning is cleaned for the second time by the second cleaning solution (alkaline solution), and the formed oxide layer can be removed, and the secondary cleaning can further remove the residual semiconductor particles. Under the action of the first cleaning solution, some residual pollutants are sealed in the oxide layer formed by oxidation cleaning. Therefore, extending the cleaning time of the first cleaning solution may not remove the residual pollutants sealed in the oxide layer formed by oxidation cleaning. During the secondary cleaning, the alkaline solution can open the oxide layer formed during the oxidation cleaning process, exposing the residual pollutants originally sealed in the oxide layer. As the secondary cleaning proceeds, the residual pollutants originally sealed in the oxide layer can be removed. In other words, after multiple cleanings, the purpose of enhancing the removal of stubborn residues and pollution can be achieved.

[0032] By using the cleaning method, organic residues such as oil and residual semiconductor particles on the surface of the back contact solar cell substrate can be removed without damaging the back contact solar cell substrate, which is beneficial to the subsequent process. After removing the semiconductor particles on the surface of the back contact solar cell substrate, the traps and carrier recombination formed by the defects on the surface of the back contact solar cell substrate caused by the semiconductor particles can be eliminated, and finally the open circuit voltage of the solar cell is improved, and the photoelectric conversion efficiency of the prepared back contact solar cell is improved. In addition, after the back contact solar cell substrate is cleaned by the cleaning method, the portion of the silicon substrate exposed by the gap of the first functional pattern layer can be further passivated.

[0033] These features and advantages of the present application will be disclosed in detail in the following specific embodiments and drawings. The best embodiments or means of the present application will be described in detail in conjunction with the drawings, but they are not intended to limit the technical solutions of the present application. In addition, there are multiple features, elements, and components that appear in each of the following texts and drawings, and different symbols or numbers are marked for convenience, but they all represent components with the same or similar structures or functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present application is further described below in conjunction with the accompanying drawings:

[0035] Figure 1 A flow chart of an implementation of a cleaning cycle in the cleaning method provided in the present application;

[0036] Figure 2A flow chart of another embodiment of the cleaning method provided by the present application;

[0037] Figure 3 A flow chart of an embodiment of the preparation method provided in this application;

[0038] Figure 4 A schematic diagram of an implementation of a back contact solar cell in the related art;

[0039] Figure 5 A schematic diagram of an embodiment of a back contact solar cell substrate;

[0040] Figure 6 A schematic diagram of an embodiment of a solar cell provided in the present application;

[0041] Figure 7 is a schematic diagram of an optional implementation of step S230;

[0042] Figure 8a is a PL effect diagram of the back contact solar cell substrate after one cleaning cycle in Example 1;

[0043] Figure 8b is a PL effect diagram of the back contact solar cell substrate after two cleaning cycles in Example 1;

[0044] Figure 8c is a PL effect diagram of the back contact solar cell substrate after three cleaning cycles in Example 1;

[0045] Figure 9a is a PL effect diagram of the back contact solar cell substrate after one cleaning cycle in Example 2;

[0046] Figure 9b is a PL effect diagram of the back contact solar cell substrate after two cleaning cycles in Example 2;

[0047] Fig.9c is a PL effect diagram of the back contact solar cell substrate after three cleaning cycles in Example 2;

[0048] Fig.10 What is shown in FIG. 1 is a PL effect diagram of the initial substrate obtained in Preparation Example 2 after cleaning.

[0049] Description of Reference Numerals

[0050] 100: Silicon substrate 101: Passivation layer

[0051] 102: first intrinsic pattern layer 103: first doped pattern layer

[0052] 104: Insulation pattern layer 105: Anti-reflection layer

[0053] 110: first functional graphic layer 200: second functional graphic layer

[0054] 200a: The portion of the second functional graphic layer located on the first functional graphic layer

[0055] 200b: the portion of the second functional pattern layer located in the gap

[0056] 202a: first intrinsic pattern portion 202b: second intrinsic pattern portion

[0057] 203a: first doped pattern portion 203b: second doped pattern portion

[0058] 301a: first light-transmitting electrode 301b: second light-transmitting electrode

[0059] 302a: first metal electrode 302b: second metal electrode DETAILED DESCRIPTION

[0060] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments based on the embodiments are intended to be used to explain the present application and cannot be understood as limiting the present application.

[0061] References in this specification to "one embodiment" or "an example" or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment itself may be included in at least one embodiment of the present patent disclosure. The appearance of the phrase "in one embodiment" in various places in the specification does not necessarily refer to the same embodiment.

[0062] It should be pointed out that the “front side” mentioned in this application refers to the surface on the back-contact solar cell for receiving sunlight, and the “back side” mentioned in this application is the surface opposite to the “front side” of the back-contact solar cell.

