Photovoltaic cell and preparation method thereof

Abstract

The invention relates to a photovoltaic cell and a preparation method thereof, and the method comprises the steps: sequentially forming a plurality of aluminum oxide passivation layers on a substrate through trimethylaluminum, oxygen and water vapor, the ratio of the oxygen flow to the water vapor flow for forming the next aluminum oxide passivation layer is smaller than the ratio of the oxygen flow to the water vapor flow for forming the previous aluminum oxide passivation layer, so that the refractive index of the next formed aluminum oxide passivation layer is smaller than that of the previous formed aluminum oxide passivation layer; the refractive index of the prepared multi-layer aluminum oxide passivation layer is reduced from the side close to the substrate to the side far away from the substrate, so that the prepared multi-layer aluminum oxide passivation layer has a good antireflection effect, and the photoelectric conversion efficiency of the finally prepared photovoltaic cell can be improved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a photovoltaic cell and a preparation method thereof. Background Art

[0002] The photoelectric conversion efficiency of the photovoltaic cells in the prior art is low. Summary of the invention

[0003] In view of this, the present application provides a photovoltaic cell and a preparation method, which can improve the photoelectric conversion efficiency of the photovoltaic cell.

[0004] In a first aspect, the present application provides a method for preparing a photovoltaic cell, the method comprising:

[0005] Step S1: introducing a precursor into a reaction chamber, wherein a substrate has been placed in the reaction chamber, and the precursor includes trimethylaluminum.

[0006] Step S2: introducing a protective gas into the reaction chamber and extracting the remaining precursor and by-products.

[0007] Step S3: introducing a post-processing agent into the reaction chamber to form an aluminum oxide passivation layer on the substrate, wherein the post-processing agent includes oxygen and water vapor.

[0008] Step S4: introducing a protective gas into the reaction chamber and extracting the remaining after-products and by-products.

[0009] Step S1, step S2, step S3 and step S4 are cyclically performed to form at least two aluminum oxide passivation layers on the substrate, wherein the number of cycles is at least two groups of cycles, so that the ratio of oxygen flow rate to water vapor flow rate in the latter group of cycles is smaller than the ratio of oxygen flow rate to water vapor flow rate in the former group of cycles.

[0010] Step S5: forming an anti-reflection layer on the side of the outermost aluminum oxide passivation layer facing away from the substrate.

[0011] Step S6: Annealing treatment.

[0012] Optionally, the method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies any of the following settings:

[0013] Setting (1): Make the oxygen flow rate of the latter group of cycles smaller than that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles the same as that of the former group of cycles.

[0014] Setting (2): Make the oxygen flow rate of the latter group of cycles the same as that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles greater than that of the former group of cycles.

[0015] Setting (3): Make the oxygen flow rate of the latter group of cycles smaller than that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles larger than that of the former group of cycles.

[0016] Optionally, the method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies at least one of the following settings:

[0017] Setting (a): The ratio of oxygen flow rate to water vapor flow rate in the first group of cycles is 1.8 to 2.2.

[0018] Setting (b): Make the ratio of oxygen flow rate to water vapor flow rate in the last set of cycles 0.3-0.7.

[0019] Optionally, the method of making the ratio of oxygen flow rate to water vapor flow rate of the latter group of cycles smaller than the ratio of oxygen flow rate to water vapor flow rate of the former group of cycles comprises:

[0020] The ratio of the oxygen flow rate to the water vapor flow rate in the latter group of cycles is made to have a difference with the ratio of the oxygen flow rate to the water vapor flow rate in the former group of cycles, and the absolute value of the latter difference is made smaller than the absolute value of the former difference.

[0021] Optionally, the same group of cycles includes at least two cycles, and the ratio of the oxygen flow rate to the water vapor flow rate in the latter cycle is the same as the ratio of the oxygen flow rate to the water vapor flow rate in the former cycle.

[0022] Optionally, the preparation method includes six sets of cycles, each set of cycles includes five cycles.

[0023] Optionally, any loop satisfies at least one of the following settings:

[0024] Setting (α): Time T for a single introduction of precursor into the reaction chamber 1 It is 5S to 10S.

[0025] Setting (β): Time T for a single injection of the post-processing agent into the reaction chamber 2 It is 5S to 10S.

[0026] Setting (γ): Time T for introducing protective gas into the reaction chamber once 3 It is 10S to 15S.

[0027] Optionally, before performing step S1, the preparation method further includes:

[0028] Step S01: introducing water vapor into a reaction chamber, wherein a substrate has been placed in the reaction chamber;

[0029] Step S02: introducing protective gas into the reaction chamber and extracting the remaining water vapor.

