Heterojunction solar cell and preparation method thereof, photovoltaic module and photovoltaic system

Abstract

The invention relates to the technical field of heterojunction cells, in particular to a heterojunction solar cell and a preparation method thereof, a photovoltaic module and a photovoltaic system. The heterojunction solar cell at least comprises a composite assembly, the composite assembly comprises an indium-free TCO thin film and a grid line electrode arranged on the surface of the indium-free TCO thin film, and the grid line electrode sequentially comprises a TCO grid line layer, a metal transition layer and a metal electrode in the first direction; the TCO grid line layer is made of an indium oxide-based TCO material, and the first direction is the direction in which the indium-free TCO thin film points to the grid line electrode. In the heterojunction cell, the contact resistance between the metal electrode and the indium-free material is small, and the photoelectric conversion efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of heterojunction battery technology, specifically to a heterojunction solar cell and its preparation method, photovoltaic module, and photovoltaic system. Background Technology

[0002] Silicon-based heterojunction (HJT) solar cells typically use n-type monocrystalline silicon (nc-Si) as a substrate. After cleaning and texturing, intrinsic hydrogenated amorphous silicon thin films or microcrystalline silicon thin films are deposited on both sides of the substrate to generate passivation. Subsequently, n-type amorphous silicon and p-type amorphous silicon (pn junction) are deposited on the front and back sides as doping layers, respectively. After depositing a transparent conductive oxide (TCO) thin film on the top layer, conductive electrodes are fabricated using screen printing technology. HJT solar cells prepared in this way have many performance advantages.

[0003] In the cost of non-silicon materials, the total thermal oxidizing agent (TCO) and electrode silver paste account for the majority. The TCO layer typically uses indium-based materials, which, while possessing good conductivity and light transmittance, are expensive and have limited reserves. Therefore, using indium-free materials to replace existing indium-based TCOs has become a development trend in heterojunction solar cells. However, indium-free materials such as tin oxide and zinc oxide have high contact resistance with the metal electrode. High contact resistance reduces the fill factor (FF), increases power loss, and affects carrier collection, thus impacting the cell's conversion efficiency. Therefore, reducing the contact resistance between indium-free materials and the metal electrode is of great significance. Summary of the Invention

[0004] The heterojunction solar cell provided by this invention has low contact resistance between the metal electrode and the indium-free material, resulting in high photoelectric conversion efficiency.

[0005] The method for fabricating heterojunction solar cells provided by this invention can produce heterojunction solar cells with low internal contact resistance and high photoelectric conversion efficiency.

[0006] The photovoltaic module provided by this invention has a high photoelectric conversion efficiency.

[0007] The photovoltaic system provided by this invention has high photoelectric conversion efficiency.

[0008] The first aspect of the present invention provides a heterojunction solar cell, comprising at least a composite component, the composite component comprising an indium-free TCO thin film and a grid electrode disposed on the surface of the indium-free TCO thin film, the grid electrode comprising, in sequence along a first direction, a TCO grid layer, a metal transition layer and a metal electrode; the material of the TCO grid layer is an indium oxide-based TCO material, and the first direction is the direction from the indium-free TCO thin film to the grid electrode.

[0009] In the heterojunction solar cell described above, the work function of the metal transition layer is 4.3-5.1 eV.

[0010] In the heterojunction solar cell described above, the metal in the metal transition layer includes one or more of Ni, Au, and Cu.

[0011] In the heterojunction solar cell described above, the material of the TCO grid layer includes one or more of IWO and ICO.

[0012] In the heterojunction solar cell described above, the metal electrode is a silver electrode.

[0013] In the heterojunction solar cell described above, the thickness of the TCO gate layer is 10-50 nm.

[0014] In the heterojunction solar cell described above, the thickness of the metal transition layer is 10-50 nm.

[0015] In the heterojunction solar cell described above, the thickness of the metal electrode is 14-18 μm.

[0016] The heterojunction solar cell described above includes a substrate, on the first main surface of which an intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side TCO thin film, and a front-side grid electrode are sequentially disposed.

[0017] An intrinsic hydrogenated amorphous silicon thin film, a p-type amorphous silicon thin film, and a composite component are sequentially disposed on the second main surface of the substrate.

[0018] The first main surface and the second main surface are two surfaces of the substrate that face away from each other.

[0019] In the heterojunction solar cell described above, the front TCO thin film is an indium-free TCO thin film, and the front grid line electrode includes a stacked TCO grid line layer and a metal electrode, with the TCO grid line layer located on the side of the metal electrode close to the front TCO thin film.

[0020] In the heterojunction solar cell described above, the front-side TCO thin film includes a first front-side TCO thin film and a second front-side TCO thin film. The work function of the first front-side TCO thin film is 3.6-4.1 eV, and the work function of the second front-side TCO thin film is 3.6-5.2 eV.

[0021] As described above, in the heterojunction solar cell, the indium-free TCO thin film in the composite module includes a first back TCO thin film and a second back TCO thin film stacked together. The work function of the first back TCO thin film is ≥5.0 eV, and the work function of the second back TCO thin film is 3.6-5.2 eV.

[0022] In the heterojunction solar cell described above, the material of the first TCO film on the front side is a Li-doped tin oxide-based TCO film; the material of the second TCO film on the front side is a tin oxide-based TCO film.

[0023] In the heterojunction solar cell described above, the material of the first TCO film on the back is zinc oxide-based TCO material, and the material of the second TCO film on the back is tin oxide-based TCO material.

