Nano structured solar cells provide an opportunity for increased open circuit voltages and and short circuit currents in solar cells due to quantum confinement of the window and absorber materials and an increase in the optical path length for the incident light. In this study, both bulk and nano heterojunctions of CIS/CdS and Cu2S/CdS devices have been fabricated and studied on plain glass substrates and inside porous alumina templates to compare their performance. The devices have also been characterized SEM, XRD and JV measurements. The J-V curves have also been analyzed for series resistance, diode ideality factor and reverse saturation current density.

In this study, InSe and CdS thin films were deposited by thermal evaporation method onto glass substrates. Schottky and heterojunction devices were fabricated by deposition of InSe and CdS thin films onto SnO2 coated glass substrates with various top metal contacts such as Ag, Au, In, Al and C. The structural, electrical and optical properties of the films were investigated prior to characterization of the fabricated devices. The structural properties of the deposited InSe and CdS thin films were examined through SEM and EDXA analysis. XRD and electrical measurements have indicated that undoped InSe thin films deposited on cold substrates were amorphous with p-type conductivity lying in the range of 10-4-10-5 (&amp / #61527 / .cm)-1 at room temperature. Cd doping and post-depositional annealing effect on the samples were investigated and it was observed that annealing at 100 oC did not show any significant effect on the film properties, whereas the conductivity of the samples increased as the Cd content increases. Temperature dependent I-V and Hall effect measurements have shown that conductivity and carrier concentration increases with increasing absolute temperature while mobility is almost temperature independent in the studied temperature range of 100-430 K. The structural and electrical analysis on the as-grown CdS thin films have shown that the films were polycrystalline with n-type conductivity. Temperature dependent conductivity and Hall effect measurements have indicated that conductivity, mobility and carrier concentrations increases with increasing temperature. Transmission measurements on the as-grown InSe and CdS films revealed optical band gaps around 1.74 and 2.36 eV, respectively. Schottky diode structures in the form of TO/p-InSe/Metal were fabricated with a contact area of around 8x10-3 cm2 and characterized. The best rectifying devices obtained with Ag contacts while diodes with Au contacts have shown slight rectification. The ideality factor and barrier height of the best rectifying structure were determined to be 2.0 and 0.7 eV, respectively. Illuminated I-V measurements revealed open-circuit voltages around 300 mV with short circuit current 3.2x10-7 A. High series resistance effect was observed for the structure which was found to be around 588 &amp / #61527 / . Validity of SCLC mechanism for Schottky structures was also investigated and it was found that the mechanism was related with the bulk of InSe itself. Heterostructures were obtained in the form of TO/n-CdS/p-InSe/Metal and the devices with Au and C contacts have shown the best photovoltaic response with open circuit voltage around 400 mV and short circuit current 4.9x10-8 A. The ideality factor of the cells was found to be around 2.5. High series resistance effect was also observed for the heterojunction devices and the fill factors were determined to be around 0.4 which explains low efficiencies observed for the devices.

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-06Bitstream added on 2014-06-13T19:50:18Z : No. of bitstreams: 1 pineiz_tf_me_bauru.pdf: 2151623 bytes, checksum: a3aa74574b72ca684cf6ef1a0dc34297 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Dióxido de estanho (Sn'X IND. 2') é um semicondutor de bandgap largo com condutividade do tipo-n na forma não dopada, sendo aplicado em dispositivos diversos. Neste trabalho, filmes finos e géis secos de Sn'X IND. 2' dopados com os íons terras-raras 'Ce POT. 3+' e Eu POT 3+' foram sintetizados através do processo sol-gel. Por outro lado, filmes finos de GaAs têm também sido amplamente utilizados, devido a alta mobilidade eletrônica e transição direta. Neste trabalho, também foram produzidos filmes finos de GaAs através da técnica de evaporação resistiva. Serão mostrados e discutidos aqui resultados referentes a filmes finos de Sn'X IND. 2' dopado com íons terras-raras, filmes finos de GaAs e resultados referentes ao crescimento de filmes finos de GaAs sobre filmes finos de SnO2 dopados com terras-raras. Medidas de absorção óptica permitiram avaliar a qualidade óptica dos filmes e estimar a energia do bandgap. Dados de difração de raios-X mostraram estrutura do tipo rutilo