Functional film layer structure for solar cell, solar cell and preparation method of functional film layer structure

Abstract

The invention relates to the technical field of solar cells, and particularly discloses a functional film layer structure for a solar cell, the solar cell and a preparation method of the solar cell. The functional film layer structure comprises a dielectric passivation layer and an ultraviolet light absorption layer which are sequentially arranged on the surface of a cell substrate, the ultraviolet light absorption layer is at least one of a zinc oxide layer, a gallium nitride layer and an indium tin oxide layer, and the thickness of the ultraviolet light absorption layer is 0.5-3 nm. Through the cooperation of the dielectric passivation layer and the ultraviolet light absorption layer, on the premise that the absorption of the functional film layer structure on 300-1200 nm wave band light is reduced as much as possible, the functional film layer structure can better absorb and filter out ultraviolet light in natural light, the ultraviolet resistance of the solar cell is improved, ultraviolet induced attenuation is reduced, sintering abnormity does not occur, and the service life of the solar cell is prolonged. The series resistance is not obviously increased, and the passivation effect of the solar cell can be improved, so that the functional film layer structure is beneficial to improving the electrical property of the solar cell and prolonging the service life of the solar cell.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to a functional film layer structure for a solar cell, a solar cell and a preparation method thereof. Background Art

[0002] A solar cell is a microelectronic device that directly converts light energy into electrical energy. After years of development, currently, the TOPCon cell (Tunnel Oxide Passivated Contact Solar Cell) is a cell structure with a relatively high market share. Generally, the TOPCon cell uses an N-type silicon wafer as a substrate, prepares a positive electrode (such as a P+ emitter) on the front side of the cell (the front side of the cell corresponds to the front side of the silicon wafer), and uses aluminum oxide (i.e., AlOx, such as Al 2 O 3 ) as the main passivation layer; prepares a negative electrode (such as a doped polysilicon layer) on the back side of the cell (the back side of the cell corresponds to the back side of the silicon wafer), specifically as follows: prepares a thin tunneling oxide layer (SiOx) on the back side of the cell, and grows a heavily doped polysilicon layer (Poly-Si) on the surface of the tunneling oxide layer. The tunneling oxide layer and the doped polysilicon layer together form a passivation contact structure that can improve the passivation performance and contact performance of the cell. Therefore, the double-sided passivated TOPCon cell (that is, both the front and back sides of the cell have a passivation contact structure) has higher passivation ability and conversion efficiency, which also makes the TOPCon cell the first choice for large-scale mass production.

[0003] In practice, sunlight contains not only visible light, but also a large amount of ultraviolet light (UV) and infrared light; ultraviolet light accounts for 7% in the solar spectrum, visible light accounts for 50%, and infrared light accounts for 43%. Ultraviolet light refers to the general term for light with wavelengths ranging from 10 - 400 nm in the electromagnetic spectrum. According to different wavelengths, ultraviolet light is usually subdivided into the following three bands: 1) UVA (long-wave ultraviolet light): its wavelength range is 320 - 400 nm; 2) UVB (medium-wave ultraviolet light): its wavelength range is 280 - 320 nm; 3) UVC (short-wave ultraviolet light): its wavelength range is 100 - 280 nm. Among them, UVA accounts for more than 95% of the ultraviolet light radiation reaching the Earth's surface, UVB accounts for about 5% of the ultraviolet light radiation reaching the Earth's surface, and UVC is almost completely blocked by the atmosphere.

[0004] However, compared with other types of batteries, the structure of TOPCon batteries is more susceptible to ultraviolet light. Due to the existence of ultraviolet induced degradation (UVID) in solar cells, the performance parameters such as open-circuit voltage, short-circuit current, and conversion efficiency of solar cells (especially TOPCon batteries) will decrease under ultraviolet irradiation, greatly affecting the service life of solar cells for long-term outdoor use.

[0005] As shown in the publication numbers CN116936648A and CN216528903U, in n-TOPCon batteries, AlOx (aluminum oxide) is generally used as the passivation layer for the front P+ emitter. As a polar material, aluminum oxide can accumulate negative charges to passivate the P+ emitter by means of field. Moreover, a part of elemental [H] can be retained in the aluminum oxide film during the preparation of aluminum oxide to chemically passivate the dangling bonds. At the same time, the bandgap width of aluminum oxide is 3.6 - 9 eV, and it absorbs light in the wavelength range of 137 - 344 nm, which belongs to the ultraviolet light band; therefore, thick aluminum oxide can absorb ultraviolet light, prevent ultraviolet light from entering the interior of the solar cell and causing damage to the cell, effectively improving UVID.

[0006] However, in terms of ultraviolet resistance, aluminum oxide is not a perfect material.

