Schottky solar cell preparation method based on graphene / Cu NPs / silicon heterojunction

Abstract

The invention relates to a graphene / Cu NPs / silicon heterojunction-based Schottky solar cell preparation method, which relates to the photovoltaic technical field, and comprises the following steps: 1) pre-treating a silicon wafer; 2) evaporating a copper nano film on the surface of the pretreated silicon wafer; 3) depositing a graphene film on the copper nano film; 4) carrying out annealing treatment on the heterojunction; 5) evaporating an electrode layer on the back surface of the silicon wafer; and 6) evaporating an electrode layer on the front surface of the silicon wafer. According to the preparation method of the Schottky solar cell based on the graphene / Cu NPs / silicon heterojunction, the photoelectric conversion efficiency of the Schottky solar cell is remarkably improved to 15% or above, meanwhile, the material cost is reduced to 1 / 100 of that of a traditional precious metal system, and 2-5 nano copper nanoparticles formed after annealing have triple functions in the cell at the same time, so that the photoelectric conversion efficiency of the Schottky solar cell is greatly improved. As a back electrode material, the material cooperates with a silver-aluminum electrode to provide a low-resistance conductive path, the contact resistance is lower than 0.1 ohm square centimeter, an efficient Schottky junction is formed with a silicon substrate interface to enhance light capture, and the light absorption efficiency is improved by 30%.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, specifically to a method for fabricating Schottky solar cells based on graphene / Cu NPs / silicon heterojunction. Background Technology

[0002] Schottky solar cells, as an important branch of photovoltaic technology, have attracted much attention in the fields of flexible electronics and low-cost photovoltaics in recent years due to their advantages such as simple structure, low manufacturing cost and excellent weak light response. However, the performance improvement of traditional Schottky solar cells is limited by the single function of materials and the complexity of manufacturing processes: the electrodes, light absorption layer and electron transport layer usually need to adopt multiple material systems such as noble metals (such as Au, Ag) or inorganic oxides (such as TiO2, ZnO), resulting in lengthy processes, frequent interface defects and high costs. With the rapid development of nanotechnology, copper-based nanomaterials have become an ideal candidate for realizing the "one material, multiple uses" strategy due to their high conductivity, excellent light absorption characteristics and significant cost advantages (copper resources are abundant and the price is only 1 / 100 of gold).

[0003] Existing Schottky solar cell fabrication technologies have significant drawbacks: First, materials and processes are highly fragmented. Electrodes (such as Au electrodes), light-absorbing layers (such as silicon-based heterojunctions), and electron transport layers (such as TiO2 nanoparticles) need to be synthesized and deposited independently, involving multiple steps of vacuum coating or solution processing, which extends the fabrication cycle by more than 30% and doubles the equipment investment. Second, interface compatibility is poor. High energy barriers and charge recombination centers are easily generated at multi-material interfaces (such as the Au / Si interface barrier of up to 0.8 eV), resulting in an open-circuit voltage generally below 0.6 V, making it difficult to break through 12% in photoelectric conversion efficiency. Third, high-temperature processes damage the substrate. Traditional annealing (>700℃) often causes lattice distortion on the silicon wafer surface, reducing light-harvesting efficiency. For example, Cu2O / silicon Schottky cells reported in the literature require the introduction of an additional electron transport layer (such as ZnO), which not only increases costs but also reduces the fill factor to below 60% due to interface mismatch. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for fabricating Schottky solar cells based on graphene / Cu NPs / silicon heterojunctions, which has advantages such as high photoelectric conversion efficiency and low cost, and solves the problem of limited material functionality in traditional Schottky solar cells.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction, comprising the following steps:

[0006] 1) Pre-treatment of silicon wafers: The cut silicon wafers are ultrasonically cleaned twice each in acetone, alcohol and deionized water. Then, the surface oxide layer is removed with HF solution, the surface is activated with NaOH solution, and neutralized with HCl solution. Then, they are thoroughly cleaned with standard RCA cleaning process. Finally, a uniform pyramid-shaped textured surface is formed on the silicon wafer surface using alkaline solution etching method.

[0007] 2) Deposit copper nanofilms on the pretreated silicon wafer surface: The texturized silicon wafer is fixed on the coating machine turntable, and a vacuum is drawn to below 1×10⁻³Pa using a mechanical pump and a molecular pump. A copper nanofilm layer with a thickness of 200-500nm is deposited by electron beam evaporation, and the deposition thickness is monitored in real time by a quartz crystal oscillator.

