Kitt Reinhardt

Broadband Light Absorption Enhancement in Thin-Film Silicon Solar Cells

Currently, the performances of thin film solar cells are limited by poor light absorption and carrier collection. In this research, large, broadband, and polarization-insensitive light absorption enhancement was realized via integrating with unique metallic nanogratings. Through simulation, three possible mechanisms were identified to be responsible for such an enormous enhancement. A test for totaling the absorption over the solar spectrum shows an up to approximately 30% broadband absorption enhancement when comparing to bare thin film cells.

Strong Enhancement of Solar Cell Efficiency Due to Quantum Dots with Built-In Charge

We report a 50% increase in the power conversion efficiency of InAs/GaAs quantum dot solar cells due to n-doping of the interdot space. The n-doped device was compared with GaAs reference cell, undoped, and p-doped devices. We found that the quantum dots with built-in charge (Q-BIC) enhance electron intersubband quantum dot transitions, suppress fast electron capture processes, and preclude deterioration of the open circuit voltage in the n-doped structures. These factors lead to enhanced harvesting and efficient conversion of IR energy in the Q-BIC solar cells.

Applications of colloidal quantum dots

This paper addresses a number of major trends underlying the continuing effort to realize practical optoelectronic, electronic, and information-processing devices based on ensembles of quantum dots assembled in a variety of matrix materials. The great diversity of such structures makes it possible to fabricate numerous ensemble-based devices for applications underlying photoluminescent devices, light-emitting diodes, displays, photodetectors, photovoltaic devices, and solar cells. In addition, the application of colloidal quantum dots to allied technologies such as nanobiotechnology is considered for the case of monitoring conformational changes in biomolecules using luminescent quantum dots.

Dynamic Data Driven Applications System Concept for Information Fusion

Abstract We present a framework of Information Fusion (IF) using the Dynamic Data Driven Applications Systems (DDDAS) concept. Existing literature at the intersection of these two topics supports environmental modeling (e.g., terrain understanding) for context enhanced applications. Taking advantage of sensor models, statistical methods, and situation- specific spatio-temporal fusion products derived from wide area sensor networks, DDDAS demonstrates robust multi-scale and multi-resolution geographical terrain computations. We highlight the complementary nature of these seemingly parallel approaches and propose a more integrated analytical framework in the context of a cooperative multimodal sensing application. In particular, we use a Wide-Area Motion Imagery (WAMI) application to draw parallels and contrasts between IF and DDDAS systems that warrants an integrated perspective. This elementary work is aimed at triggering a sequence of deeper insightful research towards exploiting sparsely sampled piecewise dense WAMI measurements – an application where the challenges of big-data with regards to mathematical fusion relationships and high-performance computations remain significant and will persist. Dynamic data-driven adaptive computations are required to effectively handle the challenges with exponentially increasing data volume for advanced information fusion systems solutions such as simultaneous target tracking and identification.

Multijunction solar cell iso-junction dark current study

Single-crystal multijunction solar cells show great promise for achieving 30-40% conversion efficiency under air mass zero (AM0) conditions, and have been identified as an enabling technology for next-generation government and commercial satellites. In this note we report on an approach to better understand the dark current-voltage (I-V) behavior in multijunction solar cells and its effect on conversion efficiency. This technique is based on determining the impact of dark-current behavior within individual p-n junctions on monolithic triple-junction GaInP/sub 2//GaAs/Ge solar cell performance. The GaInP/sub 2//GaAs/Ge tandem solar cells used in this study were developed, in part, under the US Air Forces Manufacturing Technology (ManTech) Program and exhibited measured efficiencies of 24-25% (AM0).

