Novel Ru (II) complex with TPA derivatives as a donor for dye-sensitized solar cells

Abstract

Novel heteroleptic ruthenium(II) complex [Ru(CF₃-ppyd-TPA)(tctpy)]⁺ (ppyd = 2-phenyl-6-(pyridin-2-yl)pyridine, TPA = triphenylamine, and tctpy = 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine) was designed and investigated to increase its molar absorptivity compared to [Ru(ppd)(tctpy)]⁺ (ppd = 2-(3-(pyridin-2-yl)phenyl)pyridine). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to gain insight into the factors responsible for the photovoltaic properties of a dye sensitizer. [Ru(CF₃-ppyd-TPA)(tctpy)]⁺ showed a broad absorption spectrum and enhanced the molar extinction coefficient. Significant improvements to light absorption were exhibited by enhancing the metal-to-ligand charge transfer (MLCT) characteristics through the addition of the electron-withdrawing group-CF₃ para to the organometallic bond and by increasing the transition dipole moment through the addition of TPA as an electron-donating group compared to the [Ru(ppd)(tctpy)]⁺. This study suggests that a ruthenium-based dye sensitizer would show improved photovoltaic performance in conversion efficiency for DSSCs by adding electron-donating and electron-withdrawing groups.