Orientador: Francisco Carlos Lavarda / Banca: Luiz Carlos da Silva Filho / Banca: Welber Gianni Quirino / Resumo: Atualmente existe uma grande demanda no desenvolvimento de novas fontes de energia. Uma das possíveis alternativas para produção de energia são as células solares e, dentre estas, as células solares orgânicas. Estas ainda apresentam baixa eficiência na conversão de energia, por isso um grande número de pesquisas vem sendo realizadas com o intuito de melhorar suas características. No presente trabalho estudamos os componentes aceitadores de elétrons, utilizados na camada ativa das células solares orgânicas, especificamente aqueles formados por C60 e seu derivados, que têm sido amplamente estudados, devido ao seu bom desempenho. Estes estudos visam principalmente ajustar os níveis eletrônicos, assim possibilitando o aumento da tensão de circuito aberto e, por sua vez, aumentando a eficiência de conversão de energia. Nesse trabalho propõe-se uma metodologia que apresenta bons resultados na representação das propriedades estruturais e eletrônicas dos sistemas aqui estudados. Esta metodologia utiliza níveis de teoria semi-empíricos e ab initio. Também foram investigados métodos para correlacionar as propriedades eletrônicas dos materiais estudados com a tensão de circuito aberto, já que esta tensão está diretamente relacionada à eficiência das células solares orgânicas. Através deste trabalho encontramos um método capaz de simular a tensão de circuito aberto com desvio médio de 13%. Por fim, investigamos possíveis substituições químicas em derivados de C60. A partir desse estudo, notamos padrões de comportamentos nos níveis eletrônicos ocasionados de acordo com o tipo de substituinte / Abstract: Today, there is a great demand in the development of new energy resources. One of the possible alternatives for energy production are solar cells and, among them, organic solar cells. They still have low efficiency in energy conversion, therefore a lot of research has been conducted in order to improve their characteristics. In this work we studied the electron acceptor components, used in the active layer of organic solar cells, specifically those formed by C60 and its derivatives, which have been widely studied because their good charge transport properties. These studies mainly aim at adjusting the electronic levels, thus enabling the increase of the open circuit voltage and increasing the efficiency of energy conversion. In this work we propose a methodology that provides good results in the representation of the structural and electronic properties of the systems hereby studied. This methodology is a mix of semiempirical and ab initio theory levels. We also investigated methods to correlate the electronic properties of materials studied with the open circuit voltage, as this is directly linked to the efficiency of organic solar cells. Through this work we found a method to simulate the open-circuit voltage with a medium deviation of 13%. And finally, we investigate possible chemical substitutions on the C60 derivatives. From this study, we observed patterns in electron levels behavior caused according to the type of the substituent / Mestre

