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Metal halide perovskite solar cells have progressed rapidly over the past decade, providing an exceptional opportunity for space photovoltaic (PV) power applications. However, the solar cells to be...

There is a need for characterization of multi-junction solar cell based test coupons under collimated sunlight for both terrestrial and space applications. These applications include solar cell angle measurements and concentrator systems. The U.S. Naval Research Laboratory (NRL) has modified a 3-zone Spectrolab LAPSS (Large Area Pulsed Solar Simulator) to provide a tunable spectrum with a 1° collimation for testing of solar arrays. NRL has added filters and a complete measuring system capable of testing individual cells and small concentrator coupons requiring collimation comparable to the sun.

A method is proposed for large area, highly uniform photoluminescence imaging of single and multi-junction solar cells and solar cell arrays. Relative photoluminescence across a large area can be rapidly determined due to highly uniform excitation illumination and minimal measurement artifacts. Varying the wavelength of the excitation illumination enables the measurement of the photoluminescence of a variety of solar cell materials and of multiple sub-cells in a multi-junction device. This method allows for rapid characterization of spatially resolved device parameters. Thereby providing insight to the condition of solar cells including the nature of potential degradation that would not be readily conveyed via overall performance measurements using techniques that can be performed while the array is installed into a functional end use system.

We report a space tandem solar cell enabling an enhanced power conversion efficiency with radiation tolerance in low radiation environments for space photovoltaic (PV) applications. The presented space perovskite/Si 4-terminal tandem cell features an efficient semitransparent perovskite top cell with the bandgap of 1.61 eV on a thin Si space solar cell specifically designed for high radiation tolerance in space. Under a simulated air mass zero (AM0) spectrum (136.6 mW/cm2), the space tandem solar cell by combining the perovskite solar cell with a thin Si space solar cell results in a power conversion efficiency of 21.1% surpasses a limited efficiency of ~17% in a single junction Si space solar cell. Considering the potential for developing more efficient, low-cost perovskite PV technology, our approach of using the thin Si space solar for the space tandem cells makes it possible to realize cost-effective PV power generation in space.

The Naval Research Laboratory has developed a low-power, real-time displacement damage dosimeter (RT3D). RT3D consists of two components; one being the measurement electronics and the second being the actual dosimeter (GaAs diode) exposed to the radiation source. RT3D accumulates displacement damage passively (without power) and the displacement damage dose (DDD) is measured at will with measurement electronics by measuring the GaAs diode dark current at one or more forward bias voltages. The DDD is subsequently determined in real-time from a calibration curve derived from ground-based testing. The dosimeter is capable of measuring approximately three orders of magnitude in DDD. The dosage measurement range of the sensor can be modified by placing an absorber material over the sensor. Proton testing performed in situ yielded an error estimate determination to within 10% for simulated space use.

In this study, we investigate the impact of the deposition of indium tin oxide (ITO) via DC magnetron sputtering on tunnel oxide passivating poly-Si contacts. Before ITO deposition to the tunnel SiO x passivating n+ poly-Si rear-contact on the cell structure with an SiN x /Al2O 3 passivating boron emitter, the implied open-circuit voltage (iV oc ) and implied fill factor (iFF) were measured to be 694±10 mV and 83±0.6%, respectively. After ITO sputtering and curing annealing, the iV oc and iFF were almost fully recovered, resulting in the iVoc of 685±11 mV and iFF of 81.9±0.8%. The characteristic of fully recovered effective lifetime is attributed to unique sputtering conditions employing a very low power density at room temperature and curing.

Flight endurance and power are limiting factors affecting UAV applications today due to battery weight and capacity. Solar arrays integrated into the wing surface can provide additional power dependent on the sun, weight, wing area, and efficiency, and have demonstrated more than doubled flight times. With most wing surfaces having some degree of curvature and flexure during flight, stresses can be induced on the solar arrays. Photoluminescence is used to assess wing stresses by optically identifying crack propagation in the cells. NRL has built a variety of wings for UAVs from solar cell technologies. This paper intends to provide a demonstration of using this technique to study solar cell cracking through the array assembly process from wing integration to flight.