[0007] First of all, the wavelength range of UVA is 320 - 400 nm, while the absorption wavelength range of aluminum oxide is 137 - 344 nm, and aluminum oxide cannot completely block ultraviolet light.

[0008] Secondly, in order to obtain higher ultraviolet resistance, it is necessary to increase the film thickness of aluminum oxide; however, if the dense and non-conductive aluminum oxide film layer is too thick, it will cause an increase in the series resistance of the solar cell, thereby affecting the electrical performance of the solar cell.

[0009] Moreover, in the process of metallization of solar cells to prepare metal grid lines (or metal electrodes), it is necessary to make the glass powder (mainly composed of PbO, etc.) in the metal paste burn through the insulating film layer such as aluminum oxide on the surface of the cell to form an ohmic contact between the metal grid line (or metal electrode) and the semiconductor, so that the photogenerated carriers generated by the solar cell can be led out. Too thick aluminum oxide film layer will cause abnormal sintering of the metal paste, resulting in undesirable phenomena such as broken grid. If the burn-through ability of the metal paste is to be increased, the glass powder content in the metal paste needs to be increased; but this will affect the stability of the solar cell module during long-term use, because PbO will be corroded by the acid generated by hydrolysis during the use of the solar cell module, causing the electrical performance of the solar cell module to decrease. Therefore, it is urgent to improve and optimize the film structure of the solar cell to improve the performance parameters such as open circuit voltage, short circuit current and conversion efficiency of the solar cell (especially TOPCon cell) under ultraviolet irradiation, so as to extend the service life of the solar cell for long-term outdoor use. Summary of the invention

[0010] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a functional film structure for a solar cell, a solar cell and a method for preparing the same.

[0011] Based on this, the present invention discloses a functional film structure for solar cells, comprising a dielectric passivation layer disposed on the surface of a cell substrate and an ultraviolet light absorption layer disposed on the surface of the dielectric passivation layer;

[0012] The ultraviolet light absorption layer is at least one of a zinc oxide layer, a gallium nitride layer, and an indium tin oxide layer, and the thickness of the ultraviolet light absorption layer is 0.5-3 nm.

[0013] Preferably, the ultraviolet light absorbing layer is a zinc oxide layer, and the thickness of the zinc oxide layer is 1-3 nm.

[0014] Preferably, the ultraviolet light absorption layer is a gallium nitride layer, and the thickness of the gallium nitride layer is 0.5-1.5 nm.

[0015] Preferably, the ultraviolet light absorbing layer is an indium tin oxide layer, and the thickness of the indium tin oxide layer is 1-3 nm.

[0016] Preferably, the dielectric passivation layer is an aluminum oxide layer with a thickness of 3-8 nm.

[0017] Further preferably, the dielectric passivation layer is an aluminum oxide layer with a thickness of 5 nm; and the ultraviolet light absorption layer is a zinc oxide layer with a thickness of 1 nm.

[0018] Preferably, a functional film structure for a solar cell further comprises a passivation anti-reflection film disposed on the surface of the ultraviolet light absorbing layer;

[0019] The passivation and antireflection film is a silicon nitride film with a thickness of 70 - 100 nm.

[0020] In the functional film layer structure for the solar cell of the present invention, the ultraviolet light absorption layer is at least one of a zinc oxide layer (ZnO layer), a gallium nitride layer, and an indium tin oxide layer, and the thickness of the ultraviolet light absorption layer is relatively thin, only 0.5 - 3 nm. Taking the ZnO layer as an example, the function of the ultraviolet light absorption layer selected in the present invention is described as follows:

[0021] ZnO (zinc oxide) is a wide-bandgap semiconductor material. At room temperature, the bandgap width is about 3.37 eV, and its absorption peak corresponds to long-wave ultraviolet light (368 nm). Therefore, ZnO has a strong absorption ability for ultraviolet light (ZnO has a strong absorption effect on ultraviolet light UVA with a wavelength less than 380 nm), while the absorption of visible light is relatively weak. Therefore, a relatively thin ZnO layer can achieve strong ultraviolet resistance.

[0022] Moreover, ZnO usually has a hexagonal wurtzite structure. In this structure, the arrangement of zinc (Zn) atoms and oxygen (O) atoms is not completely symmetric. Therefore, the ZnO layer, like the aluminum oxide layer, is negatively polarized and also has a certain field passivation effect. In addition, using a relatively thin ZnO layer as the ultraviolet light absorption layer of the functional film layer structure will not cause abnormal sintering due to the excessive thickness of the functional film layer structure. The ZnO layer also has a certain electrical conductivity, and a relatively thin ZnO will not significantly increase the series resistance of the solar cell.

[0023] The present invention also discloses a solar cell, including a cell substrate and a functional film layer structure disposed on the surface of the cell substrate;

[0024] The cell substrate is a silicon wafer; the functional film layer structure is a functional film layer structure for a solar cell as described above in the present invention.