Monolithic crystalline multijunction solar cell development and analysis at the US Air Force research laboratory

As satellite payload electrical power system requirements continue to grow, satellite systems employing flat panel arrays have reached limits set by either on-orbit dynamics that limit the size and shape of the deployed array, mass constraints set by the launch vehicle, or by the limits set by the volume constraints of the launch shroud. This has caused several satellite programs to approach power margin limits early in the design cycle, and to either compromise on satellite capabilities or perform costly redesigns. A very leveraging parameter for raising satellite power levels and reducing costs is the efficiency of the solar cells employed by satellite systems. State of the art efficiencies have reached 26.5% efficiency at load, and 30.1% for prototype cells, and solar arrays using GaAs based multijunction solar cells have achieved deployed solar array power densities of 70 W/kg and stowed volume power densities of 8 kW/m3. A simplified approach to the unwieldy dark current electrical analysis of multijunction solar cells has been developed, correlated with the performance of dual and triple junction solar cells, and explains ideality factors and reverse saturation currents that appear large. It was found that introducing a fourth junction with modest performance could raise the efficiency of multijunction solar cells to 31.5% efficiency at load, raise total power levels to 22 kW, raise the power densities to 100 W/kg and 9 kW/m3 with no impact to the configuration or operation of satellite solar arrays.

Developments in thin-film photovoltaics for space

Thin-film solar cells are important for space because of their low cost, high power density, and radiation resistance. However, significant technological hurdles remain before thin-film technology may be implemented as the primary power source for spacecraft. A large-area fabrication process for high-efficiency (>10% AMO) cells on a lightweight substrate must still be demonstrated, and there are many issues associated with space qualification of both the photovoltaic material itself and the substrate which must be resolved. Also, new deployment, interconnection and control schemes must be developed. Ongoing efforts led and supported by the Air Force to overcome these obstacles are discussed.

Directions in US Air Force space power technology for global virtual presence

Recent trends in the development of high efficiency, light-weight, compact, reliable and cost-effective space power technologies needed to support the development of next-generation military and commercial satellites will be discussed. Development of new light-weight and reduced volume electrical power system (EPS) technologies are required to enable the design of future “smallsats” with power requirements less than 1500W, to “monstersats” having projected power levels ranging from 10–50kW for commercial communication and military space based radar type satellites. In support of these projected requirements a complement of power generation, power management and distribution, and energy storage technologies are under development at the Air Force Research Laboratory’s Space Vehicles Directorate. The technologies presented in this paper include high efficiency multijunction solar cells, alkali metal thermal electric converters (AMTEC), high-voltage (70–130V)/high-efficiency/high-density power management and ...

Alkali metal thermal-to-electric converter development

Initial impedance measurements of multi-BASE tube AMTEC cells have been accomplished. These measurements were based on theoretical analyses performed by the Jet Propulsion Laboratory. These factors are derived from a plot of the apparent charge transfer resistance, Ract, as a function of the electrical potential across the beta alumina solid electrolyte. These include the morphology factor, G, the exchange current J00, and α, the transfer coefficient. The factor G was given a value of 50 as a result of the inability of present equipment to achieve 1.6 V across a single electrolyte element. Average values for the temperature independent charge exchange factor, B, are also reported. These results were taken from cells with as few as 3300 h to as many as 12,000 h of operation. The results show that if the value for G is somewhat close to actual values, then J00 and α are much lower than those reported in previous literature, resulting in an increase in the charge transfer resistance.

Space Power Technology in Power Management and Distribution Electronics

Signie cantadvancementsinthedevelopmentoflightweight,compact,reliable,andcost-effectiveelectricalpower systemcomponentsarerequiredtoenablehigh-powerdesignsoffuturegenerationsofsatellites.ThegoaloftheU.S. Air Force Phillips Laboratory is to minimize the cost impact of high-power missions by reducing electrical power system mass to 10% of thesatellite mass, thereby allowing the use ofsmallerlaunch vehicles. By designing payload power converters to operate at higher frequencies and incorporating state-of-the-art packaging techniques, the specie c power of payload power converters will reach greater than 100 W/kg and 3 W/cm 3 , with substantially increased radiation hardness. Operating these converters at higher input voltage (120 V) will signie cantly reduce harnessmassforhigherpowermissions.Thissametechnology hasalsobenee ttedbatterychargingand discharging units, solar array power regulation devices, and switching and fault protection devices. Finally, high-temperature wide band gap devices were found to reduce the overall satellite mass by eliminating heaters for worst-case cold environment and by reducing the size of radiator components for hot environments.