In this paper, we report findings from a micro CPV module, employing 170 μm GaAs-based 2J CPV cells, assembled on glass substrates using micro-transfer printing. The CPV array uses all-glass lens arrays to focus the light with a geometric concentration ratio of 740 suns, and a bifacial, monocrystalline silicon solar cell behind the substrate to capture the diffuse component of the light. We found that the diffuse capture creates a significant performance boost over CPV alone, and study the role of bifacial capture on the overall performance. The highest combined efficiency with respect to global normal irradiance was 25.4% for the module, measured by outdoor testing in Washington, DC.

This study investigates maximizing net power input from a solar-photovoltaic array and/or a thermal updraft while performing constant bank angle, circular flight-path turns (that is, an orbit). The process inputs are the aircraft sink polar (or, equivalently, the power required curve), the date, the time, the location, and the flight altitude. A solar insolation model is combined with a best-turn performance calculation to determine the bank angle that maximizes power input from a solar-photovoltaic array at varying sun elevation angles. In general, for low sun elevation angles, the maximum net power gain from solar input and drag output is found at higher bank angles and shows 15% (absolute) gain over the limiting case of wings-level orbits in the same conditions. For high sun elevation angles, the maximum net power is found at low bank angles. The break point between high and low sun elevation angles varies with aircraft parameters and is approximately 25 deg for the example aircraft in this paper. The ...

We focus on utilizing sputtered indium tin oxide (ITO) as a recombination layer, having low junction damage to an n-type silicon solar cell with a front-side tunnel oxide passivating electron contact, thereby enabling the development of a high efficiency monolithic perovskite/Si tandem device. High transparency and low resistivity ITO films are deposited via low power DC magnetron sputtering at room temperature onto a front-side thin SiOx/n+ poly-Si contact in a complete Cz n-Si cell with a back-side Al2O3/SiNx passivating boron-diffused p+-emitter on a random pyramid textured surface. We report the cell characteristics before and after ITO sputtering, and we find a cure at 250 °C in air is highly effective at mitigating any sputtering induced damage. Our ITO coated sample resulted in an implied open-circuit voltage (iVoc) of 684.7 ± 11.3 mV with the total saturation current density of 49.2 ± 14.8 fA/cm2, an implied fill factor (iFF) of 81.9 ± 0.8%, and a contact resistivity in the range of 60 mΩ-cm2 to 90 mΩ-cm2. After formation of a local Ag contact to the rear emitter and sputtered ITO film as the front-side contact without grid fingers, the pseudo-efficiency of 20.2 ± 0.5% was obtained with the Voc of 670.4 ± 7 mV and pseudo FF of 77.3 ± 1.3% under simulated one sun with the calculated short-circuit current density of 30.9 mA/cm2 from the measured external quantum efficiency. Our modelling result shows that efficiency exceeding 25% under one sun is practically achievable in perovskite/Si tandem configuration using the ITO recombination layer connecting a perovskite top cell and a poly-Si bottom cell.

Foldable PV modules based upon different PV technologies were evaluated in the Naval Research Laboratory (NRL) for mobile solar power generation. We performed outdoor PV performance comparison of foldable and flexible modules that were mounted on the NRL rooftop for 75 days. We show that foldable PV modules based on CIGS and crystalline Si cells have good stability without performance losses. Other prototype PV modules consisting of amorphous Si, III-V based multijunction solar cells show a significant decrease in power at maximum power point (Pmpp) with losses of more than 10% due to non-optimized module encapsulation materials and processing. For the selected modules, reliability and durability testing results including damp heat test will be discussed.

Modern silicon photovoltaic (PV) cells have high external quantum efficiencies (>70%) from 900nm-1070nm, and are ideally suited as laser power receivers to match the wavelength of high power lasers available today. Silicon PV cells are $\sim 300\mathrm{X}$ less expensive than III-V photovoltaic cells making them economical alternatives for large area receivers. A large receiver benefits the laser side of a wireless power system by reducing the requirement for maintaining a small beam at a great distance and eases the wireless receiver design by allowing waste heat to be spread over a larger surface area. Finally, a silicon PV array can efficiently combine solar energy harvesting during the day, and laser energy power transfer at night with a single low-cost array. In this paper we study commercially available silicon solar cells, evaluate their suitability for a laser power converter, and discuss some of the system related aspects of fielding a laser power converter.