[0024] In the heterojunction solar cell described above, the thickness ratio of the first TCO film on the front side to the second TCO film on the front side is (10-90):(10-90).

[0025] In the heterojunction solar cell described above, the thickness ratio of the first TCO film on the back side to the second TCO film on the back side is (10-90):(10-90).

[0026] In the heterojunction solar cell described above, the thickness of the front-side TCO thin film is 80-120 nm.

[0027] In the heterojunction solar cell described above, the thickness of the indium-free TCO thin film in the composite component is 80-120 nm.

[0028] The present invention also provides a method for fabricating a heterojunction solar cell as described in the first aspect above, comprising at least:

[0029] The steps involve sequentially fabricating a TCO gate layer, a metal transition layer, and a metal electrode on an indium-free TCO thin film to form the gate electrode.

[0030] The method for fabricating heterojunction solar cells described above includes:

[0031] An intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side first TCO thin film, and a front-side second TCO thin film are sequentially fabricated on one side of the first main surface of the substrate. A TCO gate layer and a metal electrode are sequentially fabricated on the front-side second TCO thin film to form a front-side gate electrode.

[0032] An intrinsic hydrogenated amorphous silicon thin film, a P-type amorphous silicon thin film, a first TCO thin film on the back side, and a second TCO thin film on the back side are sequentially fabricated on one side of the second main surface of the substrate. A TCO gate layer, a metal transition layer, and a metal electrode are sequentially fabricated on the second TCO thin film on the back side to form a back gate electrode.

[0033] The present invention also provides a photovoltaic module, including the heterojunction solar cell described above or the heterojunction solar cell prepared by the above preparation method.

[0034] The present invention also provides a photovoltaic system, including the photovoltaic module described above.

[0035] This invention employs a stacked electrode comprising a TCO gate layer, a metal transition layer, and a metal electrode. This stacked electrode effectively reduces the contact resistance between the metal electrode and the indium-free material, thereby effectively improving the photoelectric conversion efficiency of heterojunction solar cells. Attached Figure Description

[0036] Figure 1 These are schematic diagrams of the heterojunction solar cells provided in Embodiments 1-6 of the present invention.

[0037] Figure 2 This is a schematic diagram of the heterojunction solar cell provided in Embodiment 7 of the invention;

[0038] Figure 3 A schematic diagram of the structure of a heterojunction solar cell provided for comparative example 1 of the invention;

[0039] Figure 4 A schematic diagram of the structure of a heterojunction solar cell provided for comparative example 2 of the invention;

[0040] Figure 5 This is a schematic diagram of the test sample structure used in contact resistivity testing.

[0041] In the figure, 1 is the substrate, 2 is the intrinsic hydrogenated amorphous silicon thin film, 3 is the n-type amorphous silicon thin film, 4 is the p-type amorphous silicon thin film, 51 is the first TCO thin film on the front side, 52 is the first TCO thin film on the back side, 61 is the second TCO thin film on the front side, 62 is the second TCO thin film on the back side, 7 is the TCO gate layer, 8 is the metal transition layer, and 9 is the metal electrode. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] Based on the problem that in the existing technology, when indium-free materials are used as transparent conductive oxide (TCO) films, the contact resistance between the films and metal electrodes is large, which affects the performance of the cells, this invention provides a new heterojunction solar cell, which includes at least a composite component. The composite component includes an indium-free TCO film and grid line electrodes disposed on the surface of the indium-free TCO film.

[0044] To improve the problem of high contact resistance between indium-free materials and metal electrodes, the heterojunction cell provided by the present invention includes a TCO gate layer, a metal transition layer and a metal electrode in sequence along a first direction, wherein the material of the TCO gate layer is indium oxide-based TCO material (i.e., ITO).

[0045] The first direction mentioned above is the direction in which the TCO thin film points towards the gate electrode.

[0046] This invention employs a multilayer electrode, which effectively reduces the contact resistance between the metal electrode and the indium-free material, thereby effectively improving the photoelectric conversion efficiency of heterojunction solar cells.

[0047] In detail: the metal electrode is used to provide a low-resistance current transport path, the TCO gate layer can improve the contact between the metal electrode and the indium-free material, and the metal transition layer reduces the contact barrier through work function matching, which is more conducive to carrier transport, enhances the conductivity of the gate electrode and the indium-free TCO film, and reduces current loss.

[0048] Furthermore, the TCO grid layer is made of indium oxide-based TCO (ITO). Due to the smooth surface and excellent conductivity of the ITO layer, it can form uniform and dense contacts, which helps to further reduce contact resistance and decrease current transmission resistance. During high-temperature string bonding, due to the high conductivity of the electrodes (such as silver) and the good contact properties of the ITO layer, this electrode structure can withstand higher temperatures without contact loss or melting, ensuring the stability of the bonding joints. In other words, this structure can further improve the stability of the battery during long-term operation, reduce the impact of constantly changing contact resistance, and thus improve the reliability of the module.

[0049] In some specific embodiments, the work function of the metal transition layer is 4.3-5.1 eV. Under this condition, the contact barrier can be better reduced through work function matching, enhancing the conductivity between the metal electrode and the indium-free TCO thin film and reducing current loss. Specifically, the work function of the TCO gate layer (ITO) is 4.5-5.3 eV, and the work function of the metal electrode (such as Ag) is 4.26 eV. Therefore, ensuring that the work function of the metal transition layer is between 4.3-5.1 eV is beneficial for reducing the potential barrier.

