This PDF file contains the front matter associated with SPIE Proceedings Volume 8035, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The Energy crisis happens to be one of the greatest challenges we are facing today. In this view, much effort has been made in developing new, cost effective, environmentally friendly energy conversion and storage devices. The performance of such devices is fundamentally related to material properties. Hence, innovative materials engineering is important in solving the energy crisis problem. One such innovation in materials engineering is porous materials for energy storage. Porous electrode materials for lithium-ion batteries (LIBs) offer a high degree of electrolyte-electrode wettability, thus enhancing the electrochemical activity within the material. Among the porous materials, mesoporous materials draw special attention, owing to shorter diffusion lengths for Li⁺ and electronic movement. Nanostructured mesoporous materials also offer better packing density compared to their nanostructured counterparts such as nanopowders, nanowires, nanotubes etc., thus opening a window for developing electrode materials with high volumetric energy densities. This would directly translate into a scenario of building batteries which are much lighter than today's commercial LIBs. In this article, the authors present a simple, soft template approach for preparing both cathode and anode materials with high packing density for LIBs. The impact of porosity on the electrochemical storage performance is highlighted.

The threats of climate change and the issues of secure energy supply are among the fundamental challenges of the 21^stcentury that push humanity to adopt a sustainable development and to favour the use of renewable sources of energy. In addition to their historical use, LIBs seem on the road to power the next "Zero Emission" vehicles or could be used to assist the integration of renewable energy sources both on- and off-the-grid. Consequently, production of LIBs is expected to keep on growing. However LIBs are nearly exclusively based on inorganic compounds, non-renewable and energy-greedy materials. Thus in parallel with regular research on inorganic-based LIBs, we have recently proposed to probe an alternative pathway by searching for redox-active organic materials, easier to discard while possibly derived from biomass resources. As solid-state electrochemistry of organics is not that well documented, our current approach consists in a global survey of selected organic structures in order to grasp relevant parameters that affect the redox potential, the stability upon cycling and so on. In this report, we extend our current database of redox-active organic structures by evaluating vs. Li bulky pyrazine-based structures and dilithium polyporate as a supplementary specimen of p-benzoquinone derivatives.

Intermetallic compounds of tin and first-row transition metals have been considered as potential anode materials for Li-ion batteries that could improve the performance of pure tin. Particularly, the solids dispersed at the nano scale provide interesting behavior. Thus CoSn, FeSn₂ and CoSn₃ nanocrystalline samples have been obtained at low temperatures. As compared with micrometric particles of CoSn, significantly higher reversible capacities are found for nanocrystalline CoSn. For nanocrystalline CoSn₃ maximum reversible capacities of 690 mAh g^-1 were observed in lithium test cells. Nanocrystalline products in the series CoSn₂-FeSn₂ could be prepared by chemical reduction in polyol solvents using a "one-pot" method. Superparamagnetic nanocrystalline FeSn₂ delivers reversible capacities of ca. 600 mAhg^-1 by the formation of Li_xSn phases and superparamagnetic iron nanoparticles. A comparison between the properties of nano- FeSn₂ and micro-FeSn₂ shows a significantly better electrochemical behavior and electrode stability for the nanocrystalline material. For Fe_1-xCo_xSn₂ solid solutions with x= 0.25, 0.3, 0.5, 0.6 and 0.8, particle diameters of about 20 nm and different morphologies were obtained. The substitution of iron by cobalt induces a contraction of the unit cell volume and the hyperfine parameters of the ⁵⁷Fe Mössbauer spectra reveal a superparamagnetic behavior. The intermediate compositions exhibit better electrochemical performance than the limit compositions CoSn₂ and FeSn₂. To improve the performance of CoSn_x intermetallics, composites in which the nanocrystalline intermetallic material is embedded in an amorphous layer based on the polyacrylonitrile (PAN) polymer were used. The PAN shell contributes to stabilize the intermetallic phases upon electrochemical cycling.

