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.