The performance of photovoltaic (PV) modules in terms of their ability to convert incident photon to electrical energy (efficiency) depends mostly on the spectral distribution of incident radiation from the sun. The incident spectrum finally perceived by the module depends strongly on the composition of the medium in which it has traveled. The composition of the earth’s atmosphere, which includes, amongst others, water vapour, gases such as carbon dioxide and oxygen, absorbs or scatters some of the sunlight. The incident solar spectrum is also modified by the diffuse aspect of radiation from the sky which strongly depends on aerosol concentration, cloudiness and local reflection of the earth’s surface. Although it is well known that the changes in outdoor spectrum affect device performance, little work has been conducted to support this theory. This is probably due to lack of spectral data or in certain instances where data is available, little knowledge of interpreting that data. The outdoor spectral data that one obtains in the field does not come clearly for just simple interpretation. Different analytical interpretation procedures have been proposed, all trying to explain and quantify the spectral influence on PV devices. In this study an assessment methodology for evaluating the effects of outdoor spectra on device performance parameters during the course of the day, seasons and or cloudy cover has been developed. The methodology consists of developing a device dependant concept, Weighted Useful Fraction (WUF) using the outdoor measured spectral data. For measuring PV module’s performance parameters, a current-voltage (I-V) tester was developed in order to monitor the performance of six different module technologies. The Gaussian distribution was used to interpret the data. For hot-spot analysis, different techniques were used, which include Infrared thermographic technique for identifying the hot-spots in the solar cells, SEM and EDX techniques. The AES technique was also used in order to identify other elements at hot-spots sites that could not be detected by the EDX technique. iii Results obtained indicate that multicrystalline modules performance is affected by the changes in the outdoor spectrum during summer or winter seasons. The modules prefer a spectrum characterized by WUF = 0.809 during summer season. This spectrum corresponds to AM 2.19 which is different from AM 1.5 used for device ratings. In winter, the mc-Si module’s WUF (0.7125) peaks at 13h00 at a value corresponding to AM 1.83. Although these devices have a wider wavelength range, they respond differently in real outdoor environment. Results for mono – Si module showed that the device performs best at WUF = 0.6457 which corresponds to AM 1.83 during summer season, while it operates optimally under a winter spectrum indicated by WUF of 0.5691 (AM2.58). The seasonal changes resulted in the shift in WUF during day time corresponding to the “preferred” spectrum. This shift indicates that these devices should be rated using AM values that correspond to the WUF values under which the device operates optimally. For poly-Si, it was also observed the WUF values are lower than the other two crystalline-Si counterparts. The pc-Si was observed to prefer a lower AM value indicated by WUF = 0.5813 during winter season while for summer it prefers a spectrum characterized by WUF = 0.5541 at AM 3.36. The performance of the single junction a-Si module degraded by 67 percent after an initial outdoor exposure of 16 kWh/m² while the HIT module did not exhibit the initial degradation regardless of their similarities in material composition. It was established that the WUF before degradation peaks at 15h00 at a value of 0.7130 corresponding to AM 4.50 while the WUF after degradation “prefers” the spectrum (WUF = 0.6578) experienced at 15h30 corresponding to AM value of 5.57. Comparing the before and after degradation scenarios of a-Si:H, it was observed that the device spends less time under the red spectrum which implies that the device “prefers” a full spectrum to operate optimally. The degradation of a-Si:H device revealed that the device spectral response was also shifted by a 7.7 percent after degradation. A higher percentage difference (61.8 percent) for spectral range for the HIT module is observed, but with no effects on device parameters. Seasonal changes (summer/winter) resulted in the outdoor spectrum of CuInSe2 to vary by WUF = 1.5 percent, which resulted in the decrease in Isc. This was ascertained by iv analyzing the percentage change in WUF and evaluating the corresponding change in Isc. The analysis showed that there was a large percentage difference of the module’s Isc as the outdoor spectrum changed during the course of the day. This confirmed that the 17 percent decrease in Isc was due to a WUF of 1.5 percent. In mc-Si solar cells used in this study, it was found that elemental composition across the entire solar cell was not homogenously distributed resulting in high concentration of transition metals which were detected at hot spot areas. The presence of transition metals causes hot-spot formation in crystalline solar cells. Although several transition elements exist at hot-spot regions, the presence of oxygen, carbon, iron and platinum was detected in high concentrations. From this study, it is highly recommended that transition elements and oxygen must be minimized so as to increase the life expectancy of these devices and improve overall systems reliability

