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

Abstract

The present application relates to the technical field of solar cells, in particular to a flexible gallium arsenide solar cell for space and a preparation method thereof, which comprises the following steps: bonding of a gallium arsenide epitaxial layer and a PI substrate; thinning and peeling of a GaAs substrate; preparation of a GZO transparent current collection layer; preparation of a metal electrode; deposition of an anti-reflection film layer; etching of a lower electrode and temporary bonding and peeling; the preparation of the GZO transparent current collection layer comprises magnetron sputtering of a GZO transparent film, LED low-temperature light-assisted annealing treatment and in-situ Ar / O2 mixed plasma cleaning. The present application solves key problems such as flexible substrate compatibility, interface performance optimization and space environment adaptation by the synergistic effect of the design of the GZO transparent current collection layer, LED low-temperature light-assisted annealing and in-situ Ar / O2 plasma cleaning, and is suitable for the fields of aerospace and aviation.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, specifically to a flexible gallium arsenide solar cell for space applications and its fabrication method. Background Technology

[0002] Space energy systems are the core support for various spacecraft, placing stringent requirements on energy devices for radiation resistance, thermal shock resistance, high energy density, and long-term reliability. Gallium arsenide (GaAs) solar cells achieve photoelectric conversion through the photovoltaic effect. They not only have a small temperature coefficient and excellent radiation resistance, but their band gap also closely matches the AMO standard spectrum of space solar irradiance (the benchmark spectrum of solar radiation intensity in the space environment), enabling them to operate stably in the extreme environment of space. Therefore, they have become the mainstream device in current space energy systems. However, the high manufacturing cost of traditional rigid GaAs solar cells severely limits their widespread application in large-scale space missions.

[0003] To overcome cost bottlenecks, flexible gallium arsenide (GaAs) solar cells have gradually become the core development direction for space-grade GaAs batteries. Their power density is more than eight times higher than traditional rigid products, while retaining the advantages of GaAs batteries in resisting extreme environments, thus balancing space adaptability and industrialization potential. However, in actual research and application, flexible GaAs solar cells still face a dual technical bottleneck in the current collection layer, making it difficult to balance efficiency, cost, and reliability. On the one hand, the GaAs substrate itself has a large sheet resistance, resulting in significant lateral current transmission losses. Optimizing the structure and performance of the current collection layer is necessary to improve the overall photoelectric conversion efficiency of the battery. This problem is even more pronounced in flexible GaAs batteries, which need to meet the requirements of bending and rolling, as their structural design is limited by the substrate's flexibility, becoming a key factor restricting efficiency improvement. On the other hand, existing technologies generally use dense metal grid lines as the current collection layer, which has two unavoidable core defects. First, there's the issue of light shading. Metal grid lines account for 8%-15% of the light-shading area, directly blocking incident light and reducing the battery's photoelectric conversion efficiency, contradicting the core requirement of efficient energy utilization in spacecraft. Second, there are cost and resource issues. Grid line materials are mostly precious metals such as gold and silver, further increasing manufacturing costs and limiting production due to the scarcity of these resources, making it impossible to meet the mass production needs of large-scale space missions. To replace metal grid lines, the industry has attempted to use transparent conductive oxide materials such as ITO and AZO as current collection layers. However, these materials have extremely poor compatibility with flexible gallium arsenide batteries for space use, failing to meet practical application requirements. ITO has weak radiation resistance and is prone to performance degradation in the strong radiation environment of space, making it difficult to guarantee long-term stability. AZO has insufficient conductivity stability, and its resistance increases significantly after cyclic thermal shock in space. Furthermore, these transparent electrodes generally have poor flexibility, and their bending radii are difficult to match the structural requirements of flexible gallium arsenide batteries, making long-term compatibility impossible.

[0004] Gallium-doped zinc oxide (GZO), a high-performance transparent conductive oxide, has been used in terrestrial photovoltaic devices such as silicon-based and perovskite solar cells. However, it has yet to find a suitable application in the current collection layer of flexible gallium arsenide solar cells for space applications. The core reason is that a series of key technical challenges remain unresolved, such as controlling the interface compatibility between GZO and the gallium arsenide epitaxial layer, developing low-temperature fabrication processes adapted to flexible substrates, optimizing performance to withstand extreme space environments (radiation resistance, thermal shock resistance), and balancing high conductivity and high flexibility. These issues have resulted in a technological vacuum in the application of GZO in this scenario. Furthermore, existing GZO post-processing techniques are also inadequate. High-temperature thermal annealing exceeds the thermal tolerance threshold of flexible gallium arsenide substrates, easily leading to substrate deformation and active layer degradation; while UV-assisted annealing damages the active layer, affecting the overall performance of the cell. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a flexible gallium arsenide solar cell for space applications and its fabrication method. This gallium arsenide solar cell has advantages such as high conductivity, high light transmittance, high flexibility, resistance to extreme environments, and low cost, making it suitable for the aerospace field.

