A space carbon electrode gallium arsenide solar cell and a method for manufacturing the same

Abstract

This invention relates to the field of solar cell technology, specifically to a space-grade gallium arsenide solar cell with a carbon electrode and its fabrication method. The gallium arsenide solar cell, from top to bottom, comprises an antireflection coating, a metal top electrode, a triple-junction GaAs epitaxial layer, and a composite carbon-based back electrode. The composite carbon-based back electrode, from top to bottom, comprises a MoO3 ultrathin interface layer, a V2C MXene current transport layer, and a graphite / carbon black / composite conductive binder composite layer. This solar cell, using a carbon-based electrode as the back electrode, exhibits low cost, high power-to-weight ratio, high conductivity, and high stability, making it suitable for extreme space environments.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a space-use carbon electrode gallium arsenide solar cell and its fabrication method. Background Technology

[0002] Gallium arsenide (GaAs), as a group III-V compound semiconductor material, possesses a direct bandgap (1.43 eV) and high carrier mobility (hole mobility can reach 400 cm⁻¹). 2 With its core advantages such as high efficiency (V / s) and excellent resistance to space radiation, GaAs solar cells have a conversion efficiency far exceeding that of traditional silicon-based solar cells, making them the mainstream photovoltaic energy conversion device in the current space field. The electrode structure is a core component of GaAs solar cells, directly determining carrier collection efficiency, mechanical stability, and long-term lifespan. Existing space-use GaAs solar cells commonly employ noble metal multilayer film structures for their back electrodes (hole collection side), typically Au / Pd / Ag composite electrodes. These noble metal electrodes possess advantages such as excellent conductivity, stable interfacial contact, and resistance to aging in the space vacuum environment, and have been widely used in the space photovoltaic field.

[0003] However, as space exploration missions evolve towards longer lifecycles, lighter weight, and lower cost, traditional precious metal electrodes suffer from drawbacks such as high cost, high density, and poor interfacial stability. Carbon-based materials, on the other hand, possess significant advantages, including tunable bandgap, low cost, low density, strong chemical inertness, excellent resistance to space radiation and temperature cycling, and low light reflectivity. Furthermore, through proper proportioning, they can form highly conductive networks, theoretically meeting the electrode performance requirements of GaAs solar cells for space applications. However, existing carbon-based electrodes are primarily used in perovskite and silicon terrestrial photovoltaic devices. Direct application in GaAs solar cell systems faces technical bottlenecks such as poor film formation, poor interfacial compatibility, insufficient mechanical stability, and difficulty in balancing conductivity and adhesion performance. These limitations fail to meet the core requirements of the space environment for GaAs solar cells: low cost, lightweight, high conversion efficiency, and long lifespan. Therefore, developing a carbon-based electrode structure suitable for space applications, possessing high conductivity, strong mechanical stability, and excellent interfacial compatibility, along with a corresponding gallium arsenide solar cell, has become a pressing technical challenge in the field of space photovoltaics. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a space-use carbon electrode gallium arsenide solar cell and its fabrication method. This solar cell uses a carbon-based electrode as the back electrode and features low cost, high power-to-weight ratio, high conductivity, and high stability, making it suitable for extreme space environments.

[0005] The first objective of this invention is to provide a gallium arsenide solar cell with carbon electrode for space use, wherein the gallium arsenide solar cell comprises, from top to bottom, an antireflection coating, a metal top electrode, a triple-junction GaAs epitaxial layer, and a composite carbon-based back electrode; The composite carbon-based back electrode consists of, from top to bottom, an ultrathin MoO3 interface layer, a V2C MXene current transport layer, and a graphite / carbon black / composite conductive adhesive composite layer.

[0006] The triple-junction GaAs epitaxial layer consists of a GaInP top cell, a GaAs middle cell, and a Ge bottom cell, from top to bottom.

[0007] Existing carbon-based electrodes in photovoltaic devices mostly employ a single-layer structure of carbon material mixed with binder, or a simple stacked structure with fragmented functions. These structures can only achieve a single conductive function and cannot simultaneously address multiple requirements such as interface adhesion, carrier transport, and mechanical buffering. Furthermore, the interlayer connections are loose, making them prone to delamination under varying temperature and vibration conditions, and difficult to adapt to the energy level matching and hole collection requirements between the Ge substrate and the carbon electrode. This invention designs an integrated composite carbon-based back electrode synergistic architecture consisting of a MoO3 ultrathin interface layer, a V2C MXene current transport layer, and graphite / carbon black / conductive binder. Through functional synergy between the layers, stacked sequentially starting from the Ge substrate side, it achieves the construction of a three-dimensional highly conductive network, strong interface adhesion between the active layer and the carbon electrode, precise energy level matching, and mechanical buffering under varying temperature conditions. This architecture is suitable for the hole collection characteristics of gallium arsenide triple-junction cells and the requirements of extreme space environments, effectively improving the cell's decoding bonding strength, conductivity, and stability.