[0008] 3) Deposition of graphene film on copper nanofilm: Place silicon wafer / copper nanofilm in PECVD furnace chamber, introduce appropriate amount of methane and hydrogen gas, heat to 300-400℃, maintain for 10-60 minutes under the assistance of infrared light source to achieve low temperature induced methane reduction deposition to form graphene film.

[0009] 4) Annealing treatment of heterojunction: Place silicon wafer / copper nanofilm / graphene material in a quartz boat, put it in the middle section of the furnace tube of a single-temperature zone annealing furnace, and after vacuuming and pressure holding, keep it at a temperature of 500-600℃ for 60-120 minutes to convert copper nanofilm into copper nanoparticles.

[0010] 5) Electrode layer deposition on the back of silicon wafer: An Ag / Al composite electrode layer with a thickness of 100-200 nm is deposited on the back of the silicon substrate using electron beam evaporation.

[0011] 6) Electrode layer deposition on the front side of silicon wafer: An Au gate electrode layer is deposited on the front side of the silicon substrate using electron beam evaporation to form a grid structure, thus completing the fabrication of the Schottky solar cell.

[0012] Furthermore, in the silicon wafer pretreatment step, the alkaline solution etching method uses a 10% NaOH solution and etches for 10 minutes at 80°C to form a pyramid-shaped textured surface with a height of 1-2 μm.

[0013] Furthermore, in the copper nanofilm evaporation step, the electron beam current is controlled within the range of 50 to 100 mA to adjust the deposition rate to 0.5 to 2 nm / s.

[0014] Furthermore, in the graphene film deposition step, the flow ratio of methane to hydrogen is 1:1 to 5:1, and the total gas flow rate is 50 to 200 sccm, which is used to optimize the crystallinity and conductivity of the graphene film.

[0015] Furthermore, in the graphene film deposition step, the power of the infrared light source is 50-100W, and the auxiliary temperature is maintained in the range of room temperature to ambient temperature.

[0016] Furthermore, in the annealing process, the vacuum degree is maintained below 1×10⁻³Pa, and the annealing temperature gradient is from room temperature to 500-600℃ at a rate of 5℃ / min, followed by holding at that temperature and then cooling down to room temperature at a rate of 3℃ / min.

[0017] Furthermore, the copper nanoparticles formed after the annealing treatment have a particle size of 2-5 nm and are uniformly distributed on the surface of the silicon substrate, serving as the core functional material of Schottky solar cells.

[0018] Furthermore, the copper nanoparticles simultaneously perform three functions in the Schottky solar cell: as a back electrode material to provide a conductive path, as a light-absorbing material to form a heterojunction with the silicon substrate to enhance light capture, and as an electron transport material to modify the ITO / semiconductor interface and reduce the interface energy barrier.

[0019] Furthermore, in the Ag / Al electrode layer of the back electrode layer, the weight ratio of Ag to Al is 8:2 to 9:1 to balance light transmittance and conductivity; the Au gate electrode layer of the front electrode layer has a linewidth of 10 to 50 μm and a spacing of 100 to 200 μm.

[0020] Furthermore, the graphene film deposition step employs a controlled variable method, by adjusting the deposition pressure (0.1~1 Torr), gas flow ratio, and time parameters to prepare different batches of graphene film materials.

[0021] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0022] 1. This method for fabricating Schottky solar cells based on graphene / Cu NPs / silicon heterojunctions significantly improves the photoelectric conversion efficiency of Schottky solar cells to over 15% through the "one material, three uses" design of copper nanoparticles. Simultaneously, it reduces material costs to 1 / 100 of traditional precious metal systems. The 2- to 5-nanometer copper nanoparticles formed after annealing simultaneously perform three functions in the cell: serving as a back electrode material and working synergistically with silver-aluminum electrodes to provide a low-resistance conductive path with a contact resistance below 0.1 ohm square centimeters; forming a highly efficient Schottky junction with the silicon substrate interface to enhance light capture, increasing light absorption efficiency by 30%; and modifying the indium tin oxide / semiconductor interface to lower the electron transport barrier from 0.8 eV to 0.3 eV. This achieves excellent electrical performance with an open-circuit voltage of not less than 0.7 volts and a fill factor of not less than 75%, far exceeding the existing technology's open-circuit voltage of less than 0.6 volts and efficiency of less than 12%.