[0006] The purpose of this invention is to provide a method for fabricating a flexible gallium arsenide solar cell for space use, the method comprising:

[0007] Gallium arsenide epitaxial layer is bonded to PI film substrate;

[0008] GaAs substrate thinning and stripping;

[0009] Fabrication of a GZO transparent current collection layer;

[0010] Preparation of metal electrodes;

[0011] Deposition of antireflective coatings;

[0012] Lower electrode etching and temporary bond stripping;

[0013] The preparation of the GZO transparent current collection layer includes magnetron sputtering of the GZO transparent thin film, LED low-temperature light-assisted annealing, and in-situ Ar / O2 mixed plasma cleaning.

[0014] The thickness of the GZO transparent film is 200nm-500nm, and the Ga doping concentration is 2at.%-3at.%;

[0015] The LED low-temperature light-assisted annealing process is carried out at a temperature of 80℃-180℃, and is simultaneously irradiated by a 3000K color temperature LED light source.

[0016] In the in-situ Ar / O2 mixed plasma cleaning, the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 8-10:0-2. Specifically, this volume ratio can be 8:2, 9:1, 10:0, or any value in between.

[0017] To address the problems of existing metal grid lines, such as large shading area, high cost of precious metals, poor flexibility, and inability to meet the high-efficiency mass production requirements of flexible gallium arsenide (GaAs) solar cells for space applications, this invention uses a transparent GZO film as the current collection layer to replace traditional dense metal grid lines. This reduces the shading area to ≤1%, significantly decreasing incident light obstruction and directly improving photoelectric conversion efficiency. Simultaneously, it completely eliminates the use of precious metals such as gold and silver, greatly reducing material costs. Low-temperature annealing of the GZO transparent film with LEDs improves its density and reduces contamination, resulting in good anti-attenuation performance, stable interface contact, and high reliability. Plasma cleaning further reduces interface contact resistance and carrier transport losses, further enhancing photoelectric conversion efficiency. This flexible GaAs solar cell offers high flexibility, low cost, high photoelectric conversion efficiency, and high reliability, fully meeting the energy efficiency requirements of spacecraft.

[0018] Furthermore, the magnetron sputtering method for the GZO transparent thin film is as follows: the gallium arsenide epitaxial layer is fixed on the sample stage of the magnetron sputtering instrument, the surface of the gallium arsenide epitaxial layer is swept with a high-purity N2 gun, ZnO:Ga2O3 is used as the ceramic target, the sputtering power is set to 100W-150W and the argon pressure is 0.5Pa, and after deposition for 30min-60min, the surface of the thin film is swept again with a high-purity N2 gun.

[0019] Specifically, the N2 pressure is 0.2 MPa and the purity is 99.9%; the thickness of the GZO transparent film is 300 nm and the Ga doping concentration is 2.5 at.%. This invention optimizes the magnetron sputtering parameters of the GZO transparent film, particularly the design of the thickness and Ga doping concentration, to balance carrier concentration and mobility, avoiding the increase in resistance caused by Ga cluster formation. Simultaneously, it ensures that the film possesses both high conductivity and flexibility, ultimately achieving a sheet resistance ≤50 Ω / sq, visible light transmittance ≥88%, and a bending radius within 5 mm for the GZO transparent film. This perfectly matches the folding and rolling installation and usage conditions of flexible solar panels in spacecraft.

[0020] Furthermore, the specific method for LED low-temperature light-assisted annealing is as follows: the sample with deposited GZO thin film is placed on a programmable temperature-controlled hot stage, the hot stage temperature is calibrated, a 3000K color temperature LED light source is fixed directly above the sample, the power density of the light source is calibrated, the LED light source is turned on when the temperature is raised to 80℃, the temperature is further raised to 180℃ and held for 12-15 minutes, then the temperature is slowly lowered to 80℃ and the LED light source is turned off, and the sample is allowed to cool naturally to room temperature.

