Space Solar Cells Research Articles

Reliability of micro-resistance welded dissimilar connection between Ag-plated Kovar foil and GaAs space solar cell: Processing, microstructure and bonding strength

Solar panels in low earth orbit (LEO) can suffer from damage caused by atomic oxygen (AO) exposure and thermal shock, which may shorten the service life of their interconnectors and joints. Ag-plated Kovar foil has emerged as a promising material for interconnecting solar cell arrays. This study uses parallel gap resistance welding (PGRW) to conduct ultrafast Ag-plated Kovar foil and solar cell bonding in just 190 ms. The bonding strength depends on the current densities, with a diffused interface observed at a density of 475 A/mm2. The EBSD results show that grains of Ag layer and Au layer grow at the central bonding interface, whereas grains of Ag layer and Au layer form a weakened bonded line at the edge bonding interface. The thermal reliability of joints with Ag-plated Kovar foil is better than traditional Ag foil, with no decline in tensile-shear force observed even after multiple thermal cycles. Although the Ag layer of Kovar foil oxidizes as AgO and Ag2O in an AO environment, the joining interface remains unaffected. This investigation into PGRW joints of Ag-plated Kovar foil is critical for enhancing the high reliability of solar arrays in harsh temperatures and AO space environments.

Optimization design of surface optical characteristics of space solar cells based on transfer matrix method

The antireflection coating (ARC) can improve the photoelectric conversion efficiency of photovoltaic (PV) cells. In this paper, the influence of film thickness and refractive index of single-layer and double-layer ARC on solar light absorption under different spectral conditions is simulated by the transfer matrix method. The optimum values of ARC film thickness and refractive index are obtained. To optimize it at AM 0 (air mass 0) solar irradiance, a 66 nm thick SiN x ARC with a refractive index of 2.0 was used. The PV cell’s maximum power density is 89.87. The maximum power density of the PV cell with double-layer SiN x as ARC is 90.94. This work provides a theoretical basis for the application of ARC in ground PV power generation systems and space solar power systems.

Calibration for Space Solar Cells: Progress, Prospects, and Challenges

Space solar cells, have been providing a consistent supply of energy for various spacecraft for decades. Currently, the third‐generation solar cells, such as perovskite solar cells (PSCs) and organic solar cells, have demonstrated significant potential for space applications. However, their real performance in space environments is not yet clear. To assess crucial performance parameters, solar cells need to be calibrated under the standard space spectral irradiance before deployment in space. This is known as AM0 calibration. This review article focuses on the calibration techniques and methods for space solar cells. The topics covered include space environment and standard testing condition for solar cells, the measurements of key parameters for traditional solar cells, advancements in PSCs and organic solar cells for space applications, and a comprehensive review of diverse calibration methods. The discussion spans from near‐ground calibration to near‐space calibration and space calibration, encompassing approaches, key technologies, developmental milestones, and the respective merits of each calibration methods, especially focus on high altitude balloon calibration. Finally, the article addresses the challenges and future trends of space solar cell calibration based on the aforementioned discussions.

Sustainable Production of Ultrathin Ge Freestanding Membranes

Germanium (Ge) is a critical material for applications in space solar cells, integrated photonics, infrared imaging, sensing, and photodetectors. However, the corresponding cost and limited availability hinder its potential for widespread applications. However, using Ge freestanding membranes (FSMs) allows for a significant reduction in the material consumption during device fabrication while offering additional advantages such as lightweight and flexible form factor for novel applications. In this work, we present the Ge FSM production process involving sequential porous Ge (PGe) structure formation, Ge membrane epitaxial growth, detachment, substrate cleaning, and subsequent reuse. This process enables the fabrication of multiple high-quality monocrystalline Ge FSMs from the same substrate through efficient substrate reuse at a 100 mm wafer scale by a simple and low-cost chemical cleaning process. A uniform, high-quality PGe layer is produced on the entire recovered substrate. By circumventing the use of conventional high-cost chemical–mechanical polishing or even substantial chemical wet-etching, and by using an optimized PGe structure with reduced thickness, the developed process allows for both cost and an environmental impact reduction in Ge FSMs production, lowering the amount of Ge used per membrane fabrication. Moreover, this process employs large-scale compatible techniques paving the way for the sustainable production of group IV FSMs for next-generation flexible optoelectronics.