[0008] Furthermore, the thickness of the MoO3 ultrathin interface layer is 5nm to 10nm, and the material is highly crystalline MoO3. This invention introduces an ultrathin MoO3 interface layer between the Ge substrate and the V2C MXene layer. This layer not only acts as an energy level bridge, constructing an efficient hole transport barrier to achieve rapid hole tunneling, but also provides interface passivation, effectively suppressing oxidation of the Ge substrate surface and reducing the interface state density. Simultaneously, it acts as a physical barrier, preventing interdiffusion and ion migration between carbon-based materials and Ge atoms, fundamentally solving the technical problems of poor contact and instability at the interface between the Ge substrate and the carbon-based electrode.

[0009] Furthermore, the thickness of the V2C MXene current transport layer is 50nm to 200nm, and V2C MXene powder is used as the material; the thickness of the V2C MXene powder sheet is 1nm to 5nm, and the sheet diameter is 0.5μm to 2μm.

[0010] The application of V2C MXene (a vanadium-based MXene material) in space photovoltaics has significant limitations. Its two-dimensional sheet structure is prone to agglomeration and stacking, resulting in high carrier transport losses and inefficient connection between electrodes and active layers, making it difficult to meet the transport performance requirements of space GaAs solar cells. The core of this invention, the V2C MXene transport layer, lies in overcoming these limitations. Based on its two-dimensional sheet nature, it achieves orderly interlocking and stacking of V2C MXene sheets through vacuum spin coating, constructing a three-dimensional continuous conductive network. This effectively solves the industry pain points of easy agglomeration and high carrier transport losses in two-dimensional materials. Simultaneously, it achieves efficient connection with the MoO3 interface layer and carbon electrodes, establishing a stable, low-loss carrier transport channel, further improving the battery's conductivity and structural stability.

[0011] Furthermore, the thickness of the graphite / carbon black / composite conductive adhesive composite layer is 1μm to 5μm, and it is composed of conductive filler and composite conductive adhesive. The conductive filler is a mixture of graphite and carbon black in a mass ratio of 6:4 to 7:3. The particle size of the graphite is 1μm to 5μm, and the particle size of the carbon black is 20nm to 50nm.

[0012] Furthermore, the composite conductive adhesive is a carboxyl-modified multi-walled carbon nanotube-ethyl cellulose-reduced graphene oxide (carboxyl CNT-EC-rGO) composite system, which, by mass percentage, contains 10% to 15% carboxyl-modified multi-walled carbon nanotubes (10nm to 20nm in diameter), 3% to 5% reduced graphene oxide (1μm to 5μm in sheet diameter), and 5% to 8% ethyl cellulose; the amount of the composite conductive adhesive added accounts for 20wt% to 25wt% of the solids of the graphite / carbon black / composite conductive adhesive composite layer.

[0013] Traditional binders, such as pure ethyl cellulose, have poor conductivity, or highly conductive fillers, such as carbon black, have poor dispersibility, making it difficult to achieve both high conductivity and strong adhesion. Furthermore, high interfacial resistance arises between layers due to binder incompatibility. Therefore, this invention uses a carboxyl-modified multi-walled carbon nanotube-ethyl cellulose-reduced graphene oxide (carboxyl-modified CNT-EC-rGO) composite conductive binder as a dispersed phase, which is uniformly incorporated into the graphite-carbon black conductive layer to prepare a carbon electrode with high conductivity, strong interfacial bonding, and excellent dispersibility.

[0014] A second objective of this invention is to provide a method for fabricating a space-use carbon electrode gallium arsenide solar cell, comprising the following steps: (1) After pretreatment of the triple-junction GaAs epitaxial layer, a metal top electrode and an anti-reflection film are deposited sequentially on its surface; (2) A MoO3 ultrathin interface layer is deposited on the back surface of the epitaxial wafer (Ge substrate side); (3) Prepare V2C MXene dispersion, spin-coat the V2C MXene dispersion onto the surface of MoO3 ultrathin interface layer under vacuum conditions, and anneal it and cool it naturally to obtain V2C MXene current transport layer; (4) Prepare a composite conductive adhesive slurry and mix it with a mixture of graphite and carbon black. The resulting mixture is coated on the surface of the V2C MXene current transmission layer using a multi-layer thin coating process. After coating, the mixture is annealed and naturally cooled to complete the fabrication of the carbon electrode gallium arsenide solar cell.

