1,720,986 research outputs found
Growth, Characterization & Applications of Carbon Nanomaterials
No full textThe purpose of this research is to develop and improve the process of massive growth of carbon nanotubes (CNTs) via chemical vapor deposition (CVD). Beside the growth of CNTs and their potential applications, CNTs based polymer composites properties were also explored. The thesis may be divided into two major sections. In the first section a comprehensive introduction to carbon nanomaterials specifically CNTs (which includes the structure, types, growth mechanism and techniques, characterization techniques and properties) is described. Then the CVD growth procedure adopted in our lab to grow different carbon nanomaterials in particular Multiwall Carbon nanotubes (MWCNTs) under differential experimental conditions is discussed. We have grown upto 3mm thick MWCNTs carpet on Si substrate with MWCNTs diameter in the range 20nm-80nm. The individual length of MWCNTs is as long as few hundreds of micrometer. MWCNTs based structures were also grown on patterned surfaces. The patterning of the surfaces is performed by soft photolithography. These MWCNT structures have very interesting applications e.g. a). The vertical cylinders were use to produce SiC hollow cylinders, and b). CNT based fins grown on Si substrate were used to enhance the convective heat transfer properties. Several treatments (thermal annealing, acid treatment and plasma treatment) were also performed on MWCNTs in order to modify their characteristics. These procedures are useful for purification, functionalization and graphitization of MWCNTs. The second section about CNT based polymer composites starts with the brief introduction to polymer composites, processing techniques, major issues in mixing the CNTs in different polymers and finally the mixing tools used for better dispersion. The optical characterization of PDMS based MWCNTs composites films are studied. These films can have application in optical limiting devices. Furthermore, the transparency of these films is also used to calculate a unique parameter absorption cross section of a single MWCNT. The absorption cross section of individual MWCNTs having widely different aspect ratios scales with their volume. The approximation of absorption cross section per carbon atom is also in close agreement with that of graphite. The electrical conductivity phenomena in epoxy based carbon nanomaterials (CNMs) composites are also discussed. A total number of 16 types of different CNMs were used. Several conduction behaviors have been found e.g. from highly conductive CNTs which showed linear Ohmic curve, to non-linear diode-like trend to completely insulating one. The best performances have been reached by the shortest and thinner MWCNTs (both as grown and slightly functionalized with COOH groups), which can underline that small fillers can be better dispersed inside the composite and create a better conductive net within the matrix. We have also applied physical models such as the percolation theory and the fluctuation mediated tunnelling theory to the most conductive nanocomposites, with poor agreement between experimental data and theoretical prediction. Finally, we applied a recently revised model based on tunnelling-percolation theory and obtained a good fit between experimental and theoretical result
Optical Absorption Cross Section of Individual Multi-Walled Carbon Nanotubes in the Visible Region
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Silicon carbide hollow cylinders using carbon nanotubes structures as template
No full textAbstract In this work we present the production of Silicon Carbide (SiC) hollow structures using two components: Multi Walled Carbon Nanotubes (MWCNTs) structures and Silicon (Si) powder. First of all, the MWCNTs based structures were grown by Chemical Vapour Deposition (CVD) technique on patterned Silicon (Si) substrates. The patterning of Si substrates was performed by Soft photolithography technique. The grown CNTs structures were detached from the substrate and were put at high temperature along with Si powder at 1380 C for 4 h and then at 1700 C for 30 min in presence of inert atmosphere which allows the creation of a uniform SiC shell around these structures. Subsequently the removal of the carbon core at 900 C in air permit to obtain SiC hallow structure. In particular, here we have reported, as an example, a hollow cylinder of 250 μm (approx.) of SiC as a final result. The way to produce hollow SiC structures opens new opportunity in the field of high resistance microstructures from chemical and mechanical point of view
In-Situ Spectroscopic Analyses of the Dye Uptake on ZnO and TiO2 Photoanodes for Dye-Sensitized Solar Cells
No full textUV-Vis spectroscopic measurements have been performed on Dye-Sensitized Solar Cell (DSSC) photoanodes at different dye impregnation times ranging from few minutes to 24 hours. In addition to the traditional absorbance experiments, based on diffuse and specular reflectance of dye impregnated thin films and on the desorption of dye molecules from the photoanodes by means of a basic solution, an alternative In-Situ solution depletion measurement, which enables fast and continuous evaluation of dye uptake, has been employed. Two different nanostructured semiconducting oxide films (mesoporous TiO2 and sponge-like ZnO) and two different dyes, the traditional Ruthenizer 535-bisTBA (N719) and a newly introduced metal-free organic dye based on a hemi-squaraine molecule (CT1), have been analyzed. DSSCs have been fabricated with the dye-impregnated photoanodes using a customized microfluidic architecture. The dye adsorption results are discussed and correlated to the obtained DSSC electrical performances such as photovoltaic conversion efficiencies and Incident Photon-to-electron Conversion Efficiency (IPCE) spectra. It is shown that simple UV-Vis measurements can give useful insights on the dye adsorption mechanisms and on the evaluation of the optimal impregnation time