e fase cassiterita dos filmes de Sn'X IND. 2' e também as direções principais dos filmes de GaAs. A microscopia eletrônica de varredura permitiu a espessura e a qualidade morfológica da heterojunção, tanto com relação à interface Sn'X IND. 2'/GaAs como da superfície. A investigação das propriedades elétricas em Sn'X IND. 2' mostra a alta resistividade do material devido ao caráter aceitador de íons terras-raras na matriz. Foi investigada também a captura de elétrons fotoexcitados por centros de 'Ce POT 3+' termicamente ativados. Do modelo proposto, foram obtidos parâmetros importantes, como a barreira de captura devido aos defeitos dominantes. Resistividade em função da temperatura na heterojunção Sn'X IND. 2'/GaAs mostrou a diminuição da resistência do conjunto. / Tin dioxide (Sn'X IND. 2') is a wide bandgap semiconductor material whith n-type conductivity the undoped form. This compound has been applied for several kinds of devices. In this work, thin films and xeogels of Sn'X IND. 2' doped with the rare-earth ions 'Ce POT. 3+' and Eu POT 3+' have been produced by the sol-gel process. On the other band, GaAs thin films have also been widely used, due to high electronic mobility and direct bandgap transition. In this work, GaAs thin films have been deposited by the resistive evaporation technique. It is shown and discussed here results concerning rare-earth doped Sn'X IND. 2' thin films. GaAs thin films and the growing of GaAs on the top of rare-earth doped Sn'X IND. 2'. Through the optical absorption spectra it has been possible to evaluate the films optical quality and to estimate the optical bandgap. X-ray diffraction data show the rutile like structure and cassiterie phase of Sn'X IND. 2' thin films and also show the main directions of GaAs films. Scanning electron microscopy allowed evaluating the thickness and morphological quality of the heterojunction, concerning the infarce as well as the surface. Investigation of electrical properties of Sn'X IND. 2' shows high resistivity of this material due to the acceptor-lide character of rare-earth ions in the matrix. It has also been investigated the trapping of photo-induced electrons by the thermally activated Ce centers. From a proposed model, it has been obtained some relevant parameters, such as the capture barrier due to the dominant defects. Data of resistivity as function of temperature for the Sn'X IND. 2'/GaAs heterojunction show the decrease of overall resistance.

Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-07-27T21:01:57Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-10-05T19:08:11Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) / Made available in DSpace on 2018-10-05T19:08:11Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) Previous issue date: 2018 / Com a crescente relev?ncia da produ??o do biodiesel no cen?rio atual, intensifica-se tamb?m a gera??o de glicerol bruto. O glicerol ? formado em abund?ncia nessa cadeia produtiva, representando 10% em peso do produto final. Dessa forma, a fim de permitir maior competitividade para a ind?stria do biodiesel, faz-se imprescind?vel a investiga??o por alternativas que visem o aproveitamento desse subproduto. Entre as poss?veis transforma??es promissoras para o glicerol bruto, encontra-se o emprego de c?lulas fotoeletroqu?micas. Nessas c?lulas, solu??es aquosas de glicerol s?o convertidas em hidrog?nio gasoso quando energia luminosa suficiente ? incidida sobre o fotocatalisador. Apesar do grande potencial das c?lulas fotoeletroqu?micas para o aproveitamento do glicerol, o desafio prevalecente ? sintetizar um fotocatalisador que gere uma alta corrente fotovoltaica nas condi??es envolvidas, e tenha uma alta estabilidade e capacidade de absor??o da luz v?sivel. Neste trabalho, sintetizou-se fotocatalisadores ? base de BiVO4, WO3 e V2O5 por m?todo drop coating, a fim de avaliar seu potencial emprego em c?lulas fotoeletroqu?micas em solu??es de glicerol. As propriedades fotoeletroqu?micas dos materiais foram investigadas por voltametria c?clica, imped?ncia eletroqu?mica, Mott-Schottky, cronoamperometria e cronopotenciometria em solu??es de Na2SO4 e Na2SO3. Al?m disso, caracterizou-se os materiais por reflect?ncia difusa (DRS), Difra??o de Raios-X (DRX) e microscopia eletr?nica de varredura (MEV). Os resultados mostram que as heterojun??es sintetizadas s?o fotocatalisadores eficientes para clivagem da ?gua. Particularmente, a heterojun??o de BiVO4/WO3/V2O5 se destaca pela gera??o de alta corrente fotovoltaica e boas propriedades fotoeletroqu?micas, mostrando que a jun??o dos tr?s materiais foi realizada com ?xito. Testes em solu??es de glicerina geraram resultados ainda melhores, enaltecendo o desempenho dessa heterojun??o em c?lulas fotoeletroqu?micas para aproveitamento de