abstract: As crystalline silicon solar cells continue to get thinner, the recombination of carriers at the surfaces of the cell plays an ever-important role in controlling the cell efficiency. One tool to minimize surface recombination is field effect passivation from the charges present in the thin films applied on the cell surfaces. The focus of this work is to understand the properties of charges present in the SiNx films and then to develop a mechanism to manipulate the polarity of charges to either negative or positive based on the end-application. Specific silicon-nitrogen dangling bonds (·Si-N), known as K center defects, are the primary charge trapping defects present in the SiNx films. A custom built corona charging tool was used to externally inject positive or negative charges in the SiNx film. Detailed Capacitance-Voltage (C-V) measurements taken on corona charged SiNx samples confirmed the presence of a net positive or negative charge density, as high as +/- 8 x 1012 cm-2, present in the SiNx film. High-energy (~ 4.9 eV) UV radiation was used to control and neutralize the charges in the SiNx films. Electron-Spin-Resonance (ESR) technique was used to detect and quantify the density of neutral K0 defects that are paramagnetically active. The density of the neutral K0 defects increased after UV treatment and decreased after high temperature annealing and charging treatments. Etch-back C-V measurements on SiNx films showed that the K centers are spread throughout the bulk of the SiNx film and not just near the SiNx-Si interface. It was also shown that the negative injected charges in the SiNx film were stable and present even after 1 year under indoor room-temperature conditions. Lastly, a stack of SiO2/SiNx dielectric layers applicable to standard commercial solar cells was developed using a low temperature (< 400 °C) PECVD process. Excellent surface passivation on FZ and CZ Si substrates for both n- and p-type samples was achieved by manipulating and controlling the charge in SiNx films. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

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

Organic solar cell (OSC) has been an active research field over the past decades, due to their intrinsic advantages, such as low consumption of materials and energy, the applicability on flexible substrates and the degradability of the organic components. Compared with the solution processing technology using polymers as electron donor materials, small molecule vacuum deposition is regarded as a promising fabrication method, avoiding the use of toxic aromatic solvents and guaranteeing constant batch-to-batch performance. Moreover, it is much easier to realize multi-junction tandem solar cells (TSCs) by thermal deposition, and the leading power conversion efficiency (PCE) of 13.2% was achieved using three different absorbers by vacuum deposition (“Heliatek sets new organic photovoltaic world record efficiency of 13.2%” 2016). In this dissertation, novel electron donor materials are synthesized based on the molecular skeleton of a famous chromophore, boron dipyrromethene (BODIPY), and chemical modifications are carried out to tune the intense absorption bands of these dyes to near infrared (NIR, λ>750,nm) region. Efficient small molecule NIR absorbers are highly required for TSCs, because they can construct a complementary absorption over the visible and NIR spectral region in cooperation with a wide bandgap material. Three β-fused aza-BODIPY molecules with heterocyclic substituents on α-positions are prepared using organolithium reagents and phthalonitrile as the starting materials. The organolithium reagents, namely N-methylpyrrole, N-methylindole and 2-trimethylsilylthiophene, are used instead of commonly used Grignard reagents. Moreover, three corresponding aza-BODIPY derivatives are obtained by replacing one fluorine atom in the BF_{2} moiety by a cyano group. UV-vis absorption spectra reveal that all these materials are strong NIR absorbers, and their abortion in solid state cover a wide range from 600 to 1000,nm. OSCs with these aza-BODIPY donors give a best PCE of 3.0%, which is a reasonable value for the NIR devices with the maximum and the onset of the EQE spectrum around 850 and 950,nm respectively. A series of furan-fused BODIPYs with a electron withdrawing CF_{3} group on the meso-C are synthesized, and the photophysical/electrochemical properties can be tuned easily by the electronic properties of the substituents on the peripheral aromatic rings. The most promising candidate gives a high PCE of 6.1% in a single junction OSC with a J_{sc} of 13.3,mA/cm^{2}, a V_{oc} of 0.73,V, and a FF of 62.7%. A serial connected TSC is fabricated using this BODIPY as the low bandgap donor and a “green” donor, and its EQE spectrum covers a wide range from 400 to 900,nm. The PCE reaches 9.9% with a J_{sc} of 9.9,mA/cm^{2}, a V_{oc} of 1.70,V, and a FF of 59.0%. Based on the general structure of furan-fused BODIPY, alkyl or fluorinated alkyl substituents with larger volume is introduced on either peripheral aromatic rings or the meso-C. The variations that caused by these substituents on the photophysical and electrochemical properties are negligible. The investigations on the OSCs demonstrate that the introduction of these alkyl chain substituents have positive influence on the PCE values, which benefit mainly from the increased photocurrent. However, there is no positive relationship between the device performance and the volume of the alkyl chain substituents. BODIPY molecules have been demonstrated as efficient and promising NIR electron donor materials for vacuum-deposited OSCs. Taking advantages of facile molecular modification, oustanding photophysical behaviors and tunable electrochemical properties, this series of dyes are also intereting for other semiconductor devices.

