This PDF file contains the front matter associated with SPIE Proceedings Volume 9865, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Cadmium telluride (CdTe) has been recognized as a promising photovoltaic material for thin-film solar cell applications due to its near optimum bandgap of ∼1.5 eV and high absorption coefficient. The energy gap is near optimum for a single-junction solar cell. The high absorption coefficient allows films as thin as 2.5 μm to absorb more than 98% of the above-bandgap radiation. Cells with efficiencies near 20% have been produced with poly-CdTe materials. This paper examines n/p heterostructure device architecture. The performance limitations related to doping concentrations, minority carrier lifetimes, absorber layer thickness, and surface recombination velocities at the back and front interfaces is assessed. Ultimately, the paper explores device architectures of poly- CdTe and crystalline CdTe to achieve performance comparable to gallium arsenide (GaAs).

The advent of ultrathin crystalline silicon (c-Si) solar cells has significantly reduced the cost of silicon solar cells by consuming less material. However, the very small thickness of ultrathin solar cells poses a challenge to the absorption of sufficient light to provide efficiency that is competitive to commercial solar cells. Light trapping mechanisms utilizing nanostructure technologies have been utilized to alleviate this problem. Unfortunately, a significant portion of light is still being lost even before entering the solar cells because of reflection. Different kinds of nanostructures have been employed to reduce reflection from solar cells, but reflection losses still prevail. In an effort to reduce reflection loss, we have used an array of modified nanostructures based cones or pyramids with curved sides, which matches the refractive index of air to that of silicon. Moreover, use of these modified nano-pyramids provides a quintic (fifth power) gradient index layer between air and silicon, which significantly reduces reflection. The solar cells made of such nanostructures not only significantly increase conversion efficiency at reduced usage of crystalline silicon material (e.g. thinner), but it also helps to make the c-Si based solar cell flexible. Design and optimization of flexible c-Si solar cell is presented in the paper.

Thin-film III-V materials are an attractive candidate material for solar energy harvesting devices capable of supplying portable and mobile power in both terrestrial and space environments. Nanostructured quantum well and quantum dot solar cells are being widely investigated as a means of extending infrared absorption and enhancing photovoltaic device performance. In this paper, we will review recent progress on realizing high-voltage InGaAs/GaAs quantum well solar cells that operate at or near the radiative limit of performance. These high-voltage nanostructured device designs provide a pathway to enhance the performance of existing device technologies, and can also be leveraged for next-generation solar cells.

The use of Graphics Processing Unit (GPU) for computational work has revolutionized how complex electromagnetic problems are solved. Complex problems which required supercomputers in the past for analysis can now be tackled and solved using personal computers by channeling the computational work towards GPUs instead of the traditional computer Central Processing Unit (CPU). Finite-Difference Time-Domain (FDTD) analysis, which is a computationally expensive method of solving electromagnetic problems is highly parallel in nature and can be readily executed in a GPU. We have developed an algorithm for three dimensional FDTD analysis of optical devices with micro and nano-structures using Compute Unified Device Architecture (CUDA). The developed algorithm exploits the benefits of multiple cores of GPU chips and boosts the speed of simulation without sacrificing its accuracy. We achieved a 25-fold speed up of simulation using CUDA compared to MATLAB code in CPU.

Li₄Ti₅O₁₂ (LTO) is one of the most promising anode materials for lithium-ion batteries (LIBs) due to its excellent cyclability and extraordinary structure stability during lithium-ion intercalation and deintercalation. However, LTO suffers from the low electronic conductivity and low theoretical capacity, which results in poor rate capability and low energy density. The present work reviews the latest achievement on improving both energy and power density of LTO based anode materials for LIBs. In addition, our recent results on electrostatic spray deposition (ESD) derived LTO electrode is also discussed. Electrochemical test shows that the resulting LTO has a large specific capacity of 293 mAh g^-1 under a current density of 0.15 A g^-1 and high rate capacity of 73 mAh g^-1 under 3 A g^-1. As compared with commercial LTO nano-particle electrode, the improved electrochemical performance of ESD-LTO could be attributed to the structure advantages generate from ESD which could lead to reduced diffusion length for lithium ions and electrons.

Conventional Electrochemical double-layer capacitors (EDLCs) are well suited as power devices that can provide large bursts of energy in short time periods. However, their relatively inferior energy densities as compared to their secondary battery counterparts limit their application in devices that require simultaneous supply of both high energy and high power. In the wake of addressing this shortcoming of EDLCs, the concept of hybridization of lithium-ion batteries (LIBs) and EDLCs has attracted significant scientific interest in recent years. Such a device, generally referred to as the "lithium-ion capacitor" typically utilizes a lithium intercalating electrode along with a fast charging capacitor electrode. Herein we have constructed a lithium hybrid electrochemical capacitor comprising a Li₄Ti₅O₁₂-TiO₂ (LTO-TiO₂) anode and a reduced graphene oxide and carbon nanotube (rGO-CNT) composite cathode using electrostatic spray deposition (ESD). The electrodes were characterized using scanning electron microscopy and X-ray diffraction studies. Cyclic voltammetry and galvanostatic charge-discharge measurements were carried out to evaluate the electrochemical performance of the individual electrodes and the full hybrid cells.