[0030] Optionally, step S01 and step S02 are executed in a loop, and the number of loops is three to seven loops.

[0031] In a second aspect, the present application provides a photovoltaic cell, which is prepared by the photovoltaic cell preparation method described above, and the photovoltaic cell includes a silicon substrate and at least two adjacent aluminum oxide passivation layers, and the refractive index of the at least two adjacent aluminum oxide passivation layers decreases in the direction from the silicon substrate to the outermost aluminum oxide passivation layer.

[0032] The concentration of aluminum oxide in the aluminum oxide passivation layer formed later is lower than that in the aluminum oxide passivation layer formed earlier, and the refractive index of the aluminum oxide passivation layer formed later is lower than that of the aluminum oxide passivation layer formed earlier, that is, the refractive index of the prepared aluminum oxide passivation layer decreases from the inside to the outside, and accordingly the prepared aluminum oxide passivation layer has a better anti-reflection effect, the efficiency of sunlight incident from the aluminum oxide passivation layer to the silicon substrate is higher, and the efficiency of generating free electrons and holes in the silicon substrate is higher, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 is a schematic structural diagram of a substrate in a specific embodiment;

[0035] Figure 2 A schematic diagram of a structure in which an aluminum oxide passivation layer is formed on the surface of a substrate;

[0036] Figure 3 It is a schematic diagram of the local structure of the aluminum oxide passivation layer;

[0037] Figure 4 It is a schematic diagram of the structure of a photovoltaic cell in a specific embodiment.

[0038] 10- Photovoltaic cells;

[0039] 1-N type silicon substrate;

[0040] 2-P type diffusion layer;

[0041] 3- Tunneling layer;

[0042] 4-N-type doped dielectric layer;

[0043] 5-aluminum oxide passivation layer, 51-first aluminum oxide passivation layer, 52-second aluminum oxide passivation layer, 53-third aluminum oxide passivation layer, 54-fourth aluminum oxide passivation layer, 55-fifth aluminum oxide passivation layer, 56-sixth aluminum oxide passivation layer;

[0044] 6-top anti-reflection layer;

[0045] 7- back anti-reflection layer;

[0046] 8- negative electrode grid line;

[0047] 9- Positive grid line. DETAILED DESCRIPTION

[0048] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail in conjunction with the accompanying drawings. It should be clear that the described embodiments are only a part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the protection scope of the present application. The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the attached claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should be understood that the term "and / or" used in this article is only an association relationship describing the associated objects, indicating that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are an "or" relationship.

[0049] In the figures of this document, direction X is perpendicular to direction Y, and direction X is the direction from the back side of the photovoltaic cell to the top side.

[0050] In a first aspect, an embodiment of the present application provides a method for preparing a photovoltaic cell, the method comprising the following contents:

[0051] Step S0: placing a substrate into a reaction chamber.

[0052] The substrate may include Figure 1The N-type silicon substrate 1, P-type diffusion layer 2, tunneling layer 3 and N-type doped dielectric layer 4 are shown. The P-type diffusion layer 2 is located on one side of the N-type silicon substrate 13, the tunneling layer 3 is located on the other side of the N-type silicon substrate 1, and the N-type doped dielectric layer 4 is located on the side of the tunneling layer 3 away from the N-type silicon substrate 1. The N-type silicon substrate 1 can be doped with at least one N-type element (element of the fifth main group in the periodic table of chemical elements), such as phosphorus, arsenic, antimony and other N-type elements; the P-type diffusion layer 2 can be doped with at least one P-type element (element of the third main group in the periodic table of chemical elements), such as boron, gallium, aluminum and other P-type elements; a PN junction is formed between the N-type silicon substrate 1 and the P-type diffusion layer 2; the tunneling layer 3 may include at least one of silicon oxide, silicon nitride and silicon oxynitride; the N-type doped dielectric layer 4 may also be doped with at least one N-type element, and before annealing, the N-type doped dielectric layer 4 may include at least one of polycrystalline silicon, amorphous silicon and microcrystalline silicon. Formation as shown Figure 1 The preparation process of the substrate shown may include: texturing, boron diffusion, back side etching, preparation of tunnel passivation contact structure, and front side etching.

[0053] In other embodiments (not shown in the figure), the substrate may also be in other configurations. Therefore, the preparation method provided in the embodiment of the present application may also be applicable to any photovoltaic cell that requires aluminum oxide as a passivation layer.

[0054] The following content of this article mainly introduces the preparation method provided in the embodiment of the present application by taking the substrate shown in the figure as an example.

