الفهرس 
Introduction and Literature ReviewOnly 14 pages are availabe for public view
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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.