Photoabsorption Efficiency Improvement for Photovoltaic Solar Cells by Using the Honeycomb Nanostructures

In this paper we propose a designs of solar cells based on III-V semiconductors which can deliver more efficient, less expensive solar cells. Recently proposed approaches to enhance the efficiency utilize the novel III-V nanomaterials containing quantum dots, and new concepts like intermediate bandgap quantum dot based solar cells promise the efficiency over 50% [1]. Needs for thin flexible space solar cells are supposed to be fulfilled with Inverted Metamorphic Multijunction (IMM) solar [2]. In this paper we consider the alternative design of flexible solar cells, which is based on a honeycomb nanostructure consisting of embedded semiconductor pillars in a flexible film [3]. Such nanostructures are flexible and solar cells therefore are suitable for wider range of applications compared to ones with solid panel design, and are less expensive due to the smaller fraction of the active semiconductor material. However this kind of design may reduce the efficiency of the solar cell due to the volume filling factor.

Effect of electron irradiation on perovskite films and devices for novel space solar cells

Perovskite solar cells (PSCs) are considered as one of the strong contenders for next-generation space solar cells due to their advantages of high efficiency, low cost, high specific power, and remarkable irradiation resistance compared with those of silicon-based and III-V compound solar cells. At present, one focuses on the irradiation effects of perovskite solar cells, but there are a few studies on the irradiation damage mechanism of the core perovskite film. To advance the spatial application of perovskite solar cells, this study conducts a comprehensive examination of the performance fluctuations exhibited by mixed-cation perovskite films and solar cells under electron irradiation. Initially, the Monte Carlo method is employed to simulate and predict the effect of electron irradiation on perovskite solar cells. Subsequently, in conjunction with the microstructure characterization and the comparison of optical/electrical performance of perovskite films before and after irradiation, the irradiation damage mechanism of film is elucidated and the electron irradiation reliability of perovskite solar cells is evaluated. The research demonstrates that mixed-cation perovskite film and solar cells exhibit outstanding resistance to electron irradiation. Even when exposed to 100 keV electron irradiation with a cumulative fluence of 5×10<sup>15</sup> e·cm<sup>–2</sup>, the PSCs maintain an average power conversion efficiency of 17.29%, retaining approximately 85% of their initial efficiency. This study provides sound theoretical and experimental evidence for designing the irradiation-resistant reinforcement of new-generation space solar cells, contributing to the improvement of their operational performance and reliability in space applications.

Simulation of displacement damage of InP induced by protons and α-particles in low Earth orbit

Indium phosphide (InP) material hasmany advantages, such as large band gap, high electron mobility, high photoelectric conversion efficiency, high temperature resistance, and radiation resistance, which is superior to silicon (Si) and gallium arsenide (GaAs). Meanwhile InP is widely used in optical communication, high-frequency millimeter waves, optoelectronic integrated circuits, satellite communication, space solar cells, and other fields. Radiation particles incident on InP device can generate displacement atoms inside the device through elastic processes. And these displacement atoms continue cascade collisions to generate lattice defects which are vacancies, interstitials, and clusters. These defects capture electrons-holes by defective energy levels in the energy band, and then resulting in a decrease in the life of minority carriers which is the reason of degradation of InP devices. The process of degradation of InP device, induced by lattice defects from ion-irradiation, is called displacement damage effect (DDE). The non-ionizing loss energy (NIEL) scaling is a useful method to predict the degradation of device caused by DDE of radiation particles. Many studies have shown that the NIEL is linearly related to the damage coefficient of InP device. Previous studies of radiation damage effect of InP device mainly focused on single-energy protons, electrons, and neutrons. Of the particles in low earth orbit (LEO),the vast majority of particles are protons, with a few being α particles and electrons, while the electron’s NIEL is too small and its DDE is negligible. The InP’s NIEL induced by proton and α energy in LEO has not been studied in detail. Therefore, this paper uses Monte Carlo software Geant4 to study the NIEL, damage energy distribution with depth, and annual total non-ionization loss energy generated by protons and α particles in LEO in 500/1000/5000 μm InP materials. The shielding of 150-μm-thick SiO<sub>2</sub> layer and 2.54-mm-thick Al layer from protons and α particles are used as InP solar cell and InP devices in spacecraft, respectively. It is found that the energy spectrum determines the non-ionizing damage energy <inline-formula><tex-math id="M1">\begin{document}$ {T}_{\text{dam}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231499_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231499_M1.png"/></alternatives></inline-formula> distribution, and then influences the NIEL value: the NIEL value increases with <inline-formula><tex-math id="M2">\begin{document}$ {T}_{\text{dam}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231499_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231499_M2.png"/></alternatives></inline-formula> increasing and thickness of InP material decreasing. And α NIEL is larger than proton’s, the single particle DDE of InP device, induced by α particles, should be concerned. The annual non-ionizing damage energy of proton accounts for 98%, which means that proton is the main factor degrading InP devices in LEO.