[0055] In addition, the reaction chamber is used to provide an environment for implementing the atomic layer deposition (ALD) process, so that in the subsequent process, a layer such as Figure 2 The aluminum oxide passivation layer 5 is shown. The process of forming the aluminum oxide passivation layer 5 includes the following steps S1, S2, S3 and S4.

[0056] Step S1: introducing a precursor into the reaction chamber, wherein the precursor includes trimethylaluminum (TMA), the chemical formula of which is Al(CH 3 ) 3 (g). Under this setting, the hydroxyl groups on the surface of the P-type diffusion layer 2 facing away from the N-type silicon substrate 1 (described later for the top surface of the P-type diffusion layer 2) can react with trimethylaluminum to generate an intermediate and a by-product, the chemical formula of the intermediate being (Al-O) 2 -Al(CH 3 )*(s), the by-product is methane (CH 4 ).

[0057] Step S2: introducing a protective gas into the reaction chamber, and extracting the remaining precursor and by-products at the same time. After the remaining precursor and by-products are extracted, the reaction chamber is filled with a protective gas so that the substrate is in an environment filled with a protective gas. After the reaction chamber is filled with a protective gas, the gas extraction is stopped. The protective gas may include nitrogen and / or an inert gas (such as helium, argon or krypton, etc.), and the protective gas mentioned in the subsequent content can refer to the introduction here.

[0058] Step S3: introducing a post-processing body into the reaction chamber, wherein the post-processing body includes oxygen and water vapor. Under this setting, the oxygen and water vapor react with the intermediate on the top surface of the P-type diffusion layer 2 to form an aluminum oxide passivation layer, and at the same time generate a byproduct of methane (CH 4 ).

[0059] Step S4: introducing a protective gas into the reaction chamber and simultaneously extracting the remaining after-products and by-products. After the remaining after-products and by-products are extracted, the reaction chamber is filled with the protective gas so that the substrate is in an environment filled with the protective gas. After the reaction chamber is filled with the protective gas, the extraction is stopped.

[0060] Step S1, step S2, step S3 and step S4 are cyclically performed to form at least two aluminum oxide passivation layers on the top surface of the P-type diffusion layer 2, for example, Figure 3 As shown, the first aluminum oxide passivation layer 51 is formed first, then the second aluminum oxide passivation layer 52 is formed, then the third aluminum oxide passivation layer 53 is formed, then the fourth aluminum oxide passivation layer 54 is formed, and then the fifth aluminum oxide passivation layer 55 and the sixth aluminum oxide passivation layer 66 are formed in sequence.

[0061] Among them, the number of cycles of cyclic execution of step S1, step S2, step S3 and step S4 is at least two groups of cycles, so that the ratio of oxygen flow rate and water vapor flow rate in the latter group of cycles is less than the ratio of oxygen flow rate and water vapor flow rate in the previous group of cycles. Under this setting, the concentration of aluminum oxide in the aluminum oxide passivation layer (e.g., the second aluminum oxide passivation layer 52) formed in the latter group of cycles is lower than the concentration of aluminum oxide in the aluminum oxide passivation layer (e.g., the first aluminum oxide passivation layer 51) formed in the previous group of cycles, so that the refractive index of the aluminum oxide passivation layer formed in the latter group of cycles is lower than the refractive index of the aluminum oxide passivation layer formed in the previous group of cycles. It can also be understood that the refractive index of the prepared aluminum oxide passivation layer 5 decreases from the inside to the outside along the direction X. This setting can make the prepared aluminum oxide passivation layer 5 have a better anti-reflection effect, the efficiency of sunlight incident from the aluminum oxide passivation layer 5 to the silicon substrate 1 is high, and the efficiency of generating free electrons and holes in the silicon substrate 1 is high, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is high.

[0062] Among them, oxygen has a strong oxidizing ability, and the molecular structure of oxygen is more stable. The oxidizing property of oxygen has a greater influence on the rate of forming aluminum oxide. The concentration of oxygen can be controlled to control the concentration of aluminum oxide in the aluminum oxide passivation layer. If the oxygen concentration is relatively low, the concentration of aluminum oxide in the formed aluminum oxide passivation layer will also be relatively low, that is, the refractive index of the formed aluminum oxide passivation layer is low. It can also be said from another perspective that if the oxygen concentration is relatively low, the density of aluminum oxide in the formed aluminum oxide passivation layer will also be relatively low, that is, the formed aluminum oxide passivation layer is relatively loose, and the refractive index of the relatively loose aluminum oxide passivation layer is lower.

[0063] In addition, the preparation method provided in the embodiments of the present application may include two sets of cycles, three sets of cycles, four sets of cycles, five sets of cycles, six sets of cycles or seven sets of cycles.

