Passivation contact heterojunction solar cell and preparation method thereof

Abstract

The invention provides a passivation contact heterojunction solar cell and a preparation method thereof, and belongs to the technical field of photovoltaic power generation. The cell structure comprises a metal gate line electrode, a first transparent conductive film, an N-type heavily-doped polycrystalline silicon germanium film, a first intrinsic amorphous silicon passivation film, a crystalline silicon substrate, a second intrinsic amorphous silicon passivation film, a P-type heavily-doped polycrystalline silicon germanium film, a second transparent conductive film and a metal gate electrode. According to the invention, the polycrystalline silicon germanium thin film growing technology is applied to the passivation contact heterojunction crystalline silicon solar cell, so that the solar cell has higher doping concentration and lower light absorption coefficient; meanwhile, growth of N-type and P-type heavily-doped silicon germanium films can be realized at a relatively low temperature, so that a passivation contact structure is realized on the crystalline silicon substrate; therefore, on one hand, the surface state density is reduced, on the other hand, selective collection of the carriers is realized, and recombination of the carriers is effectively reduced, so that the photoelectric conversion efficiency of the cell is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and particularly to a passivated contact heterojunction solar cell and a preparation method thereof. Background Art

[0002] Since the carbon peak and carbon neutrality goals were proposed in China, the global consensus on carbon neutrality has been further reached, and carbon peak and carbon neutrality have also become a hot topic of concern to all sectors of society. In the process of achieving carbon peak and carbon neutrality, renewable energy represented by photovoltaic and wind energy is undoubtedly the main force. Crystalline silicon solar cells (also known as "solar cells") are one of the mainstream products in the photovoltaic market, currently occupying 95% of the market share. Among them, how to further improve the conversion efficiency of solar cells while reducing production costs is one of the main technical problems in the industry.

[0003] In the field of high-efficiency crystalline silicon solar cells, many foreign research institutions and enterprises have carried out a large number of studies and developed many high-efficiency crystalline silicon solar cells with new structures, such as grooved buried grid, selective emitter, crystalline silicon heterojunction (HJT), tunnel oxide passivated contact solar cell (TOPCon), etc. Currently, one of the high-efficiency structures of double-sided contact crystalline silicon solar cells is the heterojunction solar cell, and the conversion efficiency can reach 26.81%.

[0004] Compared with general solar cells, crystalline silicon heterojunction cells use an intrinsic amorphous silicon and doped amorphous silicon composite passivation film, effectively improving the open-circuit voltage of the cells. Crystalline silicon heterojunction solar cells can use a thinner silicon substrate and have outstanding advantages such as higher efficiency, lower attenuation, better temperature coefficient, and higher bifaciality, which is the development direction of the industrialization of crystalline silicon solar cells.

[0005] Due to the relatively high defect density of the amorphous silicon thin film, the effective doping concentration is generally lightly doped or moderately doped, and its doping concentration is lower than 1×10 18 cm -3 , so it is necessary to deposit a transparent conductive thin film on the amorphous silicon thin film to reduce the transport resistance of photo-generated carriers and the contact resistance of metal electrodes. Moreover, the amorphous silicon thin film has a relatively high light absorption coefficient, and every 10 nm of the amorphous silicon thin film will cause a short-circuit current density loss of 1.5 mA / cm 2 .

[0006] By using doped microcrystalline silicon thin film to replace the conventional amorphous silicon thin film, the conversion efficiency of the heterojunction solar cell is further improved. The microcrystalline silicon thin film has higher doping efficiency, lower resistivity and smaller optical absorption coefficient than the amorphous silicon thin film. However, the growth conditions of the microcrystalline silicon thin film are extremely harsh. Especially when obtaining a microcrystalline silicon thin film with a certain crystallization rate within a thickness of about 10 nm, it is necessary to stepwise modulate the growth process of the intrinsic amorphous silicon thin film and the growth process of the microcrystalline silicon thin film, and reduce the thickness of the seed layer to achieve this. In the existing preparation process of the heterojunction crystalline silicon solar cell, the growth process of the doped microcrystalline silicon thin film is complex, its preparation difficulty is high, and the process window is narrow, which is not conducive to mass production and large-scale industrialization. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the present invention provides a passivated contact heterojunction solar cell and its preparation method. The solar cell adopts the polysilicon germanium thin film technology, which has higher doping efficiency and lower optical absorption coefficient compared with the microcrystalline silicon thin film, effectively reduces the surface state density, realizes the selective collection of carriers, effectively reduces the carrier recombination, and thus effectively improves the photoelectric conversion efficiency of the battery.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a passivated contact heterojunction solar cell, including:

