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Title: Structure-property relationships of dyes as applied to dye-sensitized solar cells
Author: Gong, Yun
ISNI:       0000 0004 7228 6036
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2018
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This work investigates the correlation of structural and photovoltaic properties of dyes used in dye-sensitized solar cells. Experimental methods, including ultraviolet-visible spectroscopy, fluorescence spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy are employed to study optical and electrochemical properties of dye molecules. Computational methods, including density functional theory and time-dependent density functional theory, are used to validate and predict the optical and electronic properties of dye molecules, in their isolated state and once embedded into a working electrode device environment that comprises a dye...TiO2 interface. The results chapters begin with the presentation of a series of quinodimethene dyes that are experimentally validated for their photovoltaic application, and associated computational studies reveal that an inner structural factor - a phenyl ring rotation occurring during the optical excitation process - leads to the competitive photovoltaic device performance of these dyes. Carbazole-based dyes are then systematically studied by computation, especially considering charge transfer paths and binding modes of these dyes on a titania surface. The theoretical models for the basic building block of this chemical family of dyes, known as MK-44, successfully support and explain structural discoveries from X-ray diffraction and reflectometry that impact of their function. A benzothiadiazole-based dye, RK-1, is then systematically studied by both experimental and computational methods, and the results show that the π-bridge composed of thiophene, benzothiadiazole and benzene rings leads to excellent charge separation; and the rotation of these rings during the optical excitation process may well be consistent with the fluorescence spectrum. Finally, the well-known ruthenium-based dyes are theoretically studied to determine the properties of different ligands connected to the metal core of the complex. Conformations with different NCS ligands are calculated in terms of energy and explain well the corresponding results from X-ray diffraction. Acid-base properties of carboxyl groups connected to pyridine ligands in N3 and N749 are theoretically calculated based on thermodynamics and density functional theory. Implicit and explicit models are both adopted to predict these acid dissociative constant values, which are generally in a good agreement with the reported experimental data. The thesis concludes with conclusions and a future outlook.
Supervisor: Cole, Jacqueline Sponsor: Cambridge Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Dye-Sensitized Solar Cell (DSSC) ; Density Functional Theory (DFT) ; Time-Dependent DFT (TDDFT) ; Organic dyes ; Quinodimethane-based dyes ; Carbazole-based dyes ; Benzothiadiazole-based dye ; MK44 ; RK1 ; Ruthenium-based dyes ; N3 dye ; N749 dye (Black Dye) ; Acid dissociation constant (pKa) ; Ultraviolet-Visible (UV-vis) spectroscopy ; Fluorescence spectroscopy ; Electrochemical Impedance Spectroscopy (EIS) ; Cyclic Voltammetry (CV) ; Photovoltaic performance ; I-V curves