[0025] Preferably, the solar cell is a TOPCon cell; an emitter, the functional film layer structure, and a front metal electrode are sequentially disposed on the front surface of the silicon wafer, and the front metal electrode makes an ohmic contact with the emitter after passing through the functional film layer structure;

[0026] A tunneling oxide layer, a doped polysilicon layer, a passivation and antireflection film, and a back metal electrode are sequentially disposed on the back surface of the silicon wafer, and the back metal electrode makes an ohmic contact with the doped polysilicon layer after passing through the passivation and antireflection film on the back surface.

[0027] The present invention also discloses a preparation method for a solar cell as described above in the present invention, including the following preparation steps:

[0028] S1. After the surface of the silicon wafer is subjected to texturing treatment, an emitter is prepared on the front surface of the silicon wafer;

[0029] S2. After the back side of the silicon wafer is polished, a tunneling oxide layer and a doped polysilicon layer are sequentially formed on the back side of the silicon wafer;

[0030] S3. A functional film layer structure for a solar cell as described above in the present invention is formed on the front side of the emitter, and a passivation and antireflection film is formed on the back side of the doped polysilicon layer;

[0031] S4. Metallization treatment is performed to fabricate a front metal electrode and a back metal electrode.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] Based on the deficiencies of the prior art, the present invention proposes a method for optimizing ultraviolet-induced degradation in solar cells, photovoltaic modules, and photovoltaic systems, that is, to provide a functional film layer structure for a solar cell. The functional film layer structure for a solar cell is provided with an ultraviolet light absorption layer with a thickness of 0.5 - 3 nm on the surface of the dielectric passivation layer, and the ultraviolet light absorption layer is defined as at least one of a zinc oxide layer, a gallium nitride layer, and an indium tin oxide layer; thus, a material layer with stronger ultraviolet absorption ability such as ZnO with a relatively thin thickness is used as the ultraviolet light absorption layer of the solar cell (especially the TOPCon cell) in combination on the surface of the dielectric passivation layer, which can better absorb and filter out ultraviolet light (especially UVA) in natural light while minimizing the absorption of light in the 300 - 1200 nm band (the solar cell can use light in the 300 - 1200 nm band for photoelectric conversion) by the functional film layer structure, effectively improving the ultraviolet resistance of the solar cell and reducing UVID (ultraviolet-induced degradation) more. Moreover, the dielectric passivation layer is combined with an ultraviolet light absorption layer such as ZnO with a relatively thin thickness, and there will be no abnormal sintering problems caused by the excessive thickness of the functional film layer structure; the ultraviolet light absorption layer such as ZnO has good conductivity and a relatively thin thickness, so it will not significantly increase the series resistance of the solar cell. In addition, the ultraviolet light absorption layer such as ZnO can also improve the passivation effect of the solar cell.

[0034] Therefore, the functional film layer structure for a solar cell of the present invention can effectively improve the UVID (ultraviolet-induced degradation) of the solar cell, contribute to improving performance parameters such as the open-circuit voltage, short-circuit current, and conversion efficiency of the solar cell (especially the TOPCon cell) under ultraviolet irradiation, and thus contribute to extending the service life of the solar cell during long-term outdoor use. Description of the Drawings

[0035] Figure 1 It is a schematic cross-sectional structure diagram of a solar cell of the present invention.

[0036] Figure 2 It is a graph of the photocurrent density data of solar cells with different film layer combinations.

[0037] Figure 3 Battery efficiency data graph for solar cells with different film layer combinations.

[0038] Figure 4 Ultraviolet-induced attenuation rate data graph for solar cell samples with different combinations.

[0039] Explanation of reference numerals in the attached drawings: silicon wafer 10; P+ emitter 11; dielectric passivation layer 12; ultraviolet light absorption layer 13; first passivation and antireflection film 14; front metal electrode 15;

[0040] Tunneling oxide layer 21; doped polysilicon layer 22; second passivation and antireflection film 23; back metal electrode 24. Detailed implementation manners

[0041] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0042] Example 1

[0043] A preparation method of a solar cell in this example includes the following preparation steps:

[0044] Step 1, surface texturing treatment: Select silicon wafer 10 as the battery substrate, and use an alkaline solution to perform texturing treatment on the surface (such as the front and back surfaces) of silicon wafer 10 (such as an n-type Czochralski silicon wafer 10 with a thickness of 130 μm and a sheet resistance of 1 Ω / □), so that a randomly distributed pyramid structure is formed on the surface of silicon wafer 10 to reduce light reflection and improve the light absorption rate of the solar cell.

