No description available.

Neste trabalho buscou-se produzir filmes de nanopartículas de dióxido de titânio e de nanopartículas de dióxido de titânio contendo o complexo sintetizado undecatungstofosfatomanganês(melamina) suportados em cela tubular de vidro borossiliacato e testar sua reatividade como fotocatalisadores frente à atrazina. Os ensaios de fotodegradação da atrazina foram realizados através de um reator fotocatalítico tendo como fonte de irradiação ultravioleta uma lâmpada de vapor de mercúrio de alta pressão de potência de 125 W desprovida do bulbo externo. A degradação da atrazina ocorrida nos experimentos de fotocatálise heterogênea foram acompanhados através da técnica de Espectroscopia de Absorção na Região do Ultravioleta e Visível (UV-vis) e para as amostras inicíais e finais de cada ensaio foram realizadas medidas de teor de Carbono Orgânico Total (TOC). Assim, foi possível estimar a porcentagem de degradação parcial e de mineralização da atrazina. As porcentagens de degradação obtidas para soluções contendo concentração inicial de 10 ppm de atrazina foram: no caso de filmes de nanopartículas de dióxido de titânio, obteve-se porcentagem de degradação parcial da atrazina de 42,2% a partir da análise de UV-vis e 21,8% de mineralização através da análise de TOC. Para o mesmo sistema após 72 horas, as porcentagens de degradação parcial chegaram a 71,5% a partir da análise de UV-vis e 55,5% de mineralização pela análise de TOC. Para o filme de nanopartículas de dióxido de titânio contendo undecatungstofosfatomanganês(melamina) através da técnica de UV-vis obteve-se uma degradação parcial da atrazina de 44,7% ao final de 12 horas e através da análise de TOC obteve-se 22,4% de mineralização. / In this work, films of titanium oxide nanoparticles and of titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine) immobilized in a borosilicate glass cylindrical cell were prepared and their reactivity as photocatalyst for atrazine were tested. The photodegradation essays of atrazine were made in a phocatalytic reactor where the ultraviolet irradiation source was one mercury vapor lamp of 125 W without the external bulb. The atrazine degradation in heterogeneous photocatalysis experiments were checked by Ultraviolet and visible spectroscopy (UV-vis) and for first and last samples for each essay were made analysis of Total Organic Carbon (TOC). So, it was possible to estimate the percentage of the partial degradation and mineralization of atrazine. The partial degradation percentages obtained for solutions with initial concentration of 10 ppm of atrazine were: In the case for films of titanium oxide nanoparticles, the partial degradation percentage for atrazine was 42,2% in UV-vis analysis and 21,8% of mineralization obtained by TOC analysis. For the same system after 72 hours, the partial degradation percentages were 71,5% in UV-vis analysis and 55,5% of mineralization obtained by TOC analysis. For the film with titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine), after 12 hours, the partial degradation of atrazine was 44,7% in UV-vis analysis and 22,4% of mineralization obtained by TOC analysis.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 189-197).