glicerol. / Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Biocombust?veis, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2018. / The growing relevance of biodiesel production in the current scenario, it also intensifies the generation of crude glycerol. Crude glycerol is formed in abundance in this productive chain, representing 10% by weight of the final product. Thus, in order to allow greater competitiveness for biodiesel industry, it is essential to search for alternatives that aim at new applications for this by-product. Among possible promising transformations for crude glycerol, it can be used in photoelectrochemical cells. In these cells, aqueous solutions of glycerol can be converted into gaseous hydrogen if sufficient light energy is irradiated on the photocatalyst. Despite the great potential of photoelectrochemical cells, the most challenge issue is to synthesize a photocatalyst that generates a high photovoltaic current, has a good stability and excellent light absorption capacity. In this work, photocatalysts based on BiVO4, WO3 and V2O5 were synthesized by drop coating technique, in order to evaluate their potential in photoelectrochemical cells containing glycerol aqueous solutions. To evaluate their photoelectrical properties, electrochemical impedance, Mott-Schottky, chronoamperometry and chronopotentiometry were performed in Na2SO4 and Na2SO3 solutions. In addition, the semiconductors were characterized by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the heterojunctions formed are promising photocatalysts. Particularly, the BiVO4/WO3/V2O5 heterejunction stands out for the generation of high photovoltaic current and good properties, showing that this triple junction was successfully made. Tests in glycerol solutions generated even better results, highlighting the performance of this material for photoelectrochemical cells using glycerol.

Orientador: Luis Vicente de Andrade Scalvi / Banca: Valmor Roberto Mastelaro / Banca: Paulo Noronha Lisboa Filho / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Dióxido de estanho (Sn'X IND. 2') é um semicondutor de bandgap largo com condutividade do tipo-n na forma não dopada, sendo aplicado em dispositivos diversos. Neste trabalho, filmes finos e géis secos de Sn'X IND. 2' dopados com os íons terras-raras 'Ce POT. 3+' e "Eu POT 3+' foram sintetizados através do processo sol-gel. Por outro lado, filmes finos de GaAs têm também sido amplamente utilizados, devido a alta mobilidade eletrônica e transição direta. Neste trabalho, também foram produzidos filmes finos de GaAs através da técnica de evaporação resistiva. Serão mostrados e discutidos aqui resultados referentes a filmes finos de Sn'X IND. 2' dopado com íons terras-raras, filmes finos de GaAs e resultados referentes ao crescimento de filmes finos de GaAs sobre filmes finos de SnO2 dopados com terras-raras. Medidas de absorção óptica permitiram avaliar a qualidade óptica dos filmes e estimar a energia do bandgap. Dados de difração de raios-X mostraram estrutura do tipo rutilo e fase cassiterita dos filmes de Sn'X IND. 2' e também as direções principais dos filmes de GaAs. A microscopia eletrônica de varredura permitiu a espessura e a qualidade morfológica da heterojunção, tanto com relação à interface Sn'X IND. 2'/GaAs como da superfície. A investigação das propriedades elétricas em Sn'X IND. 2' mostra a alta resistividade do material devido ao caráter aceitador de íons terras-raras na matriz. Foi investigada também a captura de elétrons fotoexcitados por centros de 'Ce POT 3+' termicamente ativados. Do modelo proposto, foram obtidos parâmetros importantes, como a barreira de captura devido aos defeitos dominantes. Resistividade em função da temperatura na heterojunção Sn'X IND. 2'/GaAs mostrou a diminuição da resistência do conjunto. / Abstract: Tin dioxide (Sn'X IND. 2') is a wide bandgap semiconductor material whith n-type conductivity the undoped form. This compound has been applied for several kinds of devices. In this work, thin films and xeogels of Sn'X IND. 2' doped with the rare-earth ions 'Ce POT. 3+' and "Eu POT 3+' have been produced by the sol-gel process. On the other band, GaAs thin films have also been widely used, due to high electronic mobility and direct bandgap transition. In this work, GaAs thin films have been deposited by the resistive evaporation technique. It is shown and discussed here results concerning rare-earth doped Sn'X IND. 2' thin films. GaAs thin films and the growing of GaAs on the top of rare-earth doped Sn'X IND. 2'. Through the optical absorption spectra it has been possible to evaluate the films optical quality and to estimate the optical bandgap. X-ray diffraction data show the rutile like structure and cassiterie phase of Sn'X IND. 2' thin films and also show the main directions of GaAs films. Scanning electron microscopy allowed evaluating the thickness and morphological quality of the heterojunction, concerning the infarce as well as the surface. Investigation of electrical properties of Sn'X IND. 2' shows high resistivity of this material due to the acceptor-lide character of rare-earth ions in the matrix. It has also been investigated the trapping of photo-induced electrons by the thermally activated Ce centers. From a proposed model, it has been obtained some relevant parameters, such as the capture barrier due to the dominant defects. Data of resistivity as function of temperature for the Sn'X IND. 2'/GaAs heterojunction show the decrease of overall resistance. / Mestre