[0045] Step 2, preparation of the emitter: Prepare P+ emitter 11 on the front surface of silicon wafer 10 through a boron diffusion process. In Step 2, during the boron diffusion process, a tube furnace is used and silicon wafer 10 is heat-treated in a BBr 3 atmosphere, so that a boron emitter (also called P+ emitter 11) with a sheet resistance of 120 Ω / □ is formed on the front surface of silicon wafer 10.

[0046] In practice, while preparing P+ emitter 11 by the boron diffusion process, a boron-doped plating-around area will also be formed in a local area on the back surface of silicon wafer 10.

[0047] Step 3, single-sided etching: Perform single-sided etching on the back surface of silicon wafer 10 to remove the boron-doped plating-around area on the back surface of silicon wafer 10. In Step 3, the etching solution uses an acidic etching solution (such as a mixture of existing HF and deionized water).

[0048] Step 4, back polishing: Use an alkaline solution to chemically polish the back surface of silicon wafer 10 to form a flat surface on the back surface of silicon wafer 10, providing a reliable substrate for the subsequent preparation of the back structure.

[0049] Step 5, Back contact preparation: A tunneling oxide layer 21 and a doped amorphous silicon layer (n+a-Si layer) are sequentially prepared on the polished back surface of the silicon wafer 10. In step 5, the preparation methods of the tunneling oxide layer 21 and the doped amorphous silicon layer include but are not limited to existing plasma deposition methods and thermal oxidation methods (such as wet oxidation). Among them, the tunneling oxide layer 21 is preferably a silicon oxide layer (SiOx layer) with a thickness of, for example, 1.5 nm.

[0050] Step 6, Perform high-temperature annealing treatment (such as at a temperature of 900 °C) to convert the doped amorphous silicon layer into a doped polycrystalline silicon layer 22 (n+-poly-Si layer) through thermal crystallization. After the treatment in step 6, a passivation contact structure composed of the tunneling oxide layer 21 and the doped polycrystalline silicon layer 22 can be formed on the back surface of the silicon wafer 10.

[0051] Step 7, Clean the surface of the silicon wafer 10 treated in step 6, and let the cleaning solution perform micro-oxidation and etching on its surface (such as the front surface of the P+ emitter 11 and the back surface of the doped polycrystalline silicon layer 22) to remove organic residues and non-conductive oxide layers on the surface.

[0052] Step 8, Grow a dielectric passivation layer 12: Using atomic layer deposition (ALD) method, deposit a dielectric passivation layer 12 on the front surface of the P+ emitter 11 on the front surface of the silicon wafer 10. In step 8, the dielectric passivation layer 12 is preferably an AlOx layer (aluminum oxide layer), and the thickness of the aluminum oxide layer is 3 - 8 nm (such as 5 nm).

[0053] Step 9, Grow an ultraviolet light absorption layer 13: Using atomic layer deposition method or magnetron sputtering method, deposit an ultraviolet light absorption layer 13 on the front surface of the dielectric passivation layer 12. In step 9, the ultraviolet light absorption layer 13 is a ZnO layer (zinc oxide layer) with a thickness of 1 - 3 nm (such as 1 nm).

[0054] Step 10, Prepare a passivation antireflection film: Using a deposition method such as PECVD, deposit and prepare a first passivation antireflection film 14 (such as a front surface silicon nitride film, also called front surface SiNx film) and a second passivation antireflection film 23 (such as a back surface silicon nitride film, also called back surface SiNx film) on the front surface of the ultraviolet light absorption layer 13 and the back surface of the doped polycrystalline silicon layer 22 respectively. The passivation antireflection film is preferably a silicon nitride film with a thickness of 70 - 100 nm; for example, the thickness of the front surface silicon nitride film is 75 nm, and the thickness of the back surface silicon nitride film is 90 nm.

[0055] The above steps 8 - 10 are a preparation method of a functional film layer structure for a solar cell in this embodiment. The functional film layer structure for a solar cell, as Figure 1 shown, includes the dielectric passivation layer 12, the ultraviolet light absorption layer 13, and the first passivation antireflection film 14 sequentially disposed on the surface (such as the front surface) of the battery substrate (such as the silicon wafer 10).

[0056] Step 11. Metallization: After screen printing on the front side of the first passivation and antireflection film 14 and the back side of the second passivation and antireflection film 23, sintering is carried out to form a front metal electrode 15 and a back metal electrode 24 respectively. Among them, the front metal electrode 15 passes through the first passivation and antireflection film 14, the ultraviolet light absorption layer 13 and the dielectric passivation layer 12, and then makes an ohmic contact with the P+ emitter 11; the back metal electrode 24 passes through the second passivation and antireflection film 23 and makes an ohmic contact with the doped polysilicon layer 22.

