Solar cell, preparation method thereof and photovoltaic module

Abstract

The invention relates to the field of solar cells, and discloses a solar cell and a preparation method thereof, and a photovoltaic module, the solar cell comprises a bottom structure, a transparent conductive layer and a metal layer, the transparent conductive layer and the metal layer are sequentially arranged on the bottom structure, the material of the transparent conductive layer comprises a metal oxide doped with a first doped metal element and a second doped metal element at the same time, wherein the ion radius of the second doped metal element is smaller than that of the first doped metal element, and the ion radius of the first doped metal element is smaller than that of the metal element in the metal oxide body; the material of the metal layer comprises metal elementary substances of which the types are the same as those of metal elements in the body; the electrode is arranged on the surface of the side, away from the transparent conductive layer, of the metal layer. According to the solar cell, the metal layer and the transparent conducting layer have good contact performance, the electrode and the metal layer have a high contact effect, the carrier transmission capacity is effectively optimized, and then the photoelectric conversion efficiency of the solar cell is improved.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a solar cell and its preparation method, and a photovoltaic module. Background Technology

[0002] In solar cells, the interfacial contact between the transparent conductive layer and the electrodes affects the ability to collect charge carriers. Poor interfacial contact results in a high interfacial barrier and high contact resistance, which in turn leads to lower charge carrier collection efficiency and makes it difficult to effectively improve the photoelectric conversion efficiency of the solar cell. Summary of the Invention

[0003] This invention discloses a solar cell and its fabrication method, as well as a photovoltaic module. In the solar cell of this application, the metal layer and the transparent conductive layer have good contact performance, and the electrode and the metal layer have a high contact effect, which effectively optimizes the carrier transport capability and thus improves the photoelectric conversion efficiency of the solar cell.

[0004] In a first aspect, this application discloses a solar cell, said solar cell comprising: Bottom structure; A transparent conductive layer is disposed on the bottom structure. The material of the transparent conductive layer includes a metal oxide that is simultaneously doped with a first doped metal element and a second doped metal element, wherein the ionic radius of the second doped metal element is smaller than the ionic radius of the first doped metal element, and the ionic radius of the first doped metal element is smaller than the ionic radius of the metal element in the bulk of the metal oxide. A metal layer is disposed on the surface of the transparent conductive layer opposite to the bottom structure, and the material of the metal layer includes a metallic element of the same type as the metal element in the body. An electrode is disposed on the side surface of the metal layer opposite to the transparent conductive layer.

[0005] Furthermore, the thickness of the metal layer is 1 nm to 5 nm; and / or, The roughness Ra of the metal layer is 10 nm to 30 nm.

[0006] Furthermore, the metal layer is prepared by reacting the metal oxide doped with the first doped metal element with a reaction source having the second doped metal element.

[0007] Further, the second doped metal element includes at least one selected from titanium, tungsten, zinc, tin, and aluminum; and / or, The energy level of the transparent conductive layer is 3.71 eV to 4.0 eV; and / or, The ionic radius of the second doped metal element is 30 pm to 55 pm; and / or, The ionic radius of the first doped metal element is 65 pm to 75 pm; and / or, The ionic radius of the metal element in the bulk is 78 pm to 85 pm; and / or, The metallic element in the body includes at least one of indium and zinc; and / or, The first doped metal element is tin or zinc; and / or, The electrode comprises a copper layer and a silver layer covering the copper layer; and / or, The solar cell is a heterojunction solar cell. The bottom structure includes a substrate, a passivation layer and a doped silicon layer stacked on the substrate, and a transparent conductive layer disposed on the side surface of the doped silicon layer opposite to the passivation layer.

[0008] Secondly, this application discloses a method for fabricating a solar cell, the method comprising the following steps: A transparent conductive layer and a metal layer are fabricated on a bottom structure. The transparent conductive layer is made of a metal oxide simultaneously doped with a first doped metal element and a second doped metal element. The ionic radius of the second doped metal element is smaller than that of the first doped metal element, and the ionic radius of the first doped metal element is smaller than that of the metal element in the bulk of the metal oxide. The metal layer is disposed on the surface of the transparent conductive layer facing away from the bottom structure, and the metal layer is made of a metallic element of the same type as that in the bulk structure. Electrodes are fabricated on the metal layer.

[0009] Further, the steps for preparing the metal layer and the transparent conductive layer include: The transparent conductive precursor layer is oxidized to prepare the transparent conductive precursor layer with hydroxyl groups, wherein the material of the transparent conductive precursor layer includes the metal oxide doped with the first doped metal element. A reaction source having the second doped metal element is introduced to form at least one metal precursor layer on the transparent conductive precursor layer, and the transparent conductive precursor layer having hydroxyl groups reacts with the metal precursor layer to obtain the transparent conductive layer and the metal layer, respectively.

[0010] Furthermore, in the step of oxidizing the transparent conductive precursor layer, the preparation parameters include: power of 50 W to 200 W, oxygen flow rate of 20 sccm to 50 sccm, and time of 1 min to 5 min.

[0011] Further, in the step of introducing a reaction source having the second doped metal element, at least one layer of the metal precursor layer is prepared using atomic layer deposition, wherein the step of preparing one layer of the metal precursor layer includes: The reaction source is carried by a non-reactive gas and introduced into the reaction chamber; The reaction source is shut off, and the reaction chamber is purged with the non-reactive gas.