Os polímeros conjugados têm sido objeto de estudo nos últimos vinte anos devido à grande variação observada em sua condutividade quando sob dopagem química. A maioria dos polímeros dessa família passa de isolante, quando não dopados ou fracamente dopados, a bons condutores de eletricidade quando fortemente dopados. Em dopagens intermediárias apresentam um comportamento semicondutor, inclusive efeitos de fotocondução, fotovoltagem e luminescência. Nesse trabalho exploramos algumas dessas propriedades, mais comuns aos semicondutores inorgânicos, e mostramos que é possível obter dispositivos eletrônicos e/ou optoeletrônicos com os polímeros orgânicos. Em estruturas de diodos, tipo Schottky e pin, fabricamos e caracterizamos dispositivos fotovoltaicos com polianilina e poli(o-metoxianilina). Nesses materiais, sob fraca dopagem foi observado um efeito de fotocondução negativa. Já com o poli(2-metoxi, 5-hexiloxi-1,4fenileno vinileno) fabricamos e caracterizamos células fotovoltaicas e mostramos que esse tipo de estrutura permite a fabricação de um dispositivo reversível: fotovoltaico e eletroluminescente. / Conjugated polymers have been extensively studied in the last twenty years due to their high conductivity variation under doping. They are insulating materials when non-doped or weakly doped and good conductors when strongly doped. In intermediate doping concentration they behave as semiconductors, exhibiting photoconduction, photovoltaic and luminescent effects. In this work we explore some of these properties and we show that metoxyaniline), using Schottky and pin structures, were fabricated and characterized. These materiaIs, when weakly doped, showed a negative photoconductivity. Schottky diodes were also fabricated with poly (2¬methoxy, 5-hexyloxy, 1-4 phenylene-vynilene) and besides the photovoltaic effect this device exhibited the reversible eletroluminescent effect.

As células solares orgânicas, também conhecidas como (OPVs), fazem parte da terceira geração dos dispositivos fotovoltaicos. Entre outras tecnologias emergentes, a dos OPVs tem a vantagem de ser de fácil processamento e de baixo custo. Ou seja, uma tecnologia comercialmente promissora na área de conversão de energia solar em energia elétrica. No entanto, grandes desafios precisam ser superados para colocar estas células no mercado dos fotovoltaicos. Dentre esses desafios, pode estar incluído, inevitavelmente, a compreensão dos processos físicos envolvidos na fotogeração em OPVs, dentre os quais pode-se destacar o da recombinação de cargas fotogeradas. A recombinação é o principal responsável pela perda de eficiência em OPVs, uma vez que ela elimina uma fração relativamente grande de portadores de carga, diminuindo consideravelmente a potência de saída da célula. Para estudar este efeito indesejado em células orgânicas, desenvolvemos um modelo analítico para fotocorrente em OPVs do tipo bulk heterojunction (BHJ), assumindo uma recombinação bimolecular de cinética de segunda ordem. O modelo é representado por uma expressão analítica obtida a partir das equações fundamentais da eletrodinâmica clássica, onde despreza-se a contribuição da corrente de difusão e as mobilidades dos elétrons e dos buracos são consideradas iguais. Essa expressão foi de grande valia na análise dos resultados experimentais, sobretudo os de corrente-tensão (J-V) sob iluminação, e além disso, ela permitiu extrair parâmetros intrínsecos do transporte de carga, como mobilidade e coeficiente de recombinação. Neste sentido, foram fabricados dispositivos cuja estrutura foi ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, e com eles foram realizados inúmeros experimentos. As técnicas usadas na parte experimental foram: medidas J-V, no escuro e sob iluminação, medidas de transiente de fotovoltagem (TPV), de transiente de fotocorrente (TPC), e de Foto-CELIV (Charge Extraction Linear Increasing Voltage). Usamos como parâmetros experimentais a temperatura e intensidade de iluminação. Das medidas J-V sob iluminação, foram extraídos os parâmetros essenciais da célula: corrente de curto (Jsc), potencial de circuito aberto (Voc), fator de preenchimento (FF) e a eficiência (PCE). A partir das abordagens experimental e teórica, exploramos a influência da recombinação bimolecular no comportamento fotovoltaico dos dispositivos. O desenvolvimento do modelo teve contribuição de trabalhos que se basearam em modelagem numérica a partir de condições físicas semelhantes às usadas em nosso tratamento e que foram levadas em consideração no processo de análise dos resultados experimentais. / Organic solar cells, also known as (OPVs), are part of the third generation of photovoltaic devices. Among other emerging technologies, OPVs have the advantage of being easy to process and exhibits low cost of production. That is, it is a promising commercial technology in the area of converting solar energy into electricity. However, major challenges need to be overcome to put these cells in the photovoltaic market. Among them, it can be included, inevitably, the comprehension of the physical processes involved in photogeneration in OPVs, of which, the recombination of photogenerated carriers is included. Recombination is primarily factor responsible for the loss of efficiency in OPVs, since recombination eliminates a large fraction of the carriers, considerably reducing the output power of the cell. To study this undesirable effect in organic cells, we developed an analytical model for the photocurrent in bulk heterojunction cells (BHJ), which assumes the bimolecular recombination of second order kinetics. The model is represented by an analytical expression obtained by the equations of the classical electrodynamics, where we neglected the contribution of the diffusion current and assumed that electrons and holes have equal mobilities. The expression was of great value for the analysis of the experimental results, especially the current-voltage (J-V) measurements under illumination, and it allowed to extract intrinsic parameters of charge transport effects, such as mobility and recombination coefficient. For this, it were fabricated devices whose structure was ITO/PEDOT:PSS/P3HT:PCBM/Ca-Al, and with them were performed numerous experiments. The techniques used in the experimental part were: J-V measurements, in the dark and under illumination, transient photovoltage (TPV), transient photocurrent (TPC), and of Charge Extraction Linear Increasing Voltage (Photo-CELIV). We used as experimental parameters the temperature and the intensity of. From J-V measurements under illumination we extracted the essential cell parameters: short current (Jsc), open circuit potential (Voc), fill factor (FF) and efficiency (PCE). From the experimental and theoretical approaches, we explored the influence of bimolecular recombination on the photovoltaic behavior of the devices. The development of the model had contributions of works based on numerical modelings from physical conditions similar to those used in our treatment and that were taken into account in the process of analysis of the experimental results.

