Dinuclear Ru(ii) dyes for improved performance of dye-sensitized TiO2 solar cells

Abstract

In this study, a Ru(II) dye was linked to another TiO₂-attached Ru(II) dye through the linker, trans-1,2-bis(4-pyridyl)ethylene (tbpe), and such TiO₂ film electrodes were used in dye-sensitized solar cells (DSSCs). The mononuclear Ru(II) dyes selected were N3 ([Ru(dcbpyH₂)₂(NCS)₂], dcbpyH₂ = 2,2′-bipyridyl-4,4′-dicarboxylic acid), N719 ([(C₄H₉)₄N]₂[Ru(dcbpyH)₂(NCS)₂]), and N749 ([(C₄H₉)₄N]₃[Ru(tcterpy)(NCS)₃]·3H₂O, tcterpy = 4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine). The photovoltaic characteristics of the DSSCs prepared using the above-mentioned TiO₂ film electrodes were examined. The DSSC with the dinuclear dye, N719-tbpe-N719 had the highest short-circuit photocurrent density (J_sc) and thereby the highest conversion efficiency compared with the other cells sensitized by the other mononuclear or dinuclear Ru(II) dyes. The J_sc enhancement was attributed to an increase in the conduction band electrons of TiO₂ due to the efficient intramolecular charge and energy transfer from the linked dye molecule to the immobilized molecule through a chain of conjugated double bonds in tbpe. These transfers are explained based on the relative LUMO levels of the dyes.