[0012] Further, in the step of using a non-reactive gas to carry the reaction source and introduce it into the reaction chamber, the preparation parameters include: the reaction source is trimethylaluminum, the non-reactive gas includes argon, the introduction time is 0.1 s to 0.3 s, and the pressure is 50 Pa to 100 Pa; and / or, In the step of shutting off the reaction source and purging the reaction chamber with the non-reactive gas, the preparation parameters include: purging time of 5 s to 10 s and vacuum degree of 1×10⁻⁶. -4 Pa~5×10 -4 Pa.

[0013] Furthermore, the thickness of the metal precursor layer is 1 nm to 5 nm; and / or, The uniformity of the film thickness of the metal precursor layer is less than ±5%; and / or, The surface roughness Ra of the metal precursor layer is less than or equal to 5 nm; and / or, Before the step of oxidizing the transparent conductive precursor layer, the preparation method further includes cleaning the transparent conductive precursor layer.

[0014] Thirdly, this application discloses a photovoltaic module, which includes: the solar cell described in any one of the first aspects, or the solar cell prepared by the preparation method described in any one of the second aspects.

[0015] Compared with the prior art, the beneficial effects of this application are as follows: The transparent conductive layer and the metal layer in the solar cell of this application have good interface contact, which is more conducive to the transfer of charge carriers to the metal layer. In turn, the lower contact resistance between the electrode and the metal layer improves the collection efficiency of charge carriers by the electrode, thereby improving the photoelectric conversion efficiency of the solar cell.

[0016] The solar cell of this application has a transparent conductive layer, a metal layer, and electrodes sequentially disposed on its bottom structure. The transparent conductive layer is made of a metal oxide simultaneously doped with a first doped metal element and a second doped metal element, wherein the ionic radius of the second doped metal element is less than the ionic radius of the first doped metal element and less than the ionic radius of the metal in the bulk metal oxide. The co-doping of the first doped metal element with a relatively smaller ionic radius and the second doped metal element with an even smaller ionic radius can synergistically enhance the internal stress field and intensify the degree of lattice distortion. This enhanced lattice distortion and internal stress field can effectively prevent grain migration and merging growth, thereby making the grain size in the prepared transparent conductive layer small and uniform. At the same time, the second doped metal element with a smaller ionic radius can also regulate the surface energy and growth kinetics of the bulk, suppress the preferential growth of some crystal faces in the grain, make the growth rate of the grain in all directions equal, and enable the crystal faces in the grain to grow more uniformly, further making the grain size in the transparent conductive layer small and uniform, improving the film quality of the transparent conductive layer, and reducing the recombination loss of charge carriers in the transparent conductive layer.

[0017] Furthermore, when the transparent conductive layer has high-quality film, it can effectively optimize the interfacial contact between the transparent conductive layer and the metal layer, reducing the recombination loss of charge carriers at the interface. Moreover, the metal element in the metal oxide of the transparent conductive layer and the metal element in the metal layer are two different forms of the same element. This design makes the interface compatibility of the two layers high, further optimizing the contact effect between the transparent conductive layer and the metal layer, and further helping to improve the transport capability of charge carriers from the transparent conductive layer to the metal layer.

[0018] Furthermore, the electrodes in this application are in direct contact with the metal layer. Since the metal layer contains elemental metals, it has high conductivity, resulting in low contact resistance between the metal layer and the electrodes. This effectively improves the transport of charge carriers and further enhances the photoelectric conversion efficiency of the solar cell. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of a solar cell provided in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of a solar cell provided in an embodiment of this application (the bottom structure is shown in the solar cell). Figure 3 This is a schematic diagram illustrating the preparation of a transparent conductive precursor layer with hydroxyl groups, provided in an embodiment of this application. Figure 4 This is a schematic diagram illustrating the preparation of a metal precursor layer according to an embodiment of this application; Figure 5 This is a schematic diagram illustrating the preparation of a metal precursor layer into a metal elemental layer according to an embodiment of this application.

[0021] Icons: 1. Bottom structure; 11. Substrate; 111. Light-receiving surface; 112. Backlight-receiving surface; 12. First passivation layer; 13. First doped silicon layer; 14. Second passivation layer; 15. Second doped silicon layer; 2. Transparent conductive layer; 21. First transparent conductive layer; 22. Second transparent conductive layer; 2a. Transparent conductive precursor layer; 3. Metal layer; 31. First metal layer; 32. Second metal layer; 4. Electrode; 41. First electrode; 42. Second electrode. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0024] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0025] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, components, or parts (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, components, or parts. Unless otherwise stated, "a plurality of" means two or more.

[0026] The technical solutions provided in this application will be further described below with reference to the embodiments and accompanying drawings.

[0027] In solar cells, the transparent conductive layer not only collects photogenerated charge carriers but also needs to make ohmic contact with the electrodes to transport the collected charge carriers to the external circuitry. The effectiveness of this contact between the electrodes and the transparent conductive layer directly affects the series resistance and fill factor of the solar cell, thus determining its photoelectric conversion efficiency. However, the surface of the transparent conductive oxide layer contains a large number of dangling bonds and defect states. The presence of these dangling bonds and defect states results in a high interfacial barrier between the transparent conductive layer and the electrode, forming a Schottky contact rather than an ideal ohmic contact, which increases the contact resistance between the transparent conductive layer and the electrode.

[0028] Contact resistance can be reduced by increasing the carrier concentration in the transparent conductive layer or by increasing the silver content in the electrodes. However, increasing the carrier concentration in the transparent conductive layer will lead to enhanced optical absorption in the transparent conductive layer and reduced solar light absorption and utilization. On the other hand, increasing the silver content in the electrodes will increase the manufacturing cost of solar cells.