Submitted by DIEGO HENRIQUE DE OLIVEIRA MACHADO null (diegomachado@fc.unesp.br) on 2016-03-05T16:15:24Z No. of bitstreams: 1 Dissertação Diego versão Final.pdf: 4313685 bytes, checksum: 2ca802e4be1ac3d595efb5b0ea06251e (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-03-07T13:58:23Z (GMT) No. of bitstreams: 1 machado_dho_me_bauru.pdf: 4313685 bytes, checksum: 2ca802e4be1ac3d595efb5b0ea06251e (MD5) / Made available in DSpace on 2016-03-07T13:58:23Z (GMT). No. of bitstreams: 1 machado_dho_me_bauru.pdf: 4313685 bytes, checksum: 2ca802e4be1ac3d595efb5b0ea06251e (MD5) Previous issue date: 2016-03-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho apresenta o desenvolvimento e algumas conclusões do estudo da heterojunção de filmes finos de SnO2 e GaAs. Os filmes de SnO2, dopados com Ce3+, foram depositados a partir do método sol-gel usando as técnicas de dip e spin coating; os filmes de GaAs foram depositados por evaporação resistiva e por sputtering. As heterojunçõesforam constituídas de filmes de SnO2 sobre filmes de GaAs, e filmes de GaAs sobre filmes de SnO2. Foram investigadas as propriedades ópticas, estruturais, morfológicas e elétricas de filmes finos constituintes das heterojunções e também a influência do dopante Ce3+. Entre os experimentos realizados estão: transmitância óptica, difração de raios X, microscopia eletrônica de varredura (MEV), microscopia óptica, microscopia de força atômica (AFM), fotoluminescência e medidas elétricas na presença de excitações com diferentes fontes de luz monocromáticas (quarto harmônico do laser Nd:YAG (266nm), laser He-Ne (628nm), LED InGaN (450nm)). Entre as principais conclusões, verificou-se: 1) em algumas situações, condutividade independente da temperatura, sugerindo a participação de um gás de elétrons bidimensional (2DEG) na interface SnO2/GaAs; 2) o tamanho dos cristalitos, calculado a partir das análises de difração de raios X, fornece valores da ordem de 10nm tanto para filmes de SnO2 como para filmes de GaAs; 3) a energia de bandgap, avaliada com base em dados de medidas de absorbância, fornece um valor máximo de 3,6 eV para filmes de dióxido de estanho e 1,6eV para filmes de GaAs; 4) MEV e microscopia óptica de para filmes de GaAs (depositado por evaporação resistiva e sputtering) apresentam sua superfície heterogênea, com partículas de variados tamanhos. Além disso, a aderência de filmes de SnO2 sobre filmes de GaAs está relacionada com a técnica utilizada para depositar os filmes da camada de base, o melhor resultado foi obtido quando a camada é a de GaAs depositado por evaporação resistiva. Isto foi verificado utilizando microscopia de força atômica, onde ficou evidente que filmes de GaAs depositado por evaporação resistiva possuem grandes aglomerados enquanto filmes depositados por sputtering possuem uma superfície com material distribuído de maneira uniforme. Também foram realizadas medidas de fotoluminescência com excitação de um laser de Kr+ sintonizado na linha de 350nm e também utilizando um laser de He-Cd na linha de 325nm, tanto em filmes como em pastilhas de SnO2 dopado com 1at% Ce3+e também em filmes da heterojunção SnO2:Ce3+/GaAs, sendo observadas pequenas bandas características do Ce3+. / The aim of this work is to present the development and the main conclusions, related the investigation of thin film SnO2/GaAs heterojunction. Ce3+- doped SnO2 thin films were deposited by the sol-gel-dip and -spin coating techniques, whereas GaAs films were deposited by resistive evaporation and sputtering. Heterojunctions were deposited by SnO2 layer growth on top of GaAs film, and in the opposite order: GaAs on top of SnO2. Optical, structural, morphologic and electrical properties of heterojunction films were investigated, as well as the influence of Ce-doping in these measurements. Experiments carried out include: optical transmission, X-ray diffraction, scanning electron microscopy (SEM), optical microscopy, atomic force microscopy (AFM), photoluminescence and electrical measurements under optical excitation. In this last case the excitation sources are monochromatic light from the fourth harmonic of a Nd:YAG laser (266nm), a He-Ne laser (628nm) and a InGaN LED (450nm). Among the main