Degradation characteristics and equivalent analysis of InGaAsP space solar cells under proton and neutron irradiation

The effects of 2 MeV, 30 MeV proton and neutron irradiation on the performance of InGaAsP single junction solar cells were investigated. The degradation of electrical and optical properties was studied by experiment, such as I-V curve, external quantum efficiency, photoluminescence (PL) and scanning electron microscopy (SEM). Results show that the performance parameters of the solar cell degrade seriously with the increasing of the displacement damage dose. The PL results indicate that irradiation has a destructive effect on the photoelectric properties of materials. The carrier parameters were quantitatively calculated according to the PL normalized peak. The minority carrier lifetime attenuation model and equivalent displacement damage model were established to evaluate the on-orbit behavior of the InGaAsP solar cell.

A Comprehensive Review on the Thermal Stability Assessment of Polymers and Composites for Aeronautics and Space Applications.

This review article provides an exhaustive survey on experimental investigations regarding the thermal stability assessment of polymers and polymer-based composites intended for applications in the aeronautical and space fields. This review aims to: (1) come up with a systematic and critical overview of the state-of-the-art knowledge and research on the thermal stability of various polymers and composites, such as polyimides, epoxy composites, and carbon-filled composites; (2) identify the key factors, mechanisms, methods, and challenges that affect the thermal stability of polymers and composites, such as the temperature, radiation, oxygen, and degradation; (3) highlight the current and potential applications, benefits, limitations, and opportunities of polymers and composites with high thermal stability, such as thermal control, structural reinforcement, protection, and energy conversion; (4) give a glimpse of future research directions by providing indications for improving the thermal stability of polymers and composites, such as novel materials, hybrid composites, smart materials, and advanced processing methods. In this context, thermal analysis plays a crucial role in the development of polyimide-based materials for the radiation shielding of space solar cells or spacecraft components. The main strategies that have been explored to improve the processability, optical transparency, and radiation resistance of polyimide-based materials without compromising their thermal stability are highlighted. The combination of different types of polyimides, such as linear and hyperbranched, as well as the incorporation of bulky pendant groups, are reported as routes for improving the mechanical behavior and optical transparency while retaining the thermal stability and radiation shielding properties. Furthermore, the thermal stability of polymer/carbon nanocomposites is discussed with particular reference to the role of the filler in radiation monitoring systems and electromagnetic interference shielding in the space environment. Finally, the thermal stability of epoxy-based composites and how it is influenced by the type and content of epoxy resin, curing agent, degree of cross-linking, and the addition of fillers or modifiers are critically reviewed. Some studies have reported that incorporating mesoporous silica micro-filler or microencapsulated phase change materials (MPCM) into epoxy resin can enhance its thermal stability and mechanical properties. The mesoporous silica composite exhibited the highest glass transition temperature and activation energy for thermal degradation among all the epoxy-silica nano/micro-composites. Indeed, an average activation energy value of 148.86 kJ/mol was recorded for the thermal degradation of unfilled epoxy resin. The maximum activation energy range was instead recorded for composites loaded with mesoporous microsilica. The EMC-5p50 sample showed the highest mean value of 217.6 kJ/mol. This remarkable enhancement was ascribed to the polymer invading the silica pores and forging formidable interfacial bonds.