[0029] To address the above problems, this application provides a solar cell and its fabrication method, as well as a photovoltaic module. The solutions optimize the structural composition between the transparent conductive layer and the electrodes in the solar cell. This solar cell exhibits good interfacial contact between the transparent conductive layer and the metal layer, which facilitates the transfer of charge carriers to the metal layer. Furthermore, the lower contact resistance between the electrodes and the metal layer enhances the collection efficiency of charge carriers by the electrodes, thereby improving the photoelectric conversion efficiency of the solar cell.

[0030] This application discloses a solar cell, such as Figure 1 As shown, the solar cell includes: Bottom structure 1; A transparent conductive layer 2 is disposed on the bottom structure 1. The material of the transparent conductive layer 2 includes a metal oxide that is simultaneously doped with a first doped metal element and a second doped metal element. The ionic radius of the second doped metal element is smaller than that of the first doped metal element, and the ionic radius of the first doped metal element is smaller than that of the metal element in the body of the metal oxide. Metal layer 3 is disposed on the side surface of transparent conductive layer 2 away from bottom structure 1. The material of metal layer 3 includes elemental metals of the same type as those in the main body. Electrode 4 is disposed on the side of the metal layer 3 facing away from the transparent conductive layer 2.

[0031] Here, bottom structure 1 refers to other functional film layers located below transparent conductive layer 2. For example, when the solar cell is a heterojunction solar cell, bottom structure 1 includes a substrate, and a passivation layer and a doped silicon layer sequentially disposed on the substrate.

[0032] The bulk of the metal oxide refers to the main component in the transparent conductive layer 2. For example, when the transparent conductive layer 2 is made of indium tin aluminum oxide, the bulk refers to indium oxide. Additionally, the second doped metal element includes at least one of titanium, tungsten, zinc, tin, and aluminum, the first doped metal element is tin or zinc, and the bulk metal element includes at least one of indium and zinc.

[0033] Metal layer 3 refers to a film layer containing metallic substances in the material, wherein the metallic substances include elemental metals and the elemental metals are of the same type as the metallic elements in the bulk material.

[0034] Furthermore, the type of metal element in the film layer of this application can be tested using energy dispersive spectroscopy (EDS). Specifically, electrode 4 can be stripped off first, and then EDS can be used to test the type of metal element in metal layer 3; then, metal layer 3 can be further stripped off, and then EDS can be used to test the type of metal element in the transparent conductive oxide layer. Moreover, the valence state of the metal in metal layer 3 can be tested using X-ray photoelectron spectroscopy (XPS). Specifically, after confirming the type of metal element in metal layer 3 through EDS, XPS is used to test the valence state of the metal element to confirm its form of existence. This application does not limit the specific testing method, as long as it meets the requirements of this application.

[0035] The bottom structure 1 of the solar cell of this application is sequentially provided with a transparent conductive layer 2, a metal layer 3, and an electrode 4. The transparent conductive layer 2 is made of a metal oxide doped with a first doped metal element and a second doped metal element. The ionic radius of the second doped metal element is less than that of the first doped metal element, which is less than that of the metal element in the bulk metal oxide. The first doped metal element, with its relatively smaller ionic radius, can replace the metal element in the bulk metal oxide, thereby increasing the internal stress field and the degree of lattice distortion in the transparent conductive layer 2. Under the interaction of the internal stress field and the lattice distortion, the migration and merging of grains are further hindered, resulting in small grain size and high uniformity in the transparent conductive layer 2. In addition, the transparent conductive layer 2 also has a second doped metal element with a smaller ionic radius than the first doped metal element. The presence of the second doped metal element further strengthens the internal stress field and the degree of lattice distortion in the transparent conductive layer 2, which further helps to ensure that a transparent conductive layer 2 with smaller grain size and higher uniformity is prepared.

[0036] Furthermore, the second doped metal element can regulate the surface energy and growth kinetics of the bulk, suppressing the preferential growth of certain crystal planes within the grain and ensuring a balanced growth rate of the grain in all directions. This allows each crystal plane to expand uniformly during grain growth, resulting in small, uniformly distributed grains in the transparent conductive layer 2, improving the film quality of the transparent conductive layer 2 and reducing carrier recombination losses within it.

[0037] In other words, the first and second doped metal elements can affect the crystal growth process of the grains. They can not only effectively block the migration and merging of the grains, but also make the growth rate of each crystal facet of the grains comparable, which helps to prepare smaller and more uniformly distributed grains and improves the film quality of the transparent conductive layer 2.

[0038] Among them, the high-quality transparent conductive layer 2 not only helps to reduce the defects of the transparent conductive layer 2 itself and reduce the recombination loss of charge carriers, but also enables the transparent conductive layer 2 and the metal layer 3 to have a high interface contact effect, reducing the recombination loss of charge carriers at the interface. Furthermore, the metal element in the metal oxide of the transparent conductive layer 2 and the metal element in the metal layer 3 are two different forms of the same element. This design makes the thermal expansion coefficients and work functions of the two interfaces similar, thereby making the interface compatibility of the two layers high, further optimizing the interface contact effect between the transparent conductive layer 2 and the metal layer 3, and further helping to improve the transport capability of charge carriers from the transparent conductive layer 2 to the metal layer 3.

[0039] Furthermore, in this application, the electrode 4 is in direct contact with the metal layer 3, and the material of the metal layer 3 includes elemental metals, which gives the metal layer 3 high conductivity. The contact resistance between the metal layer 3 and the electrode 4 is low, which can effectively improve the transport efficiency of charge carriers when they are transported from the metal layer 3 to the electrode 4, and thus further help to improve the photoelectric conversion efficiency of the solar cell.