[0015] Furthermore, in step (2), the vapor deposition process of the MoO3 ultrathin interface layer is as follows: in a vacuum thermal vapor deposition machine, the vacuum level is ≤1×10⁻⁶. -4 The substrate temperature was controlled at 40℃~60℃. MoO3 powder was used as the evaporation source, and the evaporation rate was adjusted to 0.1nm / s. The film thickness was deposited to 5nm~10nm. After the deposition was completed, the film was cooled to room temperature while maintaining a vacuum environment. This technical solution uses a vacuum thermal evaporation process to prepare the film. The surface is uniform, crack-free, and pinhole-free, with complete coverage. At the same time, it can achieve energy level bridging, interface passivation, and physical barrier, solving the interface adaptation problem between Ge substrate and carbon-based electrode and reducing interface contact resistance.

[0016] Further, in step (3), the preparation method of the V2C MXene dispersion is as follows: Take V2C MXene powder, add deionized water and sodium dodecylbenzenesulfonate dispersant to prepare a mixture with a V2C MXene powder concentration of 1 mg / mL and a dispersant concentration of 0.03 mg / mL, then put the mixture into an ultrasonic cell disruptor and ultrasonically disperse it at a power of 100W to 200W for 40 min to 50 min to obtain the dispersion; the spin coating rate is 4000 r / min to 4500 r / min, the spin coating time is 40 s to 50 s, and the vacuum degree is controlled at 3 × 10⁻⁶. -3 Below Pa; annealing in an inert gas, heating to 250±10℃ at a heating rate of 8℃ / min, and holding for 40min~50min. This technical solution uses V2C MXene powder as the core raw material, which is dispersed to form a uniform dispersion, prepared by vacuum spin coating, and then annealed to form an ordered, interlocking, stacked three-dimensional continuous conductive network. This ensures low-loss carrier transport and achieves tight bonding with the MoO3 ultrathin interface layer and the graphite / carbon black / composite conductive adhesive composite layer.

[0017] Furthermore, in step (4), the preparation method of the composite conductive adhesive slurry is as follows: a. Weigh 78g of anhydrous terpineol and 6g of ethyl cellulose per 100g of slurry, pour them into a polytetrafluoroethylene beaker, place it on a 60℃ water bath magnetic stirrer, and stir at 500r / min~600r / min for 30min~40min until the ethyl cellulose is completely dissolved. Cool to room temperature to obtain a transparent viscous base liquid. b. Add 12g of carboxyl-modified multi-walled nanotubes and 4g of reduced graphene oxide to the transparent viscous base liquid, and stir magnetically at 300r / min~400r / min for 10min~15min to make the conductive particles uniformly dispersed in the base liquid to form a preliminary mixture. c. Transfer the preliminary mixture into a polytetrafluoroethylene ball mill jar, add zirconia ball milling beads, seal and place in a planetary ball mill, and ball mill at a speed of 200 r / min to 300 r / min for 1 h to 1.5 h to break up the conductive phase agglomerates; d. Filter the slurry with a 200-mesh polytetrafluoroethylene filter to remove large undispersed particles. Place the filtered slurry in a vacuum drying oven to degas for 10 to 15 minutes, adjust the viscosity to 18000±100 mPa·s, and refrigerate at 4℃ for later use.

[0018] Furthermore, in step (4), the multilayer thin coating process is as follows: the thickness of each single layer is 0.5μm to 1.5μm. After coating, it is immediately placed in a drying oven at 60℃ to 80℃ for 15min to 25min. The coating is repeated 2 to 4 times until the target thickness is reached. The annealing temperature is 110±10℃ and the temperature is maintained for 20min to 30min.

[0019] Compared with the prior art, the present invention has the following advantages: 1. This invention uses a composite carbon-based back electrode to completely replace the traditional precious metal back electrode, which significantly reduces the cost of gallium arsenide solar cells, while reducing the cell mass (the density of carbon electrodes of the same volume is much smaller than that of metal electrodes), and improving the mass-to-power ratio, which meets the development needs of lightweight and low-cost space exploration missions.

[0020] 2. The composite carbon-based back electrode of this invention consists of a three-layer integrated synergistic architecture: an ultrathin MoO3 interface layer, a V2C MXene current transport layer, and a graphite / carbon black / conductive binder composite layer. The ultrathin MoO3 interface layer fundamentally solves the interface compatibility problem between the Ge substrate and the carbon-based electrode, reducing interface contact resistance and improving the battery's open-circuit voltage and long-term stability. The V2C MXene current transport layer, through a structurally optimized three-dimensional continuous conductive network, solves the problem of two-dimensional material aggregation and stacking, improving carrier transport efficiency and further enhancing battery conversion efficiency. The development of the composite conductive binder system enables uniform dispersion of conductive fillers, balancing the high conductivity and strong adhesion of the carbon electrode, while simultaneously improving the carbon electrode's resistance to space irradiation and high / low temperature cycling stability, ensuring long-term stable operation of the battery in extreme space environments. The synergistic effect of these three elements resolves the contradiction between the conductivity and adhesion of conventional single carbon-based electrodes, achieving precise energy level matching, low-loss carrier transport, and mechanical buffering, adapting to extreme environments such as space temperature changes and vibrations, with strong interlayer adhesion and no interlayer delamination.

