One-pot synthesis, photophysical, electrochemical and molecular property of mixed-ligands ruthenium complex functionalities: Potential materials for dye-sensitized solar cells (DSSCs)

Abstract

In our search for excellent photoactive materials for optolectronic applications such as dye-sensitized solar cells, four highly emissive, new fluorescent ruthenium coordinated dye complexes (A-D) having pyridyl-3,5-dicarboxylic acid and triphenylphosphine as the two common monodentate ligands formulated as RuCl₂(PPh₃)₂(dca)₂, RuCl₂(PPh₃)Bpy(dca), RuCl₂(PPh₃)Hbpy(dca) and RuCl₂(PPh₃)Phen(dca) were prepared in a one-pot synthetic method, purified and characterized by IR, UV–Vis, PL, ¹H, ¹³C, ³¹P- NMR spectroscopy, elemental analysis, electrochemistry and mass spectrometry. The UV–Vis absorption spectra revealed three to four well-define absorption peaks in the region λ_max 265–560 nm which were assigned to the π–π∗ transitions, two ligand-to-ligand charge-transfer (LLCT) bands and dπ(Ru)–π∗(L) transitions respectively. High intensity and broad emissive photoluminescent properties in the mid-infrared region λ_em (>640 nm) were recorded for all complexes. The electron-donating and/or electron-withdrawing ability of the carboxylic acid and chloride groups present in the complexes possibly favoured a one-electron oxidation reaction, stability of Ru³⁺/Ru²⁺ redox properties and the potential of their applications in dye-sensitized solar cells and/or optoelectronics. The calculated results suggest that the frontiers Molecular Orbitals (FMOs), open-circuit voltage ($V_{\text{oc}}$), light-harvesting efficiency ($\text{LHE}$), driving force for electron injection ($\Delta G_{inj}$), dye driving force regeneration ($\Delta G_{reg}$), molecular electrostatic potential (MESP), and density of states ($\text{DOS}$) are affected by substituents groups introduced in the ruthenium complex. The $\eta$ of all the dyes are theoretically calculated at J_SC 9, 12, and 15 mA cm⁻² to give the higher power conversion efficiency ($\eta$) of the solar cell obtained for dye B at (9.36 %). The comparative investigation shows that extended π-spacer variation in the ligands is essential in the fine-tuning of the overall performance of the DSSCs in the ruthenium complexes.