conclusions, it was verified that: 1) in some situations, a temperature independent electrical resistivity was observed and attributed to the possible formation of a two-dimensional electron gas (2DEG) at SnO2/GaAs interface; 2) crystallite size was calculated from X-ray diffraction data, being about 10 nm either for SnO2 films as GaAs films; 3) bandgap energy, evaluated from absorbance data yield a maximum value of about 3.6eV for tin dioxide and 1.6eV for GaAs films; 4) SEM images, obtained for GaAs thin films deposited by resistive evaporation and for the heterojunction SnO2/GaAs, and optical microscopy, for sputtering deposited GaAs films and heterojunction samples, show that GaAs films present an heterogeneous surface, with particles of several distinct sizes. Besides, the adherence of SnO2 films on the GaAs layer is related to the used technique for depositing the base layer, being better in the case of resistive evaporation deposited GaAs. This was verified by atomic force microscopy, where it was evidenced that resistive evaporation deposited GaAs films present large agglomerates whereas sputtering deposited films present a surface with more uniformly distributed material. Photoluminescence data was also obtained with excitation by a Kr+ laser tuned at 350nm as well as a He-Cd laser at 325nm, either in Ce 1at% doped SnO2 pellets as SnO2:Ce3+/GaAs heterojunction, being observed small bands, characteristic of Ce3+.

La compréhension des propriétés électriques de nano-objets est essentielle pour le développement s des nanotechnologies. La microscopie à force Kelvin (KFM) est une des techniques les plus utiles pour cartographier simultanément la topographie et la différence de potentiel de contact (CPD) à l'échelle nanométrique. Après 20 ans de développement, la KFM est principalement utilisé dans des conditions normales de pression et de température, permettant d'effectuer, de manière simple, de multiples analyses comparatives. Toutefois, sous ultra-vide (UHV), comme la surface est contrôlée et que la sensibilité est meilleure, des mesures plus précises et plus fiables sont réalisables. Dans la première partie, la mesure KFM sous atmosphère ambiante est améliorée en développant la technique simple-passage à la fois en modulation de fréquence (FM) et en modulation d'amplitude (AM). Une électronique externe Nanonis a été adaptée sur les AFMs commerciaux (Dimension 3100 et MultiMode, Bruker). Une étude comparative avec le mode Lift a été réalisée sur des couches de graphène épitaxié sur échantillon de SiC. L'effet de la distance pointe-échantillon sur le contraste et la résolution est décrit ainsi que l'influence des paramètres expérimentaux. Une amélioration significative du contraste et de la résolution est clairement observée sur les résultats obtenus par la technique simple passage en modulation de fréquence, indépendamment de la distance pointe-échantillon. Dans une deuxième partie, la technique KFM est développée sous vide secondaire. Le travail instrumental est réalisé sur un AFM EnviroScope de chez Bruker, qui a été équipé d'une électronique externe Nanonis, permettant de mesurer simultanément la topographie en mode non-contact et la CPD en modulation d'amplitude ou de fréquence. Les résultats montrent que la CPD mesurée est comparable à celle obtenue avec une mesure sous ultravide. Enfin, après avoir posé les bases à la fois expérimentale et théorique de la KFM, cette technique est utilisée pour caractériser les hétérostructures CdTe/CdS en films minces utilisés pour les applications de cellules solaires. Un protocole de préparation d'échantillon sur la tranche a été spécialement développé. L'hétérojonction CdTe/CdS est étudiée sous polarisation à la fois dans l'obscurité et sous éclairement. L'influence de l'épaisseur de la couche de CdS est également étudiée pour comprendre son effet dramatique sur le rendement des cellules solaires. / The development of nanoscience makes the understanding of the electrical properties of nano-objects essential. The Kelvin Force Microscopy (KFM) is one of the most useful techniques to map at the nanoscale and simultaneously both the topography and contact potential difference (CPD). After 20 years of development, KFM is mainly operated under air at normal pressure, allowing to perform, in an easy way, multiple comparative analyses. However, under UHV, as the surface is controlled and the sensitivity improved, more accurate and reliable measurements can be achieved. In the first part, KFM under ambient atmosphere is improved by developing the single-scan method using either a frequency modulation (FM) or an amplitude modulation (AM) mode. An external Nanonis electronic has been implemented on commercial AFMs (Dimension 3100 and MultiMode, Bruker). A comparative study with the common Lift-mode is done by imaging epitaxial graphene