[0064] Optionally, the method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies any of the following settings:

[0065] Setting (1): Make the oxygen flow rate of the latter group of cycles smaller than that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles the same as that of the former group of cycles.

[0066] Setting (2): Make the oxygen flow rate of the latter group of cycles the same as that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles greater than that of the former group of cycles.

[0067] Setting (3): Make the oxygen flow rate of the latter group of cycles smaller than that of the former group of cycles, and make the water vapor flow rate of the latter group of cycles larger than that of the former group of cycles.

[0068] Setting (1), setting (2) and setting (3) can all achieve that the refractive index of the aluminum oxide passivation layer 5 to be prepared gradually decreases from the inside to the outside along the direction X, so that the prepared aluminum oxide passivation layer 5 has a better anti-reflection effect.

[0069] Optionally, the method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies at least one of the following settings:

[0070] Setting (a): The ratio of oxygen flow rate to water vapor flow rate in the first group of cycles is 1.8 to 2.2. Specifically, the ratio can be 1.8, 1.9, 2.0, 2.1 or 2.2. Since the aluminum oxide passivation layer (e.g., the first aluminum oxide passivation layer 51) formed in the first group of cycles is closest to the P-type diffusion layer 2, if the ratio is less than 1.8, the concentration of aluminum oxide in the aluminum oxide passivation layer formed in the first group of cycles is low, and accordingly, the density of negative charges in the aluminum oxide passivation layer formed in the first group of cycles is too low, and the density of positive charges induced by negative charges in the aluminum oxide passivation layer formed in the first group of cycles in the P-type diffusion layer 2 is also too small. Correspondingly, the built-in electric field formed by the aluminum oxide passivation layer and the P-type diffusion layer 2 is too weak, and the minority carriers (free electrons) in the P-type diffusion layer 2 are not easy to move away from the contact surface between the P-type diffusion layer 2 and the aluminum oxide passivation layer under the action of the too weak built-in electric field. The minority carriers (free electrons) in the P-type diffusion layer 2 are easy to recombine with holes at the contact surface, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is too low. If the ratio is greater than 2.2, the concentration of aluminum oxide in the aluminum oxide passivation layer formed in the first group of cycles is too high, and the refractive index of the aluminum oxide passivation layer formed in the first group of cycles is too large. Correspondingly, the aluminum oxide passivation layer formed in the first group of cycles has too strong reflection effect on light, and the efficiency of light incident from the aluminum oxide passivation layer formed in the first group of cycles to the silicon substrate is too low, and the efficiency of generating free electrons and holes in the silicon substrate is too low, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is too low. Therefore, it is better to make the ratio of oxygen flow rate to water vapor flow rate in the first group of cycles within the range of 1.8 to 2.2.

[0071] Setting (b): The ratio of oxygen flow rate to water vapor flow rate in the last group of cycles is 0.3 to 0.7. Specifically, the ratio can be 0.3, 0.4, 0.5, 0.6 or 0.7. Since the aluminum oxide passivation layer (e.g., the sixth aluminum oxide passivation layer 56) formed in the last group of cycles is farthest from the P-type diffusion layer 2, if the ratio is greater than 0.7, the concentration of aluminum oxide in the aluminum oxide passivation layer formed in the last group of cycles is too high, and the refractive index of the aluminum oxide passivation layer formed in the last group of cycles is too large. Correspondingly, the aluminum oxide passivation layer formed in the last group of cycles has too strong a reflection effect on light, and the efficiency of light incident from the aluminum oxide passivation layer formed in the last group of cycles to the aluminum oxide passivation layer located on the inner side is too low, and finally the efficiency of light incident on the silicon substrate is too low, and the efficiency of generating free electrons and holes in the silicon substrate is too low, so that the photoelectric conversion efficiency of the prepared photovoltaic cell is low. If the ratio is less than 0.3, the rate of forming the aluminum oxide passivation layer in the last group of cycles is slow, resulting in a longer preparation time. Therefore, the ratio of oxygen flow rate to water vapor flow rate in the last set of cycles is preferably in the range of 0.3 to 0.7.

