abstract: High speed image sensors are used as a diagnostic tool to analyze high speed processes for industrial, automotive, defense and biomedical application. The high fame rate of these sensors, capture a series of images that enables the viewer to understand and analyze the high speed phenomena. However, the pixel readout circuits designed for these sensors with a high frame rate (100fps to 1 Mfps) have a very low fill factor which are less than 58%. For high speed operation, the exposure time is less and (or) the light intensity incident on the image sensor is less. This makes it difficult for the sensor to detect faint light signals and gives a lower limit on the signal levels being detected by the sensor. Moreover, the leakage paths in the pixel readout circuit also sets a limit on the signal level being detected. Therefore, the fill factor of the pixel should be maximized and the leakage currents in the readout circuits should be minimized. This thesis work presents the design of the pixel readout circuit suitable for high speed and low light imaging application. The circuit is an improvement to the 6T pixel readout architecture. The designed readout circuit minimizes the leakage currents in the circuit and detects light producing a signal level of 350µV at the cathode of the photodiode. A novel layout technique is used for the pixel, which improves the fill factor of the pixel to 64.625%. The read out circuit designed is an integral part of high speed image sensor, which is fabricated using a 0.18 µm CMOS technology with the die size of 3.1mm x 3.4 mm, the pixel size of 20µm x 20 µm, number of pixel of 96 x 96 and four 10-bit pipelined ADC’s. The image sensor achieves a high frame rate of 10508 fps and readout speed of 96 M pixels / sec. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

This thesis focuses on the analysis of the external quantum efficiency of quantum dot-enhanced multi-junction solar cells. Divided in four major parts, it uses the experimental methodology developed in the SUNLAB. At first, a model is introduced to calculate the external quantum efficiency of single and multi-junction solar cells. This model takes into account the semiconductor physics governing the electrical property of the solar cell. It furthermore takes into account the optical transmission and reflection in the semiconductor structure using a transfer matrix method. The calculated curve fits a single junction GaAs solar cell's external quantum efficiency to a high degree of precision. Finally, an InGaP/GaAs/Ge solar cell's external quantum efficiency is calculated and it reproduces accurately the behavior of a measured cell. Second, the reflectivity of a solar cell is studied. An analysis technique involving using the fast Fourier transform of the oscillation in the reflectivity is introduced. This technique extracts the thicknesses of the top and middle subcells. The reflectivity is subsequently calculated using the transfer matrix method and it reproduces the behavior of the measured samples. Third, the effect of the addition of quantum dots in the middle subcell is studied. It is demonstrated that they extend the absorption range of the middle subcell. This is completed by first modeling the quantum mechanical behavior of the electrons and holes in the nanostructure. Their emission and absorption properties are derived. Those derived properties are verified by experimentally measured photoluminescence and electroluminescence of the nanostructures. The resulting model is then compared to experimentally measured external quantum efficiencies of single junction and multi-junction quantum dot-enhanced solar cells. Finally, a study of the bottom subcell artifact is completed. Using the fill-factor bias experiment, each of the contribution of the light coupling and the internal voltage biasing is decoupled. For the measured sample, an optimal voltage of 2.1 V is found to minimize the artifact. At this point, the internal voltage biasing creates an artifact of 1 % and the light coupling artifact is 8 %.