The projected doubling of world energy consumption in the next fifty years requires certain measures to meet this demand. The ideal energy provider is reliable, efficient, with low emissions source - wind, solar, etc. The low carbon footprint of renewables is an added benefit, which makes them especially attractive during this era of environmental consciousness. Unfortunately, the intermittent nature of energy from these renewables is not suitable for the commercial and residential grid application, unless the power delivery is 24/7, with minimum fluctuation. This requires intervention of efficient electrical energy storage technology to make power generation from renewable practical. The progress to higher energy and power density especially for battery technology will push material to the edge of stability and yet these materials must be rendered safe, stable and with reliable operation throughout their long life. A major challenge for chemical energy storage is developing the ability to store more energy while maintaining stable electrode-electrolyte interface. A structural transformation occurs during charge-discharge cycle, accompanied by a volume change, degrading the microstructure over-time. The need to mitigate this volume and structural change accompanying charge-discharge cycle necessitates going to nanostructured and multifunctional materials that have the potential of dramatically enhancing the energy density and power density.

Solid electrolytes with high lithium conductivity may serve as useful components for enabling novel lithium ion battery system design. This work demonstrates the integration of lithium lanthanum titanate (Li_0.29La_0.57TiO₃) into a battery system separating electrodes based on liquid electrolyte. Specifically, binder free electrodes based on graphite and LiCoO₂ were tested against lithium metal in liquid electrolyte with an intermediate solid electrolyte. The system was characterized by cyclic voltammetry, and electrochemical impedance.

Demand for safe lithium-ion batteries (LiBs) for varied applications such as portable electronics, transportation, space technologies have lead to significant emphasis on development of new materials and concepts. This talk will focus on prospective soft matter electrolytes which have been synthesized from liquids (e.g. molecular solvents, ionic liquids) as the starting medium. Although conversion from liquid to the soft matter state constrains intrinsic spatial and temporal disorder of the liquid solvent, the materials properties in the soft matter state however, are far more interesting and beneficial than the liquid state. Assembly of various soft matter electrolytes in cells containing in-house synthesized nanostructured (nanotubes/sheets, mesoporous) non-carbonaceous anode and cathode materials show improved battery performance compared to the liquid electrolytes. The talk will also discuss mechanistics of ion transport in the electrolytes.

Fabrication of all-solid-state Li battery has been strongly required to overcome safety issue of present Li battery. One of promising structures for ceramics electrolyte in all-solid-state battery is 2-layered structure composed of 3 dimensionally ordered macroporous layer (3DOM) and dense layer. In this study, we prepared Li_0.35La_0.55TiO₃ (LLT) ceramics electrolyte with the 2-layered structure by suspension filtration method. Thicknesses of the dense and the porous layers were about 23 and 105 μm, respectively. The porous layer involved uniform pores of 1.8 μm in diameter. An electrochemical property of LiMn₂O₄ / 2-layered LLT composite, prepared by impregnation of precursor sol for LiMn₂O₄ into the pores followed by calcination, was tested. A rechargeable behavior of the composite electrode was clearly observed. From this result, it can be said that the composite can work as rechargeable battery. The discharge capacity of the composite was 27 mA h g^-1.

Based on a four-probe electrical measurement, we have developed a Battery Internal Temperature Sensor. BITS, unlike a surface-mounted thermocouple, provides a direct measure of the internal temperature. We have demonstrate in several different rechargeable lithium-ion cells ranging in capacity from 2- to 50-Ah, the existence of an intrinsic relationship between a cell's internal temperature and a readily measurable electrical parameter. Today, container rupture and fire are the most detrimental consequences of thermal runaway in rechargeable Li-ion cells. Although storing or operating Li-ion cells in high-temperature environments is not advisable, high internal temperature has a greater potential to initiate catastrophic events. Measuring the environmental temperature at any proximity to the surface of the cell is insufficient to know or intervene with fast-rising internal heat. For example, monitoring internal temperature in real time has direct relevance to the thermal runaway caused by external and internal short circuits that may have no relevance to the external temperature. Yet, until now, there has been no simple technique to monitor the internal temperature of a single cell or multiple cells in Li-ion batteries. BITS, developed by the Johns Hopkins University Applied Physics Laboratory, is a miniature instrument, with demonstrated capability to measure and report internal temperature of individual cells in a multi-cell battery pack at the rate of 200-ms/cell.

