الفهرس 
Chapter 1: introductionOnly 14 pages are availabe for public view
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Abstract
The thesis consists of three chapters which could be summarized as
follows:
Chapter 1: presents types of energy resources and the need for renewable
and clean energy sources. We briefly gave a short background on solar
energy which represents one of the promising energy resources. Our
concern in this work was paid to one type of solar energy, namely dye
sensitized solar cells (DSSCs). So, we shortly reviewed its components:
The working electrode, a sensitizer (dye), an electrolyte/hole transporter,
a counter electrode and also discussed the process of operation. We also
discussed the structures of dyes which can be successfully employed in
DSSCs. The structure of the dye consists of a donor moiety, π bridge and
an acceptor moiety. We also briefly discussed some general principles to
construct an efficient dye and efficient DSSCs. The factors affecting the
efficiency of DSSCs were also studied. Sensitizers commonly used in
DSSCs are also being reviewed which includes triphenylamine (TPA) as
an electron donor moiety and acrylic acid as an electron acceptor moiety.
Some experimental and theoretical studies on TPA-based dyes were also
introduced to validate and compare our results with them. We also gave a
brief study on metal oxides which are employed successfully on DSSCs.
We will test different metal oxides: anatase ,rutile , brokite, magnesium
oxide, copper oxide, iron oxide and zinc oxide and the possibility to be
employed in DSSCs.
We also designed a series of (TPA)‐based sensitizers and put them in two
groups :
-group 1 includes gradual insertion of nitrogen atoms in the benzene
linker (0N) as the π‐spacers for dye‐sensitized solar cells (1N-4N).
-group 2 includes the replacement of benzene linker by five membered
rings: cyclopentadiene, silole, pyrolle, furan and thiophene (2a-2e) as the
π‐spacer for DSSCs and the results will be compared with the parent
molecule 0N.
Chapter 2: includes a short background on quantum chemical
calculations and a detail description of the procedures used throughout this
work. Geometry optimizations have been performed at the B3LYP/3-
21G(d) level of theory then a single point energy calculations in
dichloromethane using polarizable continuum model (PCM) and 6-
31+G(d,p) basis set. The TD-CAM-B3LYP/6-31+G(d,p) level has been
used to calculate the excitation energies for the selected dyes .The
combination of TD-CAM-B3LYP with the split-valence basis sets with
polarization and diffuse functions guarantees accurate absorption spectra.
For Fukui functions calculations: We made a single point calculations of
the optimized structures with changing the charges to calculate the
energies of cations and anions using Hirschfield population. The
calculations have been carried out in dichloromethane to match the
experimental conditions.
Geometry optimizations of the investigated metal oxides were
performed by PM6 method then a single point energy calculations using
B3LYP 3-21 G(d) level has been used to calculate the Frontier molecular
orbital energies.
All calculations have been conducted with the Gaussian 09 program.
Chapter 3: presents results and discussion. Our findings can be
summarized as follows:
We studied the electronic properties of these crystal structures as we
calculated the energies of the valence and conduction bands and also the
band gaps between the conduction bands and the LUMOs of the dyes.
We proved that: anatase, rutile, brokite, iron oxide and zinc oxide can be
employed successfully as excellent photoelectrodes in DSSCs as their
conduction bands lay below the LUMO of the dyes and so they can
achieve efficient electron injection. However, magnesium oxide and
copper oxide won’t be efficient electrodes when used in DSSCs as their
conduction bands lay higher than LUMO of the dyes which makes
electron injection difficult.
The dye (2b) /anatase systems was also simulated to show the
electronic structure at the interface, and we show that when binding to
anatase, strong electronic coupling between dyes LUMO and the TiO2
conduction band is found, which is favorable for an efficient electron
injection from the dye to the semiconductor surface.
The influence of π‐linkers of a series of triphenylamine (TPA)-
based dye sensitizers on their electronic and optical properties was
studied. Our simulations show that the electron‐deficient thiadiazole
derivatives demonstrated great effect on the spectra and electrochemical
properties of the TPA‐based organic dyes.
The results indicated that the gradual insertion of nitrogen at benzene
π‐linker shows an enhanced spectral response (compared to 0N) in the
UV/Vis solar spectrum due to sharp lowering in the LUMO level and
smaller HOMO-LUMO energy gap.
HOMO and LUMO of the dyes are located above and below the
conduction band of TiO2 photoelectrode and the HOMO of the I-/I3
- redox
couple, respectively, which could guarantee efficient electron injection
and regeneration assuming a good alignment of energy levels among the
constituents of the solar cell. The HOMO-LUMO energy gap decreases
with increasing number of nitrogen atoms in the benzene linker. Tetrazine
bridge seems more efficient as it shows a remarkable red shift in the
absorption band compared to other dyes.
The HOMO of the studied dyes is delocalized over the π-conjugated
system with the highest electron density concentrated on the TPA moiety.
On the other hand, the LUMO is localized on the anchoring group
through the π-bridge. Compared to previous work, the new dyes give
reasonable Δ . This ensures better electron injection.
Our simulations could suggest the new dyes as efficient sensitizers in
DSSCs.
The tested parameters: condensed fukui function, local softness,
relative electophilicity and Hirshfeld charges of anchor atoms have been
employed successfully at series of triphenylamine (TPA)-based dye
sensitizers.
group 2 compounds show enhanced results compared to molecule
0N. 2a and 2b have the lowest nucleophilic sites and the highest
electrophilic ones for all the anchor atoms compared to other compounds
suggesting them to be more prone to be attacked by electrophile. They’re
also expected to have a stable contact with TiO2.
group 2 compounds show an enhanced spectral response
(compared to molecule 0N) in the UV/Vis solar spectrum especially 2a
and 2b with distinguished red shift (79,128 nm) respectively. This is due
to sharp lowering in the LUMO level and smaller HOMO-LUMO energy
gap. 2a and 2b also have the lowest HOMO-LUMO energy gap
compared to other dyes.
The LUMO and HOMO of the dyes are located above and below
the conduction band of TiO2 photoelectrode and the HOMO of the I-/I3
-
redox couple, respectively, which could guarantee efficient electron
injection and regeneration assuming a good alignment of energy levels
among the constituents of the solar cell. The HOMOs of the studied dyes
are delocalized over the π-conjugated system with the highest electron
density concentrated on the TPA moiety. On the other hand, the LUMOs
are localized on the anchoring group through the π-bridge.
It’s obvious that the tested parameters are good candidate to be
employed in the future DSSCs papers. Our simulations could suggest 2a
and 2b as efficient sensitizers in DSSCs.