[0057] After being processed by Step 11, a solar cell as shown in Figure 1 can be obtained. It is a TOPCon cell, which includes: a cell substrate (such as silicon wafer 10), the front side of the silicon wafer 10 is successively provided with an emitter (such as P+ emitter 11), the functional film layer structure and the front metal electrode 15, and the front metal electrode 15 passes through the functional film layer structure and makes an ohmic contact with the emitter; the back side of the silicon wafer 10 is successively provided with a tunneling oxide layer 21, a doped polysilicon layer 22, a second passivation and antireflection film 23 and a back metal electrode 24, and the back metal electrode 24 passes through the second passivation and antireflection film 23 on the back side and makes an ohmic contact with the doped polysilicon layer 22.

[0058] Step 12. Secondary auxiliary metallization: Using the Laser-enhanced contact optimization (LECO) technology, the solar cell is sintered for the second time to enhance the ohmic contact of the metal electrode.

[0059] Step 13. Testing and sorting.

[0060] Example 2

[0061] A functional film layer structure, a solar cell and a preparation method thereof in this example all refer to Example 1. The difference between it and Example 1 is that:

[0062] Step 9 in Example 1 is replaced by: Growing a GaN layer (gallium nitride layer) with a thickness of 0.5 - 1.5 nm (such as 1 nm) on the front side of the dielectric passivation layer 12 (aluminum oxide layer) as the ultraviolet light absorption layer 13 (such as Figure 1 shown); the remaining steps all refer to Example 1.

[0063] Example 3

[0064] A functional film layer structure, a solar cell and a preparation method thereof in this example all refer to Example 1. The difference between it and Example 1 is that:

[0065] Replace step 9 of Example 1 with: Grow an ITO layer (indium tin oxide layer) with a thickness of 1 - 3 nm (such as 2 nm) on the front surface of the dielectric passivation layer 12 (aluminum oxide layer) as the ultraviolet light absorption layer 13 (such as Figure 1 shown); the remaining steps are all referred to Example 1.

[0066] Performance Test

[0067] 1. First, use the online optical simulation program wafer raytracer in the optics block under the software pvlighthouse to verify the functional film layer structures suitable for Examples 1 - 3.

[0068] The main parameters for the simulation test are set as follows: Set the test conditions to standard 1.5 Amg (standard sunlight); the front surface of the solar cells in Examples 1 - 3 has a textured pyramid structure, and the back surface has a polished flat surface structure; the solar cells in Examples 1 - 3 are set to use a silicon wafer with a thickness of 130 μm as the substrate. In the simulation test, the back surface structure of the solar cells in Examples 1 - 3 remains unchanged, and a 1 nm thick SiO 2 (as the tunneling oxide layer) and a 100 nm thick N - type doped polysilicon layer are jointly used for passivation contact passivation, and a 90 nm thick back - surface silicon nitride film. Among them, the front - surface functional film layer structure (abbreviated as the front film) of the solar cell in Example 1 includes an aluminum oxide layer, a ZnO layer, and a 75 nm thick front - surface silicon nitride film sequentially disposed on the front surface of the silicon wafer. The front film of the solar cell in Example 2 includes an aluminum oxide layer, a GaN layer, and a 75 nm thick front - surface silicon nitride film sequentially disposed on the front surface of the silicon wafer. The front film of the solar cell in Example 3 includes an aluminum oxide layer, an ITO layer, and a 75 nm thick front - surface silicon nitride film sequentially disposed on the front surface of the silicon wafer.

[0069] In the simulation test, change the combined thickness of the aluminum oxide layer and the ZnO layer on the front surface of the solar cell in Example 1 (or change the combined thickness of the aluminum oxide layer and the GaN layer on the front surface of the solar cell in Example 2, or change the combined thickness of the aluminum oxide layer and the ITO layer on the front surface of the solar cell in Example 3), and measure the photon current density (J A,F , with the unit of mA / cm 2 ) of the front film in the ultraviolet light band of 280 - 400 nm (since UVC is completely absorbed and blocked by the atmosphere, the ultraviolet light band of UVC is not calculated here), and the absorption condition of the front film in the light absorption band of 300 - 1200 nm of the solar cell.

[0070] 1.1. In the present invention, simulation tests and comparisons are carried out on combinations of 6 groups of aluminum oxide layers and ZnO layers with different thicknesses (the combination names are: Combination 1, Combination 2, Combination 3, Combination 4, Combination 5, and Combination 6); among them, Combination 1 does not have a ZnO layer and uses a conventional solar cell structure with a 5-nm-thick front aluminum oxide layer as a control group; the results of its simulation tests are shown in Table 1 below:

[0071] Table 1 Influence of combinations of film layers with different thicknesses in Example 1 on the absorption of ultraviolet light and light in the 300 - 1200 nm band

[0072]

[0073] According to the data in Table 1, it can be seen that:

[0074] 1) By comparing the simulation test results of Combination 1 and 5, it can be seen that: when the thickness of the aluminum oxide layer increases from 5 nm to 8 nm, the absorption rate of the positive film for UV (ultraviolet light) only increases by 0.63%; therefore, the increase in the thickness of the aluminum oxide layer can improve the ultraviolet resistance, but it is very limited.

