This thesis has focused on three different aspects. The first was improving of bio-photovoltaic cells based on dye-sensitized sensitized solar cells (DSC) based mainly on using extract of spinach as natural and cheap dye instead of laboratory-synthesized dyes. The extraction was performed using four methods with solvents of acetone, petroleum ether, methanol and dioxane. The yield of extract was 0.16-0.31 mg from 200 g of spinach leaves. Then the extract was used to manufacture DSC devices. The factors that can affect the efficiency of the cells have been studied including the dyeing solvent, the temperature and time of sintering, the thickness of the TiO₂ film, the treatment of photoelectrode
films with acids and/or TiC1₄ solution, the type of TiO₂ paste used, the
electrolyte and the design of cell. The highest efficiency and short current (J_sc) reached were 0.71 % and 1.77 mA.cm^-2, respectively by passive dyeing which increased using ultra-fast sensitization to 1.13% and 2.67 mA.cm-2, respectively. To our knowledge, this is a higher efficiency for a spinach extract than that published in the literature.
Afterwards, the Mg²⁺ ion in chlorophyll was replaced by metal ions ( either Zn²⁺ or Cu²⁺) to prepare Zn-chlorophyll or Cu-chlorophyll, respectively which were then used in DSC devices that achieved efficiency of 0.93% and 0.30%, respectively.
The extract of spinach was separated by two techniques, column chromatography or preparative TLC. The separated pigments which included chlorophyll-a, chlorophyll-b, carotene and xanthophylls were characterized by colour, TLC, UV-Vis spectroscopy and HPLC, and then were introduced to manufacture bio-photovoltaic cells that recorded 0.14, 0.09, 0.15 and 0.18%, respectively.
Chlorophyll and N719 dye were used as co-sensitizing dyes to manufacture DSC cell. The efficiencies were 1.34% (3.38 mA.cm^-2) and 4.31% (10.95 mA.cm^-2) using 90/10 and 10/90 v/v of chlorophyll/N719, respectively compared to 0.92% (2.29 mA.cm^-2) and 4.04% (9.98 mA.cm^-2) using chlorophyll and N719 dye respectively when DSC photoelectrodes were dyed individually.
The second aspect was the development of a new procedure to manufacture TiO₂ photoelectrodes at low temperature (300°C) by adding metal peroxides to P25 paste. The films were characterized by TGA, XRD, BET, UV-Vis spectroscopy and dye adsorption studies. A typical cell that used N719 dye and ZnO₂/P25 sintered at 300°C showed efficiency of 3.94% that increased to 4.57% after the sintering at 300°C followed by UV treatment compared to cell used P25 sintered at 450°C that showed efficiency of 3.23% or 3.63% after the sintering at 450°C followed by UV treatment. ZnO₂/P25 films made using the same conditions (sintering at 300°C followed by UV treatment) were used to manufacture bio-photovoltaic cell with chlorophyll dye and achieving efficiency of
0.64%.
The last aspect for this study focused on development of flexible solar cells. Photoelectrodes were prepared using ITO-plastic substrates instead of FTO glass substrates were prepared by UV treatment and with or without sintering at 120°C. The best efficiencies for these devices were 3.24%.and 0.18% when using N719 or chlorophyll as sensitizers, respectively.