[0023] 2. This Schottky solar cell fabrication method based on graphene / Cu NPs / silicon heterojunction simplifies the traditional 6-step process of Schottky solar cell fabrication into a 4-step core process, shortening the fabrication cycle by more than 30% and avoiding interface compatibility issues. The annealing process is completed at a low temperature of 500 to 600 degrees Celsius, lower than the traditional 700 degrees Celsius process, effectively preventing thermal damage to the silicon substrate, and the textured surface structure retention rate is higher than 95%. The one-step method of in-situ conversion of copper nanofilms into copper nanoparticles eliminates the additional material introduction step, reducing equipment investment by 40%. At the same time, the graphene deposition methane to hydrogen flow ratio optimized by the controlled variable method between 1:1 and 5:1 ensures the uniformity of the film and improves the product yield to more than 85%, providing a highly reliable and low-threshold fabrication solution for the photovoltaic industry. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the main structure of the heterojunction of the present invention;

[0025] Figure 2 This is a comparison diagram of the band structure of the device before and after modification with copper nanoparticles according to the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0027] Please see Figure 1-2 This embodiment describes a method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction, comprising the following steps:

[0028] 1) Pre-treatment of silicon wafers: The cut silicon wafers are ultrasonically cleaned twice each in acetone, alcohol and deionized water. Then, the surface oxide layer is removed with HF solution, the surface is activated with NaOH solution, and neutralized with HCl solution. Then, they are thoroughly cleaned with standard RCA cleaning process. Finally, a uniform pyramid-shaped textured surface is formed on the silicon wafer surface using alkaline solution etching method.

[0029] 2) Deposit copper nanofilms on the pretreated silicon wafer surface: The texturized silicon wafer is fixed on the coating machine turntable, and a vacuum is drawn to below 1×10⁻³Pa using a mechanical pump and a molecular pump. A copper nanofilm layer with a thickness of 200-500nm is deposited by electron beam evaporation, and the deposition thickness is monitored in real time by a quartz crystal oscillator.

[0030] 3) Deposition of graphene film on copper nanofilm: Place silicon wafer / copper nanofilm in PECVD furnace chamber, introduce appropriate amount of methane and hydrogen gas, heat to 300-400℃, maintain for 10-60 minutes under the assistance of infrared light source to achieve low temperature induced methane reduction deposition to form graphene film.

[0031] 4) Annealing treatment of heterojunction: Place silicon wafer / copper nanofilm / graphene material in a quartz boat, put it in the middle section of the furnace tube of a single-temperature zone annealing furnace, and after vacuuming and pressure holding, keep it at a temperature of 500-600℃ for 60-120 minutes to convert copper nanofilm into copper nanoparticles.

[0032] 5) Electrode layer deposition on the back of silicon wafer: An Ag / Al composite electrode layer with a thickness of 100-200 nm is deposited on the back of the silicon substrate using electron beam evaporation.

[0033] 6) Electrode layer deposition on the front side of silicon wafer: An Au gate electrode layer is deposited on the front side of the silicon substrate using electron beam evaporation to form a grid structure, thus completing the fabrication of the Schottky solar cell.

[0034] It should be noted that by integrating six core steps—silicon wafer pretreatment, copper nanofilm evaporation, graphene deposition, annealing, back electrode evaporation, and front electrode evaporation—the complex process of traditional Schottky solar cell fabrication is simplified into a highly efficient process, significantly shortening the fabrication cycle and reducing equipment investment, thus providing a highly reliable foundation for industrialization.

[0035] In the silicon wafer pretreatment step, the alkaline solution etching method uses a 10% NaOH solution and etches for 10 minutes at 80°C to form a pyramid-shaped textured surface with a height of 1-2 μm.

[0036] It should be noted that the detailed procedures for standard silicon wafer pretreatment include ultrasonic cleaning with acetone, alcohol, and deionized water, damage removal treatment with HF, NaOH, and HCl, and etching with alkaline solution to form a pyramid-shaped textured surface. These procedures ensure the cleanliness of the silicon wafer surface and light capture efficiency, effectively improving the light absorption capacity and overall performance stability of the battery.

[0037] In the copper nanofilm evaporation step, the electron beam current is controlled within the range of 50 to 100 mA to adjust the deposition rate to 0.5 to 2 nm / s.

[0038] It should be noted that the copper nanofilm deposition thickness is limited to 200 to 500 nanometers. By precisely controlling the electron beam current to adjust the deposition rate, the copper nanofilm layer is ensured to be uniform and dense, providing a reliable structural basis for subsequent annealing and conversion into functional copper nanoparticles, and avoiding performance defects caused by uneven thickness.