Ce travail de thèse a pour but de comprendre l’impact des propriétés électriques du silicium cristallin sur les performances des cellules solaires Silicium à HétéroJonction (SHJ) et de déterminer des spécifications matériaux nécessaires en termes de durée de vie des porteurs de charge et de résistivité.Dans une première partie de cette thèse, le potentiel du silicium mono-like a été évalué pour la fabrication de cellules solaires SHJ. La forte productivité de cette technique permet de réduire considérablement les coûts de fabrication des plaquettes. Des rendements de conversion de 20% équivalents à ceux des matériaux du marché ont été obtenus ainsi qu’un rendement de 21.6% avec l’utilisation d’un procédé de fabrication de cellules haut rendements. Ces valeurs ont été obtenues pour des durées de vie volumiques moyennes sur les plaquettes supérieures à 1ms. Les principaux limitations de la qualité du matériau mono-like ont été identifiés. D’abord, la présence de zones multicristallines sur certaines plaquettes rend le matériau incomptable avec le procédé SHJ notamment en ce qui concerne les étapes de texturation des surfaces et ensuite l’uniformité en épaisseur des couches déposées. Ce type de défauts fait chuter en premier lieu la Jcc, puis la Vco et le FF et finalement le rendement de conversion. De plus, la présence de contamination et la génération de dislocations aux extrémités du lingot font également chuter la durée de vie volumique et les paramètres photovoltaïques des cellules. Finalement, seulement 30% de la hauteur de lingot a pu être utilisé pour des hauts rendements de conversion.La deuxième partie a été consacrée à l’étude et l’optimisation, avec la technologie SHJ, d’une technique de dopage innovante remplaçant celles utilisant des impuretés dopantes, telle que le phosphore, en générant des donneurs thermiques dans le substrat silicium cristallin. Cette méthode de dopage présente l’avantage d’utiliser l’oxygène naturellement présent dans le silicium en transformant en dopant par des recuits à 450°C. Cette technique est uniquement valable avec une procédé basse température tel que celui utilisé dans ce travail de thèse et permettrait de contrôler les propriétés électriques du silicium sur l’ensemble d’un lingot Cz afin d’augmenter le rendement matière. La compatibilité du silicium cristallin dopé par des DT a été validée pour une gamme de résistivité de 3-10Ω.cm et durées de vie volumique de 3-10ms. La limite d’utilisation des DT pour l’obtention de hauts rendements correspond à une concentration inférieure à 7x1014cm-3 (3Ω.cm, 3ms). La technique de dopage a été transférée avec succès à l’échelle du lingot et a permis d’obtenir de rendement de 20.7% avec un procédé industriel et même de 21.7% avec une métallisation « smart-wire ». Une perte de FF a été observée par rapport aux références, liées à une résistance série élevée dont l’origine n’a pas encore été confirmée mais dont la source la plus probable serait l’inhomogénéité radiale de résistivité générée par le dopage. / This study aims to understand the electrical properties impact of the crystalline Silicon on the HeteroJunction (SHJ) solar cells performances and define the required material specifications in terms of minority carrier lifetime and bulk resistivity.In the first part of this work, the potential of the mono-like silicon was evaluated for SHJ solar cells production The high productivity of the crystallization method allows to significantly reduce the material cost. 20% efficiencies comparable to reference wafers were obtained for industrial process and had reached 21.6% values have been reached with a high efficiency process. Values above 1ms bulk lifetime were mandatory to obtain these results. The main limitations of the material properties were identified. First, the presence of multicrystalline zones on the material is incompatible with the SHJ process especially regarding the texturization step and then layers thickness’ uniformity. This defects drive down, at the first order, the Jsc and then the Voc and FF. Moreover, the metallic contamination and the dislocations generation at the ingots ends induce also a bulk lifetime degradation and PV performances drop. Finally, only 30% of the ingot height was usable to obtain high solar cell efficiencies.In the second part of this work, an innovative doping method, replacing the ones which use doping impurities, such as phosphorus, by generating thermal donors (TD) was studied. The advantages of this doping method are to use the oxygen naturally content in the silicon to generate the doping after 450°C annealing. This method is only possible if low temperature solar cell process is performed such the one used in this work. It could control the electrical properties of the crystalline silicon throughout a complete Cz ingot and increase the material yield. For a resistivity range of 3-10Ω.cm and bulk lifetime between 3 and 10ms, the TD doped material is compatible with SHJ technology. The maximum TD concentration for a SHJ application was estimated to 7x1014cm-3.The doping method was successfully transferred to the ingot scale and allowed reaching 20.7% efficiency with an industrial process and 21.7% with the “smart-wire” improved metallization. A FF loss was observed compared to the references, related to high series resistances. The origin has not been confirmed yet, but the most likely source would be the radial resistivity inhomogeneity generated by doping on silicon bulk.