[0021] 3. The preparation process of this invention is simple and highly operable, requiring no additional complex equipment. It is compatible with the existing large-scale production process of space GaAs solar cells, facilitating industrial promotion and application. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure after the metal upper electrode and antireflection film of the present invention have been fabricated; Figure 2 This is a schematic diagram of the structure after the MoO3 ultrathin interface layer is deposited by vapor deposition according to the present invention; Figure 3 This is a schematic diagram of the structure of the V2C MXene current transport layer after its fabrication in this invention. Figure 4 This is a schematic diagram of the structure of the gallium arsenide solar cell with carbon electrode for space use according to the present invention.

[0023] Explanation of the labels in the diagram: 1. Antireflective coating; 2. Metal top electrode; 3. Triple-junction GaAs epitaxial layer; 4. MoO3 ultrathin interface layer; 5. V2CMXene current transport layer; 6. Graphite / carbon black / conductive binder composite layer. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] In the description of this application, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

[0026] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0027] Please see Figures 1 to 4 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the shape, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0028] One embodiment of the present invention provides a space-use carbon electrode gallium arsenide solar cell, the schematic diagram of which is shown below. Figure 4 As shown, the gallium arsenide solar cell consists of, from top to bottom, an antireflection film layer 1, a metal top electrode 2, a triple-junction GaAs epitaxial layer 3, a MoO3 ultrathin interface layer 4, a V2C MXene current transport layer 5, and a graphite / carbon black / composite conductive binder composite layer 6. The composite carbon-based back electrode consists of a MoO3 ultrathin interface layer, a V2C MXene current transport layer, and a graphite / carbon black / composite conductive adhesive composite layer.

[0029] The triple-junction GaAs epitaxial layer adopts a conventional space-level GaAs triple-junction structure, consisting of a GaInP top cell, a GaAs middle cell, and a Ge bottom cell from top to bottom. The thickness and doping concentration of each junction are designed according to the parameters of conventional space-level GaAs solar cells. The window layer uses AlGaInP material with a thickness of 50nm to 100nm. The antireflection film layer adopts a TiO2 / Al2O3 bilayer structure with a thickness of 700nm to 800nm ​​and a refractive index matching design to reduce light reflection loss. The metal top electrode uses common composite electrodes such as Au / Ge / Ag, and is prepared by conventional photolithography and evaporation processes to meet the carrier collection requirements of the GaAs triple-junction active layer.

[0030] In some embodiments, the thickness of the MoO3 ultrathin interface layer is 5nm to 10nm, and the material is highly crystalline MoO3.

[0031] In some embodiments, the thickness of the V2C MXene current transport layer is 50nm to 200nm, and V2C MXene powder is used as the material; the thickness of the V2C MXene powder sheet is 1nm to 5nm, and the sheet diameter is 0.5μm to 2μm.

[0032] In some embodiments, the thickness of the graphite / carbon black / composite conductive adhesive composite layer is 1 μm to 5 μm, and it is composed of conductive filler and composite conductive adhesive. The conductive filler is a mixture of graphite and carbon black in a mass ratio of 6:4 to 7:3; the particle size of the graphite is 1 μm to 5 μm, and the particle size of the carbon black is 20 nm to 50 nm. The composite conductive adhesive is a carboxyl-modified multi-walled carbon nanotube-ethyl cellulose-reduced graphene oxide (carboxyl CNT-EC-rGO) composite system, which, relative to the total mass (by mass percentage) of the composite conductive adhesive, contains 10% to 15% carboxyl-modified multi-walled carbon nanotubes (10 nm to 20 nm in diameter), 3% to 5% reduced graphene oxide (1 μm to 5 μm in sheet diameter), and 5% to 8% ethyl cellulose. The amount of the composite conductive adhesive added accounts for 20 wt% to 25 wt% of the solids of the graphite / carbon black / composite conductive adhesive composite layer.

