Photovoltaic performance of bipyridine and dipyridophenazine ligands anchored ruthenium complex sensitizers for efficient dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSCs) can be influenced by the sensitizer. Therefore, three heteroleptic ruthenium complexes, cis-[Ru(dcbpy)(bpy)(NCS)₂] (Ru-bpy), cis-[Ru(dcbpy)(dppz)(NCS)₂] (Ru-dppz) and cis-[Ru(dcbpy)(dppx)(NCS)₂] (Ru-dppx) (dcbpy = 4,4′-dicarboxylic-2,2′-bipyridine, NCS = isothiocyanate) sensitizers, were synthesized using one pot synthesis. The structures and functionalization of the ligands in each complex sensitizer were confirmed using FT-IR and NMR analyses. They were then systematically studied to determine their light absorption spectrum, the metal-centered oxidation peak, and electron recombination properties using a UV–vis spectrophotometer and electroanalytical techniques (i.e., CV, EIS, and LSV). The criteria for an efficient DSSC ruthenium sensitizer were drawn based on the structure-property relationship. It was found that the power conversion efficiency (ɳ) of the sensitizers were in the sequence of Ru-dppz (ɳ = 0.40%) < Ru-bpy (ɳ = 0.58%) < Ru-dppx (ɳ = 0.61%) in comparison to a commercialized sensitizer N719 (ɳ = 0.93%), The introduction of the dimethyl group altered the LUMO to enhance the electron injection to the TiO₂ conduction band and thus increased the power conversion efficiency of the DSSC.