Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-14T14:14:33Z No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:20:25Z (GMT) No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-09-16T19:20:33Z (GMT) No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) / Made available in DSpace on 2016-09-16T19:20:46Z (GMT). No. of bitstreams: 1 TeseVHP.pdf: 3273273 bytes, checksum: afe82ad5c25bb61d489c9fcaec24a835 (MD5) Previous issue date: 2015-05-07 / Não recebi financiamento / Demineralization and caries are often present in patients with orthodontic braces due to the increased accumulation of dental biofilm containing Streptococcus mutans, which produces acids that attack the tooth surface. The Antimicrobial Photodynamic Therapy (APDT) has been shown as an alternative in microbial inactivation in dentistry. This work, carried out both in vitro and in vivo, aims to evaluate the antimicrobial effect of APDT on Streptococcus mutans present in the dental biofilm accumulated on the metal surface of orthodontic appliances and in patients undergoing orthodontic treatment. The in vitro study evaluated the susceptibility of biofilm formed by S. mutans on the metal surface under the application of orthodontic appliances APDT induced Curcumin diluted surfactant (SDS) and blue light-emitting diode (LED). The samples were treated with the photosensitizer (PS) at a concentration of 1 g/L, 0.1% surfactant and exposed to LED light (455 ± 10 nm, 46mW/cm²), fluence of 30 J/cm². The experimental groups studied were: control group (P-L-S-); light (P-L+S-), surfactant (P-L-S+) and photosensitizer (P+L-S-) groups; surfactant-light (P-L+S+), photosensitizer-surfactant (P+L-S+) and PDT (P+L+S-) groups; and the PDT-surfactant (P+L+S+) group. Each group was named accordingly to the addiction or not of the photosensitizer (P+ or P-), surfactant (S+ or S-) and application or not of light (L+ or L-), respectively. The colonies grown on plates of brain heart infusion (BHI) were counted (CFU / mL) and the results were analyzed by ANOVA and the post hoc Tukey test (p <0.05). The results showed that in this research protocol, the group P+L+S+ was able to promote significant decrease (p<0.001) on the population of S. mutans of 99.999% compared to the control group. In the in vivo study, 24 volunteers were randomly selected in order to evaluate the clinical utility of APDT and the APDT association with the surfactant (SDS) as oral decontamination agents in orthodontic patients. The selected patients (n = 24) were randomly divided into seven groups: G1 - Negative control, G2 - Curcumin mouthwash, G3 - Curcumin mouthwash+SDS, G4 - light irradiation, G5 - APDT, G6 - APDT+SDS and G7 - Positive Control (chlorhexidine 0.12% moutwash). Saliva samples were collected from unstimulated way of each patient in three steps (S) as follows: S1 - initial condition S2 - Treatment with rinsing (water, curcumin or chlorhexidine) and S3 - After APDT. The photosensitiser used was curcumin with concentration of 1 g/L. Two types of blue LED light source emitting in 450±10nm were used in the present study: one emitting with an intensity of 33.54 mW/cm² and other with 212 mW/cm². Evaluation of microbial reduction, and survival fraction in each of the studied levels, was performed using the Kruskal-Wallis ANOVA test. Statistical analysis showed that only G6 and G7 presented results of bacterial inactivation that showed statistically significant differences (p<0.05) compared to those observed in G1. These results indicated that APDT, when combined with SDS surfactant, may be used as an adjunct agent for convenient oral decontamination promoter in vivo. / Desmineralizações e cáries dentais estão comumente presentes em indivíduos portadores de aparelho fixo ortodôntico, isto ocorre devido ao aumento de acúmulo de biofilme dental contendo Streptococcus mutans, os quais produzem ácidos que atacam a superfície dental. A terapia fotodinâmica antimicrobial (TFDA) tem sido mostrada como alternativa em inativação microbiana na Odontologia. Este trabalho, realizado in vitro e in vivo, tem o objetivo de avaliar o efeito antimicrobiano da TFDA sobre Streptococcus mutans em biofilme dental sobre superfície metálica de acessórios ortodônticos e em indivíduos sob tratamento ortodôntico. O estudo in vitro avaliou a susceptilidade de biofilme formado por S. mutans sobre superfície metálica de acessórios ortodônticos sob aplicação de TFDA induzida por Curcumina diluída em surfactante (SDS) e por diodo emissor de luz azul (LED). Nas amostras obtidas de lâminas de bandas ortodônticas foram formados biofilmes e tratadas com fotossensibilizador (FS) com concentração de 1g/L, surfactante a 0,1% e exposto a luz LED (455±10 nm, 46mW/cm²), com fluência de30J/cm2. Os grupos experimentais estudados foram: C- (somente lavagem com solução fisiológica); L+ (aplicação apenas de luz); S+L- (aplicação de surfactante); S+L+ (aplicação de surfactante e luz); F+L- (aplicação de fotossensibilizador sem luz); F+L+ (aplicação de fotossensibilizador e luz); F+L-S+ (aplicação de fotossensibilizador sem luz + surfactante) e F+L+S+ (aplicação de fotossensibilizador e luz + surfactante). As colônias cultivadas em placas com Brain Heart Infusion (BHI) foram contadas (UFC/mL) e