Theoretical insights into the photovoltaic properties of ruthenium(ii) bipyridyl photosensitizers through variation of the anchoring groups

Abstract

In this study, eleven Ru-based dyes have been theoretically designed by substitution of different anchors. Their light harvesting capability in dye-sensitized solar cells (DSSCs) and non-linear optical (NLO) properties were subsequently explored. The structural, optoelectronic and NLO properties of these Ru(II) complexes are analyzed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods in both the gas phase and acetonitrile. The results illustrate that the changing of the anchoring groups on the bpy ligand of complex [Ru(bpy)₂(NCS)₂] could reduce the energy gap (E_g), redshift the maximum absorption wavelengths (λ_max), increase the oscillator strength (ƒ) and light-harvesting efficiency (LHE), and enhance the driving force of injection (ΔG_inj), thus amplifying the efficiency of the DSSC. According to the results, the presence of nitro (–NO₂) anchors in the complex [Ru(bpy)₂(NCS)₂] (Ru-dye 8) led to a reduction in open circuit voltage (V_oc = 0.45 eV), while significantly decreasing the energy gap (2.05 eV) and notably increasing the excitation wavelength (657 nm). Ru-dye 9 exhibited the largest static first hyperpolarizability (β₀ = 273 × 10⁻³⁰ e.s.u.) compared to the other Ru-dyes. This study provides valuable insights into the understanding of Ru-based dyes in DSSC devices and NLO materials.