Browsing by Author "Malashi,Nyanda"

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    A Dissertation Submitted in Partial Fulfilment of the Requirements for the Award of the Degree of Doctor of Philosophy in Materials Science and Engineering of the Nelson Mandela African Institution of Science and Technology
    (NM-AIST, 2025-07) Malashi,Nyanda
    Dye-sensitized solar cells (DSSCs) are promising third-generation photovoltaic cell technology due to their easy fabrication and environmental friendliness. In DSSCs, a photosensitizer is crucial for photon absorption, and electron transfer. Natural pigments are investigated as photosensitizers in DSSCs due to their abundance and environmental friendliness. However, their narrow solar spectrum absorption and weak bonding with the semiconductor limit their wide application, necessitating the design of novel photosensitizers. This work focuses on the theoretical design of Braz-Bd-ether, Braze-Bd-ether, Aliz-Bd-ether, Braz-Bd-oxane, Aliz-Bd oxane, Quinaliz-Bd- oxane molecules via etherification and bi-etherification reactions. Moreover, Braz 01, Braz 01b, Braz 01t, Braz 01tb, Braz 02, Braz 02b, Braz 02t and Braz 02tb molecules were obtained from the chemical structure modification of brazilin dye. The photoelectrical, optoelectronic and structural properties of the isolated dye, dye@(TiO2)9H4 and dye@I2, were examined using DFT and TD-DFT methods. The DSSCs’ performance was simulated using TiberCAD software. The results reveal that Braz-Bd-oxane, Braze-Bd-ether, Aliz-Bd-ether, Aliz-Bd-oxane and Quinaliz-Bd-oxane complexes exhibited improved non linear optical properties (NLO), reduced energy gap, lower exciton binding energy (Eb), lower total reorganization energy (λt), and red-shifted absorption spectra by 10.29 nm ‒ 54.83 nm regarding betanidin dye. The frontier molecular orbital (FMO) plots, ∆Ginj (-0.248 ‒ -0.453 eV), ΔGreg, and energy level alignment plots indicate that all designed complex dyes inject electrons into TiO2 and are regenerated by I‒/I3‒ redox electrolyte, satisfying the photosensitizer requirement. For Braz 01-Braz 02tb, are predicted to have improved charge transfer due to reduced λtotal (0.951 eV ‒ 0.528 eV), increased EA (1.021 ‒ 3.472 eV), and decreased IP (5.591 5.252 eV). Additionally, the designed dyes (Braz01‒Braz02 tb) exhibited high current density and minimal charge recombination compared to the brazilin dye, attributed to their red-shifted absorption spectra, reduced Eg (5.074‒2.46 eV) and Eb (0.591‒0.137 eV). Negative Eads for the dyes@(TiO2)9H4 and dye@I2 were noticed for all dyes, signifying spontaneous chemisorption adsorption. Moreover, the 1D-DSSCs sensitized with designed complex dyes exhibit greater power conversion efficiency (PCE) than natural dyes forming these complexes. Aliz-Bd-oxane and Braz-Bd-oxane exhibited higher PCEs of 14.78% and 14.74% among the designed complexes. Also, Braz 01-Braz 02tb demonstrated higher PCE than brazilin dye. The 1D DSSC-Braz 01tb dye has the highest PCE of 13.44%. Therefore, the designed molecules Braz Bd-oxane, Aliz-Bd-oxane, Braze-Bd-ether, and Braz 01tb are better photosensitizers in DSSC.