Largely Enhanced Surface Flashover Voltage of Poly(ether Imide) by Scalable and Durable ZnO Coating: A Gift from In Situ Growth.

Dielectric materials with high surface electric insulation strength are in great demand in a high-power space solar cell array (SSCA). A moderately conductive surface is favorable to inhibit charge accumulation and mitigate electric field distortion, thus improving the surface flashover voltage. Although numerous modification methods have been proposed to achieve this goal, the facile, efficient, scalable, and environmentally friendly modification strategy remains a critical challenge to date. Considering the excellent charge modulation ability of ZnO and its mild preparation conditions, a facile and economical hydrothermal strategy was proposed to fabricate in situ a durable poly(ether imide)/zinc oxide (PEI/ZnO) coating with a high charge decay rate. The blooming flower-like ZnO in the coating is proved to play a key role in enhancing lateral charge dissipation on the surface of PEI, thereby suppressing surface charge accumulation. It was also shown that the shielding effect of ZnO on high-energy photons during flashover and the catalytic effect of Zn2+ on PEI molecular chains during hydrothermal treatment had a facilitating and suppressing effect on outgassing, respectively, and consequently affected the flashover. Excitingly, the synergistic effects of both accelerated charge dissipation and suppressed outgassing helped to improve the flashover voltage of PEI by up to 36.7%. The strategy selected here is efficient, scalable, and facile, and the coating is durable, which makes sense for commercial promotion.

3D Printing of Batteries from Lunar and Martian Regolith

To maximize the sustainability of future space missions, the utilization of local resources available on the Moon or Mars, also known as in-situ resource utilization (ISRU), is crucial to develop infrastructures such as habitation modules, power generation, and energy storage facilities.1–3 This work presents a perspective aiming to introduce the future of batteries manufacturing on the lunar and martian environment from ISRU materials. Based on the composition of the lunar and martian soil,4–7 the choice of the battery technology and materials for the different battery components (electrodes, electrolyte, current collectors and packaging) are examined. The motivations for selecting additive manufacturing technologies as a unique approach to support human operations in space, on the surface of the Moon or Mars, and any other locations where cargo resupply is not as readily available, as well as the need for high resolution multi-material printing methods, are discussed. Additive manufacturing paves the way to three-dimensional rechargeable battery architectures with enhanced specific surface area, three-dimensional ion diffusion, and improved power performances, while also allowing the development of shape-conformable batteries to maximize the energy storage within the final application.8–15 The in-space additive manufacturing process of shape-conformable batteries using in-situ resources is in direct alignment with the NASA’s objectives to demonstrate in-space autonomous manufacturing and assembly of complete systems by 2030, and to enable Humans survival, explore