No description available.

In this thesis, we propose a new structure of GaP/a-Si:H/BulkSi solar cell in which the additional a-Si:H layer due to the concept of energy bandgap is used to improve the open-circuit voltage. As the a-Si:H doping concentration is increased, the upward bandgap bending is expected to be observed; hence, a high open-circuit voltage is obtained. But in this situation, the upward bandgap bending also hinders the carrier transport, leading a low short-circuit current density. It is worth noting that the proposed solar cell can have a high open-circuit voltage of 0.758 V. In addition, we carefully investigate the characteristics of wide-bandgap gallium phosphide (GaP) material used for silicon-based solar cells. According to the simulated results, the absorption of GaP is better than silicon with a wavelength below 450 nm. Also, the GaP/BulkSi solar cell is shown to have a lower reflectivity value than the conventional PN_BulkSi solar cell. Hence we can prove that the internal quantum efficiency and external quantum efficiency are improved accordingly. As a result, the short-circuit current density is increased about 10 %. In addition, the optimized parameters of a GaP/BulkSi solar cell are as follows: the short-circuit current density is 21.264 mA/cm2, the open-circuit voltage is 0.624 V, the fill factor is 82.4 %, the conversion efficiency is 11.236 %, respectively.

Lithium-ion (Li-ion) batteries are the most popular energy storage technology in consumer electronics and electric vehicles and are increasingly applied in stationary storage systems. Yet, concerns about safety and reliability remain major obstacles, which must be addressed in order to improve the acceptance of this technology. The gradual degradation of Li-ion cells over time lies at the heart of this problem. Time, usage and environmental conditions lead to performance deterioration and cell failures, which, in rare cases, can be catastrophic due to res or explosions. The physical and chemical mechanisms responsible for degradation are numerous, complex and interdependent. Our understanding of degradation and failure of Li-ion cells is still very limited and more limited yet are reliable and practical methods for the detection and prediction of these phenomena. This thesis presents a comprehensive approach for the diagnosis and prognosis of degradation in Li-ion cells. The key to this approach is the extraction of information on electrode-speci c degradation through open circuit voltage (OCV) measurements. This is achieved in three stages. Firstly, a parametric OCV model is created, which computes the OCV of each electrode. Secondly, a diagnostic algorithm is devised, through which the OCV model is tted to OCV measurements recorded on Li-ion cells at various stages throughout their cycle life. The algorithm identi es the nature and quanti es the extent of degradation experienced by the cells. Lastly, the outputs of the algorithm are used to identify the likely failure modes of the cells and predict their end-of-life. The presented methods improve safe operation and predictions of remaining useful cycle life for commercial Li-ion cells. Greater certainty about the reliability, safety, required maintenance and depreciation of Li-ion battery systems can signi cantly enhance the competitiveness of battery electric storage in both automotive and stationary applications. The ndings presented in this work are therefore not only of technological but also of commercial interest.

Cadmium Telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal bandgap of 1.45 eV and its high optical absorption coefficient. Advancements in efficiencies of CdTe/CdS solar cells over the past few decades have come from improving the short circuit current (JSC) and Fill Factor (FF) but the Open Circuit Voltage (VOC) has been stagnant. Further improvements in efficiencies should come from increased VOC’s. VOC’s can be improved by increasing the acceptor concentration and minority carrier lifetime. Both these parameters can be controlled by manipulating the native defect concentration in CdTe which can be achieved by varying CdTe stoichiometry. In this study, a deposition system called Elemental Vapor Transport was used to vary the CdTe stoichiometry with an intent to change the native defect concentration and therefore pave way to increase acceptor concentration and lifetimes. Elemental cadmium and tellurium were heated in dedicated zones and their vapors were transported to the substrate using a carrier gas. By varying the temperatures and flowrates of the carrier gas through the zones, the gas phase Cd/Te ratio was varied to deposit Cd-rich, Te-rich and stoichiometric films. Structural properties were investigated using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (EDS). Electrical characterization of completed devices was carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V), and Spectral Response (SR) and Deep Level Transient Spectroscopy (DLTS) measurements. Cd-rich films showed smaller grain sizes and lesser degree of preferential orientation. Te-rich films showed increased acceptor concentration and carrier lifetimes and solar cells fabricated using these films showed higher VOC’s compared to Cd-rich and stoichiometric films .Higher degree of CdTe-CdS mixing was observed at the interface for films deposited at increased substrate temperatures.

