As of 21st September 2017, industrial use of hexavalent chromium (Cr(VI)) will, due to its environmental toxicity and carcinogenicity, be restricted by REACH regulations. Saab Aeronautics is therefore shifting anticorrosion surface treatment of aluminum alloys from hexavalent chromium conversion to trivalent chromium (Cr(III)) passivation. The purpose of this thesis is to investigate the characteristics of conversion coatings formed with the passivation chemical SurTec 650V, in order to facilitate transfer to the more environmental friendly alternative. Process parameters, such as pH and immersion time in SurTec 650V passivation baths, have been investigated for passivation of three different aluminum alloys; 2024, 6061 and 7075. The characteristics of the Cr(III) conversion coatings achieved at laboratory scale in the thesis work have been compared with SurTec 650V process in production scale and with Cr(VI) containing Alodine 1200 and Alodine 1500 processes. The impact of varying process parameters have been investigated with goniometry, x-ray photoelectron spectroscopy (XPS), auger electron spectroscopy (AES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to analyse characteristics of the conversion coatings. Differences in chemical composition on the surface and in depth profile was detected with XPS and AES, respectively and topology of coatings was found to differ for different aluminium alloys and parameter combinations. With TEM, the thickness of the conversion coating was found to be approximately 30-50 nm, which is thinner than the coatings formed with Cr(VI) passivation. Characteristics of coatings formed with Cr(III) passivation is concluded to be very dependent on parameter variation, especially for alloy 2024. Differences also occur between passivation at laboratory and production scale. Further evaluation of the production scale SurTec 650V process and corrosion testing should be performed, and an elaboration of a process control is required before the shift to an environmental friendly passivation process can be completely successful at Saab.

In this thesis, the process of fabricating PEDOT:PSS/c-Si hybrid solar cells has been investigated with the goal of performing a proof of concept as well as to determine the influence on solar cell performance of some processing parameters. Properties of PEDOT:PSS film formation and metal contact formation were investigated as a first step. Additionally, the surface passivation properties of PEDOT:PSS on n-Si have been studied and carrier lifetimes of 300 <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmu" />s were measured by quasi steady-state photoconductance and photoluminescence carrier lifetime imaging of silicon substrates that had PEDOT:PSS spin-coated onto both sides. Finally, working PEDOT:PSS/c-Si hybrid solar cells of both the FrontPEDOT and BackPEDOT concepts were successfully fabricated and their current-voltage characteristics were measured. The champion device showed a JSC of 23.0 mA/cm2, a VOC of 520 mV and a FF of 59% as measured directly after fabrication. Repeating the measurements the following day showed a strong degradation of the cells, particularly of the JSC. It can be concluded from this work that fully working PEDOT:PSS/c-Si hybrid solarcells of both the FrontPEDOT and BackPEDOT types can be fabricated through a simple and low-cost production route. The quality of the metal contacts is of very high importance for the function of the cells. The cells are heavily degraded within less than 24 hours when stored in atmoshperic conditions, but some of the function can be regained by annealing and edge isolation. Achieving better wetting on Si substrates after certain cleaning procedures is an important point for further study. PEDOT:PSS has been seen to have some excellent passivation properties on c-Si, although these results show a strong dependency on the specific type of PEDOT:PSS. / I denna uppsats har tillverkningen av PEDOT:PSS/c-Si hybridsolceller undersökts med målet att tillverka en fungerande solcell samt att bestämma påverkan på cellens prestanda av vissa processparametrar. Polymerfilmbildning och metallkontaktbildning undersöktes som ett första steg. Dessutom studerades polymerfilmens förmåga att passivera n-Si ytor, och livstider hos laddningsbärare på ca 300<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmu" />s mättes genom QSSPC och PL-I på kiselsubstrat med polymerfilmer på båda sidor. Slutligen tillverkades fungerande polymer/kisel hybridsolceller av både FrontPEDOT och BackPEDOT typ och de elektriska egenskaperna bestämdes. Den bästa cellen hade JSC=23.0 mA/cm2, VOC=520 mV och FF=59%, uppmätt direkt efter tillverkningen. Upprepning av mätningarna följande dag visade en stark degradering av cellerna, i synnerhet av kortslutningsströmmen. Man kan dra slutsatsen från detta arbete att fullt fungerande polymer/kisel hybridsolceller av både FrontPEDOT och BackPEDOT typ kan tillverkas genom en enkel och kostnadseffektiv produktionsväg. Kvaliteten på metallkontakterna är av mycket stor betydelse för cellernas funktion. Cellerna försämras kraftigt inom mindre än 24 timmar vid förvaring i atmosfäriska förhållanden, men en del av funktionen kan återfås genom upphettning och kantisolering. Att uppnå bättre vätning på kiselsubstrat efter vissa rengöringsmetoder är en viktig punkt för vidare studier. Polymerfilmer av PEDOT:PSS har visat sig ha utmärkta passiveringsegenskaper på kiselytor, även om dessa resultat visar ett starkt beroende på den specifika typen av PEDOT:PSS.