Since the report of high dielectric value was published for the calcium copper titanate of the stoichiometry CaCu₃Ti₄O₁₂ (CCTO), several of its analogs such as Yittrium copper titanate Y_2/3Cu₃Ti₄O₁₂ (YCTO), Pr_2/3Cu₃Ti₄O₁₂ (PCTO) and several other compounds have been studied extensively. Most of these materials have demonstrated very high dielectric constants. However, the roadblock is their low resistivity. To overcome this problem, several approaches have been considered, including doping and substitution. In order to solve this problem, we have synthesized the stoichiometric composition and used low temperature processing to grow grains of La_2/3Cu₃Ti₄O₁₂ (LCTO) stoichiometric compound. LCTO with excess copper oxide was also prepared to determine its effect on the morphology and dielectric constant of the stoichiometric LCTO compound. In spite of the low melting point of copper oxide, we observed that excess copper oxide did not show any faster grain growth. Also, the dielectric constant of LCTO was lower than CCTO and unlike CCTO, LCTO showed significant changes as the function of frequency. The measured resistivity was slightly higher than CCTO.

Reserve power sources are used extensively in munitions and other devices such as emergency devices or remote sensors that have to be powered only once and for a relatively short duration. Current chemical reserve power sources, including thermal batteries and liquid reserve batteries require sometimes in excess of 100 msec to become fully activated. In many applications, however, electrical energy is required in a few msec following the launch event. In such applications, other power sources have to be provided to provide power until the reserve battery is fully activated. The amount of electrical energy that is required by most munitions before chemical reserve batteries are fully activated is generally small and can be provided by properly designed piezoelectric-based energy harvesting devices. In this paper the development of a hybrid reserve power source obtained by the integration of a piezoelectric-based energy harvesting device with a reserve battery that can provide power almost instantaneously upon munitions firing or other similar events is being reported. A review of the state of the art in piezoelectric-based electrical energy harvesting methods and devices and their charge collection electronics for use in the developed hybrid power sources is also provided together with the results of testing of the piezoelectric component of the power source and its electronic safety and charge collection electronics.

This paper describes how a solar power source can enable in-space 3D printing without requiring conversion to electric power and back. A design for an in-space 3D printer is presented, with a particular focus on the power generation system. Then, key benefits are presented and evaluated. Specifically, the approach facilitates the design of a spacecraft that can be built, launched, and operated at very low cost levels. The proposed approach also facilitates easy configuration of the amount of energy that is supplied. Finally, it facilitates easier disposal by removing the heavy metals and radioactive materials required for a nuclear-power solution.

The power usage of CubeSat's onboard systems has increased with the complexity of the systems included. This paper presents a deployment system design which creates a plane of solar panels to collect energy. This allows more panels to be in direct normal sunlight at any given point (in conjunction with the onboard attitude determination and control system), facilitating increased power generation. The deployable system is comprised of a printed circuit board (holding the solar cells) which is attached to an aluminum hinge. The efficacy of this approach for power generation and its simplicity, as compared to other prospective approaches, are assessed herein.

This paper presents work on the development of an Origami-style solar panel technology. This approach increases a satellite’s solar array’s power generation surface area, given constrained space and mass. The same deployable structure (used for the solar panels) can also house a phased array on the reverse side. For a proposed Mars demonstration mission, this array is used for communications and microwave wireless power transmission.

The design of the solution is presented in detail, including a discussion of the pre-deployment configuration, the deployment process, and the final configuration. The panels, prior to deployment, are folded around the square base of the spacecraft, covering all four of its sides. To deploy them, a slight circular motion can be introduced to use centrifugal force to cause each side to fold out from the side of the satellite. A simple hinge mechanism is used to interconnect the panels and inflatable tubes or wire that is designed to stiffen in a straightened orientation when electrified, are used to move the panels into their final position and provide rigidity.

The efficacy of the proposed technology is considered in the context of the Martian mission. This demonstrates its mass and volume efficiency as well as the utility of the approach for enabling the mission. A qualitative analysis of the benefits and drawbacks of the approach is presented. A discussion of the technology’s overall impact on mission design is presented, before concluding with a discussion of the next steps for the research.

This paper presents work on the development of Origami-style solar panels and their adaption and efficacy for use in Earth orbit. It focuses on the enabling capability of this technology for the generation and transmission of power. The proposed approach provides increased collection (solar panel) and transmission (microwave radiation) surface area, as compared to other systems with similar mass and volume. An overview of the system is presented, including its pre-deployment configuration, the deployment process and its final configuration. Its utility for wireless power transmission mission is then considered. An economic discussion is then presented to consider how the mass and volume efficiencies provided enable the system to approach target willingness-to-pay values that were presented and considered in prior work.

