Can Polypyridyl Cu(I)-based Complexes Provide Promising Sensitizers for Dye-Sensitized Solar Cells? A Theoretical Insight into Cu(I) versus Ru(II) Sensitizers

Design of light-absorbent dyes with cheaper, safer, and more sustainable materials is one of the key issues for the future development of dye-sensitized solar cells (DSSCs). We report herein a theoretical investigation on a series of polypyridyl Cu(I)-based complexes with general formula [CuLL′]⁺ (L and L′ represent bipyridyl ligands) by density functional theory (DFT) and time-dependent DFT. Molecular geometries, electronic structures, and optical absorption spectra are predicted in both the gas phase and methyl cyanide solution. Our results show that all the [CuLL′]⁺ derivatives display Cu → bipyridine metal-to-ligand charge transfer absorption spectra in the range of 350−700 nm. Structural optimizations by enhancing π-conjugation and introducing heteroaromatic groups on ancillary ligands lead to upshift of molecular orbital energies, increase in oscillator strength, and red shift of absorption spectra. Compared with Ru(II) sensitizers, polypridyl Cu(I)-based complexes show similar optical properties and improving trend of the DSSCs performance along with the optimizations of structures. The results of this work highlight the point that polypyridyl Cu(I)-based complexes could provide promising sensitizers for efficient next-generation DSSCs.