La recherche sur les sources d'électrons modulées en temps connaît actuellement un vif intérêt, notamment dans le domaine des sciences fondamentales ou pour certaines applications exigeantes. C'est dans ce contexte que ce travail exploratoire sur l'émission de champ (EC) photo-assistée de nanofils de silicium s'inscrit. Nous explorons dans un premier temps les caractéristiques émissives de ces nanofils semi-conducteurs présentant un régime de saturation très prononcé, très sensible à la température et à la lumière, et encore jamais observé pour de telles structures à température ambiante. Le rôle important joué par la surface dans la saturation est prouvé par des traitements in-situ ayant des conséquences radicales sur les caractéristiques courant-tension de l'EC. Grâce à des cycles de passivation à l'hydrogène nous avons pu montrer le rôle des liaisons pendantes à l'interface matériau/oxyde dans la saturation et basculer de façon réversible entre un comportement quasi-métallique et semiconducteur. Nous étudions ensuite la réponse de ces émetteurs à une excitation optique modulée en temps. Leur réponse est attribuée à la photoconduction due à l'absorption directe : les effets thermiques peuvent être exclus à ces puissances laser. Nous avons alors mis en évidence la présence de deux constantes de temps associées à l'éclairement et la relaxation de l'échantillon. Le rôle des états pièges en surface prend là encore une part importante dans le temps de réponse de l'échantillon en limitant celui-ci à quelques dizaines de microsecondes seulement. Enfin nous avons mis en évidence un effet complètement nouveau en EC sous éclairage laser : une double résistance différentielle négative. Dans les dispositifs à semiconducteurs, cet effet est généralement associé à des oscillations de courant à haute fréquence et ouvre la perspective vers des sources EC compactes et auto-oscillantes à très hautes fréquences / There is currently a notable rise in research on time modulated electron sources for new fundamental science and for several demanding applications. Our exploratory work on photo-assisted field emission (FE) from silicon nanowires falls within this context. We first explore FE characteristics of these semiconducting nanowires, which are very sensitive to temperature and light and present a very pronounced current saturation regime, never observed before on such structures. The strong influence of surface states on the saturation regime is proven by in-situ treatments, which radically alter the FE current-voltage characteristics. H-passivation cycles reveal the role of dangling bonds at material/oxide interface in the saturation regime and allow to reversibly switch between a quasi-metal and semiconductor behavior. We then study the response of these emitters to a time modulated optical excitation. The response is attributed to direct absorption photoconduction after excluding thermal effects at these laser powers. The existence of two time constants associated with illumination and relaxation time is shown. The role of the surface state traps again plays an important part in the response time, limiting it to some tens of microseconds. Finally, a completely new effect in FE under laser illumination is identified : a double negative differential resistance. In semiconductor devices this effect is usually associated with high frequency current oscillations and thus opens perspectives toward compact and high frequency self-oscillating FE sources

O armazenamento de energia em larga escala é um dos maiores desafios que temos que sanar em médio prazo para que tenhamos um impacto importante na matriz energética. As baterias aparecem como fortes candidatas para esta função, porém, é preciso melhorar todos os componentes das baterias, como eletrodos e eletrólitos, para aplicação em larga escala. Líquidos Iônicos (LIs) são interessantes alternativas para a utilização como eletrólito em bateria, pois abrem ampla possibilidades, como a utilização de ânodos metálicos e operação em alta temperatura. Sendo assim, este trabalho apresenta o estudo do uso do LI bis(trifluorometanosulfonil)imideto de N-n-butil-N-metilpiperidínio ([BMP][Tf2N]) na eletrodeposição de Mg utilizando vários procedimentos eletroquímicos e analíticos. A deposição/dissolução de Mg é irreversível quando há água (50 mmol L-1) no sistema, e uma reversibilidade de apenas 7,4 % em sistemas mais secos (5 mmol L-1). Imagens de MEV e espectros de EDS mostram que há Mg na superfície do eletrodo, porém é indicada a formação de um filme passivador. Além disso, também foi estudado o comportamento eletroquímico de Cu no LI [BMP][Tf2N], que apresenta um ânion com boa capacidade de coordenação e no LI tetracianoborato de N-n-butil-N-metilpiperidínio ([BMP][B(CN)4]), que apresenta um ânion com baixa capacidade de coordenação. A propriedade de coordenação tem grande influência na oxidação e corrosão do metal, enquanto que no [Tf2N] há corrosão por pitting e não há passivação do metal, o