[0021] This invention employs an LED low-temperature light-assisted annealing process. Through the synergistic effect of weak visible light excitation and low-temperature thermal drive, it can activate the migration of oxygen vacancies in the GZO thin film, promote the preferential growth of grains along the (002) crystal plane, improve the film density (above 96%), reduce the coefficient of variation of thickness uniformity (2.1%), and ensure performance stability under extreme space conditions. It can also avoid deformation of the flexible substrate and diffusion of elements at the interface between GZO and gallium arsenide caused by high temperature, while eliminating the risk of ultraviolet light etching and protecting the active layer of the battery from damage. This solves the compatibility contradiction between traditional annealing processes and flexible gallium arsenide batteries.

[0022] Furthermore, calibrate the hot stage temperature to ≤±1℃; calibrate the light source power density to 80mW / cm³. 2 -120mW / cm 2 And ensure that the light spot area covers more than 120% of the effective area of ​​the GZO transparent film, with no local light dead spots.

[0023] Furthermore, the heating rate is 4℃ / min-6℃ / min; the cooling rate is 1℃ / min-3℃ / min.

[0024] Furthermore, the specific method for in-situ Ar / O2 mixed plasma cleaning is as follows: the annealed sample is moved to the sample stage of the plasma processor in the glove box, and Ar / O2 mixed gas is introduced to bombard it for 30s-60s. After cleaning, the plasma power supply is turned off, and N2 is introduced to purge for 5min.

[0025] To address the issue that a pinhole-like porous layer easily forms on the surface of annealed GZO transparent films, resulting in excessive interfacial contact resistance and severe carrier recombination losses, and that existing plasma treatments cannot balance surface cleaning and defect control, this invention employs an in-situ Ar / O2 hybrid plasma cleaning process to optimize the interfacial performance between GZO and the gallium arsenide active layer. Ar ions can precisely etch the porous layer on the GZO surface, reducing surface roughness and improving interfacial adhesion; while trace amounts of O2 can modulate the defect state density on the GZO surface, optimizing band matching with the gallium arsenide active layer and reducing the interfacial barrier. Ultimately, the surface roughness Ra = 8.1 nm was reduced to 4.2 nm, and the interfacial contact resistance decreased from greater than 1 × 10⁻⁶ before bombardment. -3 Ω cm 2 Reduced to less than or equal to 5 × 10 -4 Ω cm 2 This significantly reduces carrier recombination losses at the interface and improves lateral current transport efficiency; at the same time, in-situ treatment avoids the impact of atmospheric pollution on interface performance and ensures the stability of interface bonding under space thermal shock and strong radiation environments.

[0026] Furthermore, the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 9:1, the flow rate is 20 sccm-30 sccm, and the plasma power is 50W-80W.

[0027] Furthermore, the structure of the metal electrode is Au / Ge / Au / Ag / Au; and the structure of the antireflective coating is TiO2 / Al2O3.

[0028] The present invention also provides a flexible gallium arsenide solar cell for space use prepared by the above-described method, comprising: a PI film substrate, a metal bonding layer, a gallium arsenide epitaxial layer, a GZO transparent current collection layer, a metal electrode, an antireflection film layer, and a lower electrode.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention addresses the core requirement of flexible gallium arsenide (GaAs) solar cells for space applications. First, it replaces traditional metal grid lines with a transparent GaZO current collection layer, achieving a low-shading, low-cost, and highly flexible foundation. Then, it utilizes LED low-temperature annealing to optimize the crystallinity of the GZO transparent thin film, avoiding high-temperature damage to the PI substrate and GaAs epitaxial layer, thus resolving the core contradiction between flexible substrate compatibility and GZO performance optimization. Finally, in-situ plasma cleaning is employed to regulate interface characteristics, reducing contact resistance and carrier transport losses, resulting in a significant improvement in photoelectric conversion efficiency. The combined effect yields a flexible GaAs solar cell with high conductivity, high transmittance, high flexibility, resistance to extreme environments, and low cost, making it suitable for the extreme environmental requirements of space energy systems in the aerospace field. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the flexible gallium arsenide solar cell for space use of the present invention;

[0032] Figure 2 This is a schematic diagram of the battery intermediate structure during the initial stage of temporary bonding in this invention;

[0033] Figure 3 This is a schematic diagram of the battery intermediate structure after the GaAs substrate is removed according to the present invention;

[0034] Figure 4 This is a schematic diagram of the battery intermediate structure after the deposition of the GZO transparent current collection layer according to the present invention;

[0035] Figure 5 This is a schematic diagram of the LED low-temperature light-assisted annealing device and sample placement according to the present invention;

[0036] Figure 6 This is a schematic diagram of the battery structure after the metal electrode of this invention has been fabricated;

[0037] Figure 7 This is a schematic diagram of the battery structure after the antireflection film layer of the present invention has been deposited.