[0050] For example, the metal in the metal transition layer includes one or more of Ni, Au, and Cu.

[0051] In this invention, the material of the TCO gate layer can be one or more of tungsten-doped indium oxide (IWO) and cerium-doped indium oxide (ICO). The metal electrode is typically a conventional silver electrode, which can be fabricated using silver paste.

[0052] In this invention, the thicknesses of the TCO gate layer, the metal transition layer, and the metal electrode are not specifically limited. In some embodiments, the thickness of the TCO gate layer is 10-50 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any value between any two of the above ranges; the thickness of the metal transition layer is 10-50 nm, such as 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any value between any two of the above ranges; the thickness of the metal electrode is 14-18 μm, such as 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any value between any two of the above ranges. Within this range, bandgap matching can be better achieved, and interlayer contact resistance can be reduced.

[0053] The composite components mentioned above can be either composite components located on a P-type amorphous silicon thin film or composite components located on an n-type amorphous silicon thin film. Correspondingly, in a heterojunction cell, only the composite components on the front side (located on an n-type amorphous silicon thin film) or the back side (located on a p-type amorphous silicon thin film) can adopt the above structure, or both of the above structures can be adopted simultaneously.

[0054] In some specific embodiments, a heterojunction solar cell includes a substrate. An intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side TCO thin film, and a front-side grid electrode are sequentially disposed on a first main surface of the substrate. An intrinsic hydrogenated amorphous silicon thin film, a p-type amorphous silicon thin film, and a composite module are sequentially disposed on a second main surface of the substrate. The first and second main surfaces are two back-to-back surfaces of the substrate.

[0055] In the above, there are no specific limitations on the substrate, intrinsic hydrogenated amorphous silicon thin film, n-type amorphous silicon thin film, and p-type amorphous silicon thin film; they can be prepared using conventional materials and methods in this field. Further details are omitted here.

[0056] In some embodiments, the front TCO film is an indium-free TCO film, and the front gate electrode includes a stacked TCO gate layer and a metal electrode, with the TCO gate layer located on the side of the metal electrode close to the front TCO film.

[0057] Both the front and back TCO films are made of indium-free materials, which can better reduce costs. The TCO gate layer is also made of indium oxide-based TCO material, which is beneficial to improving conductivity.

[0058] Specifically, the materials for the TCO gate layer are as described above and will not be repeated here. The low contact resistance between the electrode (e.g., silver) and ITO is attributed to their excellent bandgap matching. The highly conductive electrode is compatible with the electronic structure of ITO, resulting in a low contact interface barrier. This structure facilitates rapid charge collection and transport, forming an ohmic contact interface.

[0059] In heterojunction solar cells, at the front α-Si:H(n) / TCO interface, the TCO film has a low conduction band level, and the internal electric field build-up direction of the TCO / α-Si:H(n) Schottky contact is the same as that of α-Si:H(n) / c-Si, resulting in good band matching and allowing for normal electron transport. At the a-Si:H(p) / TCO interface, when the activation energy of the a-Si:H(p) film is lower than the band gap between the conduction band and Fermi level of the TCO film, hole levels in the a-Si:H(p) film are transferred to the conduction band of the TCO film, resulting in a functional emission transition. This transition is based on level transitions within the band gap of the TCO film and trap-assisted transitions. Therefore, the work function of the TCO film is a crucial parameter affecting band matching.

[0060] Therefore, considering the work function matching angle, the front-side TCO film includes a first front-side TCO film and a second front-side TCO film, with the work function of the first front-side TCO film being 3.6-4.1 eV and the work function of the second front-side TCO film being 3.6-5.2 eV. By setting the front-side TCO film as a bilayer structure, it can better match the work function of the doped layer (n-type amorphous silicon film) and the front-side gate electrode, reducing the contact barrier, decreasing contact resistance, and improving battery efficiency.

[0061] Furthermore, the indium-free TCO film in the composite module includes a first TCO film and a second TCO film stacked on the back side. The work function of the first TCO film on the back side is ≥5.0 eV, and the work function of the second TCO film on the back side is 3.6-5.2 eV. In this case, the work functions of the doped layer (p-type amorphous silicon film) and the back gate electrode can be better matched, reducing the contact barrier, reducing the contact resistance, and improving the battery efficiency.

[0062] For example, the material of the first TCO film on the front side can be a Li-doped tin oxide-based TCO film, and the material of the second TCO film on the front side can be a tin oxide-based TCO film, wherein the mass percentage of the doping element is 0-3%.

[0063] For example, the material of the first TCO film on the back side can be a zinc oxide-based TCO material, including but not limited to aluminum-doped zinc oxide (AZO), fluorine (F)-doped zinc oxide (FZO), and magnesium gallium co-doped zinc oxide (MgZO), with the mass percentage of the doping element typically being 0-3%.

[0064] In some embodiments, the first TCO film on the back side is AZO. The work function of AZO is typically around 4.5 eV. By adjusting the physical vapor deposition (PVD) deposition process of the AZO material, the work function can be increased to a maximum of 5.6 eV. The work function between the TCO film and the P-type amorphous silicon doped layer can be controlled by band matching.