[0033] Another embodiment of the present invention provides a method for fabricating a space-use carbon electrode gallium arsenide solar cell, comprising the following steps: (1) After pretreatment of the triple-junction GaAs epitaxial layer, a metal top electrode and an anti-reflection film are deposited sequentially on its surface; Specifically, the triple-junction GaAs epitaxial wafer (from top to bottom: GaInP top cell, GaAs middle cell, Ge bottom cell) is first placed in acetone and isopropanol solutions and ultrasonically cleaned for 10-20 minutes respectively to remove surface oil and impurities. After rinsing with deionized water, it is dried in a 110℃ drying oven for 10-20 minutes and cooled to room temperature for later use, ensuring the epitaxial wafer surface is clean and free of contaminants. Then, the top surface (GaInP side) metal gate electrodes (Au, Ge, Ag, etc.) are deposited through spin coating, exposure, development, and evaporation. Next, antireflective coatings (ARC layer, 700nm-800nm) of TiO2 and Al2O3 are sequentially deposited on the surface of the metal top electrode, and the antireflective coating on the surface of the metal top electrode is removed by etching. Finally, photoresist is coated on the ARC layer side for protection, and the Ge substrate side is ground, polished, and cleaned for later use. The structural schematic diagram is shown below. Figure 1 As shown.

[0034] (2) A MoO3 ultrathin interface layer is deposited on the surface of the epitaxial wafer; Specifically, in a vacuum thermal evaporation coating machine, the vacuum level is ≤1×10⁻⁶. -4 Pa, controlling the substrate temperature at 40℃~60℃, using MoO3 powder as the evaporation source, adjusting the evaporation rate to 0.1nm / s, evaporating to a film thickness of 5nm~10nm, after evaporation, maintaining a vacuum environment to cool to room temperature, the structural schematic diagram is shown below. Figure 2 As shown.

[0035] (3) Prepare V2C MXene dispersion, spin-coat the V2C MXene dispersion onto the surface of MoO3 ultrathin interface layer under vacuum conditions, and anneal it and cool it naturally to obtain V2C MXene current transport layer; Specifically, the preparation method of V2C MXene dispersion is as follows: Take V2C MXene powder, add deionized water and sodium dodecylbenzenesulfonate dispersant to prepare a mixture with a V2C MXene powder concentration of 1 mg / mL and a dispersant concentration of 0.03 mg / mL. Then, place the mixture in an ultrasonic cell disruptor and ultrasonically disperse it at a power of 100W-200W for 40-50 minutes. Then, place the obtained substrate on a vacuum spin coater, dropwise add the V2C MXene dispersion, adjust the spin coat speed to 4000 r / min-4500 r / min, the spin coat time to 40-50 s, and control the vacuum degree at 3×10⁻⁶. -3 Below Pa; finally, the spin-coated substrate is placed in an inert gas protected annealing furnace, and 99.999% pure argon gas is introduced. The temperature is increased to 250±10℃ at a heating rate of 8℃ / min, held for 40min~50min, and then naturally cooled to room temperature to obtain a substrate with a V2C MXene current transport layer. The structural schematic diagram is shown below. Figure 3 As shown, the V2C MXene sheets form an ordered, interlocking, stacked three-dimensional continuous conductive network.

[0036] (4) Prepare a composite conductive adhesive slurry and mix it with a mixture of graphite and carbon black. The resulting mixture is coated onto the surface of the V2C MXene current transport layer using a multilayer thin-coating process. After coating, annealing and natural cooling are performed to complete the fabrication of the carbon electrode gallium arsenide solar cell. The structural schematic diagram is shown below. Figure 4 As shown.

[0037] Specifically, the composite conductive adhesive slurry is first prepared: a. Weigh 78g of anhydrous terpineol and 6g of ethyl cellulose per 100g of slurry, pour them into a polytetrafluoroethylene beaker, place it on a 60℃ water bath magnetic stirrer, and stir at 500r / min~600r / min for 30min~40min until the ethyl cellulose is completely dissolved. Cool to room temperature to obtain a transparent viscous base liquid. b. Add 12g of carboxyl-modified multi-walled nanotubes (10nm-20nm diameter) and 4g of reduced graphene oxide (1μm-5μm diameter) to the transparent viscous base liquid, and stir magnetically at 300r / min-400r / min for 10min-15min to uniformly disperse the conductive particles in the base liquid and form a preliminary mixture. c. Transfer the preliminary mixture into a polytetrafluoroethylene ball mill jar, add zirconia ball milling beads, seal and place in a planetary ball mill, and ball mill at a speed of 200 r / min to 300 r / min for 1 h to 1.5 h to break up the conductive phase agglomerates; d. Filter the slurry with a 200-mesh polytetrafluoroethylene filter to remove large undispersed particles. Place the filtered slurry in a vacuum drying oven to degas for 10 to 15 minutes, adjust the viscosity to 18000±100 mPa·s, and refrigerate at 4℃ for later use. Use within 48 hours after preparation.