Unmanned Aerial Vehicles (UAVs) are expanding in both military and commercial markets. Most UAVs are limited in flight duration and due in part to the weight of energy storage. Solar cells integrated into the wing surface can provide additional power dependent on the sun, weight, wing area, and efficiency. NRL has built a variety of wings for UAVs from solar cell technologies which include Si, thin flexible GaAs, triple junction InGaP/GaAs/Ge, and Inverted Metamorphic MultiJunction (IMM) for comparison. NRL has flown these solar technologies demonstrating flights in excess of 10 hrs with only 4 hrs of onboard energy storage. This paper intends to provide a side-by-side comparison of these technologies for design and cost considerations on mission feasibility.

The response of triple-junction solar cells to proton and electron irradiation is analyzed using electroluminescence (EL) measurements. This analysis allows the dark current of each individual subjunction to be determined providing insight into the radiation response mechanisms.

We examine the potential to enhance cell performance using wide bandgap metal oxide films as full-area rear contacts to p-type crystalline Si (c-Si) solar cells. We aim to introduce a band offset through wide bandgap nickel oxide rather than introducing a band bending through transition metal oxides (e.g. MoO x , V 2 Ox, WO x ). Our numerical simulation shows it is possible to achieve one-sun efficiency of 21.6% with the open-circuit voltage (V oc ) of 652 mV, the short-circuit current density (J sc ) of 39.9 mA/cm2 and the fill factor (FF) of 82.5% when the back surface recombination velocities is 100 cm/s at p-Si/NiO x .

Unmanned Aerial Vehicles (UAVs) are rapidly growing in both military and commercial markets. One shortfall of UAVs is the amount of time they can fly, being limited by the energy storage. Solar cells can be integrated into the wing surface to provide additional power, dependent on the sun, weight, wing area, and efficiency. NRL is building a UAV with wings from a variety of solar cell technologies, which includes high efficiency Si, thin flexible GaAs, triple junction InGaP/GaAs/Ge, and Inverted Metamorphic Multi-Junction (IMM) for direct comparison and to improve flight endurance. The UAV also incorporates the necessary power management system required to maximize the solar power available. In addition to solar cells, this plane can also utilize thermal updrafts to soar. Flight data is provided which includes all electrical parameters for comparison studies.

Space Solar Power (SSP) is broadly defined as the collection of solar energy in space and its wireless transmission for use on Earth. The implementation of such a system could offer energy security, environmental, and technological advantages. The Integrated Symmetrical Concentrator (ISC) and Modular Symmetrical Concentrator (MSC) concepts have received considerable attention among recent commonly proposed SSP implementations. Each concept employs an array of modules for performing conversion of concentrated sunlight into microwaves for transmission to Earth. Until the efforts of the U.S. Naval Research Laboratory, no module prototypes had been subjected to the challenging conditions inherent to the space environment. The customized space simulation testing and the associated development described in this paper detail the efforts to test a prototype module in vacuum under multiple suns of solar concentration. A small vacuum chamber and 4000W Xenon light source were adapted to provide the desired test conditions. In particular, much effort was devoted to arriving at an effective, inexpensive solution that was consistent with the budget constraints of the project without compromising the fidelity and relevance of the tests.

In this paper, a detailed analysis on the radiation response of solar cells with multi quantum wells (MQW) included in the quasi-intrinsic region between the emitter and the base layer is presented. While the primary source of radiation damage of photovoltaic devices is minority carrier lifetime reduction, we found that in the case of MQW devices, carrier removal (CR) effects are also observed. Experimental measurements and numerical simulations reveal that with increasing radiation dose, CR can cause the initially quasi-intrinsic background doping of the MQW region to become specifically n- or p-type. This can result in a significant narrowing and even the collapse of the electric field between the emitter and the base where the MQWs are located. The implications of the CR-induced modification of the electric field on the current-voltage characteristics and on the collection efficiency of carriers generated within the emitter, the MQW region, and the base are discussed for different radiation dose conditions. This paper concludes with a discussion of improved radiation hard MQW device designs.

