A transparent conductive oxide film for heterojunction cells and a method of making

Abstract

The application discloses a transparent conductive oxide film for a heterojunction cell and a preparation method thereof. The transparent conductive oxide film substrate is sequentially provided with an intrinsic amorphous silicon film and a doped amorphous silicon film and is stably formed into a uniform pyramid structure with a size of 1-2 microns on the surface of a silicon wafer. A buffer layer is grown on the surface of the doped amorphous silicon, and the buffer layer is located between an indium titanium oxide (ITIO) film and the doped amorphous silicon. The application grows a buffer layer with a thickness less than 10 nanometers on the surface of the doped amorphous silicon. The growth process cannot physically damage the effective doping sites of the amorphous silicon. The buffer layer can block the direct bombardment of high-energy particles, protect the doped amorphous silicon film from damage, ensure the smooth progress of the deposition process, make the transparent conductive oxide film still have good conductive performance, make the transparent conductive oxide film have high light transmittance, and thus be favorable to the improvement of the efficiency of the heterojunction solar cell.

Description

Technical Field

[0001] This invention belongs to the field of heterojunction solar cells, and specifically relates to a transparent conductive oxide thin film for heterojunction cells and its preparation method. Background Technology

[0002] With the continuous development of solar cell technology, the demand for high-efficiency, low-cost transparent electrode films will increase significantly. In this development process, the industry has actively explored and developed various technical routes for the material composition and deposition technology of transparent conductive oxides in solar cells. Among them, the more mature technologies mainly include PVD (represented by magnetron sputtering) deposition of ITO (indium tin oxide) films and RPD (reactive plasma deposition) preparation of IWO (indium tungsten oxide) films. The former, due to its outstanding advantages such as suitability for large-area deposition and process stability, is very suitable for mass production and is therefore widely used by most manufacturers. However, the films obtained by this method are not ideal in terms of light transmittance and conductivity, and there is still room for improvement. The latter mainly relies on Sumitomo Corporation of Japan to provide the corresponding thin film deposition equipment and matching special targets. Undeniably, although the films prepared by this method have advantages over the former in terms of conductivity and light transmittance, the resulting film structure is relatively loose. Moreover, the cost of this equipment and the price of the target materials are very high, making it unsuitable for mass production from a cost perspective.

[0003] Furthermore, it is important to note that the transparent conductive oxide film in heterojunction solar cells is deposited on heavily doped n-type or p-type amorphous silicon films. These heavily doped amorphous silicon films are deposited on n-type silicon wafers that have undergone texturing to form a pyramidal surface structure and on which an intrinsic passivation layer has been deposited. The thickness of both the doped and intrinsic amorphous silicon films ranges from several nanometers to tens of nanometers. The complex and unique structure of the substrate used for this transparent conductive oxide deposition undoubtedly places special demands on the deposition materials and processes. This special substrate structure requires the deposition materials to possess good compatibility, enabling them to bond well with the amorphous silicon film and the intrinsic passivation layer on the silicon wafer surface. Simultaneously, the deposition process must precisely control the film growth to ensure that the film's quality and performance meet the high requirements of heterojunction solar cells. By continuously optimizing material selection, preparation methods, and performance optimization strategies, oxide transparent electrode films with better performance and lower cost can be fabricated, providing strong support for the development of crystalline silicon heterojunction solar cells.

[0004] Therefore, there is an urgent need for a transparent conductive oxide thin film for heterojunction solar cells and a method for preparing it to produce a transparent oxide electrode thin film with better performance and lower cost. Summary of the Invention

[0005] The purpose of this invention is to provide a transparent conductive oxide thin film for heterojunction solar cells and a method for its preparation, thereby improving the optical and electrical properties of the transparent conductive oxide thin film and improving the contact between the transparent conductive oxide thin film and the doped nanocrystalline silicon layer to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, this invention provides a transparent conductive oxide thin film for heterojunction solar cells. The transparent conductive oxide thin film substrate is a pyramid structure with an intrinsic amorphous silicon thin film and a doped amorphous silicon thin film deposited sequentially and stably formed on the silicon wafer surface in a uniform size of 1-2 μm. This structure is beneficial for increasing light absorption and scattering, improving the light-harvesting ability of the solar cell, and thus improving the cell's conversion efficiency. A buffer layer is grown on the surface of the doped amorphous silicon. The buffer layer is located between the indium titanium oxide (ITIO) thin film and the doped amorphous silicon. The buffer layer grown on the surface of the doped amorphous silicon, located between the indium titanium oxide (ITIO) thin film and the doped amorphous silicon, can effectively reduce interface defects, improve carrier transport efficiency, and reduce resistance loss. At the same time, the presence of the buffer layer can protect the doped amorphous silicon thin film from damage in subsequent processes, improving the stability and reliability of the cell.