[0063] like Figure 5 As shown, the back contact solar cell substrate includes a silicon substrate 100 and a first functional pattern layer 110 disposed on the back of the silicon substrate 100, wherein the first functional pattern layer 110 includes an insulating pattern layer 104. Generally, the insulating pattern layer 104 is made of silicon nitride or silicon oxynitride.

[0064] Reference Figure 1 As shown, the first aspect of the present application provides a method for cleaning a back contact solar cell substrate, wherein the cleaning method comprises at least two cleaning cycles, and the cleaning cycle comprises:

[0065] In step S110, the back-contact solar cell substrate is oxidatively cleaned using a first cleaning solution, wherein the first cleaning solution is an oxidative alkaline cleaning solution for removing dirt particles on the surface of the back-contact solar cell substrate;

[0066] In step S120, the back contact solar cell substrate after oxidation cleaning is secondarily cleaned with a second cleaning liquid, wherein the second cleaning liquid is an alkaline solution, and the second cleaning liquid is suitable for dissolving silicon oxide.

[0067] To further maintain the cleanliness of the back contact solar cell substrate, optionally, as Figure 2 As shown, the cleaning method also includes:

[0068] In step S130, the back contact solar cell substrate cleaned through at least one cleaning cycle is acid-washed using a non-oxidizing acid.

[0069] After step S130, the non-oxidizing acid can neutralize the alkali solution remaining on the back contact solar cell substrate and remove the metal particles on the back contact solar cell substrate, thereby ensuring the cleanliness of the surface of the back contact solar cell substrate.

[0070] In the embodiment of the present application, after the etching process is completed, there will be residual oil stains. The residual oil stains and particles attached to the surface of the back contact solar cell substrate due to the oil stains (the particles are mostly residual semiconductor materials in the first functional graphic layer) can be removed by using an oxidizing alkaline cleaning solution.

[0071] At the same time, during the oxidation cleaning process, the oxidation effect of the first cleaning solution not only forms an oxide layer on the surface of the silicon substrate 100, but also protects the first functional graphic layer 110 on the back contact solar cell substrate, especially the insulating graphic layer 104 of the first functional graphic layer 110.

[0072] The oxide layer formed by oxidation cleaning is mostly silicon oxide. The oxide layer formed can be removed by performing secondary cleaning on the back contact solar cell substrate after oxidation cleaning with a second cleaning liquid (alkaline solution). In addition, the secondary cleaning can further remove the residual semiconductor material particles. Since the second cleaning liquid is an alkaline solution, the insulating pattern layer 104 is minimally damaged during the secondary cleaning process. The thickness of the insulating pattern layer 104 removed by each cleaning is approximately between 0.3nm and 5nm. Therefore, after multiple cleaning cycles, the integrity of the first functional pattern layer 110 on the solar cell substrate can still be ensured. In addition, the alkaline solution can further passivate the portion of the silicon substrate 100 exposed through the gap of the first functional pattern layer 110.

[0073] By means of the cleaning method, organic residues such as oil stains on the surface of the back contact solar cell substrate and residual semiconductor particles can be removed without damaging the back contact solar cell substrate, which is beneficial to the subsequent process. After removing the semiconductor particles on the surface of the back contact solar cell substrate, the traps and carrier recombination formed by the defects on the surface of the back contact solar cell substrate caused by the semiconductor particles can be eliminated, and finally the open circuit voltage of the solar cell is improved, and the photoelectric conversion efficiency of the prepared back contact solar cell is improved. In addition, after the back contact solar cell substrate is cleaned by the cleaning method, the part of the silicon substrate 100 exposed by the notch on the first functional pattern layer 110 is further passivated, which can avoid the "trap effect" and "recombination effect" caused by the semiconductor material particles on the surface of the back contact solar cell substrate, and finally the open circuit voltage of the solar cell is improved, and the photoelectric conversion efficiency of the prepared back contact solar cell is improved.

[0074] Before cleaning, there are residual contaminants on the surface of the back contact solar cell substrate. In the cleaning method provided in the embodiment of the present application, oxidation cleaning is first performed, and under the action of the first cleaning liquid, part of the residual contaminants are sealed in the oxide layer formed by the oxidation cleaning. Therefore, extending the cleaning time of the first cleaning liquid may not remove the residual contaminants sealed in the oxide layer formed by the oxidation cleaning. During the secondary cleaning, the alkaline solution can open the oxide layer formed during the oxidation cleaning process, exposing the residual contaminants originally sealed in the oxide layer. As the secondary cleaning is further performed, the residual contaminants originally sealed in the oxide layer can be removed. In other words, after multiple cleanings, the purpose of enhancing the removal of stubborn residues and pollution can be achieved.