uso do [B(CN)4] leva a precipitação do sal Cu[B(CN)4], causando a passivação do metal. Além disso, mesmo em baixa concentração de água, há formação de óxido durante a oxidação do metal nos dois LIs. Como a água afeta o comportamento eletroquímico dos LIs, foi realizado um estudo das propriedades físico-químicas do LI bis(trifluorometanosulfonil)imideto de 1-n-butil-2,3-dimetilimidazólio ([BMMI][Tf2N]) e sua mistura com Li+ com diferentes quantidades de água. A presença de Li+ causa um grande aumento na capacidade do LI hidrofóbico em absorver água. Experimentos sugerem que há uma quebra nos agregados Li+-ânion, que foi confirmado por dinâmica molecular (DM). Ainda, a água apresenta grande modificação nas propriedades como densidade, viscosidade e condutividade iônica, sem contar que os resultados experimentais sugerem uma quebra na regra de Walden em altas temperaturas. Por fim, foi avaliado a estrutura local do LI tetracianoborato de 1-n-butil-2,3-dimetilimidazólio ([BMMI][B(CN)4]), para entender como é a interação entre o ânion de baixa capacidade de coordenação e o Li+. A distância entre os ânions e o Li+ é maior do que no caso do [Tf2N], indicando assim uma menor interação entre estes dois. A utilização de LIs como eletrólitos para baterias se apresenta como alternativa promissora, porém ainda demanda estudos para encontrar o melhor sistema. / Energy storage at large scale is one of the most important challenges that needs to be solved in medium term to have an important impact in the electrical grid. Batteries seem to be strong candidates for this function, however, it is needed to improve all battery components, as electrodes and electrolytes, to be applied in large scale. Ionic Liquids (ILs) are interesting alternatives to be used as electrolyte in a battery, since they open a wide range of possibilities, as the use of metallic anodes and operation at high temperature. This work presents the study of electrodeposition of Mg using the IL N-butyl,methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide ([BMP][Tf2N]) by several electrochemical and analytical techniques. The deposition/dissolution is irreversible in presence of high water concentration (50 mmol L-1), and a small reversibility of 7.4 % in dryer system (5 mmol L-1). EDS spectra show Mg presence in the electrode surface, however it is also observed the formation of passivating film. Besides this, it was also studied the electrochemical behavior of Cu in the IL [BMP][Tf2N], which presents a strong coordinating anion and in the IL N-butyl,methyl-piperidinium tetracyanoborate ([BMP][B(CN)4]), which presents a weak coordinating anion. It was observed that the oxidation and corrosion of Cu depends strongly on the anions coordinating properties, while on [Tf2N] it was observed pitting corrosion and no metal passivation, the use of [B(CN)4] leads to salt (Cu[B(CN)4]) precipitation, causing the metal passivation. It was also observed that even at low water concentration there is the formation of oxide in both ILs. As the water affects the electrochemical behavior of the ILs, it was realized a study of the physicochemical properties of the IL 1-Butyl-2,3-dimethylimidazolium bis((trifluoromethyl)sulfonyl)imide ([BMMI][Tf2N]) and its mixture with Li+ with different amounts of water. The Li+ presence provokes a huge increase in the water absorption ability of the hydrophobic IL. Experiments suggest that there is a break in the Li+-anion aggregates, which was confirmed by molecular dynamics (MD) simulations. In addition, water causes important changes in properties as density, viscosity and ionic conductivity; moreover, the experimental results suggest a break in the Walden\'s rule at high temperatures, due to aggregates modification. Lastly, it was evaluated the local structure of the IL 1-Butyl-2,3-dimethylimidazolium tetracyanoborate ([BMMI][B(CN)4]), to understand how a weak coordinating anion and the Li+ interact. It was showed by MD simulations that this property results in a bigger distance between anion and Li+ than in the case of [Tf2N], indicating a lower interaction between both. The use of ILs as electrolytes for batteries is a promising alternative, however it is needed more studies to find the best system.