[0039] In the graphene film deposition step, the flow ratio of methane to hydrogen is 1:1 to 5:1, and the total gas flow rate is 50 to 200 sccm, which is used to optimize the crystallinity and conductivity of the graphene film.

[0040] It should be noted that setting the infrared-assisted PECVD deposition temperature to 300 to 400 degrees Celsius enables low-temperature and high-efficiency graphene film deposition, optimizes crystal quality and conductivity, avoids damage to the silicon substrate caused by high-temperature processes, and improves film uniformity and interface compatibility.

[0041] In the graphene film deposition step, the power of the infrared light source is 50-100W, and the auxiliary temperature is maintained in the range of room temperature to ambient temperature.

[0042] It should be noted that the infrared light-assisted PECVD deposition time is specified to be 10 to 60 minutes to precisely control the graphene formation process, ensure film integrity and quality stability, effectively prevent fluctuations in electrical properties caused by insufficient or excessive deposition, and improve product consistency.

[0043] In the annealing process, the vacuum level is maintained below 1×10⁻³Pa, and the annealing temperature gradient is from room temperature to 500~600℃ at a rate of 5℃ / min, followed by holding at that temperature and then cooling down to room temperature at a rate of 3℃ / min.

[0044] It should be noted that the annealing temperature is limited to 500 to 600 degrees Celsius. The low-temperature process enables the in-situ transformation of copper nanofilms into copper nanoparticles, avoiding the thermal damage to the silicon substrate caused by the traditional high temperature of over 700 degrees Celsius, maintaining a high retention rate of the textured surface structure, and simultaneously completing the material's functional transformation.

[0045] The copper nanoparticles formed after annealing have a particle size of 2–5 nm and are uniformly distributed on the surface of the silicon substrate, serving as the core functional material for Schottky solar cells.

[0046] It should be noted that ensuring the copper nanoparticles have a particle size of 2 to 5 nanometers and are uniformly distributed after annealing maximizes their triple synergistic effect as an electrode material providing a low-resistance conductive path, a light-absorbing material enhancing light-harvesting efficiency, and an electron transport material reducing the interface energy barrier, thus significantly improving the photoelectric conversion efficiency.

[0047] In Schottky solar cells, copper nanoparticles simultaneously perform three functions: providing a conductive path as a back electrode material, forming a heterojunction with the silicon substrate to enhance light capture as a light-absorbing material, and modifying the ITO / semiconductor interface as an electron transport material to lower the interface energy barrier.

[0048] It should be noted that clarifying the triple functional integration mechanism of copper nanoparticles completely solves the problem of poor interface compatibility in traditional multi-material systems, achieving excellent performance with an open-circuit voltage of not less than 0.7 volts and a fill factor of not less than 75%, thus breaking through the efficiency bottleneck of existing technologies.

[0049] In the Ag / Al electrode layer of the back electrode layer, the weight ratio of Ag to Al is 8:2 to 9:1 to balance light transmittance and conductivity; the Au gate electrode layer of the front electrode layer has a linewidth of 10 to 50 μm and a spacing of 100 to 200 μm.

[0050] It should be noted that by refining the parameter design of the electrode layer, the weight ratio of the silver-aluminum electrode on the back is 8:2 to 9:1 and the linewidth of the gold grid electrode on the front is 10 to 50 micrometers with a spacing of 100 to 200 micrometers, thus optimizing the balance between light transmittance and conductivity and improving the battery's electrical performance and long-term reliability.

[0051] In the graphene film deposition step, the controlled variable method was used. By adjusting the deposition pressure (0.1~1 Torr), gas flow ratio and time parameters, different batches of graphene film materials were prepared.

[0052] It should be noted that the graphene deposition process uses a controlled variable method to adjust the deposition pressure, gas flow rate ratio, and time parameters, flexibly optimizing the thin film characteristics, increasing the product yield to over 85%, enhancing process adaptability, and significantly improving the repeatability of photoelectric conversion efficiency.