Novel high power density cathode and anode materials for thin film battery are reported here. The layered Li(NiMnCo)_1/3O₂ film fabricated by sputtering shows a capacity as high as 190 mAhg^-1 in the range of 3-4.9 V and a capacity retention of 90% after 100 cycles. Novel oxide anode is synthesized by sputtering at room temperature, delivering a special capacity as high as 700 mAhg^-1 and a good capacity retention. The thin film battery using these materials shows a good cyclability and high rate ability.

The present study has concerned on some electrochemical reactions in non-aqueous electrolytes containing 1,3- substituted imidazolium cations, having unique planar(aromatic) structures and properties such as forming hydrogen bond, which are expected to provide pseudo-capacitance in the application for electrochemical capacitor systems. The pseudo-capacitance of ruthenium oxide can be obtained in these electrolytes. The composite electrode of ruthenium oxide nano-particles dispersed with large surface area activated carbon support provides capacitance available in practical system. The tuning of capacitance by molecular design of imidazolium cation is also possible. The intercalation of imidazolium ion into interlayer space of graphite is promoted by the well-defined crystalline graphite and appropriate solvent such as acetonitrile. Such dependence of solvent species for pseudo-capacitive reactions is somewhat in relation to the solvation status of imidazolium cation.

All solid electrochemical capacitors (EC) have been demonstrated using proton conducting silicotungstic acid (SiWA) and poly(vinyl alcohol) (PVA) based polymer electrolytes. Graphite electrodes were utilized for electrochemical double layer capacitors (EDLC), while RuO₂ electrodes were employed as pseudocapacitive electrodes. Both solid EDLC and pseudocapacitors exhibited very high charge/discharge rate capability. Especially for solid EDLC, a charge/discharge rate of 25 V/s and a 10 ms time constant ("factor of merit") were obtained. The rate capability of the solid EC is attributable to thin film thickness, good proton conductivity of the polymer electrolyte, and intimate contact between electrode and electrolyte. These results demonstrate promise of polymer electrolytes as enablers of high rate and high performance solid EC devices.

Synthesis of poly (3,4-ethylenedioxythiophene)/V₂O₅ (PEDOT/V₂O₅) by in-situ oxidation of monomer (3,4-ethylenedioxythiophene) into crystalline nanostrip V₂O₅ using microwave hydrothermal technique is reported. The synthesized compounds are characterized by powder XRD, IR spectra, four probe conductivity and thermal analysis (TGA/DTA).The interlayer spacing of V₂O₅ upon intercalation of the polymer expands from 4.3 to 14 Å as observed in powder X-ray diffraction by exfoliation and restacking of the layers. The morphological changes of the compounds are further investigated using FE-SEM. The electrochemical properties are studied by CV and galvanostatic charge-discharge cycling. The initial SC of PEDOT/V₂O₅ (237 F g^-1) is higher than that of either pristine V₂O₅ or PEDOT indicating the synergic effect of the nanocomposites.

Development of miniaturized electronic systems has stimulated the demand for miniaturized power sources that can be integrated into such systems. Among the different micro power sources micro electrochemical energy storage and conversion devices are particularly attractive because of their high efficiency and relatively high energy density. Electrochemical micro-capacitors or micro-supercapacitors offer higher power density compared to micro-batteries and micro-fuel cells. In this paper, development of on-chip micro-supercapacitors based on interdigitated C-MEMS electrode microarrays is introduced. C-MEMS electrodes are employed both as electrode material for electric double layer capacitor (EDLC) or as three dimensional (3D) current collectors of EDLC or pseudo-capacitive materials. Recent advancements in fabrication methods of C-MEMS based micro-supercapacitors are discussed and electrochemical properties of C-MEMS electrodes and it composites are reviewed.

