Effect of Side Groups for Ruthenium Bipyridyl Dye on the Interactions with Iodine in Dye-Sensitized Solar Cells

Abstract

A density functional theory (DFT) study was performed to elucidate the effect of the side group (X) in Ru(H2dcbpy)(X2bpy)(NCS)2 dye on the interactions with iodide ions (I– and I3–) and iodine molecule (I2), where X is a carboxyl, nonyl, amino, or 1-pyrrolyl group, and dcbpy and X2bpy represent 4,4′-dicarboxy-2,2′-bipyridine and 4,4′-X2-2,2′-bipyridine, respectively. Oxidized dyes interact with I– via the S atom of the NCS ligand perpendicular to the H2dcbpy ligand. The relative interaction strength between the dye and I– is amino < nonyl <1-pyrrolyl < carboxyl group. Except for dye possessing amino groups, a second I– bonds to the first I–, and the iodides weakly interact with the C–H bond of X2dcbpy ligand. Additionally, I2 interacts via the S atom of the NCS ligand perpendicular to H2dcbpy of the neutral dye, and this interaction becomes stronger in the order of carboxyl < 1-pyrrolyl < nonyl < amino group dye. Only the neutral dye possessing amino groups interacts with I3– via N–H···I bonds. On the basis of theoretical results, the effect of side groups for Ru bipyridyl dye on both regeneration of oxidized dye with I– species and recombination related to the interactions with I2 and I3– species in the dye-sensitized solar cells is discussed.