Orientador: Ana Flavia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-10T16:04:48Z (GMT). No. of bitstreams: 1 Lomba_BrunoStelutti_M.pdf: 2789085 bytes, checksum: c5cf56c110af4564ce46cde2fd239d4f (MD5) Previous issue date: 2007 / Resumo: Nanotubos de carbono de paredes simples (SWNT) têm atraído grande interesse devido a sua aplicação em diversas áreas de pesquisa, incluindo novos materiais e dispositivos optoeletrônicos. Entretanto uma boa dispersão destes materiais é um fator necessário na obtenção de filmes homogêneos, com menor grau de agregação para se obter dispositivos com maior desempenho. Neste trabalho, foi realizada uma modificação química das extremidades e defeitos dos SWNT com grupos tiofenos com a finalidade de melhorar a interação do nanotubo de carbono com a matriz polimérica de poli(3-octiltiofeno) (POT). De fato, células solares com melhor desempenho foram obtidas. O SWNT modificado e seu compósito com POT foram caracterizados por espectroscopia Raman, espectroscopia no infravermelho, espectroscopia UV-VIS e voltametria cíclica. A melhor célula solar de heterojunção dispersa foi obtida usando 5 % m m de SWNT modificado (SWNT-TIOF), e apresentou potencial de circuito aberto (Voc), fotocorrente (Isc) e eficiência (h) de 0,75 V, 9,5 mA cm e 0,184 %, respectivamente. O uso de um derivado de indenofluoreno (DPIF) como camada transportadora de buraco no lugar do polietilenodioxitiofeno dopado com sulfato de poliestireno (PEDOT:PPS) também foi investigado. Os resultados iniciais indicam que o uso dessa camada pode ser uma tentativa interessante para melhorar o Voc de células solares orgânicas / Abstract: Single-wall carbon nanotubes (SWNT) have attracted great interst for applications in a variety of research areas, including electronics and functional materials. However, a good dispersion of these materials is a demanding factor in order to obtain more homogeneous and less bundled films for constructing devices. In this report we describe how a covalent modification with thiophene groups at the edges and defects of SWNT can improve interaction with a polymer matrix, resulting in solar cells with improved performance. The modified SWNT and its composite with poly(3-octylthiophene) were characterized by Raman, Infrared and UV-VIS spectroscopies and cyclic voltammetry. The best bulk heterojunction solar cell was obtained using 5 wt % of the modified carbon nanotube (SWNT-THIOP) and shows open circuit voltage (Voc), photocurrent (Isc) and efficiency (h) of 0.75 V, 9.5 mA cm e 0,184 %, respectively. The use of an idenofluorene derivative as a hole transport layer in replacement of the PEDOT:PPS was also investigated. The primary results indicate that the use of this layer can be an interesting approach to improve the open-circuit voltage in polymer/nanotube solar cells / Mestrado / Quimica Inorganica / Mestre em Química

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-03-22T17:58:05Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao_bismarck_final_estudo_da_conversao_descendente.pdf: 9102695 bytes, checksum: f43bbe4be7ee1b5ccf50bbd67bdbabc1 (MD5) / Made available in DSpace on 2016-03-22T17:58:05Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) dissertacao_bismarck_final_estudo_da_conversao_descendente.pdf: 9102695 bytes, checksum: f43bbe4be7ee1b5ccf50bbd67bdbabc1 (MD5) Previous issue date: 2015-04-13 / CAPES, CNPq, FACEPE / C elulas solares apresentam-se como uma alternativa vi avel para a gera c~ao de energia limpa e renov avel pela sua capacidade de convers~ao da energia solar em el etrica atrav es do efeito fotovoltaico. Entretanto, um dos fatores limitantes na utiliza c~ao deste tipo de energia tem sido a incompatibilidade espectral, a qual implica que apenas uma determinada parte do espectro solar seja efetivamente utilizado no processo de convers~ao fotovoltaica. Entre os diversos materiais fot^onicos, pesquisas em materiais dopados com ons de Terras Raras capazes de