The Effective Mixture of Anatase–Rutile Nanoparticles as Dye-Sensitized Solar Cell (DSSC) Using Natural Dye of Garcinia mangostana and Rhoeo spathacea Extract

A synergistic effect between anatase and rutile TiO₂ is known to be able to improve light harvesting and the overall solar conversion efficiency. Dye-sensitized solar cell (DSSC) was fabricated using the mixture of anatase–rutile phase of TiO₂ nanoparticles prepared through co-precipitation method with TiCl₃ precursors. The particle’s sizes were 30 nm for anatase and 44.9 nm for rutile as characterized by using XRD (X-ray diffraction). The natural dyes employed were Garcinia mangostana pericarp extract and Rhoeo spathacea extract. The two selected dyes were used because of their abundant availability and good performance for being used as photosensitizer as indicated by their absorbance wavelength of 392.5 nm for G. mangostana extract and 432 and 658 nm for R. spathacea. Both dyes contain anthocyanin pigment, which is a known visible-light trapper that undergoes charge excitation, and upon complexation with a metal oxide semiconductor like TiO₂, a charge-transfer process occurs. Our results show that the best performance of DSSC having anatase/rutile ratio of 90:10 (η = 0.076%) and (η = 0.063%) was obtained for samples sensitized with G. mangostana extract and R. spathacea extract, respectively. This ratio has the largest surface area and smallest particle size. The synergistic effect of the two phases is due to the ease of electron migration from rutile to anatase conduction band and larger surface area allowing more dye being able to be absorbed.