[0040] In summary, the arrangement of the transparent conductive layer 2, the metal layer 3, and the electrode 4 in this application results in a high film quality for the transparent conductive layer 2. This high film quality reduces recombination losses of charge carriers in the transparent conductive layer 2, as well as between the transparent conductive layer 2 and the metal layer 3. This further enhances the charge carrier collection capability of the electrode 4, thereby improving the photoelectric conversion efficiency of the solar cell to a greater extent.

[0041] Furthermore, the thickness of the metal layer 3 is 1 nm to 5 nm. When the thickness of the metal layer 3 is within the above range, it can effectively ensure the transmittance of sunlight and also enable it to have a good contact effect with the electrode 4, thereby further improving the photoelectric conversion efficiency of the solar cell. For example, the thickness is 1 nm, 2 nm, 3 nm, 4 nm, or 5 nm, etc.

[0042] Furthermore, the thickness of the metal layer 3 can be measured using an ellipsometer. Specifically, at least five points are taken on the metal layer 3, and the thickness values ​​at these five points are measured respectively, thereby obtaining the average value of the measurement data. This application does not limit the specific testing method, as long as it achieves the purpose of this application. For example, an ellipsometer manufactured by Sentch GmbH, Germany, model SE-800, can be used to measure the film thickness.

[0043] Furthermore, the roughness Ra of the metal layer 3 is 10 nm to 30 nm. When the roughness of the metal layer 3 is within the above range, the contact effect between the metal layer 3 and the electrode 4 can be effectively ensured, thereby further improving the collection capability of the electrode 4 for charge carriers. For example, Ra is 10 nm, 15 nm, 20 nm, 25 nm, or 30 nm, etc.

[0044] The surface roughness Ra of this application can be tested using an atomic force microscope, specifically the Dimension Icon model manufactured by Bruker Corporation in the United States.

[0045] Furthermore, the metal layer 3 is prepared by reacting a metal oxide doped with a first doped metal element with a reaction source having a second doped metal element. The metal layer 3 is prepared by reacting the second doped metal element with the metal oxide doped with the first doped metal element. This method allows the second doped metal element to be incorporated into the bulk of the metal oxide while simultaneously reducing the metal in the metal oxide to obtain the metal layer 3. Moreover, this preparation method eliminates the obvious interface between the metal layer 3 and the transparent conductive layer 2, improving the interfacial contact between them and thus facilitating the transport of charge carriers from the transparent conductive layer 2 to the metal layer 3.

[0046] Furthermore, the energy level of the transparent conductive layer 2 is 3.71 eV to 4.0 eV. Through the synergistic effect of the first and second doped metal elements, the energy level of the transparent conductive layer 2 can be effectively adjusted to fall within the aforementioned range. This further facilitates a higher energy level matching between the transparent conductive layer 2 and the bottom structure 1, thereby reducing the interface barrier and improving the carrier transport effect from the bottom structure 1 to the transparent conductive layer 2. For example, the energy levels of the transparent conductive layer 2 are 3.71 eV, 3.78 eV, 3.84 eV, 3.92 eV, or 4.0 eV, etc.

[0047] The second doped metal element has an ionic radius of 30 pm to 55 pm; the first doped metal element has an ionic radius of 65 pm to 75 pm; and the bulk metal has an ionic radius of 78 pm to 85 pm. When the ionic radii of the first and second doped metal elements are within these ranges, they exhibit higher matching, which helps ensure the fabrication of a higher quality transparent conductive layer 2, thereby more effectively improving the photoelectric conversion efficiency of the solar cell. For example, the ionic radius of the second doped metal element is 30 pm, 38 pm, 46 pm, 52 pm, or 55 pm, etc.; the ionic radius of the first doped metal element is 65 pm, 67 pm, 69 pm, 72 pm, or 75 pm, etc.; and the ionic radius of the bulk metal is 78 pm, 80 pm, 82 pm, 84 pm, or 85 pm, etc.

[0048] Furthermore, electrode 4 includes a copper layer and a silver layer covering the copper layer. The silver layer is placed on top of the copper layer, which is mainly to prevent the copper from being oxidized, thereby ensuring the performance of electrode 4 to a greater extent.

[0049] Among them, solar cells can be heterojunction solar cells or perovskite solar cells.

[0050] In one alternative implementation, such as Figure 2 As shown, the solar cell is a heterojunction solar cell, and the bottom structure 1 includes: The substrate 11 includes a light-receiving surface 111 and a back-lighting surface 112 disposed opposite to each other; The light-receiving surface 111 of the substrate 11 is sequentially provided with a first passivation layer 12 and a first doped silicon layer 13; The backlight surface 112 of the substrate 11 is sequentially provided with a second passivation layer 14 and a second doped silicon layer 15; In addition, heterojunction solar cells also include: The transparent conductive layer 2 includes a first transparent conductive layer 21 and a second transparent conductive layer 22. The first transparent conductive layer 21 is disposed on the side surface of the first passivation layer 12 away from the first doped silicon layer 13, and the second transparent conductive layer 22 is disposed on the side surface of the second passivation layer 14 away from the second doped silicon layer 15. The metal layer 3 includes a first metal layer 31 and a second metal layer 32. The first metal layer 31 is disposed on the side surface of the first transparent conductive layer 21 that is away from the first doped silicon layer 13, and the second metal layer 32 is disposed on the side surface of the second transparent conductive layer 22 that is away from the second doped silicon layer 15. Electrode 4 includes a first electrode 41 and a second electrode 42. The first electrode 41 is disposed on the side of the first metal layer 31 away from the first transparent conductive layer 21, and the second electrode 42 is disposed on the side of the second metal layer 32 away from the second transparent conductive layer 22. Among them, one of the first electrode 41 and the second electrode 42 is a positive electrode and the other is a negative electrode; one of the first doped silicon layer 13 and the second doped silicon layer 15 is an N-type doped layer and the other is a P-type doped layer.