P3HT single layer, P3HT/PCBM bilayer and P3HT/PCBM inverted bilayer devices were produced by spin coating organic layers onto ITO patterned glass in air, and clamping it with an Au coated silicon wafer, as top electrode, at the end (Figure13). Normal and inverted bilayer devices were also fabricated with and without PEDOT:PSS. All devices were divided into two groups by changing concentration of P3HT solution. The first group of devices contained 1.0 wt. % P3HT solution (P3HT in dichlorobenzene); the second group 0.56wt %. Power conversion efficiency, short circuit current, open circuit voltage, fill factor and maximum extracted power were measured on all produced devices. In contrast, all devices with 1.0wt % P3HT concentration showed better result than the devices with 0.56wt %. The highest result was obtained for P3HT single layer devices in both cases with short circuit current 56uA/cm2, open circuit voltage 0.94mV, maximum power 11.4uW/cm2 and power conversion efficiency of 0.11%. Inverted bilayer devices performed better than the non-inverted one. The devices with PEDOT:PSS got slightly better performance than the non-PEDOT:PSS used one. Charge carrier mobility measurement was done for all fabricated devices with charge extraction by linearly increasing voltage (CELIV) and dark injected space charge limited current (DI-SCLC) methods. All devices showed same magnitude of charge carrier mobility 10-5 cm2/V.s, the highest value still belongs to P3HT single layer device. The charge carrier mobility in all devices observed by DI-SCLC technique is one order of magnitude higher than by CELIV technique. This may be due to DI-SCLC method`s restriction on ohmic contacts between material and electrode. / بۇ تەتقىقاتتا ئورگانىك ماتېرىيالدىن پايدىلنىپ ئۈچ خىل قۇياش ئىنىرگىيەلىك باتارىيە ئادەتتىكى ئۆي مۇھىتىدا ياساپ چىقىلدى. ئەڭ چوڭ توك كۈچى، ئەڭ                                                    يۇقىرى بېسىم، ئەڭ يۇقىرى قۇۋەت ۋە زەرەت يۆتكۈلۈش تېزلىكى ئۆلچەپ چىقىلدى ئۇيغۇر

Foram desenvolvidos sistemas de medidas visando a caracterização de células solares de sílico monocristalino. Para isso, foram determinadas as características I x V no escuro para diferentes níveis de iluminação. Curvas de resposta espectral e capacitância em função da tensão inversa aplicada foram também obtidas. Foi feita uma avaliação do comportamento dessas células em função da temperatura e realizadas medidas de profundidade de junção utilizando-se três métodos distintos. Os principais parâmetros, que determinam o desempenho dessas células, foram obtidos boa concordância com a teoria e com os resultados apresentados na literatura. / Systems of measurements were developed for the characterization of single crystal silicon solar cells. For that, the curves I x V were measured in the dark and for different intensity of illumination. Curves of spectral response and of capacitance as a function of the reciprocal of the voltage were also measured. The behavior of the cells as a function of temperature was analysed and also measurements of junction depth were made by three different methods. Values for the parameters that characterize the cells were obtained, showing a good agreement with theoretical values and also with already reported values.

Foram desenvolvidos sistemas de medidas visando a caracterização de células solares de sílico monocristalino. Para isso, foram determinadas as características I x V no escuro para diferentes níveis de iluminação. Curvas de resposta espectral e capacitância em função da tensão inversa aplicada foram também obtidas. Foi feita uma avaliação do comportamento dessas células em função da temperatura e realizadas medidas de profundidade de junção utilizando-se três métodos distintos. Os principais parâmetros, que determinam o desempenho dessas células, foram obtidos boa concordância com a teoria e com os resultados apresentados na literatura. / Systems of measurements were developed for the characterization of single crystal silicon solar cells. For that, the curves I x V were measured in the dark and for different intensity of illumination. Curves of spectral response and of capacitance as a function of the reciprocal of the voltage were also measured. The behavior of the cells as a function of temperature was analysed and also measurements of junction depth were made by three different methods. Values for the parameters that characterize the cells were obtained, showing a good agreement with theoretical values and also with already reported values.

The objective of this study is analysing the characteristics of five different solar cell technologies regarding their efficiency, fill factor, cost and environmental impacts and comparing their improvement records over years considering their efficiency. The five solar cell technologies of interest are amorphous silicon, monocrystalline silicon, polycrystalline silicon, cupper indium gallium selenide thin film and cadmium telluride thin film. The structure and manufacturing process of each of cell technologies were discussed. The study was conducted by the aid of available scientific reports regarding the electrical characteristics of different solar cell technologies. The extracted information regarding efficiency rate and fill factor was analysed using graphs and significant findings are discussed. The five technologies are also compared regarding their cost and ease of fabrication and their impacts on environment and recycling challenges. The result of this study is suggesting the most promising technology that may be the optimal option for further investment and research.