[0072] Optionally, the method for making the ratio of oxygen flow rate to water vapor flow rate of the latter group of cycles smaller than the ratio of oxygen flow rate to water vapor flow rate of the former group of cycles includes: making the ratio of oxygen flow rate to water vapor flow rate of the latter group of cycles have a difference with the ratio of oxygen flow rate to water vapor flow rate of the former group of cycles, and making the absolute value of the latter difference smaller than the absolute value of the former difference. For example, making the ratio of oxygen flow rate to water vapor flow rate of the second group of cycles have a first difference with the ratio of oxygen flow rate to water vapor flow rate of the first group of cycles, making the ratio of oxygen flow rate to water vapor flow rate of the third group of cycles have a second difference with the ratio of oxygen flow rate to water vapor flow rate of the second group of cycles, and making the absolute value of the second difference smaller than the absolute value of the first difference. By analogy, the absolute value of the third difference is smaller than the absolute value of the second difference, and the absolute value of the last difference is smaller than the absolute value of the second-to-last difference. Correspondingly, the difference between the refractive index of the last aluminum oxide passivation layer formed (for example, the sixth aluminum oxide passivation layer 56) and the refractive index of the second to last aluminum oxide passivation layer formed (the fifth aluminum oxide passivation layer 55) is relatively small, and the difference between the refractive index of the second to last aluminum oxide passivation layer formed (the fifth aluminum oxide passivation layer 55) and the refractive index of the third to last aluminum oxide passivation layer formed (the fourth aluminum oxide passivation layer 54) is also relatively small. When sunlight first passes through these aluminum oxide passivation layers with relatively low refractive indices and relatively small refractive index changes, the part of sunlight reflected is relatively small, which is conducive to more sunlight energy being incident on relatively deep parts of the aluminum oxide passivation layer (such as the third aluminum oxide passivation layer 53, the second aluminum oxide passivation layer 52 and the first aluminum oxide passivation layer 51). Even if the refractive index of the relatively deep part is relatively large, resulting in part of the light being reflected, the reflected light will still be reflected back by the relatively shallow aluminum oxide passivation layer. Therefore, it is conducive to the silicon substrate to absorb more light, so that the silicon substrate can generate more free electrons and photogenerated holes, thereby making the photoelectric conversion efficiency of the prepared photovoltaic cell higher.

[0073] In other embodiments, the latter difference may also be the same as the former difference.

[0074] It should be noted that two or more adjacent cycles with the same ratio of oxygen flow rate to water vapor flow rate can be classified as the same group of cycles. Therefore, the same group of cycles can include at least two cycles, and in the same group of cycles, the ratio of oxygen flow rate to water vapor flow rate in the latter cycle is the same as the ratio of oxygen flow rate to water vapor flow rate in the previous cycle. Therefore, the refractive index of the aluminum oxide passivation layer formed in the latter cycle is the same as the refractive index of the aluminum oxide passivation layer formed in the previous cycle. In the same group of cycles, since each cycle uses a protective gas to purge the reaction chamber, the by-products in the reaction chamber can be cleaned in time, so that an aluminum oxide passivation layer with a certain thickness, high purity and the same refractive index can be formed in the same group of cycles.

[0075] The same group of cycles may include two cycles, three cycles, four cycles, five cycles or six cycles.

[0076] In other embodiments, a group of cycles may include only one cycle.

[0077] Optionally, any loop satisfies at least one of the following settings:

[0078] Setting (α): Time T for a single introduction of precursor into the reaction chamber 1 5S~10S, where time T 1 Specifically, it can be 5S, 6S, 7S, 8S, 9S or 10S. Setting (α) can ensure that the substrate surface can have sufficient time to adsorb trimethylaluminum in the current cycle.

[0079] Setting (β): Time T for a single injection of the post-processing agent into the reaction chamber 2 5S~10S, where time T 2 Specifically, it can be 5S, 6S, 7S, 8S, 9S or 10S. Setting (β) can ensure that there is sufficient time to form an aluminum oxide passivation layer under the current cycle.

[0080] Setting (γ): Time T for introducing protective gas into the reaction chamber once 3 is 10S~15S, where time T 3 Specifically, it can be 10S, 11S, 12S, 13S, 14S or 15S. Setting (γ) can ensure that the remaining precursors, post-products and by-products are completely removed in the current cycle.

[0081] Optionally, before performing step S1, the preparation method of the embodiment of the present application further includes pretreatment, and the pretreatment method includes:

[0082] Step S01: water vapor is introduced into the reaction chamber, wherein a substrate is also arranged in the reaction chamber. Under this setting, the top surface of the P-type diffusion layer 2 of the substrate is wetted, or in other words, liquid water is stored on the top surface of the P-type diffusion layer 2 of the substrate, so that the trimethylaluminum introduced in the first subsequent cycle can be dissolved in the liquid water on the top surface of the P-type diffusion layer 2, which is conducive to more trimethylaluminum combining with the hydroxyl groups on the top surface of the P-type diffusion layer 2, thereby increasing the rate of generating intermediates.

[0083] The time T for executing step S01 once is 3 is 4S~6S, where time T 3 Specifically, it can be 4S, 5S or 6S.

