Sensitization and stability studies of anthocyanin based sensitization dyes on nanoporous ti02 thin film photoelectrochemical solar cells
Abstract
Dye sensitized Ti02 solar cells have been prepared by the sol gel process. Three groups
of naturally occurring anthocyanin dye pigments have been extracted and tested for
sensitization alongside ruthenium complex (RuL, L = 2,2 - bipyridine 4,4 dicarboxylaic
acid complex) dye. The dyes (delphinidin purple, cyanidin 3,5 diglucose (C35D), and
pelargonidin) exhibited strong optical absorption in the visible range of the spectrum but
weak sensitization. Sensitization mechanism was found to improve with the addition of
O.l M sodium nitrate and sodium benzoate to the dyes.
The current-voltage characteristics showed that the widths of the conducting glass
substrates affected the performance of the solar cells and in particular the fill factor (FF).
This quantity (FF) was found to decrease with an increase in widths of the conducting
glass substrates. The best width was found to be 1cm and was the one that was used in
this study. Measured photovoltages were found to decrease with the increasing
temperature which also determined the activation energy at the semiconductor/electrolyte
interface (SEI). Solar cells sensitized with ruthenium complex dye exhibited the highest
activation energy of 520m V while delphinidin purple, C35D and pelargonidin had
activation energies of 470mV, 390m V and 270m V, respectively.
The overall efficiencies of the cells were affected by factors such as the resistances in the
cells, the electrolyte and FF. The calculated efficiencies were 4.84% for RuL, 3.16% for
delphinidin purple, 2.97% for C35D and 0.02% for pelargonidin dye sensitized solar
cells. With controlled atmosphere for preparation and testing of samples (like glove
chambers and fume chambers), the overall efficiencies could be higher than the ones
obtained in this study.
The cells' performance in terms of photovoltage was found to drop with time. RuL
exhibited most stability over the anthocyanin dyes with highest photovoltages and least
drop over the same period. Pelargonidin dye recorded the least stability, with
photovoltages running below 10mV just after one month of exposure.