[0053] The working principle of the above embodiments is based on the "one material, three uses" functional integration of annealed copper nanoparticles. In the battery structure, copper nanoparticles simultaneously achieve three functions through in-situ conversion from copper nanofilm to copper nanoparticles: as an electrode, they serve as a back conductive layer, forming a low-resistance path with the silver-aluminum electrode; as a light absorption layer, they construct a nanoscale Schottky junction at the silicon substrate interface, utilizing high specific surface area to enhance light capture and promote electron-hole separation; and as an electron transport layer, they form an energy level matching layer at the indium tin oxide / semiconductor interface, reducing the interface energy barrier from 0.8 eV to 0.3 eV, significantly reducing charge recombination loss. This mechanism simultaneously completes material conversion and functional integration on the silicon substrate surface through a one-step annealing process, completely avoiding the efficiency degradation caused by the accumulation of interface defects in traditional multi-material systems.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction, characterized in that, Includes the following steps: 1) Pre-treatment of silicon wafers: The cut silicon wafers are ultrasonically cleaned twice each in acetone, alcohol and deionized water. Then, the surface oxide layer is removed with HF solution, the surface is activated with NaOH solution, and neutralized with HCl solution. Then, they are thoroughly cleaned with standard RCA cleaning process. Finally, a uniform pyramid-shaped textured surface is formed on the silicon wafer surface using alkaline solution etching method. 2) Deposit copper nanofilms on the pretreated silicon wafer surface: The texturized silicon wafer is fixed on the coating machine turntable, and a vacuum is drawn to below 1×10⁻³Pa using a mechanical pump and a molecular pump. A copper nanofilm layer with a thickness of 200-500nm is deposited by electron beam evaporation, and the deposition thickness is monitored in real time by a quartz crystal oscillator. 3) Deposition of graphene film on copper nanofilm: Place silicon wafer / copper nanofilm in PECVD furnace chamber, introduce appropriate amount of methane and hydrogen gas, heat to 300-400℃, maintain for 10-60 minutes under the assistance of infrared light source to achieve low temperature induced methane reduction deposition to form graphene film. 4) Annealing treatment of heterojunction: Place silicon wafer / copper nanofilm / graphene material in a quartz boat, put it in the middle section of the furnace tube of a single-temperature zone annealing furnace, and after vacuuming and pressure holding, keep it at a temperature of 500-600℃ for 60-120 minutes to convert copper nanofilm into copper nanoparticles. 5) Electrode layer deposition on the back of silicon wafer: An Ag / Al composite electrode layer with a thickness of 100-200 nm is deposited on the back of the silicon substrate using electron beam evaporation. 6) Electrode layer deposition on the front side of silicon wafer: An Au gate electrode layer is deposited on the front side of the silicon substrate using electron beam evaporation to form a grid structure, thus completing the fabrication of the Schottky solar cell.

2. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the silicon wafer pretreatment step, the alkaline solution etching method uses a 10% NaOH solution and etches for 10 minutes at 80°C to form a pyramid-shaped textured surface with a height of 1-2 μm.

3. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the copper nanofilm evaporation step, the electron beam current is controlled within the range of 50 to 100 mA to adjust the deposition rate to 0.5 to 2 nm / s.

4. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the graphene film deposition step, the flow ratio of methane to hydrogen is 1:1 to 5:1, and the total gas flow rate is 50 to 200 sccm, which is used to optimize the crystallinity and conductivity of the graphene film.

5. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the graphene film deposition step, the power of the infrared light source is 50-100W, and the auxiliary temperature is maintained in the range of room temperature to ambient temperature.

6. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the annealing process, the vacuum level is maintained below 1×10⁻³Pa, and the annealing temperature gradient is from room temperature to 500-600℃ at a rate of 5℃ / min, followed by holding at that temperature and then cooling down to room temperature at a rate of 3℃ / min.

7. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: The copper nanoparticles formed after the annealing treatment have a particle size of 2-5 nm and are uniformly distributed on the surface of the silicon substrate, serving as the core functional material of Schottky solar cells.

8. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: The copper nanoparticles simultaneously perform three functions in Schottky solar cells: as a back electrode material to provide a conductive path, as a light-absorbing material to form a heterojunction with the silicon substrate to enhance light capture, and as an electron transport material to modify the ITO / semiconductor interface and reduce the interface energy barrier.

9. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: In the Ag / Al electrode layer of the back electrode layer, the weight ratio of Ag to Al is 8:2 to 9:1 to balance light transmittance and conductivity; the Au gate electrode layer of the front electrode layer has a linewidth of 10 to 50 μm and a spacing of 100 to 200 μm.

10. The method for fabricating a Schottky solar cell based on a graphene / Cu NPs / silicon heterojunction according to claim 1, characterized in that: The graphene film deposition step employs a controlled variable method, where different batches of graphene film materials are prepared by adjusting the deposition pressure (0.1–1 Torr), gas flow ratio, and time parameters.

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