Orientador: Carlos Frederico de Oliveira Graeff / Banca: Alejandra Hortencia Miranda Gonzáles / Banca: Francisco Eduardo Gontijo Guimarães / Banca Alexandre Fontes da Fonseca / Resumo: Este trabalho tem como objetivo estudar e desenvolver materiais para aplicações em células solares de terceira geração. Os materiais sintetizados são derivados de fulereno, óxido de titânio e nanopartículas híbrido (óxido@polímero). Os polímeros derivados de fulereno, de tipo n, foram planejados para conter C60 na cadeia principal. Três produtos diferentes foram obtidos, variando o comprimento da cadeia alquílica do co-monômero utilizando uma nova rota de polimerização. Os dispositivos fotovoltaicos foram preparados utilizando a configuração de heterojunção no volume e a maior eficiência alcançada foi de 1,84 %, o que representa um desempenho promissor para um novo material. As nanopartículas de dióxido de titânio foram sintetizadas usando a técnica hidrotermal assistida por micro-ondas em diferentes condições reacionais, tais como pH, temperatura e tempo, de modo a obter a morfologia nano dimensionada bem definida, rendimentos elevados e alta área superficial. Além disso, estudou-se a influência dos íons Na+ no crescimento cristalino dos óxidos e em sua morfologia, onde foram obtidas nanopartículas, estruturas tipo agulas e estruturas tipo nanotubos. As nanopartículas híbridas foram sintetizadas utilizando os óxidos sintetizados e um polímero, P3HT, funcionalizado de modo a ligar-se covalentemente aos óxidos. As nanopartículas foram opticamente caracterizadas e concluímos que estas podem ser utilizadas para estudar a transferência de carga em sistemas híbridos. / Abstract: This work aims to study and develop materials for applications in third generation solar cells. The synthesized materials are fullerene derivatives, titanium oxide, and hybrid (polymer@oxide) nanoparticles. The fullerene derivatives, n-types polymers, were designed to contain C60 in the main chain. Different products were obtained, varying the comonomer alkyl length using a new polymerization route discovery in this work. The photovoltaic devices were prepared using the bulk heterojunction configuration and the highest efficiency reached was 1,84%, representating a very promising performance for a novel materials. The titanium dioxide nanoparticles were synthesized using microwave assisted hydrothermal technique in different reaction condition, such as pH, temperature and time, in order to obtain well defined nano-sized morphologies, high yields and high surface areas. Also, it was investigated the influence of the Na+ions on the crystalline growth and morphologies of the oxides, where nanoparticles, needles and nanotube-like structures were obtained. The hybrid nanoparticles were synthesized using the prepared oxides and a P3HT functionalized in order to bond covalently with the the oxides. The nanoparticles were optically characterized and concluded to be possible to use for studies of charge transfer in hybrid systems / Doutor

Orientador: Francisco Carlos Lavarda / Banca: Luiz Carlos da Silva Filho / Banca: Julio Ricardo Sambrano / Banca: Paula Homem de Mello / Banca: Mauricio Domingues Coutinho Neto / Resumo: Materiais orgânicos vêm sendo utilizados em diversos tipos de dispositivos eletrônicos e optoeletrônicos, sendo um dos destaques seu uso em células solares. Atualmente, células solares que utilizam materiais orgânicos na camada ativa já atingem eficiências em torno de 12% na conversão da energia solar em elétrica. Apesar destes materiais apresentarem vantagens em relação ao custo do produto final e processamento comparado aos inorgânicos, a comunidade científica ainda se depara com problemas relacionados às propriedades intrínsecas, como por exemplo, baixa estabilidade à oxidação e energias de bandgap elevadas; deste modo, ainda é viável encontrar novos materiais orgânicos que superem tais problemas. Este trabalho teve como finalidade a busca de novos materiais orgânicos, mais especificamente polímeros conjugados, para aplicações em camada ativa de células solares utilizando métodos teóricos de modelagem de materiais em níveis de teoria semi-empírico e DFT. A primeira parte deste trabalho focou no estudo de novos copolímeros de comonômeros similares e novos homopolímeros derivados de P3HT. Aqui foi possível verificar que, através de substituições químicas realizadas no P3HT, pode-se encontrar novos polímeros com valores mais apropriados para as energias dos orbitais moleculares de fronteira e maiores mobilidades de carga, propriedades que estão intimamente relacionadas à eficiência e à estabilidade que a célula solar pode atingir. Um dos novos polímeros que apresentou potenci... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Organic materials have been used in various types of electronic and optoelectronic devices, with prominent application in solar cells. Solar cells in which the active layers are composed of organic materials already reach efficiencies of around 12% in the conversion of solar energy into electricity. Although these materials have advantages in relation to the final cost and processing compared to the inorganics, the scientific community still face problems related to intrinsic properties, such as low oxidation stability and high bandgap energy; thus, it is desirable to find new organic materials that overcome these problems. This work aimed sy the search for new organic materials - specifically conjugated polymers - for applications in active layers of solar cells employing theoretical methods of material modeling of semi-empirical and DFT theory levels. The first part of this work focuses on the study of new cepolymers of similar comonomers and new P3HT derivatives. Here it was observed that, through chemical substitutions made in P3HT, one may find new polymers with appropriate values for the energies of the frontier molecular orbitals and increased charge mobility, properties that are closely related to the efficiency and stability that the solar cell can achieve. One of the novel polymers found which have potential for use in active layers was the fluorinated P3HT, later confirmed by experimental works. For copolymers of similar comonomers, it was found that the electronic and optical properties of these materials exhibit a linear dependence with the same properties and the monomers proportion of the homopolymers that were used as comonomers in the construction of the copolymer; most important is that through this linear relatioship one may design new copolymers of similar comonomers before a possible synthesis. The second part of this study evaluated the methodologies for modeling of organic... (Complete abstract electronic access below) / Doutor

