الفهرس 
DedicationOnly 14 pages are availabe for public view
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Abstract
Increasing worldwide demand for energy and limited fossil fuels reserves on the planet require development of reliable and renewable energy sources. Among the various technologies available nowadays, photovoltaics is believed to be one of the cleanest ways in achieving this goals. But the high cost of manufacturing solar cells was the main reason behind the non-widespread of these cells and used as a substitute of traditional sources.
Nanotechnology enables novel approaches to solar-to-electric energy conversion that may provide both high efficiencies and simpler manufacturing methods. For example, nanometer-size semiconductor crystallites, or semiconductor quantum dots (QDs), can be used as photoactive materials in solar cells to potentially achieve a maximum theoretical power conversion efficiency which exceeds that of current mainstay solar technology at a much lower cost. However, the novel concepts of quantum dot solar cells and their energy conversion designs are still very much in their infancy, as a general understanding of their assembly and operation is limited. This thesis introduces one of the various innovative and novel solar cell architectures based on semiconductor nanoparticles which is quantum dot sensitized solar cell (QDSSC). The thesis also provides a fundamental understanding of the operating principles that govern the performance of this type of solar cells.
At the beginning, Cadmium selenide (CdSe) QDs of size 5 nm was prepared using organometallic synthesis method. The size of the nanoparticles has been determined from the UV- Visible absorption spectrum of the sample which shows a first excitionic band at wavelength of 567 nm. The size of CdSe QDs was confirmed by transmission electron microscope (TEM).
The working electrodes of our sample cells consist of TiO2 mesoporous layer on a conducting glass slides sensitized by CdSe QDs using direct adsorption method for different times. The main counter electrodes in our work are made of Graphite and Carbon black mixture coated on another conducting glass slide. The working electrode and the counter electrode are assembled in sandwich type cell with triiodide\ iodine electrolyte filling the space between the two electrodes. Platinum (Pt) counter electrode is also used in order to compare the effectiveness of the carbonized electrodes we were used in our sample solar cells. Polysulfide electrolyte is employed also in our work to study the effect of changing the electrolyte type on the parameters of our sample cells. The effect of changing the QDs solvent from which the QDs were directly adsorbed on TiO2 is also studied in our work.
UV – Visible absorption of the working electrodes were used to monitor the increase in the quantity CdSe QDs loaded on the TiO2 electrode by increasing the dipping time. CdSe quantum dot sensitized solar cells were characterized under simulated sun light of intensity 100 mW\cm2 and 1.5 AM. We have found that by increasing the dipping time the overall performance of the cells use carbonized counter electrode is enhanced. A conversion efficiency of 0.05% and the short circuit current to 266 µA\cm2 are obtained for the cell that use working electrode sensitized for 24 hours dipping time in CdSe QDs dispersed in toluene. We also found that, the graphite-carbon black counter electrode is an effective low cost counter electrode compared to the expensive platinum one.
When polysulfide electrolyte used instead of triiodide\iodine electrolyte in CdSe QDSSC, we found that the cell gives a higher short circuit current but with very low fill factor. This low fill factor reduces the overall conversion efficiency of the cell. We also found that, using hexane as a solvent for CdSe QDs instead of toluene is better for the loading process of the QDs on TiO2 mesoporous layer since it needs less time for the loading process.