Comparative study of natural dyes extracted from dark red and yellow Frangipani flowers (Plumeria rubra L.) as DSSC sensitizer

Dye-sensitized solar cells (DSSC) provide credible alternative for the inorganic solid-state photovoltaic devices. In this work, natural sensitizer extracted from Plumeria rubra L. flower (Frangipani) in ethanol has been used as the sensitizer dye. Dark red and yellow species of Frangipani flower petals extracted natural dyes have been studied for their comparative performance as sensitizer dye. FTIR revealed the presence of hydroxyl and carbonyl group in the sensitizer dye, which helped in binding with TiO₂. UV-Visible analysis revealed absorption in visible region, which got broadened for dye loaded TiO₂. Mass spectrometry confirmed major chemical constituents present in Plumeria rubra L. flower. For the HOMO and LUMO levels of dark red and yellow Frangipani flowers, the density functional theory (DFT) calculation was performed. Light-to-electricity conversion efficiency (ɳ%) of dark red Frangipani flowers was achieved 0.148 % with V_oc 0.27 V, J_sc 0.88 mA/cm² and FF 0.62, which was comparatively higher than yellow Frangipani flowers-based cell having ɳ% 0.128 % with V_oc 0.54 V, J_sc 0.37 mA/cm² and FF 0.64, respectively. For analyzing the charge transfer characteristics, electrochemical impedance spectroscopy (EIS) studies were carried out. The dark red species of Frangipani flower showed better result as sensitizer dye compared to the yellow species.