Effect of seed layer on the performance of ZnO nanorods-based photoanodes for dye-sensitized solar cells
Full text linkIn this paper, zinc oxide nanorods (ZnONRs) were synthesized by chemical bath deposition (CBD) method at 90 °C by using zinc nitrate hexahydrate and hexamethylenetetramine as precursors. In a first stage, the ZnO NRs were grown on un-seeded and pre-seeded fluorine-doped tin oxide (FTO) glass substrates by direct CBD method to study the effect of the ZnO seed layer on the NRs structural, morphological and optical properties. The X-ray diffraction (XRD) analysis performed on the preseeded NRs revealed a pure ZnO hexagonal wurtzite crystalline phase, while the Field Emission Scanning Electron Microscopy (FESEM) unveiled that the pre-seeded NRs exhibit a smaller diameter, higher density, higher aspect ratio and improved orientation along the c-axiswith respect to the un-seeded NRs. In a second stage, the powder obtained by aging, centrifuging and drying the precipitates formed during the CBD growth was analyzed by XRD to assess its crystal structure and phase purity and subsequently coated on un-seeded and pre-seeded FTO glass substrates by doctor blade technique. The ZnO NRs based seeded and non-seeded films fabricated by the two methods were finally used as photoanodes in dye-sensitized solar cells (DSSCs). Interestingly, the employment of pre-seeded ZnO NRs films deposited by doctor blade technique in comparison to the counterpart electrodes synthesized by direct CBD growth has led to a noticeable increase in the DSSC photoconversion efficiency from 0.35 to
1.86%. On the other hand, the inclusion of the seed layer has effectively improved the fill factor of the DSSC I-V curves for both the photoanode deposition techniques
Real time monitoring of ultrafast sensitization for Dye-Sensitized Solar Cell photoanodes
No full textIn this paper, the real time monitoring of a microfluidic based ultrafast sensitization process is proposed for two different nanostructured semiconducting oxides (transparent TiO2 and sponge-like ZnO) to be employed as photoanodes in Dye-Sensitized Solar Cells (DSSCs). A home-made set-up has been appositely developed in which the semiconducting oxide film is sandwiched into a microfluidic cell architecture connected to a pumping system. This innovative housing system allows impregnation of the photoanodes under continuous flow regime, thus ensuring a considerable reduction in the loading time and in the employed dye amount. This improvement is of particular interest in view of the device production at industrial scale. The effect of the dye concentration on the sensitization process is analyzed through dye adsorption analysis, obtained both by real time absorption monitoring and traditional desorption methods. The dye-impregnated TiO2 and ZnO photoanodes have been used for DSSCs fabrication, using the same customized microfluidic architecture. The results are thoroughly discussed and correlated to the obtained DSSCs electrical performances such as photovoltaic conversion efficiencies and Incident Photon-to-electron Conversion Efficiency (IPCE) spectr
Counter electrode materials based on carbon nanotubes for dye-sensitized solar cells
Full text linkEfficiency, stability, and cost-effectiveness are the prime challenges in research of materials for solar cells. Technologically as well as scientifically, attention gained by dye-sensitized solar cells (DSSCs) stems from their low material and fabrication costs as well as high efficiency projections. The aim of this study is to explore the carbon nanotubes (CNTs) based counter electrode (CE) materials for DSSCs and to reconnoiter the suitable alternative materials in place of noble metals such as Platinum (Pt), and Gold (Au).. Various classes of CE materials based on CNTs including pure single walled, double walled, and multiwalled CNTs, doped CNTs and their hybrid composites with various polymers, and transition metal compounds are discussed comprehensively in light of the research work started since the inspection of DSSCs and CNTs.The properties associated with such materials, including surface morphology, structural determination, thermal stability, and electrochemical activity, are also thoroughly analyzed and compared. This work provides a thorough insight into the possibility of exploiting CNTs as alternative CE materials. In addition to the above, this study also includes the working and brief overview of materials for other components of DSSCs such as photoanode, electrolyte, and sensitizer.
Solution‐Processed Zinc‐Tin‐Based Ternary Oxide Electron Transport Layers for Planar Perovskite Solar Cells
No full textPerovskite solar cells (PSCs) have acquired popularity owing to their high efficiency, ease of fabrication, and affordability. In this context, the development of electron transport layers (ETLs) for highly efficient planar photovoltaic devices has received considerable attention. This study investigates the potential of zinc-tin-based ternary metal oxide ETLs for application in planar PSCs. Solution-processed methods are used to fabricate crystalline zinc stannate (Zn2SnO4), amorphous zinc-tin oxide (ZTO), and Zn2SnO4/ZTO-based bilayer films, and their structural, morphological, and optoelectronic properties are thoroughly studied. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) images show enhanced crystallite size and better surface morphology of perovskite films deposited on bilayer ETL. Photoluminescence (PL) studies and Hall effect measurements reveal superior charge extraction, improved charge carrier mobility (21.84 cm2 V-1 s-1) and enhanced n-type conductivity in the bilayer ETL. Moreover, contact angle analysis of perovskite layer deposited on bilayer ETL shows increased resistance to moisture erosion (52.20°), which is particularly significant given the detrimental effects moisture can have on the performance of PSCs
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