deep space, and visit planetary surfaces by 2040.16 Such initiatives also contribute to reducing power-related payload weight and volume in future missions, thus reducing the risk for long term Moon or even Mars missions where rapid resupply will be logistically infeasible. In this context, this presentation will provide a perspective of what is required to 3D print batteries on lunar and martian surfaces,17 an overview of our ongoing project dedicated to AM of sodium-ion batteries from resources available on the Moon and Mars and our recent work on 3D printing of TiO2 negative electrode material by means of the vat photopolymerization process.18 (1) Anand, M. et al. A Brief Review of Chemical and Mineralogical Resources on the Moon and Likely Initial in Situ Resource Utilization (ISRU) Applications. Planet. Space Sci. 2012, 74 (1), 42–48.(2) Edmunson. Building a Sustainable Human Presence on the Moon and Mars. New Horizons Summit.(3) McMillon-Brown, L. et al. What Would It Take to Manufacture Perovskite Solar Cells in Space? ACS Energy Lett. 2022, 7 (3), 1040–1042.(4) Heiken, G. et al. Lunar Sourcebook: A User’s Guide to the Moon; CUP Archive, 1991.(5) Dreibus, G. et al. Lithium and Halogens in Lunar Samples. Philos. Trans. R. Soc. Lond. A 1977, 285 (1327), 49–54.(6) Taylor, G. J. The Bulk Composition of Mars. Geochem. Explor. Environ. Analy. 2013, 73 (4), 401–420.(7) Yoshizaki, T. et al. The Composition of Mars. Geochim. Cosmochim. Acta 2020, 273, 137–162.(8) Maurel, A. et al. Highly Loaded Graphite-Polylactic Acid Composite-Based Filaments for Lithium-Ion Battery Three-Dimensional Printing. Chem. Mater. 2018, 30 (21), 7484–7493.(9) Maurel, A. et al. Considering Lithium-Ion Battery 3D-Printing via Thermoplastic Material Extrusion and Polymer Powder Bed Fusion. Additive Manufacturing 2020, 101651.(10) Martinez, A. C. et al. Additive Manufacturing of LiNi1/3Mn1/3Co1/3O2 Battery Electrode Material via Vat Photopolymerization Precursor Approach. Sci. Rep. 2022, 12 (1), 1–13.(11) Maurel, A. et al. Overview on Lithium-Ion Battery 3D-Printing By Means of Material Extrusion. ECS Trans. 2020, 98 (13), 3–21.(12) Maurel, A. et al. Toward High Resolution 3D Printing of Shape-Conformable Batteries via Vat Photopolymerization: Review and Perspective. IEEE Access 2021, 9, 140654–140666.(13) Maurel, A. et al. Ag-Coated Cu/Polylactic Acid Composite Filament for Lithium and Sodium-Ion Battery Current Collector Three-Dimensional Printing via Thermoplastic Material Extrusion. Frontiers in Energy Research 2021, 9 (70). https://doi.org/10.3389/fenrg.2021.651041.(14) Ragones, H. et al. Towards Smart Free Form-Factor 3D Printable Batteries. Sustainable Energy & Fuels 2018, 2 (7), 1542–1549.(15) Egorov, V. et al. Evolution of 3D Printing Methods and Materials for Electrochemical Energy Storage. Adv. Mater. 2020, 32 (29). https://doi.org/10.1002/adma.202000556.(16) Murphy, P. STMD’s New Strategic Framework Update, 2017. https://www.nasa.gov/sites/default/files/atoms/files/336429-508-to5_nac_dec_2017_strategicplanningintegration_tagged.pdf.(17) Maurel, A. et al. What Would Battery Manufacturing on the Moon and Mars Look Like? (submitted).(18) Maurel, A. et al. 3D Printed TiO2 Negative Electrodes for Sodium-Ion and Lithium-Ion Batteries Using Vat Photopolymerization (submitted).

