Low-cost silicon heterojunction solar cell and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, in particular to a low-cost silicon heterojunction solar cell and a preparation method thereof, a light receiving surface of the low-cost silicon heterojunction solar cell comprises a microcrystalline silicon film and a metal electrode, a front transparent conductive film is arranged on the microcrystalline silicon film below the metal electrode, and anti-reflection films are arranged on other microcrystalline silicon films. The front transparent conductive film is arranged below the metal electrode, so that compared with a conventional heterojunction solar cell, the area of the front transparent conductive film is reduced, and the production cost is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a low-cost silicon heterojunction solar cell and a preparation method thereof. Background Art

[0002] Heterojunction solar cells are a new type of solar cell technology that combines the advantages of crystalline silicon cells and thin-film cells. Due to its high efficiency, high stability and low temperature coefficient, it is suitable for traditional photovoltaic power stations, and can also be used in building integrated photovoltaics (BIPV), portable electronic devices, aerospace and other fields. As the technology continues to mature, heterojunction solar cells occupy an important position in the photovoltaic market. Its preparation method: first, the N-type single crystal silicon wafer is cleaned and textured, and then a very thin intrinsic amorphous silicon film and an N-type microcrystalline silicon oxygen film are deposited on the front of the N-type single crystal silicon wafer using PECVD equipment, and then a very thin intrinsic amorphous silicon film and a P-type microcrystalline silicon film are deposited on the back of the silicon wafer; then a transparent oxide conductive film is deposited on both sides of the battery by PVD, and finally a metal electrode is made on the transparent oxide conductive film.

[0003] The preparation process requires the use of a transparent conductive film, generally an indium-doped metal oxide (ITO) with a high indium content, which is extremely expensive, resulting in the commercialization of heterojunction solar cells not progressing as well as other N-type crystalline silicon solar cells. Summary of the invention

[0004] The purpose of the present invention is to provide a low-cost silicon heterojunction solar cell and a preparation method thereof, so as to solve the technical problem that the transparent conductive film in the prior art is extremely costly, resulting in a high cost of heterojunction solar cells.

[0005] The invention discloses a low-cost silicon heterojunction solar cell, whose light-receiving surface comprises a microcrystalline silicon film and a metal electrode, a front transparent conductive film is arranged on the microcrystalline silicon film below the metal electrode, and an anti-reflection film is arranged on the remaining microcrystalline silicon films.

[0006] By setting a front transparent conductive film under the metal electrode, the area of ​​the front transparent conductive film is reduced compared to conventional heterojunction solar cells, greatly reducing production costs. At the same time, it has a lower contact resistance between the metal electrode and the front transparent conductive film. Since the front transparent conductive film is only prepared in the metal electrode area, the metal electrode will be prepared on this film layer to derive current later, and the coverage area is small, the front transparent conductive film does not need very excellent optical properties. Its electrical properties can be improved by sacrificing some optical properties through process optimization, greatly reducing the square resistance of the front transparent conductive film. The low square resistance of the front transparent conductive film can bring lower contact resistance when in contact with the metal electrode, reducing the series resistance of the solar cell.

[0007] Furthermore, the thickness of the front transparent conductive film is less than or equal to 100 nm, and the width is one to three times the width of the metal electrode.

[0008] Furthermore, the front transparent conductive film has a square resistance of less than or equal to 25Ω / sq after annealing, and a carrier mobility of greater than or equal to 65cm 2 V -1 s -1 , thickness is less than or equal to 100nm.

[0009] Since the transparent conductive film needs to take into account optical properties, its sheet resistance is relatively high. When a metal electrode is prepared on it, the contact resistance between the metal electrode and the transparent conductive film is relatively high. At the same time, when the transparent conductive film maintains a high transmittance, its sheet resistance is difficult to reduce, resulting in the inability to achieve good optical and electrical properties at the same time. This has a significant impact on the photoelectric conversion efficiency of heterojunction solar cells. By arranging a front transparent conductive film under the metal electrode, the use of the transparent conductive film is reduced, and the demand for optical properties of the transparent conductive film is reduced.

[0010] Furthermore, the light-receiving surface microcrystalline silicon film is an N-type microcrystalline silicon oxide film μc-SiOx:H(N).

[0011] Furthermore, the conductivity of the N-type microcrystalline silicon oxide film is greater than or equal to 0.5S / m, the crystallization rate is greater than or equal to 40%, the bandgap is greater than or equal to 1.6eV, the refractive index n value is less than or equal to 2.5, and the thickness is less than or equal to 25nm. The purpose is to make the crystallization rate and conductivity of the microcrystalline silicon layer relatively high, so as to make up for the problem that the lateral resistance of the battery is too large due to the lack of a transparent conductive film, and the lateral transmission of carriers is blocked.

