Papers by Author: Norani Muti Mohamed

Abstract: Electrolyte as one of the major components in dye sensitized solar cells (DSSCs) plays an important role in dye regeneration and as the inner charge carrier transport between electrodes. Gel polymer electrolyte is a potential alternative to liquid electrolytes which suffer of leakage and solvent evaporation. In this present research, functionalization of chitosan by the quaternization reaction of chitosan with iodopropane forming tripropyl chitosan iodide is proposed for the preparation of gel polymer electrolyte. Tripropyl chitosan iodide was characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Four different polymer electrolytes were tested at different compositions in presence of iodide/triiodide redox salt and imidazolium ionic liquid in DSSCs configurations. The results show that the gel polymer electrolyte containing the tripropyl chitosan iodide in presence of 1-propyl-3-methylimidazolium iodide ionic liquid showed better performance with power conversion efficiency of 0.415% as compared to the gel polymer electrolyte film without ionic liquid with power conversion efficiency of 0.075%. The results shown the synergistic effects of the polycationic tripropyl chitosan iodide with the ionic liquid 1-propyl-3-methylimidazolium iodide on the photovoltaic performance.

Abstract: Novel nanocomposite made of one-dimensional (1-D) multi-walled carbon nanotube (MWCNT) and two-dimensional (2-D) graphene was prepared. MWCNT was spin coated onto copper foil and followed by chemical vapor deposition (CVD) growth of graphene. The MWCNT-Graphene nanocomposite was transferred onto target substrate by using a standard polymer-based transfer technique. HRTEM and Raman spectroscopy showed high crystallinity of fused MWCNT and graphene layer. Low defect-related D-peak was also observed even after the nanocomposite underwent high temperature processing. As compared to pristine graphene, electrical characterization of MWCNT-Graphene nanocomposite also revealed the reduction of sheet resistance by ~71% and almost 2-fold improvement in room-temperature carrier mobility. These improvements are surmised due to additional conducting channels formed by MWCNT in the graphene layer. Hence, higher electrical conductivity can be expected. With the introduction of MWCNT across the graphene layer, highly desirable electrical properties can be achieved and as such leveraging the viability of graphene-based nanoelectronics devices.

Abstract: In this study, Fe₂O₃/Al₂O₃ catalyst was prepared by using co-precipitation method. This catalyst weight was varied from 0.1 to 0.5 g and multiwalled carbon nanotubes (MWCNTs) bundles were synthesized with ethylene as a carbon precursor at reaction temperature of 800°C by using floating catalytic chemical vapor deposition reactor. The grown MWCNTs bundles were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The obtained data revealed that as prepared CNTs actually existed in bundles and these should be attributed to the Fe₂O₃/Al₂O₃ catalyst, as transition metal Mo was not used in the catalyst. It was noted that an increase in weight of the catalyst significantly affects the quality, quantity, crystallinity, diameter and the growth of nanotubes bundles. Nanotubes yield increased with an increase in Fe₂O₃/Al₂O₃ weight. The carbon yield obtained with different weights of Fe₂O₃/Al₂O₃ was ranging from 68-93%. However, the surface defects in the grown tubes were also increased with an increase in the catalyst weight. High purity and high yield with the low surface defects was found for 0.3 g catalyst. It was found that less value of I_D/I_G ratio (0.78) was obtained in case of 0.3 g catalyst which indicated the structural perfection and low defect levels. The average outer diameter of the grown CNTs bundles were ranged from 240 to 550 nm. The formation of CNTs bundles were found defective with few black spots and impure above and below the use of 0.3 g catalyst.

Abstract: TiO₂ aggregates-based dye solar cells (DSCs) have gained an increasing attention due to their enhanced harvesting of light radiance. The capability of this photoelectrode material is attributed to the submicron spherical aggregates that introduce light scattering effect which can generate more electrons whilst high internal surface area for dye chemisorption is provided by nanocrystallites which made up the aggregates. Here, TiO₂ aggregates (0.45-0.20 μm) composing of nanocrystallites (10-28 nm) with desired physicochemical properties for enhanced overall light conversion efficiency of DSC were synthesized by varying the water content in the hydrolysis of titanium alkoxide in ethanol and calcination temperature. TiO₂ aggregates obtained were characterized using FESEM, XRD and UV-Vis spectroscopy. The assembled DSCs were then evaluated using solar simulator under AM 1.5 (100 mW/cm²) simulated sunlight. With higher water content in the hydrolysis process, the aggregates reduce in size and lose their spherical shapes resulting in lower absorption intensity indicating the occurrence of low light scattering in the TiO₂ film. Nanocrystallites were found to have an increasing size of 12 nm to 28 nm with increasing calcination temperature of 400°C to 700°C. Sample of aggregates calcined at 450°C recorded the highest efficiency (~4%). Highest conversion efficiency was observed for DSC that used well-defined spherical TiO₂ aggregates composing of nanocrystallites which were synthesized at optimum synthesis parameter which is by using ethanol with low water content (0.9 vol%) followed by calcination at 450°C. Thus, optimized TiO₂ nanocrystallites which form spherical aggregate is critical in order to improve light harvesting efficiency of DSCs.

Abstract: TiO2 aggregates-based dye solar cells (DSCs) have gained an increasing interest due to their better light harvesting efficiency as a result of enhanced light scattering effect from the submicron spherical aggregates that can generate more electrons and the high internal surface area for dye chemisorption provided by nanocrystallites which made up the aggregates. Optimized TiO2 aggregates (0.45 µm) composing of nanocrystallites (10-40 nm) with desired physicochemical properties for enhanced overall light conversion efficiency of DSC were synthesized by varying the calcination temperature and water content in the hydrolysis of titanium alkoxide in ethanol. TiO2 aggregates obtained were characterized using FESEM, XRD and UV-Vis spectroscopy. The assembled DSCs were then evaluated using solar simulator under AM 1.5 (100 mW/cm2) simulated sunlight. Nanocrystallites were found to have an increasing size of 12 nm to 36 nm with increasing calcination temperature of 400C to 600C. Sample of aggregates calcined at 500C recorded the highest efficiency (4.456%) as the 20-nm nanocrystallites produced is considered to be the optimum size for dye absorption. With higher water content in the hydrolysis process, the aggregates lose their spherical shapes resulting in lower absorption intensity indicating the occurrence of low light scattering in the TiO2 film. Highest conversion efficiency was observed for DSC that used well-defined spherical TiO2 aggregates composing of 20-nm nanocrystallites which were synthesized using ethanol with low water content (0.9 vol%) followed by calcination at 500C. Thus, optimized TiO2 nanocrystallites which form spherical aggregate is critical in order to improve light harvesting efficiency of DSCs.

Abstract: Carbon nanotube (CNT) can be thought of as a hexagonal network of carbon atoms that has been rolled up to make a seamless cylinder. If they are consisting of one layer, they are termed singled-walled CNTs (SWNTs) while if there are multiple walls, they are called multi-walled CNTs (MWNTs). For most functional devices application, an aligned arrangement of CNTs is desired. Aligned multiwalled carbon nanotubes (MWNTs) have been successfully grown by the inclusion of a buffer layer of oxidized Al. An Al2O3 layer has been proven to be an important contributing factor towards obtaining good quality aligned CNTs. In this work, Al is deposited onto the Si wafer using electron beam evaporation and later oxidized by heating in air. A thin layer of iron catalyst is then deposited on top of the oxidized Al layer and annealed at 400oC. The result shows an improvement in the intensity of the graphitization peak (G-band) in the Raman spectra and aligned MWNTs is observed in these samples compared to the ones that have undergone the same process parameter except the Al2O3 layer.