[0084] Step S02: introducing a protective gas into the reaction chamber and extracting the remaining water vapor. After the remaining water vapor is extracted, the reaction chamber is filled with the protective gas so that the substrate is in an environment filled with the protective gas. After the reaction chamber is filled with the protective gas, stopping the extraction.

[0085] The time T for executing step S02 once is 4 is 4S~6S, where time T 4 Specifically, it can be 10S, 11S or 12S.

[0086] Optionally, step S01 and step S02 are executed cyclically, and the number of cycles may be three cycles, four cycles, five cycles, six cycles or seven cycles. Under this setting, more liquid water can be stored on the top surface of the P-type diffusion layer 2, but more liquid water will not condense on the inner wall of the reaction chamber, so that more water vapor that cannot condense on the top surface of the P-type diffusion layer 2 can be extracted in time, thereby facilitating the improvement of the recycling rate of water vapor.

[0087] In other embodiments, during the preprocessing process, step S01 and step S02 may be performed only once.

[0088] In other embodiments, the preprocessing including step S01 and step S02 may not be performed.

[0089] During the pretreatment process, the preparation method of the embodiment of the present application may include five cycles of pretreatment. During the preparation of the aluminum oxide passivation layer, the preparation method of the embodiment of the present application may include six groups of cycles, six groups of cycles are used to form six layers of aluminum oxide passivation layers with different refractive indices, each group of cycles includes five cycles, and five cycles are used to form aluminum oxide passivation layers with the same refractive index. Therefore, the preparation method provided by the embodiment of the present application may include a total of thirty-five cycles, as shown in Table 1 below.

[0090] Table 1

[0091]

[0092] After the required aluminum oxide passivation layer 5 is prepared, the preparation method of the embodiment of the present application further includes:

[0093] Step S5: forming an anti-reflection layer on the side of the outermost aluminum oxide passivation layer (e.g., the sixth aluminum oxide passivation layer 56) facing away from the substrate. Figure 4 The top anti-reflection layer 6 shown in FIG. 5 comprises silicon nitride and hydrogen. Accordingly, an anti-reflection layer is also formed on the side of the substrate away from the innermost aluminum oxide passivation layer (eg, the first aluminum oxide passivation layer 51). Figure 4The back anti-reflection layer 7 shown includes silicon nitride and hydrogen. Both the top anti-reflection layer 6 and the back anti-reflection layer 7 play an anti-reflection role on sunlight, so that more light can enter the silicon substrate 1, so that more free electrons and holes are generated in the silicon substrate 1, thereby improving the photoelectric conversion efficiency.

[0094] The process for preparing the anti-reflection layer may be low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) or atmospheric pressure chemical vapor deposition (APCVD).

[0095] In other embodiments, the material of the anti-reflection layer may also include at least one of titanium oxide, silicon oxide and cesium oxide.

[0096] Step S6: Annealing treatment. For example, the substrate formed with the multi-layer aluminum oxide passivation layer and the anti-reflection layer is sent into an annealing furnace, and the internal stress of the substrate, the aluminum oxide passivation layer and the anti-reflection layer is eliminated by high temperature, and the hydrogen element in the anti-reflection layer is promoted to diffuse to the surface of the silicon substrate by high temperature, so that the hydrogen atoms are combined with the dangling bonds on the surface of the silicon substrate, so as to achieve the effect of passivating the surface of the silicon substrate.

[0097] Step S7: Figure 4 As shown, a positive gate line 9 is formed in metallization contact with the P-type diffusion layer 2, and a negative gate line 8 is formed in metallization contact with the N-type doped medium layer 4. The process of forming the gate line may include screen printing-sintering, electroplating, evaporation, laser transfer, etc.

[0098] Among them, step S6 can be executed before step S7; or, step S6 can be executed after step S7; or, step S6 can be executed before step S7, and step S6 can be executed again after step S7.

[0099] In a second aspect, an embodiment of the present application provides a photovoltaic cell, which is prepared by the preparation method described above, and has good anti-reflection advantages and high photoelectric conversion efficiency. The photovoltaic cell includes a silicon substrate and at least two adjacent aluminum oxide passivation layers, and the refractive index of the at least two adjacent aluminum oxide passivation layers decreases in the direction from the silicon substrate to the outermost aluminum oxide passivation layer.

[0100] For example, as shown in the figure, the photovoltaic cell 10 may include an N-type silicon substrate 1, a P-type diffusion layer 2, a tunneling layer 3, an N-type doped medium layer 4, an aluminum oxide passivation layer 5, a top anti-reflection layer 6, a back anti-reflection layer 7, a negative electrode grid line 8 and a positive electrode grid line 9.