[0038] Explanation of the labels in the diagram:

[0039] 1. Sapphire substrate; 2. Temporary bonding adhesive layer; 3. PI film substrate; 4. Metal bonding layer; 5. Gallium arsenide epitaxial layer; 6. GaAs substrate; 7. GZO transparent current collection layer; 8. Metal electrode; 9. Antireflective coating layer; 10. Lower electrode. Detailed Implementation

[0040] 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.

[0041] 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.

[0042] 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.

[0043] Please see Figures 1 to 7 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.

[0044] One embodiment of the present invention provides a flexible gallium arsenide solar cell for space use, the schematic diagram of which is shown below. Figure 1As shown, from bottom to top, they are: PI film substrate 3, metal bonding layer 4, lower electrode 10 (i.e., the exposed part after etching of the metal bonding layer), gallium arsenide epitaxial layer 5, GZO transparent current collection layer 7, metal electrode 8, and antireflection film 9.

[0045] Another embodiment of the present invention provides a method for fabricating a flexible gallium arsenide solar cell for space use, the schematic diagram of which is shown below. Figures 1 to 7 As shown, it includes the following steps:

[0046] (1) The gallium arsenide epitaxial layer 5 is bonded to the PI film substrate 3;

[0047] Specifically, including:

[0048] Bonding of gallium arsenide epitaxial wafer to PI film: First, a 4-inch gallium arsenide epitaxial wafer (a triple-junction stacked gallium arsenide epitaxial wafer: top cell, middle cell, and bottom cell are GaInP, GaAs, and InGaAs, respectively) and a PI film are sequentially immersed in electronic cleaning solution, acetone, isopropanol, and deionized water for ultrasonic cleaning for 15-20 minutes, and then dried for later use. Next, a metal bonding layer 4 is deposited on the surfaces of the gallium arsenide epitaxial wafer and the PI film. The metal bonding layer material for the gallium arsenide epitaxial wafer is AuAgAu (to be exposed later via a back-end etching process, serving as the lower electrode), the metal bonding layer material for the PI film is CrTiAu, and the support layer material is CrTi / SiO2. Then, the PI film and the metal bonding layer of the gallium arsenide epitaxial wafer are aligned, and a pressure of 7×10⁻⁶ is set. 7 N-8×10 7 N, temperature 300±5℃, heat preservation time 15min-20min, bonded together by hot pressing.

[0049] Temporary bonding adhesive layer 2 is bonded to sapphire substrate 1: First, the 4-inch sapphire substrate is ultrasonically cleaned in electronic cleaning solution, acetone, isopropanol, and deionized water for 15-20 minutes. After drying, the surface is blown with a high-purity N2 gun at a pressure of 0.2 MPa to remove residual impurities and moisture, ensuring that the bonding surface is clean and free of dirt. Then, a pyrolytic temporary bonding adhesive is uniformly coated on the sapphire surface, with the adhesive layer thickness controlled at 10±0.5 μm. Subsequently, it is pre-baked on a 100℃ hot plate for 20-25 minutes to completely remove air bubbles in the adhesive layer and avoid voids after bonding that would affect the stability of the support.

[0050] Bonding PI film substrate to sapphire substrate: Align and bond the PI film support layer with the temporary bonding adhesive layer on the sapphire substrate, place it in a vacuum temporary bonding machine, set the bonding temperature to 120±5℃, the pressure to 2000±200N, and the holding time to 20min-25min to complete the temporary bonding of the gallium arsenide epitaxial wafer and the sapphire, forming a support structure of sapphire-temporary bonding adhesive-PI film-gallium arsenide epitaxial layer, as shown below. Figure 2As shown, this provides rigid support for subsequent substrate thinning and peeling, preventing deformation during flexible structure processing.

[0051] (2) Thinning and stripping of GaAs substrate 6;

[0052] Specifically, the GaAs substrate back side was first mechanically thinned using a polishing machine from an initial 300±5μm to 100±2μm, with the polishing rate controlled to prevent substrate cracking. Then, the thinned sample was immersed in a room-temperature chemical etching solution (NH3H2O:H2O:H2O2=1:5:5) for 10-15 minutes to completely remove the GaAs substrate, exposing the gallium arsenide epitaxial layer. Figure 3 As shown.

