New bipyridine ruthenium dye complexes with amide based ancillary ligands as sensitizers in semitransparent quasi-solid-state dye sensitized solar cells

Abstract

A series of three heteroleptic ruthenium complexes containing 2,2'-bipyridine-4,4'-dicarboxamide ligands with different substituents (propyl, benzyl or 2-phenylethyl) was synthesized as possible sensitizers for dye sensitized solar cells (DSSCs). Their structure was characterized with 1H NMR and FTIR while their optical and electrochemical properties were also investigated. The observed optical differences were associated to structural properties of the three complexes and different electron donor strength of the ancillary ligands. In particular, ruthenium complex with propyl based ligand showed higher molar extinction coefficient succeeding better light harvesting. Semitransparent dye sensitized solar cells employing quasi-solid-state electrolyte and the three ruthenium complexes were constructed under the same fabrication conditions and electrically characterized under standard conditions of light irradiance (100 mW/cm2, AM 1.5). Their behavior was compared with that of commercially available ruthenium complex D907 with increased conjugation length of the ancillary ligand, in terms of current–voltage characteristic curves under simulated solar light and in the dark while electrochemical impedance spectroscopy was also used for local resistance to charge transfer across the TiO2-dye/electrolyte interface. The influence of ancillary ligands into ruthenium complexes was discussed in terms of the cells’ efficiency. A maximum overall performance of 5.0% was monitored for ruthenium complex with propyl substituent in comparison to 5.1% that was measured for semitransparent quasi-solid state devices with commercial D907. © 2018 Elsevier B.V.