Magister Scientiae - MSc / In this research, novel hybrid perovskite materials were synthesized, characterized and applied in photovoltaic cells (PVCs) to enhance the performance of PVCs. Mixed-organic-cations tin halide perovskites (MOCTPs) were successfully synthesized using sol-gel method. These MOCTPs include guanidinium dimethylammonium tin iodide ([GA][(CH3)2NH2]SnI3) and guanidinium ethylmmonium tin iodide ([GA][CH3CH2NH3]SnI3). The MOCTPs were studied in comparison to their single-organic-cation tin perovskites (SOCTPs), which include guanidinium tin iodide (GASnI3), ethylammonium tin iodide ([CH3CH2NH3]SnI3) and dimethylammonium tin iodide [(CH3)2NH2]SnI3. High Resolution Scanning Electron Microscopy (HR SEM) of the five perovskite materials showed good crystallinity and tetragonal and hexagonal cubic shapes, characteristic of perovskites. These shapes were also confirmed from High Resolution Transmission Electron Microscopy (HR TEM), and the internal structure of the perovskites gave similar zone axes (ZAs) with those obtained from X-ray Diffraction (XRD). XRD showed tetragonal lattice shape for these perovskite materials. Fourier Transform Infrared (FTIR) demonstrated similar functional groups for both the SOCTPs and MOCTPs. FTIR bands that were observed are; N-H, C-H sp3, C-H aldehyde, N-H bend, C-N sp3 and N-H wag. From the 13C Nuclear Magnetic Resonance (NMR) results, the carbon atom of guanidinium iodide precursor shifts from downfield to upfield position, e.g. from 110.57 ppm to 38.49 ppm in GASnI3 SOCTP. This confirms a shift upfield of the carbon atom in guanidinium iodide precursor as it bonded to Sn metal in the perovskite chemical structure. Similar behavior was also observed for the NMR spectra of [GA][CH3CH2NH3]SnI3 MOCTP, where C-2 and C-3 atoms of ethylammonium iodide precursor shifted upfield from 37.03 ppm to 15.69 ppm and 16.06 ppm to 14.39 ppm respectively.

Magister Scientiae - MSc / Solar energy generation arises as a result of direct conversion of sunlight into electricity a by solar cell; which is mainly made up of a semiconducting material incorporated into a system. It is emerging as one of the most reliable and cost efficient renewable energy sources. Within the solar field, organic bulk heterojunction photovoltaic cells have proved of being able to have a great impact in the future years; mainly due to the easy processability of the active layer and substrate, their cost effectiveness and above all, a good power conversion efficiency associated to the close 3-dimensional interpenetrating network that is generated from blending donor and acceptor semiconducting materials together in a bulk heterojunction active layer. In this research work, we therefore report on the study of a newly developed organic bulk heterojunction active layer based on a blend of a star-copolymer generation 1 poly(propylenethiophenoimine)-co-poly(ethylenedioxythiophene) (G1PPT-co-PEDOT) as donor material with N,N-diisopropylnaphthalene diimide (NDI) as acceptor material. Both materials were chemically synthesized. The synthesis of G1PPT-co-PEDOT started first by the functionalization of generation 1 poly(propyleneimine) tetramine, G1PPI into G1PPT by condensation reaction in the presence of 2-thiophene carboxaldehyde under Nitrogen gas followed by the copolymerization of G1PPT with ethylene dioxythiophene (EDOT) monomer in the presence of ammonium persulfate, (NH4)2S2O8 as oxidant. On the other hand, NDI was also synthesized via condensation reaction of 1,4,5,8-naphthalene tetracarboxylic dianhydride in the presence of two (2) equivalences of N,N-diisopropylamine at 110 oC overnight in DMF. Both materials were characterized using FT-IR, UV-Vis spectroscopy, Fluorescence spectroscopy, Voltammetry, HRSEM microscopy and XRD. Based on the cyclic voltammetry and UV-Vis results, we were able to calculate the HOMO, LUMO and band gap energy (Eg) values of both the donor and acceptor to be -4.03 eV, -6.287 eV and 2.25 eV for iii the donor G1PPT-co-PEDOT respectively and -4.302 eV, -7.572 eV and 3.27 eV for the acceptor respectively. From these results, the energy diagram for both donor and acceptor was drawn and it comes out that the separation between the HOMO of the donor and the LUMO of the acceptor ΔEg = 1.985 eV, the ideal value for a good donor-acceptor combination. Also the offset energy that is, the energy difference between the LUMO of the donor and the LUMO of the acceptor is 0.302 eV.