[0065] The material of the second TCO film on the back can be a tin oxide-based TCO material, including but not limited to tantalum (Ta)-doped tin oxide film (TTO), fluorine-doped tin oxide (FTO), lithium-doped tin oxide (LiTO), and tungsten (W)-doped tin oxide film (WTO), with the mass percentage of the doping element generally being 0-3%. Tin oxide (SnO) x The work function of the atom (1≤x≤2) is 3.6-4.0eV. Adding different doping elements can adjust the work function range to 3.6-5.2eV and improve the electrical performance.

[0066] Furthermore, in practical applications, single-layer indium-free thin films (such as aluminum-doped zinc oxide (AZO)) are susceptible to environmental corrosion, leading to decreased photoelectric performance and low battery efficiency. The aforementioned double-layer indium-free TCO thin films exhibit higher stability compared to single-layer films (such as AZO). For example, the sheet resistance of a 100nm thick AZO film increases fourfold after 200 hours under humid and hot conditions, while the sheet resistance increases further after adding a 30nm thick SnO film to its surface. x After the thin film is used as the second TCO film on the back side, it can form a dense physical barrier to prevent water and oxygen penetration while undertaking the function of lateral carrier transport. This reduces the water vapor corrosion rate of the AZO layer and keeps the sheet resistance unchanged after 200 hours under humid and hot conditions, thereby effectively extending the battery life and reducing degradation.

[0067] In some specific embodiments, the thickness ratio of the first TCO film on the back side to the second TCO film on the back side is (10-90):(10-90).

[0068] It should be noted that, in this invention, the indium-free thin film (i.e., the front TCO thin film and / or the back TCO thin film) can also be prepared by stacking a variety of high-performance materials to improve the light transmittance and conductivity of the TCO and other properties.

[0069] There is no specific limitation on the thickness of the TCO film; a conventional thickness is sufficient. For example, in some specific embodiments, the thickness of the front TCO film is 80-120 nm, and the thickness of the indium-free TCO film in the composite component is also 80-120 nm.

[0070] The present invention also provides a method for fabricating the above-mentioned heterojunction solar cell, which includes at least the step of sequentially fabricating a TCO grid layer, a metal transition layer and a metal electrode to form the grid electrode on an indium-free TCO thin film.

[0071] To illustrate the preparation method of the present invention in more detail, the present invention provides a preferred method for fabricating the heterojunction solar cell, which includes the following steps:

[0072] An intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side first TCO thin film, and a front-side second TCO thin film are sequentially fabricated on one side of the first main surface of the substrate. A TCO gate layer and a metal electrode are sequentially fabricated on the front-side second TCO thin film to form a front-side gate electrode.

[0073] An intrinsic hydrogenated amorphous silicon thin film, a P-type amorphous silicon thin film, a first TCO thin film on the back side, and a second TCO thin film on the back side are sequentially fabricated on one side of the second main surface of the substrate. A TCO gate layer, a metal transition layer, and a metal electrode are sequentially fabricated on the second TCO thin film on the back side to form a back gate electrode.

[0074] The present invention provides a photovoltaic module, which contains the above-described heterojunction solar cell or a heterojunction solar cell prepared by the above-described preparation method.

[0075] In some implementations, heterojunction solar cells can be connected together by string welding, thereby collecting the electrical energy generated by each individual solar cell for subsequent transmission.

[0076] In some implementations, solar cells can be arranged at intervals or stacked together in a shingled manner.

[0077] For example, a photovoltaic module also includes an encapsulation layer and a cover plate, the encapsulation layer being used to cover the surface of the battery string and the cover plate being used to cover the surface of the encapsulation layer away from the battery string.

[0078] The present invention also proposes a photovoltaic system including the aforementioned photovoltaic module.

[0079] Photovoltaic systems can be applied in photovoltaic power plants, such as ground-mounted, rooftop, and floating power plants, as well as in equipment or devices that utilize solar energy to generate electricity, such as user solar power supplies, solar streetlights, solar cars, and solar buildings. Of course, it's understandable that the application scenarios of photovoltaic systems are not limited to these; that is, photovoltaic systems can be applied in all fields that require solar energy to generate electricity. Taking a photovoltaic power generation network as an example, a photovoltaic system can include photovoltaic arrays, combiner boxes, and inverters. A photovoltaic array can be an array combination of multiple photovoltaic modules; for example, multiple photovoltaic modules can form multiple photovoltaic arrays. The photovoltaic arrays are connected to combiner boxes, which collect the current generated by the photovoltaic arrays. The collected current flows through an inverter, converts it into AC power required by the mains grid, and then connects to the mains grid to achieve solar power supply.

[0080] Example 1

[0081] This embodiment provides a heterojunction solar cell and its fabrication method, wherein, as shown in the example... Figure 1 As shown, the heterojunction solar cell includes a substrate 1. On the first main surface of the substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, an n-type amorphous silicon thin film 3, a front first TCO thin film 51, a front second TCO thin film 61, and a front gate electrode are sequentially disposed. The front gate electrode includes a TCO gate layer 7 and a metal electrode 9, and the TCO gate layer 7 is located on the side of the metal electrode 9 close to the front second TCO thin film 61.

[0082] On the second main surface of substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, a p-type amorphous silicon thin film 4, a first TCO thin film 52 on the back side, a second TCO thin film 62 on the back side, and a back gate electrode are sequentially disposed. The back gate electrode includes a TCO gate layer 7, a metal transition layer 8, and a metal electrode 9 in sequence, and the TCO gate layer 7 is adjacent to the second TCO thin film 62 on the back side.

[0083] The first TCO film 52 on the back side, the second TCO film 62 on the back side, and the back grid line electrode together constitute the composite component.

