Browsing by Author "Njoroge, David Kimemia"

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    Fabrication and characterization of a graphite dispersed titanium dioxide solid solar cell
    (2017-11) Njoroge, David Kimemia
    Energy is globally recognized as one of the most fundamental inputs to social and economic development. Most energy sources are serious pollutants resulting to serious negative effects on the environment. To overcome this challenge, the presence of abundant sunshine has been exploited through the use of solar cells to generate this vital resource through photovoltaic cells. However most photovoltaic cells are silicon based photovoltaic cells which are expensive. This study reports on the fabrication of a cost effective and environmental friendly solar cell by the use of TiO2 and I2/ KI (dispersed in graphite-Cx) layers in their solid form to provide an alternative source of clean energy. TiO2 was preferred due to its photo generation property when excited with a radiation and chemical stability over a wide pH range. The photo excited electrons were replenished by use of iodine/iodide complex and their migration was facilitated by graphite. The mixtures at varying ratios were made into pellets and their electrical properties investigated. The experimental design involved preparation of various ratios of titanium dioxide: graphite /iodine/KI mixtures in each respective layer. Optimization was carried out by varying the mass of the constituents of each layer while maintaining the others constant to obtain the highest current - voltage outputs. The study investigated the effect of the thickness of TiO2, (the photo active layer) and the electronegative material layers on current-voltage output of the fabricated solar cell. The optimum electricity generation was observed at the ratio of TiO2/ Cx: I2: KI as 0.4: 0.3: 0.17: 0.01 g respectively. The presence of KI enabled solubility of iodine enhancing it disperse evenly in graphite whose mass was constant at 0.01g in all the cells fabricated. The effect of the optimized thicknesses of the photo active layer and that of the electronegative layer were investigated and the optimal thicknesses were found to be 2.00 and 1.00 mm respectively. The highest open circuit voltage (Voc) of 0.979V and a short circuit current density (Jsc/cm2) of 12.037μA was observed, giving efficiency (η) of 0.006% and a Fill factor (FF) of 0.64. During the entire three years of study, no corrosion effects were observed because the medium for the charge carrier migration was in dry solid state and thus it was suitable for photovoltaic application. A solar cell was successfully fabricated and characterized. The ratio of constituent materials (TiO2/ Cx: I2: KI) and the optimal thickness of both the photo active and the electronegative layers which generated the optimum Current-Voltage output were determined. The efficiency and Fill factor were calculated from the fabricated overall corrosion-free solar cell. It is therefore recommended that further research work be done using TCO (transparent conducting oxide) as the cathode in addition to employing technologies that can reduce air packets in the solar cell
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    Synthesis, Fabrication and Characterization of Solid Titanium Dioxide - Based Solar Cell Doped with Different Organic and Inorganic Luminescent Materials
    (Kenyatta University, 2024-01) Njoroge, David Kimemia
    Energy is globally recognized as an important resource for social and economic development. Majority of the world population relies on fossil fuels, hydro and solar radiation as a source of energy. Fossil fuels immensely contribute to air pollution and global warming. Solar cells have been exploited and controlled to generate electrical energy from solar radiation. The available solar radiation is not constant at all times of the day and differs depending on the season of the year. Consequently, the solar cell output varies with the incident radiation. The study investigated use of photo luminescent materials as dopants in the photoactive layer of TiO2 –based solar cells with an aim to prolong the cell output in diminished radiation. Inorganic (Sb/Ca/Mn/Ag:) and organic (rhiodamine, allicin, gingerol, quinolone and neohesperidosyl: extracted from their fresh organic complexes) photo luminescent materials were used as dopants in TiO2 photoactive layer of the solar cell while a mixture of graphite, iodine and potassium iodate was used as the receptive layer. The effect of varying mass ratios and the thicknesses of both photo active and the receptive layers was investigated based on the solar cell output parameters. The synthesized inorganic (Sb/Ca/Mn/Ag) and the extracted organic luminescent materials were chemically characterized using the FTIR. Different masses of the photoactive TiO2 material, inorganic and organic luminescent materials were weighed separately and compressed to form the photoactive layer. Known masses of graphite powder mixed with a matrix of potassium iodate (KI3) were introduced into the molding dice over the photoactive layer and compressed to bind them sufficiently. Potential and short circuit generated by the cells were monitored and the data obtained used to determine their fill factor, and efficiency. The study concluded that the inorganic (Sb/Ca/Mn/Ag) and organic rhiodamine, flourene, allicin, gingerol, quinoline and neohesperidosyl particles absorbed radiation at different wavelengths. The absorption bands were evident at {(360 – 3750), (434.96-3950), (697.28-3750), (290.29-3850), (463.89-3850), (260.39-3750) and (273.90-3700)} cm-1 respectively. All the investigated photo luminescent materials showed promising properties for improving solar cell output in diminished solar radiation. The results obtained also showed different potential delay by the varied thicknesses with improved responsivity and efficiency. The fabricated solar cell employing rhiodamine doped -TiO2 photoactive layer (0.136) mm and 0.164 mm receptive thickness layer had the highest open circuit voltage (VOC =1.023V), and a residual potential of 0.586 V in diminished radiation after one hour. The corresponding fill factor and efficiency were determined as 0.416 and 2.32%, respectively. The study also concluded that optimized FSCs layers generated enhanced open circuit and residual potentials (VOC) observed after 60 minutes. The study recommends that dopant synthesis should be expanded to enhance further d-orbitals splitting for improved charged species d→d transitions and transpose IR spectrum into fluorescence, dopants molecular size with less energy instability should be extended to achieve uniform potential difference with less attenuation, wider dopants complexes ratios should be done to minimize recombination at the convergence within the solute and enhance quantum yield for higher charge carriers’ densities excitation, modified ratios relative dimensions should be investigated together with ambient conditions moderating pigments to balance FSCs interacting systems for uniform output parameters.