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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.

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.

The performance of non-fullerene acceptor (NFA)- based organic solar cells (OSC) has shown continuous increase in recent years, reaching power-conversion efficiencies up to 17% through the design and synthesis of efficient acceptor materials. Recent research is directed towards achieving higher efficiency of OSC, which is limited by the open-circuit voltage (Voc) which is lower than the Voc values achieved in inorganic or perovskites solar cells with comparable bandgaps. In this work, voltage losses in NFA based OSC were calculated by investigating charge-transfer state energy (ECT) using electroluminescence spectroscopy and sensitive external quantum efficiency in three polymer:non-fullerene bulk heterojunction solar cells. PCE10:ITIC device acquired the highest ECT with a Voc of 0.82V, and a a power conversion efficiency (PCE) of 7.91%. While PCE10:O-IDTBR obtained the highest Voc of 1.03V, a PCE of 8.02% compared to PCE10:O-IDTBCN solar cell that has a lower Voc of 0.73V with a PCE of 7.98%. Both radiative and non-radiative voltage losses were calculated. In this thesis, the high open circuit voltage of PCE10:O-IDTBR is explained by the low non-radiative voltage losses compared to PCE10:O-IDTBCN and PCE10:ITIC devices.

The main objective of this research was to develop efficient CuIn1-xGaxS2 (CIGS2)/CdS thin film solar cells for photoelectrochemical (PEC) water splitting to produce very pure hydrogen and oxygen. Efficiencies obtained using CIGS2 have been lower than those achieved using CuInSe2 and CuIn1-xGaxSe2. The basic limitation in the efficiencies is attributed to lower open circuit voltages with respect to the bandgap of the material. Presently, the main mechanism used to increase the open circuit voltage of these copper chalcopyrites (CuInSe2 and CuInS2) is the addition of gallium. However, addition of gallium has its own challenges. This research was intended to (i) elucidate the advantages and disadvantages of gallium addition, (ii) provide an alternative technique to the photovoltaic (PV) community to increase the open circuit voltage which is independent of gallium additions, (iii) develop highly efficient CIGS2/CdS thin film solar cells and (iv) provide an alternative material in the form of CIGS2/CdS thin film solar cells and an advanced technology in the form of a multiple bandgap tandem for PEC water splitting. High gallium content was achieved by the incorporation of a highly excess copper composition. Attempts to achieve high gallium content produced reasonable but not the best solar cell performance. Few solar cells developed on a molybdenum back contact and an ITO/MoS2 transparent conducting back contact showed a PV conversion efficiency of 7.93% and 5.97%, respectively. The solar cells developed on the ITO/MoS2 back contact form the first generation CIGS2/CdS thin film solar cells and 5.97% is the first ever reported efficiency on an ITO/MoS2 transparent back contact. Reasons for the moderate performance of these solar cells were attributed to significant porosity and remnants of unsulfurized CuGa alloy in the bulk of CIGS2. This was the first attempt to a detailed study of materials and device characteristics of CIGS2/CdS thin film solar cells prepared starting with a highly excess copper content CIGS2 layer. Next, excess copper composition of 1.4 (equivalent to gallium content, x = 0.3) was chosen with the aim to achieve the best efficiency. The open circuit voltage was enhanced by depositing an intermediate layer of intrinsic ZnO between CdS and ZnO:Al layers. The systematic study of requirements for such a layer and further optimization of its thickness to achieve a higher open circuit voltage (which is the greatest challenge of the scientific community) forms an important scientific contribution of this research. The PV parameters for CIGS2/CdS thin film solar cell as measured officially at the National Renewable Energy Laboratory were: open circuit voltage of 830.5 mV, short circuit current density of 21.88 mA/cm2, fill factor of 69.13% and photovoltaic conversion efficiency of 11.99% which sets a new world record for CIGS2 cells developed using sulfurization and the open circuit voltage of 830.5 mV has become the "Voc champion value". New PEC setups with the RuS2 and Ru0.99Fe0.01S2 photoanodes were developed. RuS2 and Ru0.99Fe0.01S2 photoanodes were more stable in the electrolyte and showed better I-V characteristics than the RuO2 anode earlier used. Using two CIGS2/CdS thin film solar cells, a PEC efficiency of 8.78% was achieved with a RuS2 anode and a platinum cathode. Results of this research constitute a significant advance towards achieving practical feasibility and industrially viability of the technology of PEC hydrogen generation by water splitting.

In this paper, an algorithm for estimating lead-acid battery state of charge (SOC) is implemented. The algorithm, named “Improved Coulomb Counting Algorithm”, was developed within a master thesis project (M. M. Samolyk & J. Sobczak, “Development of an algorithm for estimating Lead-acid Battery State of Charge and State of Health”, M.S. thesis, Dept. Signal Processing, Blekinge Institute of Technology, Karlskrona, Sweden, 2013) with cooperation of a Swedish company – Micropower – Research and Development department.  Currently used method at Micropower is Coulomb Counting; implemented algorithm compares coulomb counting method with open circuit voltage method and uses current, terminal voltage and temperature measurements to finally produce improvement for the very same coulomb counting method and get a better estimation of SOC.  The algorithm was implemented on Micropower Access Battery Monitoring Unit (BMU) using C programming language, so that it can be tested in real time application of the regular battery operation. In the end specific gravity measurements were also presented to comparing the methods.

<p> The MIS tunnel solar cell has recently attracted most of the attention in the solar energy conversion field. Construction is very simple and eliminates the costly diffusion of dopants. As in the Schottky type, a metal of proper work function is chosen to induce an inversion layer at the surface of the semiconductor (Al in the case of p type Si). An ultra thin (< 1.5 nm) oxide between the semiconductor and the metal passivates the surface by reducing surface states while permitting tunneling from the semiconductor to the metal.</p> <p> Good fill factors (> .7) have been obtained but high reflectivity of the Al has reduced the current output. Open circuit voltages greater than .61 volts and short circuit current density of 21 ma/cm^2 have been measured. Experimental evidence of the presence of an oxide different from SiO2 within 1.4 nm of the surface will be given and related to the thickness variation of the open circuit voltage. A maximum in VOC around 1.4 nm was found. A maximum efficiency of 7% was achieved without anti reflexion coating and a curve factor of .81 was observed in one of the cells. A slight variation in efficiency with the cell area was also observed.</p> / Thesis / Master of Engineering (MEngr)