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-11-23T18:25:44Z No. of bitstreams: 1 Vinicius de Kayser Ortolan_.pdf: 6695172 bytes, checksum: 34dc13d07ab13e197255fa0d891b011c (MD5) / Made available in DSpace on 2015-11-23T18:25:44Z (GMT). No. of bitstreams: 1 Vinicius de Kayser Ortolan_.pdf: 6695172 bytes, checksum: 34dc13d07ab13e197255fa0d891b011c (MD5) Previous issue date: 2015-08-28 / itt Performance - Instituto Tecnológico em Desempenho da Construção Civil / UNISINOS - Universidade do Vale do Rio dos Sinos / A corrosão do aço é uma das principais formas de degradação das estruturas de concreto armado. Substituições parciais do cimento Portland por elevados teores de adições pozolânicas resultam em diminuição da concentração de hidróxido de cálcio, levando a uma redução do pH da solução do poro e influenciando na formação dos filmes de passivação sobre o aço. Este trabalho teve por objetivo avaliar a influência do pH e da força iônica da solução dos poros na resistência à corrosão em concretos armados produzidos com substituições parciais do cimento por cinza volante e por sílica ativa, determinação da composição química da solução dos poros (a fim de quantificar a força iônica e o pH), e medição da resistência à corrosão com o auxílio de ensaios eletroquímicos, em diferentes idades. Seis traços de concreto foram produzidos, com variados teores de substituição, com o intuito de reduzir o pH da solução dos poros. Além do traço de referência (0%), foram confeccionados concretos com 25%, 50% e 75% de cinza volante, e 5% e 10% de sílica ativa. A composição química da solução dos poros de cada traço foi medida nas idades de 4 horas, 3 dias, 7 dias, 28 dias e 91 dias, e os valores obtidos para o pH e força iônica destas soluções foi utilizado para auxiliar na interpretação dos resultados obtidos nos ensaios de potencial de corrosão, resistência de polarização e resistividade elétrica, também realizados ao longo de 91 dias em blocos de concreto armados com aço CA-50. Os resultados obtidos são consistentes com estudos anteriores, que mostram que o efeito do pH sobre a formação dos filmes de passivação depende do valor da força iônica da solução do poro. Os resultados mostram que, principalmente nas primeiras idades, quando os filmes de passivação estão sendo formados, as substituições parciais do cimento por cinza volante ou sílica ativa melhoram o desempenho da passivação da armadura, mesmo com uma leve diminuição do pH, desde que acompanhada da redução da força iônica das soluções. Este efeito é explicado pela diminuição da solubilidade dos óxidos e hidróxidos formadores dos filmes de passivação, associados à diminuição da condutividade elétrica da solução em virtude da redução da força iônica. Cabe ressaltar que neste período inicial (ao longo dos primeiros 7 dias), a resistividade elétrica do concreto manteve-se aproximadamente constante para os diferentes traços, não exercendo efeito significativo na melhoria da resistência à corrosão observada para os concretos com adições minerais. Assim, observa-se que é possível substituir parcialmente o cimento por cinza volante ou sílica ativa, sem causar danos à passivação da armadura, mesmo com uma leve redução do pH. / Corrosion of steel is one of the major forms of deterioration of reinforced concrete structures. Partial replacement of cement Portland by high levels of pozzolanic additions result in decreased concentration of calcium hydroxide, leading to a reduction in the pH of the pore solution and influencing the formation of passive films on steel. This study aimed to evaluate the influence of pH and the ionic strength of the pore’s solution in the corrosion resistance of reinforced concrete made with partial replacement of cement with fly ash and silica fume, determining the chemical composition of the pore solution (in order to quantify the ionic strength and pH), and corrosion resistance measurement with the aid of electrochemical tests, at different ages. Six concrete mixtures were produced with various substitution concentrations, in the order to reduce the pH of the pore solution. Besides the reference (0%), it was prepared concretes with 25%, 50% and 75% of fly ash, 5% and 10% of silica fume. The chemical composition pore’s solution of each proportion was measured at ages of 4 hours, 3 days, 7 days and 91 days, and the values obtained for pH and ionic strength of these solutions was used to assist in interpreting the results obtained from the tests of corrosion potential, polarization resistance and electrical resistivity, also conducted over 91 days in reinforced concrete blocks with CA-50 steel. The final results are consistent with previous studies, showing the effect of pH on the formation of passivation films depends on the ionic strength value of the pore solution. The results show that, mainly in early ages, when the passivation films are being formed, the partial cement replacement by fly ash and silica fume improves the passivation steel performance, even with a slight decrease in pH, if accompanied the reducing the ionic strength of the solutions. This effect is explained by decrease in solubility of the oxides and hydroxides of maker’s passivation films, associated with decrease electrical conductivity of the solutions due the reduction of the ionic strength. Note that in this initial period (over the first seven days), the concrete resistivity remained approximately constant for different proportion, no exercising significant effects on improving corrosion resistance for additions mineral concrete. Thus, it is observed that it is possible to partially replace cement by fly ash or silica fume, without causing damage to passivation of steel, even with a slight reduction on the pH.