[0075] In addition, after at least one cleaning cycle, the back contact solar cell substrate is cleaned with a non-oxidizing acid to neutralize the alkali solution remaining in the previous cleaning cycle. Then, the back contact solar cell substrate can be directly cleaned with an oxidizing alkaline cleaning solution in the next cleaning cycle without any excess hardening, thereby improving the cleaning efficiency of the first cleaning solution.

[0076] In the embodiments of the present application, there is no special limitation on the number of cleaning cycles, and the number of cleaning cycles can be determined based on actual conditions (for example, the oxidizing properties of the first cleaning solution, the specific semiconductor material, the specific type of the second cleaning solution, etc.), as long as the particles remaining on the surface of the back-contact solar cell substrate and the oxides formed on the surface of the back-contact solar cell substrate can be removed.

[0077] In the embodiment of the present application, there is no particular limitation on the specific components of the first cleaning solution, as long as it can remove oil stains and does not corrode the insulating pattern layer on the back contact solar cell substrate. As an optional implementation, the components of the first cleaning solution include an oxidant and an alkali.

[0078] The role of the oxidant is to slightly oxidize the back contact solar cell substrate to protect the insulating layer, and the role of the alkali is to remove oil stains.

[0079] In the embodiment of the present application, there is no special limitation on the solvent of the first cleaning solution, as long as it can dissolve the oxidant and the alkali and does not cause secondary contamination to the back contact solar cell substrate. For example, the solvent of the first cleaning solution can be water. In other words, the first cleaning solution includes water, an oxidant and an alkali.

[0080] In the embodiment of the present application, there is no special limitation on the oxidant in the first cleaning solution, as long as it does not corrode the insulating pattern layer of the back contact solar cell substrate and does not cause excessive damage to the silicon substrate when oxidizing the silicon substrate of the back contact solar cell substrate.

[0081] As an optional embodiment, the oxidant may include hydrogen peroxide, and accordingly, the mass ratio of alkali, hydrogen peroxide and water in the first cleaning solution is (0.1-1): (0.1-1): (5-10). Accordingly, in each cleaning cycle, the cleaning temperature of the oxidative cleaning is 40°C-80°C, and the cleaning time is 120s-240s.

[0082] As an optional implementation, the percentage concentration of the second cleaning solution is 0.1% to 30%. Accordingly, in each cleaning cycle, the cleaning temperature of the secondary cleaning is 40° C. to 80° C., and the cleaning time is 10s to 240s.

[0083] In the embodiments of the present application, the type of alkali in the secondary cleaning solution is not particularly limited. As long as it can dissolve silicon oxides without damaging the insulating layer. As an optional embodiment, the solute of the secondary cleaning solution includes one or more of ammonia water, potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide.

[0084] In the embodiment of the present application, the material of the insulating pattern layer can be silicon oxide or silicon nitride. When the insulating pattern layer is cleaned by the secondary cleaning solution, the thickness removed each time is approximately between 0.5nm and 3nm. Therefore, the thickness of the insulating pattern layer can be between 30nm and 70nm, thereby ensuring that the thickness of the insulating pattern layer on the back contact solar cell substrate is still above 20nm at the end of the cleaning method. In other words, at the end of the cleaning method, there is still a sufficiently thick insulating pattern layer on the back contact solar cell substrate.

[0085] Further optionally, the thickness of the insulating pattern layer may be 50 nm.

[0086] As an optional embodiment, the cleaning cycle further includes the following steps performed between the oxidation cleaning step and the secondary cleaning step:

[0087] The back contact solar cell substrate after oxidation cleaning is washed with water.

[0088] By washing the back contact solar cell substrate after oxidation cleaning with water, the first cleaning liquid remaining on the back contact solar cell substrate can be removed.

[0089] As an optional implementation, the number of cleaning cycles is 2 to 5 times.

[0090] As an optional implementation, during the cleaning cycle, ultrasonic waves may be provided to assist in cleaning, and the first cleaning liquid and / or the second cleaning liquid may be provided in a spraying manner.

[0091] By using ultrasonic waves and / or spraying, the number of cleaning cycles can be reduced, and the amount of the first cleaning liquid and the second cleaning liquid can be reduced.

[0092] As an optional implementation, the non-oxidizing acid is hydrochloric acid, and the percentage concentration of the non-oxidizing acid is 1% to 15%.

[0093] In the application example, the structure of the first functional pattern layer 110 on the back contact solar cell substrate is not particularly limited. As an optional embodiment, the back contact solar cell substrate is a substrate of a back contact heterojunction solar cell. Figure 5 As shown, a plurality of gaps are formed on the first functional pattern layer 110, wherein the first functional pattern layer 110 includes a first intrinsic pattern layer 102, a first doped pattern layer 103, and an insulating pattern layer 104 which are sequentially stacked along a thickness direction.