[0012] Furthermore, a front amorphous silicon film is disposed on the back side of the N-type microcrystalline silicon oxide film.

[0013] Furthermore, a silicon wafer is disposed on the back side of the front amorphous silicon film.

[0014] Furthermore, the silicon wafer is an N-type single crystal silicon wafer.

[0015] Furthermore, a back amorphous silicon film is provided on the back side of the silicon wafer.

[0016] Furthermore, a P-type microcrystalline silicon layer is disposed on the back side of the back amorphous silicon film.

[0017] Furthermore, a back transparent conductive film covering the P-type microcrystalline silicon layer is disposed on the back side of the P-type microcrystalline silicon layer.

[0018] A method for preparing a low-cost silicon heterojunction solar cell comprises the following steps:

[0019] On the microcrystalline silicon layer on the light-receiving side of the solar cell, a front transparent conductive film is prepared only in the area below the metal electrode, and an anti-reflection film is prepared on the remaining microcrystalline silicon films.

[0020] Furthermore, the back transparent conductive film and the front transparent conductive film are both ITO films.

[0021] Furthermore, the anti-reflection film is a magnesium fluoride, silicon oxide or silicon nitride anti-reflection film.

[0022] Furthermore, the front transparent conductive film is prepared only in the metal electrode region using a mask.

[0023] Furthermore, after the front transparent conductive film is prepared, an anti-reflection film is prepared in the non-metallic electrode area using a mask.

[0024] Furthermore, the front transparent conductive film on the mask is recycled and reused.

[0025] Furthermore, the front transparent conductive film is prepared by physical vapor deposition (PVD).

[0026] Furthermore, the anti-reflection film is prepared by reactive plasma deposition (RPD) or polyethylene chemiluminescent chemical vapor deposition (PECVD).

[0027] Furthermore, the metal electrode is prepared by screen printing.

[0028] Furthermore, before preparing the front transparent conductive film, the process also includes steps of cleaning the silicon wafer, texturing the surface, and preparing an amorphous silicon film and microcrystalline silicon films on both the front and back sides.

[0029] Furthermore, after the anti-reflection film is prepared, the metal electrode is prepared.

[0030] Furthermore, the cleaning is chain cleaning.

[0031] Furthermore, the amorphous silicon film and the microcrystalline silicon films on the front and back sides are prepared by chemical vapor deposition (PECVD).

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

[0033] 1. The front structure of the cell is redesigned in the present invention, which can significantly reduce the use of rare metal indium. The metal electrode on the front of the heterojunction solar cell occupies less than 4.5% of the entire cell area. The width of the front transparent conductive film is one to three times the width of the metal electrode. Therefore, the area occupied by the transparent conductive film is about 4.5%-13.5%, which can reduce the use of rare metal indium by 86.5%-95.5%;

[0034] 2. The introduction of anti-reflection film further improves the utilization rate of incident photons on the front of the battery. Taking a single-layer MgF2 film and an ITO film as examples, the average reflectivity of a single-layer MgF2 film in the visible light band is about 4.2% or less, and the average reflectivity of a single-layer ITO film in the visible light band is about 10% or less. Using MgF2 film as an anti-reflection film reduces the reflectivity by 5.8% compared to the conventional heterojunction solar cell ITO film, thereby increasing the utilization rate of incident photons by the solar cell;

[0035] 3. Since the front transparent conductive film is prepared only in the metal electrode area, a metal electrode will be prepared on this film layer to conduct current later, and the coverage area is small. Therefore, the front transparent conductive film does not need very excellent optical properties. Its electrical properties can be improved by sacrificing part of the optical properties through process optimization, which can greatly reduce the square resistance of the front transparent conductive film. The low square resistance of the front transparent conductive film can bring lower contact resistance when in contact with the metal electrode, thereby reducing the series resistance of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 It is a schematic diagram of the structure of a heterojunction solar cell of the present invention.

[0038] Figure 2 The contact resistance comparison diagram of Example 1 of the present invention and the conventional method is shown in FIG.

[0039] Figure 3 This is a comparison chart of the pressure opening of Example 1 of the present invention and the conventional method.

[0040] Figure 4 This is a comparison chart of the filling factors of Example 1 of the present invention and the conventional method.

[0041] Figure 5 It is a comparison chart of current density between Example 1 of the present invention and the conventional method.