Autonomous systems are increasingly used to provide situational awareness and long-term environment monitoring. Photovoltaics (PV) are favored as a long-endurance power source for many of these applications. To date, the use of PV is limited to space and terrestrial (dry-land) installations. The need for a persistent power source also exists for underwater (UW) systems, which currently rely on surface PV arrays or batteries. In this paper, we demonstrate that high-bandgap-InGaP solar cells can provide useful power UW.

The military's need to reduce both fuel and battery resupply is a real-time requirement for increasing combat effectiveness and decreasing vulnerability. Mobile photovoltaics (PV) is a technology that can address these needs by leveraging emerging, flexible space PV technology. In this project, the development and production of a semirigid, lightweight, efficient solar blanket with the ability to mount on, or stow in, a backpack and recharge a high-capacity rechargeable lithium-ion battery was undertaken. The 19% efficient blanket consists of a 10 × 3 solar array of 20 cm2 and single-junction epitaxial lift-off solar cells, which have an efficiency of ∼22% under AM1.5G illumination. A power-conditioning module was also developed to interface the solar panel to the battery. Thirteen systems were outfitted during a Limited Objective Experiment-1 in February 2012, and based on the results, a second version of the system is in development.

© 2016, National Academy of Sciences. All rights reserved. Emerging classes ofconcentrator photovoltaic (CPV) modules reach efficiencies that are far greater than those of even the highest performance flat-plate PV technologies, with architectures that have the potential to provide the lowest cost of energy in locations with high direct normal irradiance (DNI). A disadvantage is their inability to effectively use diffuse sunlight, thereby constraining widespread geographic deployment and limiting performance even under the most favorable DNI conditions. This study introduces a module design that integrates capabilities in flat-plate PV directly with the most sophisticated CPV technologies, for capture of both direct and diffuse sunlight, thereby achieving efficiency in PV conversion of the global solar radiation. Specific examples of this scheme exploit commodity silicon (Si) cells integrated with two different CPV module designs, where they capture light that is not efficiently directed by the concentrator optics onto large-scale arrays of miniature multijunction (MJ) solar cells that use advanced III-V semiconductor technologies. In this CPV+scheme ("+" denotes the addition of diffuse collector), the Si and MJ cells operate independently on indirect and direct solar radiation, respectively. On-sun experimental studies of CPV+modules at latitudes of 35.9886° N (Durham, NC), 40.1125° N (Bondville, IL), and 38.9072° N (Washington, DC) show improvements in absolute module efficiencies of between 1.02% and 8.45% over values obtained using otherwise similar CPV modules, depending on weather conditions. These concepts have the potential to expand the geographic reach and improve the cost-effectiveness of the highest efficiency forms of PV power generation.

We have developed an InGaP solar cell structure capable of operating at 450°C under N 2 ambient. This structure has been annealed for over 70h without degradation in room temperature performance. This type of structure has applications in hybrid solar energy plants which combine photovoltaic and thermal collection systems to maximize overall conversion efficiency. We anticipate that this device will be able to achieve up to 17% efficiency at 400°C and 500x concentration based on simulations with incorporated optical and electrical high-temperature semiconductor parameters.

Laboratory measurement of the IV parameters of multi-junction (MJ) solar cells is performed using solar simulators designed to match the desired illumination environment as closely as possible. This paper examines the impact of non-idealities in solar simulator spectrum on the measurement of MJ solar cell IV parameter through the use of a multi-zone solar simulator capable of varying light output on each MJ subcell independently. It is shown through offsets in solar simulator spectrum that standard characterization methodology may result in significant error in IV parameter measurement resulting in over or underestimation of cell performance, largely as a result of luminescent coupling.

Applications and uses for UAVs are rapidly expanding as the constituent technologies mature. One major drawback of UAVs is the length of time they can fly, which is limited by the energy storage. Solar cells can be added to the wing surface and provide additional power dependent on the sun, weight, wing surface area, and efficiency. Inverted Metamorphic Multi-junction (IMM) solar cells offer advantages over conventional cell technology because they are lighter, more efficient, and more mechanically flexible than crystalline Si allowing for coverage of the curved surface of the wing. NRL is building an UAV with IMM solar cells to improve flight endurance. The aircraft also incorporates the necessary power management system required to maximize the solar power available. In addition to solar cells, this plane will also utilize thermal updrafts to soar.