[0038] Then, weigh flake graphite and carbon black at a mass ratio of 6:4 to 7:3 and mix them evenly as conductive fillers. Add the above-mentioned composite conductive adhesive slurry (accounting for 20wt% to 25wt% of the solids in the composite layer) to the conductive filler, and place it in a high-speed shear disperser. Disperse the slurry at a speed of 2000 r / min to 2500 r / min for 20 min to 25 min to prepare a uniform carbon electrode slurry. Then, use a multi-layer thin-coating superposition process and a doctor blade coater to coat the carbon electrode slurry onto V2C. The surface of the MXene current transport layer is coated with a single layer thickness of 0.5μm to 1.5μm. After coating, the sample is immediately placed in a drying oven at 60℃ to 80℃ for 15min to 25min. The coating is repeated 2 to 4 times until the target thickness is reached. Finally, the coated sample is placed in a rapid annealing furnace, high-purity nitrogen gas (purity 99.999%) is introduced, the temperature is controlled at 110±10℃, and the sample is held at this temperature for 20min to 30min for post-processing. The sample is then naturally cooled to room temperature to complete the preparation of the composite carbon-based back electrode and obtain a complete gallium arsenide solar cell.

[0039] The following is a further explanation with reference to specific embodiments: Example 1 A method for fabricating a space-use carbon electrode gallium arsenide solar cell includes the following steps: (1) First, place the triple-junction GaAs epitaxial wafer (GaInP top cell, GaAs middle cell, and Ge bottom cell from top to bottom) into acetone and isopropanol solutions and ultrasonically clean them for 15 minutes to remove surface oil and impurities. After rinsing with deionized water, place them in a 110℃ drying oven for 10 minutes and cool them to room temperature for later use to ensure that the surface of the epitaxial wafer is clean and free of dirt. Then, through homogenization, exposure, development, and evaporation of metal gate electrodes (Au, Ge, Ag, etc.) on the top surface (GaInP side), antireflection film layers of TiO2 and Al2O3 (750nm) are deposited sequentially on the surface of the metal top electrode and the antireflection film on the surface of the metal top electrode is removed by etching. Finally, photoresist is coated on the ARC layer side for protection, and the Ge substrate side is ground, polished and cleaned for later use.

[0040] (2) Place the epitaxial wafer obtained in step (1) into a vacuum thermal evaporation coating machine and evacuate it to a vacuum degree ≤ 1×10 -4 Pa, controlling the substrate temperature at 50℃, using MoO3 powder as the evaporation source, adjusting the evaporation rate to 0.1nm / s, evaporating to a film thickness of 10nm, and after evaporation, maintaining a vacuum environment to cool to room temperature.

[0041] (3) First, prepare the V2C MXene dispersion: Take V2C MXene powder, add deionized water and sodium dodecylbenzenesulfonate dispersant to prepare a mixture with a V2C MXene powder concentration of 1 mg / mL and a dispersant concentration of 0.03 mg / mL. Then, put the mixture into an ultrasonic cell disruptor and ultrasonically disperse it for 45 min at 150 W. Then, place the obtained substrate on a vacuum spin coater, add the V2C MXene dispersion, adjust the spin coat speed to 4000 r / min, the spin coat time to 45 s, and control the vacuum degree at 3 × 10⁻⁶. -3 Below Pa, spin coating is completed; finally, the spin-coated substrate is placed in an inert gas protected annealing furnace, and argon gas with a purity of 99.999% is introduced. The temperature is raised to 250℃ at a heating rate of 8℃ / min, held for 45min, and then naturally cooled to room temperature to obtain a substrate with a 120nm V2C MXene current transport layer. The V2C MXene sheets form an ordered, interlocked, stacked three-dimensional continuous conductive network.

[0042] (4) First, prepare the composite conductive adhesive slurry: a. Weigh 78g of anhydrous terpineol and 6g of ethyl cellulose per 100g of slurry, pour them into a polytetrafluoroethylene beaker, place it on a 60℃ water bath magnetic stirrer, stir at 600r / min for 30min until the ethyl cellulose is completely dissolved, and cool to room temperature to obtain a transparent viscous base liquid. b. Add 12g of carboxyl-modified multi-walled nanotubes (10nm-20nm diameter) and 4g of reduced graphene oxide (1μm-5μm diameter) to the transparent viscous base liquid, and stir magnetically at 400r / min for 10min to uniformly disperse the conductive particles in the base liquid and form a preliminary mixture. c. Transfer the preliminary mixture into a polytetrafluoroethylene ball mill jar, add zirconia ball milling beads (ball-to-material ratio 3:1, 0.5mm and 1mm bead diameter mixed in a 1:1 ratio)), seal it, and place it in a planetary ball mill. Mill at 300r / min for 1.2h to break up the conductive phase agglomerates. d. Filter the slurry with a 200-mesh polytetrafluoroethylene filter to remove large undispersed particles. Place the filtered slurry in a vacuum drying oven to degas for 10 minutes, adjust the viscosity to 18000 mPa·s, and refrigerate at 4℃ for later use.