[0075] 2) By comparing the simulation test results of Combination 2, 3, and 4, it can be seen that: when the thickness of the aluminum oxide layer remains unchanged and the thickness of the ZnO layer increases from 1 nm to 3 nm, the absorption rate of the positive film for UV increases rapidly. Compared with the conventional Combination 1, the absorption rate of the positive film of Combination 4 for UV increases by an additional 27.19%, but the blocking of the positive film of Combination 4 for the 300 - 1200 nm light absorption band of the solar cell also increases by 16.54% (the solar cell can convert the light in the 300 - 1200 nm band into electrical energy). Therefore, the increase in the thickness of the ZnO layer in the positive film will increase the blocking of the 300 - 1200 nm band light that the solar cell can effectively utilize while increasing the absorption rate of ultraviolet light, which will lead to a decrease in the photocurrent density (J sc ) of the solar cell, and further the cell efficiency (i.e., the photoelectric conversion efficiency of the cell) will decrease. Calculated based on the conventional cell efficiency of 26%, when using Combination 4, the photocurrent density decreases by 0.22% and the cell efficiency decreases by 0.06%; so the thickness of the ZnO layer should not be too thick.

[0076] 3) ZnO usually has a hexagonal wurtzite structure. In this structure, the arrangement of zinc (Zn) atoms and oxygen (O) atoms is not completely symmetric. Therefore, like the aluminum oxide layer, the ZnO layer is also negatively polarized and has a certain field passivation effect. The passivation effect of the ZnO layer can be seen from the comparison between Combination 1 and 6: when reducing the thickness of the aluminum oxide layer (from 5 nm to 4 nm) and increasing the thickness of the ZnO layer (from 0 to 1 nm), the photocurrent density J sc remains basically unchanged (if the ZnO layer has no passivation ability, the photocurrent density will decrease sharply).

[0077] Since the ZnO layer also has a passivation ability, compared with the conventional combination 1, in combination 6, the thickness of the alumina layer is reduced, and a ZnO layer with a corresponding thickness is prepared, which can minimize the light absorption rate of the front film in the 300 - 1200 nm band as much as possible, and can ensure that the front film will not cause the glass powder to be difficult to burn through the front film during the sintering of the metal paste (including the metal material and glass powder forming the metal electrode). Comparing with combination 1, it can be seen that the UV absorption rate of the front film in combination 6 has increased by 8.32%, and the photocurrent density has only decreased by 0.10%.

[0078] 4) By comparing combinations 1 and 2, it can be seen that when the thickness of the alumina layer in combination 2 (5 nm) remains unchanged and the thickness of the ZnO layer is 1 nm, the UV absorption rate of the front film has increased by 8.85%, and the absorption rate of the front film in combination 2 in the 300 - 1200 nm band has only increased by 5.12%. Still calculated with the conventional battery efficiency of 26%, when using combination 2, the photocurrent density decreases by 0.05%, and the battery efficiency decreases by 0.013%, which is almost negligible.

[0079] Combined with Table 1, it can be known that in the front film of the solar cell of the present invention, when an alumina layer with a thickness of 3 - 8 nm and a ZnO layer with a thickness of 1 - 3 nm are sequentially stacked, while minimizing the light absorption of the front film in the 300 - 1200 nm band, the front film can better absorb and filter out ultraviolet light, so it can reduce UVID (ultraviolet-induced degradation) more; furthermore, it is more helpful to improve the performance parameters such as the open-circuit voltage, short-circuit current, and conversion efficiency of the solar cell (especially the TOPCon cell) under ultraviolet irradiation, so as to extend the service life of the solar cell during long-term outdoor use.

[0080] According to the ultraviolet light absorption J of the front film in Table 1 A,F (the more ultraviolet light absorption J of the front film A,F the better) and the photocurrent loss ratio (the smaller the photocurrent loss ratio, the smaller the loss of light in the 300 - 1200 nm band available for solar cell power generation), it can be determined that the effect of combination 2 is the best in the simulation test of Table 1.