[0094] After the first functional pattern layer 110 is formed by the patterning process, the material particles of the first intrinsic pattern layer 102 and the material particles of the first doped pattern layer 103 will remain on the surface of the back contact solar cell substrate together with the oil stains. The back contact solar cell substrate is cleaned by the cleaning method provided in the present application, which can effectively remove the material particles of the first intrinsic pattern layer 102, the material particles of the first doped pattern layer 103, and the oil stains, and not only will the insulating pattern layer 104 not be damaged, but also the portion of the silicon substrate 100 exposed by the gap of the first functional pattern layer 110 can be further passivated.

[0095] In the present application, the first doped pattern layer 103 may be an N-type doped pattern layer or a P-type doped pattern layer.

[0096] As another optional embodiment, the contact solar cell substrate may also include a passivation layer 101 arranged on the front side of the silicon substrate 100. The material of the passivation layer 101 is usually intrinsic hydrogenated amorphous silicon. Therefore, the cleaning method provided in the present application will not cause damage to the passivation layer 101.

[0097] As a second aspect of the present application, a method for preparing a solar cell is provided, wherein: Figure 3 As shown, the preparation method comprises:

[0098] In step S210, a back-contact solar cell substrate is provided, wherein the back-contact solar cell substrate comprises a silicon substrate 100 and a first functional pattern layer 110 disposed on the back side of the silicon substrate 100, wherein the first functional pattern layer 110 comprises an insulating pattern layer 104;

[0099] In step S220, the back contact solar cell substrate is cleaned using the cleaning method provided in the first aspect of the present application;

[0100] In step S230, an electrode layer is formed on the back side of the cleaned back contact solar cell substrate.

[0101] As described above, in the embodiment of the present application, there will be residual oil stains after the etching process is completed. The residual oil stains and particles attached to the surface of the back contact solar cell substrate due to the oil stains (the particles are mostly material residues of the intrinsic graphic layer and material residues of the doped graphic layer) can be removed by using an oxidizing alkaline cleaning solution.

[0102] Meanwhile, during the oxidation cleaning process, the oxidation effect of the first cleaning solution not only forms an oxide layer on the surface of the silicon substrate of the back contact solar cell substrate, but also protects the insulating layer of the back contact solar cell substrate.

[0103] The oxide layer formed by oxidation cleaning is mostly silicon oxide. The oxide layer formed can be removed by performing a secondary cleaning on the back contact solar cell substrate after oxidation cleaning with a second cleaning liquid (alkaline solution). In addition, the secondary cleaning can further remove the residual semiconductor material. Since the second cleaning liquid is an alkaline solution, it will not damage the insulating pattern layer on the back contact solar cell substrate, and can further passivate the portion of the silicon substrate exposed by the gap in the first functional pattern layer.

[0104] The surface of the back-contact solar cell substrate cleaned by the cleaning method provided in the first aspect of the present application is cleaner, avoiding the "trap effect" and "compound effect" caused by "impurity particles" on the surface of the back-contact solar cell substrate, ultimately increasing the open circuit voltage of the solar cell and improving the photoelectric conversion efficiency of the prepared solar cell.

[0105] In this application, the specific structure of the back contact solar cell substrate is not particularly limited. As an optional embodiment, Figure 5 As shown, a plurality of notches are formed on the first functional graphic layer 110 of the back contact solar cell substrate, wherein the first functional graphic layer 110 includes a first intrinsic graphic layer 102, a first doped graphic layer 103, and an insulating graphic layer 104 which are sequentially stacked along the thickness direction, wherein the first intrinsic graphic layer 102 is formed on the back side of the silicon substrate 100.

[0106] like Figure 7 As shown in , the electrode layer is formed on the back side of the cleaned back contact solar cell substrate, comprising:

[0107] In step S231, a second functional material layer is formed, wherein the second functional material layer includes a second intrinsic material layer and a second doping material layer sequentially stacked in a thickness direction, wherein a material of the first doping pattern layer is selected from one of an N-type doping material and a P-type doping material, and a material of the second doping material layer is selected from the other of the N-type doping material and the P-type doping material;

[0108] In step S232, the second functional material layer and the first functional pattern layer are patterned to form a plurality of electrode openings, and a second functional pattern layer is formed, wherein the electrode openings and the notches are alternately arranged, and the electrode openings penetrate the second doped material layer, the second intrinsic material layer, and the insulating pattern layer;

[0109] In step S233, an electrode layer is formed on the back contact solar cell substrate having the second functional pattern layer formed thereon.

[0110] In the embodiment of the present application, step S231 may also be referred to as “repair plating”.

[0111] like Figure 6As shown in , the second functional pattern layer 200 includes a portion 200a located on the first functional pattern layer and a portion 200b of the second functional pattern layer located in the notch of the first functional pattern layer. The second doped pattern portion 203b is located in the notch of the first functional pattern layer. Further, the portion 200a located on the first functional pattern layer includes a first intrinsic pattern portion 202a and a first doped pattern portion 203a, and the portion 200b located in the notch of the first functional pattern layer includes a second intrinsic pattern portion 202b and a second doped pattern portion 203b.