[0043] Then, 13g of flake graphite and 7g of carbon black were weighed at a mass ratio of 6.5:3.5 and mixed evenly as conductive filler. 7.5g of the above-mentioned composite conductive adhesive slurry (accounting for 25wt% of the solid content of the composite layer) was added to the conductive filler and placed in a high-speed shear disperser and dispersed at 2000r / min for 20min to prepare a uniform carbon electrode slurry. Then, a multi-layer thin coating process was used to coat the carbon electrode slurry onto the surface of the V2C MXene current transmission layer with a doctor blade coater. The thickness of each single layer was 1.5μm. After coating, the sample was immediately placed in an 80℃ drying oven for 15min. The coating was repeated twice until the target thickness of 3μm was reached. Finally, the coated sample was placed in a rapid annealing furnace, high-purity nitrogen (purity 99.999%) was introduced, the temperature was controlled at 110℃, and the sample was held for 30min for post-treatment. After natural cooling to room temperature, the composite carbon-based back electrode was prepared, and a complete gallium arsenide solar cell was obtained.

[0044] Comparative Example 1 Gallium arsenide solar cells were fabricated according to the method in Example 1, except that Au, Ag, Pd, and Pt metal back electrodes were directly deposited after grinding, polishing, and cleaning the Ge substrate.

[0045] The solar cells prepared in Example 1 and Comparative Example 1 were subjected to performance tests, and the results are shown in Table 1. The photovoltaic performance parameters—open-circuit voltage (Voc), short-circuit current (Isc), fill factor (FF), and conversion efficiency (Eff)—were tested using a solar simulator in an ambient atmospheric environment with an AMO spectrum. The interfacial contact resistance was tested using the transmission line model (TLM) method. The thermal shock degradation performance was determined by retesting the photovoltaic performance of the samples after cyclic shocks within the range of -180℃ to 100℃ five times, and comparing the results with the initial values ​​before the shocks. The interlayer peel strength was characterized by peeling the tape tightly adhered to the electrode surface at an angle of 45° to 90° using a tensile testing machine, and the required peel strength was used for characterization.

[0046] Table 1 Performance Test Results

[0047] As can be seen from the test results in Table 1, the gallium arsenide solar cell of Example 1 using a composite carbon-based back electrode is comparable to the gallium arsenide solar cell of Comparative Example 1 using a metal back electrode in terms of photovoltaic performance parameters. However, it is significantly better than Comparative Example 1 in key performance aspects such as interface contact resistance, extreme environment stability, and interlayer adhesion. These results fully demonstrate that the technical solution of the present invention has obvious technical advantages. Moreover, the composite carbon-based back electrode used in Example 1 reduces the cost by more than 30% and significantly reduces the weight compared to the noble metal back electrode of Comparative Example 1, which meets the requirements of space exploration missions.

[0048] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A space-use carbon electrode gallium arsenide solar cell, characterized in that, The gallium arsenide solar cell consists of, from top to bottom, an anti-reflection coating, a metal top electrode, a triple-junction GaAs epitaxial layer, and a composite carbon-based back electrode. The composite carbon-based back electrode consists of, from top to bottom, an ultrathin MoO3 interface layer, a V2C MXene current transport layer, and a graphite / carbon black / composite conductive adhesive composite layer.

2. A space-use carbon electrode gallium arsenide solar cell according to claim 1, characterized in that, The thickness of the MoO3 ultrathin interface layer is 5nm to 10nm, and the material is highly crystalline MoO3.

3. A space-use carbon electrode gallium arsenide solar cell according to claim 1, characterized in that, The thickness of the V2CMXene current transport layer is 50nm to 200nm, and V2C MXene powder is used as the material; the thickness of the V2C MXene powder sheet is 1nm to 5nm, and the sheet diameter is 0.5μm to 2μm.