realizar a convers~ao de f otons de infravermelho para vis vel-UV ou vice-versa tem sido realizadas. Em aplica c~oes fotovoltaicas, este efeito pode melhorar a coleta da radia c~ao solar. Para a realiza c~ao desta tarefa dois mecanismos s~ao utilizados: Convers~ao Ascendente de Frequ^encia e Convers~ao Descendente de Frequ^encia. Este trabalho teve como objetivo estudar as propriedades espectrosc opicas e o mecanismo de Convers~ao Descendente de Frequ^encia em vidros dopados com os ons de Terras Raras Tb3+/Yb3+, Eu3+ e Er3+, e veri car suas poss veis aplica c~oes no melhoramento da e ci^encia de c elulas solares. A mesma matriz hospedeira foi utilizada. O estudo das propriedades espectrosc opicas foi realizado atrav es de medidas de absor c~ao, luminesc^encia e evolu c~ao temporal da luminesc^encia. Observamos o processo de convers~ao descendente de frequ^encia com emiss~ao no infravermelho, regi~ao que as c elulas solares de sil cio cristalino possuem maior e ci^encia, com excita c~ao em 355nm, que promoveu uma maior e ci^encia, e 482nm. Em seguida, para as matrizes dopadas com ons de Tb3+/Yb3+, foi determinado o mecanismo gerador do processo de convers~ao descendente de frequ^encia e a e ci^encia de transfer^encia de energia. Foi obtida uma e ci^encia de transfer^ encia de energia m axima de 112,7%. Para as matrizes dopadas com Eu3+ e Er3+ foram realizadas medidas de luminesc^encia com excita c~ao via laser de 482nm. Como aplica c~ao, foram realizadas medidas el etricas, para c elulas convencionais de Si e GaP, usando como fonte de radia c~ao um simulador solar com ltro AM 1.5. Os resultados foram avaliadas na presen ca e aus^encia dos vidros dopados com ons de Terras Raras na superf cie da c elula solar. Foi observado um aumento na e ci^encia de convers~ao fotovoltaica das c elulas de sil cio cobertas pelos vidros dopadas com 1%Tb3+ e 1%Eu3+ em rela c~ao a matriz sem dopagem. / Solar cells are shown as a viable alternative for generation renewable and clean energy due their ability of converter solar power in electric power by the photovoltaic e ect. However, one of the limitant facts to use photovoltaic devices to make electricity is spectral mismatch, that implies only a speci c range of solar spectrum is e ectively used in the process of photovoltaic conversion. Between the several photonics devices, research in Rare Earth ions doped materials able to do the conversion of infrared photons in visible-UV photons or the opposite have been performed. In photovoltaic applications, this e ect can enhance the harvesting of solar light. To realize this task two mechanism are used: Frequency up-conversion and frequency down-conversion. This work had the goal of study the spectroscopic properties and the Frequency Down-conversion mechanism in Tb3+/Yb3+, Eu3+ and Er3+ Rare Earth doped glasses, and check their possible applications to enhance solar cell e ciency. The same host matrix are used. The spectroscopic study was realized by luminescence, absorption, and temporal evolution luminescence measurements. We observe the frequency down-conversion and infrared emission, zone that crystaline silicon solar cell have the best e ciency, with 355nm excitation, that promote the best e ciency, and 482nm excitation. Then, for host matrix doped with Tb3+/Yb3+ ions, was determined the generation mechanism of frequency down-conversion and energy transfer e ciency. The major energy transfer e ciency was 112,7%. For host matriz doped with Eu3+ and Er3+ ions, was realized luminescence measurements with 482nm excitaion. Was realized electric measurements as applications in Si and GaP cells, solar simulator with AM 1.5 lter was used as radiation source. The results were evaluated with and without Rare Earth ions doped glasses on the surface of solar cell. We observed the enhancement of photovoltaic conversion when the silicon solar cell are covered with by glasses doped with 1%Tb3+ and 1%Eu3+ with respect to matrix covered.