Historically, the interfaces and charge transportation layers dictate the performance in heterojunction solar cells. This thesis addresses the interface behaviours and the interfacial layers within perovskite solar cells (PSCs), and provides insights and practicable solutions to facilitate the realisation of efficient PSCs. To achieve efficient charge collection with interlayer fabricated with low-temperature processes, a graphene-TiO₂ nanocomposite is demonstrated; By investigating the carrier transport, we found the insertion of graphene improved the electron collection efficiency with its high surface area and ballistic carrier conduction properties, and in conjunction with pre-synthesised TiO₂, we have successfully circumvented the need for high-temperature annealing, enabling the whole device to be fabricated at under 150 °C. While the anomalous hysteresis behaviour which is widely observed in regular PSCs structure is a significant problem, the quest of stable PSCs seems to be answered by the use of inverted PSCs structures. We show a detailed development of inverted PSCs which are deconstructed layer by layer. Numerous approaches have been tailored to improve interfaces, and energy levels between layers, leading to an efficient and hysteresis-free perovskite solar cells. Lastly, an in-depth study of impurity doping is investigated using Al³⁺. The doping with small metal ions in the perovskite precursor has been found to influenced the crystallisation and optoelectronic properties of the perovskite crystals. Here, for the first time, the correlation between reduced structural crystal defects is clearly linked to enhanced photovoltaic properties, with the best performance for the lowest electronic disorder in the CH₃NH₃PbI₃ crystal.

No description available.

No description available.

No description available.

Mesoporous TiO2 thin film has been considered as a benchmark material in the applications of dye sensitised solar cells (DSSCs) due to a combination of the physical properties that are inherent to the metal oxide and its particular structuring, in addition to its chemical stability and commercial availability. For DSSCs, a more important functionality of mesoporous TiO2 thin films is their extremely high surface and internal surface areas, resulting in high adsorption of dye molecules. However, a major drawback of fabrication of mesoporous TiO2 thin films is its high-temperature furnace sintering at 450à ̄‚°C-500à ̄‚°C for 30 min. The high-temperature process prevents the possibility of integrating different electro-optical devices on the same substrate, and the sintering time required would be a hurdle for potentially rapid manufacturing of mesoporous metal oxide thin films for DSSCs. This thesis demonstrates for the first time the use of a fibre laser with a wavelength of 1070 nm and a pulse width of milliseconds for generation of 1) mesoporous nanocrystalline (nc) TiO2 thin films on ITO coated glass, and 2) compact TiO2 layer and mesoporous TiO2 film on ITO coated glass. The first one was achieved by complete vaporisation of organic binder and inter-connection of TiO2 nanoparticles; and the second one was achieved by full crystallisation of TiO2 precursor to form the compact TiO2 layer and the same sintering process described above. Both processes were one-step, and achieved by stationary laser beam irradiation of 1 minute, compared with 30 min for furnace-sintering to form a mesoporous TiO2 film, and 2 h for two-step furnace treatment to form compact layer and mesoporous film on ITO glass. No thermally damaging of the ITO layers and the glass substrates was observed. The DSSC with the laser-sintered TiO2 photoanode at the optimised laser processing condition of 85 W/cm2 and 100 ms/50 ms pulse mode reached higher power conversion efficiency (PCE) of 3.20% for the TiO2 film thickness of 6 à ̄­m compared with 2.99% for the furnace-sintered; the DSSC with the laser-treated compact TiO2 layer and mesoporous TiO2 film on ITO glass at the optimised laser treatment condition of 85 W/cm2 and 125 ms/25 ms, reached 5.76% compared to 4.83% with the furnace-treated. Electrochemical impedance spectroscopy (EIS) studies revealed that the laser sintering effectively decreased charge transfer resistance and increased electron lifetime of the TiO2 thin films. It is believed that the use of the fibre laser with over 40% wall-plug efficiency offers an economically-feasible, industrial viable solution to the major challenge of rapid fabrication of large scale, mass production of mesoporous metal oxide thin film based solar energy systems, potentially for perovskite and monolithic tandem solar cells, in the future. Another part of the thesis presents a detailed investigation on the improvement of photovoltaic performance of furnace-sintered TiO2 films on ITO-coated glass using an excimer laser with a wavelength of 248 nm and possesses a rectangular beam profile and has a full width at half maximum (FWHM) pulse duration of 13-20 ns. This was achieved by modifying the surface of the furnace-sintered TiO2 films to increase the roughness, which led to increased optical absorbance via light-trapping. The laser process was carried out with variation of laser fluence and number of pulses per unit area. Under the optimised laser fluence of 34 mJ/cm2 and number of pulses of 50, the DSSC with the laser-modified TiO2 photoanode showed a high power conversion efficiency of 2.99% than 2.10% without the laser treatment. EIS studies showed that the films modified under the optimised laser parameter effectively decreased charge transfer resistance and increased electron lifetime of the TiO2 thin films.