[0010] A crystalline silicon substrate;

[0011] A first intrinsic amorphous silicon passivation film, which is disposed on the upper surface of the crystalline silicon substrate;

[0012] A second intrinsic amorphous silicon passivation film, which is disposed on the lower surface of the crystalline silicon substrate;

[0013] An N-type heavily doped polysilicon germanium thin film, which is disposed on the upper surface of the first intrinsic amorphous silicon passivation film;

[0014] A P-type heavily doped polysilicon germanium thin film, which is disposed on the lower surface of the second intrinsic amorphous silicon passivation film;

[0015] A first transparent conductive thin film, which is disposed on the upper surface of the N-type heavily doped polysilicon germanium thin film;

[0016] A second transparent conductive thin film, which is disposed on the lower surface of the P-type heavily doped polysilicon germanium thin film;

[0017] A metal grid electrode, which is disposed on the upper surface of the first transparent conductive film and the lower surface of the second transparent conductive film.

[0018] Further, the crystalline silicon substrate is an N-type crystalline silicon substrate with a thickness of 90 - 150 μm.

[0019] Further, the thickness of the first intrinsic amorphous silicon passivation film and the second intrinsic amorphous silicon passivation film is 4 - 10 nm.

[0020] Further, the dopant of the N-type heavily doped polycrystalline silicon germanium film is selected from at least one of phosphine and arsine, and the doping atom concentration is 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness of this layer is 10 - 50 nm.

[0021] Further, the dopant of the P-type heavily doped polycrystalline silicon germanium film is selected from at least one of borane, trimethylboron or boron trifluoride, and the doping atom concentration is 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness of this layer is 10 - 50 nm.

[0022] Further, the first transparent conductive film and the second transparent conductive film are independently selected from one or more of ITO, IWO, IHO, IZO, ICO, AZO, GZO, etc.

[0023] Further, the thickness of the first transparent conductive film and the second transparent conductive film is 60 - 90 nm.

[0024] Further, the metal grid electrode includes at least one of a metal silver electrode, silver-coated copper, and electroplated copper.

[0025] The present invention also provides a method for preparing a passivated contact heterojunction solar cell, including the following steps:

[0026] (1) Pretreat the crystalline silicon substrate;

[0027] (2) Grow a first intrinsic amorphous silicon passivation film and a second intrinsic amorphous silicon passivation film on the upper and lower surfaces of the crystalline silicon substrate respectively;

[0028] (3) Introduce a germanium source gas onto the upper and lower surfaces of the crystalline silicon to treat the first intrinsic amorphous silicon passivation film and the second intrinsic amorphous silicon passivation film to form a surface seed layer;

[0029] (4) Grow an N-type heavily doped polysilicon germanium thin film on the surface of the processed first intrinsic amorphous silicon passivation film, and grow a P-type heavily doped polysilicon germanium thin film on the surface of the second intrinsic amorphous silicon passivation film;

[0030] (5) Grow a first transparent conductive thin film and a second transparent conductive thin film on the surfaces of the N-type heavily doped polysilicon germanium thin film and the P-type heavily doped polysilicon germanium thin film respectively;

[0031] (6) Prepare metal grid line electrodes on the surfaces of the first transparent conductive thin film and the second transparent conductive thin film respectively.

[0032] Furthermore, the pretreatment in step (1) includes texturing and cleaning; the texturing uses a conventional texturing method in the art, and a textured surface structure appears on both the upper and lower surfaces of the crystalline silicon substrate after texturing; the cleaning uses the RCA standard cleaning method to remove organic contaminants and metal particles on the surface of the crystalline silicon substrate.

[0033] Furthermore, the growth method of the intrinsic amorphous silicon passivation film in step (2) uses plasma-enhanced chemical vapor deposition (PECVD) or hot wire chemical vapor deposition (HWCVD).

[0034] Furthermore, the germanium source gas in step (3) is germanium tetrafluoride (GeF4).

