The effect of ruthenium on the performance of porphyrin dye and porphyrin–fullerene (PF) dyad solar cells is investigated
by using density functional theory and time-dependant density functional theory calculations. The results reveal that
ruthenium facilitates rapid electron injection from porphyrin to fullerene, narrows the band gaps of porphyrin dye and PF
dyad and alters the density of states near the corresponding Fermi levels. The HOMOs are localised on the donor moieties
and the LUMOs on the acceptor moieties. The donor and acceptor dyads form good donor–acceptor pairs for photo-tocurrent
conversion under the effect of ruthenium. HOMOs of porphyrin and ruthenium metalloporphyrin dyes fall within the
(TiO2)60 and Ti38O76 gaps, and support the issue of typical interfacial electron transfer reaction. The calculated transition
energies of porphyrin are almost insensitive to ethanol solvent effects. The introduction of ruthenium to the porphyrin ring
leads to more active nonlinear optical performance, stronger response to the external electric field and induces higher phototo-
current conversion efficiency. Moreover, ruthenium shifts the absorption bands of porphyrin and makes it a potential
candidate for harvesting light for photovoltaic applications.