The emerging 2D materials are potential solutions to the scaling of electronic devices to smaller sizes with lower energy cost and faster computing speed. Unlike traditional semiconductors e.g. Si, Ge, 2D materials do not have surface dangling bonds and the short-channel effect. A wide variety of band structure is available for different functions. The aim of the thesis is to calculate the electronic structures of several important 2D materials and study their application in particular devices, using density functional theory (DFT) which provides robust results. The Schottky barrier height (SBH) is calculated for hexagonal nitrides. The SBH has a linear relationship with metal work function but the slope does not always equal because Fermi level pinning (FLP) arises. The chemical trend of FLP is investigated. Then we show that the pinning factor of Si can be tuned by inserting an oxide interlayer, which is important in the application to dopant-free Si solar cells. Apart from contact resistance, we want to improve the conductivity of the electrode. This can be done by using a physisorbed contact layer like FeCl3, AuCl3, and SbF5 etc. to dope the graphene without making the graphene pucker so these dopants do not degrade the graphene's carrier mobility. Then we consider the defect formation of 2D HfS2 and SnS2 which are candidates in the n-type part of a tunnel FET. We found that these two materials have high mobility but there are also intrinsic defects including the S vacancy, S interstitial, and Hf/Sn interstitial. Finally, we study how to make defect states chemically inactive, namely passivation. The S vacancy is the most important defect in mechanically exfoliated 2D MoS2. We found that in the most successful superacid bis(trifluoromethane) sulfonamide (TFSI) treatment, H is the passivation agent. A symmetric adsorption geometry of 3H in the -1 charge state can remove all gap states and return the Fermi level to the midgap.

abstract: Recent technology advancements in photovoltaics have enabled crystalline silicon (c-Si) solar cells to establish outstanding photoconversion efficiency records. Remarkable progresses in research and development have been made both on the silicon feedstock quality as well as the technology required for surface passivation, the two dominant sources of performance loss via recombination of photo-generated charge carriers within advanced solar cell architectures. As these two aspects of the solar cell framework improve, the need for a thorough analysis of their respective contribution under varying operation conditions has emerged along with challenges related to the lack of sensitivity of available characterization techniques. The main objective of my thesis work has been to establish a deep understanding of both “intrinsic” and “extrinsic” recombination processes that govern performance in high-quality silicon absorbers. By studying each recombination mechanism as a function of illumination and temperature, I strive to identify the lifetime limiting defects and propose a path to engineer the ultimate silicon solar cell. This dissertation presents a detailed description of the experimental procedure required to deconvolute surface recombination contributions from bulk recombination contributions when performing lifetime spectroscopy analysis. This work proves that temperature- and injection-dependent lifetime spectroscopy (TIDLS) sensitivity can be extended to impurities concentrations down to 109 cm-3, orders of magnitude below any other characterization technique available today. A new method for the analysis of TIDLS data denominated Defect Parameters Contour Mapping (DPCM) is presented with the aim of providing a visual and intuitive tool to identify the lifetime limiting impurities in silicon material. Surface recombination velocity results are modelled by applying appropriate approaches from literature to our experimentally evaluated data, demonstrating for the first time their capability to interpret temperature-dependent data. In this way, several new results are obtained which solve long disputed aspects of surface passivation mechanisms. Finally, we experimentally evaluate the temperature-dependence of Auger lifetime and its impact on a theoretical intrinsically limited solar cell. These results decisively point to the need for a new Auger lifetime parameterization accounting for its temperature-dependence, which would in turn help understand the ultimate theoretical efficiency limit for a solar cell under real operation conditions. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018

