The effect of pH was also investigated in this study. The
original pH of rosella extracted anthocyanin was found to
be 3.2. As shown in Table 4, the pH of extract solution has
a significant effect on the performance of DSSCs. The
efficiency was found to increase with decreasing pH and
reached a maximum at the optimum pH 1.0. This is might
be due to the fact that at pH 1.0, the photoanode made
from the rosella extract can absorb more light, indicated by
peak intensity as shown in Fig. 7. DSSC stability was also
improved by adjusting the pH of the extract from 3.2 to
1.0. As can be seen from Table 4, efficiency loss of DSSCs
decreased with a decreasing pH from 17.3% to 5.7%, after
being exposed to the simulated sunlight for 3 h. A reason
for the better efficiency and stability is that, at pH below 2,
anthocyanin existed as flavylium ion, which is stable form
of anthocyanin, an increasing pH hydrated this ion to
quinonoidal bases. These compounds are labile and can be
transformed into the colorless carbinol pseudobase and
chalcone [18]. It was evident that at low pH the formation
of flavylium ion form is favorable [18]. However, the cell
deterioration by acid leaching is expected as the pH goes
lower (pHo1), which results in a lower efficiency [19].