[0084] The preparation method of the above heterojunction solar cell is as follows:

[0085] (1) The single-crystal silicon substrate (N-type) is subjected to getter treatment to purify the single-crystal silicon substrate, thereby effectively reducing the impurity content in the silicon wafer and increasing the effective carrier concentration.

[0086] (2) The single crystal silicon substrate after gettering is wet texturing to form a pyramid-shaped double-textured light-trapping microstructure, which reduces the surface reflection of the silicon wafer and increases the absorption of sunlight by the silicon wafer.

[0087] (3) Using a textured monocrystalline silicon wafer as a substrate, an intrinsic hydrogenated amorphous silicon thin film as a passivation layer is deposited on both sides of the silicon wafer by plasma-enhanced chemical vapor deposition (PECVD). Then, doped n-type amorphous silicon thin film and p-type amorphous silicon thin film are deposited sequentially on the intrinsic hydrogenated amorphous silicon thin film on the front and back sides.

[0088] (4) Using a single-crystal silicon wafer coated by PECVD as a substrate, a first TCO film is deposited on the front side using reactive plasma deposition (RPD). The material is a Li-doped tin oxide-based TCO film (LiTO, work function of 3.9eV) with a thickness of 30nm; a first TCO film is deposited on the back side using aluminum-doped zinc oxide (AZO, work function of 5.1eV) with a thickness of 30nm.

[0089] A second TCO film was deposited on the front and back sides of the first TCO film using the RPD method, with SnO as the material. x (1≤x≤2, work function is 4.9eV), thickness is 70nm;

[0090] (5) Based on step (4), a metal mask is covered on the front second TCO film and the back second TCO film respectively. The shape of the mask is consistent with the screen printing screen. A high-mobility ICO film (cerium-doped indium oxide film with a work function of 5.0 eV) is deposited on it using the RPD method as the TCO gate layer. The thickness of the TCO gate layer is 30 nm.

[0091] (6) Based on step (5), the back metal mask remains stationary, and a layer of Ni metal gate line (work function of 4.6eV) is deposited on the back TCO gate line electrode as a metal transition layer gate line with a thickness of 20nm.

[0092] (7) Based on step (6), double-sided screen printing is performed, and a 14μm thick metal electrode is printed using low-temperature silver paste. The electrode is then dried and annealed at 180°C for 30 minutes in a curing oven to form the metal electrode.

[0093] Example 2

[0094] This embodiment provides a heterojunction solar cell and its fabrication method. The difference from Embodiment 1 is that the material of the first TCO film on the back is tantalum-doped tin oxide (TTO, work function 5.2 eV), and the materials of the second TCO film on the front and back are FTO (work function 4.4 eV). Specifically, as shown... Figure 1 As shown, the heterojunction solar cell includes a substrate 1. On the first main surface of the substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, an n-type amorphous silicon thin film 3, a front first TCO thin film 51, a front second TCO thin film 61, and a front gate electrode are sequentially disposed. The front gate electrode includes a TCO gate layer 7 and a metal electrode 9, and the TCO gate layer 7 is located on the side of the metal electrode 9 close to the front second TCO thin film 61.

[0095] On the second main surface of substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, a p-type amorphous silicon thin film 4, a first TCO thin film 52 on the back side, a second TCO thin film 62 on the back side, and a back gate electrode are sequentially disposed. The back gate electrode includes a TCO gate layer 7, a metal transition layer 8, and a metal electrode 9 in sequence, and the TCO gate layer 7 is adjacent to the second TCO thin film 62 on the back side.

[0096] The first TCO film 52 on the back side, the second TCO film 62 on the back side, and the back grid line electrode together constitute the composite component.

[0097] The preparation method of the above heterojunction solar cell is as follows:

[0098] (1) The single-crystal silicon substrate (N-type) is subjected to getter treatment to purify the single-crystal silicon substrate, thereby effectively reducing the impurity content in the silicon wafer and increasing the effective carrier concentration.

[0099] (2) The single crystal silicon substrate after gettering is wet texturing to form a pyramid-shaped double-textured light-trapping microstructure, which reduces the surface reflection of the silicon wafer and increases the absorption of sunlight by the silicon wafer.

[0100] (3) Using a textured monocrystalline silicon wafer as a substrate, an intrinsic hydrogenated amorphous silicon thin film as a passivation layer is deposited on both sides of the silicon wafer by plasma-enhanced chemical vapor deposition (PECVD). Then, doped n-type amorphous silicon thin film and p-type amorphous silicon thin film are deposited sequentially on the intrinsic hydrogenated amorphous silicon thin film on the front and back sides.

[0101] (4) Using a single-crystal silicon wafer coated by PECVD as a substrate, a first TCO film is deposited on the front side using reactive plasma deposition (RPD). The material is a Li-doped tin oxide-based TCO film (LiTO, work function of 3.9eV) with a thickness of 30nm; a first TCO film is deposited on the back side using tantalum-doped tin oxide (TTO, work function of 5.2eV) with a thickness of 30nm.

[0102] A second TCO film was deposited on the front and back sides of the first TCO film using the RPD method. The material was FTO (work function of 4.4 eV), and the thickness of each film was 70 nm.

[0103] (5) Based on step (4), a metal mask is covered on the front second TCO film and the back second TCO film respectively. The shape of the mask is consistent with the screen printing screen. A high-mobility ICO film (cerium-doped indium oxide film with a work function of 5.0 eV) is deposited on it using the RPD method as the TCO gate layer. The thickness of the TCO gate layer is 30 nm.