[0007] Furthermore, the thickness of the buffer layer is not less than 10 nm.

[0008] Furthermore, the target material used in preparing the transparent conductive oxide thin film is one of ITO (indium tin oxide), ZnO and AZO (aluminum-doped zinc oxide), BZO (boron-doped zinc oxide), GZO (gallium-doped zinc oxide), and indium-doped cadmium oxide. These materials have good conductivity and light transmittance, which can improve the photoelectric conversion efficiency of the battery.

[0009] Furthermore, the thickness of the transparent conductive oxide film ranges from 70nm to 120nm, which can achieve optimal optical and electrical properties.

[0010] Furthermore, the doped amorphous silicon is either an n-type nanocrystalline silicon oxide film or a p-type nanocrystalline silicon oxide film. Using n-type and p-type nanocrystalline silicon oxide films as doped amorphous silicon can increase carrier concentration and mobility, thereby improving the battery's conductivity. Simultaneously, the nanocrystalline silicon oxide film exhibits high stability and anti-aging properties, which is beneficial for extending the battery's lifespan.

[0011] Furthermore, the deposition includes one of CVD (chemical vapor deposition), APCVD (atmospheric pressure chemical vapor deposition), ALD (atomic layer deposition), PECVD (plasma-enhanced chemical vapor deposition), MOCVD (metal-organic chemical vapor deposition), and magnetron sputtering.

[0012] Furthermore, the present invention also provides a method for preparing a transparent conductive oxide thin film for heterojunction solar cells, specifically including the following steps: Using an N-type silicon wafer as a substrate, intrinsic amorphous silicon thin films, doped amorphous silicon thin films, and transparent conductive oxide thin films are sequentially deposited using magnetron sputtering. Magnetron sputtering offers advantages such as high deposition rate, uniform film layer, and strong adhesion, enabling high-quality thin film deposition. Furthermore, by controlling the sputtering power density from 1.0 to 20 W / cm² and the flow ratio of argon to oxygen in the reaction gases at 200:1.5, the properties of the thin films can be precisely adjusted to meet diverse application requirements.

[0013] Furthermore, no heating is performed during deposition, and annealing is carried out after deposition. Not heating during deposition can avoid thermal damage to the silicon wafer and other thin films, ensuring the performance and stability of the battery.

[0014] Furthermore, annealing temperatures of 180-230℃ and annealing times of 20-50 min can further improve the crystallinity and electrical properties of the film, thereby increasing the conversion efficiency of the battery.

[0015] Furthermore, the flow rate ratio of argon to oxygen is 200:1.5.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention proposes a transparent conductive oxide thin film for heterojunction solar cells. The doped amorphous silicon thin film, often only a few nanometers thick, bears the crucial responsibility of carrier transport and photoelectric conversion in the cell. However, bombardment by high-energy particles during deposition can disrupt its crystal structure, damaging effective doping sites and thus affecting the film's photoelectric performance. Therefore, this invention grows a buffer layer less than 10 nanometers thick on the surface of the doped amorphous silicon. The growth process avoids physical damage to the effective doping sites of the amorphous silicon, thus both blocking direct bombardment by high-energy particles and protecting the doped amorphous silicon film from damage, while ensuring the smooth progress of the deposition process. This allows the transparent conductive oxide thin film to maintain good conductivity and also gives it high light transmittance, thereby contributing to improved efficiency of heterojunction solar cells.

[0017] Specifically, the doped amorphous silicon is an n-type nanocrystalline silicon oxide film and a p-type nanocrystalline silicon oxide film. The n-type nanocrystalline silicon oxide film can improve the short-circuit current of the solar cell, while ensuring the crystallinity ratio of the film and improving the doping efficiency to ensure the effective transport of charge carriers, thereby improving the fill factor. The p-type nanocrystalline silicon oxide film improves the activation rate of the doping elements, giving the film high electrical conductivity, while improving the contact characteristics with the transparent conductive oxide film, thereby achieving the purpose of improving the fill factor and conversion efficiency.