Orientadores: Paulo Roberto Mei, Francisco das Chagas Marques / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-11-07T13:41:06Z (GMT). No. of bitstreams: 1 Cortes_AndresaDeoclidiaSoares_D.pdf: 28493660 bytes, checksum: 9830a2bc4fe51f04b181cb72224978a8 (MD5) Previous issue date: 2011 / Resumo: A principal barreira para a expansão do setor fotovoltaico corresponde ao elevado custo da produção do silício grau eletrônico (Si-GE) obtido pelo processo Siemens, matéria-prima para fabricação de mais de 85 % de todas as células fotovoltaicas. Em todo o mundo grupos de pesquisa trabalham em rotas metalúrgicas alternativas para purificação do silício grau metalúrgicas (Si-GM), a fim de produzir um material de menor pureza e de menor custo que o Si-GE, mas que ainda seja adequado para a produção de células fotovoltaicas. Esse material é chamado de silício grau metalúrgico melhorado (Si-GMM). Esta tese apresenta os resultados obtidos na produção do Si-GMM e na fabricação de células fotovoltaicas com o mesmo, testando também processos de gettering com fósforo para a captura de impurezas metálicas. Foram utilizadas, para comparação, lâminas comerciais de Si-GE importadas de diferentes empresas e lâminas de Si-GMM da empresa Rima Industrial S/A. Observou-se que a diferença de composição química entre as lâminas comerciais de Si-GE e as lâminas de Si-GMM da Rima Industrial S/A é devido à concentração de boro e de fósforo. Enquanto que no Si-GE a concentração de boro é menor que 0,1 ppm, no Si- GMM situa-se em torno de 3 ppm, ou seja, um valor 30 vezes maior. Soma-se a isto o fato destes dois elementos serem dopantes, os quais influenciam enormemente o desempenho das células fotovoltaicas. Com a associação de desgaseificação a vácuo em forno de feixe de elétrons e crescimento Czochralski foi possível obter um lingote de silício monocristalino com concentração total de impurezas metálicas igual a 6 ppm, sendo 5,5 ppm de boro, partindo de um silício grau metalúrgico com 219 ppm de impurezas metálicas e 5,5 ppm de boro, o que significa que nenhum dos processos reduziu o teor de boro do silício. A resistividade do silício desgaseificado a vácuo passou de 0,06 para 0,30 ohm.cm após crescimento Czochralski, indicando que o mesmo, além de reduzir a quantidade de impurezas metálicas, que passou de 13 para 6 ppm, também contribuiu para a melhoria da qualidade estrutural do silício ao produzir um lingote monocristalino. O uso de gettering de fósforo na fabricação de células de Si-GMM proporcionou um aumento no comprimento de difusão dos portadores de carga com consequente aumento da eficiência de conversão das mesmas. Dentre os processos de gettering aplicados, os que incluíram etapas de recozimento foram mais eficazes na captura de impurezas metálicas. O resultado obtido com o emprego do gettering na fabricação das células de Si-GMM purificado nesta tese atingiu o valor de 9,7 % de eficiência de conversão fotovoltaica. Com uma otimização no processo de produção de células chegou-se a 13 % de eficiência usando lâminas de Si-GMM com 3 ppm de boro e 3 ppm de fósforo, um valor recorde obtido com este tipo de silício na literatura / Abstract: The main barrier