Theoretical insight into the spectral characteristics of Fe(II)-based complexes for dye-sensitized solar cells: Functionalized bipyridyl chromophores

• Functionalized chromophore of π-conjugation and heteroaromatics add in Fe(II) dyes.
• Fine-tuning electronic structure improves spectral response range and intensity.
• Similar spectral characteristics but better improving trend than Ru(II) dyes.

Fine tuning of electronic properties by virtue of the proper choice of functionalized chromophores would improve performance of absorption spectrum for dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of bipyridyl Fe(II)-based complexes with general formula [FeLL′(NCS)2] (L, L′ = 4,4′-substituted-2,2′-bipyridine) by density functional theory (DFT) and time-dependent DFT (TD-DFT). Molecular geometries, electronic structures, and optical absorption spectra are predicted in methyl cyanide (MeCN) solution. [FeLL′(NCS)2] derivatives display Fe → bipyridine metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) in the range of 350–700 nm. Structural modifications by enhancing π-conjugation and introducing heteroaromatic groups on ancillary ligands lead to the upshift of most of molecular orbital energies, and remarkable increase in absorption intensity. Compared with Ru(II)-based sensitizers, bipyridyl Fe(II)-based complexes exhibit similar absorption spectral characteristics but better improving trend along with structural optimizations.

Series of bipyridyl Fe(II)-based complexes with general formula [FeLL′(NCS)2] (L, L′ = 4,4′-substituted-2,2′-bipyridine) have been investigated using DFT/TD-DFT approach in MeCN solution. The molecular geometries, electronic structures, optical absorption spectra, and relation between structural optimizations and spectral characteristics were analyzed to compare with those of Ru(II)-based complexes.Figure optionsDownload as PowerPoint slide