Neste trabalho buscou-se produzir filmes de nanopartículas de dióxido de titânio e de nanopartículas de dióxido de titânio contendo o complexo sintetizado undecatungstofosfatomanganês(melamina) suportados em cela tubular de vidro borossiliacato e testar sua reatividade como fotocatalisadores frente à atrazina. Os ensaios de fotodegradação da atrazina foram realizados através de um reator fotocatalítico tendo como fonte de irradiação ultravioleta uma lâmpada de vapor de mercúrio de alta pressão de potência de 125 W desprovida do bulbo externo. A degradação da atrazina ocorrida nos experimentos de fotocatálise heterogênea foram acompanhados através da técnica de Espectroscopia de Absorção na Região do Ultravioleta e Visível (UV-vis) e para as amostras inicíais e finais de cada ensaio foram realizadas medidas de teor de Carbono Orgânico Total (TOC). Assim, foi possível estimar a porcentagem de degradação parcial e de mineralização da atrazina. As porcentagens de degradação obtidas para soluções contendo concentração inicial de 10 ppm de atrazina foram: no caso de filmes de nanopartículas de dióxido de titânio, obteve-se porcentagem de degradação parcial da atrazina de 42,2% a partir da análise de UV-vis e 21,8% de mineralização através da análise de TOC. Para o mesmo sistema após 72 horas, as porcentagens de degradação parcial chegaram a 71,5% a partir da análise de UV-vis e 55,5% de mineralização pela análise de TOC. Para o filme de nanopartículas de dióxido de titânio contendo undecatungstofosfatomanganês(melamina) através da técnica de UV-vis obteve-se uma degradação parcial da atrazina de 44,7% ao final de 12 horas e através da análise de TOC obteve-se 22,4% de mineralização. / In this work, films of titanium oxide nanoparticles and of titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine) immobilized in a borosilicate glass cylindrical cell were prepared and their reactivity as photocatalyst for atrazine were tested. The photodegradation essays of atrazine were made in a phocatalytic reactor where the ultraviolet irradiation source was one mercury vapor lamp of 125 W without the external bulb. The atrazine degradation in heterogeneous photocatalysis experiments were checked by Ultraviolet and visible spectroscopy (UV-vis) and for first and last samples for each essay were made analysis of Total Organic Carbon (TOC). So, it was possible to estimate the percentage of the partial degradation and mineralization of atrazine. The partial degradation percentages obtained for solutions with initial concentration of 10 ppm of atrazine were: In the case for films of titanium oxide nanoparticles, the partial degradation percentage for atrazine was 42,2% in UV-vis analysis and 21,8% of mineralization obtained by TOC analysis. For the same system after 72 hours, the partial degradation percentages were 71,5% in UV-vis analysis and 55,5% of mineralization obtained by TOC analysis. For the film with titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine), after 12 hours, the partial degradation of atrazine was 44,7% in UV-vis analysis and 22,4% of mineralization obtained by TOC analysis.

No description available.

The work in this thesis examines the effects of the application of oxide coatings on the performance of the single crystalline silicon photovoltaic solar cells. A variety of potential oxide materials for solar cells performance enhancement are investigated. These films are silicon oxide, titanium oxide and rare earth ion-doped gadolinium oxysulfide phosphor. This study compares the electrical characteristics, optical properties and surface chemical composition of mono-crystalline silicon cells before and after coating. The first study investigates the potential for using single and double layers of silicon oxide films produced by low-temperature Plasma Enhanced Chemical Vapour Deposition (PECVD) using tetramethylsilane as a silicon precursor and potassium permanganate oxidising agent for efficiency enhancement of solar cells at low manufacturing cost. Deposition of the films contributes to the increase of the conversion energy of the solar cells on one hand while the variety of colours obtained in this study can be of great importance for building-integrated photovoltaic application on the other hand. The obtained results demonstrated a relative enhancement of 3% in the conversion efficiency of the crystalline silicon solar cell. In the second study, the effects of using a single layer of titanium oxide and a stack of silicon oxide and titanium oxide on the performance of solar cell are demonstrated. Moreover, this study shows the use of different sputtering configurations and oxidation methods. The experimental results showed a relative enhancement of 1.6% for solar cells coated with a stack of silicon oxide/titanium oxide. In the third study, silicon cells were coated with a luminescent layer consisting of down-converting phosphor, gadolinium oxysulfide doped with erbium and terbium, and a polymeric binder of EVA using doctor-blade screen printing technique. A relative enhancement of 4.45% in the energy conversion efficiency of PV solar cell was achieved. Also, the effects of combining silicon oxide layers together with the luminescent composite are also presented in this study.