[0081] 1.2. In the present invention, simulation test comparisons are carried out on four groups of combinations of alumina layers and GaN layers with different thicknesses (the combination names are: combination 1, combination 7, combination 8, combination 9); among them, combination 1 does not set a GaN layer and uses a conventional solar cell structure with a 5 nm thick front alumina layer as a control group; the results of its simulation test are shown in Table 2 below:

[0082] Table 2 Influence of different thickness film layer combinations in Example 2 on ultraviolet light and light absorption in the 300 - 1200 nm band

[0083]

[0084] 1.3. In the present invention, simulation tests and comparisons are carried out on combinations of four groups of aluminum oxide layers and ITO layers with different thicknesses (the combination names are: Combination 1, Combination 10, Combination 11, and Combination 12); among them, Combination 1 does not have an ITO layer and uses a conventional solar cell structure with a 5-nm-thick front aluminum oxide layer as a control group; the results of its simulation tests are shown in Table 3 below:

[0085] Table 3 Influence of film layer combinations with different thicknesses in Example 3 on the absorption of ultraviolet light and light in the 300 - 1200 nm band

[0086]

[0087] Referring to the data in Table 2 - 3, it can be seen that: when a material layer with a bandgap of about 3.37 eV, such as a GaN layer (or an ITO layer), is paired with an aluminum oxide layer, a good ultraviolet light blocking effect can also be achieved.

[0088] Referring to Table 1 - 3, compared with the aluminum oxide layer of the conventional Combination 1, the absorption rate of ultraviolet light by the positive films of the combinations of different thickness film layers in Combinations 2 - 4 and Combinations 6 - 12 increases by 6 - 320% respectively.

[0089] Referring to Table 2, by comparing Combinations 1, 7, 8, and 9, it can be seen that: when the GaN layer is used as an ultraviolet light absorption layer, its ultraviolet light absorption ability is extremely strong, but at the same time, the loss of its photocurrent density is also relatively large; considering comprehensively, the thickness range of the GaN layer as an ultraviolet light absorption layer should be controlled between 0.5 - 1.5 nm.

[0090] Referring to Table 3, by comparing Combinations 1, 10, 11, and 12, it can be seen that: when the ITO layer is used as an ultraviolet light absorption layer, its ultraviolet absorption ability is moderate, and at the same time, the loss of its photocurrent density is not high; considering comprehensively, the thickness range of the ITO layer as an ultraviolet light absorption layer should be controlled between 1 - 3 nm.

[0091] Combined with Tables 1 - 3, it can be known that: other material layers with a bandgap of about 3.37 eV (such as GaN layers, ITO layers) can all absorb ultraviolet light. Other material layers with a bandgap of about 3.37 eV (such as GaN layers, ITO layers) can also be used in combination with aluminum oxide layers.

[0092] In Example 1 of the present invention, ZnO layer is selected as the preference to match with the alumina layer. On the one hand, the combination of ZnO layer and alumina layer can enable the positive film to better absorb and filter ultraviolet light on the premise of minimizing the light absorption of the positive film in the 300 - 1200 nm band as much as possible. On the other hand, the preparation process of ZnO layer can be compatible with that of alumina layer, and both can be prepared by ALD (Atomic layer deposition), so the ZnO layer and alumina layer can be prepared by using the same ALD equipment, which can greatly reduce the preparation cost of the film layer combination.

[0093] However, the preparation cost of other material layers with a band gap of about 3.37 eV is higher. For example, the preparation of GaN layer requires the use of relatively expensive MOCVD (Metal-organic Chemical Vapor Deposition) and MBE (Molecular beam epitaxy) technologies. However, it is undeniable that layers such as GaN layer (gallium nitride layer) and ITO layer (indium tin oxide layer) can also be used as ultraviolet light absorption materials to match with the alumina layer.

[0094] 2. In the present invention, the film layer combination 2 is used to prepare a solar cell (the preparation method of the solar cell refers to Example 1), and it is compared with the solar cell prepared by the conventional combination 1. 30 solar cells of each of the film layer combinations 1 and 2 are prepared. After removing fragments and outliers, the statistics show that:

[0095] As Figures 2-3 shown, the solar cell of combination 1 uses a conventional 5-nm-thick alumina layer + 0-nm-thick ZnO layer, and the solar cell of combination 2 uses a 5-nm-thick alumina layer + 1-nm-thick ZnO layer. The photocurrent density J SC (see Figure 2 ) of the solar cell: the average of the solar cells of combination 1 is 42.073 mA / cm 2 , and the average of the solar cells of combination 2 is 42.063 mA / cm 2 , a decrease of 0.010 mA / cm 2 . In terms of the battery efficiency (Eta) (see Figure 3 ): the average battery efficiency of the solar cells of combination 1 is 26.353%, and the average battery efficiency of the solar cells of combination 2 is 26.344%, with the battery efficiency decreasing by 0.009%. It can be seen that Figures 2-3 the test results of the solar cells of combinations 1 and 2 shown are basically consistent with the simulation test results in Table 1.

