الفهرس 
Introduction and literature ReviewOnly 14 pages are availabe for public view
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Abstract
The world’s conventional energy resources (oil, natural gas, and coal) have shown signs of deficiency beside their negative impact on the environment. Therefore, searching for renewable energy resources is taking place. One of the most prominent clean energy resources is the sun, which is a clean and infinite external energy source. The solar cell is a device used to convert solar energy into electricity directly by the photovoltaic effect. In 1954, the first solar cell made of silicon was developed. Solar cells can be classified into different types such as thin film cells, nanocrystalline, organic cells and so on. Although the highest efficiency of solar cells is around 40% in the Lab; the cost of its production is still high and the technology is not commercially available. As a result, low-cost solar cells (such as Quantum Dot Sensitized Solar Cells (QDSSCs)) have been studied extensively to get low-cost cells with considerable efficiency. QDSSCs have many advantages such as inexpensive material, easy fabrication, and relatively high efficiency. A typical QDSSC consists of a working electrode (photoanode) which is a transparent conducting oxide (TCO) substrate covered with a film of quantum dots-sensitized semiconductor oxides, a counter electrode and an electrolyte which is sandwiched between the two electrodes. Upon light irradiation, quantum dots molecules are photoexcited and the excited electron is then injected into the conduction band of the semiconductor oxide. Then, the injected electron migrates to the TCO of the photoanode. Afterward, the electron reaches the counter electrode through external circuit. The electron is then transferred to the electrolyte where it reduces the oxidant species. Subsequently, the holes of the quantum dots are restored by electron donation from the reduced
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species in the electrolyte to complete the circuit. Continuous efforts have been invested around the world to enhance the efficiency of QDSSC. In this work, we prepared and characterized CuInS/ZnS quantum dots which employed as the sensitizer for quantum dot sensitized solar cell (QDSSC) devices. we investigate the effect of both CuInS/ZnS sensitizing time and introducing ZnS with different passivation layer number on the performance and efficiency of the manufactured QDSSCs. This was carried out by measuring the parameters of the solar cells under simulated solar radiation. The thesis consists of three chapters: Chapter I: Introduction and literature review
This chapter contains an introduction to the history, structure, operation of QDSSCs etc. and a literature review.
Chapter II: Experimental Work
We employed CuInS/ZnS QDs solution to prepare a series of CuInS/ZnS QDs with different sensitization time and another two solutions (zinc acetate solution and sodium sulfide solution) to prepare a series of CuInS/ZnS treated with different passivation layer number of ZnS photoanodes. In addition, preparation of TiO2 paste, electrolyte preparation, counter electrode preparation, and QDSSC assembly were carried out.
The optical properties of the prepared QDs solution were studied through UV-vis and photoluminescence (PL). While the crystal structure was carried out by using XRD, SEM, and EDX. The electrical characteristics of QDSSCs were achieved by current density-voltage (J-V) measurements.
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Chapter III: Results and Discussion
UV-Vis, PL, XRD, TEM, SEM and EDX were used to investigate the samples under study. In addition, the influence of sensitization time with CuInS/ZnS QDs and different passivation layer number of ZnS on the photovoltaic efficiency of QDSSCs were studied. This chapter includes Three parts:
Part one: TiO2 photoanodes sensitized with CuInS/ZnS at different times of (1, 2, 3 and 4) days were prepared. The photocurrent density-voltage curves of QDSSCs revealed an increase in both open circuit voltage (Voc ) and short-circuit current density (Jsc) with increasing sensitization time up to 3 days which was attributed to an increase in QDs loading. On the other hand, the further increase in sensitization time caused a decrease in Voc and Jsc values which referred to increase in aggregations. The optimal value of sensitization time 3 days for Voc, Jsc and cell efficiency (η).
Part two: In this part the effect of introducing ZnS passivation layer with different numbers (0, 9, 11, 13 and 15) of cycles on the optimum sensitization time (3 days) from part one was studied. EDX analysis of TiO2 photoanodes sensitized with CuInS/ZnS QDs and passivated with ZnS indicates the presence of Ti, O2, Sn, Cu, In, S and Zn in the prepared samples. Photocurrent density-voltage curves of QDSSCs revealed that both Jsc and Voc were increased with increasing of passivation layer cycle up to 13 cycles while the furthermore increase in layer cycle decreased all cell parameters.
Part three: In this part the effect of sensitizing TiO2 film with CuInS/ZnS prepared with 1-mercaptoacetic acid (MAA) at different times (1, 2, 3, 4, 5 and 6) days was studied. The photocurrent density-voltage curves of QDSSCs revealed an increase in both open circuit voltage (Voc) and
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short-circuit current density (Jsc) with increasing sensitization time up to 5 days which was attributed to an increase in QDs loading. On the other hand, the further increase in sensitization time caused a decrease in Voc and Jsc values and referred to increase in aggregations and series resistance. The optimal value of sensitization time is 5 days for Voc, Jsc and cell efficiency (η). Also, the optimum 5 days sample was improved by introducing 13 cycled of ZnS passivation layer which increased Voc, Jsc and η. The last step in improving our QDSSC is using platinum counter electrode with the optimum cell which enhanced all cell parameters Voc, Jsc, FF and η.