[0035] Furthermore, steps (3) and (4) are processed using thermal chemical vapor deposition (TCVD).

[0036] Furthermore, the gases in the vapor deposition process of step (4) include disilane, hydrogen, helium, and argon; the dopant is selected from at least one of phosphine and borane.

[0037] Furthermore, in step (4), the temperature is controlled within 250 °C, and the doping atom concentration of the N-type heavily doped polysilicon germanium thin film and the P-type heavily doped polysilicon germanium thin film is 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness is 10 - 50 nm.

[0038] The doping atom concentration is achieved by controlling the flow ratio of the dopant to disilane.

[0039] Furthermore, the first transparent conductive thin film and the second transparent conductive thin film in step (5) are formed in a magnetron sputtering system or a reactive plasma coating system, and the film thickness is controlled within 60 - 90 nm.

[0040] Furthermore, in step (6), metal grid electrodes are prepared on the surfaces of the first transparent conductive thin film and the second transparent conductive thin film respectively by means of screen printing or copper electroplating.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] By growing polycrystalline silicon germanium thin film technology and applying it to passivated contact heterojunction crystalline silicon solar cells, the present invention has a higher doping concentration, thus having a lower light absorption coefficient; at the same time, the growth of N-type and P-type heavily doped silicon germanium thin films can be realized at a lower temperature, so as to realize a passivated contact structure on the crystalline silicon substrate; in this way, on the one hand, the surface state density is reduced, and on the other hand, the selective collection of carriers is realized, effectively reducing the recombination of carriers, thereby effectively improving the photoelectric conversion efficiency of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a structural diagram of the polycrystalline silicon germanium thin film solar cell of the present invention.

[0044] REFERENCE SIGNS IN THE DRAWINGS

[0045] 1 - Metal grid line electrode, 2 - First transparent conductive thin film, 3 - N-type heavily doped polycrystalline silicon germanium thin film, 4 - First intrinsic amorphous silicon passivation film, 5 - Crystalline silicon substrate, 6 - Second intrinsic amorphous silicon passivation film, 7 - P-type heavily doped polycrystalline silicon germanium thin film, 8 - Second transparent conductive film, 9 - Metal grid electrode. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0048] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features.

[0049] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over", "on top of" and "upper surface" of the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "below", "beneath" and "lower surface" of the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply indicates that the horizontal height of the first feature is less than that of the second feature.

[0050] In addition, unless otherwise specified, the methods used in the present invention are all conventional methods; the raw materials and devices used, unless otherwise specified, are all conventional commercially available products.

[0051] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments to help understand the content of the present invention.

[0052] Example 1

[0053] This example provides a polysilicon germanium thin film solar cell, the structure of which is as Figure 1 shown, and includes, from top to bottom in sequence: a metal grid electrode 1, a first transparent conductive thin film 2, an N-type heavily doped polysilicon germanium thin film 3, a first intrinsic amorphous silicon passivation film 4, a crystalline silicon substrate 5, a second intrinsic amorphous silicon passivation film 6, a P-type heavily doped polysilicon germanium thin film 7, a second transparent conductive film 8, and a metal grid electrode 9.

[0054] The crystalline silicon substrate 5 is an N-type crystalline silicon substrate with a thickness of 120 μm.

[0055] The thickness of the first intrinsic amorphous silicon passivation film and the second intrinsic amorphous silicon passivation film is 6 nm.

[0056] The dopant of the N-type heavily doped polysilicon germanium thin film is phosphine, and the doping atom concentration is 1×10 20 cm -3 , and the thickness of this layer is 15 nm.

[0057] The dopant of the P-type heavily doped polysilicon germanium thin film is diborane, and the doping concentration is 1×10 20 cm -3 , and the thickness of this layer is 20 nm.

[0058] The first transparent conductive thin film and the second transparent conductive thin film are ITO with a thickness of 75 nm.

[0059] The metal grid electrode is an Ag electrode.

[0060] The preparation method of the polysilicon germanium thin film solar cell comprises the following steps:

[0061] First, according to the conventional preparation steps, a rough processed N-type crystalline silicon wafer is prepared and used as a substrate for subsequent processing steps.

