الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
Chapter I: Design and Synthesis of novel bichalcophene derivatives with double anchoring groups for dye-sensitized solar cell applications: Sensitization and Co-sensitization with N-719. 1.1.Chemistry Preparation of the new bithiophene-pyrimidine-2,4,6-trione derivative 4a (F1) began with Knoevenagel condensation reaction by treatment of 5-bromothiophene-2-carboxaldehyde with 1,3-dimethylbarbituric acid to afford the bromo compound 3a, followed by a stille-type homocoupling reaction using hexabutylditin mediated homocoupling conditions for 3a in the presence of catalytic Pd(PPh3)4 using refluxing toluene as a solvent to afford the desired compound F1. Adopting the same methodology used for the preparation of 3a, starting with 5-bromofuran-2-carboxaldehyde instead of 5-bromothiophene-2-carboxaldehyde to afford the bromo compound 3b, which also underwent a stille homocoupling reaction to afford the anticipated bifuran-pyrimidine-2,4,6-trione derivative 4b (F2) as outlined in scheme 1. Scheme 2 outlines the preparation of the new unsymmetrical bichalcophene dye 7 (F3) starting with Suzuki coupling by treatment of bromothiophene aldehyde 2a with (5-formylfuran-2-yl)boronic acid (5) to furnish dialdehyde compound 6, which is subsequently condensed with 2 equivalents of 1,3-dimethylbarbituric acid to afford the target compound F3. 1.2. Solar Cell Applications of Structures F1-F3 Novel dyes F1-3 based on bichalcophene-pyrimidine-2,4,6-trione derivatives with dual anchoring were developed, synthesized, and evaluated as sensitizers and co-sensitizers for dye-sensitized solar cells (DSSCs). F1 displayed the best DSSC performance (η, PCE = 4.41%) and the highest photovoltaic parameters, which were as follows: current density, JSC = 10.66 mA.cm−2, photovoltage, VOC = 0.654 V, and fill factor, FF = 64.3%. These findings can be ascribed to F1’s superior optical and electrochemical characteristics when compared to other structures such as F2 and F3. Interestingly, devices that rely on the F1 + N-719 co-sensitization approach had greater photocurrent and photovoltage than the standard N-719 dye, generating a power conversion efficiency ( PCE) of 9.97%. This improved performance was mostly due to a higher JSC value of 23.28 mA.cm−2 for the dye F1 and a maximum molar extinction coefficient in the 350-550 nm region, which enhanced the light-harvesting capacity of the N-719 dye. Chapter II: Design, Synthesis, and Performance Evaluation of TiO2-Dye Sensitized Solar Cells Using 2,2’-Bithiophene-Based Co-Sensitizers. 2.1.Chemistry The bithienylbenzonitrile derivatives 10a-c were prepared via refluxing bromo bithienyl derivative 8 with 4-methoxyphenylboronic acid (9a), 3,4-dimethoxyphenylboronic acid (9b), and 3,5-dimethoxyphenylboronic acid (9c) in 1,4-dioxane as a solvent using Pd(PPh3)4 as a catalyst, and K2CO3 as a base (Scheme 3). Scheme 4 outlines the preparation of the bithienylfluorobenzonitrile derivatives 12a-c starting with a Suzuki coupling reaction via cross-coupling reaction of bromo bithienyl derivative 11 with the proper phenylboronic acids 9a–c. Structures of bithienylfluorobenzonitriles 12a-c were confirmed based on their elemental and spectral analyses. 2.2. Solar Cell Applications of Structures 10a-c & 12a-c We report on the synthesis and characterization of six novel 2,2’-bithiophene-based organic compounds (10a-c and 12a-c) that are designed to serve as co-sensitizers for dye-sensitized solar cells (DSSCs) based on TiO2. The compounds are linked to various donor and acceptor groups, and we confirm their chemical structures through spectral analyses. Our focus is on enhancing the performance of metal based N3, and the compounds were designed to operate at the nanoscale. We performed absorption and fluorescence emission measurements in dimethylformamide (DMF), where one of our compounds 12a exhibited the longest maximum absorption and maximum emission wavelengths, indicating the significant impact of the para methoxy group as a strong electron-donating group. Our dyes 12a + N3 (η = 7.42%) and 12c + N3 (η = 6.57%) outperformed N3 (η = 6.16%) alone, where