Despite a recent focus in developing energy harvesting technologies from a variety of sources, no work has been done in capturing blackbody radiation from the surrounding environment. This work aims to extend semiconductor-based solar energy harvesting into the infrared (IR) range of the electromagnetic spectrum so as to take advantage of this blackbody radiation. We have investigated the use of mercury cadmium telluride (HgCdTe) p-n junction devices in order to achieve this goal. A device simulation tool, named MCT-SIM, was developed in order to obtain the photovoltaic characteristics of P+/N-/N+ structures exposed to blackbody radiation and an applied voltage bias. An IR energy harvesting system was developed and evaluated with the use of this tool. When this system is exposed to blackbody radiation at a temperature of 300 K, it generates a series-limited photocurrent of 28.115 mA/cm²; this value can be increased through further optimization. Subsequent analysis shows that performance limitations of this system are due to the presence of a large intrinsic carrier concentration and associated Auger effects within the absorbing layer of HgCdTe.

We report the substantial increase in power efficiency in InAs/GaAs quantum dot (QD) solar cells due to n-doping of the inter-dot space in p⁺-δ-n⁺ structures and investigate the physical mechanisms that provide this significant improvement. We have compared the GaAs reference cell to undoped, n-doped and p-doped QD solar cell structures and found that the short circuit current, J_SC, of the undoped QD solar cell is comparable to that of the GaAs reference cell. On the other hand, while p-doping deteriorates the device performance, n-doping significantly increases J_SC without degradation of the open circuit voltage, V_OC. The photovoltaic device, n-doped to provide approximately six electrons per dot, demonstrates 60% increase in J_SC, from 15.07 mA/cm² to 24.30 mA/cm². Strong increase in the photoresponse and J_SC of the IR portion of the solar spectrum has been observed for the n-doped structures. From the photoluminescence data, the electron capture noticeably dominates over hole capture leading to an accumulation of electrons in the dots. We have observed that QDs with built-in charge (Q-BIC) enhances harvesting of IR energy, suppresses the fast electron capture process, and stabilizes the open circuit voltage. All of these factors lead to a significant improvement of the cell efficiency.

Small metal particles are investigated as scattering centers to increase the effective optical thickness of thin-film solar cells. The particular type of particles used is known as "metal-black", well known as an IR absorber for bolometric infrared detectors. Gold-black was deposited on commercial thin-film solar cells using a thermal evaporator in nitrogen ambient at pressures of ~1 Torr. A broad range of length scales, as revealed by scanning electron microscope images gives rise to effective scattering over a range of wavelengths across the solar spectrum. The solar cell efficiency was determined both as a function of wavelength and for a solar spectrum produced by a Xe lamp and appropriate filters. Up to 20% increase in short-circuit photo-current, and a 5% increase in efficiency at the maximum power point, were observed.

A reversible solid oxide fuel cell (RSOFC) provides the dual function of performing energy storage and power generation, all in one unit. When functioning as an energy storage device, the RSOFC acts like an electrolyzer in water electrolysis mode; whereby the electric energy is stored as (electrolyzed) hydrogen and oxygen gases. While hydrogen is useful as a transportation fuel and in other industrial applications, the RSOFC also acts as a fuel cell in power generation mode to produce electricity when needed. The RSOFC would be a competitive technology in the upcoming hydrogen economy on the basis of its low cost, simple structure, and high efficiency. This paper reports on the design and manufacturing of its membrane electrode assembly using commercially available materials. Also reported are the resulting performance, both in electrolysis and fuel cell modes, as a function of its operating parameters such as temperature and current density. We found that the RSOFC performance improved with increasing temperature and its fuel cell mode had a better performance than its electrolysis mode due to a limited humidity inlet causing concentration polarization.

Enzymatic biofuel cells (EBFCs) that oxidize biological fuels using enzyme-modified electrodes are considered a promising candidate for implantable power sources. However, there are still challenges to overcome before biofuel cells become competitive in any practical applications. Currently, the short lifespan of the catalytic enzymes and poor power density are the most critical issues in developing EBFCs. In this paper, we will review the recent development of biofuel cells and highlight the progress in Carbon-microelectromechanical system (C-MEMS) based micro biofuel cells by both computational modeling and experimental work. Also, our effort on utilizing a covalent immobilization technique for the attachment of enzymes onto the substrate which is expected to increase the enzyme loading efficiency and the power density of devices is discussed in this paper.