Orientador: Ana Flávia Nogueira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-17T19:59:01Z (GMT). No. of bitstreams: 1 Benedetti_JoaoEduardo_D.pdf: 8810025 bytes, checksum: 02324ef0185baef0d7794ea229fb5cda (MD5) Previous issue date: 2010 / Resumo: Este trabalho consistiu na preparação, caracterização e posterior aplicação de eletrólitos poliméricos gel em celulas solares de TiO2/corante. No Capítulo I, e apresentado uma introdução geral sobre células solares e eletrólitos poliméricos. O Capítulo II contém os objetivos deste trabalho. No Capítulo III, são preparados os eletrólitos polimérico gel utilizando a matriz polimérica de poli(oxido de etileno-co-2-(2-metoxietoxi) etil glicidil eter) (P(EO/EM)) contendo I2 e várias concentrações de g-butirolactona (GBL) e LiI. Esses eletrólitos foram caracterizados por medidas de calorimetria exploratória diferencial (DSC), ressonância magnética de Li (RMN), termogravimetria (TGA), difração de raios-X (DRX), condutividade e voltametria cíclica (VC). O eletrólito polimérico gel P(EO/EM)/GBL/LiI/I2 apresentou excelentes propriedades químicas e eletroquímicas. Esses eletrólitos foram aplicados nas células solares de TiO2/corante, conforme e apresentado no Capítulo IV. As células solares foram caracterizadas por meio das curvas de corrente-potencial (J-V), estimativa do tempo de vida do eletron e espectroscopia de absorção transiente (TAS). De modo geral, os dispositivos montados com o eletrólito polimérico (P(EO/EM)/GBL/LiI/I2 apresentaram um aumento da fotocorrente com a incorporação de GBL no eletrólito. Esse resultado e influência da maior difusão das especies redox no meio. Em contrapartida, o aumento da concentração de GBL no eletrólito também provocou uma acentuada perda no potencial de circuito aberto, o que foi relacionado ao aumento dos processos de recombinação na interfaces, contribuindo para a perda da eficiência das células solares. Para minimizar esses efeitos, no Capítulo V, e apresentada a caracterização por meio das curvas de corrente-potencial da célula solar de TiO2/corante montadas com o eletrólito P(EO/EM)/GBL/LiI/I2 preparado com terc-butilpiridina e éter coroa. A incorporação desses aditivos proporcionou um aumento de Voc das células solares e, consequentemente, da eficiência dos dispositivos. O Capítulo VI apresenta os testes de estabilidade das células solares de TiO2/corante preparadas com o eletrólito polimérico gel, no qual apresentou estabilidade apropriada durante 30 dias de teste. O Capítulo VII contém as principais conclusões deste trabalho e perspectiva de continuação para esta linha de pesquisa / Abstract: This thesis consisted in the preparation, characterization and application of gel polymer electrolytes in dye-sensitized TiO2 solar cells. A general introduction to solar cells and to polymer electrolytes will be presented in Chapter I. Chapter II describes the aims of this work. Chapter III deals with the preparation of gel polymer electrolytes based on the poly(ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether) (P(EO/EM)) polymer matrix containing I2 and different concentrations of g-butyrolactone (GBL) and LiI. These electrolyte samples were characterized by differential scanning calorimetry (DSC), Li nuclear magnetic resonance (Li RMN), thermogravimetry (TGA), X-ray diffraction (RDX), conductivity measurements and cyclic voltammetry (VC). The gel polymer electrolyte P(EO/EM)/GBL/LiI/I2 provided excellent chemical and electrochemical properties. The electrolytes were applied in dye-sensitized TiO2 solar cells, as discussed in Chapter IV. Solar cells were characterized by current-voltage (IV) curves, electron lifetime measurements and transient absorption spectroscopy (TAS). Most of the solar cells based on the polymer electrolyte P(EO/EM)/GBL/LiI/I2 presented an increase in photocurrent with the addition of GBL to the electrolyte composition. This result may be explained by the enhanced diffusion of redox species in the medium. However, a significant decrease in open-circuit voltage was observed after increasing the GBL concentration in the electrolyte composition. The decrease in open-circuit voltage was assigned to an increase in recombination losses taking place at the interfaces, which resulted in solar cells with lower performance. In order to minimize these drawbacks, dye-sensitized TiO2 solar cells were assembled with the electrolyte P(EO/EM)/GBL/LiI/I2 containing 4-tert-butylpyridine and crown ether molecules. The addition of these additives provided an increase in Voc and, consequently, improved device performance. The characterization of these solar cells based on gel polymer electrolyte containing additives was carried out by means of current-voltage (I-V) curves, as discussed in Chapter V. Dye-sensitized TiO2 solar cells based on gel polymer electrolyte were subjected to durability tests. Good durability results were achieved during a 30-day test, which are discussed in Chapter VI. Chapter VII deals with the main conclusions of this work and outlines some perspectives for the next steps of this research / Doutorado / Quimica Inorganica / Doutor em Ciências