os resultados foram analisados por ANOVA e teste Tukey post hoc (p<0.05). Os resultados obtidos demonstraram que no protocolo deste estudo o grupo F+S+L+ foi capaz de promover diminuição significativa(p<0,001) da população de S. mutans em 99,999% comparado ao grupo controle. No estudo in vivo, 24 voluntários foram selecionados aleatoriamente, com o objetivo de avaliar a eficiência clínica da TFDA e da associação da TFDA com o surfactante SDS como agentes de descontaminação bucal em indivíduos ortodônticos. Os indivíduos selecionados foram distribuídos aleatoriamente em sete grupos experimentais: G1 - controle negativo, G2 - bochechos com curcumina, G3 – bochechos com curcumina + SDS, G4 - irradiação com luz apenas, G5 - TFDA, G6 - TFDA + SDS e G7 - Controle Positivo (clorexidina 0,12%). Amostras de saliva foram coletadas de maneira não estimulada de cada um dos indivíduos em três etapas (s), como segue: S1 - Condição inicial, S2 - Tratamento com bochechos (água, clorexidina ou curcumina) e S3 - Após TFDA. O fotossensibilizador usado foi a Curcumina em concentração de 1g/L. Foi utilizado no estudo dois tipos de equipamentos de luz com LED azul (450 ± 10nm, 33.54 mW/cm2 e 212 mW/cm2). A avaliação da redução microbiana, e da fração de sobrevivência em cada um dos níveis estudados, foi realizada utilizando-se o teste ANOVA Kruskal-Wallis. A análise estatística mostrou que apenas os grupos 6 e 7 apresentaram resultados de inativação bacteriana que apresentavam diferenças estatisticamente significantes (p <0,05) em relação aos resultados observados no grupo 1. Estes resultados indicam que a TFDA associada com o surfactante SDS pode ser utilizado como agente auxiliar conveniente para promover a descontaminação bucal.

No description available.

No description available.

In order to meet the requests of the application as pixel switch and current driver in next generation active-matrix liquid crystal displays (AMLCD) and active-matrix organic light-emitting diodes (AMOLED). The materials of low temperature poly-silicon (LTPS) and metal-oxide are supposed to be the most potential material for active layer of thin-film transistors (TFTs) due to their high mobility compared to the traditional amorphous silicon TFTs. Therefore, in order to make the LTPS TFTs and metal-oxide TFTs affordable for the practical applications, the understanding of instability and reliability is critically important. In the first part, we studied the nonvolatile memory characteristics of polycrystalline-silicon thin-film-transistors (poly-Si TFTs) with a silicon-oxide-nitride-oxide-silicon (SONOS) structure. As the device was programmed, significant gate induced drain leakage current was observed due to the extra programmed electrons trapped in the nitride layer which. In order to suppress the leakage current and thereby avoid signal misidentification, we utilized band-to-band hot hole injection method to counteract programmed electrons and this method can exhibit good sustainability because the injected hot holes can remain in the nitride layer after repeated operations. On the other hand, we also investigated the degradation behavior of SONOS-TFT under off-state stress. After the electrical stress, the significant on-state degradation indicates that the interface states accompanied with hot-hole injection. Moreover, the ISE-TCAD simulation tool was utilized to model the degradation mechanism and analyze trap states distribution. Furthermore, we also performed the identical off-state stress for the device with different memory states. The different degradation behavior under different memory states is attributed to the different overlap region of injected holes and trap states. In the second part, the degradation mechanism of indium-gallium-zinc oxide (IGZO) thin film transistors (TFTs) caused by gate-bias stress performed in the dark and light illumination was investigated. The parallel threshold voltage indicates that charge trapping model dominates the degradation behavior under positive gate-bias stress. However, the degradation of negative gate bias stress is much slighter than the positive gate bias stress since the IGZO material is hard to induced hole inversion layer. In addition, the hole mobility is much lower than electron resulting in ignorable hole trapping effect. On the other hand, the identical positive and negative gate bias stress performed under light illumination exhibit opposite degradation behavior compared with dark stress. This degradation variation under dark and light illumination can be attributed to the effectively energy barrier variation of electron and hole trapping. Furthermore, to further investigate the light induced instability for IGZO TFTs, the device with and without a SiOx passivation were investigated under light illumination. The experiment results indicate that oxygen adsorption and desorption dominate the light induced instability for unpassivated device and the trap states caused during the passivation layer deposition process will induce apparent subthreshold photo-leakage current under light illumination. In the third part, we investigated the degradation mechanism of IGZO TFTs under hot-carrier and self-heating stress. Under hot-carrier stress, except the electron