Abstract Founding new materials and structures for solar cells is a challenge in the photovoltaic field. This work evaluated the effect of the lignin in the photovoltaic activity by compounding with TiO2/lignin as photoanode for the dye sensitized solar cells (DSSC’s). Hybrid films (TiO2/lignin) with different concentrations of lignin (5, 10 and 15%) were deposited by spin coating over commercial TiO2 thin films. The cells were sandwich assembled. The characterizations were done through analysis of absorbance, band gap, x-ray diffraction, morphological and electrical. The lignin at 15% reduced the TiO2 band gap from 3.66 to 2.84 eV, favoring the short current density to 11.06 mA/cm2 and efficiency of 4.65%, an increase of 103.95% compared to the TiO2 structure without lignin.

ABSTRACT Nanoparticles of TiO2 have been the main semiconductor applied in Dye-sensitized solar cells (DSSCs). In this work, solar cells were developed from the electrophoretic deposition of anatase titanium dioxide (TiO2) films on conductive glasses. The electrophoretic deposition was perfomed with a constant voltage of 80V for 2 minutes and, after drying, the films were sintered at three different temperatures: 450 °C, 550 °C and 600 °C. In the assembly of the cells, the titanium dioxide films were sensitized by Ruthenizer 535-bisTBA dye (N719) and an electrolyte containing the iodide / tri-iodide redox pair and a commercial transparent platinum counter electrode were used. TiO2 films were characterized by scanning electron microscopy, dispersive energy spectroscopy and X-ray diffraction and photo-electrochemical techniques. The energy conversion rates were 0.2646% for the sintered film at 450 °C, 0.1209% for the sintered film at 550 °C and 0.1137% for the film sintered at 600 °C.

RESUMO Filmes de estanho/óxido de zinco foram depositados em óxido condutor transparente por banho químico, a porcentagens de 5, 10 e 15% de estanho (Sn) na estrutura de óxido de zinco (ZnO). Todos os filmes foram tratados termicamente para melhorar sua cristanilidade. Os filmes produzidos foram caracterizados por difração de raios x e medidas ópticas, como absorbância, transmitância e reflectância. O espectro de raios x mostrou a formação de ZnO na forma de wurtzite e os tamanhos dos cristalitos foram de 53,74; 79,59 e 66,38 nm para os fotoanodos a 5, 10 e 15% de estanho (Sn), respectivamente, na estrutura do óxido de zinco. Os valores calculados para a energia de banda proibida dos filmes revelaram que a presença de estanho pode reduzir o valor da energia até aproximadamente 3,2 eV. Esses filmes foram usados como fotoanodos em células solares sensibilizadas por corante (CSSC) para observar os efeitos do estanho (Sn) na atividade fotovoltaica do semicondutor de óxido de zinco (ZnO). Parâmetros como eficiência e densidade de corrente de curto- circuito foram particularmente afetados pela presença de estanho na composição, com o filme de ZnO a 5% de Sn apresentando os melhores resultados de 7,56% de eficiência e 34,35 mA/cm2 de densidade de corrente de curto-circuito, os demais filmes apresentaram menores valores para a eficiência, o que pode ser atribuído aos menores valores alcançados para a corrente de curto circuito.

ABSTRACT Tin Zinc Oxide thin films were deposited on transparent conductive oxide by chemical bath, at percentages of 5, 10 and 15% of tin (Sn) on the zinc oxide (ZnO) structure. All films were thermally treated to improve its crystallinity. The produced films with tin were characterized by x-ray diffraction and optical measurements, such as absorbance, transmittance and reflectance. The x-ray spectrum showed the formation of the ZnO wurtzite and the crystallite size of the films were calculated to be 53.74; 79.59 and 66.38 nm for the photoanodes at 5, 10 and 15% of tin (Sn), respectively, on the zinc oxide structure. The calculated band gap energy of the films revealed that the presence of tin can reduce the band gap energy to about 3.2 eV. Those films were used as photoanodes on dye sensitized solar cells (DSSC) to observe the effects of the tin (Sn) on the photovoltaic activity of the zinc oxide (ZnO) semiconductor. Parameters such as efficiency and short circuit current density were particularly affected by the presence of tin in the composition, with the 5% Sn ZnO film presenting the best results of 7.56 % efficiency and 34.35 mA/cm2, short circuit current density, the other films presented lower values for efficiency, which can be attributed to lower values of short-current density.

Abstract A low cost spin coater was constructed in this work for the deposition of thin films of titanium dioxide (TiO2) on conductive substrate of FTO (fluoride doped tin oxide) with application on dye sensitized solar cells. The results showed a 95% precision between the speed values obtained by the software of C#sharp language and the spin values observed directly on the device. The TiO2 films deposited through the spin coater with different angular speeds were characterized by UV-Vis optical spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurements on an active area of 0.25 cm2. The DSSCs assembled with the TiO2 films of double layer deposited by the spin coater had an efficiency value of 12.74%, while the cell with a single layer presented 4.05% efficiency. Therefore, it is concluded that the spin coater assembled in this study at low costs successfully can produce TiO2 electrodes for DSSCs.