[0112] The second doped pattern portion 203b and the first doped pattern portion 203a are both from the second doped material layer, and the first intrinsic pattern portion 202a and the second intrinsic pattern portion 202b are both from the second intrinsic material layer. That is, after step S232, the second doped material layer is formed to include the first doped pattern portion 203a and the second doped pattern portion 203b. The second intrinsic material layer is formed to include the first intrinsic pattern portion 202a and the second intrinsic pattern portion 202b. In the embodiment of the present application, the material of the second intrinsic material layer can be the same as or different from the material of the first intrinsic pattern layer 102, as long as the silicon substrate can be intrinsically passivated.

[0113] Accordingly, in the embodiment of the present application, there is no particular limitation on how to provide a back-contact solar cell substrate for a back-contact heterojunction solar cell. As an optional implementation, step S210 may include:

[0114] providing a silicon substrate;

[0115] forming a passivation layer on the front side of the silicon substrate;

[0116] forming an intrinsic material layer, a doped material layer, and an insulating material layer in sequence on the back side of the silicon substrate;

[0117] A patterning etching process is performed to form a first intrinsic pattern layer, a first doped pattern layer, and an insulating pattern layer.

[0118] It should be noted that the first intrinsic pattern layer, the first doped pattern layer, and the insulating pattern layer have the same shape and have a gap exposing the silicon substrate. In other words, the stacked first intrinsic pattern layer, the first doped pattern layer, and the insulating pattern layer form a first functional pattern layer.

[0119] As an optional implementation, the intrinsic material layer, the doping material layer, and the insulating material layer may be formed by chemical vapor deposition (CVD).

[0120] In the embodiment of the present invention, there is no special limitation on how to specifically perform step S231. The second intrinsic material layer and the second doping material layer may be formed by chemical vapor deposition (CVD).

[0121] In the embodiment of the present application, there is no special limitation on how to specifically perform step S233. As an optional implementation, step S233 may include:

[0122] forming a light-transmitting electrode layer;

[0123] Patterning the light-transmitting electrode layer to obtain a plurality of light-transmitting electrodes;

[0124] A metal electrode layer is formed.

[0125] like Figure 6 As shown, the plurality of light-transmitting electrodes include a first light-transmitting electrode 301 a corresponding to the electrode opening and a second light-transmitting electrode 301 b corresponding to the notch.

[0126] Furthermore, the first light-transmitting electrode 301a includes a first overlapping portion, a first connecting portion, and a second overlapping portion connected in sequence, the first overlapping portion overlapping the surface of the first doped pattern portion 203a on one side of the electrode opening, the second overlapping portion overlapping the surface of the first doped pattern portion 203a on the other side of the electrode opening, the first connecting portion is located in the electrode opening, and is bonded to the portion of the first doped pattern 103 located in the electrode opening; the second light-transmitting electrode 301b includes a third overlapping portion, a second connecting portion, and a fourth overlapping portion connected in sequence, the third overlapping portion overlapping the surface of the first doped pattern portion 203a on one side of the notch, the fourth overlapping portion overlapping the surface of the first doped pattern portion 203a on the other side of the notch, the second connecting portion is located in the notch, and is bonded to the second doped pattern portion 203b where the second functional pattern layer is located in the notch.

[0127] like Figure 6 As shown, the metal electrode layer includes a plurality of first metal electrodes 302a and a plurality of second metal electrodes 302b, wherein the first metal electrodes 302a are arranged on the portion of the first light-transmitting electrode 301a located in the electrode opening, and the second metal electrodes 302b are arranged on the portion of the second light-transmitting electrode 301b located in the gap.

[0128] As an optional implementation, the light-transmitting electrode may be made of TCO material, and the metal electrode may be made of metal silver.

[0129] As an optional implementation, between step S220 and step S230, the preparation method may further include:

[0130] The cleaned back contact solar cell substrate is subjected to water washing treatment and / or drying treatment.

[0131] In an embodiment of the present application, the step of providing a silicon substrate may include:

[0132] providing an initial silicon substrate;

[0133] At least the first surface of the initial silicon base is textured to obtain the silicon substrate.

[0134] As an optional implementation, an anti-reflection layer 105 may be further disposed outside the passivation layer 101. As an optional implementation, the material of the anti-reflection layer 105 may be silicon nitride.

[0135] As a third aspect of the present application, a solar cell is provided, wherein the solar cell is a solar cell prepared by the preparation method provided in the second aspect of the present application.