[0018] This invention also provides a method for preparing transparent conductive oxide thin films for heterojunction solar cells, employing relatively low-cost materials and processes. For the target material selection, common transparent conductive oxide materials such as ITO (indium tin oxide), ZnO (zinc oxide), AZO (aluminum-doped zinc oxide), BZO (boron-doped zinc oxide), GZO (gallium-doped zinc oxide), and indium-doped cadmium oxide are chosen. These materials not only possess good conductivity and light transmittance, meeting the photoelectric conversion efficiency requirements of solar cells, but are also relatively inexpensive and readily available, thus reducing raw material costs. This invention utilizes magnetron sputtering, which offers advantages such as high deposition rate, uniform film layer, and strong adhesion, ensuring the quality and performance of the thin film. Compared to traditional physical vapor deposition or chemical vapor deposition methods, magnetron sputtering requires lower equipment and maintenance costs, is simpler to operate, and is easily industrialized. Furthermore, the deposition process employs a non-heating method, avoiding thermal damage to the silicon wafer and other thin films, ensuring the performance and stability of the battery. After deposition, appropriate annealing was performed to further improve the crystallinity and electrical properties of the film, thereby increasing the conversion efficiency of the battery. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating a method for preparing a transparent conductive oxide thin film for heterojunction solar cells according to an embodiment of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] The present invention provides a transparent conductive oxide thin film for heterojunction solar cells, with reference to the accompanying drawings. See Figure 1 A transparent conductive oxide thin film for heterojunction solar cells is disclosed. The transparent conductive oxide film substrate is a pyramid structure with a uniform size of 1-2 μm, on which an intrinsic amorphous silicon thin film and a doped amorphous silicon thin film are sequentially deposited and stabilized on the silicon wafer surface. A buffer layer with a thickness of not less than 10 nm is grown on the surface of the doped amorphous silicon, located between the indium titanium oxide (ITIO) thin film and the doped amorphous silicon. The pyramid structure facilitates increased light absorption and scattering, improving the light-harvesting capability of the solar cell and thus enhancing its conversion efficiency. The buffer layer grown on the surface of the doped amorphous silicon, located between the ITIO thin film and the doped amorphous silicon, effectively reduces interface defects, improves carrier transport efficiency, and reduces resistance loss. Simultaneously, the presence of the buffer layer protects the doped amorphous silicon thin film from damage by subsequent processes, improving the stability and reliability of the solar cell.

[0023] Meanwhile, the buffer layer structure has high light transmittance to ensure that sunlight can smoothly penetrate and reach the photosensitive layer of the solar cell, thereby maximizing the capture of light energy; it also has high conductivity to ensure that the current inside the cell can be smoothly transmitted and reduce energy loss; in order to improve the transport efficiency of charge carriers at the interface, the design of the buffer layer also needs to consider the high probability of interface tunneling, so that charge carriers can more easily cross the interface and enter the next thin film.

[0024] Example 2 A transparent conductive oxide thin film for heterojunction solar cells is disclosed. The transparent conductive oxide thin film substrate is formed by sequentially depositing an intrinsic amorphous silicon thin film and a doped amorphous silicon thin film, which are stably deposited on the silicon wafer surface in a uniform pyramid structure with a size of 1-2 μm. The target material used to prepare the transparent conductive oxide thin film is one of ITO (indium tin oxide), ZnO and AZO (aluminum-doped zinc oxide), BZO (boron-doped zinc oxide), GZO (gallium-doped zinc oxide), and indium-doped cadmium oxide. These materials have good conductivity and light transmittance, which can improve the photoelectric conversion efficiency of the cell. The thickness of the transparent conductive oxide thin film is in the range of 70 nm-120 nm, which can achieve optimal optical and electrical performance.

[0025] Example 3 A transparent conductive oxide thin film for heterojunction solar cells is disclosed. The transparent conductive oxide film substrate is a pyramid structure with a uniform size of 1-2 μm, on which an intrinsic amorphous silicon thin film and a doped amorphous silicon thin film are sequentially deposited and stabilized on the silicon wafer surface. The doped amorphous silicon is selected from n-type and p-type nanocrystalline silicon oxide thin films, which can improve the concentration and mobility of charge carriers and enhance the conductivity of the cell. Simultaneously, the nanocrystalline silicon oxide thin film exhibits high stability and anti-aging properties, which is beneficial for improving the battery's lifespan. The deposition process includes one of the following: CVD (chemical vapor deposition), APCVD (atmospheric pressure chemical vapor deposition), ALD (atomic layer deposition), PECVD (plasma-enhanced chemical vapor deposition), MOCVD (metal-organic chemical vapor deposition), and magnetron sputtering.

[0026] n-type microcrystalline silicon oxide, with its high electrical conductivity and low absorption coefficient, is the optimal field passivation film. Adjusting the microstructure of the n-type silicon film on the light-facing side towards nanocrystalline shape requires, on the one hand, widening the optical bandgap to enhance light absorption to the crystalline silicon substrate, thereby increasing the short-circuit current of the solar cell. On the other hand, ensuring the crystallinity ratio of the film and improving doping efficiency guarantee effective carrier transport, thus improving the fill factor. To reduce carrier transport losses caused by defects in p-type doped amorphous silicon films and contact losses with transparent conductive oxide films, the microstructure of the p-type amorphous silicon film is adjusted towards crystallinity. This increases the activation rate of the dopant elements, giving the film high electrical conductivity, and simultaneously improving the contact characteristics with the transparent conductive oxide film, thereby increasing the fill factor and conversion efficiency.