trapping induced positive Vt shift, an apparent on-current degradation behavior indicates that trap states creation. On the other hand, the identical hot-carrier stress performed in the asymmetric source/drain structure exhibits different degradation behavior compared with symmetric source/drain structure. For asymmetric structure, the strong electrical field in the I-shaped drain electrode will induce channel hot electron injection near the drain side and cause asymmetric threshold voltage degradation. In this part we also investigated the degradation behavior under self-heating stress. The apparent positive threshold voltage (Vt) shift and on-current degradation indicate that the combination of trap states generation and electron trapping effect occur during stress. The trap states generation is caused by the combination of Joule heating and the large vertical field. Moreover, the Joule heating generated by self-heating operation can enhance electron trapping effect and cause larger Vt shift in comparison with the gate-bias stress. Finally, the electrical properties and photo sensitivity of dual gate IGZO TFTs were investigated. The asymmetric electrical properties and photo sensitivity under top gate and bottom gate operation is attributed to the variation of gate control region. Furthermore, the obvious asymmetric photo sensitivity can be utilized to the In-cell touch panel technology and lower the process cost compared with the traditional a-Si TFTs due to the elimination of black matrix.

Photo-induced charge transfer which occurs between molecules or different parts of a large molecule is the pivotal process related to performances of organic electronics. In particular, injection of charge carriers into conjugated polymers and dissociation of photo-generated excitons at the heterojunction between a donor and acceptor system are of great importance in determining the luminescence efficiency of organic light emitting diodes (OLEDs) and solar energy conversion efficiency of organic solar cells, respectively. However, the complex nature of organic semiconductors as well as complicated primary processes involved in the functioning of these devices have prevented us from understanding unique characteristics of these processes and thereby engineering better materials for higher performances. In this dissertation, two different types of photo-induced (or -related) charge transfer processes occurring in organic semiconductors were investigated by using single molecule spectroscopy (SMS) techniques to unravel the complexities of these processes. The carefully designed functioning capacitor-like model devices similar to OLEDs and photovoltaic cells were fabricated where isolated single nanoparticles were introduced as an active medium to mitigate the complexities of these materials. We observed that injection of positively charged carriers (holes) into poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) single nanoparticles from the carbazole hole transport layer does not occur in the absence of light. We denoted the observed hole injection in aid of light as the light-induced hole transfer mechanism (LIHT). It was revealed that the charging dynamics are highly consistent with a cooperative charging effect. In addition, the LIHT was proposed as the possible source for the formation of deep trapped hole in organic devices. Local exciton dissociation yields across a nanostructured domain between poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) single nanoparticles and either poly(9,9- dioctylfluorene - co - bis-N,N- (4 -butylphenyl)-bis-N,N-phenyl-1,4-phenylene diamine) (PFB) or poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) film in model photovoltaic devices was also investigated. A wide distribution of exciton dissociation yields was observed from each nanodomain due to the device geometry. The observed hysteresis in fluorescence voltage curve was ascribed to accumulated charges following charge separations. The dynamics of charge separation under the applied electric field was described in more detail. / text

Cette thèse s’est focalisée sur le développement et l’optimisation de techniques de métallisation électrochimique permettant le dépôt de métaux conducteurs, l’argent et le cuivre, par voie électrolytique ou par la technique dite LIP (Light-Induced Plating). Deux approches ont été abordées pour l’élaboration des contacts en face avant : l’épaississement de contacts sérigraphiés d’une part, et la réalisation de contacts entièrement par voie électrochimique sans recours à la sérigraphie. Pour cette dernière solution, le dépôt d’une couche d’accroche avant l’étape d’épaississement est nécessaire afin d’assurer une résistivité de contact faible, une bonne adhérence et une bonne sélectivité au travers de la couche anti-reflet. Ces objectifs ont été atteints grâce à la mise en œuvre et l’optimisation de dépôts electroless de nickel-phosphore (NiP), y compris sur émetteur peu dopé. Les investigations menées ont également permis une meilleure compréhension des mécanismes de formation du contact NiP/Si. La faisabilité des techniques de dépôt électrochimique a été démontrée pour diverses applications: cellules avec contacts électrochimiques NiP/Ag en face avant, cellules