Chemical-looping combustion is an indirect oxygen combustion strategy, considered to be the most cost-effective power generation technology with the CO2 inherently concentrated. In this process, a solid oxygen carrier is used to transfer oxygen from the air reactor to the fuel reactor, which completely isolates nitrogen in air to meet with fuels. The oxygen carriers in the combustion process are subjected to the severe environments, such as high temperatures, multi-cycle operations, and thermodynamic limitations. Thus, the preparation of an oxygen carrier with high durability and better kinetics under harsh environment could be an essential part of Chemical-looping combustion development. In this study, modified wet impregnation and co-precipitation methods have been developed. The active ingredient is copper(II) oxide, and the supporting material is either directly from titanium(IV) oxide (anatase 99%) or that prepared from other titanium resources such as titanium tetrachloride and tetrabutyl titanate. Preliminary results showed the prepared oxygen carriers functioned properly in the multi-cycles of oxidization and reduction in TGA at different temperatures. Characterization of used oxygen carriers was carried out using techniques of XRD, and SEM-EDS, which provide information for the difference between oxygen carriers from different preparation methods. Through the comparison, the oxygen carrier from the sol-gel preparation method has better dispersion and oxidation activity than those from mechanical mixing, wet-impregnation, and cox precipitation method. Moreover, towards the oxygen carrier from sol-gel method, nucleation model and diffusion models were determined at different reaction periods.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 216-224).

Photovoltaic technologies use light from the sun to create electricity, using a wide range of materials and mechanisms. The generation of clean, renewable energy using this technology must become price competitive with conventional power generation if it is to succeed on a large scale. The field of photovoltaics can be split into many sub-groups, however the overall aim of each is to reduce the cost per watt of the produced electricity. One such solar cell which has potential to reduce the cost significantly is the dye sensitised solar cell (DSC), which utilises cheap materials and processing methods. The reduction in cost of the generated electricity is largely dependent on two parameters. Firstly, the efficiency that the solar cell can convert light into electricity and secondly, the cost to deposit the solar cell. This thesis aims to address both factors, specifically looking at altering the transparent conducting oxide (TCO) and substrate in the solar cell. One method to improve the overall conversion efficiency of the device is to implement the DSC as the top cell in a tandem structure, with a bottom infra-red absorbing solar cell. The top solar cell in such a structure must not needlessly absorb photons which the bottom solar cell can utilise, which can be the case in solar cells utilising standard transparent contacts such as fluorine-doped tin oxide. In this work, transparent conducting oxides with high mobility such as titanium-doped indium oxide (ITiO) have been used to successfully increase the amount of photons through a DSC, available for a bottom infra-red sensitive solar cell such as Cu(In,Ga)Se2 (CIGS). Although electrically and optically of very high quality, the production of DSCs on this material is difficult due to the heat and chemical instability of the film, as well as the poor adhesion of TiO2 on the ITiO surface. Deposition of a interfacial SnO2 layer and a post-deposition annealing treatment in vacuum aided the deposition process, and transparent DSCs of 7.4% have been fabricated. The deposition of a high quality TCO utilising cheap materials is another method to improve the cost/watt ratio. Aluminium-doped zinc oxide (AZO) is a TCO which offers very high optical and electronic quality, whilst avoiding the high cost of indium based TCOs. The chemical and thermal instability of AZO films though present a problem due to the processing steps used in DSC fabrication. Such films etch very easily in slightly acidic environments, and are susceptible to a loss of conductivity upon annealing in air, so some steps have to be taken to fabricate intact devices. In this work, thick layers of SnO2 have been used to reduce the amount of etching on the surface of the film, whilst careful control of the deposition parameters can produce AZO films of high stability. High efficiency devices close to 9% have been fabricated using these stacked layers. Finally, transferring solar cells from rigid to flexible substrates offers cost advantages, since the price of the glass substrate is a significant part of the final cost of the cell. Also, the savings associated with roll to roll deposition of solar cells is large since the production doesn't rely on a batch process, using heavy glass substrates, but a fast, continuous process. This work has explored using the high temperature stable polymer, polyimide, commonly used in CIGS and CdTe solar cells. AZO thin films have been deposited on 7.5um thick polyimide foils, and DSCs of efficiency over 4% have been fabricated on the substrates, using standard processing methods.

