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

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(dcbpyH(2))(2)(NCS)(2)], dcbpyH(2) = 2,2'-bipyridyl-4,4'-dicarboxylic acid), N719 ([(C4H9)(4)N](2)[Ru(dcbpyH)(2)(NCS)(2)]), and N749 ([(C4H9)(4)N](3)[Ru(tcterpy)(NCS)(3)]center dot 3H(2)O, 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 Jsc 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.