4. A space-use carbon electrode gallium arsenide solar cell according to claim 1, characterized in that, The thickness of the graphite / carbon black / composite conductive adhesive composite layer is 1μm to 5μm, and it is composed of conductive filler and composite conductive adhesive. The conductive filler is a mixture of graphite and carbon black in a mass ratio of 6:4 to 7:

3. The particle size of the graphite is 1μm to 5μm, and the particle size of the carbon black is 20nm to 50nm.

5. A space-use carbon electrode gallium arsenide solar cell according to claim 4, characterized in that, The composite conductive adhesive is a carboxyl-modified multi-walled carbon nanotube-ethyl cellulose-reduced graphene oxide composite system, which, by mass percentage, contains 10%–15% carboxyl-modified multi-walled carbon nanotubes, 3%–5% reduced graphene oxide, and 5%–8% ethyl cellulose; the amount of the composite conductive adhesive added accounts for 20 wt%–25 wt% of the solids of the graphite / carbon black / composite conductive adhesive composite layer.

6. A method for fabricating a space-use carbon electrode gallium arsenide solar cell according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) After pretreatment of the triple-junction GaAs epitaxial layer, a metal top electrode and an anti-reflection film are deposited sequentially on its surface; (2) A MoO3 ultrathin interface layer is deposited on the back surface of the epitaxial wafer; (3) Prepare V2C MXene dispersion, spin-coat the V2C MXene dispersion onto the surface of MoO3 ultrathin interface layer under vacuum conditions, and anneal it and cool it naturally to obtain V2C MXene current transport layer; (4) Prepare a composite conductive adhesive slurry and mix it with a mixture of graphite and carbon black. The resulting mixture is coated on the surface of the V2C MXene current transmission layer using a multi-layer thin coating process. After coating, the mixture is annealed and naturally cooled to complete the fabrication of the carbon electrode gallium arsenide solar cell.

7. The method for fabricating a space-use carbon electrode gallium arsenide solar cell according to claim 6, characterized in that, In step (2), the vapor deposition process of the MoO3 ultrathin interface layer is as follows: in a vacuum thermal vapor deposition machine, the vacuum level is ≤1×10⁻⁶. -4 Pa, control the substrate temperature at 40℃~60℃, use MoO3 powder as the evaporation source, adjust the evaporation rate to 0.1nm / s, and evaporate to a film thickness of 5nm~10nm. After evaporation, maintain a vacuum environment and cool to room temperature.

8. The method for fabricating a space-use carbon electrode gallium arsenide solar cell according to claim 6, characterized in that, In step (3), the preparation method of the V2C MXene dispersion is as follows: V2C MXene powder is taken, and deionized water and sodium dodecylbenzenesulfonate dispersant are added to prepare a mixture with a V2C MXene powder concentration of 1 mg / mL and a dispersant concentration of 0.03 mg / mL. Then, the mixture is placed in an ultrasonic cell disruptor and ultrasonically dispersed at a power of 100W to 200W for 40 to 50 minutes. The spin coating rate is 4000 r / min to 4500 r / min, the spin coating time is 40 to 50 seconds, and the vacuum degree is controlled at 3 × 10⁻⁶. -3 Below Pa; anneal in an inert gas, heating to 250±10℃ at a heating rate of 8℃ / min, and holding for 40min~50min.

9. A method for fabricating a space-use carbon electrode gallium arsenide solar cell according to claim 6, characterized in that, In step (4), the preparation method of the composite conductive adhesive slurry is as follows: a. Weigh 78g of anhydrous terpineol and 6g of ethyl cellulose per 100g of slurry, pour them into a polytetrafluoroethylene beaker, place it on a 60℃ water bath magnetic stirrer, and stir at 500r / min~600r / min for 30min~40min until the ethyl cellulose is completely dissolved. Cool to room temperature to obtain a transparent viscous base liquid. b. Add 12g of carboxyl-modified multi-walled nanotubes and 4g of reduced graphene oxide to the transparent viscous base liquid, and stir magnetically at 300r / min~400r / min for 10min~15min to make the conductive particles uniformly dispersed in the base liquid to form a preliminary mixture. c. Transfer the preliminary mixture into a polytetrafluoroethylene ball mill jar, add zirconia ball milling beads, seal and place in a planetary ball mill, and ball mill at a speed of 200 r / min to 300 r / min for 1 h to 1.5 h to break up the conductive phase agglomerates; d. Filter the slurry with a 200-mesh polytetrafluoroethylene filter to remove large undispersed particles. Place the filtered slurry in a vacuum drying oven to degas for 10 to 15 minutes, adjust the viscosity to 18000±100 mPa·s, and refrigerate at 4℃ for later use.

10. A method for fabricating a space-use carbon electrode gallium arsenide solar cell according to claim 6, characterized in that, In step (4), the multilayer thin coating process is as follows: the thickness of each single layer is 0.5μm to 1.5μm. After coating, the coating is immediately placed in a drying oven at 60℃ to 80℃ for 15min to 25min. The coating is repeated 2 to 4 times until the target thickness is reached. The annealing temperature is 110±10℃ and the temperature is maintained for 20min to 3min.

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