[0062] S1. Pretreat both sides of the prepared crystalline silicon substrate; specifically including:

[0063] S11. Texturing the surface of the crystalline silicon substrate; after texturing, a textured surface structure appears on both the front and back surfaces of the crystalline silicon substrate.

[0064] S12. Cleaning the crystalline silicon substrate by the RCA standard cleaning method to remove organic contaminants and metal particles on the surface of the crystalline silicon.

[0065] S2. After completion of the cleaning, use a PECVD system to grow an intrinsic amorphous silicon thin film on both sides of the crystalline silicon to form a surface passivation layer. Since the PECVD system utilizes gas-phase plasma deposition technology, it can well support double-sided deposition processing. While achieving uniform deposition, it can also avoid the problem of excessive stress generated by single-sided processing. Therefore, a one-time double-sided deposition processing method is adopted in this step.

[0066] S3. Place the crystalline silicon substrate with the surface passivation layer into a thermal chemical vapor deposition (TCVD) system, introduce germanium tetrafluoride (GeF4) gas on the upper surface of the crystalline silicon to process the first intrinsic amorphous silicon thin film, and form a surface seed layer (polysilicon germanium seed layer). This process can also etch off a part of the amorphous silicon thin film to reduce the light absorption loss caused by the amorphous silicon thin film.

[0067] S4. Grow an N-type heavily doped polysilicon germanium thin film on the surface of the processed first intrinsic amorphous silicon thin film, and control the process temperature within 250°C.

[0068] S5. Then turn the substrate over, and according to the steps in S3, introduce germanium tetrafluoride (GeF4) gas on the lower surface of the crystalline silicon to process the second intrinsic amorphous silicon thin film, and form a surface seed layer (polysilicon germanium seed layer); then, grow a P-type heavily doped polysilicon germanium thin film on the surface of the processed second intrinsic amorphous silicon thin film, and control the process temperature within 250°C.

[0069] S6. Place the crystalline silicon obtained in S5 into a magnetron sputtering system or a reactive plasma deposition (RPD) system to grow an indium tin oxide (ITO) transparent conductive thin film on both sides. ITO is a thin film that can both conduct electricity and has a high transparency rate in the visible light range.

[0070] S7. Prepare metal grid electrodes on the surface of the indium tin oxide transparent conductive thin film by means of screen printing or copper electroplating, etc.

[0071] The conversion efficiency of the battery obtained in this embodiment can reach 25.5%, where the open-circuit voltage can reach 749 mV, the FF reaches 85.8%, and the short-circuit current density is 39.68 mA / cm 2 .

[0072] In this embodiment, the processed intrinsic amorphous silicon thin film, on the one hand, serves as a passivation film on the surface of the silicon substrate, saturating the dangling bonds on the silicon wafer surface and reducing the surface states; on the other hand, it serves as the seed layer material for the doped polycrystalline silicon germanium thin film, promoting the growth of high-quality polycrystalline silicon germanium thin film. The intrinsic amorphous silicon thin film reacts with GeF4 gas to form a germanium seed layer on the surface. This process can etch away a part of the amorphous silicon thin film, reducing the light absorption loss caused by the amorphous silicon thin film. The doped polycrystalline silicon germanium thin film has a high effective doping concentration, can effectively induce the band bending on the surface of the silicon substrate, form good field passivation, reduce the concentration of one type of carrier, and decrease the carrier recombination rate. The superposition of the two effects reduces the surface passivation of the silicon substrate, thus improving the fill factor and open-circuit voltage of the battery, and solving the aforementioned technical problems and improving the photoelectric conversion efficiency.

[0073] It is worth mentioning that the doped polycrystalline silicon germanium thin film is grown by a reactive thermochemical vapor deposition system, and the process temperature is controlled within the range of 250 °C, which will not cause a large amount of atomic hydrogen in the intrinsic amorphous silicon thin film to escape, thereby maintaining the chemical passivation effect of the intrinsic amorphous silicon thin film; at the same time, the technical solution of the present invention not only has a low process temperature, but also has a simple, safe processing process, low equipment cost, and is suitable for large-scale production; it also avoids the cost problems faced by the microcrystalline silicon thin film technology.