[0027] Example 4 This invention provides a method for preparing a transparent conductive oxide thin film for heterojunction solar cells. Using an N-type silicon wafer as a substrate, an intrinsic amorphous silicon thin film, a doped amorphous silicon thin film, and a transparent conductive oxide thin film are sequentially deposited using magnetron sputtering. Magnetron sputtering offers advantages such as high deposition rate, uniform film layer, and strong adhesion, enabling high-quality film deposition. Furthermore, by controlling the sputtering power density to 1.0-20 W / cm² and the flow ratio of argon to oxygen in the reaction gases to 200:1.5, the film performance can be precisely adjusted to meet different application requirements. An annealing temperature of 180-230℃ and an annealing time of 20-50 min can further improve the crystallinity and electrical properties of the film, thereby increasing the cell's conversion efficiency. The argon to oxygen flow ratio is 200:1.5. No heating is performed during deposition. While heating aids film growth, high temperatures can cause thermal damage to the silicon wafer, introducing unnecessary defects and affecting the overall performance of the cell. Secondly, for other thin film layers already deposited on the silicon wafer, such as intrinsic amorphous silicon films and doped amorphous silicon films, heating may damage their structure, leading to a decrease in optoelectronic performance. The strategy of not heating during deposition and performing annealing after deposition avoids the impact of thermal damage on the silicon wafer and other thin film layers, while improving the crystallinity and electrical properties of the film through annealing.

[0028] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A transparent conductive oxide thin film for heterojunction solar cells, characterized in that, The transparent conductive oxide thin film substrate is a pyramid structure with an intrinsic amorphous silicon thin film and a doped amorphous silicon thin film deposited sequentially and stably formed on the silicon wafer surface in a uniform size of 1-2 μm; a buffer layer is grown on the surface of the doped amorphous silicon, and the buffer layer is located between the indium titanium oxide (ITIO) thin film and the doped amorphous silicon.

2. The transparent conductive oxide thin film structure based on a heterojunction solar cell according to claim 1, characterized in that, The thickness of the buffer layer is not less than 10 nm.

3. The transparent conductive oxide thin film for heterojunction solar cells according to claim 1, characterized in that, The target material used to prepare the transparent conductive oxide thin film is one of ITO (indium tin oxide), ZnO and AZO (aluminum-doped zinc oxide), BZO (boron-doped zinc oxide), GZO (gallium-doped zinc oxide), and indium-doped cadmium oxide.

4. A transparent conductive oxide thin film for heterojunction solar cells according to claim 3, characterized in that, The thickness of the transparent conductive oxide film ranges from 70 nm to 120 nm.

5. A transparent conductive oxide thin film for heterojunction solar cells according to claim 1, characterized in that, The doped amorphous silicon is an n-type nanocrystalline silicon oxide thin film and a p-type nanocrystalline silicon oxide thin film.

6. A transparent conductive oxide thin film for heterojunction solar cells according to claim 1, characterized in that, The deposition includes one of CVD (chemical vapor deposition), APCVD (atmospheric pressure chemical vapor deposition), ALD (atomic layer deposition), PECVD (plasma-enhanced chemical vapor deposition), MOCVD (metal-organic chemical vapor deposition), and magnetron sputtering.

7. A method for preparing a transparent conductive oxide thin film for heterojunction solar cells as described in claims 1-6, characterized in that, The process involves using an N-type silicon wafer as a substrate, and sequentially depositing an intrinsic amorphous silicon thin film, a doped amorphous silicon thin film, and a transparent conductive oxide thin film on both sides of the substrate using magnetron sputtering. The process parameters for magnetron sputtering are: sputtering power density of 1.0-20 W / cm², and reaction gases of argon and oxygen.

8. The method for preparing a transparent conductive oxide thin film for heterojunction solar cells according to claim 7, characterized in that, No heating is performed during deposition, and annealing is carried out after deposition is completed.

9. A method for preparing a transparent conductive oxide thin film for heterojunction solar cells according to claim 8, characterized in that, The annealing temperature is 180-230℃, and the annealing time is 20-50min.

10. A method for preparing a transparent conductive oxide thin film for a heterojunction solar cell according to claim 7, characterized in that, The flow rate ratio of argon to oxygen is 200:1.5.

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