[0096] 3. Then, take 4 solar cell samples prepared from each of the film layer combinations 1 and 2 to conduct the UVID (ultraviolet-induced degradation) test on the solar cells. The solar cell samples of combination 1 are respectively labeled as SP1-1, SP1-2, SP1-3, and SP1-4; the solar cell samples of combination 2 are respectively labeled as SP2-1, SP2-2, SP2-3, and SP2-4. Take two solar cells, SP1-4 and SP2-4, as the experimental control group (Control). Their function is that SP1-4 and SP2-4 are naturally oxidized at room temperature in the laboratory environment, and the processing time of SP1-4 and SP2-4 is the same as that of the remaining solar cell samples to be tested, so as to exclude the influence caused by natural degradation when calculating the ultraviolet-induced degradation. The experimental conditions for the UV test are: the temperature is 60°C ± 5°C; the light intensity UVA + UVB (accounting for 4%) ≤ 250 w / m²; the test time is 240 hours.

[0097] The UVID calculation formula is: Degradation rate = (Battery efficiency before the test - Battery efficiency after the degradation) / Battery efficiency before the test × 100% - Control degradation rate.

[0098] Table 4 UVID test results

[0099]

[0100] In Table 4, the average UVID degradation rate of the solar cell sample SP1 of combination 1 is 0.399%, and the average UVID degradation rate of the solar cell sample SP2 of combination 2 is 0.357%. Combining Figure 4 with the test results in Table 4, it can be seen that: compared with the conventional combination 1, the UV resistance of the solar cell prepared by using combination 2 of the present invention has been improved by (0.399 - 0.357) / 0.399 = 10.53%. Therefore, in the positive film of the solar cell of the present invention, the scheme of matching an aluminum oxide layer with a thickness of 3 - 8 nm and a ZnO layer with a thickness of 1 - 3 nm is an effective method for optimizing UVID.

[0101] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention.

[0102] The above has introduced the technical solution provided by the present invention in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A functional film structure for solar cells, characterized in that: It includes a dielectric passivation layer disposed on the surface of a battery substrate and an ultraviolet light absorbing layer disposed on the surface of the dielectric passivation layer; The ultraviolet light absorption layer is at least one of a zinc oxide layer, a gallium nitride layer, and an indium tin oxide layer, and the thickness of the ultraviolet light absorption layer is 0.5-3 nm.

2. A functional film structure for solar cells according to claim 1, characterized in that: The ultraviolet light absorbing layer is a zinc oxide layer, and the thickness of the zinc oxide layer is 1-3 nm.

3. A functional film structure for solar cells according to claim 1, characterized in that: The ultraviolet light absorption layer is a gallium nitride layer, and the thickness of the gallium nitride layer is 0.5-1.5 nm.

4. A functional film structure for solar cells according to claim 1, characterized in that: The ultraviolet light absorbing layer is an indium tin oxide layer, and the thickness of the indium tin oxide layer is 1-3 nm.

5. The functional film structure for solar cells according to claim 1, characterized in that: The dielectric passivation layer is an aluminum oxide layer with a thickness of 3-8 nm.

6. A functional film structure for solar cells according to claim 5, characterized in that: The dielectric passivation layer is an aluminum oxide layer with a thickness of 5 nm; the ultraviolet light absorption layer is a zinc oxide layer with a thickness of 1 nm.

7. The functional film structure for solar cells according to claim 1, characterized in that: It also includes a passivation anti-reflection film disposed on the surface of the ultraviolet light absorbing layer; The passivation anti-reflection film is a silicon nitride film with a thickness of 70-100 nm.

8. A solar cell, characterized in that: It includes a battery substrate and a functional film layer structure arranged on the surface of the battery substrate; The cell substrate is a silicon wafer; the functional film layer structure is a functional film layer structure for a solar cell as described in any one of claims 1 to 7.

9. A solar cell according to claim 7, characterized in that: The solar cell is a TOPCon cell; the front side of the silicon wafer is provided with an emitter, the functional film layer structure and a front metal electrode in sequence, and the front metal electrode passes through the functional film layer structure to make ohmic contact with the emitter; The back side of the silicon wafer is provided with a tunneling oxide layer, a doped polysilicon layer, a passivation anti-reflection film and a back side metal electrode in sequence, and the back side metal electrode passes through the back side passivation anti-reflection film to make ohmic contact with the doped polysilicon layer.

10. A method for preparing a solar cell according to any one of claims 8 to 9, characterized in that: The method comprises the following preparation steps: S1. After the surface of the silicon wafer is textured, an emitter is prepared on the front side of the silicon wafer; S2, after the back side of the silicon wafer is polished, a tunneling oxide layer and a doped polysilicon layer are sequentially prepared on the back side of the silicon wafer; S3. Prepare a functional film structure for a solar cell as claimed in any one of claims 1 to 7 on the front side of the emitter, and prepare a passivation anti-reflection film on the back side of the doped polysilicon layer; S4. Perform metallization treatment to prepare a front metal electrode and a back metal electrode.

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