The work presented in this thesis focuses on the investigation and improvement of the window stack of layers for thin film CdTe solar cells fabricated in the Center for Renewable Energy Systems Technology (CREST) laboratories. In particular the aim was to change the standard structure including TCO, high resistive transparent (HRT)layer and CdS which is limited by the low transparency of the CdS layer, to a better performing one. The first result chapter of the thesis describes the study of ZnO HRT layers. ZnO thin films were deposited by radio frequency (RF) magnetron sputtering with different structural, optical and electrical properties which were characterized by X-ray diffraction, electron microscopy, spectrophotometry, Hall Effect method and 4-point probe. ZnO films were then incorporated in CdTe solar cells with the structure: FTO/ZnO/CdS/CdTe/Au back contact and the performance of these devices were compared with the film properties to single out trends and identify optimal film characteristics. By varying the deposition pressure of ZnO films, it was possible to increase their transparency and significantly increase their resistivity. While better transparency positively affected the solar cell current density output and efficiency, the resistivity of ZnO films did not show any clear impact on device efficiency. By increasing the deposition temperature the ZnO film grain size was increased. Increased FF was observed in devices incorporating ZnO layers with bigger grains, although this gain was partially counterbalanced by the Voc degradation, leading to a limited efficiency improvement. Finally the addition of oxygen had the main effect of increasing the resistivity of ZnO films, similarly to what happened with the increase of the sputtering pressure. In this case however, an improvement of FF, Jsc and efficiency was observed, especially at an O2/Ar ratio of 1%. By simulating the solar cells behavior with SCAPS-1D, it was found that these performance change can be explained by the variation of interface properties, precisely the amount of interface defects, rather than by bulk properties. The study presented in the second result chapter focuses on magnesium-doped zinc oxide (MZO) and the variation of its energy band structure. MZO was initially used as the HRT layer within a solar cell structure: FTO/MZO/CdS/CdTe/Au back contact. Sputtering MZO films with a target containing MgO 11 weight% and ZnO 89 weight% allowed for and increased band gap from 3.3 eV of intrinsic ZnO to 3.65 eV for MZO deposited at room temperature. Increasing the superstrate deposition temperature allowed for a further band gap increase up to 3.95 eV at 400 °C due mainly to an conduction band minimum upward shift. It was highlighted the importance to create a positive conduction band offset with the MZO layer conduction band slightly above the CdS conduction band, with an optimum found in this case to be 0.3 eV (efficiency 10.6 %). By creating a positive conduction band offset all the performance parameters (Voc, FF, Jsc, efficiency) significantly increased. One of the reasons for this improvement was found to be a diminished interface recombination due to a more ideal MZO/CdS band alignment. In the second part of this investigation the MZO was used as a replacement for the CdS in a simplified structure: FTO/MZO/CdTe/Au back contact. The concepts used to optimise the performance of these devices also involved tuning the conduction band alignment between MZO/CdTe and efficiencies of 12.5 % were achieved with a at conduction band offset. The efficiency increase was achieved mainly thanks to a better transparency of the MZO layer and a higher Jsc output, compared to devices using a CdS buffer layer. The MZO buffers have been tested in combination with different TCOs. Results are presented in the third result chapter and showed that AZO is a good alternative to FTO working effectively in combination with MZO. AZO/MZO efficiency thin film CdTe solar cells (12.6%, compared to 12.5% with FTO). It was found that increasing the IR transparency of the TCOs leads to a potentially higher Jsc. Achieving a better transparency was obtained by using TCOs with high mobility and lower carrier concentration (AZO and ITiO) and also by using a boro-aluminosilicate glass with low iron content. ITiO yielded the best opto-electrical properties among all the TCO materials. Devices incorporating ITiO however, showed lower performance then those using FTO and AZO. ITO/MZO windows also yielded poor performance. In addition, the ITO films deposited had a high carrier concentration leading to a high NIR absorption by plasma resonance and resulted not ideal for application in thin film CdTe PV.