Synthesis and study of bipyridine ruthenium complexes containing amido groups as photosensitive dyes for solar cells

Abstract

The new ruthenium complexes containing amido groups (Dye1, Dye2 and Dye3) are synthesized and studied as sensitizing dyes in dye-sensitized solar cells (DSSC) by comparing to N3 reference dye(cis-dithiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II)). Dye1 is a Ru complex consisting of two identical bipyridine ligands, 2,2'-bipyridine-4,4'-dicarboxamide, and two thiocyanate groups. Dye2 and Dye3 consist of two different bipyridine ligands and two thiocyanate groups coordinating to Ru center. The bipyridine ligands of Dye2 are N,N'-(2,2'-bipyridine-4,4'-diyl)diacetamide and 4,4'-dicarboxy-2,2'-bipyridine while those of Dye 3 are 2,2'-bipyridine-4,4'-dicarboxamide and 4,4'-dicarboxy-2,2'-bipyridine. Two pyridine rings in each bipyridinelagand, as revealed by the ¹H NMR spectra, are magnetically inequivalent indicating that all dyes are obtained as the cis geometrical isomer. The photophysical and electrochemical properties of Dye1, Dye2 and Dye3 are similar to N3 dye with slightly lower extinction coefficient. The LUMO and HOMO levels of all three dyes, determined from cyclic voltammetry and UV-vis absorption spectroscopy,are higher than the conduction band of TiO₂ and lower than the HOMO of I3-, respectively. N3, Dye 2 and Dye3 show similar adsorptivity on TiO2 electrode while the adsorptivity of Dye 1 is only 30%of that of N3. The photovoltaic performance of the cells using Dye1, Dye2 and Dye3 as the sensitizers exhibit overall conversion efficiencies of 0.48, 1.21, 1.03% respectively, lower than the value 3.47% obtained from the cell fabricated from N3, mainly due to the lower photocurrent density. The lowest efficiency of Dye1 sensitized cell is due to the lack of the carboxylic group necessary for anchoring on nanocrystalline TiO₂ as well as its lowest molar extinction coefficient.