Mostly natural dyes which act as photosensitizers in DSSC showed very low efficiencies compared to synthetic and metal or- ganic dyes due to unavailability of specific functional groups [29]. The generation of short circuit current of the fabricated cell mainly depends on the amount of dye adsorbed on the TiO2 surface, struc- ture, light harvesting efficiency and electron injection ability of the dye [30]. More adsorption of dye molecules on the TiO2 surface generates more number of photons from sunlight which in turn leads to the rapid electron injection. The open circuit voltage and short circuit current are the important parameters which decide the efficiency of the cell. The open circuit voltage is the difference between the Fermi level of TiO2 electrode and the potential of re- dox electrolyte which mainly depends on the recombination rate and adsorption mode of the sensitizer [30,31].
An improved efficiency of the cell based on the red frangipani flowers extract is due to the presence of anthocyanin which con- tains alcoholic groups. The presence of alcoholic groups may help for maximum binding on the surface of TiO2 nanostructure through chemical adsorption phenomena [32]. Whereas ivy gourd fruits ex- tract doesn’t have any adsorbing functional groups like AOH, ACOOH as the case of b-carotene and hence the possibility of bind- ing with TiO2 surface is very low. In addition there are no electron donating and withdrawing groups, which is most essential for the flow of electrons from the dye molecule to TiO2 under illumination of light [14,15]. Hence cell fabricated with red frangipani flowers extract shows relatively higher Jsc, which could be ascribed to its higher light harvesting efficiency in the visible region [33]. In order to identify the above processes, desorption of the sensitizer from