TThe RCT values of 50 and 220 X for the counter electrode (Pt/electrolyte) and TiO2/dye/electrolyte interfaces are determined by the first and second semicircles of the impedance graph, respectively. The magnitude of RCT reveals the binding strength between the dye molecules and the TiO2 film in reverse. In comparison with N719 DSSC [29], the dye of Siahkooti extract shows greater resistance and accordingly weaker binding to TiO2 surface with a decrease in JSC, which is why the efficiency is low for the DSSCs sensitized using natural dye.Therefore, introducing a functional group, such as ACOOH, and optimizing the structure of the natural dye are necessary in order to improve the efficiency of DSSCs.