[0104] (6) Based on step (5), the back metal mask remains stationary, and a layer of Ni metal gate line (work function of 4.6eV) is deposited on the back TCO gate line electrode as a metal transition layer gate line with a thickness of 20nm.

[0105] (7) Based on step (6), double-sided screen printing is performed, and a 14μm thick metal electrode is printed using low-temperature silver paste. The electrode is then dried and annealed at 180°C for 30 minutes in a curing oven to form the metal electrode.

[0106] Example 3

[0107] This embodiment provides a heterojunction solar cell and its fabrication method. The difference between this embodiment and Embodiment 1 is that the TCO gate layer material is IWO with a work function of 4.9 eV and a thickness of 10 nm; the metal in the metal transition layer is titanium with a work function of 4.33 eV and a thickness of 30 nm.

[0108] Example 4

[0109] This embodiment provides a heterojunction solar cell and its fabrication method. The difference between this embodiment and Embodiment 1 is that the TCO gate layer material is IWO with a work function of 4.9 eV and a thickness of 50 nm; the metal in the metal transition layer is copper with a work function of 4.65 eV and a thickness of 10 nm; and the metal electrode has a thickness of 16 μm.

[0110] Example 5

[0111] This embodiment provides a heterojunction solar cell and its fabrication method. The difference between this embodiment and Embodiment 1 is that the TCO gate layer material is IWO with a work function of 4.9 eV; the metal in the metal transition layer is Ni with a work function of 4.6 eV and a thickness of 20 nm; and the metal electrode has a thickness of 18 μm.

[0112] Example 6

[0113] This embodiment provides a heterojunction solar cell and its preparation method, wherein the difference from Embodiment 1 is that the thickness of the metal transition layer is 100 nm.

[0114] Example 7

[0115] This comparative example provides a heterojunction solar cell and its fabrication method. The structural difference between this and Example 1 is that the indium-free TCO thin film is a single layer. Wherein, as... Figure 2 As shown, the heterojunction cell includes: a substrate 1, on which an intrinsic hydrogenated amorphous silicon thin film 2, an n-type amorphous silicon thin film 3, a front-side TCO thin film, and a metal electrode 9 are sequentially disposed on the first main surface of the substrate 1.

[0116] An intrinsic hydrogenated amorphous silicon thin film 2, a p-type amorphous silicon thin film 4, a back TCO thin film, and a metal electrode 9 are sequentially disposed on the second main surface of the substrate 1.

[0117] The preparation method of the above heterojunction solar cell is as follows:

[0118] (1) The single-crystal silicon substrate (N-type) is subjected to getter treatment to purify the single-crystal silicon substrate, thereby effectively reducing the impurity content in the silicon wafer and increasing the effective carrier concentration.

[0119] (2) The single crystal silicon substrate after gettering is wet texturing to form a pyramid-shaped double-textured light-trapping microstructure, which reduces the surface reflection of the silicon wafer and increases the absorption of sunlight by the silicon wafer.

[0120] (3) Using a textured monocrystalline silicon wafer as a substrate, an intrinsic hydrogenated amorphous silicon thin film as a passivation layer is deposited on both sides of the silicon wafer by plasma-enhanced chemical vapor deposition (PECVD). Then, a doped n-type amorphous silicon thin film (front side) and a p-type amorphous silicon thin film (back side) are deposited sequentially on the intrinsic hydrogenated amorphous silicon thin film on the front and back sides.

[0121] (4) Using a single crystal silicon wafer coated by PECVD as a substrate, a front TCO thin film is deposited on the front side and a back TCO thin film is deposited on the back side using reactive plasma deposition (RPD). The material is tantalum doped tin oxide (TTO, work function of 5.2eV) with a thickness of 100nm.

[0122] (5) Based on step (4), a metal mask is covered on the front TCO film and the back TCO film respectively. The shape of the mask is consistent with the screen printing screen. A high-mobility ICO film (the work function of the cerium-doped indium oxide film is 5.0 eV) is deposited on it using the RPD method as the TCO gate layer. The thickness of the TCO gate layer is 30 nm.

[0123] (6) Based on step (5), the back metal mask remains stationary, and a layer of Ni metal gate line (work function of 4.6eV) is deposited on the back TCO gate line electrode as a metal transition layer gate line with a thickness of 20nm.

[0124] (7) Based on step (6), double-sided screen printing is performed, and a 14μm thick metal electrode is printed using low-temperature silver paste. The electrode is then dried and annealed at 180°C for 30 minutes in a curing oven to form the metal electrode.

[0125] Comparative Example 1

[0126] This comparative example provides a heterojunction solar cell and its preparation method, wherein, as Figure 3 As shown, the difference from Embodiment 1 is that neither the front gate electrode nor the back gate electrode contains a metal transition layer. Specifically, the heterojunction cell includes a substrate 1, on which an intrinsic hydrogenated amorphous silicon thin film 2, an n-type amorphous silicon thin film 3, a front first TCO thin film 51, a front second TCO thin film 61, and a front gate electrode are sequentially disposed on the first main surface of the substrate 1. The front gate electrode includes a TCO gate layer 7 and a metal electrode 9, and the TCO gate layer 7 is located on the side of the metal electrode 9 close to the front second TCO thin film 61.