Orientador: Paulo Roberto Mei / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-14T07:44:38Z (GMT). No. of bitstreams: 1 Moreira_SimonedePaula_D.pdf: 8445181 bytes, checksum: a58955df1f5c0b0b975a053856fe9dc0 (MD5) Previous issue date: 2009 / Resumo: A busca por fontes renováveis de energia fez com que a produção de células solares apresentasse um crescimento explosivo nesta década, passando de 0,3 GW em 2002 para 6,0 GW em 2008, envolvendo em 2008 a cifra de 37 bilhões de dólares. A produção de Silício Grau Eletrônico (SiGE) aumentou 127% de 2007 para 2008, sendo que cerca de 90% das células solares produzidas atualmente utiliza o SiGE, que é responsável por 1/4 do custo total da instalação de um painel solar. O processo de purificação de silício utilizado em todo o mundo é o Siemens, baseado na cloração do silício, o qual possui o inconveniente de gerar resíduos químicos de alta toxidade. Esse processo produz o silício de alta pureza, com menos de 1 ppm de impurezas, chamado de Silício Grau Eletrônico (SiGE), usado tanto pela indústria microeletrônica como a de produção de células solares. Para suprir tal demanda de silício para a área fotovoltaica, existem duas alternativas. A primeira visa desenvolver processos químicos derivados do Siemens para produzir um silício de qualidade inferior e de menor custo, denominado de Silício Grau Solar (SiGS), mas que atenda a exigência para a fabricação de células solares. A segunda alternativa é tentar adaptar etapas metalúrgicas de purificação ao silício de grau metalúrgico (SiGM), de forma a obter um silício com exigências a um SiGS, foco deste trabalho. As possibilidades de inserção do Brasil no mercado fotovoltaico são muito grandes, pois além de possuir a maior reserva mundial de quartzo, é o terceiro maior produtor de silício metalúrgico do mundo e o exporta a, aproximadamente, U$ 1/kg. Entretanto a agregação de tecnologia na purificação do silício eleva exponencialmente o seu valor, chegando a US$ 100 /kg para o silício policristalino de grau eletrônico ou até US$ 4.000/kg para lâminas de silício mono e policristalino da mesma pureza. O Departamento de Engenharia de Materiais da Unicamp pesquisa o SiGS desde 1980, tendo obtido naquela época, através da lixiviação ácida e solidificação unidirecional de SIGM, um lingote com 170 ppm de impurezas metálicas na sua região mais pura. Deste lingote foram produzidas células solares com eficiência de 4 % no Instituto de Física da Unicamp. A partir de 1990, com compra de um forno de feixe de elétrons, iniciaram-se os estudos sobre a purificação do SiGM neste equipamento, tendo sido observada numa amostra circular, solidificada a 10 mm/min, a segregação radial de impurezas, com uma redução de 1100 para 15 ppm na região mais pura da amostra. Os resultados obtidos nos levaram a estudar o potencial de purificação de silício metalúrgico no forno EBM com a técnica de fusão zonal horizontal, utilizando cadinhos de cobre refrigerado à água e de grafita, com diferentes velocidades de avanço de zona (1 e 10 mm/min), foco deste trabalho. As vantagens do processo de fusão zonal horizontal (com cadinho) sobre o de fusão zonal vertical ou flutuante (sem cadinho) é que o controle do tamanho da zona é bem mais simples no primeiro, além de permitir o uso de silício em qualquer forma (pedras, granulado ou lingotes) enquanto que para o segundo somente podem ser utilizadas barras de silício Os resultados obtidos utilizando-se o SiGM fornecido pela empresa Liasa com teor total de impurezas de 1454 ppm e mais de 100 ppm de carbono e 30 ppm de oxigênio e o SiGM fornecido pela empresa Rima, com teor total de impurezas de 254 ppm e mais 140 ppm de carbono e 2500 ppm de oxigênio foram os seguintes: - O uso de cadinho de cobre refrigerado a água foi adequado, pois permitiu fácil desmoldagem do lingote sem contaminar o silício. Com 1 passada de fusão zonal em 2 lingotes, numa velocidade de 1 mm/min e uma nova passada no lingote formado pelas duas metades mais limpas, permitiu a obtenção de um teor total de impurezas de 25 ppm com silício Liasa e menos de 11 ppm com o silício Rima. O teores de carbono e oxigênio foram reduzidos para 35 e 6 ppm respectivamente, no silício Liasa e 40 e 10 ppm, no silício Rima, valores próximos do SiGE da Wacker, com 20 e 12 ppm. A perda de massa do silício por evaporação ficou em torno de 6% por passada, o que limita a aplicação da fusão zonal para um grande número de passadas; - Embora o cadinho de cobre forneça um silício bastante puro (5 noves ou 99,999%) o lingote apresentou trincas internas de solidificação e não pode ser usado diretamente na produção de células solares. Outro processo de solidificação (CZ ou HEM) posteriormente ao processo de fusão zonal deveria ser usado, obtendo assim lingote de melhor qualidade estrutural; - Todas as impurezas metálicas analisadas (Al, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Ti, V, W e Zr) além de boro e fósforo foram segregadas para o final do lingote. Além da segregação, houve a purificação por evaporação principalmente do fósforo, seguido em menores proporções de manganês, alumínio e cobre. O coeficiente de distribuição efetivo (K) de cada elemento mostrou ser dependente do teor total de impurezas e quanto maior o teor total de impurezas, maior foi o valor de K. O boro foi pouco afetado pelo processo de fusão zonal, pois não evapora e tem solubilidade próxima no sólido e no líquido; - O uso de cadinho de grafita no lugar do cadinho de cobre refrigerado a água, reduziu o consumo de energia em 20% e proporcionou a produção de um lingote de silício com boa pureza e melhor qualidade estrutural, com ausência de trincas internas. O contato do silício com o cadinho provocou, entretanto, a contaminação do silício