[0051] This application discloses a method for fabricating a solar cell, the method comprising the following steps: A transparent conductive layer and a metal layer are fabricated on the bottom structure. The transparent conductive layer is made of a metal oxide that is simultaneously doped with a first doped metal element and a second doped metal element. The ionic radius of the second doped metal element is smaller than that of the first doped metal element, and the ionic radius of the first doped metal element is smaller than that of the metal element in the metal oxide body. The metal layer is disposed on the side surface of the transparent conductive layer that is away from the bottom structure. The metal layer is made of a metal element of the same type as the metal element in the body. Electrodes are fabricated on a metal layer.

[0052] In one optional embodiment, the steps of fabricating the transparent conductive layer and the metal layer include: First, a transparent conductive layer is prepared on the bottom structure, and then a metal layer is deposited on the transparent conductive layer.

[0053] In another alternative embodiment, the steps of preparing the metal layer and the transparent conductive layer include: The transparent conductive precursor layer is oxidized to prepare a transparent conductive precursor layer with hydroxyl groups, wherein the material of the transparent conductive precursor layer includes a metal oxide doped with a first doped metal element. A reaction source having a second doped metal element is introduced to form at least one metal precursor layer on the transparent conductive precursor layer, and the transparent conductive precursor layer having hydroxyl groups reacts with the metal precursor layer to obtain a transparent conductive layer and a metal layer.

[0054] This preparation method improves the compatibility of the interface between the metal layer and the transparent conductive layer, which helps to reduce the recombination loss of charge carriers at the interface and thus helps to further improve the photoelectric conversion efficiency of solar cells.

[0055] Among them, such as Figure 3 As shown, when the transparent conductive precursor layer 2a is oxidized, highly active oxygen free radicals (O*) act on the interface of the transparent conductive precursor layer 2a, forming oxygen terminals (-O) at the interface of the transparent conductive precursor layer 2a. These oxygen terminals then adsorb water molecules, thereby forming a transparent conductive precursor layer 2a (TCO-OH) with hydroxyl groups (-OH).

[0056] Next, when the reaction source of the second doped metal element is introduced, the reaction source of the second doped metal element will first react with the hydroxyl group in the transparent conductive precursor layer to form a metal precursor layer. Then, the metal precursor layer will further react with the metal oxide in the transparent conductive layer. During the reaction, the second doped metal element will be incorporated into the bulk of the metal oxide, and the metal in the bulk of the metal oxide will be reduced to prepare the elemental metal.

[0057] For example: when the reaction source is trimethylaluminum and the transparent conductive oxide precursor layer is an indium tin oxide layer, such as Figure 4 As shown, a metal precursor layer formed by -Al(CH3)2 is prepared by reacting trimethylaluminum with hydroxyl groups. Impurities include the reaction product methane and unreacted trimethylaluminum. These impurities are discharged from the reaction chamber (the arrows in the figure indicate the direction of impurity discharge) to avoid adverse effects on subsequent deposition. Then, as... Figure 5 As shown, the metal precursor layer reacts with indium ions in the indium tin oxide layer. During the reaction, aluminum atoms replace indium ions in the indium tin oxide layer to achieve doping, and some indium ions are reduced to form elemental substances. The electrically neutral ethyl group is eventually discharged from the reaction chamber. In addition, impurities include reaction products such as ethylene (the arrow in the figure points to the direction of impurity discharge), and these impurities are further discharged from the reaction chamber.

[0058] Furthermore, in the step of oxidizing the transparent conductive precursor layer, the preparation parameters include: power of 50W~200W, oxygen flow rate of 20 sccm~50 sccm, and time of 1 min~5 min. By controlling the parameters of the oxidation treatment step within the above range, the number of hydroxyl groups in the transparent conductive layer is appropriate, which helps to ensure that the subsequently prepared metal layer has a high quality. For example, the power is 50 W, 80 W, 120 W, 160 W, or 200 W, etc.; the oxygen flow rate is 20 sccm, 28 sccm, 36 sccm, 42 sccm, or 50 sccm, etc.; and the time is 1 min, 2 min, 3 min, 4 min, or 5 min, etc.

[0059] Furthermore, in the step of introducing the reaction source of the second doped metal element, at least one metal precursor layer is prepared using atomic layer deposition, wherein the step of preparing a metal precursor layer includes: The reaction source is carried by a non-reactive gas and introduced into the reaction chamber; The reaction source is shut off, and the reaction chamber is purged with non-reactive gas.

[0060] When preparing two or more metal precursor layers, the above steps can be repeated cyclically. For example, when preparing two metal precursor layers, the above steps can be performed twice.

[0061] Furthermore, the thickness of the monolayer metal precursor layer is 0.7 nm to 1.2 nm. By controlling the thickness of the monolayer within this range, it is easier to ensure the film coverage effect and improve the quality of the metal layer to a greater extent. For example, the monolayer thickness is 0.7 nm, 0.85 nm, 1.0 nm, 1.1 nm, 1.2 nm, etc.

[0062] Furthermore, the total thickness of the metal precursor layer is 1 nm to 5 nm. Here, the total thickness refers to the sum of the thicknesses of multiple single-layer metal precursor layers.

[0063] In particular, controlling the thickness of the metal precursor layer within the aforementioned range helps ensure that the thickness of the subsequently prepared metal layer is appropriate, thereby further optimizing the photoelectric conversion efficiency of the solar cell. Examples include thicknesses of 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm.