In this work, we demonstrated an enhanced surface passivation of epitaxially grown boron-doped emitters by replacing thermal SiO 2 as a passivation layer of p+-emitter employed in a 16.8% efficient 18-μm Si solar cell on stainless steel with plasma assisted atomic layer deposition (ALD) Al 2 O 3 /PECVD SiN x stack. For the Al 2 O 3 /SiN x stacks on epitaxial p+-emitter after post-deposition anneal, the emitter saturation current density (J 0e ) values were decreased to 19.5 fA/cm2 with the corresponding iV oc of 688 mV By using advanced surface passivation scheme, further improvement in the V oc of a present 16.8% efficient ultrathin Si solar cell on steel can be expected.

Low temperature (≤450°C) ion beam deposition was employed to grow polycrystalline Germanium (Ge) films on Si (100) crystal, polymer film, and glass. The effects of deposition temperatures and energies of sputtered atoms on the crystal quality of Ge films were studied. XRD characterization of the material showed that at above 300°C, Ge films had a phase transition from amorphous to polycrystalline structure. Samples deposited at 1000eV beam energy had the best crystallinity Successful results have been achieved by growing up to 600 nm thick poly-Ge film layers at 450°C substrate temperature on plastic and glass substrates.

The NRL TacSat-4 Satellite was launched into a highly elliptical orbit on September 27th 2011. The solar panels are populated with Emcore ATJ cells. The solar panel was predicted to degrade 25% over the first year. Flight data show that the actual degradation is exceeding this prediction. Ground testing was conducted to more accurately determine the degradation and end-of-life (EOL) parameters. This consisted of irradiations of Emcore (SolAero) ATJ cells with 3 MeV protons at 8 different fluences ranging from 1 × 1011 to 1 × 1015 p/cm2 greater than any previously irradiated testing by orders of magnitude. This paper contains details related to the temperature coefficients of these cells and how they correlate to the Displacement Damage Dose (DDD). This data will help in predictions of solar panel performance in high radiation orbits.

Accurate laboratory measurement of the IV parameters of multi-junction (MJ) solar cells is highly dependent on the incident spectrum. This paper examines the influence of simulator spectrum on MJ solar cell measurements through the use of a multi-zone solar simulator capable of varying light output on each MJ subcell independently. It is shown through solar simulator spectrum offset that standard characterization methodology may result in significant error in IV parameter measurement resulting in over or underestimation of cell performance.

Advanced photovoltaic technologies were tested aboard the eighth Materials International Space Station Experiment (MISSE-8) as part of the third Forward Technology Solar Cell Experiment (FTSCE-III) over a period of approximately 26 months. The Air Force Research Laboratory Space Vehicles Directorate in collaboration with the Naval Research Laboratory flew a myriad of experiments to evaluate advanced photovoltaic cell and material technologies. Such data is critical for technology development and future transition to operational use. These experiments were comprised of inverted metamorphic (IMM) and other thin film and advanced III–V cells from multiple vendors. In addition, quantum dot enhanced solar cells and advanced solar cell coverglass replacements were flow. This paper compares the pre and post flight characterization of these advanced technologies.

A modeling and simulation effort is presented that produces a design of an novel organic photovoltaic (OPV) device specifically tailored for underwater (UW) operation. An analysis of the UW environment is presented which highlights the significant advantages of OPV for UW operation. An OPV multijunction design is presented consisting of two absorber layers with the same spectral response, enabling efficient conversion of the narrow UW spectrum and very high voltages. Novel hybrid organic/inorganic materials are introduced that are capable of forming distributed Bragg reflectors for efficient photon management and improved current. Importantly, the entire solar cell design is based on solution processed materials enabling low cost manufacturing.