[0042] In the above drawings, the meanings of the various marks are: 1-metal electrode, 2-front transparent conductive film, 3-anti-reflection film, 4-N-type microcrystalline silicon oxide film, 5-front amorphous silicon film, 6-N-type single crystal silicon wafer, 7-P-type microcrystalline silicon layer, 8-back transparent conductive film, 9-back amorphous silicon film. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0044] A low-cost silicon heterojunction solar cell, the specific structure of which is as follows Figure 1 As shown, the light receiving surface includes a microcrystalline silicon film and a metal electrode 1, a front transparent conductive film 2 is arranged on the microcrystalline silicon film below the metal electrode 1, and an anti-reflection film 3 is arranged on the remaining microcrystalline silicon films, the front transparent conductive film 2 is an ITO film, the anti-reflection film 3 is a magnesium fluoride anti-reflection film 3, the square resistance of the transparent conductive film after annealing is less than or equal to 25Ω / sq, and the carrier mobility is equal to 65cm 2 V -1 s -1 , thickness is less than or equal to 100nm, the width of the front transparent conductive film 2 is about 1-3 times of the metal electrode 1, the light-receiving surface microcrystalline silicon film is an N-type microcrystalline silicon oxygen film 4, and the back of the N-type microcrystalline silicon oxygen film 4 is provided with a front amorphous silicon film 5, and the back of the front amorphous silicon film 5 is provided with a silicon wafer, which is an N-type single crystal silicon wafer 6, and the microcrystalline silicon film on the back of the battery is a P-type microcrystalline silicon layer 7, and the back of the P-type microcrystalline silicon layer 7 is provided with a back transparent conductive film 8 covering the P-type microcrystalline silicon layer 7, and the front of the P-type microcrystalline silicon layer 7 is provided with a back amorphous silicon film 9, and the back transparent conductive film 8 and the front transparent conductive film 2 are both ITO films.

[0045] Example 1

[0046] This embodiment discloses a low-cost method for preparing a silicon heterojunction solar cell having the above structure, comprising the following steps:

[0047] 1) Chain cleaning: Place the N-type single crystal silicon wafer in potassium hydroxide cleaning solution for deep cleaning, followed by acid cleaning to completely remove impurities and pollutants on the surface of the silicon wafer, laying the foundation for subsequent processes.

[0048] 2) Surface texturing, wet chemical treatment of silicon wafers, including removing cutting damage and forming a random pyramid structure surface texture to enhance light capture and short-circuit current density.

[0049] 3) Amorphous silicon thin film deposition: Through the chemical vapor deposition (PECVD) technology, silane, hydrogen, etc. are used as raw gases to deposit intrinsic amorphous silicon thin films on the front and back sides of crystalline silicon as the passivation layer of the battery.

[0050] 4) N-type microcrystalline silicon oxide film deposition, through chemical vapor deposition (PECVD) technology, using silane, hydrogen, carbon dioxide, phosphine, etc., deposited on the front intrinsic amorphous silicon film. Its conductivity is 0.55S / m, the crystallization rate is 54%, the bandgap should be 1.72eV, the refractive index n value is 2.47, and the thickness is 21nm.

[0051] 5) P-type microcrystalline silicon film deposition, through chemical vapor deposition (PECVD) technology, using silane, hydrogen, diborane, etc. to deposit on the back intrinsic amorphous silicon film.

[0052] 6) ITO thin film deposition, through physical vapor deposition (PVD) technology, using hydrogen, argon and other gases to bombard sputter ITO target material for deposition. During deposition, a mask plate is used to mask the non-metallic electrode area on the front side of the cell, and the back side is not processed. The ITO thin film on both sides is deposited at the same time. The performance of the ITO thin film before and after annealing is shown in Table 2. The optical performance parameters of the ITO thin film are shown in Table 1 below.

[0053] 7) Magnesium fluoride anti-reflection film, through reactive plasma deposition (RPD) technology, uses argon and other gases to pass through an ion generator to generate corresponding ion flow, which passes through a controllable magnetic field and is deflected to bombard the magnesium fluoride raw material to deposit a magnesium fluoride film on the front of the battery. During deposition, a mask is used to cover the metal electrode area on the front of the battery cell. The performance parameters of the magnesium fluoride anti-reflection film are shown in Table 1 below.

[0054] 8) Preparation of metal electrodes: prepare the front and back metal electrodes respectively by screen printing technology.

[0055] Table 1I TO and MgF2 optical performance parameters

[0056]

[0057] Table 2 Comparison of ITO film performance before and after optimization

[0058] condition After annealing Film thickness Refractive Index Carrier concentration Mobility Before optimization 30 100.8 1.91 3.22 75 After optimization 22 101.5 2.05 3.45 89

[0059] Comparative Example 1

[0060] Heterojunction solar cells were prepared using conventional methods.

[0061] 1) Chain cleaning: Place the N-type single crystal silicon wafer in potassium hydroxide cleaning solution for deep cleaning, followed by acid cleaning to completely remove impurities and pollutants on the surface of the silicon wafer, laying the foundation for subsequent processes.