[0064] Furthermore, the film thickness uniformity of the metal precursor layer is less than ±5%. When the film thickness uniformity of the metal precursor layer is within the above range, it helps to ensure the uniformity of subsequent reactions, resulting in a uniform film thickness of the prepared metal layer. Exemplarily, the film thickness uniformity is -5%, -2.5%, 0%, 2.5%, or 5%, etc.

[0065] Furthermore, the surface roughness Ra of the metal precursor layer is less than or equal to 5 nm. When the surface roughness of the metal precursor layer is within the above range, it is more conducive to preparing a metal layer with lower roughness, which in turn helps to improve the contact effect between the metal layer and the electrode. For example, Ra is 0.5 nm, 2 nm, 3 nm, 4 nm, or 5 nm, etc.

[0066] Furthermore, in the step of introducing the reaction source into the reaction chamber using a non-reactive gas, the preparation parameters include: the reaction source is trimethylaluminum, the non-reactive gas includes argon, the introduction time is 0.1 s to 0.3 s, and the pressure is 50 Pa to 100 Pa. By controlling the introduction time within the above range, the transparent conductive layer and the reaction source can react fully. This avoids both insufficient surface adsorption of the transparent conductive layer due to too short an introduction time and excessive accumulation of the reaction source due to too long an introduction time, thereby ensuring a high degree of preparation effect of the metal layer. In addition, by controlling the pressure and utilizing the carrying effect of the non-reactive gas, trimethylaluminum can be uniformly diffused to the surface of the transparent conductive layer, further contributing to improving the film quality of the metal layer. For example, the introduction time is 0.1 s, 0.15 s, 0.2 s, 0.25 s, or 0.3 s, etc.; and the pressure is 50 Pa, 65 Pa, 80 Pa, 90 Pa, or 100 Pa, etc.

[0067] Non-reactive gases refer to gases that do not react with the reaction source, bottom structure, transparent conductive layer, or metal layer, including at least one of argon and nitrogen.

[0068] In the step of shutting off the reaction source and purging the reaction chamber with non-reactive gas, the preparation parameters include: purging time of 5 s to 10 s and vacuum degree of 1×10⁻⁶. -4 Pa~5×10 -4 Pa. By controlling the purging parameters within the above range, it is possible to avoid the residue of unreacted reaction sources inside the reaction chamber, preventing agglomeration or side reactions with newly injected reaction sources in subsequent cycles. Simultaneously, byproducts are removed, ensuring the independence of each deposition cycle, thereby contributing to the preparation of high-quality metal layers. Exemplarily, the purging time is 5 s, 7 s, 8 s, 9 s, or 10 s, etc.; the vacuum degree is 1×10⁻⁶. -4 Pa, 2×10 -4 Pa, 3×10 -4 Pa, 3.5 × 10 -4 Pa, 4×10 -4 Pa, or 5 × 10 -4 Pa, etc.

[0069] Furthermore, prior to the oxidation treatment of the transparent conductive precursor layer, the preparation method also includes cleaning the transparent conductive precursor layer. This cleaning step facilitates the removal of oxygen from the transparent conductive precursor layer, thereby improving the effectiveness of the subsequent metal layer.

[0070] One method for cleaning is plasma cleaning, using a non-reactive gas such as argon as the plasma source. The power is controlled at 100 W to 150 W, and the cleaning time is 30 s to 60 s to clean the transparent conductive precursor layer. Controlling the parameters within this range effectively avoids damage to the transparent conductive precursor layer and improves the surface cleanliness of the transparent conductive precursor layer. Examples include power of 100 W, 110 W, 120 W, 130 W, or 150 W, and times of 30 s, 40 s, 50 s, 55 s, or 60 s.

[0071] This application discloses a photovoltaic module, which includes: the solar cell described above, or includes: a solar cell prepared by the preparation method described above.

[0072] The technical solution of this application will be further explained below with reference to more specific embodiments and experimental test results.

[0073] Example 1: This embodiment provides a heterojunction solar cell, the fabrication method of which includes the following steps: Texturing of N-type silicon substrates.

[0074] A first intrinsic silicon layer with a thickness of 7 nm was prepared on the light-receiving surface of a silicon substrate using PECVD.

[0075] A second intrinsic silicon layer with a thickness of 8 nm was prepared on the backlight surface using PECVD.

[0076] A 35 nm thick P-type doped layer was prepared in the second intrinsic silicon layer using PECVD.

[0077] An N-type doped layer with a thickness of 20 nm was prepared on the first intrinsic silicon layer using PECVD.