La conception des futures générations de capteurs d'images CMOS, nécessite l'intégration de structures 3D telles que les tranchées profondes d'isolation, ou encore l'adoption de nouvelles architectures telles que les capteurs d'images à illumination face arrière. Cependant, l'intégration de telles architectures engendre l'apparition de nouvelles interfaces Si/SiO2, pouvant être la source d'un fort courant d'obscurité Idark, dégradant considérablement les performances électro-optiques du capteur. Ainsi, dans le but d'éliminer le Idark et d'augmenter l'efficacité de collecte et de confinement des photoporteurs au sein de la photodiode, la passivation de ces interfaces par l'introduction d'une jonction fortement dopée a été étudiée. D'une part, la passivation de la face arrière a été réalisée par implantation ionique activée par recuit laser pulsé. Grâce à un traitement très court et localisé, le recuit laser a démontré sa capacité à réaliser des jonctions minces et très abruptes. Une très bonne qualité cristalline ainsi que des taux d'activation avoisinant les 100% ont pu être atteint dans le mode fusion. Le mode sous-fusion quant à lui permet d'obtenir des résultats prometteurs en multipliant le nombre de tir laser. Les résultats électriques ont permis de distinguer les conditions optimales d'implantation et de recuit pour l'achèvement d'un faible niveau de Idark comparable à la référence en vigueur ainsi qu'une bonne sensibilité. Le deuxième axe d'étude s'est intéressé à la passivation des flancs des DTI par épitaxie sélective dopée in-situ. Des dépôts très uniformes de la cavité accompagnés d'une très bonne conformité de dopage le long des tranchées ont pu être réalisés. Les résultats sur lot électrique ont montré un très faible niveau de Idark supplantant la référence en vigueur / In order to maintain or enhance the electro-optical performances while decreasing the pixel size, advanced CMOS Image Sensors (CIS) requires the implementation of new architectures. For this purpose, deep trenches for pixel isolation (DTI) and backside illumination (BSI) have been introduced as ones of the most promising candidates. The major challenge of these architectures is the high dark current level (Idark) due to the generation/recombination centers present at both, DTI sidewalls and backside surfaces. Therefore, the creation of very shallow doped junctions at these surfaces reducing Idark and further crosstalk by drifting the photo-generated carriers to the photodiode region appears as key process step for introducing these architectures. For the backside surface passivation, a very shallow doped layer can be achieved by low-energy implantation followed by very short and localized heating provided by pulsed laser annealing (PLA). In the melt regime, box-shaped profiles with activation rates close to 100% and excellent crystalline quality have been achieved. The non-melt regime shows some potential, especially for multiple pulse conditions. In the optimal process conditions, very low level of Idark comparable to the standard reference has been achieved. In the other side, the passivation of DTI sidewalls has been performed by in-situ doped Epitaxy. Deposited layers with good uniformity and doping conformity all along the DTI cavity have been achieved. The electrical results show Idark values lower than the standard reference

In polycrystalline silicon (pc-Si) thin-film solar cells, defect passivation is critical to device performance. Isoelectronic or covalently bonded impurities, hydrogenic, extended defects and defects with localized levels in the bandgap (deep level defects) are typically introduced during the fabrication of, and/or are inherent to, pc-Si thin-film solar cells. These defects dramatically affect minority carrier lifetimes. Removing and/or passivating these defects is required to maximize minority carrier lifetimes and is typically done through thermal annealing and passivation techniques. For pc-Si thin-film solar cells on low temperature glass superstrates, rapid thermal annealing (RTA) and hydrogen plasma passivation (hydrogenation) are powerful techniques to achieve effective removal and passivation of these defects. In this thesis, three silicon thin-film solar cells structures on low-temperature glass are subjected to variations in RTA high-temperature plateaus, RTA plateau times, and hydrogen plasma passivation parameters. These solar cells are referred to as ALICIA, EVA and PLASMA. By varying the RTA plateau temperature and time at plateau, the trade-off between extensive dopant diffusion and maximum defect removal is optimized. To reduce the density of point defects and to electrically activate the majority of dopants, an RTA process is shown to be essential. For all three of the thin-film solar cell structures investigated in this thesis, a shorter, higher-temperature RTA process provides the best open-circuit voltage (Voc). Extensive RTA plateau times cause excessive dopant