Conventionally, piezoelectric materials are used to harvest the mechanical energy. However, we show that in the environment where both mechanical and magnetic field energy are available magnetoelectric mechanism can provide higher output power. A laminate structure with morphology metglas / PZT / brass / PZT / metglas was designed and tested under the conditions of (i) vibrations only and (ii) vibration and magnetic field together (dual mode). The results for both hard and soft PZT structure demonstrate that dual mode lead to improved output power. These results are quite important for applications such as powering of sensors used in health monitoring of electromagnetic motors.

As harvesting energy methods have been developed for perpetual powering of electronics, power management, storage control and regulation electronics need to match the voltage and current characteristics of the different harvested energy levels. Besides being able to harvest relatively small and large amounts of energy efficiently, the harvesting electronics must also consume very low power. The harvesting electronics storage and output must also match the power output demand. In our work to harvest solar and thermal energy, we have evaluated what electronics would be necessary to efficiently harvest, store and regulate these diverse energy sources. Expected energy levels from thermal harvest and from solar harvest will be discussed in relation to the harvesting electronics. Electronics to efficiently harvest thermal and solar energy at low and high energy levels will be discussed. During our development of thermal and solar energy harvesting, a demonstration vehicle was developed to further understand the needs of harvesting. We will detail the energy harvest demonstration vehicle learning and the details of the final integrated harvesting-storage-regulator structure with electronics.

The efficient conversion of waste thermal energy into electrical energy is of considerable interest due to the huge sources of low-grade thermal energy available in technologically advanced societies. Our group at the Oak Ridge National Laboratory (ORNL) is developing a new type of high efficiency thermal waste heat energy converter that can be used to actively cool electronic devices, concentrated photovoltaic solar cells, computers and large waste heat producing systems, while generating electricity that can be used to power remote monitoring sensor systems, or recycled to provide electrical power. The energy harvester is a temperature cycled pyroelectric thermal-to-electrical energy harvester that can be used to generate electrical energy from thermal waste streams with temperature gradients of only a few degrees. The approach uses a resonantly driven pyroelectric capacitive bimorph cantilever structure that potentially has energy conversion efficiencies several times those of any previously demonstrated pyroelectric or thermoelectric thermal energy harvesters. The goals of this effort are to demonstrate the feasibility of fabricating high conversion efficiency MEMS based pyroelectric energy converters that can be fabricated into scalable arrays using well known microscale fabrication techniques and materials. These fabrication efforts are supported by detailed modeling studies of the pyroelectric energy converter structures to demonstrate the energy conversion efficiencies and electrical energy generation capabilities of these energy converters. This paper reports on the modeling, fabrication and testing of test structures and single element devices that demonstrate the potential of this technology for the development of high efficiency thermal-to-electrical energy harvesters.

Microbial Fuel cells (MFCs) are batteries driven by bacteria. MFCs have the potential of powering small sensors in remote areas and disposing organic waste safely by harvesting the energy stored in the waste products. From previous research in this field, a few important factors for MFC performance have been identified. These include the internal resistance of MFC, the surface area of anode with catalyst for the biofilm development, the type and number of bacteria, and the abundance of nutritional supplies to the bacteria. This paper describes the design of a novel single chamber MFC (SMFC) with carbon electrodes. Experiments were conducted to establish the relationship between each parameter and the power production. It is shown here that this SCMFC can generate electrical current without the use of PEM membranes or additives; the maximum voltage of around 411 mV can be achieved at the room temperature. These results also measured a various parameters such as pH, dissolved oxygen and solution conductivity during the operation of SMFC. Finally, experiment was conducted to evaluate an innovative concept of using MFC for corrosion protection.

Ultra-high, broadband transmittance through coated glass windows is demonstrated over a wide range of incident angles. Near perfect 100% transmittance through a glass substrate has been achieved over select spectral bands, and the average transmittance increased to over 97% for photons incident between 0° and 75° with wavelengths between 400 nm and 1600 nm. The measured improvements in transmittance result from coating the windows with a new class of materials consisting of porous SiO₂ nanorods.