de type n, épaississement de contacts fins sérigraphiés… Des résultats très prometteurs d’amélioration de facteur de forme FF et de rendement η ont été obtenus et permettent d’envisager une ouverture potentielle vers de nouvelles structures de cellules photovoltaïques à haut rendement : cellules à émetteur peu dopé, cellules à émetteur sélectif avec ouverture laser de la couche anti-reflet, cellules à contacts arrières…. / This thesis is focused on the development and the optimization of electrochemical metallization techniques allowing the deposition of conductive metals, silver and the copper, by electrolytic deposition or by lip (light-induced plating). Two approaches were studied to realize the front side contacts of silicon solar cells: the thickening of screen-printed contacts and the fabrication of contacts completely by electrochemical deposition without screen-printing. For this solution, the deposition of a seed layer before thickening is necessary to insure a low contact resistivity, a satisfying adhesion and selectivity through the anti-reflection coating. These objectives were reached thanks to the optimization of electroless nickel-phosphorous (nip) deposits, including on low doped emitter. The investigations also allowed a better understanding of the NiP/Si contact formation mechanisms. The feasibility of electrochemical deposition techniques was demonstrated for various applications : cells with electrochemical front side contacts NiP/Ag, type n cells, thickening of fine line screen-printed contacts… very promising results of fill factor ff and efficiency improvement were obtained and allow to realize new structures of high efficiency photovoltaic cells : cells with low doped emitter, cells with selective emitter and with laser ablated anti-reflection coating, rear contact cells…

The present thesis deals with different aspects of the chemistry of oxovanadium(IV) complexes, their interaction with DNA and protein and photo-induced DNA and protein cleavage activity and photocytotoxicity. Chapter I presents a general introduction on various modes of interactions of organic compounds and transition metal complexes capable of targeting DNA leading to DNA strand scission, emphasizing particularly the photo-induced DNA cleavage activities for their potential application in PDT. The mechanistic pathways associated with the DNA cleavage are discussed. A comparison has been made on the advantages of photoactive metal complexes over organic conjugates. Objective of the present investigation is also dealt in this Chapter. Chapter II of the thesis deals with the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes of N-salicylidene-S-methyldithiocarbazate (salmdtc) and phenanthroline bases to explore the photo-induced DNA cleavage activity in UV-A light of 365 nm. Chapter III presents the synthesis, characterization, DNA binding and photo-induced DNA cleavage activity of ternary oxovanadium(IV) complexes containing N-salicylidene-L-methionate (salmet) and N-salicylidene-L-tryptophanate (saltrp) Schiff bases and phenanthroline bases. The objective of this work is to investigate the photo-induced DNA cleavage activity in near-IR light and to see the effect of pendant thiomethyl and indole moieties in the DNA cleavage reactions. Chapter IV deals with the synthesis, characterization, DNA binding, red-light induced DNA cleavage activity and photocytotoxicity of ternary oxovanadium(IV) complexes having N-salicylidene-L-arginine (sal-argH) and N-salicylidene-L-lysine (sal-lysH) Schiff bases and phenanthroline bases. The important results include the visible light-induced DNA cleavage activity and photocytotoxicity of the complexes in human cervical HeLa cancer cells. Chapter V describes the synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity of oxovanadium(IV) complexes containing bis(2-benzimidazolylmethyl)amine and phenanthroline bases. The significant results include DNA cleavage activity in near-IR light and photocytotoxicity of the dppz complex in non-small cell lung carcinoma/human lung adenocarcinoma A549 cells in visible light. Further, we have studied the protein cleavage activity of the complexes in UV-A light of 365 nm by using bovine serum albumin (BSA) and lysozyme. Finally, Chapter VI presents the binary oxovanadium(IV) complexes of phenanthroline bases. We have studied their synthesis, characterization, DNA binding and photo-induced DNA and protein cleavage activity and photocytotoxicity. Photocytotoxicity of dppz complex has been studied in human cervical HeLa cancer cells in visible light. Photo-induced protein cleavage activity of the complexes has been studied in UV-A light of 365 nm by using BSA and lysozyme. The references have been compiled at the end of each chapter and indicated as superscript numbers in the text. The complexes presented in this thesis are represented by bold-faced numbers. Crystallographic data of the complexes, characterized structurally by single crystal X-ray crystallography, are given in CIF format in the enclosed CD (Appendix-I). Due acknowledgements have been made wherever the work described is based on the findings of other investigators. Any omission that might have happened due to oversight or mistake is regretted.