[0136] As described above, the surface of the back-contact solar cell substrate cleaned by the cleaning method provided in the first aspect of the present application is cleaner, which is beneficial to the subsequent process and also avoids the "trap effect" and "compound effect" caused by "impurity particles" on the surface of the back-contact solar cell substrate, thereby ultimately increasing the open circuit voltage of the solar cell and improving the photoelectric conversion efficiency of the prepared solar cell.

[0137] In an embodiment of the present application, the insulating pattern layer includes at least one silicon nitride pattern layer and / or at least one silicon oxide pattern layer. Optionally, the thickness of the insulating pattern layer is between 50nm and 600nm.

[0138] As an optional implementation, Figure 6 As shown, the solar cell comprises:

[0139] Silicon substrate 100;

[0140] A passivation layer 101 is provided on the front surface of the silicon substrate 100;

[0141] an anti-reflection layer 105 stacked on the outer side of the passivation layer 101;

[0142] A first functional pattern layer 110 is disposed on the back side of the silicon substrate 100, and the first functional pattern layer 110 includes a first intrinsic pattern layer 102, a first doped pattern layer 103, and an insulating pattern layer 104 which are sequentially stacked on the back side of the silicon substrate 100; the first intrinsic pattern layer 102 and the first doped pattern layer 103 have the same shape, and the first intrinsic pattern layer 102, the first doped pattern layer 103, and the insulating pattern layer 104 are all formed with notches, and the insulating pattern layer 104 is also formed with electrode openings, and the electrode openings and the notches are alternately arranged;

[0143] A second functional pattern layer, the second functional pattern layer includes a portion 200a located on the first functional pattern layer and a portion located in the gap (i.e., a second doped pattern portion 203b). Further, the portion 200a located on the first functional pattern layer includes a first intrinsic pattern portion 202a and a first doped pattern portion 203a, and the second doped pattern portion 203b and the first doped pattern portion 203a are both from the second doped material layer, that is, after step S232, the second doped material layer is formed to include the first doped pattern portion 203a and the second doped pattern portion 203b;

[0144] The electrode layer includes a plurality of light-transmitting electrodes and a plurality of metal electrodes; the plurality of light-transmitting electrodes include a first light-transmitting electrode 301a corresponding to the electrode opening and a second light-transmitting electrode 301b corresponding to the notch. Further, the first light-transmitting electrode 301a includes a first overlapping portion, a first connecting portion, and a second overlapping portion connected in sequence, wherein the first overlapping portion overlaps the surface of the first doped pattern portion 203a on one side of the electrode opening, and the second overlapping portion overlaps the surface of the first doped pattern portion 203a on the other side of the electrode opening, and the first connecting portion is located in the electrode opening and is aligned with the portion of the first doped pattern 103 located in the electrode opening; the second light-transmitting electrode 301b includes a third overlapping portion, a second connecting portion, and a fourth overlapping portion connected in sequence, wherein the third overlapping portion overlaps the surface of the first doped pattern portion 203a on one side of the notch, and the fourth overlapping portion overlaps the surface of the first doped pattern portion 203a on the other side of the notch, and the second connecting portion is located in the notch and is aligned with the portion of the second functional pattern layer located in the notch (i.e., the second doped pattern portion 203b).

[0145] like Figure 6 As shown, the metal electrode layer includes a plurality of first metal electrodes 302a and a plurality of second metal electrodes 302b, wherein the first metal electrodes 302a are arranged on the portion of the first light-transmitting electrode 301a located in the electrode opening, and the second metal electrodes 302b are arranged on the portion of the second light-transmitting electrode 301b located in the gap.

[0146] Preparation Example 1

[0147] The back contact solar cell substrate was prepared as follows:

[0148] Providing an initial silicon substrate made of silicon wafers;

[0149] Texturing the front surface of the initial silicon substrate to obtain a silicon substrate;

[0150] A passivation layer and an anti-reflection layer are sequentially prepared on the textured surface (i.e., the front side) of the silicon substrate;

[0151] Sequentially preparing an intrinsic material layer, a doped material layer, and an insulating material layer on the back side of the textured surface of the silicon substrate;

[0152] An etching process is performed to form an intrinsic pattern layer, a doped pattern layer, and an insulating pattern layer, and finally a back contact solar cell substrate is obtained.

[0153] Preparation Example 2

[0154] Prepare the initial substrate as follows:

[0155] Providing an initial silicon substrate made of silicon wafers;

[0156] Texturing the front surface of the initial silicon substrate to obtain a silicon substrate;

[0157] A passivation layer and an anti-reflection layer are sequentially prepared on the textured surface (i.e., the front side) of the silicon substrate;

[0158] An intrinsic material layer, a doping material layer, and an insulating material layer are sequentially prepared on the back side of the textured surface of the silicon substrate to obtain an initial base.