FABRICATION OF NANOPOROUS GOLD AND BIOLOGICAL APPLICATIONS By Badharinadh Uppalapati A Dissertation submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University. Virginia Commonwealth University, 2014 Major Director: Maryanne M. Collinson, Professor, Department of Chemistry Fabrication of nanoporous gold electrodes by dealloying Au:Ag alloys has attracted much attention in sensing applications. In the first part of this work, the electrochemical response of the redox active molecule, potassium ferricyanide, in a solution of bovine serum albumin in buffer, serum or blood was studied using nanoporous gold and comparisons made to planar gold. Nanoporous gold electrodes with different surface areas and porosity were prepared by dealloying Au:Ag alloy in nitric acid for different dealloying times, specifically, 7.5, 10, 12.5, 20 minutes. Characterization was done using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and cyclic voltammetry (CV). Using cyclic voltammetry, planar gold electrodes exposed to bovine serum albumin in buffer showed a decrease in Faradaic peak current and an increase in peak splitting for potassium ferricyanide. The time required for the peak Faradaic current to drop to one-half of its original value was 3 minutes. At nanoporous gold electrodes, however, no significant reduction in Faradaic peak current or increase in peak splitting was observed. Nanoporous gold electrodes having the smallest pore size and largest surface area showed ideal results to biofouling. These electrodes are believed to impede the mass transport of large biomolecules while allowing small redox molecules to exchange electrons effectively with the electrode. In the second part of this work, the open circuit potential (OCP) of biologic solutions (e.g., blood) was measured using nanoporous gold electrodes. Historically, the measurement of blood redox potential has been hindered due to significant fouling and surface passivation of the metal electrodes. As nanoporous gold electrodes retained electrochemical activity of redox probes like potassium ferricyanide in human serum and rabbit blood, they were used to measure the OCP of blood and plasma from various animals like pig, rabbit, rat, monkey and humans. Comparisons were made to planar gold electrodes. The OCP values at both the planar gold and nanoporous gold electrodes were different from each other and there was variability due to different constituents present in blood and plasma. The OCP of rabbit blood and crashed rabbit blood was measured and the values were found to be different from each other indicating that ORP helps in measuring the animal condition. Ascorbic acid was added to rabbit and sheep blood and OCP measured at the nanoporous electrodes. Addition of reducing agent to blood at different intervals and different concentrations showed a change in potential with concentration.

Um dos problemas que contribui para a diminuição do desempenho de células a combustível de membrana trocadora de prótons é o cruzamento de combustível do compartimento anódico para o catódico. Um método de avaliar o contato do combustível anódico com o cátodo consiste da exposição do catalisador oxidado à molécula de interesse, em condições de circuito aberto. Do ponto de vista fundamental, a análise desses transientes de circuito aberto pode fornecer informações importantes acerca do mecanismo reacional associado. São apresentados nessa Dissertação, resultados da interação entre metanol ou etanol e superfícies oxidadas de paládio, em meio alcalino. Entre os parâmetros investigados, maior ênfase foi dada ao efeito da natureza do cátion alcalino presente no eletrólito. Observou-se que a presença de Li+ ou K+ no eletrólito influencia desde a quantidade de óxido formada, até o tempo requerido para a redução desses óxidos pela molécula orgânico dissolvida. A natureza do composto orgânico presente também exerce diferenças consideráveis no transiente de circuito aberto. Finalmente, foram propostos esquemas reacionais para representar a interação de circuito aberto com o metanol e etanol. Em ambos os casos, os mecanismos incluem a produção auto-catalítica de sítios livres de paládio. / One of the problems that contributes to the performance decreasing observed in proton exchange membranes is the fuel crossover from the anodic to the cathodic compartment. A method to evaluate the contact of the anodic fuel with the cathode consists of exposing the oxidized catalyst to the molecule of interest under open circuit conditions. From the fundamental point of view, the analysis of the open circuit transients may provide relevant information on the associated reaction mechanism. In this Dissertation, results of the open circuit interaction between methanol or ethanol with oxidized palladium surfaces, in alkaline media, are presented. Among the distinct investigated parameters, emphasis will be put on the effect of the nature of the alkali cation present in the electrolyte. It was observed that the presence of Li+ or K+ influences several aspects, from the amount of oxide formed to the time needed for the reduction of the oxide by the dissolved organic molecules. The identity of the dissolved organic molecule also exerts marked influence on the open circuit transients. Finally, two reaction schemes for the open circuit interaction with methanol or ethanol were proposed. In both cases, the mechanisms include the auto-catalytic production of free palladium sites.