[0101] The back anti-reflection layer 7, the N-type doped dielectric layer 4, the tunneling layer 3, the N-type silicon substrate 1, the P-type diffusion layer 2, the aluminum oxide passivation layer 5, and the top anti-reflection layer 6 are stacked along the direction X. The negative electrode grid line 8 penetrates the top anti-reflection layer 6 and the aluminum oxide passivation layer 5, the positive electrode grid line 9 is in metallization contact with the P-type diffusion layer 2, the negative electrode grid line 8 penetrates the back anti-reflection layer 7, and the negative electrode grid line 8 is in metallization contact with the N-type doped dielectric layer 4.

[0102] The N-type silicon substrate 1 may be doped with at least one N-type element (element of the fifth main group in the periodic table of chemical elements), such as phosphorus, arsenic, antimony and other N-type elements; the P-type diffusion layer 2 may be doped with at least one P-type element (element of the third main group in the periodic table of chemical elements), such as boron, gallium, aluminum and other P-type elements; the tunneling layer 3 may include at least one of silicon oxide, silicon nitride and silicon oxynitride; the N-type doped medium layer 4 may also be doped with at least one N-type element, and after annealing, the N-type doped medium layer 4 includes polycrystalline silicon.

[0103] The N-type silicon substrate 1 and the P-type diffusion layer 2 form a PN junction. Under the action of light, more free electrons can tend to the N-type silicon substrate 1 and then to the N-type doped medium layer 4, and more holes tend to the P-type diffusion layer 2, so that the negative gate line 8 is negatively charged, and the positive gate line 9 can be positively charged.

[0104] The contact surface between the P-type diffusion layer 2 and the aluminum oxide passivation layer 5 is passivated by the negative charge field of the aluminum oxide passivation layer 5 and chemically passivated by the hydrogen element in the top anti-reflection layer 6, the contact surface between the N-type silicon substrate 1 and the tunneling layer 3 is passivated by the tunneling passivation contact structure formed by the tunneling layer 3 and the N-type doped dielectric layer 4, and the contact surface between the N-type doped dielectric layer 4 and the back anti-reflection layer 7 is chemically passivated by the hydrogen element in the back anti-reflection layer 7. Under this setting, the photoelectric conversion efficiency of the photovoltaic cell is relatively high.

[0105] As shown in the figure, the aluminum oxide passivation layer 5 includes a first aluminum oxide passivation layer 51, a second aluminum oxide passivation layer 52, a third aluminum oxide passivation layer 53, a fourth aluminum oxide passivation layer 54, a fifth aluminum oxide passivation layer 55 and a sixth aluminum oxide passivation layer 56. The first aluminum oxide passivation layer 51 is closest to the P-type diffusion layer 2, and the sixth aluminum oxide passivation layer 56 is closest to the top surface anti-reflection layer 6. In the aluminum oxide passivation layer 5, the refractive index of the first aluminum oxide passivation layer 51 is the largest, the refractive index of the sixth aluminum oxide passivation layer 56 is the smallest, and the refractive index of the aluminum oxide passivation layer 5 decreases along the direction X. Under this setting, the aluminum oxide passivation layer 5 can play a good anti-reflection role on sunlight, that is, the efficiency of sunlight incident on the silicon substrate 1 through the aluminum oxide passivation layer 5 is high, and the efficiency of generating free electrons and holes in the silicon substrate 1 is high, so that the photoelectric conversion efficiency of the photovoltaic cell is high.

[0106] Among them, the refractive index of the first aluminum oxide passivation layer 51 is in the range of 1.8 to 2.0, and the refractive index of the first aluminum oxide passivation layer 51 can be specifically 1.8, 1.9 or 2.0. The refractive index of the second aluminum oxide passivation layer 52 is in the range of 1.6 to 1.8, and the refractive index of the second aluminum oxide passivation layer 52 can be specifically 1.6, 1.7 or 1.8. The refractive index of the third aluminum oxide passivation layer 53 is in the range of 1.4 to 1.6, and the refractive index of the third aluminum oxide passivation layer 53 can be specifically 1.4, 1.5 or 1.6. The refractive index of the fourth aluminum oxide passivation layer 54 is in the range of 1.2 to 1.4, and the refractive index of the fourth aluminum oxide passivation layer 54 can be specifically 1.2, 1.3 or 1.4. The refractive index of the fifth aluminum oxide passivation layer 55 is in the range of 1.0 to 1.2, and the refractive index of the fifth aluminum oxide passivation layer 55 can be specifically 1.0, 1.1 or 1.2. The refractive index of the sixth aluminum oxide passivation layer 56 is in the range of 0.8 to 1.0, and the refractive index of the sixth aluminum oxide passivation layer 56 may specifically be 0.8, 0.9 or 1.0.