Thin film superlattice (SL) based thermoelectric (TE) devices offer the potential for improved efficiency and high heat flux cooling over conventional bulk materials. We have demonstrated external cooling of 55K and heat pumping capacity of 128 W/cm² in single couples and temperature differences as high as 102K in three stage cascade structures. The high heat flux pumping capacity of these in thin film devices are also attractive for hot-spot cooling in electronics. These same materials have also been successfully employed in power generation and energy harvesting applications. In this presentation, we will discuss recent RTI advances in Bi₂Te₃-based thin-film SL (TFSL) devices for cooling and energy harvesting applications.

A new method for characterizing thermoelectric materials is described. By using non-contact radiative heat flow, parasitic heat flows that will otherwise cause error can be reduced to negligible levels. Having precise knowledge of the steady-state heat flows under conditions with low parasitics allows for accurate determination of thermal conductivity as well as bulk and thin-film device performance metrics including coefficient of performance. Measurement of thermal conductivity of bulk (Bi,Sb)₂(Se,Te)₃ alloy sample was 1.49 Watt/meter-K.

The past decade has seen significant advances in distributed sensors and sensor networks. Many of these advances have been driven by programs that support national intelligence and security interests. With these advances have come an increased interest in energy harvesting to provide continuous power sources to replace or augment existing power storage systems. The use of waste heat is an attractive source of energy for many applications where μW-mW power is required. The implementation of a thermoelectric power conversion system requires several basic elements in addition to an assumed heat source. These elements are: 1) a thermoelectric device, 2) a heat sink, 3) voltage regulation, 4) an energy storage device and 5) load management. The design and optimization of the system (and each element within the system) is highly dependent on the thermal boundary conditions and the power load. This presentation will review the key performance factors and considerations required to optimize each element of the system to achieve the required I-V characteristics for output power.

The fabrication of stoichiometric (Bi_xSb_{1- x})₂Te₃ thermoelectric films comprised of nanostructured building blocks were fabricated using solution processing compatible methods. Nanostructured films of n-type Bi₂Te₃, (Bi_0.75Sb_0.25)₂Te₃, and (Bi_0.50Sb_0.50)₂Te₃ and p-type (Bi_0.25Sb_0.75)₂Te₃ and Sb₂Te₃ TE thermoelectric materials were fabricated using intercalated and exfoliated stoichiometric bulk materials. Fine control was exerted over the composition and reaction to maintain the purity and effectiveness of the nanostructured alloys composition of the materials as they were deposited, pressed, and annealed in a Te-rich ambient. A Seebeck coefficient was measured to be -235 μVK^-1 for the n-type Bi₂Te₃ films, and 262 μVK^-1 for the p-type (Bi_0.25S_0.75)₂Te₃ films. Although limited by high resistance, due to cracking of the films, ZT was estimated to be between 0.8 and 1.69 for the n-type films and an order of magnitude lower for the p-type films.

Novel designs are presented for piezoelectric-based energy-harvesting power sources that are attached to mortar tubes to harvest energy from the firing impulse. The power sources generate electrical energy by storing mechanical potential energy in spring elements during the firing. The mass-spring unit of the power source begins to vibrate after firing, thereby applying a cyclic force to a set of piezoelectric elements to which it is attached. The mechanical energy of vibration is thereby converted to electrical energy over a relatively long period of time and stored in electrical energy storage elements such as capacitors. The power sources are shown to provide a significant portion of the required electrical energy of the fire control system.

A novel class of piezoelectric-based energy-harvesting power sources has been developed for gun-fired munitions which harvest energy from the firing acceleration. These piezoelectric-based devices have been shown to produce enough electrical energy for many applications such as fuzing, where they provide an ultrasafe power source, often eliminating the need for chemical batteries. An overview of the development of these power sources is provided, along with methods and results of laboratory and field testing performed on prototypes. Additionally, methods for integrating the generators into different classes of projectiles are discussed along with strategies for manufacturing and a side-by-side comparison with competing technologies.