Made available in DSpace on 2017-07-21T19:25:46Z (GMT). No. of bitstreams: 1 Joao Luiz Gomes Junior.pdf: 5004861 bytes, checksum: 0e45ece35c737cce76186e1babb5e257 (MD5) Previous issue date: 2015-03-26 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / In this work, the correlation between the structural morphology with thermal, optical and mechanical properties of (1 – x – y)TeO2-xLi2O-yMoO3 glasses was studied. The analysis was divided into three sets of samples, varying according to the composition for technique. The results reveal different behaviors for each set vitreous stabilities. The Raman spectroscopy and FTIR results showed a similar structural change between each set with decrease NBOs and new peaks position. The Raman and FTIR spectra results showed that with increasing content x and y, concomitantly, occur the conversion of TeO4 to TeO3+1 units, then, in addition to TeO3 units. Furthermore occurs change coordination in the structural units Mo atoms 4 to 6 and these structural changes. Li addition causes these structural changes. This fact confirmed by the Band Gap energy values, which increase with the increase of x and y, it decreases the optical basicity and refractive index values. By optical absorption measurements determined the Band Gap energy values of all samples. It was concluded that occur direct transitions allowed in all sets. The behavior of increasing Band Gap values and decreasing Optical basicity confirmed the decreasing in the NBO content leading to an indication of a more polymerized network for a variation of x mol%. Finally the behaviors elastic modulus and hardness, which shows decreased stiffness of the material with the incorporation of Li2O and MoO3 concomitantly, is presented. x / Este trabalho apresenta as correlações entre a morfologia estrutural e as propriedades térmicas, ópticas e mecânicas nos vidros (1 – x – y)TeO2 – xLi2O – yMoO3. Dividiram-se as análises em três conjuntos de amostras, de acordo com variação da composição, para cada técnica utilizada. Os resultados revelam diferentes comportamentos de estabilidades vítreas para cada conjunto. As medidas por espectroscopia de Raman e FTIR mostram mudanças estruturais similares entre cada conjunto com diminuição dos NBOs e novas posições de picos. Os resultados de Raman e FTIR mostram que com o aumento em conteúdo x e y ocorre a transformação de unidades TeO4 para TeO3 + 1 e, em seguida, para TeO3 além disso ocorre a mudança de coordenação do átomo de Mo de 4 para 6 e estas alterações estruturais têm sido relacionados com a adição de átomos de Li. Este fato é confirmado pelos valores de energia de Band Gap, que aumentam com o incremento de x e y, e diminuição dos valores de basicidade óptica e índice de refração. As energias de Band Gap, para todas as amostras, foram determinadas por medidas de absorção óptica na região do Ultravioleta. Foi concluído que ocorrem transições diretas permitidas em todos os conjuntos. E por fim apresenta-se os comportamentos de dureza e Módulo elástico, o que revela diminuição da rigidez do material com a incorporação de Li2O e MoO3 concomitantemente.

Optical properties of Tl4In3GaSe8, Tl4InGa3Se8, Tl4In3GaS8, Tl2InGaS4 and Tl4InGa3S8 chain and layered crystals were studied by means of photoluminescence (PL) and transmission-reflection experiments. Several emission bands were observed in the PL spectra within the 475-800 nm wavelength region. The results of the temperature- and excitation intensity-dependent PL measurements in 15-300 K and 0.13&times / 10-3-110.34 W cm-2 ranges, respectively, suggested that the observed bands were originated from the recombination of electrons with the holes by realization of donor-acceptor or free-to-bound type transitions. Transmission-reflection measurements in the wavelength range of 400-1100 nm revealed the values of indirect and direct band gap energies of the crystals studied. By the temperature-dependent transmission measurements in 10-300 K range, the rates of change of the indirect band gap of the samples with temperature were found to be negative. The oscillator and dispersion energies, and zero-frequency refractive indices were determined by the analysis of the refractive index dispersion data using the Wemple&ndash / DiDomenico single-effective-oscillator model. Furthermore, the structural parameters of all crystals were defined by the analysis of X-ray powder diffraction data. The determination of the compositional parameters of the studied crystals was done by energy dispersive spectral analysis experiments.

Orientador: Prof. Dr. Jeverson Teodoro Arantes Junior / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, Santo André, 2018. / Investigamos, sistematicamente, as propriedades estruturais e eletrônicas do óxido de zinco nanoporoso sob tração e compressão biaxial utilizando cálculos de primeiros princípios baseados na Teoria do Funcional da Densidade. O sistema apresenta uma alta concentração de nanoporos lineares orientados nas direções cristalográcas [0001] e [01-10], bem como um lme no nanoporoso. Para compressões maiores do que 4% com relação ao parâmetro de rede, foi observada uma distorção estrutural nas regiões menos densas do material poroso, mostrando uma tendência à mudança de fase localizada. O coe- ciente de Poisson calculado dos nanoporos orientados na direção [0001] foi negativo. Isto signica que quando o material poroso foi tracionado, expandiu-se transversalmente. Já quando comprimido, o material contraiuse na direção transversal. Os materiais que possuem esta característica são conhecidos como materiais auxéticos. Nossos resultados mostram que o valor do gap de energia foi modulado pelas deformações biaxiais com uma tendência oposta ao bulk. A densidade dos estados eletrônicos conrmou nossas observações. A tendência estrutural inversa da superfície dos nanoporos é o principal mecanismo para o comportamento inverso do gap sob compressão e tração. Dentro do nosso conhecimento, este é o primeiro reporte de um comportamento inverso do gap de energia de estruturas de ZnO sob compressão e tração biaxial. Nossos resultados sugerem que a nanoporosidade, conjuntamente com tra- ção e compressão biaxial, podem ser empregadas como um método dentro da engenharia de gap para customizar materiais funcionais que requerem controle da atividade eletrônica. / This work investigated, systematically, the structural and electronic properties of nanoporous zinc oxide, under biaxial strain, through rst-principles methods, based on total energy ab initio calculations using Density Functional Theory. The system was in a massive nanopore concentration regime. We studied linear pores in [0001] and [01-10] direction and a porous thin lm. Using a biaxial tension above 4% of the ZnO bulk lattice parameter, we observed a distortion resulting in a local phase change region in the material's structure. The calculated Poisson's coecient was negative for the [0001] pore. When stretched, they become thicker in the perpendicular direction to the applied force. These materials are known as auxetic. Our results show that the energy band gap value is tuned by the strain with an uncommon opposite trend related to the bulk. The density of electronic states conrmed the energy gap modulation. The structural inverse trend of nanopores surface is the principal mechanism for gap inverse behavior under compressive and tensile strain. From the best of our knowledge, this is the rst report about opposite Egap trend in strained nanopores. Our results suggest that nanoporosity and biaxial strain could be employed as a method within the band gap engineering for tailored functional matexi rials that require control of the electronic activity.