[0074] In this article, specific examples are used to elaborate on the principle and implementation mode 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 mode and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A passivated contact heterojunction solar cell, comprising: A crystalline silicon substrate; A first intrinsic amorphous silicon passivation film, which is disposed on the upper surface of the crystalline silicon substrate; A second intrinsic amorphous silicon passivation film, which is disposed on the lower surface of the crystalline silicon substrate; An N-type heavily doped polycrystalline silicon germanium thin film, which is disposed on the upper surface of the first intrinsic amorphous silicon passivation film; A P-type heavily doped polycrystalline silicon germanium thin film, which is disposed on the lower surface of the second intrinsic amorphous silicon passivation film; A first transparent conductive thin film, which is disposed on the upper surface of the N-type heavily doped polycrystalline silicon germanium thin film; A second transparent conductive thin film, which is disposed on the lower surface of the P-type heavily doped polycrystalline silicon germanium thin film; A metal grid electrode, which is disposed on the upper surface of the first transparent conductive thin film and the lower surface of the second transparent conductive thin film.

2. The passivated contact heterojunction solar cell according to claim 1, wherein, The crystalline silicon substrate is an N-type crystalline silicon substrate with a thickness of 90 - 150 μm; The thicknesses of the first intrinsic amorphous silicon passivation film and the second intrinsic amorphous silicon passivation film are 4 - 10 nm.

3. The passivated contact heterojunction solar cell according to claim 1, wherein The dopant of the N-type heavily doped polysilicon germanium film is selected from at least one of phosphine and arsine, and the doping atom concentration is 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness of the N-type heavily doped polysilicon germanium film is 10 to 50 nm; The dopant of the P-type heavily doped polysilicon germanium thin film is selected from at least one of borane, trimethylboron or boron trifluoride, and the doping atom concentration is 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness of the P-type heavily doped polysilicon germanium thin film is 10 to 50 nm.

4. The passivated contact heterojunction solar cell according to claim 1, wherein The first transparent conductive thin film and the second transparent conductive thin film are independently selected from one or more of ITO, IWO, IHO, IZO, ICO, AZO, GZO, etc.; The thicknesses of the first transparent conductive thin film and the second transparent conductive thin film are 60 - 90 nm.

5. The passivated contact heterojunction solar cell according to claim 1, characterized in that, The metal grid electrode includes at least one of a metal silver electrode, silver-coated copper, and electroplated copper.

6. A method for preparing a passivated contact heterojunction solar cell, comprising the following steps: (1) Pretreating the crystalline silicon substrate; (2) Growing a first intrinsic amorphous silicon passivation film and a second intrinsic amorphous silicon passivation film on the upper and lower surfaces of the crystalline silicon substrate respectively; (3) Introducing a germanium source gas onto the upper and lower surfaces of the crystalline silicon to treat the first intrinsic amorphous silicon passivation film and the second intrinsic amorphous silicon passivation film to form a surface seed layer; (4) Growing an N-type heavily doped polycrystalline silicon germanium thin film on the surface of the treated first intrinsic amorphous silicon passivation film and a P-type heavily doped polycrystalline silicon germanium thin film on the surface of the second intrinsic amorphous silicon passivation film; (5) Growing a first transparent conductive thin film and a second transparent conductive thin film on the surfaces of the N-type heavily doped polycrystalline silicon germanium thin film and the P-type heavily doped polycrystalline silicon germanium thin film respectively; (6) Preparing metal grid electrodes on the surfaces of the first transparent conductive thin film and the second transparent conductive thin film respectively.

7. The preparation method according to claim 6, characterized in that, The growth method of the intrinsic amorphous silicon passivation film in step (2) uses plasma-enhanced chemical vapor deposition or hot wire chemical vapor deposition.

8. The preparation method according to claim 6, characterized in that, The germanium source gas in step (3) is germanium tetrafluoride.

9. The preparation method according to claim 6, wherein Steps (3) and (4) are treated by thermal chemical vapor deposition; The gases in the vapor deposition process of step (4) include disilane, hydrogen, helium, and argon; the dopant is selected from at least one of phosphine and borane.

10. The preparation method according to claim 6, characterized in that, Step (4) controls the temperature within 250 °C, and the doping atom concentration of the N-type heavily doped polysilicon germanium thin film and the P-type heavily doped polysilicon germanium thin film is in the range of 1×10 18 cm -3 ~1×10 21 cm -3 , and the thickness is in the range of 10 - 50 nm.

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