Thermal energy in the environment is a potential and possible source of electric energy for low-power electronics. The ambient temperature variation can be converted into electrical current or voltage via pyroelectric effect. The possibility of the utilizing pyroelectric materials in energy harvesting from roads warrants systematic exploration to take advantage of heat absorbed by the pavements. In terms of voltage generated, the simulated performances, of a few important pyroelectric materials, including fabricated in our laboratory, shall be described by employing real pavement temperature data obtained from climatic database of MEPDG.

Nanocrystal quantum dot photovoltaics and photodetectors with performance optimized by engineering the nanocrystals size and the optoelectronic properties of the nanocrystal's chemical coating are reported. Due to the large surface-to-volume ratio inherent to nanocrystals, the surface effects of ligands used to chemically coat and passivate nanocrystals play a significant role in device performance. However, the optoelectronic properties of ligands are difficult to ascertain, as the band structure of the ligand-capped nanoparticle system is complex and difficult to model. Using density-of-states measurements, we demonstrate that modeling of electropositive and electronegative substituents and use of the Hammett equation, are useful tools in optimizing nanocrystal detector performance. A new particle, the Janus-II nanoparticles, developed using 'charge-donating' and 'charge-withdrawing' ligands distributed over opposite surfaces of the nanocrystal, is described. The polarizing ligands of the Janus-II nanoparticle form a degeneracy-splitting dipole, which reduces the overlap integral between excitonic states, and thus reduces the probability of carrier recombination, allowing carrier extraction to take place more efficiently. This is shown to allow increased photodetection efficiencies and to allow the capture of multiple exciton events in working photodetectors.

Quantum structured solar cells seek to harness a wide spectrum of photons at high voltages by embedding low energy-gap wells or dots within a high energy-gap matrix. Quantum well and quantum dot solar cells have the potential to deliver ultra-high power conversion efficiencies in single junction devices, efficiencies that in theory can approach 45% in un-concentrated sunlight over a wide range of environmental conditions. In this paper, we will briefly review the theoretical underpinnings of quantum well and quantum dot photovoltaic devices, and summarize recent experimental efforts developing quantum-structured solar cell devices. In a specific example, test devices utilizing radiation-hard, III-V nitride materials have been built using both bulk and multiple quantum well (MQW) structures. Photovoltaic devices with an InGaN MQW structure are shown to outperform devices employing a thicker, bulk InGaN layer. These results, along with the underlying theoretical foundations, suggest that quantum well and quantum dot structures can enhance the performance of photovoltaic devices for a variety of defense applications.

In many sensing applications that monitor extreme environmental conditions within sealed metallic vessels, penetrating vessel walls in order to feed through power and data cables is impractical, as this may compromise a vessels structural integrity and its environmental isolation. Frequent servicing of sensing equipment within these environments is costly, so the use of batteries is strongly undesired and power harvesting techniques are preferred. Traditional electromagnetic power delivery and communication techniques, however, are highly ineffective in these applications, due to Faraday shielding effects from the metallic vessel walls. A viable, non-destructive alternative is to use piezoelectric materials to transmit power through thick metallic barriers acoustically. We present critical elements of a high-temperature battery-less sensor system prototype, including power harvesting, voltage regulation, and data communication circuitry able to operate up to 260°C. Power transmission is achieved by coaxially aligning a pair of high-temperature piezoelectric transducers on opposite sides of a thick steel barrier. Continuous-wave excitation of the outside transducer creates an acoustic beam that is captured by the opposite transducer, forming an acoustic-electric link for power harvesting circuitry. Simultaneously, sensor data can be transmitted out of the high-temperature environment by switching the electrical impedance placed across the leads of the inside transducer, creating a reflection-based amplitude modulated signal on the outside transducer. Transducer housing, loading, and alternatives for acoustic couplants are discussed. Measurement results are presented, and it was found that the system can harvest up to 1 watt of power and communicate sensor data up to 50 kbps, while operating at 260°C.