Um dos problemas que contribui para a diminuição do desempenho de células a combustível de membrana trocadora de prótons é o cruzamento de combustível do compartimento anódico para o catódico. Um método de avaliar o contato do combustível anódico com o cátodo consiste da exposição do catalisador oxidado à molécula de interesse, em condições de circuito aberto. Do ponto de vista fundamental, a análise desses transientes de circuito aberto pode fornecer informações importantes acerca do mecanismo reacional associado. São apresentados nessa Dissertação, resultados da interação entre metanol ou etanol e superfícies oxidadas de paládio, em meio alcalino. Entre os parâmetros investigados, maior ênfase foi dada ao efeito da natureza do cátion alcalino presente no eletrólito. Observou-se que a presença de Li+ ou K+ no eletrólito influencia desde a quantidade de óxido formada, até o tempo requerido para a redução desses óxidos pela molécula orgânico dissolvida. A natureza do composto orgânico presente também exerce diferenças consideráveis no transiente de circuito aberto. Finalmente, foram propostos esquemas reacionais para representar a interação de circuito aberto com o metanol e etanol. Em ambos os casos, os mecanismos incluem a produção auto-catalítica de sítios livres de paládio. / One of the problems that contributes to the performance decreasing observed in proton exchange membranes is the fuel crossover from the anodic to the cathodic compartment. A method to evaluate the contact of the anodic fuel with the cathode consists of exposing the oxidized catalyst to the molecule of interest under open circuit conditions. From the fundamental point of view, the analysis of the open circuit transients may provide relevant information on the associated reaction mechanism. In this Dissertation, results of the open circuit interaction between methanol or ethanol with oxidized palladium surfaces, in alkaline media, are presented. Among the distinct investigated parameters, emphasis will be put on the effect of the nature of the alkali cation present in the electrolyte. It was observed that the presence of Li+ or K+ influences several aspects, from the amount of oxide formed to the time needed for the reduction of the oxide by the dissolved organic molecules. The identity of the dissolved organic molecule also exerts marked influence on the open circuit transients. Finally, two reaction schemes for the open circuit interaction with methanol or ethanol were proposed. In both cases, the mechanisms include the auto-catalytic production of free palladium sites.

In this study, we add an additional layer above and under the CIGS absorber layer as a secondary absorption layer respectively. We made the conventional structure of ZnO/CdS/CIGS/Mo becomes the structure of ZnO/CdS/CIGS/InGaP/Mo and ZnO/CdS/InGaP/CIGS/Mo which can improve the conversion efficiency. And we translate the thickness proportion of Ga and the doping concentration to find out the best parameter. According to the simulation, the wavelength of EQE in 600 nm ~ 1200 nm for our proposed CIGS solar cell which the additional layer under CIGS layer has been improved when compared to the conventional CIGS solar cell. The short-circuit current density has been increased about 9 %. And the conversion efficiency has also been increased about 9 %.When the additional layer above the CIGS absorber layer, according to the simulation, the wavelength of EQE in 300 nm ~ 600 nm for our proposed CIGS solar cell is improved when compared with the conventional CIGS solar cell. The short-circuit current density has been improved about 7.7 %, the open-circuit voltage about 7.1 %, and the conversion efficiency about 20.6 %. The main reason is that when the InGaP absorption layer under the CIGS layer which can catch the light which can¡¦t be absorbed by CIGS layer. The InGaP absorption layer above the CIGS layer which can catch the light immediately.