for expanding the photovoltaic industry corresponds to the high production costs of the Electronic grade silicon (EG-Si) obtained through the Siemens process, the raw-material for the production of more than 85% of all photovoltaic cells. Throughout the world, research groups work in alternative metallurgical routes to purify the Metallurgical grade silicon (MG-Si), in order to produce a material with lower purity and lower costs than EG-Si, but which is still adequate for the production of photovoltaic cells. Such material is called Upgraded Metallurgical grade silicon (UMG-Si). This thesis presents the results obtained during the production of UMG-Si and the manufacturing of photovoltaic cells with UMG-Si, also testing gettering processes with phosphorus in order to capture metallic impurities. For comparison, we used commercial EG-Si wafers imported from different companies, and UMG-Si wafers from the company Rima Industrial S/A. We observed that the difference in the chemical composition between the commercial EG-Si wafers and the UMG-Si wafers from Rima Industrial S/A is due to the boron and phosphorus concentration. While in EG-Si the boron concentration is lower than 0.1 ppm, in UMG-Si it corresponds to approximately 3 ppm, that is, a 30 times higher value. In addition to that, both elements are dopants, which markedly affect the development of the photovoltaic cells. With the association of vacuum degassing in an electron beam furnace and Czochralski growth, we were able to obtain a monocrystalline silicon ingot with a total metallic impurity concentration of 6 ppm, considering that 5.5 ppm is boron, from a Metallurgical grade silicon with 219 ppm of metallic impurities and 5.5 ppm of boron, which means that none of the processes reduced the silicon's boron amount. The resistance to the vacuum degassing silicon went from 0.06 to 0.30 ohm.cm after Czochralski growth, which indicates that, in addition to reducing the amount of metallic impurities, which went from 13 to 6 ppm, it also contributes to improve the silicon's structural quality by producing a monocrystalline ingot. The use of phosphorus gettering in the fabrication of UMG-Si cells provided an enhancement in the diffusion length of the charge carriers with a resulting increase in the conversion efficiency of the cells. Among the gettering processes applied, those that included annealing steps were more efficient in capturing metallic impurities. The result obtained by using gettering for the fabrication of purified UMG-Si cells in this thesis reached a 9.7 % efficiency rate for photovoltaic conversion. With an optimization of the cell production process, we reached a 13 % efficiency rate using UMG-Si wafers with 3 ppm of boron and 3 ppm of phosphorus, a record value obtained with this type of silicon in literature / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica

Yin, Ling = 銅基化合物薄膜太陽能電池 : 新透明導電電極與缺陷物理 / 尹苓. / Thesis Ph.D. Chinese University of Hong Kong 2015. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 26, October, 2016). / Yin, Ling = Tong ji hua he wu bo mo tai yang neng dian chi : xin tou ming dao dian dian ji yu que xian wu li / Yin Ling.