[0127] On the second main surface of substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, a p-type amorphous silicon thin film 4, a first TCO thin film 52 on the back side, a second TCO thin film 62 on the back side, and a back gate electrode are sequentially disposed. The back gate electrode includes a TCO gate layer 7 and a metal electrode 9 in sequence, and the TCO gate layer 7 is adjacent to the second TCO thin film 62 on the back side.

[0128] The preparation method of the above heterojunction solar cell is as follows:

[0129] (1) The single-crystal silicon substrate (N-type) is subjected to getter treatment to purify the single-crystal silicon substrate, thereby effectively reducing the impurity content in the silicon wafer and increasing the effective carrier concentration.

[0130] (2) The single crystal silicon substrate after gettering is wet texturing to form a pyramid-shaped double-textured light-trapping microstructure, which reduces the surface reflection of the silicon wafer and increases the absorption of sunlight by the silicon wafer.

[0131] (3) Using a textured monocrystalline silicon wafer as a substrate, an intrinsic hydrogenated amorphous silicon thin film as a passivation layer is deposited on both sides of the silicon wafer by plasma-enhanced chemical vapor deposition (PECVD). Then, doped n-type amorphous silicon thin film and p-type amorphous silicon thin film are deposited sequentially on the intrinsic hydrogenated amorphous silicon thin film on the front and back sides.

[0132] (4) Using a single-crystal silicon wafer coated by PECVD as a substrate, a first TCO film is deposited on the front side using reactive plasma deposition (RPD). The material is a Li-doped tin oxide-based TCO film (LiTO, work function of 3.9eV) with a thickness of 30nm; a first TCO film is deposited on the back side using aluminum-doped zinc oxide (AZO, work function of 5.1eV) with a thickness of 30nm.

[0133] A second TCO film was deposited on the front and back sides of the first TCO film using the RPD method, with SnO as the material. x (1≤x≤2, work function is 4.9eV), thickness is 70nm;

[0134] (5) Based on step (4), a metal mask is covered on the front second TCO film and the back second TCO film respectively. The shape of the mask is consistent with the screen printing screen. A high-mobility ICO film (cerium-doped indium oxide film with a work function of 5.0 eV) is deposited on it using the RPD method as the TCO gate layer. The thickness of the TCO gate layer is 30 nm.

[0135] (6) Based on step (5), double-sided screen printing is performed, and a 14μm thick metal electrode is printed using low-temperature silver paste. The electrode is then dried and annealed at 180°C for 30 minutes in a curing oven to form the metal electrode.

[0136] Comparative Example 2

[0137] This comparative example provides a heterojunction solar cell and its preparation method, wherein, as Figure 4 As shown, the difference from Embodiment 1 is that neither the front gate electrode nor the back gate electrode contains a TCO gate layer. Specifically, the heterojunction cell includes a substrate 1, on which an intrinsic hydrogenated amorphous silicon thin film 2, an n-type amorphous silicon thin film 3, a front first TCO thin film 51, a front second TCO thin film 61, and a metal electrode 9 are sequentially disposed on the first main surface of the substrate 1.

[0138] On the second main surface of substrate 1, an intrinsic hydrogenated amorphous silicon thin film 2, a p-type amorphous silicon thin film 4, a first TCO thin film 52 on the back side, a second TCO thin film 62 on the back side, and a back gate electrode are sequentially disposed. The back gate electrode includes a metal transition layer 8 and a metal electrode 9 in sequence, and the metal transition layer 8 is adjacent to the second TCO thin film 62 on the back side.

[0139] The materials and thicknesses of each film are as in Example 1, and the preparation methods are the same as in Example 1.

[0140] Performance testing:

[0141] (1) Contact resistivity

[0142] Test Method: The contact resistivity of different electrode structures was tested using the transmission line model (TLM) method. A series of metal electrode-semiconductor structures with increasing spacing were fabricated, and the total resistance between adjacent electrodes was measured. The test results were obtained through linear fitting and calculation.

[0143] A schematic diagram of the test sample structure is shown below. Figure 5 As shown ( Figure 5 The materials used in each layer and their work functions are the same as in Example 1. This structure was used to test the contact resistivity between the Ag / metal transition layer / ITO multilayer electrode and the indium-free TCO. The number of electrode layers and materials were adjusted according to the required electrode structure to prepare corresponding samples, and the contact resistivity between different electrode structures and the indium-free TCO was tested. The test results are shown in Table 1 below:

[0144] Table 1

[0145] Contact type <![CDATA[Contact resistivity (mΩ·cm 2 )]]> <![CDATA[Ag / SnO x ]]> 2.85 <![CDATA[Ag / ICO / SnO x ]]> 2.19 <![CDATA[Ag / Cu / ICO / SnO x ]]> 2.01

[0146] The results above show that using Ag / Cu / ICO / SnO x The contact resistivity of the stacked electrode is significantly lower than that of Ag / SnO. x and Ag / ICO / SnO x This indicates that using a stacked grid of (TCO grid layer, metal transition layer, metal electrode) grid electrodes is beneficial for reducing contact resistance.

[0147] (2) The photoelectric conversion efficiency of the prepared heterojunction solar cell was tested. The open-circuit voltage (Voc), short-circuit current (Jsc), fill factor (FF), and photoelectric conversion efficiency (E) of the cell were obtained by scanning the JV curve. ff The parameters and information are shown in Table 2 below.