[0062] 2) Surface texturing, wet chemical treatment of silicon wafers, including removing cutting damage and forming a random pyramid structure surface texture to enhance light capture and short-circuit current density.

[0063] 3) Amorphous silicon thin film deposition: Through the chemical vapor deposition (PECVD) technology, silane, hydrogen, etc. are used as raw gases to deposit intrinsic amorphous silicon thin films on the front and back sides of crystalline silicon as the passivation layer of the battery.

[0064] 4) N-type microcrystalline silicon oxide film deposition, through chemical vapor deposition (PECVD) technology, using silane, hydrogen, carbon dioxide, phosphine, etc. to deposit on the front intrinsic amorphous silicon film.

[0065] 5) P-type microcrystalline silicon film deposition, through chemical vapor deposition (PECVD) technology, using silane, hydrogen, diborane, etc. to deposit on the back intrinsic amorphous silicon film.

[0066] 6) ITO thin film deposition, through physical vapor deposition (PVD) technology, using hydrogen, argon and other gases to bombard and sputter ITO target material to prepare deposition, and simultaneously depositing front and back ITO films.

[0067] 8) Preparation of metal electrodes: prepare the front and back metal electrodes respectively by screen printing technology.

[0068] The batteries in Example 1 and Comparative Example 1 were tested and obtained Figure 2-Figure 5 ,from Figure 2-5 It can be seen that: by optimizing the I TO film deposition process, the contact resistance between the I TO film and the metal electrode is effectively reduced compared with conventional heterojunction solar cells; by introducing the MgF2 film anti-reflection layer, the utilization rate of incident photons is improved compared with conventional heterojunction solar cells, and the short-circuit current density is effectively increased; through the unique front structure design, compared with conventional heterojunction solar cells, the open circuit voltage is not reduced, but the fill factor has deteriorated to a certain extent, which is mainly due to the increase in the lateral resistance of the battery after removing part of the I TO film, but this degree of deterioration is acceptable through the material property setting of the N-type microcrystalline silicon oxide film.

[0069] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various forms of implementation methods under the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the scope of protection of this embodiment. The scope of protection of this embodiment shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A low-cost silicon heterojunction solar cell, characterized in that: Its light-receiving surface comprises a microcrystalline silicon film and a metal electrode (1); a front transparent conductive film (2) is arranged on the microcrystalline silicon film below the metal electrode (1); and an anti-reflection film (3) is arranged on the remaining microcrystalline silicon film.

2. A low-cost silicon heterojunction solar cell according to claim 1, characterized in that: The front transparent conductive film (2) has a thickness less than or equal to 100 nm and a width one to three times the width of the metal electrode (1).

3. A low-cost silicon heterojunction solar cell according to claim 1, characterized in that: The front transparent conductive film (2) has a square resistance of less than or equal to 25Ω / sq after annealing, and a carrier mobility of greater than or equal to 65cm 2 V -1 s -1 , thickness is less than or equal to 100nm.

4. A low-cost silicon heterojunction solar cell according to claim 1, characterized in that: The light-receiving surface microcrystalline silicon film is an N-type microcrystalline silicon oxygen film (4).

5. A low-cost silicon heterojunction solar cell according to claim 4, characterized in that: The N-type microcrystalline silicon oxide film (4) has an electrical conductivity greater than or equal to 0.5 S / m, a crystallization rate greater than or equal to 40%, a bandgap greater than or equal to 1.6 eV, a refractive index n value less than or equal to 2.5, and a thickness less than or equal to 25 nm.

6. A low-cost method for preparing a silicon heterojunction solar cell according to any one of claims 1 to 5, characterized in that: The following steps are involved: On the microcrystalline silicon layer on the light-receiving surface of the solar cell, a front transparent conductive film (2) is prepared only in the area below the metal electrode (1), and an anti-reflection film (3) is prepared on the remaining microcrystalline silicon film.

7. A method for preparing a low-cost silicon heterojunction solar cell according to claim 6, characterized in that: The front transparent conductive film (2) is an ITO film.

8. The method for preparing a low-cost silicon heterojunction solar cell according to claim 6, characterized in that: After the front transparent conductive film (2) is prepared, an anti-reflection film (3) is prepared in the non-metallic electrode (1) region using a mask.

9. A low-cost method for preparing a silicon heterojunction solar cell according to claim 6, characterized in that: Before preparing the front transparent conductive film (2), the steps of cleaning the silicon wafer, texturing the surface, preparing amorphous silicon films on both sides and microcrystalline silicon films on both sides are also included.

10. A low-cost method for preparing a silicon heterojunction solar cell according to claim 6, characterized in that: After the anti-reflection film (3) is prepared, the metal electrode (1) is prepared.

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