This research proposes a method for estimating the residual capacity of Li-ion batteries. The charging and discharging characteristics of Li-ion batteries are investigated and analyzed by a battery test system. The measurement of the initial capacity is based on the improved open-circuit voltage measurement, which compensates the effects of battery aging and self-discharging. The measurement of the used capacity is based on the improved coulomb counting measurement, which compensates the effects of output current and environmental temperature. The designed system provides various functions for battery charging and discharging, battery voltage measuring and recording, battery capacity estimation and calculation, and the log files can be used for further battery characteristics analysis.

Most electrical machines available in the market utilise some form of silicon iron (SI) as the core material. Although SI based electrical machine manufacturing methods are well established and simple, SI has significant iron losses specifically in high frequency variable-speed motor drive applications. Two alternative magnetic materials have recently been developed: amorphous magnetic material (AMM) and soft magnetic composite, which can each offer unique characteristics that can be utilised to improve the performance of electric machines. AMM offers extremely low iron losses which makes it a good candidate for high-efficiency and variable-speed motor applications. However, due to handling and cutting limitations, AMM has not been utilised widely in rotating electrical machines. A commercially viable AMM cutting technique was recently developed by the industrial partner of this project. It is thus now practical to cut the AMM ribbon into a machine stator, particularly for axial-field stators which generally require less cutting than radial-field stators. This thesis investigates an innovative motor design based on applying the cut AMM in an axial-field permanent magnet (AFPM) machine for general drive applications. It includes a detailed review of the analytical approach, finite element analysis (FEA), iron loss investigation and prototype performance comparisons. Analytical analysis of the AFPM machine was performed and the key design variables were evaluated to optimise the design parameters based on the use of AMM. The AMM cutting constraints, design and performances trade-offs were also investigated in the design. The research study provides a design procedure to determine the basic physical size and configuration (e.g. combination of the number of slots and poles, slot width and depth, number of winding layers, air gap length, magnet thickness) based on certain basic specifications. In addition, a comprehensive investigation was conducted on the iron loss of various materials to compare these with AMM. Due to the three dimensional (3D) nature of the AFPM structure, the theoretical design was validated using 3D FEA and extensive simulation results are provided. A number of AMM AFPM prototypes were successfully designed and constructed. Due to limited available materials, the prototypes were built using uncoatedAMMribbon which has substantially higher iron loss characteristics. Nevertheless, it is believed that it would still provide a valuable understanding of the real machine characteristics and allow initial design validation. The prototype was tested in a custom-built test rig to validate the analytical and 3D FEA predictions. Overall, a good correspondence between the results and predictions has been achieved. Extensive experiments have been conducted to investigate and demonstrate the characteristics of the AMM prototype machines which are based on fractional-slot concentratedwinding single-sided AFPM machines. This includes comparisons against identical silicon iron and soft magnetic composite prototypes. In addition, the laboratory experimental results also highlighted the significant effect of the open-circuit losses on the overall machine performance. Therefore, the open-circuit loss components which includes bearing, windage, magnet and iron losses were separated based on 3D FEA and experimental results. The above research studies demonstrated the potential and feasibility of cut AMM to produce highly efficient AFPM machines. In addition, the innovative cutting technique also has the potential for mass production of low-cost AMM machines. The research work in this thesis makes a significant contribution to the design of axial-field permanent magnet machines based on AMM. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1375647 / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2009