This project is concerned with both the study of different Multiple Quantum Wells (MQWs) structures using the In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP and a systematic investigation of the properties of InAs QD systems within GaAs with the aim of achieving enhancements of solar cell performance. The key challenge is the growth of QDs solar cell structures which exhibit sufficient absorption (enhanced infrared absorption) to increase short circuit current density (Jsc) but which can still maintains a high open circuit voltage (Voc). The research consists of epitaxial growth using state-of–the-art MBE, optical absorption, photoluminescence and high resolution x-ray diffraction measurements as well as device fabrication and characterization of novel solar cell structures. Optimization was performed on these novel cells to further improve their efficiency by inserting stacks of QD into different regions of the device. The effect of localized doping of such structures was used in an attempt to maintain and enhance the open-circuit voltage which in turn increases the device efficiency. The fabricated devices were characterized using measurements of the dark/light current-voltage (I-V) characteristics and spectral response (50-480 K). Solar cell external quantum efficiencies under standard air mass (AM) 1.5 spectrum were determined and the suitability of these new cells under solar concentration were assessed. Full physical simulations are performed using SILVACO semiconductors modelling software to generate models of multi-junction solar cells that were crucial in informing iterations to growth and fabrication and help to reconcile theory with experiment. One of the key findings, of this thesis, is the fact that Intermediate band photovoltaic devices using material based on InAs/GaAs vertically stacked quantum dot arrays, can be used in applications according to specific configuration criteria such as high temperature operation conditions. The intermediate band cell, including an inter-dot doped configuration, has been found to be a potential candidate as the inter dot doping profile reduces the efficiency degradation below the GaAs values including an enhancement in the open circuit voltage. It has been proved that these devices not only have a good performance at high temperatures but also by changing the vertical stacking QD layer periodicity can enhance the short circuit current density while keeping a large open circuit voltage. It was confirmed in practical device operation that thermal energy is required to enable the intermediate band in InAs/GaAs QD materials. The impact of this works can help in the future improvements of the intermediate band solar cells based on InAs on GaAs QD. The best overall efficiency of 11.6 % obtained in this work is an excellent value for so simple devices configuration. The Si3N4, tested for the first time on InAs/GaAs QD materials, reduces the reflectance on the device surface to a value of 2% and the operational wavelength can be tuned by controlling the layer thickness. A 100 nm Si3N4 antireflective coating proved to be an excellent coating from 700 to 1000 nm. In terms of short circuit current density a 37% enhancement was achieved.

<div>In this paper various applications of axial tensile load, bending load, and rolling loading has been applied to a Copper Indium Gallium Diselenide (CIGS) Solar Cell to lean how it would affect the solar cell parameters of: Open circuit voltage (Voc), Short circuit current, (Isc), Maximum power (Pmax), and Efficiency (EFF), and Fill Factor (FF). These Relationships were found for with three different experiments. The first experiment the applies axial tensile stress is to a CIGS solar cell ranging from 0 to 200 psi with various strain rates: 0.0001, 0.001, 0.01, and 0.1 in/sec as well as various relaxation time: 1min, 5min, and 10 min while the performance of solar cell is measured. The results of this gave several trends couple pertaining the Voc . The first is that open circuit voltage increases slightly with increasing stress. The second is the rate of increase (the slope) increases with longer relaxation times. The second set of trend pertains to the Isc. The first is that short circuit current generally is larger with larger stress. The second is there seems to be a general increase in the Isc up to a given threshold of stress. After that threshold the Isc seems to decrease. The threshold stress varies depending on strain rate and relaxation time. The second set of experiments consisted of holding a CIGS solar cell in a fixed curved position while it was in operational use. The radii of the curved cells were: 0.41, 0.20, 0.16, 0.13, 0.11, 0.094, and 0.082 m. The radii were performed for both concave and convex cell curvature. The trends for this show a slight decrease in all cell parameters with decreasing radii, the exception being Voc which is not effecting, the convex curvature causing a slightly faster decrease than the concave. This set of experiments were also processed to find the trends of the single diode model parameters of series resistance (Rs), shunt resistance (Rsh), dark current (I0), and saturation current (IL), which agreed with the experimental results. The second experiment consisted of rolling a CIGS solar cell in tensile (cells towards dowel.) and compression (cells away from dowel) around a dowel to create internal damage. The diameter of the dowels decreased. The dowel diameters were: 2. 1.75, 1.25, 1, 0.75, 0.5, and 0.25 inches. This experiment showed similar trends as the bending one but also had a critical diameter of 1.75 in where beyond that damage much greater. Finally a parametric study was done in COMSOL Multiphysics® to examine how changes in the CIGS material properties of electron mobility (EM), electron life time, (EL), hole mobility 15 (HM), and Hole life time (HL) effect the cell parameters. The trends are of an exponential manner that converges to a given value as the material properties increase. When EL, EM, HL are very small, on the order of 10-4 times smaller than their accepted values, a transient like responses occurs.<br></div>

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