[0107] In other embodiments (not shown in the figures), the photovoltaic cell may also be of other configurations, that is, the photovoltaic cell satisfies the setting of "having at least two adjacent aluminum oxide passivation layers, and the refractive index of at least two adjacent aluminum oxide passivation layers decreases in the direction from the silicon substrate to the outermost aluminum oxide passivation layer".

[0108] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a photovoltaic cell, characterized in that: include: Step S1: introducing a precursor into a reaction chamber, wherein a substrate has been placed in the reaction chamber, and the precursor includes trimethylaluminum; Step S2: introducing a protective gas into the reaction chamber and extracting the remaining precursor and by-products; Step S3: introducing a post-processing agent into the reaction chamber to form an aluminum oxide passivation layer on the substrate, wherein the post-processing agent includes oxygen and water vapor; Step S4: introducing a protective gas into the reaction chamber and extracting the remaining after-products and by-products; Cycling the step S1, the step S2, the step S3 and the step S4 to form at least two aluminum oxide passivation layers on the substrate, wherein the number of cycles is at least two groups of cycles, so that the ratio of the oxygen flow rate to the water vapor flow rate in the latter group of cycles is smaller than the ratio of the oxygen flow rate to the water vapor flow rate in the former group of cycles; Step S5: forming an anti-reflection layer on a side of the outermost aluminum oxide passivation layer facing away from the substrate; Step S6: Annealing treatment.

2. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies any of the following settings: Setting (1): making the oxygen flow rate of the latter group of cycles smaller than the oxygen flow rate of the former group of cycles, and making the water vapor flow rate of the latter group of cycles the same as the water vapor flow rate of the former group of cycles; Setting (2): making the oxygen flow rate of the latter group of cycles the same as the oxygen flow rate of the former group of cycles, and making the water vapor flow rate of the latter group of cycles greater than the water vapor flow rate of the former group of cycles; Setting (3): making the oxygen flow rate of the latter group of cycles smaller than the oxygen flow rate of the former group of cycles, and making the water vapor flow rate of the latter group of cycles larger than the water vapor flow rate of the former group of cycles.

3. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method of making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles satisfies at least one of the following settings: Setting (a): making the ratio of the oxygen flow rate to the water vapor flow rate in the first group of cycles be 1.8 to 2.2; Setting (b): The ratio of the oxygen flow rate to the water vapor flow rate in the last set of cycles is 0.3 to 0.

7.

4. The method for preparing a photovoltaic cell according to claim 1, characterized in that: The method for making the ratio of the oxygen flow rate to the water vapor flow rate of the latter group of cycles smaller than the ratio of the oxygen flow rate to the water vapor flow rate of the former group of cycles comprises: A difference is provided between the ratio of the oxygen flow rate to the water vapor flow rate in a later cycle and the ratio of the oxygen flow rate to the water vapor flow rate in a previous cycle, and an absolute value of the later difference is smaller than an absolute value of the previous difference.

5. The method for preparing a photovoltaic cell according to any one of claims 1 to 4, characterized in that: The same group of cycles includes at least two cycles, and the ratio of the oxygen flow rate to the water vapor flow rate in the latter cycle is the same as the ratio of the oxygen flow rate to the water vapor flow rate in the former cycle.

6. The method for preparing a photovoltaic cell according to claim 5, characterized in that: The preparation method includes six groups of cycles, and each group of cycles includes five cycles.

7. The method for preparing a photovoltaic cell according to claim 5, characterized in that: Any loop meets at least one of the following settings: Setting (α): the time T1 for introducing the precursor into the reaction chamber at a time is 5S to 10S; Setting (β): the time T2 for introducing the post-drive into the reaction chamber at a time is 5S to 10S; Setting (γ): the time T3 for introducing the protective gas into the reaction chamber at one time is 10S to 15S.

8. The method for preparing a photovoltaic cell according to any one of claims 1 to 4, characterized in that: Before performing step S1, the preparation method further includes: Step S01: introducing water vapor into the reaction chamber, wherein a substrate has been placed in the reaction chamber; Step S02: introducing a protective gas into the reaction chamber and extracting the remaining water vapor.

9. The method for preparing a photovoltaic cell according to claim 8, characterized in that: The step S01 and the step S02 are executed in a loop, and the number of the loops is three to seven loops.

10. A photovoltaic cell, characterized in that: The photovoltaic cell is prepared by the method for preparing a photovoltaic cell according to any one of claims 1 to 9, and the photovoltaic cell comprises a silicon substrate and at least two adjacent aluminum oxide passivation layers; The refractive index of at least two adjacent aluminum oxide passivation layers decreases in a direction from the silicon substrate to the outermost aluminum oxide passivation layer.

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