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Abstract 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. As 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 Dye- Sensitized Solar Cells (DSSCs)) have been studied extensively to get low-cost cells with considerable efficiency. DSSCs have many advantages such as inexpensive material cost, easy fabrication, and relatively high efficiency. A typical DSSC consists of a working electrode (photoanode) which is a transparent conducting oxide (TCO) substrate covered with a film of dye-sensitized semiconductor oxides, a counter electrode and an electrolyte which is sandwiched between the two electrodes. Upon light irradiation, dye 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 after performing electrical work on the way. The electron is then transferred to the electrolyte where it reduces the oxidant species. Subsequently, the original state of the dye is restored by electron donation from the reduced species in the electrolyte to complete the circuit. Continuous efforts have been invested around the world to enhance the efficiency of DSSC. In this work, we prepared and characterized the performance of ZnO nanoparticles films employed as the working electrodes of dyesensitized solar cell (DSSC) devices and treated with another metal oxide semiconductor. Then, we investigated the effect of both ZnO layer thickness and doping on the performance and efficiency of the manufactured DSSCs. 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 DSSCs etc. and a literature review. Chapter 11: Experimental Work We employed zinc hydroxide solution and titanium tetrachloride solution to prepare a series of ZnO with different thicknesses and another series of Ti02-doped ZnO photoanodes. In addition, preparation of dye solution, electrolyte preparation, counter electrode preparation, and DSSC assembly were carried out. The crystal structure of undoped and Ti02-doped samples was carried out by using XRD, SEM, and EDX. The electrical characteristics of DSSCs were achieved by current density-voltage (J-V) measurements. Chapter 111: Results and Discussion XRD, EDX, and SEM. were used to investigate the samples under study. In addition, the thickness and doping influence on the photovoltaic efficiency of DSSCs were studied. This chapter includes two parts: Part one: ZnO photoanodes with thicknesses of 1.8, 4.1, 6.4, 1 1.0, 14.2, and 18.34 pm were prepared. XRD analysis showed that the prepared ZnO photoanodes possess a pure wurtzite phase with a particle size of 11 nm. The photocurrent density-voltage curves of DSSCs revealed an increase in short-circuit current density (J,,) with increasing of ZnO thickness up to 11.0 pm which was attributed to an increase in dye loading. On the other hand, the further increase in thickness caused a decrease in Jsc values and referred to increase in series resistance and a decrease in light intensity with further increasing in thickness. The open circuit voltage V,, were found to be less affected by changes in thickness and an overall decrease in V,, was reported and explained in terms of surface or deep trapping states. The optimal value of thickness is 11 pm for J,,. These results were confirmed by OCVD measurements. Part two: XRD analysis of Ti02-doped ZnO photoanodes showed the absence of Ti02 peaks due to the high porosity of the prepared film, while EDX indicates the presence of Ti02 and ZnO and agrees firmily well with starting ratio of Ti02/Zn0 ratio. Photocurrent density-voltage curves of DSSCs revealed that both J,, and V,, were increased with increasing of doping content up to x=0.17 while the furthermore increase in doping decreased all cell parameters. The OCVD results demonstrate that at any given open-circuit potential, the electron lifetime of the DSSC for the optimal concentration (x=0.17) sample was longer than that of other DSSC. |