Studies of Low Cost Biological
Photovoltaic Cells
By
Dhiyaa Kareem Muslem Al-Husenawi
A thesis submitted in fulfilment of the requirements for the degree
of Doctor of Philosophy in Bangor University
March 2013
Abstract
This thesis has focused on three different aspects. The first was improving of biophotovoltaic 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 TiCl4 solution, the type of TiO2 paste used, the
electrolyte and the design of cell. The highest efficiency and short current (Jsc) reached
0.71% and 1.77 mA.cm-2 , respectively by passive dyeing which increased using ultrafast sensitization to 1.53% 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 1.94% (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
photo-electrodes were dyed individually.
The second aspect was the invention of a new procedure which was patented to
manufacture TiO2 Photo-electrodes at low temperature (250˚C) by adding metal
peroxides (MP) to P25 paste. The films were characterized by TGA, XRD, BET, UVVis spectroscopy, thermodynamic and dye adsorption studies. A typical cell that used
N719 dye and MP/P25 sintered at 250˚C showed efficiency of 3.94% that increased to
4.97% after the sintering at 250˚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. MP/P25 films made using the same conditions (sintering at
250˚C followed by UV treatment) were used to manufacture bio-photovoltaic cell with
chlorophyll dye and achieving efficiency of 0.94%.
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 100˚C. The best
efficiencies for these devices were 3.24%.and 0.18% when using N719 or chlorophyll
as sensitizers, respectively.