smearing, increasing n = 2 recombination and shunt resistance losses. Hydrogenation is shown to be an essential step to achieve maximum device performance by `healing' the defects inherent to pc-Si thin-film solar cells. If the hydrogen concentration is about 1-2 times the density of oxygen in the cells as measured by secondary ion mass spectroscopy (SIMS), the cells seem to respond best to hydrogenation, with good resultant Voc and short-circuit for all cells investigated in this thesis. The effect of hydrogen passivation on the Voc is spectacular, typically increasing it by a factor of 2 to 3.5. Hydrogen de-bonding from repeated thermal treatments at increasing temperature provides a deeper understanding of what defects exist and the nature of the defects that limit the cell voltage. The variation in RTA and hydrogenation process parameters produces significant empirical insight into the effectiveness of RTA processes for point defect removal, dopant activation, point defect and grain boundary passivation, and impurity passivation. SIMS measurements are used to determine the impurities present in the cells' bulk and the amount of hydrogen available to passivate defects. From the results presented it appears that pc-Si thin-film solar cells on low-temperature glass are a promising, and potentially lower-cost, alternative to Si wafer based cells.

The cost of crystalline silicon solar cells must be reduced in order for photovoltaics to be widely accepted as an economically viable means of electricity generation and be used on a larger scale across the world. There are several ways to achieve cost reduction, such as using thinner silicon substrates, lowering the thermal budget of the processes, and improving the efficiency of solar cells. This thesis examines the use of plasma enhanced chemical vapour deposited silicon nitride to address the criteria of cost reduction for n-type crystalline silicon solar cells. It focuses on the surface passivation quality of silicon nitride on n-type silicon, and injection-level dependent lifetime data is used extensively in this thesis to evaluate the surface passivation quality of the silicon nitride films. The thesis covers several aspects, spanning from characterisation and modelling, to process development, to device integration. The thesis begins with a review on the advantages of using n-type silicon for solar cells applications, with some recent efficiency results on n-type silicon solar cells and a review on various interdigitated backside contact structures, and key results of surface passivation for n-type silicon solar cells. It then presents an analysis of the influence of various parasitic effects on lifetime data, highlighting how these parasitic effects could affect the results of experiments that use lifetime data extensively. A plasma enhanced chemical vapour deposition process for depositing silicon nitride films is developed to passivate both diffused and non-diffused surfaces for n-type silicon solar cells application. Photoluminescence imaging, lifetime measurements, and optical microscopy are used to assess the quality of the silicon nitride films. An open circuit voltage of 719 mV is measured on an n-type, 1 Ω.cm, FZ, voltage test structure that has direct passivation by silicon nitride. Dark saturation current densities of 5 to 15 fA/cm2 are achieved on SiN-passivated boron emitters that have sheet resistances ranging from 60 to 240 Ω/□ after thermal annealing. Using the process developed, a more profound study on surface passivation by silicon nitride is conducted, where the relationship between the surface passivation quality and the film composition is investigated. It is demonstrated that the silicon-nitrogen bond density is an important parameter to achieve good surface pas-sivation and thermal stability. With the developed process and deeper understanding on the surface passivation of silicon nitride, attempts of integrating the process into the fab-rication of all-SiN passivated n-type IBC solar cells and laser doped n-type IBC solar cells are presented. Some of the limitations, inter-relationships, requirements, and challenges of novel integration of SiN into these solar cell devices are identified. Finally, a novel metallisation scheme that takes advantages of the different etching and electroless plating properties of different PECVD SiN films is described, and a preliminary evalua-tion is presented. This metallisation scheme increases the metal finger width without increasing the metal contact area with the underlying silicon, and also enables optimal distance between point contacts for point contact solar cells. It is concluded in this thesis that plasma enhanced chemical vapour deposited silicon nitride is well-suited for n-type silicon solar cells.