ABSTRACT Titanate nanotubes (TiNTs) with the chemical composition Na2Ti3O7.nH2O (NaTiNT) were obtained through a hydrothermal method in highly alkaline medium. Protonated titanates nanotubes (H-TiNTs), with the composition H2Ti3O7.nH2O, were prepared by ion exchange reaction through a suspension of Na2Ti3OγnH2O nanotubes in HCl medium, promoting the exchange of Na+ ions by H+. Both Na2Ti3O7.nH2O and H2Ti3O7.nH2O products, as well the TiO2 used as raw material for the nanotubes processing, were used as starting material for the solar cells photoelectrodes sensitized using mesoporphyrin extracted from a precursor of cashew nut shell. Exposing the NaTiNT sample to solar radiation of 1258 W/m2, a short-circuit current density (ISC) of 13 µA/cm2 and an open-circuit voltage (VOC) of 370 mV were registered and, a current density of 7.6 µA/cm2 and a voltage of 256 mV for the prototype cell based on H-TiNTs. A current density of 1.1 µA/cm2 and an open-circuit voltage of 1.6 mV were obtained for the cell using TiO2 as electrode.

RESUMO Quantificar o tamanho de materiais em escala nanométrica é um dos desafios a serem superados, uma vez que existem técnicas diferentes. A equação de Scherrer modificada foi usada para estimar o tamanho das partículas de dióxido de titânio em escala nanométrica. Dióxido de titânio com tamanho nominal de nanopartícula de 21 nm foi usado como padrão para determinar a precisão da equação modificada. A partir dos dados de raios-X, para a amostra sem tratamento térmico foi obtido um valor médio do tamanho das nanopartículas de 20,63 nm. Um tratamento estatístico foi usado para fazer uma correlação entre o valor estimando pela equação de Scherrer modificada e o valor nominal de 21nm. Um desvio de 0,70 foi encontrado entre o valor calculado e o valor nominal, indicando uma concordância entre os valores. Adicionalmente, a influência da temperatura sobre o tamanho médio das nanopartículas de dióxido de titânio foi pesquisada.

ABSTRACT The materials sizing in nano-scale is a challenge to be overcome, because the size determined by various methods differ. In order to shed light about the nanomaterials sizing, a modified Scherrer's equation was applied to estimate more accurately the nanostructured titanium dioxide crystal size. The manufactured titanium dioxide-nanostructured powder with nominal average size about 21nm was used as the reference standard to determine the accurate of modified equation. From X-ray diffraction data, an average crystal size about 20.63 nm was achieved for unheated sample. To establish a relation between the result obtained with modified Scherrer's equation and the nominal average crystal size, a statistical treatment and a comparative assessment were performed. The average absolute divergence does not exceed 0.70 nm. The value of crystal size determined from X-ray data was in good agreement with that informed by the supplier. Additionally, the behavior of sample was studied as a function of temperature.

Amongst the many parts of a silicon cells photovoltaic module, silicon is the most important and expensive constituent. Thus, research on silicon recycling from damaged cells can lead to economic and environmental benefits. In this work, the broken silicon cells were tailored to function along with the fluorine-doped tin oxide as the transparent electric conductors. The broken silicon cells were analyzed by the current density versus voltage plots, together with the Mott-Schottky, X-rays diffraction and fluorescence analysis. Under light, the damaged cells sandwiched between the two transparent electric conductors presented photovoltaic effect. However, such effect was not obtained after the removal of the antireflection layer due to the destruction of the n-type layer as demonstrated by the Mott-Schottky analysis. The X-rays diffraction revealed samples rich on silicon atoms and the presence of aluminum atoms as impurity.

Este trabalho apresenta um modelo teórico que relaciona a potência elétrica com a potência química numa célula fotossensibilizada com corante. O mesmo é baseado na junção dos conceitos presentes nos modelos de potencial químico e de potência química. Assim, a partir destas duas considerações é possível a realização de testes sob diversas condições físicas e ambientais, durante o processo de conversão de energia solar. Consequentemente, o modelo teórico proposto permite relacionar a potência química aos parâmetros solares: ângulo sólido, temperatura da fonte de radiação, comprimento de onda e temperatura da célula fotossensibilizada com corante. A geração do fluxo de elétrons dentro da célula é promovida pela absorção da energia solar incidente sobre o corante. Por isso, a principal condição consubstanciada neste trabalho baseia-se que a superfície de absorção da energia incidente seja o corante.

This paper presents a theoretical model relating the electrical power to the chemical power in a photosensitized dye-cell. The same is based on the junction of present concepts of chemical potential models and chemical power. Thus, from these two considerations is possible to perform tests under various physical and environmental conditions during the solar conversion process. Consequently, the proposed theoretical model allows relating the power to solar chemical parameters: solid angle, temperature of the radiation source, wavelength and temperature of the photosensitized dye-cell. The electrons flow generation within the cell is promoted by absorption of solar energy incident on the dye. Therefore, the main condition embodied in this work is based on the incident energy absorption surface is the dye.