The interplay of experiments and theory is essential to deepen our understanding of magnetization dynamics. This thesis aims to serve as a bridge between these two aspects by establishing a mathematical framework that enables the computation of optical observable quantities based on theoretical models. The equations are cast in a matrix representation that is well-suited for performing numerical simulations. Additionally, the generality of these methods enables their application to layered media with any geometry, regardless of whether they possess magnetic properties or not. Furthermore, it explores the various perspectives and physical mechanisms involved in magneto-optic measurements to provide the reader with a self consistent introduction to the subject matter. Numerical calculations are presented for bulk Fe, alternating layers of Fe/Au and Ni with a MgO coating and a SiO substrate for different energies, angle of incident and magnetization direction. The results demonstrate the effectiveness of the method in predicting measurable outcomes from theoretical considerations and enables the analysis of optimal experimental configurations. / Samverkan mellan experiment och teori är avgörande för fördjupa vår förståelse av magnetiska system och deras dynamik. Målet med denna uppsats är att etablera en koppling mellan dessa två aspekter genom att formulera ett matematiskt ramverk som möjliggör beräkningar av optiska observerbara storheter baserat på teoretiska modeller. Ekvationerna formuleras med matriser vilket är väl lämpat för att utföra numeriska simuleringar. Dessutom möjliggör metodens generella natur tillämpning på skiktade material av godtycklig geometri, oavsett om de har magnetiska egenskaper eller inte. Vidare utforskar uppsatsen olika perspektiv och fysikaliska mekanismer som är involverade i magneto-optiska mätningar för att ge läsaren en självständig introduktion till ämnet. Numeriska beräkningar presenteras för bulkjärn, växlande lager av Fe/Au och Ni med en MgO-beläggning och ett SiO-substrat för olika energier, infallsvinkel och magnetiseringsriktning. Resultaten visar på metodens förmåga att förutsäga mätbara resultat baserat på teoretiska överväganden och tillåter analys av optimala experimentella uppställningar.

A significant level of research is currently being carried out in the development of driver support systems as they are expected to play a key role in minimizing road vehicle accidents and creating a safe driving environment under harsh weather conditions. However, the performance of some components used by existing driver support systems like LIDAR and visual cameras are affected by extreme weather conditions such as heavy rain fall and snow. Therefore, it is paramount to identify key locations in an automotive vehicle where such systems are least affect by external weather conditions, thereby, improving their overall performance. The field of research that deals with such questions from a simulation perspective is called contamination modeling. At the moment, one of the biggest knowledge gaps in this field is how to consider the effect of different materials on the movement of liquids such as water on different automotive surfaces like glass, plastic, rubber and painted metal. The work presented in this research study has been carried out to investigate and establish the most suitable simulation strategies to match numerical predictions with experimental data for flow of water over different automotive surfaces. Following a comprehensive parametric study of simulation parameters, it was found that the most suitable model that can be tweaked to achieve different flow properties with different surfaces is a dynamic contact angle model. The Blended Kistler model available in STAR-CCM+ required specific values for static, advancing and receding contact angles to optimize a surface for a given material. Therefore, droplet experiments of two droplet sizes were initially carried out for all tested materials at different inclinations and necessary flow parameters were recorded. All experiments were carried out using an approach known as light induced fluorescence imaging where the captured images provided a very convenient method for post processing in computational software. Results from droplet experiments showed that water moved quickest on plastic and slowest on glass. Static contact angle measurements were carried out first on horizontal surfaces. Afterwards, the surface was inclined at 15, 30, 45, 60, and 75 degrees to measure changes in contact angle and velocities. The surfaces for glass and painted metal were directly taken from the door of a Volvo S60 while a separate surface was used for plastic and rubber. These results were then used to create simulation setups for rivulets in STAR-CCM+ with the multiphase modeling approach known as volume of fluid. Rivulet simulations were carried out for all four materials at five different inclinations and the results were compared and validated with experimental data. The results show good correlation between numerical predictions for rivulet movement and experimental data emphasising on the possibility of fine-tuning the surfaces of a simulation setup to represent different material properties.