[0159] Example

[0160] Example 1

[0161] A method for cleaning a back contact solar cell substrate, comprising:

[0162] Execute 3 cleaning cycles, each cleaning cycle includes: using a first cleaning liquid to perform oxidation cleaning on the back contact solar cell substrate prepared in the preparation example, specifically, in the first cleaning liquid, the ratio of potassium hydroxide, hydrogen peroxide and water is 1:1:7, the cleaning temperature is 40°C, and the cleaning time is 240s; washing with water to remove the first cleaning liquid remaining on the back contact solar cell 100; then using a second cleaning liquid to clean the back contact solar cell substrate, specifically, the second cleaning liquid is a sodium hydroxide solution with a volume ratio of 30%, the cleaning temperature is 60°C, and the cleaning time is 60s; then washing with water again to remove the residual sodium hydroxide solution;

[0163] After 3 cleaning cycles, the back contact solar cell substrate was cleaned with 15% hydrochloric acid;

[0164] The back contact solar cell substrate after being cleaned with hydrochloric acid is washed with water and dried.

[0165] Wherein, the back contact solar cell substrate is prepared by the method in Preparation Example 1.

[0166] Example 2

[0167] The back contact solar cell substrate obtained in Preparation Example 1 was cleaned using the cleaning method provided in Example 1, except that:

[0168] The first cleaning solution includes tetramethylammonium hydroxide, hydrogen peroxide and water, the ratio of tetramethylammonium hydroxide, hydrogen peroxide and water is 1:1:6, and in each oxidation cleaning step, the cleaning temperature is 60°C and the cleaning time is 240s;

[0169] The second cleaning solution is a potassium hydroxide solution with a concentration of 12%, the cleaning temperature of each secondary cleaning is 70°C, and the cleaning time is 200s;

[0170] The back contact solar cell substrate was cleaned using 7% hydrochloric acid.

[0171] Comparative Example

[0172] The initial substrate obtained in Preparation Example 2 was cleaned using the following method:

[0173] The initial substrate was first cleaned using an oxidant with a concentration of 8%, a cleaning temperature of 50°C, and a cleaning time of 240 seconds;

[0174] The initial substrate that has been cleaned for the first time is cleaned for the second time using hydrofluoric acid with a concentration of 55%, with a cleaning temperature of 30° C. and a cleaning time of 100 s.

[0175] Test Case

[0176] The following test example introduces the photoluminescence (PL) mean value to characterize the cleanliness of cleaning. The basic principle of PL luminescence imaging is to excite the sample surface to make it emit light, and then use a camera to capture the luminescence imaging. Photoluminescence technology uses optical excitation. The local luminescence intensity of the imaging is determined by the carrier density and lifetime of the area. Low carrier lifetime, low carrier doping density, local defects (forming carrier recombination centers and reducing local carrier lifetime), etc. will cause PL luminescence to weaken; while film residues, unclean cleaning, etc. will cause local defects to form carrier recombination centers, thereby aggravating carrier recombination. Therefore, PL luminescence imaging can be used to characterize whether the cleaning is clean. The higher the PL mean value, the cleaner the surface and the better the passivation performance of the silicon substrate surface.

[0177] Fig.10 2 shows the PL effect of a conventional semiconductor substrate that has not been etched after passivation, and the PL mean value after cleaning is 50657. It is observed that the insulating material layer on the initial substrate is damaged.

[0178] Table 1 shows the PL mean value of the back contact solar cell substrate after one cleaning cycle in Example 1 (see PL effect diagram Figure 8a ), PL mean value of the back contact solar cell substrate after 2 cleaning cycles (see PL effect diagram Figure 8b ), and the PL mean value of the back contact solar cell substrate after 3 cleaning cycles (see the PL effect diagram for details) Figure 8c ).

[0179] Table 1

[0180] Serial number PL mean value 1 cleaning cycle 41354 2 cleaning cycles 46112 3 cleaning cycles 52898

[0181] It can be seen from Table 1 that the surface cleanliness can be significantly improved by using the cleaning method provided in the present application to clean the back contact solar cell substrate.

[0182] Table 2 shows the PL mean value of the back contact solar cell substrate after one cleaning cycle in Example 2 (see PL effect diagram Figure 9a ), PL mean value of the back contact solar cell substrate after 2 cleaning cycles (see PL effect diagram Figure 9b ), and the PL mean value of the back contact solar cell substrate after 3 cleaning cycles (see the PL effect diagram for details) Fig.9c ).

[0183] Table 2

[0184] Serial number PL mean value 1 cleaning cycle 42871 2 cleaning cycles 50093 3 cleaning cycles 56088

[0185] It can be seen from Table 2 that the surface cleanliness can be significantly improved by using the cleaning method provided in the present application to clean the back contact solar cell substrate.