Advances in the architecture of GaInP solar cells have recently lead to ∼21% conversion efficiencies under the global spectrum due to high radiative efficiencies, and the resulting strong luminescent coupling in GaInP/GaAs tandems has lead to record dual-junction efficiencies. The suitability of these newer GaInP cells to space applications has not been examined, however. Here we present a study to compare the radiation hardness of rear-heterojunction and more traditional GaInP junctions and the resulting luminescent coupling. Pairs of GaInP/GaAs tandem cells were irradiated with 1 MeV electrons at fluences up to 1015 e/cm2. The cells were thoroughly characterized, before and after irradiation, by measuring the quantum efficiency, IV characteristics, electroluminescence and luminescent coupling. We find the luminescent coupling to be unchanged below ∼1013 e/cm2, and to decrease to zero by 1015 e/cm2. For all fluence levels, the rear heterojunction structure had a higher coupling constant than the front junction structure. Despite these advantages, the efficiency degraded at the same rate for both structures.

In this work, we investigate a transparent conducting oxide (TCO)-based, passivated contact for the potential use as a passivated tunnel contact to p-type Si. As a surface passivation layer, the Al2O3 films with varying the thickness are deposited using plasma-enhanced atomic layer deposition (PEALD) at 200 °C, followed by post-deposition annealing. For a ∼15 nm thick Al2O3 layer, a high level of surface passivation is achieved, characterized by the effective surface recombination velocity (Seff,max) of

In this work, a multijunction solar cell is developed on a GaSb substrate that can efficiently convert the long-wavelength photons typically lost in a multijunction solar cell into electricity. A combination of modeling and experimental device development is used to optimize the performance of a dual junction GaSb/InGaAsSb concentrator solar cell. Using transfer printing, a commercially available GaAs-based triple junction cell is stacked mechanically with the GaSb-based materials to create a four-terminal, five junction cell with a spectral response range covering the region containing >99% of the available direct-beam power from the Sun reaching the surface of the Earth. The cell is assembled in a mini-module with a geometric concentration ratio of 744 suns on a two-axis tracking system and demonstrated a combined module efficiency of 41.2%, measured outdoors in Durham, NC. Taking into account the measured transmission of the optics gives an implied cell efficiency of 44.5%.

We examine thermally evaporated MoO x films as a full-area rear contact to crystalline p-type Si solar cells for efficient hole-selective contacts. Prior to front- and rear-metallization, the implied open-circuit voltage (iV oc) is evaluated to be 646 mV with implied fill factor (iFF) of 82.5% for the tunnel SiO x /MoO x rear contacted cell structure with the passivated emitter on the textured surface, showing it is possible to achieve an implied 1-sun efficiency of 20.8%. Numerical simulation reveals that the electron affinity (χ) of the MoO x material strongly influences the performance of the MoO x contacted p-Si cell. Simulated band diagrams show that the values in χ of the MoO x layer must be sufficiently high in order to lower junction recombination, indicating that the highest efficiency of 21.1% is achievable for a high χ of 5.6 eV of MoO x films and back surface recombination velocity of

The realization of 3, 4 and 6-junction solar cells for space applications requires a better understanding of the atmospheric effects for all earth-based, high-altitude, AM0 solar cell calibration methods. The residual atmosphere in these methods can have a profound influence on solar cell calibration. Using atmospheric modeling, and calibration methods used past, present, and future, the error introduced by the residual atmosphere is calculated for advanced multi-junction solar cells.

Utilizing a quaternary target to sputter Cu(In,Ga)Se 2 (CIGS) yields films which are dense, polycrystalline and highly oriented. Devices fabricated from these films exhibited efficiencies >10%. In this paper, we study the electrical characteristics of these devices, including current-voltage (I–V), external quantum efficiency (EQE) and sheet and contact resistances measured by the transfer length method, to improve their overall performance. The effect of edge termination by different techniques is reviewed to investigate perimeter effects and edge defects. It was found in these particular devices that mechanical scribing of device areas contributed to both edge and bulk shunt effects. We discuss the extent of these effects in the context of increasing device efficiency through the optimization of edge termination.