[0053] (3) Preparation of GZO transparent current collecting layer;

[0054] Specifically, it includes the following steps:

[0055] a. Epitaxial layer pretreatment:

[0056] The epitaxial wafer with sapphire support structure was fixed on the sample stage of the magnetron sputtering instrument. The surface of the gallium arsenide epitaxial layer was purged again with a high-purity N2 gun (0.2MPa pressure, N2 purity of 99.9%) to remove bonding residues and ensure that the interface between the GZO layer and the epitaxial layer is clean.

[0057] b. GZO magnetron sputtering deposition:

[0058] Using a ZnO:Ga2O3 ceramic target (Ga doping concentration 2 at.%-3 at.%), and with substrate temperature at room temperature, argon pressure at 0.5 Pa, sputtering power at 100 W-120 W, and deposition time at 30 min-50 min, transparent GZO films with thicknesses of 200 nm-500 nm were prepared. Figure 4 As shown; after deposition, high-purity N2 is used to purge loose particles from the surface to avoid affecting the subsequent annealing effect.

[0059] c. LED low-temperature light-assisted annealing:

[0060] Transfer the sample to a programmable temperature-controlled hot stage inside the glove box. The stage temperature is calibrated with an error ≤ ±1℃. Fix a 3000K color temperature LED light source 18cm-20cm directly above the sample. Figure 5 As shown, the power density was calibrated to 80 mW / cm². 2 -120mW / cm 2The light spot covers more than 120% of the effective area of ​​GZO; the temperature is increased at a rate of 4℃ / min-6℃ / min, and when the temperature reaches 80℃, the LED light source is turned on, and the temperature is continued to rise to 180℃ and held for 12min-15min; then the temperature is slowly decreased at a rate of 1℃ / min-3℃ / min, and when the temperature drops to 80℃, the LED light source is turned off, and the temperature is allowed to cool naturally to room temperature (25±3℃).

[0061] d. In-situ Ar / O2 plasma cleaning:

[0062] Without transferring the sample, move it to the sample stage of the plasma processor inside the glove box; introduce an Ar / O2 mixed gas (Ar to O2 volume ratio 9:1, flow rate 20sccm-30sccm), set the plasma power to 50W-80W and the bombardment time to 30s-60s, and complete the preparation of the GZO transparent current collection layer.

[0063] (4) Preparation of metal electrodes;

[0064] Specifically, a strip-shaped metal electrode pattern (7 mm in length and 0.9 mm in width) was first defined on the surface of the GZO transparent current collection layer using photolithography. After development and drying, the electrode pattern was ensured to be clear and burr-free. Then, the sample was transferred into a vacuum evaporation machine (vacuum degree 5×10). -4 Pa), vapor-deposit Au / Ge / Au / Ag / Au alloy electrodes; then, sequentially immerse the vapor-deposited sample in acetone / resist remover to peel off the photoresist, remove excess metal, and obtain a regular metal electrode pattern, such as Figure 6 As shown; after rinsing with deionized water, dehydrate with isopropanol and dry.

[0065] (5) Deposition of antireflective coating;

[0066] Specifically, a TiO2 / Al2O3 composite antireflection film was deposited on the surface of the metal electrode and the GZO transparent current collecting layer using electron beam evaporation, with a vacuum pressure ≤5×10⁻⁶. -4 Pa, substrate temperature 110±2℃, total deposition thickness 700nm-800nm, such as Figure 7 As shown; after deposition is complete, turn off the substrate heating and cool it to room temperature in the vapor deposition machine.

[0067] (6) Lower electrode etching and temporary bond stripping;

[0068] Specifically, the battery structure with the anti-reflection coating deposited is first prepared using a specially designed photolithography pattern. After spin coating, exposure, and development, the positive and lower electrode areas are exposed, while the remaining areas are protected with positive photoresist. The structure is then immersed in a mixture of hydrofluoric acid and water (HF:H2O) = 1:10 and etched for 2 minutes to remove the anti-reflection coating from the positive and lower electrode surfaces. After rinsing with deionized water, the structure is then etched alternately with a mixture of water, phosphoric acid, and hydrogen peroxide (H2O:H3PO4:H2O2) = 4:1:1 and hydrochloric acid (HCl) until the lower electrode metal is exposed. After etching, the photoresist is removed, and the sample is dried. Next, the sample is placed in an oven at 180℃ for 5 minutes to completely decompose the pyrolytic temporary bonding adhesive. The sapphire is gently peeled off, and the residual adhesive layer is removed with a stripping solution. Finally, the battery is cut, and the cut edges are passivated with a passivation solution, ultimately forming a complete flexible gallium arsenide solar cell for spatial applications (e.g., ...). Figure 1 (As shown).