[0078] Fabrication of transparent conductive layer and metal layer: Transparent conductive indium tin oxide (ITO) precursor layers with a thickness of 100 nm were prepared on P-type doped layers and N-type doped layers, respectively, using the PVD method. The transparent conductive layer precursor layer was subjected to plasma cleaning. The plasma source was argon gas with a power of 120 W and a time of 50 s. The transparent conductive precursor layer was oxidized at an oxygen flow rate of 20 sccm for 4 min to prepare a transparent conductive precursor layer with hydroxyl groups. A reaction source with a second doped metal element is introduced to prepare at least one metal precursor layer on the transparent conductive precursor layer, thereby obtaining an indium oxide transparent conductive layer doped with both aluminum and tin and a metal indium layer with a thickness of 3 nm and a roughness of 10 nm; wherein, the three metal precursor layers are prepared by atomic layer deposition, and the preparation steps include: Open the raw material valve for trimethylaluminum, and use argon gas to carry trimethylaluminum into the reaction chamber. The pulse time is 0.2 s, and the pressure of trimethylaluminum is 60 Pa. Close the trimethylaluminum feed valve and purge the reaction chamber with argon gas for 8 seconds. The vacuum level of the reaction chamber is 3 × 10⁻⁶. -4 Pa was used to prepare a first metal precursor layer with a thickness of 1 nm. Next, the raw material valve for trimethylaluminum is opened, and trimethylaluminum is introduced into the reaction chamber using argon gas. The pulse time is 0.2 s, and the pressure of trimethylaluminum is 60 Pa. Close the trimethylaluminum feed valve and purge the reaction chamber with argon gas for 8 seconds. The vacuum level of the reaction chamber is 3 × 10⁻⁶. -4 Pa was used to prepare a second metal precursor layer with a thickness of 1 nm. Finally, the raw material valve for trimethylaluminum is opened, and trimethylaluminum is introduced into the reaction chamber using argon gas. The pulse time is 0.2 s, and the pressure of trimethylaluminum is 60 Pa. Close the trimethylaluminum feed valve and purge the reaction chamber with argon gas for 8 seconds. The vacuum level of the reaction chamber is 3 × 10⁻⁶. -4 Pa was used to prepare a third metal precursor layer with a thickness of 1 nm. The metal precursor layer was prepared by stacking the first metal precursor layer to the third metal precursor layer. The total thickness of the metal precursor layer was 3 nm, the surface roughness was less than 0.2 nm, and the film thickness uniformity was 1%.

[0079] Copper paste is printed onto a transparent conductive layer using screen printing, followed by silver paste being printed onto the copper paste to obtain the electrode.

[0080] Example 2: The only difference between this embodiment and Embodiment 1 is that the thickness of the metal layer in this embodiment is 1 nm.

[0081] Example 3: The only difference between this embodiment and Embodiment 1 is that the thickness of the metal layer in this embodiment is 5 nm.

[0082] Example 4: The only difference between this embodiment and Embodiment 1 is that the thickness of the metal layer in this embodiment is 6 nm.

[0083] Example 5: The only difference between this embodiment and Embodiment 1 is that the thickness of the metal layer in this embodiment is 0.5 nm.

[0084] Example 6: The difference between this embodiment and Embodiment 1 is that the steps for preparing the transparent conductive layer and the metal layer include: firstly, preparing an indium oxide transparent conductive layer doped with aluminum and tin using the PECVD method, and then preparing a metallic elemental indium layer on the indium oxide transparent conductive layer.

[0085] Example 7: The only difference between this embodiment and Embodiment 1 is that the transparent conductive precursor layer is not subjected to plasma cleaning; that is, after the transparent conductive precursor layer is prepared, it is directly oxidized.

[0086] Comparative Example 1: The only difference between this comparative example and Example 1 is that the transparent conductive layer in this comparative example is made of indium oxide doped with tin, meaning that the transparent conductive layer is doped with only tin.

[0087] Comparative Example 2: The only difference between this comparative example and Example 1 is that no metal layer is provided on the transparent conductive layer of this comparative example.

[0088] Comparative Example 3: The only difference between this comparative example and Example 1 is that the metal element in the metal layer of this comparative example is zinc.

[0089] Test data 1: The heterojunction solar cells prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to the following related tests: This application uses a Halm testing and sorting device to perform performance tests on the provided heterojunction solar cells, including open-circuit voltage, short-circuit current, and fill factor. The Halm device simulates sunlight and is equipped with electronic loads, data acquisition and computing equipment to test the electrical performance of photovoltaic devices (including heterojunction solar cells), such as Eta, Voc, Jsc, and FF. These parameters reflect the performance of the heterojunction solar cells. The silicon wafer used for the controlled test of the heterojunction solar cells is 1.07 cm². 2 The calibrated light intensity was 1000±50 W / m². The experimental results are as follows, where Voc represents the open-circuit voltage, Jsc represents the short-circuit current density, FF represents the fill factor, and Eta represents the photoelectric conversion efficiency. The experimental results are shown in Table 1.

[0090] Table 1 Performance test results of heterojunction solar cells

[0091] Comparing the data from Example 1 and Comparative Examples 1 to 3, it is evident that the photoelectric conversion efficiency of Example 1 is superior to that of Comparative Examples 1 to 3. This demonstrates that the present application effectively utilizes the first and second metal dopants in the metal oxide to adjust the grain size in the transparent conductive layer, thereby improving the interfacial contact between the metal layer and the transparent conductive layer. Simultaneously, since the metal layer contains elemental metals of the same type as those in the bulk metal oxide, the interfacial compatibility between the metal layer and the transparent conductive layer is effectively optimized, promoting better carrier transport from the transparent conductive layer to the metal layer. Based on this, the excellent contact between the metal layer and the electrode effectively enhances the electrode's carrier collection capability, thereby significantly improving the photoelectric conversion efficiency of the solar cell.

[0092] Comparing the data from Examples 1 to 5, it can be seen that the photoelectric conversion efficiency of Examples 1 to 3 is better than that of Examples 4 and 5. This indicates that the thickness of the metal layer in Examples 1 and 3 is more suitable. A more suitable thickness helps to improve the contact effect between the metal layer and the electrode, reduces the reflection loss of sunlight by the metal layer, and thus improves the absorption and utilization rate of sunlight.

[0093] Comparing the data from Example 1 and Example 6, it can be seen that the photoelectric conversion efficiency of Example 1 is better than that of Example 6. Therefore, the method of using trimethylaluminum to reduce indium ions in the transparent conductive layer to prepare the metal layer and the transparent conductive layer is more conducive to improving the interfacial compatibility between the metal layer and the transparent conductive layer, thereby further improving the photoelectric conversion efficiency of the solar cell.