The response of InGaAs quantum well solar cells (QWSCs) to proton irradiation is presented. The QWSCs consisted of sixteen layers of 5 nm InGaAs QWs / 10 nm InAlGaAs barriers were embedded into the i-region of a 1.0 eV InAlGaAs solar cell, and the results were compared to a 1.0 eV InAlGaAs control solar cell. We report the results of 3 MeV proton irradiation using light J-V measurements of both of these devices. Due to the specific design of the structures in this study, QW devices were found to be less radiation tolerant than the control InAlGaAs devices. EQE measurements reveal that the diffusion length in the base layer of the junction has a significant affect on the loss in short circuit current of these devices. The quantum well structures showed a particular radiation robustness in comparison, largely due to the maintenance of the electric field at these fluences.

In this paper we present the first photovoltaic devices made from the promising quaternary InAlAsSb, grown lattice matched to InP by molecular beam epitaxy. Schottky barrier solar cells using semi-transparent contacts have been fabricated, characterized and simulated using a drift-diffusion model to extract information about the barrier height, minority carrier diffusion length and optical performance of devices fabricated from this material. We have compared the performance to analogous InAlAs devices, and present a wide range of optical and electrical characterization for the materials.

The Marines have increasing battery needs as fighting technology puts higher demands on the power they use. In an effort to offset this demand, the marines are investigating alternative energy sources, one being solar power. Mobile photovoltaics (PV) are a technology that can address these needs by leveraging flexible high efficiency III–V photovoltaic technology. The development of a lightweight, high efficiency solar panel to mount on, or stow in, a backpack and used to recharge a warfighters' battery was demonstrated. The panel consists of a 10 × 3 solar array of 20 cm2 epitaxial lift-off (ELO) Inverted Metamorphic (IMM) triple junction solar cells. In the first two phases of the project, single-junction GaAs cells with an efficiency of ∼ 21% under AM1.5 illumination were used. Several of these systems were outfitted during Limited Objective Experiments (LOE) in February 2012 and August 2012. In the third and most current phase of this project, panels of triple-junction cells with an expected efficiency of 28–30% under AM1.5 illumination. Data from these LOEs are presented here. Although the panels are expensive, they have been demonstrated as a viable technology.

In this paper, a complex analysis of the radiation response of GaAs solar cells with multi quantum wells (MQW) incorporated in the i-region of the device is presented. Electronic transport properties of the MQW i-region were assessed experimentally by the electron beam induced current (EBIC) technique. A 2-D EBIC diffusion model was applied to simulate EBIC line scans across device structure for different radiation doses. The results are interpreted using numerical modeling of the electrical field distribution at different radiation levels. Type conversion from n- to p-type was found in MQW i-region at displacement damage dose as low as low as ∼9.88E9 MeV/g. This is supported by experimental and simulated EBIC and electric field distribution results.

Experimental results on triple-junction solar cells irradiated by 3 MeV proton irradiation to very high damage levels are presented. The minority carrier transport properties were obtained through quantum efficiency and EBIC measurements and an analytical drift-diffusion solver was used in understanding the results for different degradation levels where multiple damage mechanisms are evident.

On board the Mars Pathfinder spacecraft, launched in December of 1996, was a small roving vehicle named Sojourner. On Sojourner was an experiment to determine the abrasive characteristics of the Martian surface, called the Wheel Abrasion Experiment (WAE). The experiment worked as follows: one of the wheels of the rover had a strip of black anodized aluminum bonded to the tread upon which was deposited five patches or samples of three different metals ranging in thickness from 200A to 1000A. A series of candidate metals (Ag, Al, Au, Cu, Ni, Pt and W) were tested for suitability for the WAE. Optical, corrosion, abrasion and adhesion criteria were used to select aluminum, platinum and nickel. The photovoltaic sensor or photodetector developed for the WAE is described. As the wheel was spun in the Martian soil, thin patches of metal were abraded away, exposing the black surface. Abrasion of those samples was detected by the change in specular reflectance of sunlight as measured by a photodetector mounted above the wheel. The degree of abrasion occurring on the samples is discussed, along with comparisons to the abrasion seen in Earth-based laboratory experiments using Martian soil. Conclusions are reached about the hardness, grain size and angularity of the Martian simulant soil particles and about precautions to be undertaken to avoid abrasion on moving parts exposed to Martian dust.