pelo carbono e a formação de uma camada superficial de carboneto de silício, de extrema dureza, o que dificulta ou impede o corte das lâminas. Houve a quebra do cadinho de grafita durante a fusão ou a desmoldagem. Cadinhos especiais como FABMATE e SuperSiC também apresentaram a adesão do silício e quebraram; - A resistividade elétrica não mostrou correlação com o teor total de impurezas, ficando em torno de 0,08±0,04 ohm.cm para lâminas com teor total de impurezas entre 10 e 10.000 ppm. A resistividade elétrica também não mostrou correlação direta com a eficiência solar nas amostras produzidas; - A eficiência solar não mostrou relação direta com o teor total de impurezas, mas sim com a qualidade estrutural do lingote, pois as células que apresentaram maior eficiência foram produzidas no cadinho de grafita, onde as lâminas não apresentavam trincas de solidificação. / Abstract: The search for renewable energy sources has caused a boom in the production of solar cells in this decade, which rose from 0.3 GW in 2002 to 6.0 GW in 2008, totaling 37 billion dollars in 2008. The production of Electronic Grade Silicon (SiGE) increased 127% from 2007 to 2008, and approximately 90% of solar cells produced nowadays use SiGE, which is responsible for 1/4 of the total installation cost of a solar panel. The Siemens process is used all over the world to purify silicon. It is based on the chlorination of silicon and has the disadvantage of generating highly toxic chemical waste. This process produces high-purity silicon with less than 1 ppm impurities, called Electronic Grade Silicon (SiGE). It is used by the microelectronics industry and in the production of solar cells as well. There are two alternatives to meet the demand for silicon for the photovoltaic area. The first one, called Solar Grade Silicon (SiGS), aims to develop a chemical processes, derived from the Siemens process, to produce lower-quality silicon at lower costs, but which still meets the requirements for solar cell manufacture. The second alternative is to try to adapt the metallurgical purification steps of metallurgical grade silicon (SiGM) to obtain silicon that meets SiGS requirements, which is the focus of this work. The possibilities of insertion of Brazil in the photovoltaic market are very large because, besides having the largest quartz reserves in the world, it is the third largest producer of metallurgical silicon in the world and exports it at about U$ 1/kg. However, the aggregation of technology in silicon purification increases its value exponentially, reaching U$100/kg for electronic grade polycrystalline silicon and up to U$ 4.000/kg for layers of mono and polycrystalline silicon, with the same purity. The Department of Materials Engineering of Unicamp has researched SIGS since 1980, having obtained an ingot with 170 ppm metallic impurities in its purest region by acid leaching and unidirectional solidification of SiGM at that time; solar cells with 4% efficiency were produced from this ingot at the Institute of Physics at Unicamp. In 1990, with the purchase of an electron beam furnace, studies on the purification of SiGM in this equipment were started. Radial segregation of impurities was observed in a round sample solidified at 10 mm/min, with a reduction from 1100 to 15 ppm in its purest region. The results led us to study the potential for purification of metallurgical silicon in the EBM furnace with the horizontal zone melting technique, using water-cooled copper and graphite crucibles, with different zone advance speeds (1 and 10 mm/ min), which is the focus of this work. The advantages of the horizontal zone melting process (with crucible) over the vertical zone melting or floating (without crucible) process is that the control of the size of the zone is much simpler in the former, besides allowing the use of silicon in any shape (stones, granulated or ingots), while only silicon bars can be used in the latter. The results obtained using the SiGM provided by Liasa, with 1454 ppm total impurities content and more than 100 ppm and 30 ppm of carbon and oxygen, and the SiGM supplied by Rima Company, with 254 ppm total impurities content and 140 ppm carbon and 2500 ppm oxygen, were as follows: - The use of the water-cooled copper crucible was adequate because it allowed easy shakeout, with no silicon contamination. With 1 melting zone pass along 2 bars, at a speed of 1 mm/min, and a new pass along the ingot formed by the two cleanest halves, we obtained a total of 25 ppm impurities content with Liasa silicon and less than 11 ppm with Rima silicon. Carbon and oxygen contents were reduced to 35 and 6 ppm, respectively, in Liasa silicon and 40 and 10 ppm in Rima silicon; these values are near Wacker SiGE values of 20 and 12 ppm. The loss of silicon mass by evaporation was around 6% per pass, which limits the application of zone melting for a large number of passes; - Although the copper crucible leads to extremely pure silicon (5 nines or 99,999%) the ingot presented internal solidification cracks and cannot be used directly in the production of solar cells. Another solidification process (CZ or HEM) should be used after the zone melting process, leading to an ingot with better-quality structure; - All metal impurities analyzed (Al, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Ti, V, W and Zr), besides boron and phosphorus, were segregated towards the end of the block. Besides