A comprehensive study of parallel gap resistance welding joint between Ag foil and front electrode of GaAs solar cell

When space solar cell array is subjected to harsh temperature cycle, such as planet orbit, thermal fatigue cracks in bonding area are easily induced. With the aim of improving bonding quality and elucidating failure mechanism of parallel gap resistance welding (PGRW) joints in temperature cycling environment, the present research investigates the effect of current density on bonding quality and thermal fatigue behavior of PGRW joint between Ag interconnector and front electrode of GaAs solar cell. When current density is set at 417 A/mm2, a solid diffusion bonding is achieved at the Ag/Au interface, which also possesses adequate joint strength as ensured by both pressure and input energy of PGRW. Crack initiation by thermal fatigue is found at joint edge, which subsequently propagates along the interface as the environment temperature cycling continues. Further investigation reveals that the conducted temperature cycling generates serious tensile and compressive stress in the multi-layered joint structure. Since such reciprocating forces directly induce micro-plastic deformation and strain accumulation at joint interface, failure by crack is finally generated at the joining interface.

Estimation of the reliability figures of space GaInP/Ga(In)As/Ge triple junction solar cells from very high temperature accelerated life tests with forward and reverse biasing

This paper presents a temperature Accelerated Life Test (ALT) for space solar cells. The test is carried in dark conditions to circumvent the inherent problems of illumination ALTs. This ALT is an evolution of our previous ALT in dark conditions where just forward bias was used. Now, solar cell working conditions are emulated by means of forward/reverse bias. Forward bias emulates electric performance under illumination while reverse bias emulates the shadowing at eclipse periods or any other shadowing event (for example antennas might cast also shadows). The forward to reverse time ratio is 4:1. Furthermore, the high temperatures used in the current ALT (190, 210 and 230 °C) allow a considerable time reduction of the test. The results obtained in this ALT onto commercial GaInP/Ga(In)As/Ge triple junction solar cells suggest that the degradation mode is related with the decrease of parallel resistance, namely an initial degradation by shunts occurs in the GaInP top subcell which is followed by a parallel resistance reduction in the Ga(In)As middle subcell. The activation energy in current ALT is higher (1.06 eV) than in the previous one (0.88 eV). Reverse biasing promotes similar degradation than forward one but more intensely, i.e. in a shorter time. Therefore, reverse biasing produces a significant lower reliability than in previous ALT without reverse bias. Despite this reliability reduction, the time for a reliability of 90% is 32 years of continuous operation at a nominal temperature of 80 °C (typical of many GEO missions). Therefore, these solar cells seem very robust and with a high reliability for many space applications. It should be noted that these figures are related to the degradation caused exclusively by high temperatures and other stressors like radiation are not considered here.

Synergistic Modification of 2D Perovskite with Alternating Cations in the Interlayer Space and Multisite Ligand Toward High-Performance Inverted Solar Cells.

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Design and Preparation of Anti-Reflection Nanoarray Structure on the Surface of Space Solar Cell Glass Cover

Space solar cell glass covers require high radiation resistance and wide-spectrum high light transmittance. The existing research on the preparation of thin films or special optical structures on the surface of solar cells rarely involves systematic research and the precise control of the high transmittance structural parameters of specific spectral bands by glass covers. Nanoarray structures were designed and constructed on high-purity quartz glass covers, achieving high anti-reflection within the 350–1100 nm range, the high energy part of the solar spectrum on Mars, regardless of the preparation of antireflective film and its radiation resistance. First, G-Solver software package was used to establish a nanoarray structure model according to the equivalent medium theory, and the effects of structural parameters such as the grating period, grating depth, and duty cycle on the glass cover transmittance were investigated. The results show that when the grating period is 50–200 nm, the transmittance ranges from 97.8% to 99.9%. When the grating period further increases from 300 nm, the lowest point of the transmittance spectrum moves to the longwave direction, and the transmittance from 350 nm to the lowest transmittance point significantly reduces. The optimal grating depth is 500 nm for a 300 nm grating period, the transmittance at 350 nm reaches 88.91%, and the average transmittance is 98.23%. When the period is 300 nm and the depth is 500 nm, the optimal duty cycle is 0.67, the transmittance at 350 nm reaches 96.52%, and the average transmittance is 99.23%. Nanoarray structures were constructed on the glass covers with nanoimprint and plasma etching, then modified with atomic layer deposition (ALD) to adjust their depth and duty cycle. The influence rules of the grating period, depth, and duty cycle on the cover transmittance from the experimental results are basically consistent with those from the simulation calculation. The nanoarray structure increases the average transmittance within 350–1100 nm of the glass cover by an average of 2.02% and the peak transmittance by 2.66%. The research results and experimental methods of this study have application value and promotion prospects for improving the photoelectric conversion efficiency of space solar cells and ground solar cells.

Evaluation of hypervelocity impact of micrometeoroids and orbital debris on next-generation space solar cells

This paper discusses the hypervelocity impacts of micrometeoroids and orbital debris (MMODs) on inverted metamorphic triple-junction (IMM3J) and perovskite solar cells, which are much thinner than conventional triple-junction (3J) solar cells. We experimentally found that IMM3J solar cells can suffer from short-circuit faults due to the hypervelocity impacts of MMODs, unlike conventional 3J cells, and determined the projectile diameters and velocities that could cause them using a model proposed by Burt. No short-circuit mode was identified in perovskite solar cells, but they had open-circuit faults several days after the hypervelocity impact experiment, which are possibly attributed to the decomposition of the perovskite crystal by moisture in the air due to the broken seal.