layers on SiC sample. The tip-sample separation effect on the CPD contrast and resolution is described as well as experimental settings. It is shown that higher contrasts are obtained using single-scan frequency modulation KFM regardless the tip-sample operating distance. In a second part, the KFM technique under secondary vacuum is developed. The instrumental work is carried out with an EnviroScope AFM from Bruker. We outfitted our Veeco's AFMs with an external Nanonis electronic to perform simultaneously the acquisition of topography and CPD using either the amplitude or the frequency modulation mode. The upgrade of the electronic has raised compatibility issues. Our results show that the comparable results are obtained with KFM under UHV. Finally, having laid down both the experimental and theoretical groundwork of the KFM, this technique is used to characterize CdTe/CdS heterostructures used in thin films solar cell application. A protocol for the cross section sample preparation has been specifically developed. The CdTe/CdS heterojunction is studied under polarization both in dark and under illumination. The influence of the CdS layer thickness is also studied to understand its dramatic effect on the solar cell efficiency.

Orientador: Luis Vicente de Andrade Scalvi / Banca: José Antonio Malmonge / Banca: José Humberto Dias da Silva / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp / Resumo: Neste trabalho foi realizada a deposição através da técnica de evaporação resistiva, de filmes finos de GaAs (arseneto de gálio) e de Al (alumínio) com posterior oxidação deste último, formando 'Al IND. 2''O IND. 3' (óxido de alumínio ou alumina) e a caracterização dos filmes de GaAs e da heteroestrutura formada por 'Al IND. 2''O IND. 3' e GaAs. A confecção do dispositivo combinando estes compostos serviu para a investigação das características relevantes do sistema para potencial aplicação em transistores. O trabalho compreendeu investigação sobre as condições de deposição, e foram avaliadas principalmente as características elétricas dos filmes produzidos individualmente. Os resultados apresentados incluem: resistividade em função da temperatura, corrente-voltagem em função da temperatura, difração de raios-X e transmitância na região do infravermelho. Para caracterização do desempenho do sistema 'Al IND. 2''O IND. 3'/GaAs, um transistor simples foi construído sob um substrato de vidro borossilicato com uma camada de GaAs e outra de 'Al IND. 2''O IND. 3'. Os contatos de fonte, dreno e gate foram feitos de In. Essa estrutura permite a medida da corrente de fuga e a avaliação de outras características do sistema. Neste dispositivo foram avaliadas as características corrente-voltagem em função da temperatura, e também a interação com luz, já que GaAs, por apresentar gap direto, torna-se atraente para aplicações opto-eletrônicas. Assim medidas de elétricas foto-induzidas foram realizadas com excitação com fontes de luz branca. Com o intuito de se avaliar a qualidade dos filmes de GaAs obtidos pela evaporação resistiva, tanto a caracterização estrutural quando elétrica também foram feitas em filmes finos de GaAs depositados por sputtering, de modo a se ter um padrão de comparação. / Abstract: In this work, the deposition of GaAs (gallium arsenide) and Al (aluminum) thin films is carried out by the resistive evaporation technique. In the latter case, an oxidation of the film is accomplished, leading to 'Al IND. 2''O IND. 3' (alumina) formation. The characterization of GaAs thin films and the heterostructure formed by 'Al IND. 2''O IND. 3' and GaAs is also carried out. The elaboration of the device combining these compounds allows investigating the relevant characteristics of this system to potential application in transistors. The work evolved investigation on the deposition conditions, and the electrical characteristics of the films were also evaluated separately. Results includes: resistivity as function of temperature, X-ray diffraction and near infrared transmittance. For characterization of the performance of the 'Al IND. 2''O IND. 3'/GaAs system, a simple transistor was built on a borosilicate glass substrate, with a 'Al IND. 2''O IND. 3' layer on top of a GaAs layer. The contacts of source, drain and gate were done using In. This structure allows evaluating the leak current and other characteristics of this system. In this device, it was evaluated the current - voltage characteristics and the interaction with light, because GaAs, due to its direct bandgap, become very attractive for opto-electronic applications. The, the photo-induced electrical measurements were done under excitation with white light. Aiming the evaluation of the quality of films deposited by the resistive evaporation technique, electrical as well as structural characterization were also carried out for GaAs thin films deposited by sputtering, in order to have a comparing parameter. / Mestre