[0094] Comparing the data from Example 1 and Example 7, it can be seen that the photoelectric conversion efficiency of Example 1 is better than that of Example 7. This demonstrates that cleaning the transparent conductive precursor layer facilitates the bonding of the transparent conductive precursor layer with hydroxyl groups, thereby helping to ensure the quality of the prepared metal layer.

[0095] The above provides a detailed description of the solar cells, their preparation methods, and photovoltaic modules disclosed in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the solar cells, their preparation methods, and photovoltaic modules. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A solar cell, characterized in that, The solar cell includes: Bottom structure; A transparent conductive layer is disposed on the bottom structure. The material of the transparent conductive layer includes a metal oxide that is simultaneously doped with a first doped metal element and a second doped metal element, wherein the ionic radius of the second doped metal element is smaller than the ionic radius of the first doped metal element, and the ionic radius of the first doped metal element is smaller than the ionic radius of the metal element in the bulk of the metal oxide. A metal layer is disposed on the surface of the transparent conductive layer opposite to the bottom structure, and the material of the metal layer includes a metallic element of the same type as the metal element in the body. An electrode is disposed on the side surface of the metal layer opposite to the transparent conductive layer.

2. The solar cell according to claim 1, characterized in that, The thickness of the metal layer is 1 nm to 5 nm; and / or, The roughness Ra of the metal layer is 10 nm to 30 nm.

3. The solar cell according to claim 1, characterized in that, The metal layer is prepared by reacting the metal oxide doped with the first doped metal element with a reaction source having the second doped metal element.

4. The solar cell according to claim 1, characterized in that, The second doped metal element includes at least one of titanium, tungsten, zinc, tin, and aluminum; and / or, The energy level of the transparent conductive layer is 3.71 eV to 4.0 eV; and / or, The ionic radius of the second doped metal element is 30 pm to 55 pm; and / or, The ionic radius of the first doped metal element is 65 pm to 75 pm; and / or, The ionic radius of the metal element in the bulk is 78 pm to 85 pm; and / or, The metallic element in the body includes at least one of indium and zinc; and / or, The first doped metal element is tin or zinc; and / or, The electrode comprises a copper layer and a silver layer covering the copper layer; and / or, The solar cell is a heterojunction solar cell. The bottom structure includes a substrate, a passivation layer and a doped silicon layer stacked on the substrate, and a transparent conductive layer disposed on the side surface of the doped silicon layer opposite to the passivation layer.

5. A method for fabricating a solar cell, characterized in that, The preparation method includes the following steps: A transparent conductive layer and a metal layer are fabricated on a bottom structure. The transparent conductive layer is made of a metal oxide simultaneously doped with a first doped metal element and a second doped metal element. The ionic radius of the second doped metal element is smaller than that of the first doped metal element, and the ionic radius of the first doped metal element is smaller than that of the metal element in the bulk of the metal oxide. The metal layer is disposed on the surface of the transparent conductive layer facing away from the bottom structure, and the metal layer is made of a metallic element of the same type as that in the bulk structure. Electrodes are fabricated on the metal layer.

6. The preparation method according to claim 5, characterized in that, The steps for preparing the metal layer and the transparent conductive layer include: The transparent conductive precursor layer is oxidized to prepare the transparent conductive precursor layer with hydroxyl groups, wherein the material of the transparent conductive precursor layer includes the metal oxide doped with the first doped metal element. A reaction source having the second doped metal element is introduced to form at least one metal precursor layer on the transparent conductive precursor layer, and the transparent conductive precursor layer having hydroxyl groups reacts with the metal precursor layer to obtain the transparent conductive layer and the metal layer, respectively.

7. The preparation method according to claim 6, characterized in that, In the step of oxidizing the transparent conductive precursor layer, the preparation parameters include: power of 50 W to 200 W, oxygen flow rate of 20 sccm to 50 sccm, and time of 1 min to 5 min.

8. The preparation method according to claim 6, characterized in that, In the step of introducing a reaction source having the second doped metal element, at least one layer of the metal precursor layer is prepared using atomic layer deposition, wherein the step of preparing one layer of the metal precursor layer includes: The reaction source is carried by a non-reactive gas and introduced into the reaction chamber; The reaction source is shut off, and the reaction chamber is purged with the non-reactive gas.

9. The preparation method according to claim 8, characterized in that, In the step of using a non-reactive gas to carry the reaction source and introduce it into the reaction chamber, the preparation parameters include: the reaction source is trimethylaluminum, the non-reactive gas includes argon, the introduction time is 0.1 s to 0.3 s, and the pressure is 50 Pa to 100 Pa; and / or, In the step of shutting off the reaction source and purging the reaction chamber with the non-reactive gas, the preparation parameters include: purging time of 5 s to 10 s and vacuum degree of 1×10⁻⁶. -4 Pa~5×10 -4 Pa.

10. The preparation method according to any one of claims 6 to 9, characterized in that, The thickness of the metal precursor layer is 1 nm to 5 nm; and / or, The uniformity of the film thickness of the metal precursor layer is less than ±5%; and / or, The surface roughness Ra of the metal precursor layer is less than or equal to 5 nm; And / or, Before the step of oxidizing the transparent conductive precursor layer, the preparation method further includes cleaning the transparent conductive precursor layer.

11. A photovoltaic module, characterized in that, The photovoltaic module includes: the solar cell according to any one of claims 1 to 4, or the solar cell prepared by the preparation method according to any one of claims 5 to 10.

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