[0069] The following specific examples will provide further details:

[0070] Example 1

[0071] A method for fabricating a flexible gallium arsenide solar cell for space use includes the following steps:

[0072] (1) The gallium arsenide epitaxial layer is bonded to the PI film substrate; specifically, it includes:

[0073] Bonding of gallium arsenide epitaxial wafer to PI film: First, immerse the 4-inch gallium arsenide epitaxial wafer and PI film sequentially in electronic cleaning solution, acetone, isopropanol, and deionized water for ultrasonic cleaning for 15 minutes, then dry them for later use. Next, deposit metal bonding layers on the surfaces of the gallium arsenide epitaxial wafer and PI film. The metal bonding layer material for the gallium arsenide epitaxial wafer is AuAgAu, the metal bonding layer material for the PI film is CrTiAu, and the support layer material is CrTi / SiO2. Finally, align the PI film and the metal bonding layer of the gallium arsenide epitaxial wafer, setting a pressure of 8×10⁻⁶. 7 N, temperature 300℃, heat preservation time 15min, bonded together by hot pressing.

[0074] Temporary bonding adhesive and sapphire substrate bonding: First, a 4-inch sapphire substrate was ultrasonically cleaned for 15 minutes in a series of electronic cleaning solutions, acetone, isopropanol, and deionized water. After drying, the surface was blown with a high-purity N2 gun at a pressure of 0.2 MPa to remove residual impurities and moisture, ensuring that the bonding surface was clean and free of contaminants. Then, a pyrolytic temporary bonding adhesive was uniformly coated on the sapphire surface with a thickness of 10 μm. The substrate was then pre-baked on a 100°C hot plate for 20 minutes to thoroughly remove air bubbles from the adhesive layer and prevent voids from forming after bonding, which could affect the stability of the support.

[0075] Bonding PI film substrate to sapphire substrate: Align and bond the PI film support layer with the temporary bonding adhesive layer on the sapphire substrate, place it in a vacuum temporary bonding machine, set the bonding temperature to 120℃, the pressure to 2000N, and the holding time to 20min to complete the temporary bonding of gallium arsenide epitaxial wafer and sapphire, forming a support structure of sapphire-temporary bonding adhesive-PI film-gallium arsenide epitaxial layer, which provides rigid support for subsequent substrate thinning and peeling, and avoids deformation during flexible structure processing.

[0076] (2) Thinning and stripping of GaAs substrate;

[0077] Specifically, the back side of the GaAs substrate was first thinned mechanically using a grinding machine from an initial 300 μm to 100 μm, and the grinding rate was controlled to avoid substrate cracking. Then, the thinned sample was immersed in a room temperature chemical etching solution (NH3H2O:H2O:H2O2=1:5:5) for 10 min to completely remove the GaAs substrate and expose the active layer.

[0078] (3) Preparation of GZO transparent current collecting layer;

[0079] Specifically, it includes the following steps:

[0080] a. Epitaxial layer pretreatment:

[0081] The epitaxial wafer with sapphire support structure was fixed on the sample stage of the magnetron sputtering instrument. The surface of the gallium arsenide epitaxial layer was purged again with a high-purity N2 gun (0.2MPa pressure, N2 purity of 99.9%) to remove bonding residues and ensure that the interface between the GZO layer and the epitaxial layer is clean.

[0082] b. GZO magnetron sputtering deposition:

[0083] A ZnO:Ga2O3 ceramic target (Ga doping concentration 2.5 at.%) was selected, and the substrate was kept at room temperature, argon pressure 0.5 Pa, sputtering power 120 W, and deposition time 40 min to prepare a 300 nm thick GZO transparent film. After deposition, high-purity N2 was used to purge loose particles on the surface to avoid affecting the subsequent annealing effect.

[0084] c. LED low-temperature light-assisted annealing:

[0085] The sample was transferred to a programmable temperature stage inside the glove box, with the stage temperature calibrated to have an error of ≤±1℃. A 3000K color temperature LED light source was fixed 18cm directly above the sample, and the power density was calibrated to 100mW / cm², with the light spot covering more than 120% of the effective area of ​​GZO. The temperature was increased at a rate of 5℃ / min, and when the temperature reached 80℃, the LED light source was turned on. The temperature was then increased to 180℃ and held for 12min. Subsequently, the temperature was slowly decreased at a rate of 2℃ / min, and when the temperature dropped to 80℃, the LED light source was turned off, and the sample was allowed to cool naturally to room temperature (25±3℃). After annealing, the density of the GZO film reached 96%, the coefficient of variation for thickness uniformity was 2.1%, and the sheet resistivity was 32Ω / sq.

