The molecular engineering, synthesis and photovoltaic studies of a novel highly efficient Ru(ii) complex incorporating a bulky TPA ancillary ligand for DSSCs: donor versus π-spacer effects

Abstract

A novel Ru(II) complex, denoted as IA-7, incorporating a bulky donor antenna, was synthesized and characterized as a promising inexpensive alternative to conventional p–n junction solar cells to study the influence of a bulky donor antenna on the light harvesting efficiency (LHE), ground and excited state oxidation potentials and total conversion efficiency of sunlight to electricity (% η) for dye-sensitized solar cells (DSSCs), and the device performance was compared to devices with MH-12 and MH-13 dyes. The incorporation of the bulky donor enriched triphenylamine (TPA) antenna resulted in a considerable increase in J_SC and η values for DSSCs, where IA-7 outperformed MH-12 and MH-13 in terms of the total conversion efficiency and achieved a power conversion efficiency (η) of 8.86% under full sunlight irradiation (100 mW cm⁻²), compared to 8.09% for MH-12 and 8.53% for MH-13, which can be ascribed to the high open circuit voltage (V_OC) of IA-7. Molecular engineering utilizing DFT/TD-DFT was employed to calculate the electronic properties of IA-7, including the HOMO/LUMO isosurfaces, the lowest singlet–singlet electronic transitions (E_0–0), and the ground and excited state oxidation potentials, which were in ideal agreement with the empirical results. The electronic distribution of IA-7 indicated that the HOMO is delocalized not only on Ru and NCS, but also on the substituted TPA, and the LUMO is delocalized over 4,4′-bipyridyl dicarboxylic acid.