[0148] Table 2

[0149] <![CDATA[E ff (%)]]> FF (%) <![CDATA[J SC (mA / cm 2 )]]> <![CDATA[V OC (mV)]]> Example 1 24.96 84.11 39.78 746.1 Example 2 25.03 84.26 39.82 746.6 Example 3 24.90 84.02 39.73 745.8 Example 4 24.96 84.13 39.77 746.0 Example 5 24.95 84.24 39.69 746.3 Example 6 24.72 83.77 39.62 744.9 Example 7 24.56 83.64 39.40 745.3 Comparative Example 1 24.79 84.05 39.54 745.9 Comparative Example 2 24.39 83.42 39.22 745.4

[0150] The results above show that, compared with Comparative Examples 1 and 2, the photoelectric conversion efficiency of the heterojunction solar cell in Example 1 is higher than that in Comparative Examples 1 and 2. This indicates that using a stacked structure (TCO grid layer, metal transition layer, metal electrode) for the back grid line electrode is beneficial to reducing contact resistance, thereby improving the photoelectric conversion efficiency of the heterojunction solar cell.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heterojunction solar cell, characterized in that, It includes at least a composite component, the composite component including an indium-free TCO thin film and a gate electrode disposed on the surface of the indium-free TCO thin film, the gate electrode including a TCO gate layer, a metal transition layer and a metal electrode in sequence along a first direction; The TCO gate layer is made of indium oxide-based TCO material, and the first direction is the direction in which the indium-free TCO thin film points to the gate electrode.

2. The heterojunction solar cell according to claim 1, characterized in that, The work function of the metal transition layer is 4.3-5.1 eV.

3. The heterojunction solar cell according to claim 1 or 2, characterized in that, The metal in the metal transition layer includes one or more of Ni, Au, and Cu; and / or The material of the TCO gate layer includes one or more of IWO and ICO; and / or The metal electrode is a silver electrode.

4. The heterojunction solar cell according to any one of claims 1-3, characterized in that, The thickness of the TCO gate layer is 10-50 nm, and / or The thickness of the metal transition layer is 10-50 nm, and / or The thickness of the metal electrode is 14-18 μm.

5. The heterojunction solar cell according to any one of claims 1-4, characterized in that, The substrate includes an intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side TCO thin film, and a front-side gate electrode, which are sequentially disposed on the first main surface of the substrate. An intrinsic hydrogenated amorphous silicon thin film, a p-type amorphous silicon thin film, and a composite component are sequentially disposed on the second main surface of the substrate. The first main surface and the second main surface are two surfaces of the substrate that face away from each other.

6. The heterojunction solar cell according to claim 5, characterized in that, The front-side TCO film is an indium-free TCO film, and the front-side gate electrode includes a stacked TCO gate layer and a metal electrode, with the TCO gate layer located on the side of the metal electrode close to the front-side TCO film.

7. The heterojunction solar cell according to claim 5 or 6, characterized in that, The front-side TCO film includes a first front-side TCO film and a second front-side TCO film. The work function of the first front-side TCO film is 3.6-4.1 eV, and the work function of the second front-side TCO film is 3.6-5.2 eV; and / or The indium-free TCO film in the composite component includes a first back TCO film and a second back TCO film stacked together. The work function of the first back TCO film is ≥5.0 eV, and the work function of the second back TCO film is 3.6-5.2 eV.

8. The heterojunction solar cell according to claim 7, characterized in that, The material of the first TCO film on the front side is a Li-doped tin oxide-based TCO film; the material of the second TCO film on the front side is a tin oxide-based TCO film; and / or The material of the first TCO film on the back side is zinc oxide-based TCO material, and the material of the second TCO film on the back side is tin oxide-based TCO material.

9. The heterojunction solar cell according to claim 7 or 8, characterized in that, The thickness ratio of the first TCO film on the front side to the second TCO film on the front side is (10-90):(10-90); and / or The thickness ratio of the first TCO film on the back side to the second TCO film on the back side is (10-90):(10-90).

10. The heterojunction solar cell according to any one of claims 5-9, characterized in that, The thickness of the front-side TCO film is 80-120 nm; and / or The thickness of the indium-free TCO film in the composite component is 80-120 nm.

11. A method for preparing a heterojunction solar cell according to any one of claims 1-10, characterized in that, At least including: The steps involve sequentially fabricating a TCO gate layer, a metal transition layer, and a metal electrode on an indium-free TCO thin film to form the gate electrode.

12. The method for fabricating a heterojunction solar cell according to claim 11, characterized in that, The method includes: An intrinsic hydrogenated amorphous silicon thin film, an n-type amorphous silicon thin film, a front-side first TCO thin film, and a front-side second TCO thin film are sequentially fabricated on one side of the first main surface of the substrate. A TCO gate layer and a metal electrode are sequentially fabricated on the front-side second TCO thin film to form a front-side gate electrode. An intrinsic hydrogenated amorphous silicon thin film, a P-type amorphous silicon thin film, a first TCO thin film on the back side, and a second TCO thin film on the back side are sequentially fabricated on one side of the second main surface of the substrate. A TCO gate layer, a metal transition layer, and a metal electrode are sequentially fabricated on the second TCO thin film on the back side to form a back gate electrode.

13. A photovoltaic module, characterized in that, This includes the heterojunction solar cell according to any one of claims 1-10 or the heterojunction solar cell prepared by the preparation method according to any one of claims 11 or 12.

14. A photovoltaic system, characterized in that, Includes the photovoltaic module as described in claim 13.

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