the values of short current density (JSC) and open circuit voltage (VOC) for these two systems also improved. We also investigated the charge transfer resistance at the TiO2/dye/electrolyte interface using electrochemical impedance spectroscopy (EIS), which is important in the context of nanotechnology. According to the Nyquist plot, the 12a + N3 cocktail exhibited the lowest recombination rate, resulting in the highest VOC. Our theoretical calculations based on density functional theory (DFT) are also in agreement with the experimental process. These findings suggest that our compounds have great potential as efficient DSSC co-sensitizers. This study provides valuable insights into the design and synthesis of new organic compounds for use as co-sensitizers in DSSCs based on TiO2 and highlights the potential of these compounds for use in efficient solar energy conversion. Chapter III: Computational Design of High-Efficiency Organic Dyes with New Donors and Acceptors for Enhanced Performance in Dye-Sensitized Solar Cells 3.1.Chemistry 4-Formylphenyl derivatives 15a, b were prepared starting with a Suzuki coupling reaction via cross-coupling reaction of bromo thiophene derivatives 13a, b with 4-formylphenyl boronic acid 14 in 1,4-dioxane as a solvent using Pd(PPh3)4 as a catalyst, and K2CO3 as a base (Scheme 5). Compound 15a was prepared with outstanding yield (92%) but in fewer steps compared to a previous work. Scheme 6 outlines the preparation of the new fluorescent Schiff’s bases 18 a,b and 19a,b through condensation reaction of aldehyde with aromatic amine to form a Schiff’s base. Reaction of 4-formylphenyl derivative 15a with N,N-dimethyl-p-phenylenediamine 16 affords (E)-4-(5-(4-(((4-(dimethylamino) phenyl)imino)methyl)phenyl)thiophen-2-yl)benzonitrile 18a and in similar manner its fluorinated analogue 18b. Once more, reaction of formyl derivative 15a with 4-morpholinoaniline 17 afford (E)-4-(5-(4-(((4-morpholinophenyl) imino) methyl)phenyl)thiophen-2-yl)benzonitrile 19a and in similar manner its fluorinated analogue 19b. Preparation of the new fluorinated and nonfluorinated benzylidene barbituric and thiobarbituric acid derivatives 20a, b and 21a, b began with Knoevenagel condensation reaction. Preparation of compounds 20a, b was achieved by treatment of 4-formylphenyl derivatives 15a, b with barbituric acid to afford the target compounds 20a, b. In the same manner, compounds 21a, b was prepared via condensation reaction of formyl derivatives 15a, b with thiobarbituric acid as outlined in Scheme 7. 3.2.Theoretical calculations: Computational investigations were conducted on sensitizers (18a-21a) and (18b-21b) to understand the impact of characteristic donor, π-spacer, and different anchoring/acceptor groups such as benzonitrile, fluorobenzonitrile, barbituric acid, and thiobarbituric acid on the geometry of the targeted dyes and their efficiency in dye-sensitized solar cells (DSSCs). The theoretically estimated HOMO and LUMO energy levels, as well as the energy gap showed that the energy gap between the HOMO and LUMO ranges from 2.76-3.11 eV. The Eg energy of the sensitizers decreased in a sequence of 18b < 18a < 19b < 19a < 20a < 20b < 21a < 21b. The determination of the lowest energy gap (E0-0) in the 18b structure can provide insights into its superior stability and validate its reactive configuration compared to other sensitizers examined. Also, VOC of sensitizer 18b blended with flurobenzonitrile acceptor is found to be 1.25 eV. The increased value of the (VOC) observed in 18b sensitizers indicates a successful and efficient electron transfer from the donor moiety located in the (HOMO) to the acceptor moiety situated in the (LUMO) region. VOC of molecules increases in the order 21b < 21a < 20a < 20b< 19a < 19b < 18a < 18b. In the context of this study, it is noteworthy that the sensitizer 18b demonstrates a significantly lower charge recombination value (ΔGrec) of approximately -1.51 eV compared to other structures within the same class. This observation highlights the superior performance of 18b as a highly efficient dye for applications in dye-sensitized solar cells (DSSCs).