A key consideration regarding the use of wireless power transfer in Earth orbit is the reliability of the technology. This has several different areas of consideration. It must reliably supply power to its customers (or they would have to have local generation capabilities sufficient for their needs, defeating the benefit of this system). It must also be shown to reliably supply power only to designated locations (and not inadvertently or otherwise beam power at other locations). The effect of the system design (including the Origami structure and deployment / rigidity mechanisms) is considered to assess whether the use of this technology may impair either of these key mission/safety-critical goals. This analysis is presented and a discussion of mitigation techniques to several prospective problems is presented, before concluding with a discussion of future work.

The use of a wireless charging system for small, unmanned aircraft system applications is useful for both military and commercial consumers. An efficient way to keep the aircraft’s batteries charged without interrupting flight would be highly marketable. While the general concepts behind highly resonant wireless power transfer are discussed in a few publications, the details behind the system designs are not available even in academic journals, especially in relation to avionics. Combining a highly resonant charging system with a solar panel charging system can produce enough power to extend the flight time of a small, unmanned aircraft system without interruption. This paper provides an overview of a few of the wireless-charging technologies currently available and outlines a preliminary design for an aircraft-mounted battery charging system.

This paper reports on the creation of nano-manufactured catalyst for the production of hydrogen fuel via the solar thermal water splitting process. The solar thermal water splitting process is considered the holy grail of green energy as the process produces zero carbon emissions. This is made possible by focusing solar energy as the heating source, while the only reactant consumed in the process is water. For this work we are investigating the reaction dynamics of cobalt ferrite catalyst supported on an aluminum oxide support. Solar thermal water splitting occurs in two steps: reduction and oxidation reactions. The reduction step occurs by heating the catalyst, which produces oxygen and converts the cobalt ferrite/aluminum oxide to metal aluminates. The oxidation step begins by flowing water over the newly created metal aluminates. The metal aluminates react with the oxygen creating the original cobalt ferrite/aluminum oxide catalyst as well as hydrogen gas. The catalyst created for this work was done utilizing an electrospinning technique. In a one-step process the aluminum oxide support material can be incorporated with cobalt ferrite catalyst into a single nanofiber. With this technique nanofiber catalyst can be created with diameters ranging from 20 to 80 nm. Nanostructured materials allow for large surface areas >50 m²/g and surface area to volume ratios >9e7/m. The large surface area creates the opportunity for more active sites where the reactions can occur. An increase in reactivity has the potential to move fuel production rate for solar thermal water splitting closer to large-scale commercialization.

Vibration-based energy harvesting has been widely investigated to as a means to generate low levels of electrical energy for applications such as wireless sensor networks. However, for optimal performance it is necessary to ensure that resonant frequencies of the device match the ambient vibration frequencies for maximum energy harvested. Here a novel resonant frequency tuning approach is proposed by applying a bias voltage to a pre-stretched electroactive polymer (EAP) membrane, such that the resulting changes in membrane tension can tune the device to match the environmental vibration source. First, a material model which accounts for the change in properties due to the pre-stretch of a VHB 4910 EAP membrane is presented. The effect of the bias voltage on the EAP membrane, which induces an electrostatic pressure and corresponding reduction in membrane thickness, are then determined. The FEM results from ANSYS agree well with an analytical hyperelastic model of the activation response of the EAP membrane. Lastly, through a mass-loaded circular membrane vibration model, the effective resonant frequency of the energy harvester can be determined as a function of changes in membrane tension due to the applied bias voltage. In the case of an EAP membrane, pre-stretch contributes to the pre-stretch stiffness of the system while the applied bias voltage contributes to a change in bias voltage stiffness of the membrane. Preliminary experiments verified the resonant frequencies corresponding to the bias voltages predicted from the appropriate models. The proposed bias voltage tuning approach for the EAP membrane may provide a novel tuning strategy to enable energy harvesting from various ambient vibration sources in various application environments.

In this paper a bistable composite cantilever beam comprising asymmetric laminates is studied for vibration energy harvesting applications. An additional magnetic bistability is introduced to the harvesting system to lower the level of excitation that triggers the snap-through for the cantilever from one stable state to another, while retaining the favorable broadband performance. In order to achieve the, the cantilever beam is fitted with a permanent magnet at its tip that is oriented so that there is magnetic repulsion with a stationary magnet. The system performance can be adjusted by varying the separation between the magnets. Experimental results reveal that the use of magnetic bistability enhances broadband performance and improves the output power within a certain level of drive level and magnet separation. The load-deflection characteristic of the bistable beam is experimentally determined, and is subsequently used to model the system by a reduced single-degree-of-freedom (SDOF) system having the form of the Duffing equation for a double-well potential system. The dynamics of the beam are investigated using bifurcation diagrams and shows that the qualitative behavior given by the experimentally measured response is predicted well by the simple SDOF model.

In this work, development of a broadband nonlinear electromagnetic energy harvester is described. The energy harvester consists of a casing housing stationary magnets, a levitated magnet, oblique mechanical springs, and a coil. Magnetic and oblique springs introduce nonlinear behavior into the energy harvester. A mathematical model of the proposed device is developed and validated. The results show good agreement between model and experiment. The significance of adding oblique mechanical springs to the energy harvester design is investigated using the model simulation. The results from the model suggest that adding oblique springs to the energy harvester will improve the performance and increase the frequency bandwidth and amplitude response of the energy harvester.