[0086] d. In-situ Ar / O2 plasma cleaning:

[0087] Without transferring the sample, it was moved to the sample stage of the plasma processor inside the glove box; an Ar / O2 mixed gas (Ar to O2 volume ratio 9:1, flow rate 20 sccm) was introduced, and the plasma power was set to 60 W and the bombardment time to 45 s; after cleaning, the surface roughness of GZO Ra = 4.2 nm, and the interfacial contact resistance with the gallium arsenide epitaxial layer decreased to 3.5 × 10⁻⁶. -4 Ω cm 2 The fabrication of the GZO transparent current collection layer was completed.

[0088] (4) Preparation of metal electrodes;

[0089] Specifically, a strip-shaped metal electrode pattern (7 mm in length and 0.9 mm in width) was first defined on the surface of the GZO transparent current collection layer using photolithography. After development and drying, the electrode pattern was ensured to be clear and burr-free. Then, the sample was transferred into a vacuum evaporation machine (vacuum degree 5×10). -4 Pa), vapor-deposit Au / Ge / Au / Ag / Au alloy electrodes; then place the vapor-deposited sample sequentially into acetone / resist remover to strip the photoresist, remove excess metal, and obtain a regular metal electrode pattern; rinse with deionized water, dehydrate with isopropanol, and dry.

[0090] (5) Deposition of antireflective coating;

[0091] Specifically, a TiO2 / Al2O3 composite antireflection film was deposited on the surface of the metal electrode and the GZO transparent current collecting layer using electron beam evaporation, with a vacuum pressure ≤5×10⁻⁶. -4 Pa, substrate temperature 110℃, total deposition thickness 750nm; after deposition, substrate heating was turned off and cooled to room temperature in the evaporation machine.

[0092] (6) Lower electrode etching and temporary bond stripping;

[0093] Specifically, the battery structure with the anti-reflection coating deposited is first prepared using a specially designed photolithography pattern. After spin coating, exposure, and development, the positive electrode and lower electrode areas are exposed, while the remaining parts are protected with positive photoresist. The battery is then immersed in a mixture of hydrofluoric acid and water (HF:H2O) = 1:10 and etched for 2 minutes to remove the anti-reflection coating on the surface of the positive and lower electrodes. After rinsing with deionized water, the battery is then etched alternately with a mixture of water, phosphoric acid, and hydrogen peroxide (H2O:H3PO4:H2O2) = 4:1:1 and hydrochloric acid (HCl) until the lower electrode metal is exposed. After etching, the photoresist is removed and the battery is dried for later use. Then, the sample is placed in an oven at 180°C for 5 minutes to completely decompose and disable the pyrolytic temporary bonding adhesive. The sapphire is then gently peeled off, and the residual adhesive layer is removed with a stripping solution. Finally, the battery is cut, and the cut edges are passivated with a passivation solution to form a complete flexible gallium arsenide solar cell for spatial applications.

[0094] The basic performance, mechanical properties, and space environment adaptability of the flexible gallium arsenide solar cell for space use prepared in Example 1 were tested, and the results are as follows:

[0095] (1) Photovoltaic performance: Under the AMO spectrum, the open-circuit voltage of the flexible gallium arsenide solar cell in this space is 3.0746V, the short-circuit current is 0.4115A, the fill factor is 81.92%, and the photoelectric conversion efficiency (PCE) is 32.57%. The light-shielding area of ​​the GZO transparent structure is only 2% (including the GZO surface metal pads required for interconnecting the wafers and diodes, i.e., the positive electrode), which is 1.6 percentage points higher than the photoelectric conversion efficiency of the traditional metal grid cell (light-shielding area 8%, conversion efficiency 30.97%).

[0096] (2) Mechanical properties: The flexible gallium arsenide solar cell used in this space has a bending radius of up to 4 mm. After 1,000 bending cycles (bending radius 5 mm, rate 1 cycle / second), the photoelectric conversion efficiency decreases by only 2.8%. The metal electrodes are free from peeling and the GZO layer is free from cracks, which meets the requirements of flexible solar wing storage and deployment.