Cette thèse s’intéresse aux effets de la compensation des dopants sur les propriétés électriques du silicium cristallin. Nous montrons que le contrôle du dopage net, qui est indispensable à la réalisation de cellules solaires à haut rendement, s’avère difficile dans les lingots cristallisés à partir de silicium contenant à la fois du bore et du phosphore. Cette difficulté s’explique par la forte ségrégation du phosphore durant la cristallisation, qui donne lieu à d’importantes variations de dopage net le long des lingots de silicium solidifés de façon directionelle. Pour résoudre ce problème, nous proposons le co-dopage au gallium pendant la cristallisation et prouvons l’efficacité de cette technique pour contrôler le dopage net le long de lingots de type p ou n fabriqués à partir d’une charge de silicium contenant du bore et du phosphore. Nous identifions les spécificités du matériau fortement compensé ainsi obtenu comme étant: une forte sensibilité de la densité de porteurs majoritaires à l’ionisation incomplète des dopants, une réduction importante de la mobilité comparée aux modèles théoriques et une durée de vie des porteurs qui est déterminée par la densité de porteurs majoritaires et dominée après éclairement prolongé par les centres de recombinaison liés aux complexes de bore et d’oxygène. Pour permettre la modélisation de cellules solaires à base de silicium purifié par voie métallurgique, nous proposons une paramétrisation des propriétés fondamentales du silicium compensé mentionnées ci dessus. Nous étudions également la dégradation de la durée de vie des porteurs sous éclairement dans des échantillons de silicium de type p et n présentant une large gamme de niveaux de dopage et de compensation. Nous montrons que le défaut bore-oxygène est issu d’un complexe formé à partir de bore substitutionnel pendant la fabrication des lingots et activé sous injection de porteurs par une reconfiguration du défaut assistée par des charges positives. Finalement, nous appliquons le co-dopage au gallium pour la cristallisation de silicium UMG et démontrons que cette technique permet d’augmenter sensiblement la tolérance au phosphore sans compromettre le rendement matière de l’étape de cristallisation ou la performance des cellules solaires avant dégradation sous éclairement. / This thesis focuses on the effects of dopant compensation on the electrical properties of crystalline silicon relevant to the operation of solar cells. We show that the control of the net dopant density, which is essential to the fabrication of high-efficiency solar cells, is very challenging in ingots crystallized with silicon feedstock containing both boron and phosphorus such as upgraded metallurgical-grade silicon. This is because of the strong segregation of phosphorus which induces large net dopant density variations along directionally solidified silicon crystals. To overcome this issue, we propose to use gallium co-doping during crystallization, and demonstrate its potential to control the net dopant density along p-type and n-type silicon ingots grown with silicon containing boron and phosphorus. The characteristics of the resulting highly-compensated material are identified to be: a strong impact of incomplete ionization of dopants on the majority carrier density, an important reduction of the mobility compared to theoretical models and a recombination lifetime which is determined by the net dopant density and dominated after long-term illumination by the boron-oxygen recombination centre. To allow accurate modelling of upgraded-metallurgical silicon solar cells, we propose a parameterization of these fundamental properties of compensated silicon. We study the light-induced lifetime degradation in p-type and n-type Si with a wide range of dopant concentrations and compensation levels and show that the boron-oxygen defect is a grown-in complex involving substitutional boron and is rendered electrically active upon injection of carriers through a charge-driven reconfiguration of the defect. Finally, we apply gallium co-doping to the crystallization of upgraded-metallurgical silicon and demonstrate that it allows to significantly increase the tolerance to phosphorus without compromising neither the ingot yield nor the solar cells performance before light-induced degradation.