abstract: The objective of this thesis is to achieve a detailed understanding of the loss mechanisms in SHJ solar cells. The working principles of these cells and what affects the cell operation, e.g. the IV characteristics at the maximum power point (MPP) and the correspondingly ll factor (FF) are investigated. Dierent loss sources are analyzed separately, and the weight of each in the total loss at the MPP are evaluated. The total series resistance is measured and then compared with the value obtained through summation over each of its components. In other words, series resistance losses due to recombination, vertical and lateral carrier transport, metalization, etc, are individually evaluated, and then by adding all these components together, the total loss is calculated. The concept of ll factor and its direct dependence on the loss mechanisms at the MPP of the device is explained, and its sensitivity to nearly every processing step of the cell fabrication is investigated. This analysis provides a focus lens to identify the main source of losses in SHJ solar cells and pave the path for further improvements in cell efficiency. In this thesis, we provide a detailed understanding of the FF concept; we explain how it can be directly measured; how it can be calculated and what expressions can better approximate its value and under what operating conditions. The relation between FF and cell operating condition at the MPP is investigated. We separately analyzed the main FF sources of losses including recombination, sheet resistance, contact resistance and metalization. We study FF loss due to recombination and its separate components which include the Augur, radiative and SRH recombination is investigated. We study FF loss due to contact resistance and its separate components which include the contact resistance of dierent interfaces, e.g. between the intrinsic and doped a-Si layers, TCO and a-Si layers. We also study FF loss due to lateral transport and its components that including the TCO sheet resistance, the nger and the busbars resistances. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2018

abstract: Natural photosynthesis dedicates specific proteins to achieve the modular division of the essential roles of solar energy harvesting, charge separation and carrier transport within natural photosynthesis. The modern understanding of the fundamental photochemistry by which natural photosynthesis operates is well advanced and solution state mimics of the key photochemical processes have been reported previously. All of the early events in natural photosynthesis responsible for the conversion of solar energy to electric potential energy occur within proteins and phospholipid membranes that act as scaffolds for arranging the active chromophores. Accordingly, for creating artificial photovoltaic (PV) systems, scaffolds are required to imbue structure to the systems. An approach to incorporating modular design into solid-state organic mimics of the natural system is presented together with how conductive scaffolds can be utilized in organic PV systems. To support the chromophore arrays present within this design and to extract separated charges from within the structure, linear pyrazine-containing molecular ribbons were chosen as candidates for forming conductive linear scaffolds that could be functionalized orthogonally to the linear axis. A series of donor-wire-acceptor (D-W-A) compounds employing porphyrins as the donors and a C60 fullerene adduct as the acceptors have been synthesized for studying the ability of the pyrazine-containing hetero-aromatic wires to mediate photoinduced electron transfer between the porphyrin donor and fullerene acceptor. Appropriate substitutions were made and the necessary model compounds useful for dissecting the complex photochemistry that the series is expected to display were also synthesized. A dye was synthesized using a pyrazine-containing heteroaromatic spacer that features two porphyrin chromophores. The dye dramatically outperforms the control dye featuring the same porphyrin and a simple benzoic acid linker. A novel, highly soluble 6+kDa extended phthalocyanine was also synthesized and exhibits absorption out to 900nm. The extensive functionalization of the extended phthalocyanine core with dodecyl groups enabled purification and characterization of an otherwise insoluble entity. Finally, in the interest of incorporating modular design into plastic solar cells, a series of porphyrin-containing monomers have been synthesized that are intended to form dyadic and triadic molecular-heterojunction polymers with dedicated hole and electron transport pathways during electrochemical polymerization. / Dissertation/Thesis / Ph.D. Chemistry 2013