الفهرس 
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Abstract
In this thesis we used the PM6, DFT (B3LYP), TD-DFT and DFT-PCM quantum chemical methods combined with different extended basis sets to calculate the ground state properties, optimum molecular geometries, optical properties of free TPA-based dyes and its interaction with TiO2 cluster surface.
The thesis is divided into four chapters
Chapter 1: Includes a general survey on the basic principles of dye sensitized solar cells as it is the aim to reach better efficiencies of dyes, also the operation principle, the previous studies on like chromophores and why we choose this type of dyes where there are two reasons. First, the metal free organic dyes give higher molar extinction coefficient than those of metal complexes. Second, the going systematic research on Donor-π linker-Acceptor (D-π-A) component dyes especially those based on Triphenylamine (TPA) moiety which proves their high experimental efficiencies for using in DSSCs.
Chapter 2: Gives a brief on the physical description of dye sensitized solar cells, their characterization, and the calculation of their efficiency parameters also includes a description of the computational methods in quantum chemistry used on the calculations. In this work we perform our calculations on G03 package using semi-empirical and ab-initio methods.
Chapter 3: This chapter concerned with the results obtained and their discussions.
This chapter is mainly divided into 2 sections:
First one concerning the study electronic and optical properties of the free TPA-based dyes (I-X) and applying B3LYP/6-31G and B3LYP/6-31G(d,p) methods to study our modifications by changing the acceptor moiety and the donor moiety by grafting of electron donating and withdrawing substituents as amino and cyano groups in different positions and addition of an ethylene subunit
-linker between the two phenyl groups help to get better efficiency for use in DSSCs. These specific modifications introduce a maximal increase of the electron injection property, light harvesting efficiency LHE and a more exoenergic free enthalpy of injection shows an improvement of both the UV-Vis spectroscopic response and energetic parameters. We also in this section discussed our chosen for salicylate in the acceptor moiety due to the fast charge transfer and we prove that the presence of electron donating group (by resonance) like hydroxyl (OH) on the acceptor moiety increases the efficiency of the dye which make on tuning between LUMO and HOMO in the excited state and increase the resonating structures of the phenyl group. We studied these dyes in different media; vacuum, polar protic solvent (EtOH) and polar aprotic solvent (DCM) and we found that the energy gap between HOMO and LUMO increases for cyano derivatives specially for para cyano derivatives while it decreases for amino derivatives specially for para amino derivatives and for media we found that in case of EtOH, the energy for HOMO and LUMO decreases for unsubstituted and amino derivatives while increases for cyano derivatives. In the UV-Vis electronic absorption spectra of the dyes (I-X) we found that the energy gap between the LUMO and HOMO levels will get smaller leading to a shift in
towards the near IR in the order V > IV > I > III > II and X > IX > VI > VII > VIII where the amino
derivatives exhibit bathochromic shift while cyano derivatives exhibit hypochromic shift. The shift of
towards the near IR in the media considered is found to be in the order EtOH > DCM > Vacuo. As a conclusion we found that the TPAS dyes is better than TPA dyes due to the coplanarity and the extension of conjugation, as well as the amino derivatives shows higher efficiencies than cyano derivatives.
Second section is dealing with the adsorbed systems of these dyes with anatase (101) surface as it’s the better type and the most reactive for using in DSSCs. The adsorption of dyes containing salicylate occurs via different models, the bidentate bridging is the best for good MO overlapping and for better inramolecular charge transfer. The electronic properties calculated by PM6 showed similar trend with that calculated by B3LYP for free dyes in the last section, also the HOMO and LUMO for the dyes adsorbed on anatase, indicates the localization of HOMO charge on the anchoring site whereas the LUMO charge is localized on the other part of anatase unit cell. In the UV-Vis spectra there is a significant bathochromic shift of the absorption spectra for the dyes adsorbed to anatase surface where the band wavelength range appear from 340 to 730 nm while the free dyes show a band wavelength range from 270 to 670 nm, this shift is accompanied with increase of LHE of the adsorbed dyes. IR spectra showed different changes in the vibrational frequencies after adsorption of free dyes on anatase surface, especially in the carboxylate group where the formation O-Ti bonds. The thermochemistry of adsorption showed exothermic spontaneous process for all dyes which is useful in DSSCs for non-dissociative reversible reaction which decrease the efficiency of the DSSC, also all thermodynamic parameters showed higher values for TPAS dyes than TPA dyes which indicates the better efficiencies for charge transfer.
Chapter 4: Includes the conclusions from the work discussed later in