Proton radiation hardness of GaInAsP alloys for space solar cell applications

AbstractRecent technology development in space mission design has raised a demand for space solar cells with a higher level of radiation tolerance as compared with state‐of‐the‐art, commercially available products. Therefore, new material systems are being investigated. Recently, we highlighted the superior radiation tolerance of GaInAsP solar cells to 1 MeV electron irradiation as compared with standard GaAs solar cells. A high InP fraction within this semiconductor compound was found to foster the regeneration rate of electron‐induced defects when the solar cells were annealed at 60°C under AM0 illumination, which are typical space‐operating conditions. In light of considering this material system in future radiation‐hard designs, the degradation of GaInAsP solar cells subjected to proton irradiation also needs to be investigated. Here, we report on the degradation and regeneration of GaInAsP solar cells lattice‐matched to InP substrates after 1 MeV proton irradiation. A detailed description of the radiation damage is achieved by solar cell numerical modeling combined with deep‐level transient spectroscopy analysis. The irradiation‐induced defects are quantified, and their evolution during annealing is monitored. The results are compared with the degradation data of similar solar cells obtained after 1 MeV electron irradiation. A slower regeneration rate of the proton‐induced defects is found in comparison with the electron‐induced defects. This difference is ultimately attributed to a different topology of the radiation damage caused by proton irradiation.

Mechanical properties of multi-scale germanium specimens from space solar cells under electron irradiation

During long-term service in space, Gallium Arsenide (GaAs) solar cells are directly exposed to electron irradiation which usually causes a dramatic decrease in their performance. In the multilayer structure of solar cells, the germanium (Ge) layer occupies the majority of the thickness as the substrate. Due to the intrinsic brittleness of semiconductor material, there exist various defects during the preparation and assembly of solar cells, the influences of which tend to be intensified by the irradiation effect. In this work, first, Ge specimens for mechanical tests were prepared at scales from microscopic to macroscopic. Then, after different doses of electron irradiation, the mechanical properties of the Ge specimens were investigated. The experimental results demonstrate that electron irradiation has an obvious effect on the mechanical property variation of Ge in diverse scales. The four-point bending test indicates that the elastic modulus, fracture strength, and maximum displacement of the Ge specimens all increase, and reach the maximum value at the irradiation dose of 1 × 1015 e/cm2. The micrometer scale cantilever and nanoindentation tests present similar trends for Ge specimens after irradiation. Atomic Force Microscope (AFM) also observed the change in surface roughness. Finally, a fitting model was established to characterize the relation between modulus change and electron irradiation dose.

Dual anti-thermal quenching induced by defect levels of the Ba3EuAl2O7.5 phosphor

The thermal quenching effect is a serious challenge for phosphors operating at elevated temperatures. Herein, dual anti-thermal quenching is observed from 298 to 523 K in the defect-rich Ba3EuAl2O7.5 phosphor upon the excitations of 270 and 392 nm. The integrated emission intensity of Eu3+ continuously increases by 145% and 156% and reaches maximums at temperatures of 443 and 483 K under the excitations of 270 and 392 nm, respectively. The defect levels, as demonstrated by the thermoluminescence glow curves, capture the electrons and compensate for the thermal quenching of Eu3+ luminescence. The electron paramagnetic resonance and x-ray diffraction reveal that the defects are associated with oxygen vacancies. This work provides an approach to implement the anti-thermal quenching effect by introducing structural defects. Meanwhile, the outstanding thermal stability of luminescence with the excitations in the deep ultraviolet and ultraviolet regimes makes the phosphor Ba3EuAl2O7.5 a competitive candidate for space solar cells and other optical devices.

Measurements and analysis of solar spectrum in near space

The experiment for measuring the solar spectrum at different latitudes and altitudes was conducted to obtain a suitable Air Mass Zero (AM0) standard solar cell calibration strategy with high altitude balloon flight calibration method. This is the world’s first acquisition of solar spectrum data at an altitude of 35 km using high-altitude balloon platform. The solar spectrum at the upper boundary of the atmosphere was measured and the spectral distribution was obtained from 20 to 35 km during the ascent. The results show that spectral distribution at 35 km is almost equivalent to that of AM0, the peak irradiance at 35 km is close to that of AM0, and the highest peak of this spectrum is at 450.2 nm. Comparing the results taken at different altitude, the effect of ozone, oxygen and water vapor is clearly seen. The measurement methods and results discussed in this paper can assist in verifying the accuracy of space solar cell calibration using high-altitude balloons. It could also provide a reference for the design of photovoltaic energy systems for near space aircrafts. Finally, the results taken from the launch site may be of use for the air quality monitoring and the design of photovoltaic system used in ground-based solar power generation in the Qinghai-Tibet Plateau.