The high electrical conversion performance and radiation resistance of InP solar cells was discovered during the last decade. The combination of these two characteristics makes InP a very attractive material for space solar cells. To date, the best performance results for both homo-epitaxial and hetero-epitaxial InP solar cells were achieved using an n/p configuration. The p/n configuration is desirable for hetero-epitaxial growth on inexpensive, strong, lightweight group IV substrates such as Si and Ge. Furthermore, diffused-junction p/n cells demonstrated a higher radiation resistance than the n/p configuration cells; however, the testing of the p/n configuration was limited to lower quality cells as judged by their beginning-of-life (BOL) efficiencies. We have succeeded in developing p/n configuration homo-epitaxy InP solar cells with BOL efficiency values exceeding 17.6p tested under air mass zero (AM0) conditions. The high efficiency values obtained from our cells resulted from improved emitter performance, which was due to better control of the growth of Zn-doped p-type InP. © 1997 John Wiley & Sons, Ltd.

In this work solar cell anti-reflection coatings tuned to give a specific hue under solar illumination are investigated. We demonstrate that it is possible to form patterned coatings with large color contrast and high transmittance. We use colorimetric and thin film optics models to explore the relationship between the color and performance of bilayer anti-reflection coatings on crystalline Si, amorphous Si and GaAs. The colorimetric predictions were verified by measuring a series of coatings deposited on Si substrates. Finally, a patterned Si sample was produced using a simple, low-cost photolithography procedure to selectively etch only the top layer of a bilayer coating to demonstrate a high-performance anti-reflection coating with strong color contrast.

Reported is the characterization of irradiated InGaP2/GaAs/Ge multijunction (MJ) solar cells using the cathodoluminescence (CL) imaging/spectroscopy and electron beam induced current (EBIC) modes of scanning electron microscopy (SEM). These techniques were applied to verify the influence of radiation damage on the optoelectronic properties of each subcell in the monolithic triple junction structure and correlate them with the illuminated (AM0, 1 sun, 25°C) current-voltage (IV) and quantum efficiency (QE) characteristics.

The military's need to reduce both fuel and battery resupply is a real time requirement for increasing combat effectiveness and decreasing vulnerability. Mobile photovoltaics (PV) are a technology that can address these needs by leveraging emerging, flexible space photovoltaic technology. In this ongoing project, the development and production of a semi-rigid, lightweight, efficient solar blanket with the ability to mount on, or stow in, a backpack and recharge a warfighter's battery was undertaken. The blanket consists of a 10 × 3 solar array of 20 cm2 epitaxial lift-off (ELO) solar cells. In the first two phases of the project, single-junction cells with an efficiency of ~21% under AM1.5G illumination were used. Several of these systems were outfitted during Limited Objective Experiments (LOE) in February 2012 and August 2012. In the third and most current phase of this project, the panels will be made from IMM triple-junction cells with an efficiency of 28-30% under AM1.5G illumination. The results of laboratory tests of the new prototypes, as well as a test plan and expected outcome for a field experiment are presented here.

Triple junction GaInP/InGaAs/Ge solar cells were irradiated with 3 MeV protons to extreme fluences as high as 1015 p+/cm2. In this paper, IV and QE results will be presented and a model will be developed to explain the radiation behavior. A carrier removal damage mechanism is evident which actually aids in the radiation hardness of these devices.

Since the early beginnings of the space age in the 1950s, solar cells have been considered as the primary choice for long term electrical power generation of satellites and space systems. This is mainly due to their high power/mass ratio and the good scalability of solar modules according to the power requirements of a space mission. During the last decades, detailed solar cell material studies including the non-trivial interaction with high-energy space particles have led to continuous and significant improvements in device efficiency. This allowed the powering of advanced space systems like the International Space Station, rovers on the Martian surface as well as satellites which have helped to understand the universe and our planet. It is noteworthy that in addition to their success in space, these photovoltaic technologies have also broken ground for the application of photovoltaic systems in terrestrial systems. This paper discusses the development of space solar cells, gives insight into related experiments like the analysis of the interaction with space particles and provides an overview on challenges and requirements for future space missions.