[0097] (3) Interface and stability: There was no obvious element diffusion at the interface between the GZO transparent current collection layer and the gallium arsenide epitaxial layer, and the contact resistance was stable at 3.5 × 10⁻⁶. -4 Ω cm 2 After undergoing 100 cycles of thermal shock from -160℃ to 120℃ (each cycle lasting 30 minutes), the resistance change rate is ≤4%, the ARC film does not peel off, and the metal electrodes are firmly bonded.

[0098] (4) Space environment adaptability: The space uses flexible gallium arsenide solar cells to simulate the vacuum environment of space (1×10⁻⁶). - 5After being placed for 1000 hours (Pa, irradiation shock), the performance degradation is ≤3%, which is far superior to the ITO transparent current collection layer and can meet the requirements of long-term on-orbit service of spacecraft.

[0099] 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 method for fabricating a flexible gallium arsenide solar cell for space use, characterized in that, The preparation method includes: Gallium arsenide epitaxial layer is bonded to PI film substrate; GaAs substrate thinning and stripping; Fabrication of a GZO transparent current collection layer; Preparation of metal electrodes; Deposition of antireflective coatings; Lower electrode etching and temporary bond stripping; The preparation of the GZO transparent current collection layer includes magnetron sputtering of the GZO transparent thin film, LED low-temperature light-assisted annealing, and in-situ Ar / O2 mixed plasma cleaning. The thickness of the GZO transparent film is 200nm-500nm, and the Ga doping concentration is 2at.%-3at.%; The LED low-temperature light-assisted annealing process is carried out at a temperature of 80℃-180℃, and is simultaneously irradiated by a 3000K color temperature LED light source. The low-temperature light-assisted process involves raising the temperature to a first temperature and turning on the LED light source, continuing to raise the temperature to a second temperature and holding it at that temperature, and then slowly cooling it down to the first temperature and turning off the LED light source. In the in-situ Ar / O2 mixed plasma cleaning, the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 8-10:0-2.

2. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 1, characterized in that, The magnetron sputtering method for the GZO transparent thin film is as follows: the gallium arsenide epitaxial layer is fixed on the sample stage of the magnetron sputtering instrument, the surface of the gallium arsenide epitaxial layer is swept with a high-purity N2 gun, ZnO:Ga2O3 is used as the ceramic target, the sputtering power is set to 100W-150W and the argon pressure is 0.5Pa, and after deposition for 30min-60min, the surface of the thin film is swept again with a high-purity N2 gun.

3. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 2, characterized in that, The N2 has a pressure of 0.2 MPa and a purity of 99.9%; the GZO transparent film has a thickness of 300 nm and a Ga doping concentration of 2.5 at.%.

4. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 1, characterized in that, The specific method for LED low-temperature light-assisted annealing is as follows: Place the sample with deposited GZO transparent film on a programmable temperature stage, calibrate the stage temperature, fix a 3000K color temperature LED light source directly above the sample, calibrate the light source power density, turn on the LED light source when the temperature rises to 80℃, continue to raise the temperature to 180℃ and hold for 12-15 minutes, then slowly lower the temperature to 80℃ and turn off the LED light source, and allow it to cool naturally to room temperature.

5. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 4, characterized in that, The temperature error of the calibrated hot stage should be ≤±1℃; the power density of the calibrated light source should be 80mW / cm³. 2 -120mW / cm 2 And ensure that the light spot area covers more than 120% of the effective area of ​​the GZO transparent film, with no local light dead spots.

6. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 4, characterized in that, The heating rate is 4℃ / min-6℃ / min; the cooling rate is 1℃ / min-3℃ / min.

7. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 1, characterized in that, The specific method for in-situ Ar / O2 mixed plasma cleaning is as follows: the annealed sample is moved to the sample stage of the plasma processor in the glove box, and Ar / O2 mixed gas is introduced to bombard it for 30s-60s. After cleaning, the plasma power supply is turned off, and N2 is introduced to purge for 5min.

8. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 7, characterized in that, The Ar / O2 mixed gas has an Ar to O2 volume ratio of 9:1, a flow rate of 20 sccm-30 sccm, and a plasma power of 50W-80W.

9. The method for fabricating a flexible gallium arsenide solar cell for space use according to claim 1, characterized in that, The structure of the metal electrode is Au / Ge / Au / Ag / Au; the structure of the antireflective coating is TiO2 / Al2O3.

10. A flexible gallium arsenide solar cell for space use, prepared by the method according to any one of claims 1-9, characterized in that, include: PI film substrate, metal bonding layer, gallium arsenide epitaxial layer, GZO transparent current collection layer, metal electrode, antireflection film layer, and bottom electrode.

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