segregation, there was purification of phosphorus, mainly by evaporation, followed by smaller proportions of manganese, aluminum and copper. The effective distribution coefficient (K) of each element was shown to be dependent on the total impurities content, and the higher the total impurities content, the higher the value of K is. Boron was little affected by the zone melting process because it does not evaporate and its solubility is similar in the liquid and in the solid phases; - The use of the graphite crucible, instead of the water-cooled copper crucible, reduced energy consumption in 20% and led to the production of a silicon ingot with good purity and better structural quality, without internal cracks. The contact of silicon with the crucible has, however, caused the contamination of silicon by carbon and formed an extremely hard surface layer of silicon carbide, which makes it difficult to cut the layers or even prevents it. The graphite crucible broke during melting or shakeout. Special crucibles, such as FABMATE and SuperSiC, also suffered silicon adhesion and broke; - The electrical resistivity showed no correlation with the total impurities content, remaining around 0.08 ± 0.04 ohm.cm for samples with total impurities content between 10 and 10,000 ppm. The electrical resistivity also showed no direct correlation with solar efficiency in the samples produced.; - The solar efficiency showed no direct relationship to the total impurities content, but it showed a direct relationship to the structural quality of the ingot, as the higher efficiency cells were produced in the graphite crucible, with no solidification cracks in the layers; / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Submitted by Ilvana Bentes (vovoquinha.ufam@gmail.com) on 2018-09-17T15:08:05Z No. of bitstreams: 1 Final + ficha cartolografica.pdf: 3843020 bytes, checksum: ce562c916a2f1bb8366b5d9c69ea7900 (MD5) / Approved for entry into archive by Marcos Roberto Gomes (mrobertosg@gmail.com) on 2018-09-17T15:18:30Z (GMT) No. of bitstreams: 1 Final + ficha cartolografica.pdf: 3843020 bytes, checksum: ce562c916a2f1bb8366b5d9c69ea7900 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2018-09-17T17:45:03Z (GMT) No. of bitstreams: 1 Final + ficha cartolografica.pdf: 3843020 bytes, checksum: ce562c916a2f1bb8366b5d9c69ea7900 (MD5) / Made available in DSpace on 2018-09-17T17:45:03Z (GMT). No. of bitstreams: 1 Final + ficha cartolografica.pdf: 3843020 bytes, checksum: ce562c916a2f1bb8366b5d9c69ea7900 (MD5) Previous issue date: 2016-03-18 / FAPEAM - Fundação de Amparo à Pesquisa do Estado do Amazonas / Studies involving renewable energies have a leading role in the global scientific context. Due to the need of improve the use of renewable energy resources have been developed new generations of solar cells that enable made devices more efficient, with low-cost and versatile applications. The solar cells based on the use of photosensitizing dyes have a significant potential for applications in low cost photovoltaic devices. In this work were employed vegetal pigments as photosensitizing agents of the nanostructured semiconductor layer of the TiO2 in solar cells of the modified Grätzel type. The TiO2 nanoparticles were synthesized by sol-gel method, and its average particle size was determined by techniques of XRD and SEM. The structural and optical properties of the pigments and the semiconductor layer were studied using UV-Vis spectroscopy and FTIR. Were performed studies in order to optimize the performance of the devices through the modification of the composition of the non-aqueous liquid electrolyte that has been replaced by a solid polymeric electrolyte. The electrochemical characterization was made using the voltammetry techniques and electrochemical impedance spectroscopy that allowed deepen in to the efficiency parameters and the charge mobility through the different layers that constitute the photovoltaic device. The electrical characterization of FB0 Isc: 2,184X10-7, Voc: 0,17414, n: 5,521X10-5, Pmáx: 4,831x10-9, Vmp: 0,068148, ff: 12. And FB02 Isc:1,877X10-5, Voc: 0,03209, n: 0,0017, Pmáx: 1,486x10-7, Vmp: 0,016112, ff: 24. / Estudos referentes a questões energéticas estão em amplo desenvolvimento no meio científico, é o estudo da conversão de energia solar em energia elétrica, com a utilização de células solares exerce um principal papel no que se fala de energias renováveis. Baseado nisso algumas modificações vem ocorrendo no desenvolvimento de células modernas, um dos dispositivos que se destacam nesse desenvolvimento, são as células solares baseadas no uso de corantes fotoexcitáveis ou sensibilizadores. Neste trabalho utilizou-se os pigmentos FB01 e FB02, como sensibilizadores de celulas solar fotoeletroquímica. As nanopartículas de TiO2 foram sintetizadas pelo método sol-gel, e seu tamanho de partícula foi determinado por DRX (20 nm) e análise topográfica via MEV. As propriedades óticas e estruturais (TiO2, FB01 e FB02) foram investigados por espectroscopia UV-Vis e de Infravermelho. Com relação ao eletrólito, estudou-se a modificação deste por um eletrólito polimérico analisando diferentes concentrações de plastificantes (25%, 50% e 70 %). Os parâmetros elétricos são: para FB01, temos: Isc: 2,184X10-7, Voc: 0,17414, n: 5,521X10-5, Pmáx: 4,831x10-9, Vmp: 0,068148, ff: 12. E para o FB02, temos: Isc:1,877X10-5, Voc: 0,03209, n: 0,0017, Pmáx: 1,486x10-7, Vmp: 0,016112, ff: 24.