[0186] Through the above tests, it can be seen that after using the cleaning method provided in the embodiment of the present application to clean the back-contact solar cell substrate, the etching film residue can be significantly removed and an ideal cleaning effect can be achieved. It can even achieve the cleanliness and passivation level of the initial substrate before the initial substrate is etched.

[0187] The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Those skilled in the art should understand that the present application includes but is not limited to the contents described in the drawings and the above specific embodiments. Any modification that does not deviate from the functional and structural principles of the present application will be included in the scope of the claims.

Claims

1. A method for cleaning a back contact solar cell substrate, characterized in that: The cleaning method comprises at least two cleaning cycles, wherein the cleaning cycles comprise: The back-contact solar cell substrate is oxidatively cleaned by using a first cleaning liquid, wherein the first cleaning liquid is an oxidative alkaline cleaning liquid, and is used to remove dirt particles on the surface of the back-contact solar cell substrate; wherein the back-contact solar cell substrate comprises a silicon substrate, and a first functional graphic layer disposed on the back side of the silicon substrate, wherein the first functional graphic layer comprises an insulating graphic layer; Using a second cleaning solution to perform a second cleaning on the back contact solar cell substrate after oxidation cleaning, wherein the second cleaning solution is an alkaline solution suitable for etching silicon oxide on the surface of the substrate; Wherein, the cleaning method further comprises: using a non-oxidizing acid to clean the back contact solar cell substrate obtained after at least one cleaning cycle.

2. The cleaning method according to claim 1, characterized in that: The cleaning cycle also includes the following steps between the oxidation cleaning step and the secondary cleaning step: The back contact solar cell substrate after oxidation cleaning is washed with water.

3. The cleaning method according to claim 1, characterized in that: The components of the first cleaning solution include an oxidant and an alkali, the oxidant includes hydrogen peroxide, and the mass ratio of the alkali, hydrogen peroxide and water in the first cleaning solution is (0.1-1): (0.1-1): (5-10); In each cleaning cycle, the cleaning temperature of the oxidation cleaning is 40° C. to 80° C., and the cleaning time is 120s to 240s.

4. The cleaning method according to claim 1, characterized in that: The percentage concentration of the second cleaning solution is 0.1% to 30%; in each cleaning cycle, the cleaning temperature of the secondary cleaning is 40°C to 80°C, and the cleaning time is 10s to 240s. The solute of the secondary cleaning solution includes one or more of ammonia water, potassium hydroxide, sodium hydroxide and tetramethylammonium hydroxide, and the thickness of the insulating graphic layer is between 30nm and 70nm.

5. The cleaning method according to any one of claims 1 to 4, characterized in that: The number of cleaning cycles is 2 to 5 times.

6. The cleaning method according to any one of claims 1 to 4, characterized in that: The non-oxidizing acid is hydrochloric acid, and the percentage concentration of the hydrochloric acid is 1% to 15%.

7. A method for preparing a solar cell, characterized in that: The preparation method comprises: Providing a back-contact solar cell substrate, wherein the back-contact solar cell substrate comprises a silicon substrate, and a first functional pattern layer disposed on the back side of the silicon substrate, wherein the first functional pattern layer comprises an insulating pattern layer; Cleaning the back contact solar cell substrate using the cleaning method described in any one of claims 1 to 6; An electrode layer is formed on the back side of the cleaned back contact solar cell substrate.

8. The preparation method according to claim 7, characterized in that: A plurality of notches are formed on the first functional pattern layer, wherein the first functional pattern layer comprises a first intrinsic pattern layer, a first doped pattern layer, and the insulating pattern layer which are sequentially stacked in a thickness direction, wherein the first intrinsic pattern layer is formed on the back side of the silicon substrate; The method of forming an electrode layer on the back side of the cleaned back contact solar cell substrate comprises: forming a second functional material layer, the second functional material layer comprising a second intrinsic material layer and a second doping material layer sequentially stacked in a thickness direction, wherein a material of the first doping pattern layer is selected from one of an N-type doping material and a P-type doping material, and a material of the second doping material layer is selected from the other of the N-type doping material and the P-type doping material; The second functional material layer and the first functional pattern layer are patterned to form a plurality of electrode openings, and a second functional pattern layer is formed, wherein the electrode openings and the notches are alternately arranged, and the electrode openings penetrate the second doped material layer, the second intrinsic material layer, and the insulating pattern layer; An electrode layer is formed on the back contact solar cell substrate having the second functional pattern layer formed thereon.

9. A solar cell, characterized in that: The solar cell is a solar cell prepared by the preparation method according to claim 7 or 8.

10. The solar cell according to claim 9, characterized in that: The solar cell further comprises a passivation layer and an anti-reflection layer. The passivation layer is arranged on the front side of the silicon substrate, and the anti-reflection layer is located on a side of the passivation layer away from the silicon substrate.

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