Le but de ce travail est l'étude et la caractérisation des structures à base du silicium. La première partie de cette thèse traite le sujet des composants de puissance du type VDMOSFET en fonctionnement sous conditions extrêmes. Le comportement électrique des composants étudiés ainsi que l'évolution des temps de commutation sont bien étudiés en fonction de la température qui varie linéairement de 25 à 180ºC. Des contraintes électriques sont appliquées de manière à simuler expérimentalement les conditions réelles de fonctionnement. Les défauts sont ensuite caractérisés par des mesures de capacité et conductance grille-source permettant ainsi le calcul des densités des états d'interface induits par le stress. Les résultats expérimentaux montrent que les densités des états d'interface augmentent avec la durée du stress électrique appliqué. Les défauts induits et activés par le stress électrique sont aussi étudiés par la technique CDLTS qui se repose sur un balayage en largeur de l'impulsion appliquée sur la grille. Le balayage du gap a été assuré par la variation du niveau bas de l'impulsion. Différents défauts ont été détectés et les impuretés dopantes ainsi que les états d'interface ont été distingués des niveaux profonds situés au sein de la bande interdite. La deuxième partie de la thèse concerne la caractérisation et la modélisation des cellules à émetteurs dopés bore. La caractérisation électrique a été assurée par la caractérisation SIMS et la mesure des caractéristiques C(V) et I(V). La modélisation vient accompagner les résultats obtenus expérimentalement afin de tirer tout les paramètres caractéristiques de la cellule étudiée. Par la technique DLTS, un piège ayant une énergie d'activation de 0.029 eV et une section efficace de capture de 1.41 10-24 cm2 a été identifié. / The aim of this work is to study and characterize silicon based structures. The first part of this thesis deals with the operation of VDMOSFET power devices under extreme conditions. The electrical behavior of studied devices and the evolution of switching times were studied as a function of temperature (25 to 180ºC). Electrical stressing was applied in order to simulate real operating conditions. Defects are then characterized by gate-source capacitance and conductance measurements allowing the calculation of interface states densities induced by stress. Experimental results show that interface states densities increase with the stress duration. Defects induced and activated by the electrical stress are also studied by the CDLTS technique based on gate pulse width scan. The band gap was scanned by varying the pulse base level. Different defects were detected and we have distinguished the doping levels and interface states from deep levels located in the forbidden band gap. The second part of the thesis concerns the characterization and modeling of boron-doped emitter photovoltaic cells. The electrical characterization was carried out by SIMS characterization and the measurement of C(V) and I(V) characteristics. Experimental results are supported by modeling in order to estimate all the characteristic parameters of the studied cell. By the DLTS technique, a trap with activation energy of 0.029 eV and capture cross section of 1.41 10-24 cm2 has been identified.

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This thesis is focused on one of the diagnostic methods of fotovoltaic cells the LBIC (Light Beam Induced Current) method and the experimental measurement set-up for this method, which is operated by the Department of Electrical and Electronic Technology in Brno. The principle of photovoltaic cells function, the possibly used material and the problems usually encountred during production are described in this work,. There is also a review of methods that can be used to detect defects in photovoltaic cells. The main part is devoted to the proposal of a new experimental set-up for the measuring LBIC method and software development for this set-up. There is a proposal of a new method of measurement, which is also implemented using the development environment Borland C + +. Newly developed software for this method allows simpler operation and more efficient measurements.

The first part of this master’s thesis contain the history of photovoltaic technology and types of PV cells. Gave a consideration to advantages and disadvantages of solar cells. Compared their effectiveness and important parameters. In the next part described the recycling technology of modules at the end of their lifetime. Described certain recycled materials. At the end of the work described possible improvements to existing technologies used for encapsulating of cell. And wich would improve the recycling process.

Desertification is one of the main problems plaguing the Chinese countryside. The main cause is the heavy overgrazing of pastures and in this context the irrigation can be a solution to the problem. As regard the existent irrigations systems, pumps are driven manually or by diesel engines. Actually the use of electric motors would be a better solution for the irrigation development, but the lack of the access to electric network for the isolated rural areas represents a great obstacle. Therefore the use of PV stand-alone systems to produce the electricity for the motor-pumps (PVPS- Photovoltaic Pumping Systems) represents a both economic and technical good solution. However the weak point for PVPS diffusion is lack of tools to design these systems and predict their performances. This thesis work wants to provide a sizing software and the technical guidelines to select the suitable components for a PVPS. The developed sizing method has been validated applying it to two real cases where PVPS were already existing. Then, the obtained results have been compared with the characteristics of the real PVPS. The reliability of the design procedure has been verified, observing the similarity between the calculated outputs and the respective real values. Finally simulations have been done using the designed PVPS. The scope of those simulations has been to add some technical recommendations useful for the PVPS designer. The influence of the total head variations on the pumping performance and also the effect of the motor-pump subsystem choice on the final power size of PV array have been investigated.

Photovoltaic(PV) technology is promising due to its natural availability among energy harvesting technologies. There is a growing need for sustainable power sources that can function without being connected to a power source or needing regular battery replacements. Wearable PV cells are gaining popularity in different applications. However, most companies produce wearable PVs for terrestrial applications. Research on wearable PV applications for the marine environment remains limited because these cells suffer from several issues. This research compares commercially sourced wearable PV cells' maximum current consistency and electrical resistance for two testing conditions. The researcher followed standardized methods for these two laundering and corrosion testing conditions. The results revealed that current consistency values decreased over both types' laundering and corrosion testing conditions. However, electrical resistance values showed opposite trends. The findings of this study suggest that wearable PV cells may serve as a reliable source for powering electronic devices in marine environments.

Philosophiae Doctor - PhD / Fossil fuels are part of fuels that are formed from natural processes and they are called non-renewable sources of energy. These include natural gas, coal and oil. They have been used for decades to produce energy globally. However, there are some factors that related with the use of fossil fuels which results in an increase in the requirement of large amounts of energy. In addition, the use of fossil fuels as energy source has a negative impact on the environment and they cannot be reused. It is expected that at some point they will run out. Thus, a need for a renewable, clean and plentiful source of energy is urgent. Solar energy is one of the energy sources that may overcome fossil fuel drawbacks.

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